source: draft-ietf-httpbis/latest/p1-messaging.xml @ 89

Last change on this file since 89 was 89, checked in by fielding@…, 12 years ago

Resolve #45: RFC977 reference

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1<?xml version="1.0" encoding="utf-8"?>
2<!DOCTYPE rfc [
3  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
4  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
5  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
6  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
7  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
8  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
9  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
10  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
11  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
12  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
13  <!ENTITY ID-VERSION "latest">
14  <!ENTITY ID-MONTH "December">
15  <!ENTITY ID-YEAR "2007">
16  <!ENTITY caching                "<xref target='Part6' x:rel='#caching' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
17  <!ENTITY payload                "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY diff2045entity         "<xref target='Part3' x:rel='#differences.between.http.entities.and.rfc.2045.entities' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY entity                 "<xref target='Part3' x:rel='#entity' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY entity-header-fields   "<xref target='Part3' x:rel='#entity.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY qvalue                 "<xref target='Part3' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY method                 "<xref target='Part2' x:rel='#method' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36]>
37<?rfc toc="yes" ?>
38<?rfc symrefs="yes" ?>
39<?rfc sortrefs="yes" ?>
40<?rfc compact="yes"?>
41<?rfc subcompact="no" ?>
42<?rfc linkmailto="no" ?>
43<?rfc editing="no" ?>
44<?rfc-ext allow-markup-in-artwork="yes" ?>
45<?rfc-ext include-references-in-index="yes" ?>
46<rfc obsoletes="2068, 2616" category="std"
47     ipr="full3978" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
48     xmlns:x='http://purl.org/net/xml2rfc/ext' xmlns:ed="http://greenbytes.de/2002/rfcedit">
49<front>
50
51  <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
52
53  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
54    <organization abbrev="Day Software">Day Software</organization>
55    <address>
56      <postal>
57        <street>23 Corporate Plaza DR, Suite 280</street>
58        <city>Newport Beach</city>
59        <region>CA</region>
60        <code>92660</code>
61        <country>USA</country>
62      </postal>
63      <phone>+1-949-706-5300</phone>
64      <facsimile>+1-949-706-5305</facsimile>
65      <email>fielding@gbiv.com</email>
66      <uri>http://roy.gbiv.com/</uri>
67    </address>
68  </author>
69
70  <author initials="J." surname="Gettys" fullname="Jim Gettys">
71    <organization>One Laptop per Child</organization>
72    <address>
73      <postal>
74        <street>21 Oak Knoll Road</street>
75        <city>Carlisle</city>
76        <region>MA</region>
77        <code>01741</code>
78        <country>USA</country>
79      </postal>
80      <email>jg@laptop.org</email>
81      <uri>http://www.laptop.org/</uri>
82    </address>
83  </author>
84 
85  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
86    <organization abbrev="HP">Hewlett-Packard Company</organization>
87    <address>
88      <postal>
89        <street>HP Labs, Large Scale Systems Group</street>
90        <street>1501 Page Mill Road, MS 1177</street>
91        <city>Palo Alto</city>
92        <region>CA</region>
93        <code>94304</code>
94        <country>USA</country>
95      </postal>
96      <email>JeffMogul@acm.org</email>
97    </address>
98  </author>
99
100  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
101    <organization abbrev="Microsoft">Microsoft Corporation</organization>
102    <address>
103      <postal>
104        <street>1 Microsoft Way</street>
105        <city>Redmond</city>
106        <region>WA</region>
107        <code>98052</code>
108        <country>USA</country>
109      </postal>
110      <email>henrikn@microsoft.com</email>
111    </address>
112  </author>
113
114  <author initials="L." surname="Masinter" fullname="Larry Masinter">
115    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
116    <address>
117      <postal>
118        <street>345 Park Ave</street>
119        <city>San Jose</city>
120        <region>CA</region>
121        <code>95110</code>
122        <country>USA</country>
123      </postal>
124      <email>LMM@acm.org</email>
125      <uri>http://larry.masinter.net/</uri>
126    </address>
127  </author>
128 
129  <author initials="P." surname="Leach" fullname="Paul J. Leach">
130    <organization abbrev="Microsoft">Microsoft Corporation</organization>
131    <address>
132      <postal>
133        <street>1 Microsoft Way</street>
134        <city>Redmond</city>
135        <region>WA</region>
136        <code>98052</code>
137      </postal>
138      <email>paulle@microsoft.com</email>
139    </address>
140  </author>
141   
142  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
143    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
144    <address>
145      <postal>
146        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
147        <street>The Stata Center, Building 32</street>
148        <street>32 Vassar Street</street>
149        <city>Cambridge</city>
150        <region>MA</region>
151        <code>02139</code>
152        <country>USA</country>
153      </postal>
154      <email>timbl@w3.org</email>
155      <uri>http://www.w3.org/People/Berners-Lee/</uri>
156    </address>
157  </author>
158
159  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
160
161<abstract>
162<t>
163   The Hypertext Transfer Protocol (HTTP) is an application-level
164   protocol for distributed, collaborative, hypermedia information
165   systems. HTTP has been in use by the World Wide Web global information
166   initiative since 1990. This document is Part 1 of the seven-part specification
167   that defines the protocol referred to as "HTTP/1.1" and, taken together,
168   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
169   its associated terminology, defines the "http" and "https" Uniform
170   Resource Identifier (URI) schemes, defines the generic message syntax
171   and parsing requirements for HTTP message frames, and describes
172   general security concerns for implementations.
173</t>
174</abstract>
175
176<note title="Editorial Note (To be removed by RFC Editor)">
177  <t>
178    This version of the HTTP specification contains only minimal editorial
179    changes from <xref target="RFC2616"/> (abstract, introductory paragraph,
180    and authors' addresses).  All other changes are due to partitioning the
181    original into seven mostly independent parts.  The intent is for readers
182    of future drafts to able to use draft 00 as the basis for comparison
183    when the WG makes later changes to the specification text.  This draft
184    will shortly be followed by draft 01 (containing the first round of changes
185    that have already been agreed to on the mailing list). There is no point in
186    reviewing this draft other than to verify that the partitioning has been
187    done correctly.  Roy T. Fielding, Yves Lafon, and Julian Reschke
188    will be the editors after draft 00 is submitted.
189  </t>
190  <t>
191    Discussion of this draft should take place on the HTTPBIS working group
192    mailing list (ietf-http-wg@w3.org). The current issues list is
193    at <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/report/11"/>
194    and related documents (including fancy diffs) can be found at
195    <eref target="http://www3.tools.ietf.org/wg/httpbis/"/>.
196  </t>
197</note>
198</front>
199<middle>
200<section title="Introduction" anchor="introduction">
201<t>
202   This document will define aspects of HTTP related to overall network
203   operation, message framing, interaction with transport protocols, and
204   URI schemes. Right now it only includes the extracted relevant sections
205   of <xref target="RFC2616"/>.
206</t>
207<section title="Purpose" anchor="intro.purpose">
208<t>
209   The Hypertext Transfer Protocol (HTTP) is an application-level
210   protocol for distributed, collaborative, hypermedia information
211   systems. HTTP has been in use by the World-Wide Web global
212   information initiative since 1990. The first version of HTTP,
213   referred to as HTTP/0.9, was a simple protocol for raw data transfer
214   across the Internet. HTTP/1.0, as defined by RFC 1945 <xref target="RFC1945"/>, improved
215   the protocol by allowing messages to be in the format of MIME-like
216   messages, containing metainformation about the data transferred and
217   modifiers on the request/response semantics. However, HTTP/1.0 does
218   not sufficiently take into consideration the effects of hierarchical
219   proxies, caching, the need for persistent connections, or virtual
220   hosts. In addition, the proliferation of incompletely-implemented
221   applications calling themselves "HTTP/1.0" has necessitated a
222   protocol version change in order for two communicating applications
223   to determine each other's true capabilities.
224</t>
225<t>
226   This specification defines the protocol referred to as "HTTP/1.1".
227   This protocol includes more stringent requirements than HTTP/1.0 in
228   order to ensure reliable implementation of its features.
229</t>
230<t>
231   Practical information systems require more functionality than simple
232   retrieval, including search, front-end update, and annotation. HTTP
233   allows an open-ended set of methods and headers that indicate the
234   purpose of a request <xref target="RFC2324"/>. It builds on the discipline of reference
235   provided by the Uniform Resource Identifier (URI) <xref target="RFC1630"/>, as a location
236   (URL) <xref target="RFC1738"/> or name (URN) <xref target="RFC1737"/>, for indicating the resource to which a
237   method is to be applied. Messages are passed in a format similar to
238   that used by Internet mail <xref target="RFC822"/> as defined by the Multipurpose
239   Internet Mail Extensions (MIME) <xref target="RFC2045"/>.
240</t>
241<t>
242   HTTP is also used as a generic protocol for communication between
243   user agents and proxies/gateways to other Internet systems, including
244   those supported by the SMTP <xref target="RFC821"/>, NNTP <xref target="RFC3977"/>, FTP <xref target="RFC959"/>, Gopher <xref target="RFC1436"/>,
245   and WAIS <xref target="WAIS"/> protocols. In this way, HTTP allows basic hypermedia
246   access to resources available from diverse applications.
247</t>
248</section>
249
250<section title="Requirements" anchor="intro.requirements">
251<t>
252   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
253   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
254   document are to be interpreted as described in RFC 2119 <xref target="RFC2119"/>.
255</t>
256<t>
257   An implementation is not compliant if it fails to satisfy one or more
258   of the &MUST; or &REQUIRED; level requirements for the protocols it
259   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
260   level and all the &SHOULD; level requirements for its protocols is said
261   to be "unconditionally compliant"; one that satisfies all the &MUST;
262   level requirements but not all the &SHOULD; level requirements for its
263   protocols is said to be "conditionally compliant."
264</t>
265</section>
266
267<section title="Terminology" anchor="intro.terminology">
268<t>
269   This specification uses a number of terms to refer to the roles
270   played by participants in, and objects of, the HTTP communication.
271</t>
272<t>
273  <iref item="connection"/>
274  <x:dfn>connection</x:dfn>
275  <list>
276    <t>
277      A transport layer virtual circuit established between two programs
278      for the purpose of communication.
279    </t>
280  </list>
281</t>
282<t>
283  <iref item="message"/>
284  <x:dfn>message</x:dfn>
285  <list>
286    <t>
287      The basic unit of HTTP communication, consisting of a structured
288      sequence of octets matching the syntax defined in <xref target="http.message"/> and
289      transmitted via the connection.
290    </t>
291  </list>
292</t>
293<t>
294  <iref item="request"/>
295  <x:dfn>request</x:dfn>
296  <list>
297    <t>
298      An HTTP request message, as defined in <xref target="request"/>.
299    </t>
300  </list>
301</t>
302<t>
303  <iref item="response"/>
304  <x:dfn>response</x:dfn>
305  <list>
306    <t>
307      An HTTP response message, as defined in <xref target="response"/>.
308    </t>
309  </list>
310</t>
311<t>
312  <iref item="resource"/>
313  <x:dfn>resource</x:dfn>
314  <list>
315    <t>
316      A network data object or service that can be identified by a URI,
317      as defined in <xref target="uri"/>. Resources may be available in multiple
318      representations (e.g. multiple languages, data formats, size, and
319      resolutions) or vary in other ways.
320    </t>
321  </list>
322</t>
323<t>
324  <iref item="entity"/>
325  <x:dfn>entity</x:dfn>
326  <list>
327    <t>
328      The information transferred as the payload of a request or
329      response. An entity consists of metainformation in the form of
330      entity-header fields and content in the form of an entity-body, as
331      described in &entity;.
332    </t>
333  </list>
334</t>
335<t>
336  <iref item="representation"/>
337  <x:dfn>representation</x:dfn>
338  <list>
339    <t>
340      An entity included with a response that is subject to content
341      negotiation, as described in &content.negotiation;. There may exist multiple
342      representations associated with a particular response status.
343    </t>
344  </list>
345</t>
346<t>
347  <iref item="content negotiation"/>
348  <x:dfn>content negotiation</x:dfn>
349  <list>
350    <t>
351      The mechanism for selecting the appropriate representation when
352      servicing a request, as described in &content.negotiation;. The
353      representation of entities in any response can be negotiated
354      (including error responses).
355    </t>
356  </list>
357</t>
358<t>
359  <iref item="variant"/>
360  <x:dfn>variant</x:dfn>
361  <list>
362    <t>
363      A resource may have one, or more than one, representation(s)
364      associated with it at any given instant. Each of these
365      representations is termed a `variant'.  Use of the term `variant'
366      does not necessarily imply that the resource is subject to content
367      negotiation.
368    </t>
369  </list>
370</t>
371<t>
372  <iref item="client"/>
373  <x:dfn>client</x:dfn>
374  <list>
375    <t>
376      A program that establishes connections for the purpose of sending
377      requests.
378    </t>
379  </list>
380</t>
381<t>
382  <iref item="user agent"/>
383  <x:dfn>user agent</x:dfn>
384  <list>
385    <t>
386      The client which initiates a request. These are often browsers,
387      editors, spiders (web-traversing robots), or other end user tools.
388    </t>
389  </list>
390</t>
391<t>
392  <iref item="server"/>
393  <x:dfn>server</x:dfn>
394  <list>
395    <t>
396      An application program that accepts connections in order to
397      service requests by sending back responses. Any given program may
398      be capable of being both a client and a server; our use of these
399      terms refers only to the role being performed by the program for a
400      particular connection, rather than to the program's capabilities
401      in general. Likewise, any server may act as an origin server,
402      proxy, gateway, or tunnel, switching behavior based on the nature
403      of each request.
404    </t>
405  </list>
406</t>
407<t>
408  <iref item="origin server"/>
409  <x:dfn>origin server</x:dfn>
410  <list>
411    <t>
412      The server on which a given resource resides or is to be created.
413    </t>
414  </list>
415</t>
416<t>
417  <iref item="proxy"/>
418  <x:dfn>proxy</x:dfn>
419  <list>
420    <t>
421      An intermediary program which acts as both a server and a client
422      for the purpose of making requests on behalf of other clients.
423      Requests are serviced internally or by passing them on, with
424      possible translation, to other servers. A proxy &MUST; implement
425      both the client and server requirements of this specification. A
426      "transparent proxy" is a proxy that does not modify the request or
427      response beyond what is required for proxy authentication and
428      identification. A "non-transparent proxy" is a proxy that modifies
429      the request or response in order to provide some added service to
430      the user agent, such as group annotation services, media type
431      transformation, protocol reduction, or anonymity filtering. Except
432      where either transparent or non-transparent behavior is explicitly
433      stated, the HTTP proxy requirements apply to both types of
434      proxies.
435    </t>
436  </list>
437</t>
438<t>
439  <iref item="gateway"/>
440  <x:dfn>gateway</x:dfn>
441  <list>
442    <t>
443      A server which acts as an intermediary for some other server.
444      Unlike a proxy, a gateway receives requests as if it were the
445      origin server for the requested resource; the requesting client
446      may not be aware that it is communicating with a gateway.
447    </t>
448  </list>
449</t>
450<t>
451  <iref item="tunnel"/>
452  <x:dfn>tunnel</x:dfn>
453  <list>
454    <t>
455      An intermediary program which is acting as a blind relay between
456      two connections. Once active, a tunnel is not considered a party
457      to the HTTP communication, though the tunnel may have been
458      initiated by an HTTP request. The tunnel ceases to exist when both
459      ends of the relayed connections are closed.
460    </t>
461  </list>
462</t>
463<t>
464  <iref item="cache"/>
465  <x:dfn>cache</x:dfn>
466  <list>
467    <t>
468      A program's local store of response messages and the subsystem
469      that controls its message storage, retrieval, and deletion. A
470      cache stores cacheable responses in order to reduce the response
471      time and network bandwidth consumption on future, equivalent
472      requests. Any client or server may include a cache, though a cache
473      cannot be used by a server that is acting as a tunnel.
474    </t>
475  </list>
476</t>
477<t>
478  <iref item="cacheable"/>
479  <x:dfn>cacheable</x:dfn>
480  <list>
481    <t>
482      A response is cacheable if a cache is allowed to store a copy of
483      the response message for use in answering subsequent requests. The
484      rules for determining the cacheability of HTTP responses are
485      defined in &caching;. Even if a resource is cacheable, there may
486      be additional constraints on whether a cache can use the cached
487      copy for a particular request.
488    </t>
489  </list>
490</t>
491<t>
492  <iref item="upstream"/>
493  <iref item="downstream"/>
494  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
495  <list>
496    <t>
497      Upstream and downstream describe the flow of a message: all
498      messages flow from upstream to downstream.
499    </t>
500  </list>
501</t>
502<t>
503  <iref item="inbound"/>
504  <iref item="outbound"/>
505  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
506  <list>
507    <t>
508      Inbound and outbound refer to the request and response paths for
509      messages: "inbound" means "traveling toward the origin server",
510      and "outbound" means "traveling toward the user agent"
511    </t>
512  </list>
513</t>
514</section>
515
516<section title="Overall Operation" anchor="intro.overall.operation">
517<t>
518   The HTTP protocol is a request/response protocol. A client sends a
519   request to the server in the form of a request method, URI, and
520   protocol version, followed by a MIME-like message containing request
521   modifiers, client information, and possible body content over a
522   connection with a server. The server responds with a status line,
523   including the message's protocol version and a success or error code,
524   followed by a MIME-like message containing server information, entity
525   metainformation, and possible entity-body content. The relationship
526   between HTTP and MIME is described in &diff2045entity;.
527</t>
528<t>
529   Most HTTP communication is initiated by a user agent and consists of
530   a request to be applied to a resource on some origin server. In the
531   simplest case, this may be accomplished via a single connection (v)
532   between the user agent (UA) and the origin server (O).
533</t>
534<figure><artwork type="drawing">
535       request chain ------------------------&gt;
536    UA -------------------v------------------- O
537       &lt;----------------------- response chain
538</artwork></figure>
539<t>
540   A more complicated situation occurs when one or more intermediaries
541   are present in the request/response chain. There are three common
542   forms of intermediary: proxy, gateway, and tunnel. A proxy is a
543   forwarding agent, receiving requests for a URI in its absolute form,
544   rewriting all or part of the message, and forwarding the reformatted
545   request toward the server identified by the URI. A gateway is a
546   receiving agent, acting as a layer above some other server(s) and, if
547   necessary, translating the requests to the underlying server's
548   protocol. A tunnel acts as a relay point between two connections
549   without changing the messages; tunnels are used when the
550   communication needs to pass through an intermediary (such as a
551   firewall) even when the intermediary cannot understand the contents
552   of the messages.
553</t>
554<figure><artwork type="drawing">
555       request chain --------------------------------------&gt;
556    UA -----v----- A -----v----- B -----v----- C -----v----- O
557       &lt;------------------------------------- response chain
558</artwork></figure>
559<t>
560   The figure above shows three intermediaries (A, B, and C) between the
561   user agent and origin server. A request or response message that
562   travels the whole chain will pass through four separate connections.
563   This distinction is important because some HTTP communication options
564   may apply only to the connection with the nearest, non-tunnel
565   neighbor, only to the end-points of the chain, or to all connections
566   along the chain. Although the diagram is linear, each participant may
567   be engaged in multiple, simultaneous communications. For example, B
568   may be receiving requests from many clients other than A, and/or
569   forwarding requests to servers other than C, at the same time that it
570   is handling A's request.
571</t>
572<t>
573   Any party to the communication which is not acting as a tunnel may
574   employ an internal cache for handling requests. The effect of a cache
575   is that the request/response chain is shortened if one of the
576   participants along the chain has a cached response applicable to that
577   request. The following illustrates the resulting chain if B has a
578   cached copy of an earlier response from O (via C) for a request which
579   has not been cached by UA or A.
580</t>
581<figure><artwork type="drawing">
582          request chain ----------&gt;
583       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
584          &lt;--------- response chain
585</artwork></figure>
586<t>
587   Not all responses are usefully cacheable, and some requests may
588   contain modifiers which place special requirements on cache behavior.
589   HTTP requirements for cache behavior and cacheable responses are
590   defined in &caching;.
591</t>
592<t>
593   In fact, there are a wide variety of architectures and configurations
594   of caches and proxies currently being experimented with or deployed
595   across the World Wide Web. These systems include national hierarchies
596   of proxy caches to save transoceanic bandwidth, systems that
597   broadcast or multicast cache entries, organizations that distribute
598   subsets of cached data via CD-ROM, and so on. HTTP systems are used
599   in corporate intranets over high-bandwidth links, and for access via
600   PDAs with low-power radio links and intermittent connectivity. The
601   goal of HTTP/1.1 is to support the wide diversity of configurations
602   already deployed while introducing protocol constructs that meet the
603   needs of those who build web applications that require high
604   reliability and, failing that, at least reliable indications of
605   failure.
606</t>
607<t>
608   HTTP communication usually takes place over TCP/IP connections. The
609   default port is TCP 80 <xref target="RFC1700"/>, but other ports can be used. This does
610   not preclude HTTP from being implemented on top of any other protocol
611   on the Internet, or on other networks. HTTP only presumes a reliable
612   transport; any protocol that provides such guarantees can be used;
613   the mapping of the HTTP/1.1 request and response structures onto the
614   transport data units of the protocol in question is outside the scope
615   of this specification.
616</t>
617<t>
618   In HTTP/1.0, most implementations used a new connection for each
619   request/response exchange. In HTTP/1.1, a connection may be used for
620   one or more request/response exchanges, although connections may be
621   closed for a variety of reasons (see <xref target="persistent.connections"/>).
622</t>
623</section>
624</section>
625
626<section title="Notational Conventions and Generic Grammar" anchor="notation">
627
628<section title="Augmented BNF" anchor="notation.abnf">
629<t>
630   All of the mechanisms specified in this document are described in
631   both prose and an augmented Backus-Naur Form (BNF) similar to that
632   used by RFC 822 <xref target="RFC822"/>. Implementors will need to be familiar with the
633   notation in order to understand this specification. The augmented BNF
634   includes the following constructs:
635</t>
636<t>
637   name = definition
638  <list>
639    <t>
640      The name of a rule is simply the name itself (without any
641      enclosing "&lt;" and "&gt;") and is separated from its definition by the
642      equal "=" character. White space is only significant in that
643      indentation of continuation lines is used to indicate a rule
644      definition that spans more than one line. Certain basic rules are
645      in uppercase, such as SP, LWS, HT, CRLF, DIGIT, ALPHA, etc. Angle
646      brackets are used within definitions whenever their presence will
647      facilitate discerning the use of rule names.
648    </t>
649  </list>
650</t>
651<t>
652   "literal"
653  <list>
654    <t>
655      Quotation marks surround literal text. Unless stated otherwise,
656      the text is case-insensitive.
657    </t>
658  </list>
659</t>
660<t>
661   rule1 | rule2
662  <list>
663    <t>
664      Elements separated by a bar ("|") are alternatives, e.g., "yes |
665      no" will accept yes or no.
666    </t>
667  </list>
668</t>
669<t>
670   (rule1 rule2)
671  <list>
672    <t>
673      Elements enclosed in parentheses are treated as a single element.
674      Thus, "(elem (foo | bar) elem)" allows the token sequences "elem
675      foo elem" and "elem bar elem".
676    </t>
677  </list>
678</t>
679<t>
680   *rule
681  <list>
682    <t>
683      The character "*" preceding an element indicates repetition. The
684      full form is "&lt;n&gt;*&lt;m&gt;element" indicating at least &lt;n&gt; and at most
685      &lt;m&gt; occurrences of element. Default values are 0 and infinity so
686      that "*(element)" allows any number, including zero; "1*element"
687      requires at least one; and "1*2element" allows one or two.
688    </t>
689  </list>
690</t>
691<t>
692   [rule]
693  <list>
694    <t>
695      Square brackets enclose optional elements; "[foo bar]" is
696      equivalent to "*1(foo bar)".
697    </t>
698  </list>
699</t>
700<t>
701   N rule
702  <list>
703    <t>
704      Specific repetition: "&lt;n&gt;(element)" is equivalent to
705      "&lt;n&gt;*&lt;n&gt;(element)"; that is, exactly &lt;n&gt; occurrences of (element).
706      Thus 2DIGIT is a 2-digit number, and 3ALPHA is a string of three
707      alphabetic characters.
708    </t>
709  </list>
710</t>
711<t>
712   #rule
713  <list>
714    <t>
715      A construct "#" is defined, similar to "*", for defining lists of
716      elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at least
717      &lt;n&gt; and at most &lt;m&gt; elements, each separated by one or more commas
718      (",") and &OPTIONAL; linear white space (LWS). This makes the usual
719      form of lists very easy; a rule such as
720    </t>
721    <t>
722         ( *LWS element *( *LWS "," *LWS element ))
723    </t>
724    <t>
725      can be shown as
726    </t>
727    <t>
728         1#element
729    </t>
730    <t>
731      Wherever this construct is used, null elements are allowed, but do
732      not contribute to the count of elements present. That is,
733      "(element), , (element) " is permitted, but counts as only two
734      elements. Therefore, where at least one element is required, at
735      least one non-null element &MUST; be present. Default values are 0
736      and infinity so that "#element" allows any number, including zero;
737      "1#element" requires at least one; and "1#2element" allows one or
738      two.
739    </t>
740  </list>
741</t>
742<t>
743   ; comment
744  <list>
745    <t>
746      A semi-colon, set off some distance to the right of rule text,
747      starts a comment that continues to the end of line. This is a
748      simple way of including useful notes in parallel with the
749      specifications.
750    </t>
751  </list>
752</t>
753<t>
754   implied *LWS
755  <list>
756    <t>
757      The grammar described by this specification is word-based. Except
758      where noted otherwise, linear white space (LWS) can be included
759      between any two adjacent words (token or quoted-string), and
760      between adjacent words and separators, without changing the
761      interpretation of a field. At least one delimiter (LWS and/or
762      separators) &MUST; exist between any two tokens (for the definition
763      of "token" below), since they would otherwise be interpreted as a
764      single token.
765    </t>
766  </list>
767</t>
768</section>
769
770<section title="Basic Rules" anchor="basic.rules">
771<x:anchor-alias value="OCTET"/>
772<x:anchor-alias value="CHAR"/>
773<x:anchor-alias value="UPALPHA"/>
774<x:anchor-alias value="LOALPHA"/>
775<x:anchor-alias value="ALPHA"/>
776<x:anchor-alias value="DIGIT"/>
777<x:anchor-alias value="CTL"/>
778<x:anchor-alias value="CR"/>
779<x:anchor-alias value="LF"/>
780<x:anchor-alias value="SP"/>
781<x:anchor-alias value="HT"/>
782<x:anchor-alias value="CRLF"/>
783<x:anchor-alias value="LWS"/>
784<x:anchor-alias value="TEXT"/>
785<x:anchor-alias value="HEX"/>
786<x:anchor-alias value="token"/>
787<x:anchor-alias value="separators"/>
788<x:anchor-alias value="comment"/>
789<x:anchor-alias value="ctext"/>
790<x:anchor-alias value="quoted-string"/>
791<x:anchor-alias value="qdtext"/>
792<x:anchor-alias value="quoted-pair"/>
793<t>
794   The following rules are used throughout this specification to
795   describe basic parsing constructs. The US-ASCII coded character set
796   is defined by ANSI X3.4-1986 <xref target="USASCII"/>.
797</t>
798<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="OCTET"/><iref primary="true" item="Grammar" subitem="CHAR"/><iref primary="true" item="Grammar" subitem="UPALPHA"/><iref primary="true" item="Grammar" subitem="LOALPHA"/><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="HT"/>
799    OCTET          = &lt;any 8-bit sequence of data&gt;
800    CHAR           = &lt;any US-ASCII character (octets 0 - 127)&gt;
801    UPALPHA        = &lt;any US-ASCII uppercase letter "A".."Z"&gt;
802    LOALPHA        = &lt;any US-ASCII lowercase letter "a".."z"&gt;
803    ALPHA          = UPALPHA | LOALPHA
804    DIGIT          = &lt;any US-ASCII digit "0".."9"&gt;
805    CTL            = &lt;any US-ASCII control character
806                     (octets 0 - 31) and DEL (127)&gt;
807    CR             = &lt;US-ASCII CR, carriage return (13)&gt;
808    LF             = &lt;US-ASCII LF, linefeed (10)&gt;
809    SP             = &lt;US-ASCII SP, space (32)&gt;
810    HT             = &lt;US-ASCII HT, horizontal-tab (9)&gt;
811    &lt;"&gt;            = &lt;US-ASCII double-quote mark (34)&gt;
812</artwork></figure>
813<t>
814   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
815   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
816   tolerant applications). The end-of-line marker within an entity-body
817   is defined by its associated media type, as described in &payload;.
818</t>
819<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="CRLF"/>
820    CRLF           = CR LF
821</artwork></figure>
822<t>
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><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="LWS"/>
830    LWS            = [CRLF] 1*( SP | HT )
831</artwork></figure>
832<t>
833   The TEXT rule is only used for descriptive field contents and values
834   that are not intended to be interpreted by the message parser. Words
835   of *TEXT &MAY; contain characters from character sets other than ISO-8859-1
836   <xref target="ISO-8859"/> only when encoded according to the rules of RFC 2047
837   <xref target="RFC2047"/>.
838</t>
839<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TEXT"/>
840    TEXT           = &lt;any OCTET except CTLs,
841                     but including LWS&gt;
842</artwork></figure>
843<t>
844   A CRLF is allowed in the definition of TEXT only as part of a header
845   field continuation. It is expected that the folding LWS will be
846   replaced with a single SP before interpretation of the TEXT value.
847</t>
848<t>
849   Hexadecimal numeric characters are used in several protocol elements.
850</t>
851<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HEX"/>
852    HEX            = "A" | "B" | "C" | "D" | "E" | "F"
853                   | "a" | "b" | "c" | "d" | "e" | "f" | DIGIT
854</artwork></figure>
855<t>
856   Many HTTP/1.1 header field values consist of words separated by LWS
857   or special characters. These special characters &MUST; be in a quoted
858   string to be used within a parameter value (as defined in
859   <xref target="transfer.codings"/>).
860</t>
861<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="separators"/>
862    token          = 1*&lt;any CHAR except CTLs or separators&gt;
863    separators     = "(" | ")" | "&lt;" | "&gt;" | "@"
864                   | "," | ";" | ":" | "\" | &lt;"&gt;
865                   | "/" | "[" | "]" | "?" | "="
866                   | "{" | "}" | SP | HT
867</artwork></figure>
868<t>
869   Comments can be included in some HTTP header fields by surrounding
870   the comment text with parentheses. Comments are only allowed in
871   fields containing "comment" as part of their field value definition.
872   In all other fields, parentheses are considered part of the field
873   value.
874</t>
875<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
876    comment        = "(" *( ctext | quoted-pair | comment ) ")"
877    ctext          = &lt;any TEXT excluding "(" and ")"&gt;
878</artwork></figure>
879<t>
880   A string of text is parsed as a single word if it is quoted using
881   double-quote marks.
882</t>
883<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/>
884    quoted-string  = ( &lt;"&gt; *(qdtext | quoted-pair ) &lt;"&gt; )
885    qdtext         = &lt;any TEXT except &lt;"&gt;&gt;
886</artwork></figure>
887<t>
888   The backslash character ("\") &MAY; be used as a single-character
889   quoting mechanism only within quoted-string and comment constructs.
890</t>
891<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
892    quoted-pair    = "\" CHAR
893</artwork></figure>
894</section>
895</section>
896
897<section title="Protocol Parameters" anchor="protocol.parameters">
898
899<section title="HTTP Version" anchor="http.version">
900<t>
901   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
902   of the protocol. The protocol versioning policy is intended to allow
903   the sender to indicate the format of a message and its capacity for
904   understanding further HTTP communication, rather than the features
905   obtained via that communication. No change is made to the version
906   number for the addition of message components which do not affect
907   communication behavior or which only add to extensible field values.
908   The &lt;minor&gt; number is incremented when the changes made to the
909   protocol add features which do not change the general message parsing
910   algorithm, but which may add to the message semantics and imply
911   additional capabilities of the sender. The &lt;major&gt; number is
912   incremented when the format of a message within the protocol is
913   changed. See RFC 2145 <xref target="RFC2145"/> for a fuller explanation.
914</t>
915<t>
916   The version of an HTTP message is indicated by an HTTP-Version field
917   in the first line of the message. HTTP-Version is case-sensitive.
918</t>
919<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/>
920       HTTP-Version   = "HTTP" "/" 1*DIGIT "." 1*DIGIT
921</artwork></figure>
922<t>
923   Note that the major and minor numbers &MUST; be treated as separate
924   integers and that each &MAY; be incremented higher than a single digit.
925   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
926   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
927   &MUST-NOT; be sent.
928</t>
929<t>
930   An application that sends a request or response message that includes
931   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
932   with this specification. Applications that are at least conditionally
933   compliant with this specification &SHOULD; use an HTTP-Version of
934   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
935   not compatible with HTTP/1.0. For more details on when to send
936   specific HTTP-Version values, see RFC 2145 <xref target="RFC2145"/>.
937</t>
938<t>
939   The HTTP version of an application is the highest HTTP version for
940   which the application is at least conditionally compliant.
941</t>
942<t>
943   Proxy and gateway applications need to be careful when forwarding
944   messages in protocol versions different from that of the application.
945   Since the protocol version indicates the protocol capability of the
946   sender, a proxy/gateway &MUST-NOT; send a message with a version
947   indicator which is greater than its actual version. If a higher
948   version request is received, the proxy/gateway &MUST; either downgrade
949   the request version, or respond with an error, or switch to tunnel
950   behavior.
951</t>
952<t>
953   Due to interoperability problems with HTTP/1.0 proxies discovered
954   since the publication of RFC 2068 <xref target="RFC2068"/>, caching proxies MUST, gateways
955   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
956   they support. The proxy/gateway's response to that request &MUST; be in
957   the same major version as the request.
958</t>
959<t>
960  <list>
961    <t>
962      <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
963      of header fields required or forbidden by the versions involved.
964    </t>
965  </list>
966</t>
967</section>
968
969<section title="Uniform Resource Identifiers" anchor="uri">
970<t>
971   URIs have been known by many names: WWW addresses, Universal Document
972   Identifiers, Universal Resource Identifiers <xref target="RFC1630"/>, and finally the
973   combination of Uniform Resource Locators (URL) <xref target="RFC1738"/> and Names (URN)
974   <xref target="RFC1737"/>. As far as HTTP is concerned, Uniform Resource Identifiers are
975   simply formatted strings which identify--via name, location, or any
976   other characteristic--a resource.
977</t>
978
979<section title="General Syntax" anchor="general.syntax">
980<t>
981   URIs in HTTP can be represented in absolute form or relative to some
982   known base URI <xref target="RFC1808"/>, depending upon the context of their use. The two
983   forms are differentiated by the fact that absolute URIs always begin
984   with a scheme name followed by a colon. For definitive information on
985   URL syntax and semantics, see "Uniform Resource Identifiers (URI):
986   Generic Syntax and Semantics," RFC 2396 <xref target="RFC2396"/> (which replaces RFCs
987   1738 <xref target="RFC1738"/> and RFC 1808 <xref target="RFC1808"/>). This specification adopts the
988   definitions of "URI-reference", "absoluteURI", "relativeURI", "port",
989   "host","abs_path", "rel_path", and "authority" from that
990   specification.
991</t>
992<t>
993   The HTTP protocol does not place any a priori limit on the length of
994   a URI. Servers &MUST; be able to handle the URI of any resource they
995   serve, and &SHOULD; be able to handle URIs of unbounded length if they
996   provide GET-based forms that could generate such URIs. A server
997   &SHOULD; return 414 (Request-URI Too Long) status if a URI is longer
998   than the server can handle (see &status-414;).
999</t>
1000<t>
1001  <list>
1002    <t>
1003      <x:h>Note:</x:h> Servers ought to be cautious about depending on URI lengths
1004      above 255 bytes, because some older client or proxy
1005      implementations might not properly support these lengths.
1006    </t>
1007  </list>
1008</t>
1009</section>
1010
1011<section title="http URL" anchor="http.url">
1012<t>
1013   The "http" scheme is used to locate network resources via the HTTP
1014   protocol. This section defines the scheme-specific syntax and
1015   semantics for http URLs.
1016</t>
1017<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http_URL"/>
1018http_URL = "http:" "//" host [ ":" port ] [ abs_path [ "?" query ]]
1019</artwork></figure>
1020<t>
1021   If the port is empty or not given, port 80 is assumed. The semantics
1022   are that the identified resource is located at the server listening
1023   for TCP connections on that port of that host, and the Request-URI
1024   for the resource is abs_path (<xref target="request-uri"/>). The use of IP addresses
1025   in URLs &SHOULD; be avoided whenever possible (see RFC 1900 <xref target="RFC1900"/>). If
1026   the abs_path is not present in the URL, it &MUST; be given as "/" when
1027   used as a Request-URI for a resource (<xref target="request-uri"/>). If a proxy
1028
1029   receives a host name which is not a fully qualified domain name, it
1030   &MAY; add its domain to the host name it received. If a proxy receives
1031   a fully qualified domain name, the proxy &MUST-NOT; change the host
1032   name.
1033</t>
1034</section>
1035
1036<section title="URI Comparison" anchor="uri.comparison">
1037<t>
1038   When comparing two URIs to decide if they match or not, a client
1039   &SHOULD; use a case-sensitive octet-by-octet comparison of the entire
1040   URIs, with these exceptions:
1041  <list style="symbols">
1042    <t>A port that is empty or not given is equivalent to the default
1043        port for that URI-reference;</t>
1044    <t>Comparisons of host names &MUST; be case-insensitive;</t>
1045    <t>Comparisons of scheme names &MUST; be case-insensitive;</t>
1046    <t>An empty abs_path is equivalent to an abs_path of "/".</t>
1047  </list>
1048</t>
1049<t>
1050   Characters other than those in the "reserved" set (see
1051   RFC 2396 <xref target="RFC2396"/>) are equivalent to their ""%" HEX HEX" encoding.
1052</t>
1053<t>
1054   For example, the following three URIs are equivalent:
1055</t>
1056<figure><artwork type="example">
1057   http://abc.com:80/~smith/home.html
1058   http://ABC.com/%7Esmith/home.html
1059   http://ABC.com:/%7esmith/home.html
1060</artwork></figure>
1061</section>
1062</section>
1063
1064<section title="Date/Time Formats" anchor="date.time.formats">
1065<section title="Full Date" anchor="full.date">
1066<t>
1067   HTTP applications have historically allowed three different formats
1068   for the representation of date/time stamps:
1069</t>
1070<figure><artwork type="example">
1071   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 822, updated by RFC 1123
1072   Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1073   Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1074</artwork></figure>
1075<t>
1076   The first format is preferred as an Internet standard and represents
1077   a fixed-length subset of that defined by RFC 1123 <xref target="RFC1123"/> (an update to
1078   RFC 822 <xref target="RFC822"/>). The other formats are described here only for
1079   compatibility with obsolete implementations.
1080   HTTP/1.1 clients and servers that parse the date value &MUST; accept
1081   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1082   only generate the RFC 1123 format for representing HTTP-date values
1083   in header fields. See <xref target="tolerant.applications"/> for further information.
1084</t>
1085<t><list><t>
1086      <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
1087      accepting date values that may have been sent by non-HTTP
1088      applications, as is sometimes the case when retrieving or posting
1089      messages via proxies/gateways to SMTP or NNTP.
1090</t></list></t>
1091<t>
1092   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1093   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1094   equal to UTC (Coordinated Universal Time). This is indicated in the
1095   first two formats by the inclusion of "GMT" as the three-letter
1096   abbreviation for time zone, and &MUST; be assumed when reading the
1097   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1098   additional LWS beyond that specifically included as SP in the
1099   grammar.
1100</t>
1101<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/><iref primary="true" item="Grammar" subitem="rfc1123-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"/>
1102    HTTP-date    = rfc1123-date | rfc850-date | asctime-date
1103    rfc1123-date = wkday "," SP date1 SP time SP "GMT"
1104    rfc850-date  = weekday "," SP date2 SP time SP "GMT"
1105    asctime-date = wkday SP date3 SP time SP 4DIGIT
1106    date1        = 2DIGIT SP month SP 4DIGIT
1107                   ; day month year (e.g., 02 Jun 1982)
1108    date2        = 2DIGIT "-" month "-" 2DIGIT
1109                   ; day-month-year (e.g., 02-Jun-82)
1110    date3        = month SP ( 2DIGIT | ( SP 1DIGIT ))
1111                   ; month day (e.g., Jun  2)
1112    time         = 2DIGIT ":" 2DIGIT ":" 2DIGIT
1113                   ; 00:00:00 - 23:59:59
1114    wkday        = "Mon" | "Tue" | "Wed"
1115                 | "Thu" | "Fri" | "Sat" | "Sun"
1116    weekday      = "Monday" | "Tuesday" | "Wednesday"
1117                 | "Thursday" | "Friday" | "Saturday" | "Sunday"
1118    month        = "Jan" | "Feb" | "Mar" | "Apr"
1119                 | "May" | "Jun" | "Jul" | "Aug"
1120                 | "Sep" | "Oct" | "Nov" | "Dec"
1121</artwork></figure>
1122<t>
1123      <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
1124      to their usage within the protocol stream. Clients and servers are
1125      not required to use these formats for user presentation, request
1126      logging, etc.
1127</t>
1128</section>
1129</section>
1130
1131<section title="Transfer Codings" anchor="transfer.codings">
1132<t>
1133   Transfer-coding values are used to indicate an encoding
1134   transformation that has been, can be, or may need to be applied to an
1135   entity-body in order to ensure "safe transport" through the network.
1136   This differs from a content coding in that the transfer-coding is a
1137   property of the message, not of the original entity.
1138</t>
1139<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1140    transfer-coding         = "chunked" | transfer-extension
1141    transfer-extension      = token *( ";" parameter )
1142</artwork></figure>
1143<t>
1144   Parameters are in  the form of attribute/value pairs.
1145</t>
1146<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/>
1147    parameter               = attribute "=" value
1148    attribute               = token
1149    value                   = token | quoted-string
1150</artwork></figure>
1151<t>
1152   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1153   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1154   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1155</t>
1156<t>
1157   Whenever a transfer-coding is applied to a message-body, the set of
1158   transfer-codings &MUST; include "chunked", unless the message is
1159   terminated by closing the connection. When the "chunked" transfer-coding
1160   is used, it &MUST; be the last transfer-coding applied to the
1161   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
1162   than once to a message-body. These rules allow the recipient to
1163   determine the transfer-length of the message (<xref target="message.length"/>).
1164</t>
1165<t>
1166   Transfer-codings are analogous to the Content-Transfer-Encoding
1167   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
1168   binary data over a 7-bit transport service. However, safe transport
1169   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1170   the only unsafe characteristic of message-bodies is the difficulty in
1171   determining the exact body length (<xref target="message.length"/>), or the desire to
1172   encrypt data over a shared transport.
1173</t>
1174<t>
1175   The Internet Assigned Numbers Authority (IANA) acts as a registry for
1176   transfer-coding value tokens. Initially, the registry contains the
1177   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
1178   "gzip" (&payload;), "compress" (&payload;), and "deflate" (&payload;).
1179</t>
1180<t>
1181   New transfer-coding value tokens &SHOULD; be registered in the same way
1182   as new content-coding value tokens (&payload;).
1183</t>
1184<t>
1185   A server which receives an entity-body with a transfer-coding it does
1186   not understand &SHOULD; return 501 (Unimplemented), and close the
1187   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1188   client.
1189</t>
1190
1191<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1192<t>
1193   The chunked encoding modifies the body of a message in order to
1194   transfer it as a series of chunks, each with its own size indicator,
1195   followed by an &OPTIONAL; trailer containing entity-header fields. This
1196   allows dynamically produced content to be transferred along with the
1197   information necessary for the recipient to verify that it has
1198   received the full message.
1199</t>
1200<figure><artwork type="abnf2616"><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"/>
1201    Chunked-Body   = *chunk
1202                     last-chunk
1203                     trailer
1204                     CRLF
1205
1206    chunk          = chunk-size [ chunk-extension ] CRLF
1207                     chunk-data CRLF
1208    chunk-size     = 1*HEX
1209    last-chunk     = 1*("0") [ chunk-extension ] CRLF
1210
1211    chunk-extension= *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
1212    chunk-ext-name = token
1213    chunk-ext-val  = token | quoted-string
1214    chunk-data     = chunk-size(OCTET)
1215    trailer        = *(entity-header CRLF)
1216</artwork></figure>
1217<t>
1218   The chunk-size field is a string of hex digits indicating the size of
1219   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1220   zero, followed by the trailer, which is terminated by an empty line.
1221</t>
1222<t>
1223   The trailer allows the sender to include additional HTTP header
1224   fields at the end of the message. The Trailer header field can be
1225   used to indicate which header fields are included in a trailer (see
1226   <xref target="header.trailer"/>).
1227</t>
1228<t>
1229   A server using chunked transfer-coding in a response &MUST-NOT; use the
1230   trailer for any header fields unless at least one of the following is
1231   true:
1232  <list style="numbers">
1233    <t>the request included a TE header field that indicates "trailers" is
1234     acceptable in the transfer-coding of the  response, as described in
1235     <xref target="header.te"/>; or,</t>
1236
1237    <t>the server is the origin server for the response, the trailer
1238     fields consist entirely of optional metadata, and the recipient
1239     could use the message (in a manner acceptable to the origin server)
1240     without receiving this metadata.  In other words, the origin server
1241     is willing to accept the possibility that the trailer fields might
1242     be silently discarded along the path to the client.</t>
1243  </list>
1244</t>
1245<t>
1246   This requirement prevents an interoperability failure when the
1247   message is being received by an HTTP/1.1 (or later) proxy and
1248   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1249   compliance with the protocol would have necessitated a possibly
1250   infinite buffer on the proxy.
1251</t>
1252<t>
1253   A process for decoding the "chunked" transfer-coding
1254   can be represented in pseudo-code as:
1255</t>
1256<figure><artwork type="code">
1257    length := 0
1258    read chunk-size, chunk-extension (if any) and CRLF
1259    while (chunk-size &gt; 0) {
1260       read chunk-data and CRLF
1261       append chunk-data to entity-body
1262       length := length + chunk-size
1263       read chunk-size and CRLF
1264    }
1265    read entity-header
1266    while (entity-header not empty) {
1267       append entity-header to existing header fields
1268       read entity-header
1269    }
1270    Content-Length := length
1271    Remove "chunked" from Transfer-Encoding
1272</artwork></figure>
1273<t>
1274   All HTTP/1.1 applications &MUST; be able to receive and decode the
1275   "chunked" transfer-coding, and &MUST; ignore chunk-extension extensions
1276   they do not understand.
1277</t>
1278</section>
1279</section>
1280
1281</section>
1282
1283<section title="HTTP Message" anchor="http.message">
1284
1285<section title="Message Types" anchor="message.types">
1286<t>
1287   HTTP messages consist of requests from client to server and responses
1288   from server to client.
1289</t>
1290<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1291    HTTP-message   = Request | Response     ; HTTP/1.1 messages
1292</artwork></figure>
1293<t>
1294   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1295   message format of RFC 822 <xref target="RFC822"/> for transferring entities (the payload
1296   of the message). Both types of message consist of a start-line, zero
1297   or more header fields (also known as "headers"), an empty line (i.e.,
1298   a line with nothing preceding the CRLF) indicating the end of the
1299   header fields, and possibly a message-body.
1300</t>
1301<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1302     generic-message = start-line
1303                       *(message-header CRLF)
1304                       CRLF
1305                       [ message-body ]
1306     start-line      = Request-Line | Status-Line
1307</artwork></figure>
1308<t>
1309   In the interest of robustness, servers &SHOULD; ignore any empty
1310   line(s) received where a Request-Line is expected. In other words, if
1311   the server is reading the protocol stream at the beginning of a
1312   message and receives a CRLF first, it should ignore the CRLF.
1313</t>
1314<t>
1315   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1316   after a POST request. To restate what is explicitly forbidden by the
1317   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1318   extra CRLF.
1319</t>
1320</section>
1321
1322<section title="Message Headers" anchor="message.headers">
1323<t>
1324   HTTP header fields, which include general-header (<xref target="general.header.fields"/>),
1325   request-header (&request-header-fields;), response-header (&response-header-fields;), and
1326   entity-header (&entity-header-fields;) fields, follow the same generic format as
1327   that given in <xref target="RFC822" x:fmt="sec" x:sec="3.1"/> of RFC 822 <xref target="RFC822"/>. Each header field consists
1328   of a name followed by a colon (":") and the field value. Field names
1329   are case-insensitive. The field value &MAY; be preceded by any amount
1330   of LWS, though a single SP is preferred. Header fields can be
1331   extended over multiple lines by preceding each extra line with at
1332   least one SP or HT. Applications ought to follow "common form", where
1333   one is known or indicated, when generating HTTP constructs, since
1334   there might exist some implementations that fail to accept anything
1335   beyond the common forms.
1336</t>
1337<figure><artwork type="abnf2616"><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"/>
1338    message-header = field-name ":" [ field-value ]
1339    field-name     = token
1340    field-value    = *( field-content | LWS )
1341    field-content  = &lt;the OCTETs making up the field-value
1342                     and consisting of either *TEXT or combinations
1343                     of token, separators, and quoted-string&gt;
1344</artwork></figure>
1345<t>
1346   The field-content does not include any leading or trailing LWS:
1347   linear white space occurring before the first non-whitespace
1348   character of the field-value or after the last non-whitespace
1349   character of the field-value. Such leading or trailing LWS &MAY; be
1350   removed without changing the semantics of the field value. Any LWS
1351   that occurs between field-content &MAY; be replaced with a single SP
1352   before interpreting the field value or forwarding the message
1353   downstream.
1354</t>
1355<t>
1356   The order in which header fields with differing field names are
1357   received is not significant. However, it is "good practice" to send
1358   general-header fields first, followed by request-header or response-header
1359   fields, and ending with the entity-header fields.
1360</t>
1361<t>
1362   Multiple message-header fields with the same field-name &MAY; be
1363   present in a message if and only if the entire field-value for that
1364   header field is defined as a comma-separated list [i.e., #(values)].
1365   It &MUST; be possible to combine the multiple header fields into one
1366   "field-name: field-value" pair, without changing the semantics of the
1367   message, by appending each subsequent field-value to the first, each
1368   separated by a comma. The order in which header fields with the same
1369   field-name are received is therefore significant to the
1370   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1371   change the order of these field values when a message is forwarded.
1372</t>
1373</section>
1374
1375<section title="Message Body" anchor="message.body">
1376<t>
1377   The message-body (if any) of an HTTP message is used to carry the
1378   entity-body associated with the request or response. The message-body
1379   differs from the entity-body only when a transfer-coding has been
1380   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1381</t>
1382<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1383    message-body = entity-body
1384                 | &lt;entity-body encoded as per Transfer-Encoding&gt;
1385</artwork></figure>
1386<t>
1387   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1388   applied by an application to ensure safe and proper transfer of the
1389   message. Transfer-Encoding is a property of the message, not of the
1390   entity, and thus &MAY; be added or removed by any application along the
1391   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1392   when certain transfer-codings may be used.)
1393</t>
1394<t>
1395   The rules for when a message-body is allowed in a message differ for
1396   requests and responses.
1397</t>
1398<t>
1399   The presence of a message-body in a request is signaled by the
1400   inclusion of a Content-Length or Transfer-Encoding header field in
1401   the request's message-headers. A message-body &MUST-NOT; be included in
1402   a request if the specification of the request method (&method;)
1403   does not allow sending an entity-body in requests. A server &SHOULD;
1404   read and forward a message-body on any request; if the request method
1405   does not include defined semantics for an entity-body, then the
1406   message-body &SHOULD; be ignored when handling the request.
1407</t>
1408<t>
1409   For response messages, whether or not a message-body is included with
1410   a message is dependent on both the request method and the response
1411   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1412   &MUST-NOT; include a message-body, even though the presence of entity-header
1413   fields might lead one to believe they do. All 1xx
1414   (informational), 204 (no content), and 304 (not modified) responses
1415   &MUST-NOT; include a message-body. All other responses do include a
1416   message-body, although it &MAY; be of zero length.
1417</t>
1418</section>
1419
1420<section title="Message Length" anchor="message.length">
1421<t>
1422   The transfer-length of a message is the length of the message-body as
1423   it appears in the message; that is, after any transfer-codings have
1424   been applied. When a message-body is included with a message, the
1425   transfer-length of that body is determined by one of the following
1426   (in order of precedence):
1427</t>
1428<t>
1429  <list style="numbers">
1430    <x:lt><t>
1431     Any response message which "&MUST-NOT;" include a message-body (such
1432     as the 1xx, 204, and 304 responses and any response to a HEAD
1433     request) is always terminated by the first empty line after the
1434     header fields, regardless of the entity-header fields present in
1435     the message.
1436    </t></x:lt>
1437    <x:lt><t>
1438     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1439     is present, then the transfer-length is
1440     defined by use of the "chunked" transfer-coding (<xref target="transfer.codings"/>),
1441     unless the message is terminated by closing the connection.
1442    </t></x:lt>
1443    <x:lt><t>
1444     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1445     decimal value in OCTETs represents both the entity-length and the
1446     transfer-length. The Content-Length header field &MUST-NOT; be sent
1447     if these two lengths are different (i.e., if a Transfer-Encoding
1448     header field is present). If a message is received with both a
1449     Transfer-Encoding header field and a Content-Length header field,
1450     the latter &MUST; be ignored.
1451    </t></x:lt>
1452    <x:lt><t>
1453     If the message uses the media type "multipart/byteranges", and the
1454     transfer-length is not otherwise specified, then this self-delimiting
1455     media type defines the transfer-length. This media type
1456     &MUST-NOT; be used unless the sender knows that the recipient can parse
1457     it; the presence in a request of a Range header with multiple byte-range
1458     specifiers from a 1.1 client implies that the client can parse
1459     multipart/byteranges responses.
1460    <list style="empty"><t>
1461       A range header might be forwarded by a 1.0 proxy that does not
1462       understand multipart/byteranges; in this case the server &MUST;
1463       delimit the message using methods defined in items 1, 3 or 5 of
1464       this section.
1465    </t></list>
1466    </t></x:lt>
1467    <x:lt><t>
1468     By the server closing the connection. (Closing the connection
1469     cannot be used to indicate the end of a request body, since that
1470     would leave no possibility for the server to send back a response.)
1471    </t></x:lt>
1472  </list>
1473</t>
1474<t>
1475   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1476   containing a message-body &MUST; include a valid Content-Length header
1477   field unless the server is known to be HTTP/1.1 compliant. If a
1478   request contains a message-body and a Content-Length is not given,
1479   the server &SHOULD; respond with 400 (bad request) if it cannot
1480   determine the length of the message, or with 411 (length required) if
1481   it wishes to insist on receiving a valid Content-Length.
1482</t>
1483<t>
1484   All HTTP/1.1 applications that receive entities &MUST; accept the
1485   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1486   to be used for messages when the message length cannot be determined
1487   in advance.
1488</t>
1489<t>
1490   Messages &MUST-NOT; include both a Content-Length header field and a
1491   transfer-coding. If the message does include a
1492   transfer-coding, the Content-Length &MUST; be ignored.
1493</t>
1494<t>
1495   When a Content-Length is given in a message where a message-body is
1496   allowed, its field value &MUST; exactly match the number of OCTETs in
1497   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1498   invalid length is received and detected.
1499</t>
1500</section>
1501
1502<section title="General Header Fields" anchor="general.header.fields">
1503<t>
1504   There are a few header fields which have general applicability for
1505   both request and response messages, but which do not apply to the
1506   entity being transferred. These header fields apply only to the
1507   message being transmitted.
1508</t>
1509<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1510    general-header = Cache-Control            ; &header-cache-control;
1511                   | Connection               ; <xref target="header.connection"/>
1512                   | Date                     ; <xref target="header.date"/>
1513                   | Pragma                   ; &header-pragma;
1514                   | Trailer                  ; <xref target="header.trailer"/>
1515                   | Transfer-Encoding        ; <xref target="header.transfer-encoding"/>
1516                   | Upgrade                  ; <xref target="header.upgrade"/>
1517                   | Via                      ; <xref target="header.via"/>
1518                   | Warning                  ; &header-warning;
1519</artwork></figure>
1520<t>
1521   General-header field names can be extended reliably only in
1522   combination with a change in the protocol version. However, new or
1523   experimental header fields may be given the semantics of general
1524   header fields if all parties in the communication recognize them to
1525   be general-header fields. Unrecognized header fields are treated as
1526   entity-header fields.
1527</t>
1528</section>
1529</section>
1530
1531<section title="Request" anchor="request">
1532<t>
1533   A request message from a client to a server includes, within the
1534   first line of that message, the method to be applied to the resource,
1535   the identifier of the resource, and the protocol version in use.
1536</t>
1537<!--                 Host                      ; should be moved here eventually -->
1538<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1539     Request       = Request-Line              ; <xref target="request-line"/>
1540                     *(( general-header        ; <xref target="general.header.fields"/>
1541                      | request-header         ; &request-header-fields;
1542                      | entity-header ) CRLF)  ; &entity-header-fields;
1543                     CRLF
1544                     [ message-body ]          ; <xref target="message.body"/>
1545</artwork></figure>
1546
1547<section title="Request-Line" anchor="request-line">
1548<t>
1549   The Request-Line begins with a method token, followed by the
1550   Request-URI and the protocol version, and ending with CRLF. The
1551   elements are separated by SP characters. No CR or LF is allowed
1552   except in the final CRLF sequence.
1553</t>
1554<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1555     Request-Line   = Method SP Request-URI SP HTTP-Version CRLF
1556</artwork></figure>
1557
1558<section title="Method" anchor="method">
1559<t>
1560   The Method  token indicates the method to be performed on the
1561   resource identified by the Request-URI. The method is case-sensitive.
1562</t>
1563<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1564    Method         = token
1565</artwork></figure>
1566</section>
1567
1568<section title="Request-URI" anchor="request-uri">
1569<t>
1570   The Request-URI is a Uniform Resource Identifier (<xref target="uri"/>) and
1571   identifies the resource upon which to apply the request.
1572</t>
1573<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-URI"/>
1574    Request-URI    = "*"
1575                   | absoluteURI
1576                   | ( abs_path [ "?" query ] )
1577                   | authority
1578</artwork></figure>
1579<t>
1580   The four options for Request-URI are dependent on the nature of the
1581   request. The asterisk "*" means that the request does not apply to a
1582   particular resource, but to the server itself, and is only allowed
1583   when the method used does not necessarily apply to a resource. One
1584   example would be
1585</t>
1586<figure><artwork type="example">
1587    OPTIONS * HTTP/1.1
1588</artwork></figure>
1589<t>
1590   The absoluteURI form is &REQUIRED; when the request is being made to a
1591   proxy. The proxy is requested to forward the request or service it
1592   from a valid cache, and return the response. Note that the proxy &MAY;
1593   forward the request on to another proxy or directly to the server
1594   specified by the absoluteURI. In order to avoid request loops, a
1595   proxy &MUST; be able to recognize all of its server names, including
1596   any aliases, local variations, and the numeric IP address. An example
1597   Request-Line would be:
1598</t>
1599<figure><artwork type="example">
1600    GET http://www.w3.org/pub/WWW/TheProject.html HTTP/1.1
1601</artwork></figure>
1602<t>
1603   To allow for transition to absoluteURIs in all requests in future
1604   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absoluteURI
1605   form in requests, even though HTTP/1.1 clients will only generate
1606   them in requests to proxies.
1607</t>
1608<t>
1609   The authority form is only used by the CONNECT method (&CONNECT;).
1610</t>
1611<t>
1612   The most common form of Request-URI is that used to identify a
1613   resource on an origin server or gateway. In this case the absolute
1614   path of the URI &MUST; be transmitted (see <xref target="general.syntax"/>, abs_path) as
1615   the Request-URI, and the network location of the URI (authority) &MUST;
1616   be transmitted in a Host header field. For example, a client wishing
1617   to retrieve the resource above directly from the origin server would
1618   create a TCP connection to port 80 of the host "www.w3.org" and send
1619   the lines:
1620</t>
1621<figure><artwork type="example">
1622    GET /pub/WWW/TheProject.html HTTP/1.1
1623    Host: www.w3.org
1624</artwork></figure>
1625<t>
1626   followed by the remainder of the Request. Note that the absolute path
1627   cannot be empty; if none is present in the original URI, it &MUST; be
1628   given as "/" (the server root).
1629</t>
1630<t>
1631   The Request-URI is transmitted in the format specified in
1632   <xref target="general.syntax"/>. If the Request-URI is encoded using the "% HEX HEX" encoding
1633   <xref target="RFC2396"/>, the origin server &MUST; decode the Request-URI in order to
1634   properly interpret the request. Servers &SHOULD; respond to invalid
1635   Request-URIs with an appropriate status code.
1636</t>
1637<t>
1638   A transparent proxy &MUST-NOT; rewrite the "abs_path" part of the
1639   received Request-URI when forwarding it to the next inbound server,
1640   except as noted above to replace a null abs_path with "/".
1641</t>
1642<t>
1643  <list><t>
1644      <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1645      meaning of the request when the origin server is improperly using
1646      a non-reserved URI character for a reserved purpose.  Implementors
1647      should be aware that some pre-HTTP/1.1 proxies have been known to
1648      rewrite the Request-URI.
1649  </t></list>
1650</t>
1651</section>
1652</section>
1653
1654<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1655<t>
1656   The exact resource identified by an Internet request is determined by
1657   examining both the Request-URI and the Host header field.
1658</t>
1659<t>
1660   An origin server that does not allow resources to differ by the
1661   requested host &MAY; ignore the Host header field value when
1662   determining the resource identified by an HTTP/1.1 request. (But see
1663   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1664   for other requirements on Host support in HTTP/1.1.)
1665</t>
1666<t>
1667   An origin server that does differentiate resources based on the host
1668   requested (sometimes referred to as virtual hosts or vanity host
1669   names) &MUST; use the following rules for determining the requested
1670   resource on an HTTP/1.1 request:
1671  <list style="numbers">
1672    <t>If Request-URI is an absoluteURI, the host is part of the
1673     Request-URI. Any Host header field value in the request &MUST; be
1674     ignored.</t>
1675    <t>If the Request-URI is not an absoluteURI, and the request includes
1676     a Host header field, the host is determined by the Host header
1677     field value.</t>
1678    <t>If the host as determined by rule 1 or 2 is not a valid host on
1679     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1680  </list>
1681</t>
1682<t>
1683   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1684   attempt to use heuristics (e.g., examination of the URI path for
1685   something unique to a particular host) in order to determine what
1686   exact resource is being requested.
1687</t>
1688</section>
1689
1690</section>
1691
1692
1693<section title="Response" anchor="response">
1694<t>
1695   After receiving and interpreting a request message, a server responds
1696   with an HTTP response message.
1697</t>
1698<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1699    Response      = Status-Line               ; <xref target="status-line"/>
1700                    *(( general-header        ; <xref target="general.header.fields"/>
1701                     | response-header        ; &response-header-fields;
1702                     | entity-header ) CRLF)  ; &entity-header-fields;
1703                    CRLF
1704                    [ message-body ]          ; <xref target="message.body"/>
1705</artwork></figure>
1706
1707<section title="Status-Line" anchor="status-line">
1708<t>
1709   The first line of a Response message is the Status-Line, consisting
1710   of the protocol version followed by a numeric status code and its
1711   associated textual phrase, with each element separated by SP
1712   characters. No CR or LF is allowed except in the final CRLF sequence.
1713</t>
1714<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1715    Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
1716</artwork></figure>
1717
1718<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1719<t>
1720   The Status-Code element is a 3-digit integer result code of the
1721   attempt to understand and satisfy the request. These codes are fully
1722   defined in &status-codes;. The Reason-Phrase is intended to give a short
1723   textual description of the Status-Code. The Status-Code is intended
1724   for use by automata and the Reason-Phrase is intended for the human
1725   user. The client is not required to examine or display the Reason-Phrase.
1726</t>
1727<t>
1728   The first digit of the Status-Code defines the class of response. The
1729   last two digits do not have any categorization role. There are 5
1730   values for the first digit:
1731  <list style="symbols">
1732    <t>
1733      1xx: Informational - Request received, continuing process
1734    </t>
1735    <t>
1736      2xx: Success - The action was successfully received,
1737        understood, and accepted
1738    </t>
1739    <t>
1740      3xx: Redirection - Further action must be taken in order to
1741        complete the request
1742    </t>
1743    <t>
1744      4xx: Client Error - The request contains bad syntax or cannot
1745        be fulfilled
1746    </t>
1747    <t>
1748      5xx: Server Error - The server failed to fulfill an apparently
1749        valid request
1750    </t>
1751  </list>
1752</t>
1753<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="extension-code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
1754   Status-Code    = 3DIGIT
1755   Reason-Phrase  = *&lt;TEXT, excluding CR, LF&gt;
1756</artwork></figure>
1757</section>
1758</section>
1759
1760</section>
1761
1762
1763<section title="Connections" anchor="connections">
1764
1765<section title="Persistent Connections" anchor="persistent.connections">
1766
1767<section title="Purpose" anchor="persistent.purpose">
1768<t>
1769   Prior to persistent connections, a separate TCP connection was
1770   established to fetch each URL, increasing the load on HTTP servers
1771   and causing congestion on the Internet. The use of inline images and
1772   other associated data often require a client to make multiple
1773   requests of the same server in a short amount of time. Analysis of
1774   these performance problems and results from a prototype
1775   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1776   measurements of actual HTTP/1.1 (RFC 2068) implementations show good
1777   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1778   T/TCP <xref target="Tou1998"/>.
1779</t>
1780<t>
1781   Persistent HTTP connections have a number of advantages:
1782  <list style="symbols">
1783      <t>
1784        By opening and closing fewer TCP connections, CPU time is saved
1785        in routers and hosts (clients, servers, proxies, gateways,
1786        tunnels, or caches), and memory used for TCP protocol control
1787        blocks can be saved in hosts.
1788      </t>
1789      <t>
1790        HTTP requests and responses can be pipelined on a connection.
1791        Pipelining allows a client to make multiple requests without
1792        waiting for each response, allowing a single TCP connection to
1793        be used much more efficiently, with much lower elapsed time.
1794      </t>
1795      <t>
1796        Network congestion is reduced by reducing the number of packets
1797        caused by TCP opens, and by allowing TCP sufficient time to
1798        determine the congestion state of the network.
1799      </t>
1800      <t>
1801        Latency on subsequent requests is reduced since there is no time
1802        spent in TCP's connection opening handshake.
1803      </t>
1804      <t>
1805        HTTP can evolve more gracefully, since errors can be reported
1806        without the penalty of closing the TCP connection. Clients using
1807        future versions of HTTP might optimistically try a new feature,
1808        but if communicating with an older server, retry with old
1809        semantics after an error is reported.
1810      </t>
1811    </list>
1812</t>
1813<t>
1814   HTTP implementations &SHOULD; implement persistent connections.
1815</t>
1816</section>
1817
1818<section title="Overall Operation" anchor="persistent.overall">
1819<t>
1820   A significant difference between HTTP/1.1 and earlier versions of
1821   HTTP is that persistent connections are the default behavior of any
1822   HTTP connection. That is, unless otherwise indicated, the client
1823   &SHOULD; assume that the server will maintain a persistent connection,
1824   even after error responses from the server.
1825</t>
1826<t>
1827   Persistent connections provide a mechanism by which a client and a
1828   server can signal the close of a TCP connection. This signaling takes
1829   place using the Connection header field (<xref target="header.connection"/>). Once a close
1830   has been signaled, the client &MUST-NOT; send any more requests on that
1831   connection.
1832</t>
1833
1834<section title="Negotiation" anchor="persistent.negotiation">
1835<t>
1836   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1837   maintain a persistent connection unless a Connection header including
1838   the connection-token "close" was sent in the request. If the server
1839   chooses to close the connection immediately after sending the
1840   response, it &SHOULD; send a Connection header including the
1841   connection-token close.
1842</t>
1843<t>
1844   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1845   decide to keep it open based on whether the response from a server
1846   contains a Connection header with the connection-token close. In case
1847   the client does not want to maintain a connection for more than that
1848   request, it &SHOULD; send a Connection header including the
1849   connection-token close.
1850</t>
1851<t>
1852   If either the client or the server sends the close token in the
1853   Connection header, that request becomes the last one for the
1854   connection.
1855</t>
1856<t>
1857   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1858   maintained for HTTP versions less than 1.1 unless it is explicitly
1859   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1860   compatibility with HTTP/1.0 clients.
1861</t>
1862<t>
1863   In order to remain persistent, all messages on the connection &MUST;
1864   have a self-defined message length (i.e., one not defined by closure
1865   of the connection), as described in <xref target="message.length"/>.
1866</t>
1867</section>
1868
1869<section title="Pipelining" anchor="pipelining">
1870<t>
1871   A client that supports persistent connections &MAY; "pipeline" its
1872   requests (i.e., send multiple requests without waiting for each
1873   response). A server &MUST; send its responses to those requests in the
1874   same order that the requests were received.
1875</t>
1876<t>
1877   Clients which assume persistent connections and pipeline immediately
1878   after connection establishment &SHOULD; be prepared to retry their
1879   connection if the first pipelined attempt fails. If a client does
1880   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1881   persistent. Clients &MUST; also be prepared to resend their requests if
1882   the server closes the connection before sending all of the
1883   corresponding responses.
1884</t>
1885<t>
1886   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1887   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1888   premature termination of the transport connection could lead to
1889   indeterminate results. A client wishing to send a non-idempotent
1890   request &SHOULD; wait to send that request until it has received the
1891   response status for the previous request.
1892</t>
1893</section>
1894</section>
1895
1896<section title="Proxy Servers" anchor="persistent.proxy">
1897<t>
1898   It is especially important that proxies correctly implement the
1899   properties of the Connection header field as specified in <xref target="header.connection"/>.
1900</t>
1901<t>
1902   The proxy server &MUST; signal persistent connections separately with
1903   its clients and the origin servers (or other proxy servers) that it
1904   connects to. Each persistent connection applies to only one transport
1905   link.
1906</t>
1907<t>
1908   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1909   with an HTTP/1.0 client (but see RFC 2068 <xref target="RFC2068"/> for information and
1910   discussion of the problems with the Keep-Alive header implemented by
1911   many HTTP/1.0 clients).
1912</t>
1913</section>
1914
1915<section title="Practical Considerations" anchor="persistent.practical">
1916<t>
1917   Servers will usually have some time-out value beyond which they will
1918   no longer maintain an inactive connection. Proxy servers might make
1919   this a higher value since it is likely that the client will be making
1920   more connections through the same server. The use of persistent
1921   connections places no requirements on the length (or existence) of
1922   this time-out for either the client or the server.
1923</t>
1924<t>
1925   When a client or server wishes to time-out it &SHOULD; issue a graceful
1926   close on the transport connection. Clients and servers &SHOULD; both
1927   constantly watch for the other side of the transport close, and
1928   respond to it as appropriate. If a client or server does not detect
1929   the other side's close promptly it could cause unnecessary resource
1930   drain on the network.
1931</t>
1932<t>
1933   A client, server, or proxy &MAY; close the transport connection at any
1934   time. For example, a client might have started to send a new request
1935   at the same time that the server has decided to close the "idle"
1936   connection. From the server's point of view, the connection is being
1937   closed while it was idle, but from the client's point of view, a
1938   request is in progress.
1939</t>
1940<t>
1941   This means that clients, servers, and proxies &MUST; be able to recover
1942   from asynchronous close events. Client software &SHOULD; reopen the
1943   transport connection and retransmit the aborted sequence of requests
1944   without user interaction so long as the request sequence is
1945   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1946   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1947   human operator the choice of retrying the request(s). Confirmation by
1948   user-agent software with semantic understanding of the application
1949   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
1950   be repeated if the second sequence of requests fails.
1951</t>
1952<t>
1953   Servers &SHOULD; always respond to at least one request per connection,
1954   if at all possible. Servers &SHOULD-NOT;  close a connection in the
1955   middle of transmitting a response, unless a network or client failure
1956   is suspected.
1957</t>
1958<t>
1959   Clients that use persistent connections &SHOULD; limit the number of
1960   simultaneous connections that they maintain to a given server. A
1961   single-user client &SHOULD-NOT; maintain more than 2 connections with
1962   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
1963   another server or proxy, where N is the number of simultaneously
1964   active users. These guidelines are intended to improve HTTP response
1965   times and avoid congestion.
1966</t>
1967</section>
1968</section>
1969
1970<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
1971
1972<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
1973<t>
1974   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
1975   flow control mechanisms to resolve temporary overloads, rather than
1976   terminating connections with the expectation that clients will retry.
1977   The latter technique can exacerbate network congestion.
1978</t>
1979</section>
1980
1981<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
1982<t>
1983   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
1984   the network connection for an error status while it is transmitting
1985   the request. If the client sees an error status, it &SHOULD;
1986   immediately cease transmitting the body. If the body is being sent
1987   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
1988   empty trailer &MAY; be used to prematurely mark the end of the message.
1989   If the body was preceded by a Content-Length header, the client &MUST;
1990   close the connection.
1991</t>
1992</section>
1993
1994<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
1995<t>
1996   The purpose of the 100 (Continue) status (see &status-100;) is to
1997   allow a client that is sending a request message with a request body
1998   to determine if the origin server is willing to accept the request
1999   (based on the request headers) before the client sends the request
2000   body. In some cases, it might either be inappropriate or highly
2001   inefficient for the client to send the body if the server will reject
2002   the message without looking at the body.
2003</t>
2004<t>
2005   Requirements for HTTP/1.1 clients:
2006  <list style="symbols">
2007    <t>
2008        If a client will wait for a 100 (Continue) response before
2009        sending the request body, it &MUST; send an Expect request-header
2010        field (&header-expect;) with the "100-continue" expectation.
2011    </t>
2012    <t>
2013        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2014        with the "100-continue" expectation if it does not intend
2015        to send a request body.
2016    </t>
2017  </list>
2018</t>
2019<t>
2020   Because of the presence of older implementations, the protocol allows
2021   ambiguous situations in which a client may send "Expect: 100-continue"
2022   without receiving either a 417 (Expectation Failed) status
2023   or a 100 (Continue) status. Therefore, when a client sends this
2024   header field to an origin server (possibly via a proxy) from which it
2025   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
2026   for an indefinite period before sending the request body.
2027</t>
2028<t>
2029   Requirements for HTTP/1.1 origin servers:
2030  <list style="symbols">
2031    <t> Upon receiving a request which includes an Expect request-header
2032        field with the "100-continue" expectation, an origin server &MUST;
2033        either respond with 100 (Continue) status and continue to read
2034        from the input stream, or respond with a final status code. The
2035        origin server &MUST-NOT; wait for the request body before sending
2036        the 100 (Continue) response. If it responds with a final status
2037        code, it &MAY; close the transport connection or it &MAY; continue
2038        to read and discard the rest of the request.  It &MUST-NOT;
2039        perform the requested method if it returns a final status code.
2040    </t>
2041    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2042        the request message does not include an Expect request-header
2043        field with the "100-continue" expectation, and &MUST-NOT; send a
2044        100 (Continue) response if such a request comes from an HTTP/1.0
2045        (or earlier) client. There is an exception to this rule: for
2046        compatibility with RFC 2068, a server &MAY; send a 100 (Continue)
2047        status in response to an HTTP/1.1 PUT or POST request that does
2048        not include an Expect request-header field with the "100-continue"
2049        expectation. This exception, the purpose of which is
2050        to minimize any client processing delays associated with an
2051        undeclared wait for 100 (Continue) status, applies only to
2052        HTTP/1.1 requests, and not to requests with any other HTTP-version
2053        value.
2054    </t>
2055    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2056        already received some or all of the request body for the
2057        corresponding request.
2058    </t>
2059    <t> An origin server that sends a 100 (Continue) response &MUST;
2060    ultimately send a final status code, once the request body is
2061        received and processed, unless it terminates the transport
2062        connection prematurely.
2063    </t>
2064    <t> If an origin server receives a request that does not include an
2065        Expect request-header field with the "100-continue" expectation,
2066        the request includes a request body, and the server responds
2067        with a final status code before reading the entire request body
2068        from the transport connection, then the server &SHOULD-NOT;  close
2069        the transport connection until it has read the entire request,
2070        or until the client closes the connection. Otherwise, the client
2071        might not reliably receive the response message. However, this
2072        requirement is not be construed as preventing a server from
2073        defending itself against denial-of-service attacks, or from
2074        badly broken client implementations.
2075      </t>
2076    </list>
2077</t>
2078<t>
2079   Requirements for HTTP/1.1 proxies:
2080  <list style="symbols">
2081    <t> If a proxy receives a request that includes an Expect request-header
2082        field with the "100-continue" expectation, and the proxy
2083        either knows that the next-hop server complies with HTTP/1.1 or
2084        higher, or does not know the HTTP version of the next-hop
2085        server, it &MUST; forward the request, including the Expect header
2086        field.
2087    </t>
2088    <t> If the proxy knows that the version of the next-hop server is
2089        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2090        respond with a 417 (Expectation Failed) status.
2091    </t>
2092    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2093        numbers received from recently-referenced next-hop servers.
2094    </t>
2095    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2096        request message was received from an HTTP/1.0 (or earlier)
2097        client and did not include an Expect request-header field with
2098        the "100-continue" expectation. This requirement overrides the
2099        general rule for forwarding of 1xx responses (see &status-1xx;).
2100    </t>
2101  </list>
2102</t>
2103</section>
2104
2105<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2106<t>
2107   If an HTTP/1.1 client sends a request which includes a request body,
2108   but which does not include an Expect request-header field with the
2109   "100-continue" expectation, and if the client is not directly
2110   connected to an HTTP/1.1 origin server, and if the client sees the
2111   connection close before receiving any status from the server, the
2112   client &SHOULD; retry the request.  If the client does retry this
2113   request, it &MAY; use the following "binary exponential backoff"
2114   algorithm to be assured of obtaining a reliable response:
2115  <list style="numbers">
2116    <t>
2117      Initiate a new connection to the server
2118    </t>
2119    <t>
2120      Transmit the request-headers
2121    </t>
2122    <t>
2123      Initialize a variable R to the estimated round-trip time to the
2124         server (e.g., based on the time it took to establish the
2125         connection), or to a constant value of 5 seconds if the round-trip
2126         time is not available.
2127    </t>
2128    <t>
2129       Compute T = R * (2**N), where N is the number of previous
2130         retries of this request.
2131    </t>
2132    <t>
2133       Wait either for an error response from the server, or for T
2134         seconds (whichever comes first)
2135    </t>
2136    <t>
2137       If no error response is received, after T seconds transmit the
2138         body of the request.
2139    </t>
2140    <t>
2141       If client sees that the connection is closed prematurely,
2142         repeat from step 1 until the request is accepted, an error
2143         response is received, or the user becomes impatient and
2144         terminates the retry process.
2145    </t>
2146  </list>
2147</t>
2148<t>
2149   If at any point an error status is received, the client
2150  <list style="symbols">
2151      <t>&SHOULD-NOT;  continue and</t>
2152
2153      <t>&SHOULD; close the connection if it has not completed sending the
2154        request message.</t>
2155    </list>
2156</t>
2157</section>
2158</section>
2159</section>
2160
2161
2162<section title="Header Field Definitions" anchor="header.fields">
2163<t>
2164   This section defines the syntax and semantics of all standard
2165   HTTP/1.1 header fields. For entity-header fields, both sender and
2166   recipient refer to either the client or the server, depending on who
2167   sends and who receives the entity.
2168</t>
2169
2170<section title="Connection" anchor="header.connection">
2171  <iref primary="true" item="Connection header" x:for-anchor=""/>
2172  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2173<t>
2174   The Connection general-header field allows the sender to specify
2175   options that are desired for that particular connection and &MUST-NOT;
2176   be communicated by proxies over further connections.
2177</t>
2178<t>
2179   The Connection header has the following grammar:
2180</t>
2181<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2182    Connection = "Connection" ":" 1#(connection-token)
2183    connection-token  = token
2184</artwork></figure>
2185<t>
2186   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2187   message is forwarded and, for each connection-token in this field,
2188   remove any header field(s) from the message with the same name as the
2189   connection-token. Connection options are signaled by the presence of
2190   a connection-token in the Connection header field, not by any
2191   corresponding additional header field(s), since the additional header
2192   field may not be sent if there are no parameters associated with that
2193   connection option.
2194</t>
2195<t>
2196   Message headers listed in the Connection header &MUST-NOT; include
2197   end-to-end headers, such as Cache-Control.
2198</t>
2199<t>
2200   HTTP/1.1 defines the "close" connection option for the sender to
2201   signal that the connection will be closed after completion of the
2202   response. For example,
2203</t>
2204<figure><artwork type="example">
2205    Connection: close
2206</artwork></figure>
2207<t>
2208   in either the request or the response header fields indicates that
2209   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2210   after the current request/response is complete.
2211</t>
2212<t>
2213   An HTTP/1.1 client that does not support persistent connections &MUST;
2214   include the "close" connection option in every request message.
2215</t>
2216<t>
2217   An HTTP/1.1 server that does not support persistent connections &MUST;
2218   include the "close" connection option in every response message that
2219   does not have a 1xx (informational) status code.
2220</t>
2221<t>
2222   A system receiving an HTTP/1.0 (or lower-version) message that
2223   includes a Connection header MUST, for each connection-token in this
2224   field, remove and ignore any header field(s) from the message with
2225   the same name as the connection-token. This protects against mistaken
2226   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2227</t>
2228</section>
2229
2230<section title="Content-Length" anchor="header.content-length">
2231  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2232  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2233<t>
2234   The Content-Length entity-header field indicates the size of the
2235   entity-body, in decimal number of OCTETs, sent to the recipient or,
2236   in the case of the HEAD method, the size of the entity-body that
2237   would have been sent had the request been a GET.
2238</t>
2239<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
2240    Content-Length    = "Content-Length" ":" 1*DIGIT
2241</artwork></figure>
2242<t>
2243   An example is
2244</t>
2245<figure><artwork type="example">
2246    Content-Length: 3495
2247</artwork></figure>
2248<t>
2249   Applications &SHOULD; use this field to indicate the transfer-length of
2250   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2251</t>
2252<t>
2253   Any Content-Length greater than or equal to zero is a valid value.
2254   <xref target="message.length"/> describes how to determine the length of a message-body
2255   if a Content-Length is not given.
2256</t>
2257<t>
2258   Note that the meaning of this field is significantly different from
2259   the corresponding definition in MIME, where it is an optional field
2260   used within the "message/external-body" content-type. In HTTP, it
2261   &SHOULD; be sent whenever the message's length can be determined prior
2262   to being transferred, unless this is prohibited by the rules in
2263   <xref target="message.length"/>.
2264</t>
2265</section>
2266
2267<section title="Date" anchor="header.date">
2268  <iref primary="true" item="Date header" x:for-anchor=""/>
2269  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2270<t>
2271   The Date general-header field represents the date and time at which
2272   the message was originated, having the same semantics as orig-date in
2273   RFC 822. The field value is an HTTP-date, as described in <xref target="full.date"/>;
2274   it &MUST; be sent in rfc1123-date format.
2275</t>
2276<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2277    Date  = "Date" ":" HTTP-date
2278</artwork></figure>
2279<t>
2280   An example is
2281</t>
2282<figure><artwork type="example">
2283    Date: Tue, 15 Nov 1994 08:12:31 GMT
2284</artwork></figure>
2285<t>
2286   Origin servers &MUST; include a Date header field in all responses,
2287   except in these cases:
2288  <list style="numbers">
2289      <t>If the response status code is 100 (Continue) or 101 (Switching
2290         Protocols), the response &MAY; include a Date header field, at
2291         the server's option.</t>
2292
2293      <t>If the response status code conveys a server error, e.g. 500
2294         (Internal Server Error) or 503 (Service Unavailable), and it is
2295         inconvenient or impossible to generate a valid Date.</t>
2296
2297      <t>If the server does not have a clock that can provide a
2298         reasonable approximation of the current time, its responses
2299         &MUST-NOT; include a Date header field. In this case, the rules
2300         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2301  </list>
2302</t>
2303<t>
2304   A received message that does not have a Date header field &MUST; be
2305   assigned one by the recipient if the message will be cached by that
2306   recipient or gatewayed via a protocol which requires a Date. An HTTP
2307   implementation without a clock &MUST-NOT; cache responses without
2308   revalidating them on every use. An HTTP cache, especially a shared
2309   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2310   clock with a reliable external standard.
2311</t>
2312<t>
2313   Clients &SHOULD; only send a Date header field in messages that include
2314   an entity-body, as in the case of the PUT and POST requests, and even
2315   then it is optional. A client without a clock &MUST-NOT; send a Date
2316   header field in a request.
2317</t>
2318<t>
2319   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2320   time subsequent to the generation of the message. It &SHOULD; represent
2321   the best available approximation of the date and time of message
2322   generation, unless the implementation has no means of generating a
2323   reasonably accurate date and time. In theory, the date ought to
2324   represent the moment just before the entity is generated. In
2325   practice, the date can be generated at any time during the message
2326   origination without affecting its semantic value.
2327</t>
2328
2329<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2330<t>
2331   Some origin server implementations might not have a clock available.
2332   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2333   values to a response, unless these values were associated
2334   with the resource by a system or user with a reliable clock. It &MAY;
2335   assign an Expires value that is known, at or before server
2336   configuration time, to be in the past (this allows "pre-expiration"
2337   of responses without storing separate Expires values for each
2338   resource).
2339</t>
2340</section>
2341</section>
2342
2343<section title="Host" anchor="header.host">
2344  <iref primary="true" item="Host header" x:for-anchor=""/>
2345  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2346<t>
2347   The Host request-header field specifies the Internet host and port
2348   number of the resource being requested, as obtained from the original
2349   URI given by the user or referring resource (generally an HTTP URL,
2350   as described in <xref target="http.url"/>). The Host field value &MUST; represent
2351   the naming authority of the origin server or gateway given by the
2352   original URL. This allows the origin server or gateway to
2353   differentiate between internally-ambiguous URLs, such as the root "/"
2354   URL of a server for multiple host names on a single IP address.
2355</t>
2356<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2357    Host = "Host" ":" host [ ":" port ] ; <xref target="http.url"/>
2358</artwork></figure>
2359<t>
2360   A "host" without any trailing port information implies the default
2361   port for the service requested (e.g., "80" for an HTTP URL). For
2362   example, a request on the origin server for
2363   &lt;http://www.w3.org/pub/WWW/&gt; would properly include:
2364</t>
2365<figure><artwork type="example">
2366    GET /pub/WWW/ HTTP/1.1
2367    Host: www.w3.org
2368</artwork></figure>
2369<t>
2370   A client &MUST; include a Host header field in all HTTP/1.1 request
2371   messages . If the requested URI does not include an Internet host
2372   name for the service being requested, then the Host header field &MUST;
2373   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2374   request message it forwards does contain an appropriate Host header
2375   field that identifies the service being requested by the proxy. All
2376   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2377   status code to any HTTP/1.1 request message which lacks a Host header
2378   field.
2379</t>
2380<t>
2381   See sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2382   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2383   for other requirements relating to Host.
2384</t>
2385</section>
2386
2387<section title="TE" anchor="header.te">
2388  <iref primary="true" item="TE header" x:for-anchor=""/>
2389  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2390<t>
2391   The TE request-header field indicates what extension transfer-codings
2392   it is willing to accept in the response and whether or not it is
2393   willing to accept trailer fields in a chunked transfer-coding. Its
2394   value may consist of the keyword "trailers" and/or a comma-separated
2395   list of extension transfer-coding names with optional accept
2396   parameters (as described in <xref target="transfer.codings"/>).
2397</t>
2398<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="t-codings"/>
2399    TE        = "TE" ":" #( t-codings )
2400    t-codings = "trailers" | ( transfer-extension [ accept-params ] )
2401</artwork></figure>
2402<t>
2403   The presence of the keyword "trailers" indicates that the client is
2404   willing to accept trailer fields in a chunked transfer-coding, as
2405   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2406   transfer-coding values even though it does not itself represent a
2407   transfer-coding.
2408</t>
2409<t>
2410   Examples of its use are:
2411</t>
2412<figure><artwork type="example">
2413    TE: deflate
2414    TE:
2415    TE: trailers, deflate;q=0.5
2416</artwork></figure>
2417<t>
2418   The TE header field only applies to the immediate connection.
2419   Therefore, the keyword &MUST; be supplied within a Connection header
2420   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2421</t>
2422<t>
2423   A server tests whether a transfer-coding is acceptable, according to
2424   a TE field, using these rules:
2425  <list style="numbers">
2426    <x:lt>
2427      <t>The "chunked" transfer-coding is always acceptable. If the
2428         keyword "trailers" is listed, the client indicates that it is
2429         willing to accept trailer fields in the chunked response on
2430         behalf of itself and any downstream clients. The implication is
2431         that, if given, the client is stating that either all
2432         downstream clients are willing to accept trailer fields in the
2433         forwarded response, or that it will attempt to buffer the
2434         response on behalf of downstream recipients.
2435      </t><t>
2436         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2437         chunked response such that a client can be assured of buffering
2438         the entire response.</t>
2439    </x:lt>
2440    <x:lt>
2441      <t>If the transfer-coding being tested is one of the transfer-codings
2442         listed in the TE field, then it is acceptable unless it
2443         is accompanied by a qvalue of 0. (As defined in &qvalue;, a
2444         qvalue of 0 means "not acceptable.")</t>
2445    </x:lt>
2446    <x:lt>
2447      <t>If multiple transfer-codings are acceptable, then the
2448         acceptable transfer-coding with the highest non-zero qvalue is
2449         preferred.  The "chunked" transfer-coding always has a qvalue
2450         of 1.</t>
2451    </x:lt>
2452  </list>
2453</t>
2454<t>
2455   If the TE field-value is empty or if no TE field is present, the only
2456   transfer-coding  is "chunked". A message with no transfer-coding is
2457   always acceptable.
2458</t>
2459</section>
2460
2461<section title="Trailer" anchor="header.trailer">
2462  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2463  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2464<t>
2465   The Trailer general field value indicates that the given set of
2466   header fields is present in the trailer of a message encoded with
2467   chunked transfer-coding.
2468</t>
2469<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
2470    Trailer  = "Trailer" ":" 1#field-name
2471</artwork></figure>
2472<t>
2473   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2474   message using chunked transfer-coding with a non-empty trailer. Doing
2475   so allows the recipient to know which header fields to expect in the
2476   trailer.
2477</t>
2478<t>
2479   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2480   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2481   trailer fields in a "chunked" transfer-coding.
2482</t>
2483<t>
2484   Message header fields listed in the Trailer header field &MUST-NOT;
2485   include the following header fields:
2486  <list style="symbols">
2487    <t>Transfer-Encoding</t>
2488    <t>Content-Length</t>
2489    <t>Trailer</t>
2490  </list>
2491</t>
2492</section>
2493
2494<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2495  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2496  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2497<t>
2498   The Transfer-Encoding general-header field indicates what (if any)
2499   type of transformation has been applied to the message body in order
2500   to safely transfer it between the sender and the recipient. This
2501   differs from the content-coding in that the transfer-coding is a
2502   property of the message, not of the entity.
2503</t>
2504<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
2505  Transfer-Encoding       = "Transfer-Encoding" ":" 1#transfer-coding
2506</artwork></figure>
2507<t>
2508   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2509</t>
2510<figure><artwork type="example">
2511  Transfer-Encoding: chunked
2512</artwork></figure>
2513<t>
2514   If multiple encodings have been applied to an entity, the transfer-codings
2515   &MUST; be listed in the order in which they were applied.
2516   Additional information about the encoding parameters &MAY; be provided
2517   by other entity-header fields not defined by this specification.
2518</t>
2519<t>
2520   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2521   header.
2522</t>
2523</section>
2524
2525<section title="Upgrade" anchor="header.upgrade">
2526  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2527  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2528<t>
2529   The Upgrade general-header allows the client to specify what
2530   additional communication protocols it supports and would like to use
2531   if the server finds it appropriate to switch protocols. The server
2532   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2533   response to indicate which protocol(s) are being switched.
2534</t>
2535<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
2536    Upgrade        = "Upgrade" ":" 1#product
2537</artwork></figure>
2538<t>
2539   For example,
2540</t>
2541<figure><artwork type="example">
2542    Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2543</artwork></figure>
2544<t>
2545   The Upgrade header field is intended to provide a simple mechanism
2546   for transition from HTTP/1.1 to some other, incompatible protocol. It
2547   does so by allowing the client to advertise its desire to use another
2548   protocol, such as a later version of HTTP with a higher major version
2549   number, even though the current request has been made using HTTP/1.1.
2550   This eases the difficult transition between incompatible protocols by
2551   allowing the client to initiate a request in the more commonly
2552   supported protocol while indicating to the server that it would like
2553   to use a "better" protocol if available (where "better" is determined
2554   by the server, possibly according to the nature of the method and/or
2555   resource being requested).
2556</t>
2557<t>
2558   The Upgrade header field only applies to switching application-layer
2559   protocols upon the existing transport-layer connection. Upgrade
2560   cannot be used to insist on a protocol change; its acceptance and use
2561   by the server is optional. The capabilities and nature of the
2562   application-layer communication after the protocol change is entirely
2563   dependent upon the new protocol chosen, although the first action
2564   after changing the protocol &MUST; be a response to the initial HTTP
2565   request containing the Upgrade header field.
2566</t>
2567<t>
2568   The Upgrade header field only applies to the immediate connection.
2569   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2570   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2571   HTTP/1.1 message.
2572</t>
2573<t>
2574   The Upgrade header field cannot be used to indicate a switch to a
2575   protocol on a different connection. For that purpose, it is more
2576   appropriate to use a 301, 302, 303, or 305 redirection response.
2577</t>
2578<t>
2579   This specification only defines the protocol name "HTTP" for use by
2580   the family of Hypertext Transfer Protocols, as defined by the HTTP
2581   version rules of <xref target="http.version"/> and future updates to this
2582   specification. Any token can be used as a protocol name; however, it
2583   will only be useful if both the client and server associate the name
2584   with the same protocol.
2585</t>
2586</section>
2587
2588<section title="Via" anchor="header.via">
2589  <iref primary="true" item="Via header" x:for-anchor=""/>
2590  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2591<t>
2592   The Via general-header field &MUST; be used by gateways and proxies to
2593   indicate the intermediate protocols and recipients between the user
2594   agent and the server on requests, and between the origin server and
2595   the client on responses. It is analogous to the "Received" field of
2596   RFC 822 <xref target="RFC822"/> and is intended to be used for tracking message forwards,
2597   avoiding request loops, and identifying the protocol capabilities of
2598   all senders along the request/response chain.
2599</t>
2600<figure><artwork type="abnf2616"><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"/>
2601   Via =  "Via" ":" 1#( received-protocol received-by [ comment ] )
2602   received-protocol = [ protocol-name "/" ] protocol-version
2603   protocol-name     = token
2604   protocol-version  = token
2605   received-by       = ( host [ ":" port ] ) | pseudonym
2606   pseudonym         = token
2607</artwork></figure>
2608<t>
2609   The received-protocol indicates the protocol version of the message
2610   received by the server or client along each segment of the
2611   request/response chain. The received-protocol version is appended to
2612   the Via field value when the message is forwarded so that information
2613   about the protocol capabilities of upstream applications remains
2614   visible to all recipients.
2615</t>
2616<t>
2617   The protocol-name is optional if and only if it would be "HTTP". The
2618   received-by field is normally the host and optional port number of a
2619   recipient server or client that subsequently forwarded the message.
2620   However, if the real host is considered to be sensitive information,
2621   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2622   be assumed to be the default port of the received-protocol.
2623</t>
2624<t>
2625   Multiple Via field values represents each proxy or gateway that has
2626   forwarded the message. Each recipient &MUST; append its information
2627   such that the end result is ordered according to the sequence of
2628   forwarding applications.
2629</t>
2630<t>
2631   Comments &MAY; be used in the Via header field to identify the software
2632   of the recipient proxy or gateway, analogous to the User-Agent and
2633   Server header fields. However, all comments in the Via field are
2634   optional and &MAY; be removed by any recipient prior to forwarding the
2635   message.
2636</t>
2637<t>
2638   For example, a request message could be sent from an HTTP/1.0 user
2639   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2640   forward the request to a public proxy at nowhere.com, which completes
2641   the request by forwarding it to the origin server at www.ics.uci.edu.
2642   The request received by www.ics.uci.edu would then have the following
2643   Via header field:
2644</t>
2645<figure><artwork type="example">
2646    Via: 1.0 fred, 1.1 nowhere.com (Apache/1.1)
2647</artwork></figure>
2648<t>
2649   Proxies and gateways used as a portal through a network firewall
2650   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2651   the firewall region. This information &SHOULD; only be propagated if
2652   explicitly enabled. If not enabled, the received-by host of any host
2653   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2654   for that host.
2655</t>
2656<t>
2657   For organizations that have strong privacy requirements for hiding
2658   internal structures, a proxy &MAY; combine an ordered subsequence of
2659   Via header field entries with identical received-protocol values into
2660   a single such entry. For example,
2661</t>
2662<figure><artwork type="example">
2663    Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2664</artwork></figure>
2665<t>
2666        could be collapsed to
2667</t>
2668<figure><artwork type="example">
2669    Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2670</artwork></figure>
2671<t>
2672   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2673   under the same organizational control and the hosts have already been
2674   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2675   have different received-protocol values.
2676</t>
2677</section>
2678
2679</section>
2680
2681<section title="IANA Considerations" anchor="IANA.considerations">
2682<t>
2683   TBD.
2684</t>
2685</section>
2686
2687<section title="Security Considerations" anchor="security.considerations">
2688<t>
2689   This section is meant to inform application developers, information
2690   providers, and users of the security limitations in HTTP/1.1 as
2691   described by this document. The discussion does not include
2692   definitive solutions to the problems revealed, though it does make
2693   some suggestions for reducing security risks.
2694</t>
2695
2696<section title="Personal Information" anchor="personal.information">
2697<t>
2698   HTTP clients are often privy to large amounts of personal information
2699   (e.g. the user's name, location, mail address, passwords, encryption
2700   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2701   leakage of this information via the HTTP protocol to other sources.
2702   We very strongly recommend that a convenient interface be provided
2703   for the user to control dissemination of such information, and that
2704   designers and implementors be particularly careful in this area.
2705   History shows that errors in this area often create serious security
2706   and/or privacy problems and generate highly adverse publicity for the
2707   implementor's company.
2708</t>
2709</section>
2710
2711<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2712<t>
2713   A server is in the position to save personal data about a user's
2714   requests which might identify their reading patterns or subjects of
2715   interest. This information is clearly confidential in nature and its
2716   handling can be constrained by law in certain countries. People using
2717   the HTTP protocol to provide data are responsible for ensuring that
2718   such material is not distributed without the permission of any
2719   individuals that are identifiable by the published results.
2720</t>
2721</section>
2722
2723<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2724<t>
2725   Implementations of HTTP origin servers &SHOULD; be careful to restrict
2726   the documents returned by HTTP requests to be only those that were
2727   intended by the server administrators. If an HTTP server translates
2728   HTTP URIs directly into file system calls, the server &MUST; take
2729   special care not to serve files that were not intended to be
2730   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
2731   other operating systems use ".." as a path component to indicate a
2732   directory level above the current one. On such a system, an HTTP
2733   server &MUST; disallow any such construct in the Request-URI if it
2734   would otherwise allow access to a resource outside those intended to
2735   be accessible via the HTTP server. Similarly, files intended for
2736   reference only internally to the server (such as access control
2737   files, configuration files, and script code) &MUST; be protected from
2738   inappropriate retrieval, since they might contain sensitive
2739   information. Experience has shown that minor bugs in such HTTP server
2740   implementations have turned into security risks.
2741</t>
2742</section>
2743
2744<section title="DNS Spoofing" anchor="dns.spoofing">
2745<t>
2746   Clients using HTTP rely heavily on the Domain Name Service, and are
2747   thus generally prone to security attacks based on the deliberate
2748   mis-association of IP addresses and DNS names. Clients need to be
2749   cautious in assuming the continuing validity of an IP number/DNS name
2750   association.
2751</t>
2752<t>
2753   In particular, HTTP clients &SHOULD; rely on their name resolver for
2754   confirmation of an IP number/DNS name association, rather than
2755   caching the result of previous host name lookups. Many platforms
2756   already can cache host name lookups locally when appropriate, and
2757   they &SHOULD; be configured to do so. It is proper for these lookups to
2758   be cached, however, only when the TTL (Time To Live) information
2759   reported by the name server makes it likely that the cached
2760   information will remain useful.
2761</t>
2762<t>
2763   If HTTP clients cache the results of host name lookups in order to
2764   achieve a performance improvement, they &MUST; observe the TTL
2765   information reported by DNS.
2766</t>
2767<t>
2768   If HTTP clients do not observe this rule, they could be spoofed when
2769   a previously-accessed server's IP address changes. As network
2770   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
2771   possibility of this form of attack will grow. Observing this
2772   requirement thus reduces this potential security vulnerability.
2773</t>
2774<t>
2775   This requirement also improves the load-balancing behavior of clients
2776   for replicated servers using the same DNS name and reduces the
2777   likelihood of a user's experiencing failure in accessing sites which
2778   use that strategy.
2779</t>
2780</section>
2781
2782<section title="Proxies and Caching" anchor="attack.proxies">
2783<t>
2784   By their very nature, HTTP proxies are men-in-the-middle, and
2785   represent an opportunity for man-in-the-middle attacks. Compromise of
2786   the systems on which the proxies run can result in serious security
2787   and privacy problems. Proxies have access to security-related
2788   information, personal information about individual users and
2789   organizations, and proprietary information belonging to users and
2790   content providers. A compromised proxy, or a proxy implemented or
2791   configured without regard to security and privacy considerations,
2792   might be used in the commission of a wide range of potential attacks.
2793</t>
2794<t>
2795   Proxy operators should protect the systems on which proxies run as
2796   they would protect any system that contains or transports sensitive
2797   information. In particular, log information gathered at proxies often
2798   contains highly sensitive personal information, and/or information
2799   about organizations. Log information should be carefully guarded, and
2800   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
2801</t>
2802<t>
2803   Proxy implementors should consider the privacy and security
2804   implications of their design and coding decisions, and of the
2805   configuration options they provide to proxy operators (especially the
2806   default configuration).
2807</t>
2808<t>
2809   Users of a proxy need to be aware that they are no trustworthier than
2810   the people who run the proxy; HTTP itself cannot solve this problem.
2811</t>
2812<t>
2813   The judicious use of cryptography, when appropriate, may suffice to
2814   protect against a broad range of security and privacy attacks. Such
2815   cryptography is beyond the scope of the HTTP/1.1 specification.
2816</t>
2817</section>
2818
2819<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
2820<t>
2821   They exist. They are hard to defend against. Research continues.
2822   Beware.
2823</t>
2824</section>
2825</section>
2826
2827<section title="Acknowledgments" anchor="ack">
2828<t>
2829   This specification makes heavy use of the augmented BNF and generic
2830   constructs defined by David H. Crocker for RFC 822 <xref target="RFC822"/>. Similarly, it
2831   reuses many of the definitions provided by Nathaniel Borenstein and
2832   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
2833   specification will help reduce past confusion over the relationship
2834   between HTTP and Internet mail message formats.
2835</t>
2836<t>
2837   The HTTP protocol has evolved considerably over the years. It has
2838   benefited from a large and active developer community--the many
2839   people who have participated on the www-talk mailing list--and it is
2840   that community which has been most responsible for the success of
2841   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
2842   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
2843   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
2844   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
2845   VanHeyningen deserve special recognition for their efforts in
2846   defining early aspects of the protocol.
2847</t>
2848<t>
2849   This document has benefited greatly from the comments of all those
2850   participating in the HTTP-WG. In addition to those already mentioned,
2851   the following individuals have contributed to this specification:
2852</t>
2853<figure><artwork type="text/plain">
2854    Gary Adams                  Ross Patterson
2855    Harald Tveit Alvestrand     Albert Lunde
2856    Keith Ball                  John C. Mallery
2857    Brian Behlendorf            Jean-Philippe Martin-Flatin
2858    Paul Burchard               Mitra
2859    Maurizio Codogno            David Morris
2860    Mike Cowlishaw              Gavin Nicol
2861    Roman Czyborra              Bill Perry
2862    Michael A. Dolan            Jeffrey Perry
2863    David J. Fiander            Scott Powers
2864    Alan Freier                 Owen Rees
2865    Marc Hedlund                Luigi Rizzo
2866    Greg Herlihy                David Robinson
2867    Koen Holtman                Marc Salomon
2868    Alex Hopmann                Rich Salz
2869    Bob Jernigan                Allan M. Schiffman
2870    Shel Kaphan                 Jim Seidman
2871    Rohit Khare                 Chuck Shotton
2872    John Klensin                Eric W. Sink
2873    Martijn Koster              Simon E. Spero
2874    Alexei Kosut                Richard N. Taylor
2875    David M. Kristol            Robert S. Thau
2876    Daniel LaLiberte            Bill (BearHeart) Weinman
2877    Ben Laurie                  Francois Yergeau
2878    Paul J. Leach               Mary Ellen Zurko
2879    Daniel DuBois               Josh Cohen
2880</artwork></figure>
2881<t>
2882   Thanks to the "cave men" of Palo Alto. You know who you are.
2883</t>
2884<t>
2885   Jim Gettys (the current editor of this document) wishes particularly
2886   to thank Roy Fielding, the previous editor of this document, along
2887   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
2888   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
2889   Larry Masinter for their help. And thanks go particularly to Jeff
2890   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
2891</t>
2892<t>
2893   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
2894   Frystyk implemented RFC 2068 early, and we wish to thank them for the
2895   discovery of many of the problems that this document attempts to
2896   rectify.
2897</t>
2898<t>
2899   Based on an XML translation of RFC 2616 by Julian Reschke.
2900</t>
2901</section>
2902
2903</middle>
2904<back>
2905<references>
2906
2907<reference anchor="Part2">
2908   <front>
2909      <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
2910      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2911         <organization abbrev="Day Software">Day Software</organization>
2912         <address><email>fielding@gbiv.com</email></address>
2913      </author>
2914      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2915         <organization>One Laptop per Child</organization>
2916         <address><email>jg@laptop.org</email></address>
2917      </author>
2918      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2919         <organization abbrev="HP">Hewlett-Packard Company</organization>
2920         <address><email>JeffMogul@acm.org</email></address>
2921      </author>
2922      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2923         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2924         <address><email>henrikn@microsoft.com</email></address>
2925      </author>
2926      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2927         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2928         <address><email>LMM@acm.org</email></address>
2929      </author>
2930      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2931         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2932         <address><email>paulle@microsoft.com</email></address>
2933      </author>
2934      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2935         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2936         <address><email>timbl@w3.org</email></address>
2937      </author>
2938      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2939   </front>
2940   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
2941   <x:source href="p2-semantics.xml" basename="p2-semantics"/>
2942</reference>
2943
2944<reference anchor="Part3">
2945   <front>
2946      <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
2947      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2948         <organization abbrev="Day Software">Day Software</organization>
2949         <address><email>fielding@gbiv.com</email></address>
2950      </author>
2951      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2952         <organization>One Laptop per Child</organization>
2953         <address><email>jg@laptop.org</email></address>
2954      </author>
2955      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2956         <organization abbrev="HP">Hewlett-Packard Company</organization>
2957         <address><email>JeffMogul@acm.org</email></address>
2958      </author>
2959      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2960         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2961         <address><email>henrikn@microsoft.com</email></address>
2962      </author>
2963      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2964         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2965         <address><email>LMM@acm.org</email></address>
2966      </author>
2967      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2968         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2969         <address><email>paulle@microsoft.com</email></address>
2970      </author>
2971      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2972         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2973         <address><email>timbl@w3.org</email></address>
2974      </author>
2975      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2976   </front>
2977   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
2978   <x:source href="p3-payload.xml" basename="p3-payload"/>
2979</reference>
2980
2981<reference anchor="Part6">
2982   <front>
2983      <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
2984      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2985         <organization abbrev="Day Software">Day Software</organization>
2986         <address><email>fielding@gbiv.com</email></address>
2987      </author>
2988      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2989         <organization>One Laptop per Child</organization>
2990         <address><email>jg@laptop.org</email></address>
2991      </author>
2992      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2993         <organization abbrev="HP">Hewlett-Packard Company</organization>
2994         <address><email>JeffMogul@acm.org</email></address>
2995      </author>
2996      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2997         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2998         <address><email>henrikn@microsoft.com</email></address>
2999      </author>
3000      <author initials="L." surname="Masinter" fullname="Larry Masinter">
3001         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3002         <address><email>LMM@acm.org</email></address>
3003      </author>
3004      <author initials="P." surname="Leach" fullname="Paul J. Leach">
3005         <organization abbrev="Microsoft">Microsoft Corporation</organization>
3006         <address><email>paulle@microsoft.com</email></address>
3007      </author>
3008      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3009         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3010         <address><email>timbl@w3.org</email></address>
3011      </author>
3012      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3013   </front>
3014   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3015   <x:source href="p6-cache.xml" basename="p6-cache"/>
3016</reference>
3017
3018<reference anchor="RFC2616">
3019   <front>
3020      <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3021      <author initials="R." surname="Fielding" fullname="R. Fielding">
3022         <organization>University of California, Irvine</organization>
3023         <address><email>fielding@ics.uci.edu</email></address>
3024      </author>
3025      <author initials="J." surname="Gettys" fullname="J. Gettys">
3026         <organization>W3C</organization>
3027         <address><email>jg@w3.org</email></address>
3028      </author>
3029      <author initials="J." surname="Mogul" fullname="J. Mogul">
3030         <organization>Compaq Computer Corporation</organization>
3031         <address><email>mogul@wrl.dec.com</email></address>
3032      </author>
3033      <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3034         <organization>MIT Laboratory for Computer Science</organization>
3035         <address><email>frystyk@w3.org</email></address>
3036      </author>
3037      <author initials="L." surname="Masinter" fullname="L. Masinter">
3038         <organization>Xerox Corporation</organization>
3039         <address><email>masinter@parc.xerox.com</email></address>
3040      </author>
3041      <author initials="P." surname="Leach" fullname="P. Leach">
3042         <organization>Microsoft Corporation</organization>
3043         <address><email>paulle@microsoft.com</email></address>
3044      </author>
3045      <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3046         <organization>W3C</organization>
3047         <address><email>timbl@w3.org</email></address>
3048      </author>
3049      <date month="June" year="1999"/>
3050   </front>
3051   <seriesInfo name="RFC" value="2616"/>
3052</reference>
3053
3054<reference anchor="RFC1436">
3055<front>
3056<title abbrev="Gopher">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</title>
3057<author initials="F." surname="Anklesaria" fullname="Farhad Anklesaria">
3058<organization>University of Minnesota, Computer and Information Services</organization>
3059<address>
3060<postal>
3061<street>100 Union Street SE</street>
3062<street>Room 152 Shepherd Labs</street>
3063<city>Minneapolis</city>
3064<region>MN</region>
3065<code>55455</code>
3066<country>US</country></postal>
3067<phone>+1 612 625 1300</phone>
3068<email>fxa@boombox.micro.umn.edu</email></address></author>
3069<author initials="M." surname="McCahill" fullname="Mark McCahill">
3070<organization>University of Minnesota, Computer and Information Services</organization>
3071<address>
3072<postal>
3073<street>100 Union Street SE</street>
3074<street>Room 152 Shepherd Labs</street>
3075<city>Minneapolis</city>
3076<region>MN</region>
3077<code>55455</code>
3078<country>US</country></postal>
3079<phone>+1 612 625 1300</phone>
3080<email>mpm@boombox.micro.umn.edu</email></address></author>
3081<author initials="P." surname="Lindner" fullname="Paul Lindner">
3082<organization>University of Minnesota, Computer and Information Services</organization>
3083<address>
3084<postal>
3085<street>100 Union Street SE</street>
3086<street>Room 152 Shepherd Labs</street>
3087<city>Minneapolis</city>
3088<region>MN</region>
3089<code>55455</code>
3090<country>US</country></postal>
3091<phone>+1 612 625 1300</phone>
3092<email>lindner@boombox.micro.umn.edu</email></address></author>
3093<author initials="D." surname="Johnson" fullname="David Johnson">
3094<organization>University of Minnesota, Computer and Information Services</organization>
3095<address>
3096<postal>
3097<street>100 Union Street SE</street>
3098<street>Room 152 Shepherd Labs</street>
3099<city>Minneapolis</city>
3100<region>MN</region>
3101<code>55455</code>
3102<country>US</country></postal>
3103<phone>+1 612 625 1300</phone>
3104<email>dmj@boombox.micro.umn.edu</email></address></author>
3105<author initials="D." surname="Torrey" fullname="Daniel Torrey">
3106<organization>University of Minnesota, Computer and Information Services</organization>
3107<address>
3108<postal>
3109<street>100 Union Street SE</street>
3110<street>Room 152 Shepherd Labs</street>
3111<city>Minneapolis</city>
3112<region>MN</region>
3113<code>55455</code>
3114<country>US</country></postal>
3115<phone>+1 612 625 1300</phone>
3116<email>daniel@boombox.micro.umn.edu</email></address></author>
3117<author initials="B." surname="Alberti" fullname="Bob Alberti">
3118<organization>University of Minnesota, Computer and Information Services</organization>
3119<address>
3120<postal>
3121<street>100 Union Street SE</street>
3122<street>Room 152 Shepherd Labs</street>
3123<city>Minneapolis</city>
3124<region>MN</region>
3125<code>55455</code>
3126<country>US</country></postal>
3127<phone>+1 612 625 1300</phone>
3128<email>alberti@boombox.micro.umn.edu</email></address></author>
3129<date month="March" year="1993"/>
3130</front>
3131<seriesInfo name="RFC" value="1436"/>
3132</reference>
3133
3134<reference anchor="RFC1630">
3135<front>
3136<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>
3137<author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3138<organization>CERN, World-Wide Web project</organization>
3139<address>
3140<postal>
3141<street>1211 Geneva 23</street>
3142<city/>
3143<region/>
3144<code/>
3145<country>CH</country></postal>
3146<phone>+41 22 7673755</phone>
3147<facsimile>+41 22 7677155</facsimile>
3148<email>timbl@info.cern.ch</email></address></author>
3149<date month="June" year="1994"/></front>
3150<seriesInfo name="RFC" value="1630"/>
3151</reference>
3152
3153<reference anchor="RFC1738">
3154<front>
3155<title>Uniform Resource Locators (URL)</title>
3156<author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3157<organization>CERN, World-Wide Web project</organization>
3158<address>
3159<postal>
3160<street>1211 Geneva 23</street>
3161<city/>
3162<region/>
3163<code/>
3164<country>CH</country></postal>
3165<phone>+41 22 7673755</phone>
3166<facsimile>+41 22 7677155</facsimile>
3167<email>timbl@info.cern.ch</email></address></author>
3168<author initials="L." surname="Masinter" fullname="Larry Masinter">
3169<organization>Xerox PARC</organization>
3170<address>
3171<postal>
3172<street>3333 Coyote Hill Road</street>
3173<city>Palo Alto</city>
3174<region>CA</region>
3175<code>94034</code>
3176<country>US</country></postal>
3177<phone>+1 415 812 4365</phone>
3178<facsimile>+1 415 812 4333</facsimile>
3179<email>masinter@parc.xerox.com</email></address></author>
3180<author initials="M." surname="McCahill" fullname="Mark McCahill">
3181<organization>University of Minnesota, Computer and Information Services</organization>
3182<address>
3183<postal>
3184<street>100 Union Street SE, Shepherd Labs</street>
3185<street>Room 152</street>
3186<city>Minneapolis</city>
3187<region>MN</region>
3188<code>55455</code>
3189<country>US</country></postal>
3190<phone>+1 612 625 1300</phone>
3191<email>mpm@boombox.micro.umn.edu</email></address></author>
3192<date month="December" year="1994"/>
3193</front>
3194<seriesInfo name="RFC" value="1738"/>
3195</reference>
3196
3197<reference anchor="RFC1945">
3198<front>
3199<title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3200<author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3201<organization>MIT, Laboratory for Computer Science</organization>
3202<address>
3203<postal>
3204<street>545 Technology Square</street>
3205<city>Cambridge</city>
3206<region>MA</region>
3207<code>02139</code>
3208<country>US</country></postal>
3209<phone/>
3210<facsimile>+1 617 258 8682</facsimile>
3211<email>timbl@w3.org</email></address></author>
3212<author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3213<organization>University of California, Irvine, Department of Information and Computer Science</organization>
3214<address>
3215<postal>
3216<street/>
3217<city>Irvine</city>
3218<region>CA</region>
3219<code>92717-3425</code>
3220<country>US</country></postal>
3221<phone/>
3222<facsimile>+1 714 824 4056</facsimile>
3223<email>fielding@ics.uci.edu</email></address></author>
3224<author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3225<organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3226<address>
3227<postal>
3228<street>545 Technology Square</street>
3229<city>Cambridge</city>
3230<region>MA</region>
3231<code>02139</code>
3232<country>US</country></postal>
3233<phone/>
3234<facsimile>+1 617 258 8682</facsimile>
3235<email>frystyk@w3.org</email></address></author>
3236<date month="May" year="1996"/>
3237</front>
3238<seriesInfo name="RFC" value="1945"/>
3239</reference>
3240
3241<reference anchor="RFC2045">
3242<front>
3243<title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3244<author initials="N." surname="Freed" fullname="Ned Freed">
3245<organization>Innosoft International, Inc.</organization>
3246<address>
3247<postal>
3248<street>1050 East Garvey Avenue South</street>
3249<city>West Covina</city>
3250<region>CA</region>
3251<code>91790</code>
3252<country>US</country></postal>
3253<phone>+1 818 919 3600</phone>
3254<facsimile>+1 818 919 3614</facsimile>
3255<email>ned@innosoft.com</email></address></author>
3256<author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3257<organization>First Virtual Holdings</organization>
3258<address>
3259<postal>
3260<street>25 Washington Avenue</street>
3261<city>Morristown</city>
3262<region>NJ</region>
3263<code>07960</code>
3264<country>US</country></postal>
3265<phone>+1 201 540 8967</phone>
3266<facsimile>+1 201 993 3032</facsimile>
3267<email>nsb@nsb.fv.com</email></address></author>
3268<date month="November" year="1996"/>
3269</front>
3270<seriesInfo name="RFC" value="2045"/>
3271</reference>
3272
3273<reference anchor="RFC1123">
3274<front>
3275<title>Requirements for Internet Hosts - Application and Support</title>
3276<author initials="R." surname="Braden" fullname="Robert Braden">
3277<organization>University of Southern California (USC), Information Sciences Institute</organization>
3278<address>
3279<postal>
3280<street>4676 Admiralty Way</street>
3281<city>Marina del Rey</city>
3282<region>CA</region>
3283<code>90292-6695</code>
3284<country>US</country></postal>
3285<phone>+1 213 822 1511</phone>
3286<email>Braden@ISI.EDU</email></address></author>
3287<date month="October" year="1989"/></front>
3288<seriesInfo name="STD" value="3"/>
3289<seriesInfo name="RFC" value="1123"/>
3290</reference>
3291
3292<reference anchor="RFC822">
3293<front>
3294<title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
3295<author initials="D.H." surname="Crocker" fullname="David H. Crocker">
3296<organization>University of Delaware, Dept. of Electrical Engineering</organization>
3297<address>
3298<postal>
3299<street/>
3300<city>Newark</city>
3301<region>DE</region>
3302<code>19711</code>
3303<country>US</country></postal>
3304<email>DCrocker@UDel-Relay</email></address></author>
3305<date month="August" day="13" year="1982"/></front>
3306<seriesInfo name="STD" value="11"/>
3307<seriesInfo name="RFC" value="822"/>
3308</reference>
3309
3310<reference anchor="WAIS">
3311<front>
3312<title>WAIS Interface Protocol Prototype Functional Specification (v1.5)</title>
3313<author initials="F." surname="Davis" fullname="F. Davis">
3314<organization>Thinking Machines Corporation</organization>
3315</author>
3316<author initials="B." surname="Kahle" fullname="B. Kahle">
3317<organization>Thinking Machines Corporation</organization>
3318</author>
3319<author initials="H." surname="Morris" fullname="H. Morris">
3320<organization>Thinking Machines Corporation</organization>
3321</author>
3322<author initials="J." surname="Salem" fullname="J. Salem">
3323<organization>Thinking Machines Corporation</organization>
3324</author>
3325<author initials="T." surname="Shen" fullname="T. Shen">
3326<organization>Thinking Machines Corporation</organization>
3327</author>
3328<author initials="R." surname="Wang" fullname="R. Wang">
3329<organization>Thinking Machines Corporation</organization>
3330</author>
3331<author initials="J." surname="Sui" fullname="J. Sui">
3332<organization>Thinking Machines Corporation</organization>
3333</author>
3334<author initials="M." surname="Grinbaum" fullname="M. Grinbaum">
3335<organization>Thinking Machines Corporation</organization>
3336</author>
3337<date month="April" year="1990"/></front>
3338<seriesInfo name="Thinking Machines Corporation" value=""/>
3339</reference>
3340
3341<reference anchor="RFC1808">
3342<front>
3343<title>Relative Uniform Resource Locators</title>
3344<author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3345<organization>University of California Irvine, Department of Information and Computer Science</organization>
3346<address>
3347<postal>
3348<street/>
3349<city>Irvine</city>
3350<region>CA</region>
3351<code>92717-3425</code>
3352<country>US</country></postal>
3353<phone>+1 714 824 4049</phone>
3354<facsimile>+1 714 824 4056</facsimile>
3355<email>fielding@ics.uci.edu</email></address></author>
3356<date month="June" year="1995"/>
3357</front>
3358<seriesInfo name="RFC" value="1808"/>
3359</reference>
3360
3361<reference anchor='RFC3977'>
3362   <front>
3363      <title>Network News Transfer Protocol (NNTP)</title>
3364      <author initials='C.' surname='Feather' fullname='C. Feather'>
3365         <organization>THUS plc</organization>
3366         <address>
3367            <email>clive@demon.net</email>
3368         </address>
3369      </author>
3370      <date year='2006' month='October' />
3371   </front>
3372</reference>
3373
3374<reference anchor="RFC2047">
3375<front>
3376<title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3377<author initials="K." surname="Moore" fullname="Keith Moore">
3378<organization>University of Tennessee</organization>
3379<address>
3380<postal>
3381<street>107 Ayres Hall</street>
3382<street>Knoxville TN 37996-1301</street></postal>
3383<email>moore@cs.utk.edu</email></address></author>
3384<date month="November" year="1996"/>
3385<area>Applications</area>
3386<keyword>Amercian Standard Code for Information Interchange</keyword>
3387<keyword>mail</keyword>
3388<keyword>multipurpose internet mail extensions</keyword>
3389</front>
3390<seriesInfo name="RFC" value="2047"/>
3391</reference>
3392
3393<reference anchor="RFC821">
3394<front>
3395<title>Simple Mail Transfer Protocol</title>
3396<author initials="J.B." surname="Postel" fullname="Jonathan B. Postel">
3397<organization>University of Southern California (USC)/Information Sciences Institute</organization>
3398<address>
3399<postal>
3400<street>4676 Admiralty Way</street>
3401<city>Marina del Rey</city>
3402<region>CA</region>
3403<code>90291</code>
3404<country>US</country></postal>
3405<phone>+1 213 822 1511</phone></address></author>
3406<date month="August" year="1982"/></front>
3407<seriesInfo name="STD" value="10"/>
3408<seriesInfo name="RFC" value="821"/>
3409</reference>
3410
3411<reference anchor="RFC4288">
3412  <front>
3413    <title>Media Type Specifications and Registration Procedures</title>
3414    <author initials="N." surname="Freed" fullname="N. Freed">
3415      <organization>Sun Microsystems</organization>
3416      <address>
3417        <email>ned.freed@mrochek.com</email>
3418      </address>
3419    </author>
3420    <author initials="J." surname="Klensin" fullname="J. Klensin">
3421      <organization/>
3422      <address>
3423        <email>klensin+ietf@jck.com</email>
3424      </address>
3425    </author>
3426    <date year="2005" month="December"/>
3427  </front>
3428  <seriesInfo name="BCP" value="13"/>
3429  <seriesInfo name="RFC" value="4288"/>
3430</reference>
3431
3432<reference anchor="RFC959">
3433<front>
3434<title abbrev="File Transfer Protocol">File Transfer Protocol</title>
3435<author initials="J." surname="Postel" fullname="J. Postel">
3436<organization>Information Sciences Institute (ISI)</organization></author>
3437<author initials="J." surname="Reynolds" fullname="J. Reynolds">
3438<organization/></author>
3439<date month="October" year="1985"/></front>
3440<seriesInfo name="STD" value="9"/>
3441<seriesInfo name="RFC" value="959"/>
3442</reference>
3443
3444<reference anchor="RFC1700">
3445<front>
3446<title abbrev="Assigned Numbers">Assigned Numbers</title>
3447<author initials="J." surname="Reynolds" fullname="Joyce K. Reynolds">
3448<organization>USC/Information Sciences Institute</organization>
3449<address>
3450<postal>
3451<street>4676 Admiralty Way</street>
3452<city>Marina del Rey</city>
3453<region>CA</region>
3454<code>90292-6695</code>
3455<country>US</country></postal>
3456<phone>+1 310 822 1511</phone>
3457<email>jkrey@isi.edu</email></address></author>
3458<author initials="J." surname="Postel" fullname="Jon Postel">
3459<organization>USC/Information Sciences Institute</organization>
3460<address>
3461<postal>
3462<street>4676 Admiralty Way</street>
3463<city>Marina del Rey</city>
3464<region>CA</region>
3465<code>90292-6695</code>
3466<country>US</country></postal>
3467<phone>+1 310 822 1511</phone>
3468<email>postel@isi.edu</email></address></author>
3469<date month="October" year="1994"/>
3470<abstract>
3471<t/></abstract></front>
3472<seriesInfo name="STD" value="2"/>
3473<seriesInfo name="RFC" value="1700"/>
3474</reference>
3475
3476<reference anchor="RFC1737">
3477<front>
3478<title abbrev="Requirements for Uniform Resource Names">Functional Requirements for Uniform Resource Names</title>
3479<author initials="L." surname="Masinter" fullname="Larry Masinter">
3480<organization>Xerox Palo Alto Research Center</organization>
3481<address>
3482<postal>
3483<street>3333 Coyote Hill Road</street>
3484<city>Palo Alto</city>
3485<region>CA</region>
3486<code>94304</code>
3487<country>US</country></postal>
3488<phone>+1 415 812 4365</phone>
3489<facsimile>+1 415 812 4333</facsimile>
3490<email>masinter@parc.xerox.com</email></address></author>
3491<author initials="K." surname="Sollins" fullname="Karen Sollins">
3492<organization>MIT Laboratory for Computer Science</organization>
3493<address>
3494<postal>
3495<street>545 Technology Square</street>
3496<city>Cambridge</city>
3497<region>MA</region>
3498<code>02139</code>
3499<country>US</country></postal>
3500<phone>+1 617 253 2673</phone>
3501<email>sollins@lcs.mit.edu</email></address></author>
3502<date month="December" year="1994"/></front>
3503<seriesInfo name="RFC" value="1737"/>
3504</reference>
3505
3506<reference anchor="USASCII">
3507  <front>
3508    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3509    <author>
3510      <organization>American National Standards Institute</organization>
3511    </author>
3512    <date year="1986"/>
3513  </front>
3514  <seriesInfo name="ANSI" value="X3.4"/>
3515</reference>
3516
3517<reference anchor="ISO-8859">
3518<front>
3519<title>Information technology - 8-bit single byte coded graphic - character sets</title>
3520<author>
3521<organization>International Organization for Standardization</organization>
3522</author>
3523<date year="1987-1990"/>
3524</front>
3525<annotation>
3526  Part 1: Latin alphabet No. 1, ISO-8859-1:1987.
3527  Part 2: Latin alphabet No. 2, ISO-8859-2, 1987.
3528  Part 3: Latin alphabet No. 3, ISO-8859-3, 1988.
3529  Part 4: Latin alphabet No. 4, ISO-8859-4, 1988.
3530  Part 5: Latin/Cyrillic alphabet, ISO-8859-5, 1988.
3531  Part 6: Latin/Arabic alphabet, ISO-8859-6, 1987.
3532  Part 7: Latin/Greek alphabet, ISO-8859-7, 1987.
3533  Part 8: Latin/Hebrew alphabet, ISO-8859-8, 1988.
3534  Part 9: Latin alphabet No. 5, ISO-8859-9, 1990.
3535</annotation>
3536</reference>
3537
3538<reference anchor="RFC1900">
3539<front>
3540<title>Renumbering Needs Work</title>
3541<author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3542<organization>CERN, Computing and Networks Division</organization>
3543<address>
3544<postal>
3545<street>1211 Geneva 23</street>
3546<country>CH</country></postal>
3547<phone>+41 22 7674967</phone>
3548<facsimile>+41 22 7677155</facsimile>
3549<email>brian@dxcoms.cern.ch</email></address></author>
3550<author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3551<organization>cisco Systems</organization>
3552<address>
3553<postal>
3554<street>170 West Tasman Drive</street>
3555<city>San Jose</city>
3556<region>CA</region>
3557<code>95134</code>
3558<country>US</country></postal>
3559<phone>+1 914 528 0090</phone>
3560<email>yakov@cisco.com</email></address></author>
3561<date month="February" year="1996"/>
3562</front>
3563<seriesInfo name="RFC" value="1900"/>
3564</reference>
3565
3566<reference anchor="Pad1995">
3567<front>
3568<title>Improving HTTP Latency</title>
3569<author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"><organization/></author>
3570<author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"><organization/></author>
3571<date year="1995" month="Dec"/>
3572</front>
3573<seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3574<annotation>
3575  Slightly revised version of paper in Proc. 2nd International WWW Conference '94: Mosaic and the Web, Oct. 1994,
3576  which is available at <eref target="http://www.ncsa.uiuc.edu/SDG/IT94/Proceedings/DDay/mogul/HTTPLatency.html"/>.
3577</annotation>
3578</reference>
3579
3580<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
3581<front>
3582<title>Analysis of HTTP Performance</title>
3583<author initials="J." surname="Touch" fullname="Joe Touch">
3584  <organization>USC/Information Sciences Institute</organization>
3585  <address><email>touch@isi.edu</email></address>
3586</author>
3587<author initials="J." surname="Heidemann" fullname="John Heidemann">
3588  <organization>USC/Information Sciences Institute</organization>
3589  <address><email>johnh@isi.edu</email></address>
3590</author>
3591<author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3592  <organization>USC/Information Sciences Institute</organization>
3593  <address><email>katia@isi.edu</email></address>
3594</author>
3595<date year="1998" month="Aug"/>
3596</front>
3597<seriesInfo name="ISI Research Report" value="ISI/RR-98-463 (original report dated Aug.1996)"/>
3598</reference>
3599
3600<reference anchor="RFC1305">
3601<front>
3602<title>Network Time Protocol (Version 3) Specification, Implementation</title>
3603<author initials="D." surname="Mills" fullname="David L. Mills">
3604<organization>University of Delaware, Electrical Engineering Department</organization>
3605<address>
3606<postal>
3607<street/>
3608<city>Newark</city>
3609<region>DE</region>
3610<code>19716</code>
3611<country>US</country></postal>
3612<phone>+1 302 451 8247</phone>
3613<email>mills@udel.edu</email></address></author>
3614<date month="March" year="1992"/>
3615<abstract>
3616<t>This document describes the Network Time Protocol (NTP), specifies its normal structure and summarizes information useful for its implementation. NTP provides the mechanisms to synchronize time and coordinate time distribution in a large, diverse internet operating at rates from mundane to lightwave. It uses a returnable-time design in which a distributed subnet of time servers operating in a self-organizing, hierarchical-master-slave configuration synchronizes local clocks within the subnet and to national time standards via wire or radio. The servers can also redistribute reference time via local routing algorithms and time daemons.</t></abstract></front>
3617<seriesInfo name="RFC" value="1305"/>
3618</reference>
3619
3620<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
3621<front>
3622<title>Analysis of HTTP Performance Problems</title>
3623<author initials="S." surname="Spero" fullname="Simon E. Spero">
3624  <organization/>
3625</author>
3626<date/>
3627</front>
3628</reference>
3629
3630<reference anchor="RFC2068">
3631<front>
3632<title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3633<author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3634<organization>University of California, Irvine, Department of Information and Computer Science</organization>
3635<address>
3636<postal>
3637<street/>
3638<city>Irvine</city>
3639<region>CA</region>
3640<code>92717-3425</code>
3641<country>US</country></postal>
3642<facsimile>+1 714 824 4056</facsimile>
3643<email>fielding@ics.uci.edu</email></address></author>
3644<author initials="J." surname="Gettys" fullname="Jim Gettys">
3645<organization>MIT Laboratory for Computer Science</organization>
3646<address>
3647<postal>
3648<street>545 Technology Square</street>
3649<city>Cambridge</city>
3650<region>MA</region>
3651<code>02139</code>
3652<country>US</country></postal>
3653<facsimile>+1 617 258 8682</facsimile>
3654<email>jg@w3.org</email></address></author>
3655<author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3656<organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3657<address>
3658<postal>
3659<street>250 University Avenue</street>
3660<city>Palo Alto</city>
3661<region>CA</region>
3662<code>94301</code>
3663<country>US</country></postal>
3664<email>mogul@wrl.dec.com</email></address></author>
3665<author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3666<organization>MIT Laboratory for Computer Science</organization>
3667<address>
3668<postal>
3669<street>545 Technology Square</street>
3670<city>Cambridge</city>
3671<region>MA</region>
3672<code>02139</code>
3673<country>US</country></postal>
3674<facsimile>+1 617 258 8682</facsimile>
3675<email>frystyk@w3.org</email></address></author>
3676<author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3677<organization>MIT Laboratory for Computer Science</organization>
3678<address>
3679<postal>
3680<street>545 Technology Square</street>
3681<city>Cambridge</city>
3682<region>MA</region>
3683<code>02139</code>
3684<country>US</country></postal>
3685<facsimile>+1 617 258 8682</facsimile>
3686<email>timbl@w3.org</email></address></author>
3687<date month="January" year="1997"/>
3688<abstract>
3689<t>The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information systems. It is a generic, stateless, object-oriented protocol which can be used for many tasks, such as name servers and distributed object management systems, through extension of its request methods. A feature of HTTP is the typing and negotiation of data representation, allowing systems to be built independently of the data being transferred.</t>
3690<t>HTTP has been in use by the World-Wide Web global information initiative since 1990. This specification defines the protocol referred to as "HTTP/1.1".</t></abstract></front>
3691<seriesInfo name="RFC" value="2068"/>
3692</reference>
3693
3694<reference anchor="RFC2119">
3695<front>
3696<title abbrev="RFC Key Words">Key words for use in RFCs to Indicate Requirement Levels</title>
3697<author initials="S." surname="Bradner" fullname="Scott Bradner">
3698<organization>Harvard University</organization>
3699<address>
3700<postal>
3701<street>1350 Mass. Ave.</street>
3702<street>Cambridge</street>
3703<street>MA 02138</street></postal>
3704<phone>- +1 617 495 3864</phone>
3705<email>-</email></address></author>
3706<date month="March" year="1997"/>
3707<area>General</area>
3708<keyword>keyword</keyword>
3709</front>
3710
3711<seriesInfo name="BCP" value="14"/>
3712<seriesInfo name="RFC" value="2119"/>
3713</reference>
3714
3715<reference anchor="RFC2145">
3716<front>
3717<title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3718<author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3719<organization>Western Research Laboratory</organization>
3720<address>
3721<postal>
3722<street>Digital Equipment Corporation</street>
3723<street>250 University Avenue</street>
3724<street>Palo Alto</street>
3725<street>California</street>
3726<street>94305</street>
3727<country>USA</country></postal>
3728<email>mogul@wrl.dec.com</email></address></author>
3729<author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3730<organization>Department of Information and Computer Science</organization>
3731<address>
3732<postal>
3733<street>University of California</street>
3734<street>Irvine</street>
3735<street>CA 92717-3425</street>
3736<country>USA</country></postal>
3737<facsimile>+1 (714) 824-4056</facsimile>
3738<email>fielding@ics.uci.edu</email></address></author>
3739<author initials="J." surname="Gettys" fullname="Jim Gettys">
3740<organization>MIT Laboratory for Computer Science</organization>
3741<address>
3742<postal>
3743<street>545 Technology Square</street>
3744<street>Cambridge</street>
3745<street>MA 02139</street>
3746<country>USA</country></postal>
3747<facsimile>+1 (617) 258 8682</facsimile>
3748<email>jg@w3.org</email></address></author>
3749<author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3750<organization>W3 Consortium</organization>
3751<address>
3752<postal>
3753<street>MIT Laboratory for Computer Science</street>
3754<street>545 Technology Square</street>
3755<street>Cambridge</street>
3756<street>MA 02139</street>
3757<country>USA</country></postal>
3758<facsimile>+1 (617) 258 8682</facsimile>
3759<email>frystyk@w3.org</email></address></author>
3760<date month="May" year="1997"/>
3761<area>Applications</area>
3762<keyword>HTTP</keyword>
3763<keyword>hypertext transfer protocol</keyword>
3764<abstract>
3765<t>
3766   HTTP request and response messages include an HTTP protocol version
3767   number.  Some confusion exists concerning the proper use and
3768   interpretation of HTTP version numbers, and concerning
3769   interoperability of HTTP implementations of different protocol
3770   versions.  This document is an attempt to clarify the situation.  It
3771   is not a modification of the intended meaning of the existing
3772   HTTP/1.0 and HTTP/1.1 documents, but it does describe the intention
3773   of the authors of those documents, and can be considered definitive
3774   when there is any ambiguity in those documents concerning HTTP
3775   version numbers, for all versions of HTTP.
3776</t></abstract></front>
3777<seriesInfo name="RFC" value="2145"/>
3778</reference>
3779
3780<reference anchor="Nie1997">
3781<front>
3782<title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3783<author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3784  <organization/>
3785</author>
3786<author initials="J." surname="Gettys" fullname="J. Gettys">
3787  <organization/>
3788</author>
3789<author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3790  <organization/>
3791</author>
3792<author initials="H." surname="Lie" fullname="H. Lie">
3793  <organization/>
3794</author>
3795<author initials="C." surname="Lilley" fullname="C. Lilley">
3796  <organization/>
3797</author>
3798<date year="1997" month="Sep"/>
3799</front>
3800<seriesInfo name="Proceedings of ACM SIGCOMM '97, Cannes France" value=""/>
3801</reference>
3802
3803<reference anchor="RFC2396">
3804<front>
3805<title abbrev="URI Generic Syntax">Uniform Resource Identifiers (URI): Generic Syntax</title>
3806<author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3807<organization abbrev="MIT/LCS">World Wide Web Consortium</organization>
3808<address>
3809<postal>
3810<street>MIT Laboratory for Computer Science, NE43-356</street>
3811<street>545 Technology Square</street>
3812<city>Cambridge</city>
3813<region>MA</region>
3814<code>02139</code></postal>
3815<facsimile>+1(617)258-8682</facsimile>
3816<email>timbl@w3.org</email></address></author>
3817<author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3818<organization abbrev="U.C. Irvine">Department of Information and Computer Science</organization>
3819<address>
3820<postal>
3821<street>University of California, Irvine</street>
3822<city>Irvine</city>
3823<region>CA</region>
3824<code>92697-3425</code></postal>
3825<facsimile>+1(949)824-1715</facsimile>
3826<email>fielding@ics.uci.edu</email></address></author>
3827<author initials="L." surname="Masinter" fullname="Larry Masinter">
3828<organization abbrev="Xerox Corporation">Xerox PARC</organization>
3829<address>
3830<postal>
3831<street>3333 Coyote Hill Road</street>
3832<city>Palo Alto</city>
3833<region>CA</region>
3834<code>94034</code></postal>
3835<facsimile>+1(415)812-4333</facsimile>
3836<email>masinter@parc.xerox.com</email></address></author>
3837<date month="August" year="1998"/>
3838<area>Applications</area>
3839<keyword>uniform resource</keyword>
3840<keyword>URI</keyword>
3841</front>
3842<seriesInfo name="RFC" value="2396"/>
3843</reference>
3844
3845<reference anchor="RFC2324">
3846<front>
3847<title abbrev="HTCPCP/1.0">Hyper Text Coffee Pot Control Protocol (HTCPCP/1.0)</title>
3848<author initials="L." surname="Masinter" fullname="Larry Masinter">
3849<organization>Xerox Palo Alto Research Center</organization>
3850<address>
3851<postal>
3852<street>3333 Coyote Hill Road</street>
3853<city>Palo Alto</city>
3854<region>CA</region>
3855<code>94304</code></postal>
3856<email>masinter@parc.xerox.com</email></address></author>
3857<date month="April" day="1" year="1998"/>
3858<area>General</area>
3859<keyword>control protocol</keyword>
3860<keyword>coffee</keyword>
3861</front>
3862<seriesInfo name="RFC" value="2324"/>
3863</reference>
3864
3865</references>
3866
3867<section title="Internet Media Type message/http and application/http" anchor="internet.media.type.http">
3868<iref item="Media Type" subitem="message/http" primary="true"/>
3869<iref item="message/http Media Type" primary="true"/>
3870<iref item="Media Type" subitem="application/http" primary="true"/>
3871<iref item="application/http Media Type" primary="true"/>
3872<t>
3873   In addition to defining the HTTP/1.1 protocol, this document serves
3874   as the specification for the Internet media type "message/http" and
3875   "application/http". The message/http type can be used to enclose a
3876   single HTTP request or response message, provided that it obeys the
3877   MIME restrictions for all "message" types regarding line length and
3878   encodings. The application/http type can be used to enclose a
3879   pipeline of one or more HTTP request or response messages (not
3880   intermixed). The following is to be registered with IANA <xref target="RFC4288"/>.
3881</t>
3882<t>
3883  <list style="hanging" x:indent="12em">
3884    <t hangText="Media Type name:">
3885      message
3886    </t>
3887    <t hangText="Media subtype name:">
3888      http
3889    </t>
3890    <t hangText="Required parameters:">
3891      none
3892    </t>
3893    <t hangText="Optional parameters:">
3894      version, msgtype
3895      <list style="hanging">
3896        <t hangText="version:">
3897          The HTTP-Version number of the enclosed message
3898          (e.g., "1.1"). If not present, the version can be
3899          determined from the first line of the body.
3900        </t>
3901        <t hangText="msgtype:">
3902          The message type -- "request" or "response". If not
3903          present, the type can be determined from the first
3904          line of the body.
3905        </t>
3906      </list>
3907    </t>
3908    <t hangText="Encoding considerations:">
3909      only "7bit", "8bit", or "binary" are permitted
3910    </t>
3911    <t hangText="Security considerations:">
3912      none
3913    </t>
3914  </list>
3915</t>
3916<t>
3917  <list style="hanging" x:indent="12em">
3918    <t hangText="Media Type name:">
3919      application
3920    </t>
3921    <t hangText="Media subtype name:">
3922      http
3923    </t>
3924    <t hangText="Required parameters:">
3925      none
3926    </t>
3927    <t hangText="Optional parameters:">
3928      version, msgtype
3929      <list style="hanging">
3930        <t hangText="version:">
3931          The HTTP-Version number of the enclosed messages
3932          (e.g., "1.1"). If not present, the version can be
3933          determined from the first line of the body.
3934        </t>
3935        <t hangText="msgtype:">
3936          The message type -- "request" or "response". If not
3937          present, the type can be determined from the first
3938          line of the body.
3939        </t>
3940      </list>
3941    </t>
3942    <t hangText="Encoding considerations:">
3943      HTTP messages enclosed by this type
3944      are in "binary" format; use of an appropriate
3945      Content-Transfer-Encoding is required when
3946      transmitted via E-mail.
3947    </t>
3948    <t hangText="Security considerations:">
3949      none
3950    </t>
3951  </list>
3952</t>
3953</section>
3954
3955<section title="Tolerant Applications" anchor="tolerant.applications">
3956<t>
3957   Although this document specifies the requirements for the generation
3958   of HTTP/1.1 messages, not all applications will be correct in their
3959   implementation. We therefore recommend that operational applications
3960   be tolerant of deviations whenever those deviations can be
3961   interpreted unambiguously.
3962</t>
3963<t>
3964   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3965   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3966   accept any amount of SP or HT characters between fields, even though
3967   only a single SP is required.
3968</t>
3969<t>
3970   The line terminator for message-header fields is the sequence CRLF.
3971   However, we recommend that applications, when parsing such headers,
3972   recognize a single LF as a line terminator and ignore the leading CR.
3973</t>
3974<t>
3975   The character set of an entity-body &SHOULD; be labeled as the lowest
3976   common denominator of the character codes used within that body, with
3977   the exception that not labeling the entity is preferred over labeling
3978   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3979</t>
3980<t>
3981   Additional rules for requirements on parsing and encoding of dates
3982   and other potential problems with date encodings include:
3983</t>
3984<t>
3985  <list style="symbols">
3986     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3987        which appears to be more than 50 years in the future is in fact
3988        in the past (this helps solve the "year 2000" problem).</t>
3989
3990     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3991        Expires date as earlier than the proper value, but &MUST-NOT;
3992        internally represent a parsed Expires date as later than the
3993        proper value.</t>
3994
3995     <t>All expiration-related calculations &MUST; be done in GMT. The
3996        local time zone &MUST-NOT; influence the calculation or comparison
3997        of an age or expiration time.</t>
3998
3999     <t>If an HTTP header incorrectly carries a date value with a time
4000        zone other than GMT, it &MUST; be converted into GMT using the
4001        most conservative possible conversion.</t>
4002  </list>
4003</t>
4004</section>
4005
4006<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
4007<t>
4008   HTTP/1.1 uses a restricted set of date formats (<xref target="full.date"/>) to
4009   simplify the process of date comparison. Proxies and gateways from
4010   other protocols &SHOULD; ensure that any Date header field present in a
4011   message conforms to one of the HTTP/1.1 formats and rewrite the date
4012   if necessary.
4013</t>
4014</section>
4015
4016<section title="Compatibility with Previous Versions" anchor="compatibility">
4017<t>
4018   It is beyond the scope of a protocol specification to mandate
4019   compliance with previous versions. HTTP/1.1 was deliberately
4020   designed, however, to make supporting previous versions easy. It is
4021   worth noting that, at the time of composing this specification
4022   (1996), we would expect commercial HTTP/1.1 servers to:
4023  <list style="symbols">
4024     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
4025        1.1 requests;</t>
4026
4027     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
4028        1.1;</t>
4029
4030     <t>respond appropriately with a message in the same major version
4031        used by the client.</t>
4032  </list>
4033</t>
4034<t>
4035   And we would expect HTTP/1.1 clients to:
4036  <list style="symbols">
4037     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
4038        responses;</t>
4039
4040     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
4041        1.1.</t>
4042  </list>
4043</t>
4044<t>
4045   For most implementations of HTTP/1.0, each connection is established
4046   by the client prior to the request and closed by the server after
4047   sending the response. Some implementations implement the Keep-Alive
4048   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="sec" target="RFC2068"/> of RFC
4049   2068 <xref target="RFC2068"/>.
4050</t>
4051
4052<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4053<t>
4054   This section summarizes major differences between versions HTTP/1.0
4055   and HTTP/1.1.
4056</t>
4057
4058<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">
4059<t>
4060   The requirements that clients and servers support the Host request-header,
4061   report an error if the Host request-header (<xref target="header.host"/>) is
4062   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-uri"/>)
4063   are among the most important changes defined by this
4064   specification.
4065</t>
4066<t>
4067   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4068   addresses and servers; there was no other established mechanism for
4069   distinguishing the intended server of a request than the IP address
4070   to which that request was directed. The changes outlined above will
4071   allow the Internet, once older HTTP clients are no longer common, to
4072   support multiple Web sites from a single IP address, greatly
4073   simplifying large operational Web servers, where allocation of many
4074   IP addresses to a single host has created serious problems. The
4075   Internet will also be able to recover the IP addresses that have been
4076   allocated for the sole purpose of allowing special-purpose domain
4077   names to be used in root-level HTTP URLs. Given the rate of growth of
4078   the Web, and the number of servers already deployed, it is extremely
4079   important that all implementations of HTTP (including updates to
4080   existing HTTP/1.0 applications) correctly implement these
4081   requirements:
4082  <list style="symbols">
4083     <t>Both clients and servers &MUST; support the Host request-header.</t>
4084
4085     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4086
4087     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4088        request does not include a Host request-header.</t>
4089
4090     <t>Servers &MUST; accept absolute URIs.</t>
4091  </list>
4092</t>
4093</section>
4094</section>
4095
4096<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4097<t>
4098   Some clients and servers might wish to be compatible with some
4099   previous implementations of persistent connections in HTTP/1.0
4100   clients and servers. Persistent connections in HTTP/1.0 are
4101   explicitly negotiated as they are not the default behavior. HTTP/1.0
4102   experimental implementations of persistent connections are faulty,
4103   and the new facilities in HTTP/1.1 are designed to rectify these
4104   problems. The problem was that some existing 1.0 clients may be
4105   sending Keep-Alive to a proxy server that doesn't understand
4106   Connection, which would then erroneously forward it to the next
4107   inbound server, which would establish the Keep-Alive connection and
4108   result in a hung HTTP/1.0 proxy waiting for the close on the
4109   response. The result is that HTTP/1.0 clients must be prevented from
4110   using Keep-Alive when talking to proxies.
4111</t>
4112<t>
4113   However, talking to proxies is the most important use of persistent
4114   connections, so that prohibition is clearly unacceptable. Therefore,
4115   we need some other mechanism for indicating a persistent connection
4116   is desired, which is safe to use even when talking to an old proxy
4117   that ignores Connection. Persistent connections are the default for
4118   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4119   declaring non-persistence. See <xref target="header.connection"/>.
4120</t>
4121<t>
4122   The original HTTP/1.0 form of persistent connections (the Connection:
4123   Keep-Alive and Keep-Alive header) is documented in RFC 2068. <xref target="RFC2068"/>
4124</t>
4125</section>
4126
4127<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4128<t>
4129   This specification has been carefully audited to correct and
4130   disambiguate key word usage; RFC 2068 had many problems in respect to
4131   the conventions laid out in RFC 2119 <xref target="RFC2119"/>.
4132</t>
4133<t>
4134   Transfer-coding and message lengths all interact in ways that
4135   required fixing exactly when chunked encoding is used (to allow for
4136   transfer encoding that may not be self delimiting); it was important
4137   to straighten out exactly how message lengths are computed.
4138</t>
4139<t>
4140   The use and interpretation of HTTP version numbers has been clarified
4141   by RFC 2145. Require proxies to upgrade requests to highest protocol
4142   version they support to deal with problems discovered in HTTP/1.0
4143   implementations (<xref target="http.version"/>)
4144</t>
4145<t>
4146   Proxies should be able to add Content-Length when appropriate.
4147</t>
4148<t>
4149   Transfer-coding had significant problems, particularly with
4150   interactions with chunked encoding. The solution is that transfer-codings
4151   become as full fledged as content-codings. This involves
4152   adding an IANA registry for transfer-codings (separate from content
4153   codings), a new header field (TE) and enabling trailer headers in the
4154   future. Transfer encoding is a major performance benefit, so it was
4155   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4156   interoperability problem that could have occurred due to interactions
4157   between authentication trailers, chunked encoding and HTTP/1.0
4158   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4159   and <xref target="header.te" format="counter"/>)
4160</t>
4161</section>
4162</section>
4163</back>
4164</rfc>
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