source: draft-ietf-httpbis/latest/p1-messaging.xml @ 368

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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "November">
16  <!ENTITY ID-YEAR "2008">
17  <!ENTITY caching                "<xref target='Part6' x:rel='#caching' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY payload                "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY media-types            "<xref target='Part3' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY content-codings        "<xref target='Part3' x:rel='#content.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY diff2045entity         "<xref target='Part3' x:rel='#differences.between.http.entities.and.rfc.2045.entities' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY entity                 "<xref target='Part3' x:rel='#entity' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY entity-body            "<xref target='Part3' x:rel='#entity.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY entity-header-fields   "<xref target='Part3' x:rel='#entity.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-accept          "<xref target='Part3' x:rel='#header.accept' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY qvalue                 "<xref target='Part3' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY method                 "<xref target='Part2' x:rel='#method' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41]>
42<?rfc toc="yes" ?>
43<?rfc symrefs="yes" ?>
44<?rfc sortrefs="yes" ?>
45<?rfc compact="yes"?>
46<?rfc subcompact="no" ?>
47<?rfc linkmailto="no" ?>
48<?rfc editing="no" ?>
49<?rfc comments="yes"?>
50<?rfc inline="yes"?>
51<?rfc-ext allow-markup-in-artwork="yes" ?>
52<?rfc-ext include-references-in-index="yes" ?>
53<rfc obsoletes="2616" category="std" x:maturity-level="draft"
54     ipr="full3978" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
55     xmlns:x='http://purl.org/net/xml2rfc/ext'>
56<front>
57
58  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
59
60  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
61    <organization abbrev="Day Software">Day Software</organization>
62    <address>
63      <postal>
64        <street>23 Corporate Plaza DR, Suite 280</street>
65        <city>Newport Beach</city>
66        <region>CA</region>
67        <code>92660</code>
68        <country>USA</country>
69      </postal>
70      <phone>+1-949-706-5300</phone>
71      <facsimile>+1-949-706-5305</facsimile>
72      <email>fielding@gbiv.com</email>
73      <uri>http://roy.gbiv.com/</uri>
74    </address>
75  </author>
76
77  <author initials="J." surname="Gettys" fullname="Jim Gettys">
78    <organization>One Laptop per Child</organization>
79    <address>
80      <postal>
81        <street>21 Oak Knoll Road</street>
82        <city>Carlisle</city>
83        <region>MA</region>
84        <code>01741</code>
85        <country>USA</country>
86      </postal>
87      <email>jg@laptop.org</email>
88      <uri>http://www.laptop.org/</uri>
89    </address>
90  </author>
91 
92  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
93    <organization abbrev="HP">Hewlett-Packard Company</organization>
94    <address>
95      <postal>
96        <street>HP Labs, Large Scale Systems Group</street>
97        <street>1501 Page Mill Road, MS 1177</street>
98        <city>Palo Alto</city>
99        <region>CA</region>
100        <code>94304</code>
101        <country>USA</country>
102      </postal>
103      <email>JeffMogul@acm.org</email>
104    </address>
105  </author>
106
107  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
108    <organization abbrev="Microsoft">Microsoft Corporation</organization>
109    <address>
110      <postal>
111        <street>1 Microsoft Way</street>
112        <city>Redmond</city>
113        <region>WA</region>
114        <code>98052</code>
115        <country>USA</country>
116      </postal>
117      <email>henrikn@microsoft.com</email>
118    </address>
119  </author>
120
121  <author initials="L." surname="Masinter" fullname="Larry Masinter">
122    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
123    <address>
124      <postal>
125        <street>345 Park Ave</street>
126        <city>San Jose</city>
127        <region>CA</region>
128        <code>95110</code>
129        <country>USA</country>
130      </postal>
131      <email>LMM@acm.org</email>
132      <uri>http://larry.masinter.net/</uri>
133    </address>
134  </author>
135 
136  <author initials="P." surname="Leach" fullname="Paul J. Leach">
137    <organization abbrev="Microsoft">Microsoft Corporation</organization>
138    <address>
139      <postal>
140        <street>1 Microsoft Way</street>
141        <city>Redmond</city>
142        <region>WA</region>
143        <code>98052</code>
144      </postal>
145      <email>paulle@microsoft.com</email>
146    </address>
147  </author>
148   
149  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
150    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
151    <address>
152      <postal>
153        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
154        <street>The Stata Center, Building 32</street>
155        <street>32 Vassar Street</street>
156        <city>Cambridge</city>
157        <region>MA</region>
158        <code>02139</code>
159        <country>USA</country>
160      </postal>
161      <email>timbl@w3.org</email>
162      <uri>http://www.w3.org/People/Berners-Lee/</uri>
163    </address>
164  </author>
165
166  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
167    <organization abbrev="W3C">World Wide Web Consortium</organization>
168    <address>
169      <postal>
170        <street>W3C / ERCIM</street>
171        <street>2004, rte des Lucioles</street>
172        <city>Sophia-Antipolis</city>
173        <region>AM</region>
174        <code>06902</code>
175        <country>France</country>
176      </postal>
177      <email>ylafon@w3.org</email>
178      <uri>http://www.raubacapeu.net/people/yves/</uri>
179    </address>
180  </author>
181
182  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
183    <organization abbrev="greenbytes">greenbytes GmbH</organization>
184    <address>
185      <postal>
186        <street>Hafenweg 16</street>
187        <city>Muenster</city><region>NW</region><code>48155</code>
188        <country>Germany</country>
189      </postal>
190      <phone>+49 251 2807760</phone>   
191      <facsimile>+49 251 2807761</facsimile>   
192      <email>julian.reschke@greenbytes.de</email>       
193      <uri>http://greenbytes.de/tech/webdav/</uri>     
194    </address>
195  </author>
196
197  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
198
199<abstract>
200<t>
201   The Hypertext Transfer Protocol (HTTP) is an application-level
202   protocol for distributed, collaborative, hypermedia information
203   systems. HTTP has been in use by the World Wide Web global information
204   initiative since 1990. This document is Part 1 of the seven-part specification
205   that defines the protocol referred to as "HTTP/1.1" and, taken together,
206   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
207   its associated terminology, defines the "http" and "https" Uniform
208   Resource Identifier (URI) schemes, defines the generic message syntax
209   and parsing requirements for HTTP message frames, and describes
210   general security concerns for implementations.
211</t>
212</abstract>
213
214<note title="Editorial Note (To be removed by RFC Editor)">
215  <t>
216    Discussion of this draft should take place on the HTTPBIS working group
217    mailing list (ietf-http-wg@w3.org). The current issues list is
218    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
219    and related documents (including fancy diffs) can be found at
220    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
221  </t>
222  <t>
223    The changes in this draft are summarized in <xref target="changes.since.04"/>.
224  </t>
225</note>
226</front>
227<middle>
228<section title="Introduction" anchor="introduction">
229<t>
230   The Hypertext Transfer Protocol (HTTP) is an application-level
231   protocol for distributed, collaborative, hypermedia information
232   systems. HTTP has been in use by the World-Wide Web global
233   information initiative since 1990. The first version of HTTP, commonly
234   referred to as HTTP/0.9, was a simple protocol for raw data transfer
235   across the Internet with only a single method and no metadata.
236   HTTP/1.0, as defined by <xref target="RFC1945"/>, improved
237   the protocol by allowing messages to be in the format of MIME-like
238   messages, containing metadata about the data transferred and
239   modifiers on the request/response semantics. However, HTTP/1.0 did
240   not sufficiently take into consideration the effects of hierarchical
241   proxies, caching, the need for persistent connections, or name-based
242   virtual hosts. In addition, the proliferation of incompletely-implemented
243   applications calling themselves "HTTP/1.0" necessitated a
244   protocol version change in order for two communicating applications
245   to determine each other's true capabilities.
246</t>
247<t>
248   This document is Part 1 of the seven-part specification that defines
249   the protocol referred to as "HTTP/1.1", obsoleting <xref target="RFC2616"/>.
250   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
251   requirements that enable reliable implementations and adding only
252   those new features that will either be safely ignored by an HTTP/1.0
253   recipient or only sent when communicating with a party advertising
254   compliance with HTTP/1.1.
255   Part 1 defines those aspects of HTTP/1.1 related to overall network
256   operation, message framing, interaction with transport protocols, and
257   URI schemes.
258</t>
259<t>
260   This document is currently disorganized in order to minimize the changes
261   between drafts and enable reviewers to see the smaller errata changes.
262   The next draft will reorganize the sections to better reflect the content.
263   In particular, the sections will be organized according to the typical
264   process of deciding when to use HTTP (URI schemes), overall network operation,
265   connection management, message framing, and generic message parsing.
266   The current mess reflects how widely dispersed these topics and associated
267   requirements had become in <xref target="RFC2616"/>.
268</t>
269
270<section title="Purpose" anchor="intro.purpose">
271<t>
272   Practical information systems require more functionality than simple
273   retrieval, including search, front-end update, and annotation. HTTP
274   allows an open-ended set of methods and headers that indicate the
275   purpose of a request <xref target="RFC2324"/>. It builds on the discipline of reference
276   provided by the Uniform Resource Identifier (URI) <xref target="RFC1630"/>, as a location
277   (URL) <xref target="RFC1738"/> or name (URN) <xref target="RFC1737"/>, for indicating the resource to which a
278   method is to be applied. Messages are passed in a format similar to
279   that used by Internet mail <xref target="RFC5322"/> as defined by the Multipurpose
280   Internet Mail Extensions (MIME) <xref target="RFC2045"/>.
281</t>
282<t>
283   HTTP is also used as a generic protocol for communication between
284   user agents and proxies/gateways to other Internet systems, including
285   those supported by the SMTP <xref target="RFC2821"/>, NNTP <xref target="RFC3977"/>, FTP <xref target="RFC959"/>, Gopher <xref target="RFC1436"/>,
286   and WAIS <xref target="WAIS"/> protocols. In this way, HTTP allows basic hypermedia
287   access to resources available from diverse applications.
288</t>
289</section>
290
291<section title="Requirements" anchor="intro.requirements">
292<t>
293   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
294   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
295   document are to be interpreted as described in <xref target="RFC2119"/>.
296</t>
297<t>
298   An implementation is not compliant if it fails to satisfy one or more
299   of the &MUST; or &REQUIRED; level requirements for the protocols it
300   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
301   level and all the &SHOULD; level requirements for its protocols is said
302   to be "unconditionally compliant"; one that satisfies all the &MUST;
303   level requirements but not all the &SHOULD; level requirements for its
304   protocols is said to be "conditionally compliant."
305</t>
306</section>
307
308<section title="Overall Operation" anchor="intro.overall.operation">
309<t>
310   HTTP is a request/response protocol. A client sends a
311   request to the server in the form of a request method, URI, and
312   protocol version, followed by a MIME-like message containing request
313   modifiers, client information, and possible body content over a
314   connection with a server. The server responds with a status line,
315   including the message's protocol version and a success or error code,
316   followed by a MIME-like message containing server information, entity
317   metainformation, and possible entity-body content. The relationship
318   between HTTP and MIME is described in &diff2045entity;.
319</t>
320<t>
321   Most HTTP communication is initiated by a user agent and consists of
322   a request to be applied to a resource on some origin server. In the
323   simplest case, this may be accomplished via a single connection (v)
324   between the user agent (UA) and the origin server (O).
325</t>
326<figure><artwork type="drawing">
327       request chain ------------------------&gt;
328    UA -------------------v------------------- O
329       &lt;----------------------- response chain
330</artwork></figure>
331<t>
332   A more complicated situation occurs when one or more intermediaries
333   are present in the request/response chain. There are three common
334   forms of intermediary: proxy, gateway, and tunnel. A proxy is a
335   forwarding agent, receiving requests for a URI in its absolute form,
336   rewriting all or part of the message, and forwarding the reformatted
337   request toward the server identified by the URI. A gateway is a
338   receiving agent, acting as a layer above some other server(s) and, if
339   necessary, translating the requests to the underlying server's
340   protocol. A tunnel acts as a relay point between two connections
341   without changing the messages; tunnels are used when the
342   communication needs to pass through an intermediary (such as a
343   firewall) even when the intermediary cannot understand the contents
344   of the messages.
345</t>
346<figure><artwork type="drawing">
347       request chain --------------------------------------&gt;
348    UA -----v----- A -----v----- B -----v----- C -----v----- O
349       &lt;------------------------------------- response chain
350</artwork></figure>
351<t>
352   The figure above shows three intermediaries (A, B, and C) between the
353   user agent and origin server. A request or response message that
354   travels the whole chain will pass through four separate connections.
355   This distinction is important because some HTTP communication options
356   may apply only to the connection with the nearest, non-tunnel
357   neighbor, only to the end-points of the chain, or to all connections
358   along the chain. Although the diagram is linear, each participant may
359   be engaged in multiple, simultaneous communications. For example, B
360   may be receiving requests from many clients other than A, and/or
361   forwarding requests to servers other than C, at the same time that it
362   is handling A's request.
363</t>
364<t>
365   Any party to the communication which is not acting as a tunnel may
366   employ an internal cache for handling requests. The effect of a cache
367   is that the request/response chain is shortened if one of the
368   participants along the chain has a cached response applicable to that
369   request. The following illustrates the resulting chain if B has a
370   cached copy of an earlier response from O (via C) for a request which
371   has not been cached by UA or A.
372</t>
373<figure><artwork type="drawing">
374          request chain ----------&gt;
375       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
376          &lt;--------- response chain
377</artwork></figure>
378<t>
379   Not all responses are usefully cacheable, and some requests may
380   contain modifiers which place special requirements on cache behavior.
381   HTTP requirements for cache behavior and cacheable responses are
382   defined in &caching;.
383</t>
384<t>
385   In fact, there are a wide variety of architectures and configurations
386   of caches and proxies currently being experimented with or deployed
387   across the World Wide Web. These systems include national hierarchies
388   of proxy caches to save transoceanic bandwidth, systems that
389   broadcast or multicast cache entries, organizations that distribute
390   subsets of cached data via CD-ROM, and so on. HTTP systems are used
391   in corporate intranets over high-bandwidth links, and for access via
392   PDAs with low-power radio links and intermittent connectivity. The
393   goal of HTTP/1.1 is to support the wide diversity of configurations
394   already deployed while introducing protocol constructs that meet the
395   needs of those who build web applications that require high
396   reliability and, failing that, at least reliable indications of
397   failure.
398</t>
399<t>
400   HTTP communication usually takes place over TCP/IP connections. The
401   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
402   not preclude HTTP from being implemented on top of any other protocol
403   on the Internet, or on other networks. HTTP only presumes a reliable
404   transport; any protocol that provides such guarantees can be used;
405   the mapping of the HTTP/1.1 request and response structures onto the
406   transport data units of the protocol in question is outside the scope
407   of this specification.
408</t>
409<t>
410   In HTTP/1.0, most implementations used a new connection for each
411   request/response exchange. In HTTP/1.1, a connection may be used for
412   one or more request/response exchanges, although connections may be
413   closed for a variety of reasons (see <xref target="persistent.connections"/>).
414</t>
415</section>
416</section>
417
418<section title="Notational Conventions and Generic Grammar" anchor="notation">
419
420<section title="ABNF Extension: #rule" anchor="notation.abnf">
421  <t>
422    One extension to the ABNF rules of <xref target="RFC5234"/> is used to
423    improve readability.
424  </t>
425  <t>
426    A construct "#" is defined, similar to "*", for defining lists of
427    elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at least
428    &lt;n&gt; and at most &lt;m&gt; elements, each separated by one or more commas
429    (",") and &OPTIONAL; linear white space (OWS). This makes the usual
430    form of lists very easy; a rule such as
431    <figure><artwork type="example">
432 ( *<x:ref>OWS</x:ref> element *( *<x:ref>OWS</x:ref> "," *<x:ref>OWS</x:ref> element ))</artwork></figure>
433  </t>
434  <t>
435    can be shown as
436    <figure><artwork type="example">
437 1#element</artwork></figure>
438  </t>
439  <t>
440    Wherever this construct is used, null elements are allowed, but do
441    not contribute to the count of elements present. That is,
442    "(element), , (element) " is permitted, but counts as only two
443    elements. Therefore, where at least one element is required, at
444    least one non-null element &MUST; be present. Default values are 0
445    and infinity so that "#element" allows any number, including zero;
446    "1#element" requires at least one; and "1#2element" allows one or
447    two.
448  </t>
449</section>
450
451<section title="Basic Rules" anchor="basic.rules">
452<t anchor="core.rules">
453  <x:anchor-alias value="ALPHA"/>
454  <x:anchor-alias value="CHAR"/>
455  <x:anchor-alias value="CTL"/>
456  <x:anchor-alias value="CR"/>
457  <x:anchor-alias value="CRLF"/>
458  <x:anchor-alias value="DIGIT"/>
459  <x:anchor-alias value="DQUOTE"/>
460  <x:anchor-alias value="HEXDIG"/>
461  <x:anchor-alias value="HTAB"/>
462  <x:anchor-alias value="LF"/>
463  <x:anchor-alias value="OCTET"/>
464  <x:anchor-alias value="SP"/>
465  <x:anchor-alias value="WSP"/>
466   This specification uses the Augmented Backus-Naur Form (ABNF) notation
467   of <xref target="RFC5234"/>.  The following core rules are included by
468   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
469   ALPHA (letters), CHAR (any <xref target="USASCII"/> character,
470   excluding NUL), CR (carriage return), CRLF (CR LF), CTL (controls),
471   DIGIT (decimal 0-9), DQUOTE (double quote),
472   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab),
473   LF (line feed), OCTET (any 8-bit sequence of data), SP (space)
474   and WSP (white space).
475</t>
476<t anchor="rule.CRLF">
477  <x:anchor-alias value="CRLF"/>
478   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
479   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
480   tolerant applications). The end-of-line marker within an entity-body
481   is defined by its associated media type, as described in &media-types;.
482</t>
483<t anchor="rule.LWS">
484   All linear white space (LWS) in header field-values has the same semantics as SP. A
485   recipient &MAY; replace any such linear white space with a single SP before
486   interpreting the field value or forwarding the message downstream.
487</t>
488<t>
489   Historically, HTTP/1.1 header field values allow linear white space folding across
490   multiple lines. However, this specification deprecates its use; senders MUST NOT
491   produce messages that include LWS folding (i.e., use the obs-fold rule), except
492   within the message/http media type <xref target="internet.media.type.message.http"/>.
493   Receivers SHOULD still parse folded linear white space.
494</t>
495<t>
496    This specification uses three rules to denote the use of linear white space;
497    BWS ("Bad" White Space), OWS (Optional White Space), and RWS (Required White Space).
498</t>
499<t>
500        "Bad" white space is allowed by the BNF, but senders SHOULD NOT produce it in messages.
501        Receivers MUST accept it in incoming messages.
502</t>
503
504<t anchor="rule.whitespace">
505  <x:anchor-alias value="BWS"/>
506  <x:anchor-alias value="OWS"/>
507  <x:anchor-alias value="RWS"/>
508  <x:anchor-alias value="obs-fold"/>
509 
510</t>
511<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="OWS"/><iref primary="true" item="Grammar" subitem="RWS"/><iref primary="true" item="Grammar" subitem="BWS"/>
512  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
513                 ; "optional" white space
514  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
515                 ; "required" white space
516  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
517                 ; "bad" white space
518  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
519                 ; <cref>to be explained: do not produce</cref>
520</artwork></figure>
521<t anchor="rule.TEXT">
522  <x:anchor-alias value="TEXT"/>
523   The TEXT rule is only used for descriptive field contents and values
524   that are not intended to be interpreted by the message parser. Words
525   of *TEXT &MAY; contain characters from character sets other than ISO-8859-1
526   <xref target="ISO-8859-1"/> only when encoded according to the rules of
527   <xref target="RFC2047"/>.
528</t>
529<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TEXT"/>
530  <x:ref>TEXT</x:ref>           = %x20-7E / %x80-FF / <x:ref>LWS</x:ref>
531                 ; any <x:ref>OCTET</x:ref> except <x:ref>CTL</x:ref>s, but including <x:ref>LWS</x:ref>
532</artwork></figure>
533<t>
534   A CRLF is allowed in the definition of TEXT only as part of a header
535   field continuation. It is expected that the folding LWS will be
536   replaced with a single SP before interpretation of the TEXT value.
537</t>
538<t anchor="rule.token.separators">
539  <x:anchor-alias value="tchar"/>
540  <x:anchor-alias value="token"/>
541  <x:anchor-alias value="separators"/>
542   Many HTTP/1.1 header field values consist of words separated by LWS
543   or special characters. These special characters &MUST; be in a quoted
544   string to be used within a parameter value (as defined in
545   <xref target="transfer.codings"/>).
546</t>
547<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/><iref primary="true" item="Grammar" subitem="separators"/>
548  <x:ref>separators</x:ref>     = "(" / ")" / "&lt;" / "&gt;" / "@"
549                 / "," / ";" / ":" / "\" / <x:ref>DQUOTE</x:ref>
550                 / "/" / "[" / "]" / "?" / "="
551                 / "{" / "}" / <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref>
552                 
553  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
554                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
555                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
556                 ; any <x:ref>CHAR</x:ref> except <x:ref>CTL</x:ref>s or <x:ref>separators</x:ref>
557                 
558  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
559</artwork></figure>
560<t anchor="rule.comment">
561  <x:anchor-alias value="comment"/>
562  <x:anchor-alias value="ctext"/>
563   Comments can be included in some HTTP header fields by surrounding
564   the comment text with parentheses. Comments are only allowed in
565   fields containing "comment" as part of their field value definition.
566   In all other fields, parentheses are considered part of the field
567   value.
568</t>
569<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
570  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
571  <x:ref>ctext</x:ref>          = &lt;any <x:ref>TEXT</x:ref> excluding "(" and ")"&gt;
572</artwork></figure>
573<t anchor="rule.quoted-string">
574  <x:anchor-alias value="quoted-string"/>
575  <x:anchor-alias value="qdtext"/>
576   A string of text is parsed as a single word if it is quoted using
577   double-quote marks.
578</t>
579<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/>
580  <x:ref>quoted-string</x:ref>  = ( <x:ref>DQUOTE</x:ref> *(<x:ref>qdtext</x:ref> / <x:ref>quoted-pair</x:ref> ) <x:ref>DQUOTE</x:ref> )
581  <x:ref>qdtext</x:ref>         = &lt;any <x:ref>TEXT</x:ref> excluding <x:ref>DQUOTE</x:ref> and "\">
582</artwork></figure>
583<t anchor="rule.quoted-pair">
584  <x:anchor-alias value="quoted-pair"/>
585  <x:anchor-alias value="quoted-text"/>
586   The backslash character ("\") &MAY; be used as a single-character
587   quoting mechanism only within quoted-string and comment constructs.
588</t>
589<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-text"/><iref primary="true" item="Grammar" subitem="quoted-pair"/>
590  <x:ref>quoted-text</x:ref>    = %x01-09 /
591                   %x0B-0C /
592                   %x0E-FF ; Characters excluding NUL, <x:ref>CR</x:ref> and <x:ref>LF</x:ref>
593  <x:ref>quoted-pair</x:ref>    = "\" <x:ref>quoted-text</x:ref>
594</artwork></figure>
595</section>
596
597<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
598  <x:anchor-alias value="request-header"/>
599  <x:anchor-alias value="response-header"/>
600  <x:anchor-alias value="accept-params"/>
601  <x:anchor-alias value="entity-body"/>
602  <x:anchor-alias value="entity-header"/>
603  <x:anchor-alias value="Cache-Control"/>
604  <x:anchor-alias value="Pragma"/>
605  <x:anchor-alias value="Warning"/>
606<t>
607  The ABNF rules below are defined in other parts:
608</t>
609<figure><!-- Part2--><artwork type="abnf2616">
610  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
611  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
612</artwork></figure>
613<figure><!-- Part3--><artwork type="abnf2616">
614  <x:ref>accept-params</x:ref>   = &lt;accept-params, defined in &header-accept;&gt;
615  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
616  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
617</artwork></figure>
618<figure><!-- Part6--><artwork type="abnf2616">
619  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
620  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
621  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
622</artwork></figure>
623</section>
624
625</section>
626
627<section title="Protocol Parameters" anchor="protocol.parameters">
628
629<section title="HTTP Version" anchor="http.version">
630  <x:anchor-alias value="HTTP-Version"/>
631  <x:anchor-alias value="HTTP-Prot-Name"/>
632<t>
633   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
634   of the protocol. The protocol versioning policy is intended to allow
635   the sender to indicate the format of a message and its capacity for
636   understanding further HTTP communication, rather than the features
637   obtained via that communication. No change is made to the version
638   number for the addition of message components which do not affect
639   communication behavior or which only add to extensible field values.
640   The &lt;minor&gt; number is incremented when the changes made to the
641   protocol add features which do not change the general message parsing
642   algorithm, but which may add to the message semantics and imply
643   additional capabilities of the sender. The &lt;major&gt; number is
644   incremented when the format of a message within the protocol is
645   changed. See <xref target="RFC2145"/> for a fuller explanation.
646</t>
647<t>
648   The version of an HTTP message is indicated by an HTTP-Version field
649   in the first line of the message. HTTP-Version is case-sensitive.
650</t>
651<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
652  <x:ref>HTTP-Version</x:ref>   = <x:ref>HTTP-Prot-Name</x:ref> "/" 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
653  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
654</artwork></figure>
655<t>
656   Note that the major and minor numbers &MUST; be treated as separate
657   integers and that each &MAY; be incremented higher than a single digit.
658   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
659   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
660   &MUST-NOT; be sent.
661</t>
662<t>
663   An application that sends a request or response message that includes
664   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
665   with this specification. Applications that are at least conditionally
666   compliant with this specification &SHOULD; use an HTTP-Version of
667   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
668   not compatible with HTTP/1.0. For more details on when to send
669   specific HTTP-Version values, see <xref target="RFC2145"/>.
670</t>
671<t>
672   The HTTP version of an application is the highest HTTP version for
673   which the application is at least conditionally compliant.
674</t>
675<t>
676   Proxy and gateway applications need to be careful when forwarding
677   messages in protocol versions different from that of the application.
678   Since the protocol version indicates the protocol capability of the
679   sender, a proxy/gateway &MUST-NOT; send a message with a version
680   indicator which is greater than its actual version. If a higher
681   version request is received, the proxy/gateway &MUST; either downgrade
682   the request version, or respond with an error, or switch to tunnel
683   behavior.
684</t>
685<t>
686   Due to interoperability problems with HTTP/1.0 proxies discovered
687   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
688   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
689   they support. The proxy/gateway's response to that request &MUST; be in
690   the same major version as the request.
691</t>
692<t>
693  <list>
694    <t>
695      <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
696      of header fields required or forbidden by the versions involved.
697    </t>
698  </list>
699</t>
700</section>
701
702<section title="Uniform Resource Identifiers" anchor="uri">
703<t>
704   URIs have been known by many names: WWW addresses, Universal Document
705   Identifiers, Universal Resource Identifiers <xref target="RFC1630"/>, and finally the
706   combination of Uniform Resource Locators (URL) <xref target="RFC1738"/> and Names (URN)
707   <xref target="RFC1737"/>. As far as HTTP is concerned, Uniform Resource Identifiers are
708   simply formatted strings which identify--via name, location, or any
709   other characteristic--a resource.
710</t>
711
712<section title="General Syntax" anchor="general.syntax">
713  <x:anchor-alias value="absoluteURI"/>
714  <x:anchor-alias value="authority"/>
715  <x:anchor-alias value="fragment"/>
716  <x:anchor-alias value="path-absolute"/>
717  <x:anchor-alias value="port"/>
718  <x:anchor-alias value="query"/>
719  <x:anchor-alias value="relativeURI"/>
720  <x:anchor-alias value="uri-host"/>
721<t>
722   URIs in HTTP can be represented in absolute form or relative to some
723   known base URI <xref target="RFC1808"/>, depending upon the context of their use. The two
724   forms are differentiated by the fact that absolute URIs always begin
725   with a scheme name followed by a colon. For definitive information on
726   URL syntax and semantics, see "Uniform Resource Identifiers (URI):
727   Generic Syntax and Semantics," <xref target="RFC2396"/> (which replaces <xref target="RFC1738"/>
728   and <xref target="RFC1808"/>). This specification adopts the
729   definitions of "URI-reference", "absoluteURI", "fragment", "relativeURI", "port",
730   "host", "abs_path", "query", and "authority" from that specification:
731</t>
732<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="absoluteURI"/><iref primary="true" item="Grammar" subitem="authority"/><iref primary="true" item="Grammar" subitem="path-absolute"/><iref primary="true" item="Grammar" subitem="port"/><iref primary="true" item="Grammar" subitem="query"/><iref primary="true" item="Grammar" subitem="relativeURI"/><iref primary="true" item="Grammar" subitem="uri-host"/>
733  <x:ref>absoluteURI</x:ref>   = &lt;absoluteURI, defined in <xref target="RFC2396" x:fmt="," x:sec="3"/>>
734  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC2396" x:fmt="," x:sec="3.2"/>>
735  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC2396" x:fmt="," x:sec="4.1"/>>
736  <x:ref>path-absolute</x:ref> = &lt;abs_path, defined in <xref target="RFC2396" x:fmt="," x:sec="3"/>>
737  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC2396" x:fmt="," x:sec="3.2.2"/>>
738  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC2396" x:fmt="," x:sec="3.4"/>>
739  <x:ref>relativeURI</x:ref>   = &lt;relativeURI, defined in <xref target="RFC2396" x:fmt="," x:sec="5"/>>
740  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC2396" x:fmt="," x:sec="3.2.2"/>>
741</artwork></figure>
742<t>
743   HTTP does not place any a priori limit on the length of
744   a URI. Servers &MUST; be able to handle the URI of any resource they
745   serve, and &SHOULD; be able to handle URIs of unbounded length if they
746   provide GET-based forms that could generate such URIs. A server
747   &SHOULD; return 414 (Request-URI Too Long) status if a URI is longer
748   than the server can handle (see &status-414;).
749</t>
750<t>
751  <list>
752    <t>
753      <x:h>Note:</x:h> Servers ought to be cautious about depending on URI lengths
754      above 255 bytes, because some older client or proxy
755      implementations might not properly support these lengths.
756    </t>
757  </list>
758</t>
759</section>
760
761<section title="http URL" anchor="http.url">
762  <x:anchor-alias value="http-URL"/>
763  <iref item="http URI scheme" primary="true"/>
764  <iref item="URI scheme" subitem="http" primary="true"/>
765<t>
766   The "http" scheme is used to locate network resources via the HTTP
767   protocol. This section defines the scheme-specific syntax and
768   semantics for http URLs.
769</t>
770<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URL"/>
771  <x:ref>http-URL</x:ref> = "http:" "//" <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ]
772             [ <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ]]
773</artwork></figure>
774<t>
775   If the port is empty or not given, port 80 is assumed. The semantics
776   are that the identified resource is located at the server listening
777   for TCP connections on that port of that host, and the Request-URI
778   for the resource is path-absolute (<xref target="request-uri"/>). The use of IP addresses
779   in URLs &SHOULD; be avoided whenever possible (see <xref target="RFC1900"/>). If
780   the path-absolute is not present in the URL, it &MUST; be given as "/" when
781   used as a Request-URI for a resource (<xref target="request-uri"/>). If a proxy
782   receives a host name which is not a fully qualified domain name, it
783   &MAY; add its domain to the host name it received. If a proxy receives
784   a fully qualified domain name, the proxy &MUST-NOT; change the host
785   name.
786</t>
787<t><list><t>
788  <iref item="https URI scheme"/>
789  <iref item="URI scheme" subitem="https"/>
790  <x:h>Note:</x:h> the "https" scheme is defined in <xref target="RFC2818"/>.
791</t></list></t>
792</section>
793
794<section title="URI Comparison" anchor="uri.comparison">
795<t>
796   When comparing two URIs to decide if they match or not, a client
797   &SHOULD; use a case-sensitive octet-by-octet comparison of the entire
798   URIs, with these exceptions:
799  <list style="symbols">
800    <t>A port that is empty or not given is equivalent to the default
801        port for that URI-reference;</t>
802    <t>Comparisons of host names &MUST; be case-insensitive;</t>
803    <t>Comparisons of scheme names &MUST; be case-insensitive;</t>
804    <t>An empty path-absolute is equivalent to an path-absolute of "/".</t>
805  </list>
806</t>
807<t>
808   Characters other than those in the "reserved" set (see
809   <xref target="RFC2396" x:fmt="," x:sec="2.2"/>) are equivalent to their
810   ""%" <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding.
811</t>
812<t>
813   For example, the following three URIs are equivalent:
814</t>
815<figure><artwork type="example">
816   http://example.com:80/~smith/home.html
817   http://EXAMPLE.com/%7Esmith/home.html
818   http://EXAMPLE.com:/%7esmith/home.html
819</artwork></figure>
820</section>
821</section>
822
823<section title="Date/Time Formats" anchor="date.time.formats">
824<section title="Full Date" anchor="full.date">
825  <x:anchor-alias value="HTTP-date"/>
826  <x:anchor-alias value="obsolete-date"/>
827  <x:anchor-alias value="rfc1123-date"/>
828  <x:anchor-alias value="rfc850-date"/>
829  <x:anchor-alias value="asctime-date"/>
830  <x:anchor-alias value="date1"/>
831  <x:anchor-alias value="date2"/>
832  <x:anchor-alias value="date3"/>
833  <x:anchor-alias value="rfc1123-date"/>
834  <x:anchor-alias value="time"/>
835  <x:anchor-alias value="wkday"/>
836  <x:anchor-alias value="weekday"/>
837  <x:anchor-alias value="month"/>
838<t>
839   HTTP applications have historically allowed three different formats
840   for the representation of date/time stamps:
841</t>
842<figure><artwork type="example">
843   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 822, updated by RFC 1123
844   Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
845   Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
846</artwork></figure>
847<t>
848   The first format is preferred as an Internet standard and represents
849   a fixed-length subset of that defined by <xref target="RFC1123"/> (an update to
850   <xref target="RFC822"/>). The other formats are described here only for
851   compatibility with obsolete implementations.
852   HTTP/1.1 clients and servers that parse the date value &MUST; accept
853   all three formats (for compatibility with HTTP/1.0), though they &MUST;
854   only generate the RFC 1123 format for representing HTTP-date values
855   in header fields. See <xref target="tolerant.applications"/> for further information.
856</t>
857<t><list><t>
858      <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
859      accepting date values that may have been sent by non-HTTP
860      applications, as is sometimes the case when retrieving or posting
861      messages via proxies/gateways to SMTP or NNTP.
862</t></list></t>
863<t>
864   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
865   (GMT), without exception. For the purposes of HTTP, GMT is exactly
866   equal to UTC (Coordinated Universal Time). This is indicated in the
867   first two formats by the inclusion of "GMT" as the three-letter
868   abbreviation for time zone, and &MUST; be assumed when reading the
869   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
870   additional LWS beyond that specifically included as SP in the
871   grammar.
872</t>
873<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="obsolete-date"/><iref primary="true" item="Grammar" subitem="rfc850-date"/><iref primary="true" item="Grammar" subitem="asctime-date"/><iref primary="true" item="Grammar" subitem="date1"/><iref primary="true" item="Grammar" subitem="date2"/><iref primary="true" item="Grammar" subitem="date3"/><iref primary="true" item="Grammar" subitem="time"/><iref primary="true" item="Grammar" subitem="wkday"/><iref primary="true" item="Grammar" subitem="weekday"/><iref primary="true" item="Grammar" subitem="month"/>
874  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obsolete-date</x:ref>
875  <x:ref>obsolete-date</x:ref> = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
876  <x:ref>rfc1123-date</x:ref> = <x:ref>wkday</x:ref> "," <x:ref>SP</x:ref> date1 <x:ref>SP</x:ref> time <x:ref>SP</x:ref> GMT
877  <x:ref>rfc850-date</x:ref>  = <x:ref>weekday</x:ref> "," <x:ref>SP</x:ref> date2 <x:ref>SP</x:ref> time <x:ref>SP</x:ref> GMT
878  <x:ref>asctime-date</x:ref> = <x:ref>wkday</x:ref> <x:ref>SP</x:ref> <x:ref>date3</x:ref> <x:ref>SP</x:ref> <x:ref>time</x:ref> <x:ref>SP</x:ref> 4<x:ref>DIGIT</x:ref>
879  <x:ref>date1</x:ref>        = 2<x:ref>DIGIT</x:ref> <x:ref>SP</x:ref> <x:ref>month</x:ref> <x:ref>SP</x:ref> 4<x:ref>DIGIT</x:ref>
880                 ; day month year (e.g., 02 Jun 1982)
881  <x:ref>date2</x:ref>        = 2<x:ref>DIGIT</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
882                 ; day-month-year (e.g., 02-Jun-82)
883  <x:ref>date3</x:ref>        = <x:ref>month</x:ref> <x:ref>SP</x:ref> ( 2<x:ref>DIGIT</x:ref> / ( <x:ref>SP</x:ref> 1<x:ref>DIGIT</x:ref> ))
884                 ; month day (e.g., Jun  2)
885  <x:ref>time</x:ref>         = 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref>
886                 ; 00:00:00 - 23:59:59
887  <x:ref>wkday</x:ref>        = s-Mon / s-Tue / s-Wed
888               / s-Thu / s-Fri / s-Sat / s-Sun
889  <x:ref>weekday</x:ref>      = l-Mon / l-Tue / l-Wed
890               / l-Thu / l-Fri / l-Sat / l-Sun
891  <x:ref>month</x:ref>        = s-Jan / s-Feb / s-Mar / s-Apr
892               / s-May / s-Jun / s-Jul / s-Aug
893               / s-Sep / s-Oct / s-Nov / s-Dec
894               
895  GMT   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
896
897  s-Mon = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
898  s-Tue = <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
899  s-Wed = <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
900  s-Thu = <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
901  s-Fri = <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
902  s-Sat = <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
903  s-Sun = <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
904
905  l-Mon = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence>          ; "Monday", case-sensitive
906  l-Tue = <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence>       ; "Tuesday", case-sensitive
907  l-Wed = <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
908  l-Thu = <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence>    ; "Thursday", case-sensitive
909  l-Fri = <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence>          ; "Friday", case-sensitive
910  l-Sat = <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence>    ; "Saturday", case-sensitive
911  l-Sun = <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence>          ; "Sunday", case-sensitive
912
913  s-Jan = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
914  s-Feb = <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
915  s-Mar = <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
916  s-Apr = <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
917  s-May = <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
918  s-Jun = <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
919  s-Jul = <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
920  s-Aug = <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
921  s-Sep = <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
922  s-Oct = <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
923  s-Nov = <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
924  s-Dec = <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
925</artwork></figure>
926<t>
927      <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
928      to their usage within the protocol stream. Clients and servers are
929      not required to use these formats for user presentation, request
930      logging, etc.
931</t>
932</section>
933</section>
934
935<section title="Transfer Codings" anchor="transfer.codings">
936  <x:anchor-alias value="parameter"/>
937  <x:anchor-alias value="transfer-coding"/>
938  <x:anchor-alias value="transfer-extension"/>
939<t>
940   Transfer-coding values are used to indicate an encoding
941   transformation that has been, can be, or may need to be applied to an
942   entity-body in order to ensure "safe transport" through the network.
943   This differs from a content coding in that the transfer-coding is a
944   property of the message, not of the original entity.
945</t>
946<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
947  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
948  <x:ref>transfer-extension</x:ref>      = <x:ref>token</x:ref> *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
949</artwork></figure>
950<t anchor="rule.parameter">
951  <x:anchor-alias value="attribute"/>
952  <x:anchor-alias value="parameter"/>
953  <x:anchor-alias value="value"/>
954   Parameters are in  the form of attribute/value pairs.
955</t>
956<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"/>
957  <x:ref>parameter</x:ref>               = <x:ref>attribute</x:ref> <x:ref>BWS</x:ref> "=" <x:ref>BWS</x:ref> <x:ref>value</x:ref>
958  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
959  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
960</artwork></figure>
961<t>
962   All transfer-coding values are case-insensitive. HTTP/1.1 uses
963   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
964   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
965</t>
966<t>
967   Whenever a transfer-coding is applied to a message-body, the set of
968   transfer-codings &MUST; include "chunked", unless the message indicates it
969   is terminated by closing the connection. When the "chunked" transfer-coding
970   is used, it &MUST; be the last transfer-coding applied to the
971   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
972   than once to a message-body. These rules allow the recipient to
973   determine the transfer-length of the message (<xref target="message.length"/>).
974</t>
975<t>
976   Transfer-codings are analogous to the Content-Transfer-Encoding
977   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
978   binary data over a 7-bit transport service. However, safe transport
979   has a different focus for an 8bit-clean transfer protocol. In HTTP,
980   the only unsafe characteristic of message-bodies is the difficulty in
981   determining the exact body length (<xref target="message.length"/>), or the desire to
982   encrypt data over a shared transport.
983</t>
984<t>
985   The Internet Assigned Numbers Authority (IANA) acts as a registry for
986   transfer-coding value tokens. Initially, the registry contains the
987   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
988   "gzip", "compress", and "deflate" (&content-codings;).
989</t>
990<t>
991   New transfer-coding value tokens &SHOULD; be registered in the same way
992   as new content-coding value tokens (&content-codings;).
993</t>
994<t>
995   A server which receives an entity-body with a transfer-coding it does
996   not understand &SHOULD; return 501 (Not Implemented), and close the
997   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
998   client.
999</t>
1000
1001<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1002  <x:anchor-alias value="chunk"/>
1003  <x:anchor-alias value="Chunked-Body"/>
1004  <x:anchor-alias value="chunk-data"/>
1005  <x:anchor-alias value="chunk-ext"/>
1006  <x:anchor-alias value="chunk-ext-name"/>
1007  <x:anchor-alias value="chunk-ext-val"/>
1008  <x:anchor-alias value="chunk-size"/>
1009  <x:anchor-alias value="last-chunk"/>
1010  <x:anchor-alias value="trailer-part"/>
1011<t>
1012   The chunked encoding modifies the body of a message in order to
1013   transfer it as a series of chunks, each with its own size indicator,
1014   followed by an &OPTIONAL; trailer containing entity-header fields. This
1015   allows dynamically produced content to be transferred along with the
1016   information necessary for the recipient to verify that it has
1017   received the full message.
1018</t>
1019<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-ext"/><iref primary="true" item="Grammar" subitem="chunk-ext-name"/><iref primary="true" item="Grammar" subitem="chunk-ext-val"/><iref primary="true" item="Grammar" subitem="chunk-data"/><iref primary="true" item="Grammar" subitem="trailer-part"/>
1020  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1021                   <x:ref>last-chunk</x:ref>
1022                   <x:ref>trailer-part</x:ref>
1023                   <x:ref>CRLF</x:ref>
1024 
1025  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1026                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1027  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1028  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1029 
1030  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
1031  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1032  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1033  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1034  <x:ref>trailer-part</x:ref>   = *(<x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref>)
1035</artwork></figure>
1036<t>
1037   The chunk-size field is a string of hex digits indicating the size of
1038   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1039   zero, followed by the trailer, which is terminated by an empty line.
1040</t>
1041<t>
1042   The trailer allows the sender to include additional HTTP header
1043   fields at the end of the message. The Trailer header field can be
1044   used to indicate which header fields are included in a trailer (see
1045   <xref target="header.trailer"/>).
1046</t>
1047<t>
1048   A server using chunked transfer-coding in a response &MUST-NOT; use the
1049   trailer for any header fields unless at least one of the following is
1050   true:
1051  <list style="numbers">
1052    <t>the request included a TE header field that indicates "trailers" is
1053     acceptable in the transfer-coding of the  response, as described in
1054     <xref target="header.te"/>; or,</t>
1055
1056    <t>the server is the origin server for the response, the trailer
1057     fields consist entirely of optional metadata, and the recipient
1058     could use the message (in a manner acceptable to the origin server)
1059     without receiving this metadata.  In other words, the origin server
1060     is willing to accept the possibility that the trailer fields might
1061     be silently discarded along the path to the client.</t>
1062  </list>
1063</t>
1064<t>
1065   This requirement prevents an interoperability failure when the
1066   message is being received by an HTTP/1.1 (or later) proxy and
1067   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1068   compliance with the protocol would have necessitated a possibly
1069   infinite buffer on the proxy.
1070</t>
1071<t>
1072   A process for decoding the "chunked" transfer-coding
1073   can be represented in pseudo-code as:
1074</t>
1075<figure><artwork type="code">
1076  length := 0
1077  read chunk-size, chunk-ext (if any) and CRLF
1078  while (chunk-size &gt; 0) {
1079     read chunk-data and CRLF
1080     append chunk-data to entity-body
1081     length := length + chunk-size
1082     read chunk-size and CRLF
1083  }
1084  read entity-header
1085  while (entity-header not empty) {
1086     append entity-header to existing header fields
1087     read entity-header
1088  }
1089  Content-Length := length
1090  Remove "chunked" from Transfer-Encoding
1091</artwork></figure>
1092<t>
1093   All HTTP/1.1 applications &MUST; be able to receive and decode the
1094   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1095   they do not understand.
1096</t>
1097</section>
1098</section>
1099
1100<section title="Product Tokens" anchor="product.tokens">
1101  <x:anchor-alias value="product"/>
1102  <x:anchor-alias value="product-version"/>
1103<t>
1104   Product tokens are used to allow communicating applications to
1105   identify themselves by software name and version. Most fields using
1106   product tokens also allow sub-products which form a significant part
1107   of the application to be listed, separated by white space. By
1108   convention, the products are listed in order of their significance
1109   for identifying the application.
1110</t>
1111<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1112  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1113  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1114</artwork></figure>
1115<t>
1116   Examples:
1117</t>
1118<figure><artwork type="example">
1119    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1120    Server: Apache/0.8.4
1121</artwork></figure>
1122<t>
1123   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1124   used for advertising or other non-essential information. Although any
1125   token character &MAY; appear in a product-version, this token &SHOULD;
1126   only be used for a version identifier (i.e., successive versions of
1127   the same product &SHOULD; only differ in the product-version portion of
1128   the product value).
1129</t>
1130</section>
1131
1132</section>
1133
1134<section title="HTTP Message" anchor="http.message">
1135
1136<section title="Message Types" anchor="message.types">
1137  <x:anchor-alias value="generic-message"/>
1138  <x:anchor-alias value="HTTP-message"/>
1139  <x:anchor-alias value="start-line"/>
1140<t>
1141   HTTP messages consist of requests from client to server and responses
1142   from server to client.
1143</t>
1144<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1145  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1146</artwork></figure>
1147<t>
1148   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1149   message format of <xref target="RFC5322"/> for transferring entities (the payload
1150   of the message). Both types of message consist of a start-line, zero
1151   or more header fields (also known as "headers"), an empty line (i.e.,
1152   a line with nothing preceding the CRLF) indicating the end of the
1153   header fields, and possibly a message-body.
1154</t>
1155<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1156  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1157                    *(<x:ref>message-header</x:ref> <x:ref>CRLF</x:ref>)
1158                    <x:ref>CRLF</x:ref>
1159                    [ <x:ref>message-body</x:ref> ]
1160  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1161</artwork></figure>
1162<t>
1163   In the interest of robustness, servers &SHOULD; ignore any empty
1164   line(s) received where a Request-Line is expected. In other words, if
1165   the server is reading the protocol stream at the beginning of a
1166   message and receives a CRLF first, it should ignore the CRLF.
1167</t>
1168<t>
1169   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1170   after a POST request. To restate what is explicitly forbidden by the
1171   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1172   extra CRLF.
1173</t>
1174</section>
1175
1176<section title="Message Headers" anchor="message.headers">
1177  <x:anchor-alias value="field-content"/>
1178  <x:anchor-alias value="field-name"/>
1179  <x:anchor-alias value="field-value"/>
1180  <x:anchor-alias value="message-header"/>
1181<t>
1182   HTTP header fields, which include general-header (<xref target="general.header.fields"/>),
1183   request-header (&request-header-fields;), response-header (&response-header-fields;), and
1184   entity-header (&entity-header-fields;) fields, follow the same generic format as
1185   that given in <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1186   of a name followed by a colon (":") and the field value. Field names
1187   are case-insensitive. The field value &MAY; be preceded by any amount
1188   of LWS, though a single SP is preferred. Header fields can be
1189   extended over multiple lines by preceding each extra line with at
1190   least one SP or HTAB. Applications ought to follow "common form", where
1191   one is known or indicated, when generating HTTP constructs, since
1192   there might exist some implementations that fail to accept anything
1193   beyond the common forms.
1194</t>
1195<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"/>
1196  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" [ <x:ref>field-value</x:ref> ]
1197  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1198  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>LWS</x:ref> )
1199  <x:ref>field-content</x:ref>  = &lt;field content&gt;
1200                   ; the <x:ref>OCTET</x:ref>s making up the field-value
1201                   ; and consisting of either *<x:ref>TEXT</x:ref> or combinations
1202                   ; of <x:ref>token</x:ref>, <x:ref>separators</x:ref>, and <x:ref>quoted-string</x:ref>
1203</artwork></figure>
1204<t>
1205  <cref>whitespace between field-name and colon is an error and MUST NOT be accepted</cref>
1206</t>
1207<t>
1208   The field-content does not include any leading or trailing LWS:
1209   linear white space occurring before the first non-whitespace
1210   character of the field-value or after the last non-whitespace
1211   character of the field-value. Such leading or trailing LWS &MAY; be
1212   removed without changing the semantics of the field value. Any LWS
1213   that occurs between field-content &MAY; be replaced with a single SP
1214   before interpreting the field value or forwarding the message
1215   downstream.
1216</t>
1217<t>
1218   The order in which header fields with differing field names are
1219   received is not significant. However, it is "good practice" to send
1220   general-header fields first, followed by request-header or response-header
1221   fields, and ending with the entity-header fields.
1222</t>
1223<t>
1224   Multiple message-header fields with the same field-name &MAY; be
1225   present in a message if and only if the entire field-value for that
1226   header field is defined as a comma-separated list [i.e., #(values)].
1227   It &MUST; be possible to combine the multiple header fields into one
1228   "field-name: field-value" pair, without changing the semantics of the
1229   message, by appending each subsequent field-value to the first, each
1230   separated by a comma. The order in which header fields with the same
1231   field-name are received is therefore significant to the
1232   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1233   change the order of these field values when a message is forwarded.
1234</t>
1235<t>
1236  <list><t>
1237   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1238   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1239   can occur multiple times, but does not use the list syntax, and thus cannot
1240   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1241   for details.) Also note that the Set-Cookie2 header specified in
1242   <xref target="RFC2965"/> does not share this problem.
1243  </t></list>
1244</t>
1245 
1246</section>
1247
1248<section title="Message Body" anchor="message.body">
1249  <x:anchor-alias value="message-body"/>
1250<t>
1251   The message-body (if any) of an HTTP message is used to carry the
1252   entity-body associated with the request or response. The message-body
1253   differs from the entity-body only when a transfer-coding has been
1254   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1255</t>
1256<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1257  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1258               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1259</artwork></figure>
1260<t>
1261   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1262   applied by an application to ensure safe and proper transfer of the
1263   message. Transfer-Encoding is a property of the message, not of the
1264   entity, and thus &MAY; be added or removed by any application along the
1265   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1266   when certain transfer-codings may be used.)
1267</t>
1268<t>
1269   The rules for when a message-body is allowed in a message differ for
1270   requests and responses.
1271</t>
1272<t>
1273   The presence of a message-body in a request is signaled by the
1274   inclusion of a Content-Length or Transfer-Encoding header field in
1275   the request's message-headers. A message-body &MUST-NOT; be included in
1276   a request if the specification of the request method (&method;)
1277   explicitly disallows an entity-body in requests.
1278   When a request message contains both a message-body of non-zero
1279   length and a method that does not define any semantics for that
1280   request message-body, then an origin server &SHOULD; either ignore
1281   the message-body or respond with an appropriate error message
1282   (e.g., 413).  A proxy or gateway, when presented the same request,
1283   &SHOULD; either forward the request inbound with the message-body or
1284   ignore the message-body when determining a response.
1285</t>
1286<t>
1287   For response messages, whether or not a message-body is included with
1288   a message is dependent on both the request method and the response
1289   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1290   &MUST-NOT; include a message-body, even though the presence of entity-header
1291   fields might lead one to believe they do. All 1xx
1292   (informational), 204 (No Content), and 304 (Not Modified) responses
1293   &MUST-NOT; include a message-body. All other responses do include a
1294   message-body, although it &MAY; be of zero length.
1295</t>
1296</section>
1297
1298<section title="Message Length" anchor="message.length">
1299<t>
1300   The transfer-length of a message is the length of the message-body as
1301   it appears in the message; that is, after any transfer-codings have
1302   been applied. When a message-body is included with a message, the
1303   transfer-length of that body is determined by one of the following
1304   (in order of precedence):
1305</t>
1306<t>
1307  <list style="numbers">
1308    <x:lt><t>
1309     Any response message which "&MUST-NOT;" include a message-body (such
1310     as the 1xx, 204, and 304 responses and any response to a HEAD
1311     request) is always terminated by the first empty line after the
1312     header fields, regardless of the entity-header fields present in
1313     the message.
1314    </t></x:lt>
1315    <x:lt><t>
1316     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1317     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1318     is used, the transfer-length is defined by the use of this transfer-coding.
1319     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1320     is not present, the transfer-length is defined by the sender closing the connection.
1321    </t></x:lt>
1322    <x:lt><t>
1323     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1324     decimal value in OCTETs represents both the entity-length and the
1325     transfer-length. The Content-Length header field &MUST-NOT; be sent
1326     if these two lengths are different (i.e., if a Transfer-Encoding
1327     header field is present). If a message is received with both a
1328     Transfer-Encoding header field and a Content-Length header field,
1329     the latter &MUST; be ignored.
1330    </t></x:lt>
1331    <x:lt><t>
1332     If the message uses the media type "multipart/byteranges", and the
1333     transfer-length is not otherwise specified, then this self-delimiting
1334     media type defines the transfer-length. This media type
1335     &MUST-NOT; be used unless the sender knows that the recipient can parse
1336     it; the presence in a request of a Range header with multiple byte-range
1337     specifiers from a 1.1 client implies that the client can parse
1338     multipart/byteranges responses.
1339    <list style="empty"><t>
1340       A range header might be forwarded by a 1.0 proxy that does not
1341       understand multipart/byteranges; in this case the server &MUST;
1342       delimit the message using methods defined in items 1, 3 or 5 of
1343       this section.
1344    </t></list>
1345    </t></x:lt>
1346    <x:lt><t>
1347     By the server closing the connection. (Closing the connection
1348     cannot be used to indicate the end of a request body, since that
1349     would leave no possibility for the server to send back a response.)
1350    </t></x:lt>
1351  </list>
1352</t>
1353<t>
1354   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1355   containing a message-body &MUST; include a valid Content-Length header
1356   field unless the server is known to be HTTP/1.1 compliant. If a
1357   request contains a message-body and a Content-Length is not given,
1358   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1359   determine the length of the message, or with 411 (Length Required) if
1360   it wishes to insist on receiving a valid Content-Length.
1361</t>
1362<t>
1363   All HTTP/1.1 applications that receive entities &MUST; accept the
1364   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1365   to be used for messages when the message length cannot be determined
1366   in advance.
1367</t>
1368<t>
1369   Messages &MUST-NOT; include both a Content-Length header field and a
1370   transfer-coding. If the message does include a
1371   transfer-coding, the Content-Length &MUST; be ignored.
1372</t>
1373<t>
1374   When a Content-Length is given in a message where a message-body is
1375   allowed, its field value &MUST; exactly match the number of OCTETs in
1376   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1377   invalid length is received and detected.
1378</t>
1379</section>
1380
1381<section title="General Header Fields" anchor="general.header.fields">
1382  <x:anchor-alias value="general-header"/>
1383<t>
1384   There are a few header fields which have general applicability for
1385   both request and response messages, but which do not apply to the
1386   entity being transferred. These header fields apply only to the
1387   message being transmitted.
1388</t>
1389<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1390  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1391                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1392                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1393                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1394                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1395                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1396                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1397                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1398                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1399</artwork></figure>
1400<t>
1401   General-header field names can be extended reliably only in
1402   combination with a change in the protocol version. However, new or
1403   experimental header fields may be given the semantics of general
1404   header fields if all parties in the communication recognize them to
1405   be general-header fields. Unrecognized header fields are treated as
1406   entity-header fields.
1407</t>
1408</section>
1409</section>
1410
1411<section title="Request" anchor="request">
1412  <x:anchor-alias value="Request"/>
1413<t>
1414   A request message from a client to a server includes, within the
1415   first line of that message, the method to be applied to the resource,
1416   the identifier of the resource, and the protocol version in use.
1417</t>
1418<!--                 Host                      ; should be moved here eventually -->
1419<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1420  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1421                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1422                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1423                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1424                  <x:ref>CRLF</x:ref>
1425                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1426</artwork></figure>
1427
1428<section title="Request-Line" anchor="request-line">
1429  <x:anchor-alias value="Request-Line"/>
1430<t>
1431   The Request-Line begins with a method token, followed by the
1432   Request-URI and the protocol version, and ending with CRLF. The
1433   elements are separated by SP characters. No CR or LF is allowed
1434   except in the final CRLF sequence.
1435</t>
1436<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1437  <x:ref>Request-Line</x:ref>   = <x:ref>Method</x:ref> <x:ref>SP</x:ref> <x:ref>Request-URI</x:ref> <x:ref>SP</x:ref> <x:ref>HTTP-Version</x:ref> <x:ref>CRLF</x:ref>
1438</artwork></figure>
1439
1440<section title="Method" anchor="method">
1441  <x:anchor-alias value="Method"/>
1442<t>
1443   The Method  token indicates the method to be performed on the
1444   resource identified by the Request-URI. The method is case-sensitive.
1445</t>
1446<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1447  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1448</artwork></figure>
1449</section>
1450
1451<section title="Request-URI" anchor="request-uri">
1452  <x:anchor-alias value="Request-URI"/>
1453<t>
1454   The Request-URI is a Uniform Resource Identifier (<xref target="uri"/>) and
1455   identifies the resource upon which to apply the request.
1456</t>
1457<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-URI"/>
1458  <x:ref>Request-URI</x:ref>    = "*"
1459                 / <x:ref>absoluteURI</x:ref>
1460                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1461                 / <x:ref>authority</x:ref>
1462</artwork></figure>
1463<t>
1464   The four options for Request-URI are dependent on the nature of the
1465   request. The asterisk "*" means that the request does not apply to a
1466   particular resource, but to the server itself, and is only allowed
1467   when the method used does not necessarily apply to a resource. One
1468   example would be
1469</t>
1470<figure><artwork type="example">
1471    OPTIONS * HTTP/1.1
1472</artwork></figure>
1473<t>
1474   The absoluteURI form is &REQUIRED; when the request is being made to a
1475   proxy. The proxy is requested to forward the request or service it
1476   from a valid cache, and return the response. Note that the proxy &MAY;
1477   forward the request on to another proxy or directly to the server
1478   specified by the absoluteURI. In order to avoid request loops, a
1479   proxy &MUST; be able to recognize all of its server names, including
1480   any aliases, local variations, and the numeric IP address. An example
1481   Request-Line would be:
1482</t>
1483<figure><artwork type="example">
1484    GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1485</artwork></figure>
1486<t>
1487   To allow for transition to absoluteURIs in all requests in future
1488   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absoluteURI
1489   form in requests, even though HTTP/1.1 clients will only generate
1490   them in requests to proxies.
1491</t>
1492<t>
1493   The authority form is only used by the CONNECT method (&CONNECT;).
1494</t>
1495<t>
1496   The most common form of Request-URI is that used to identify a
1497   resource on an origin server or gateway. In this case the absolute
1498   path of the URI &MUST; be transmitted (see <xref target="general.syntax"/>, path-absolute) as
1499   the Request-URI, and the network location of the URI (authority) &MUST;
1500   be transmitted in a Host header field. For example, a client wishing
1501   to retrieve the resource above directly from the origin server would
1502   create a TCP connection to port 80 of the host "www.example.org" and send
1503   the lines:
1504</t>
1505<figure><artwork type="example">
1506    GET /pub/WWW/TheProject.html HTTP/1.1
1507    Host: www.example.org
1508</artwork></figure>
1509<t>
1510   followed by the remainder of the Request. Note that the absolute path
1511   cannot be empty; if none is present in the original URI, it &MUST; be
1512   given as "/" (the server root).
1513</t>
1514<t>
1515   The Request-URI is transmitted in the format specified in
1516   <xref target="general.syntax"/>. If the Request-URI is encoded using the
1517   "% <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding
1518   (<xref target="RFC2396" x:fmt="," x:sec="2.4.1"/>), the origin server
1519   &MUST; decode the Request-URI in order to
1520   properly interpret the request. Servers &SHOULD; respond to invalid
1521   Request-URIs with an appropriate status code.
1522</t>
1523<t>
1524   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1525   received Request-URI when forwarding it to the next inbound server,
1526   except as noted above to replace a null path-absolute with "/".
1527</t>
1528<t>
1529  <list><t>
1530      <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1531      meaning of the request when the origin server is improperly using
1532      a non-reserved URI character for a reserved purpose.  Implementors
1533      should be aware that some pre-HTTP/1.1 proxies have been known to
1534      rewrite the Request-URI.
1535  </t></list>
1536</t>
1537</section>
1538</section>
1539
1540<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1541<t>
1542   The exact resource identified by an Internet request is determined by
1543   examining both the Request-URI and the Host header field.
1544</t>
1545<t>
1546   An origin server that does not allow resources to differ by the
1547   requested host &MAY; ignore the Host header field value when
1548   determining the resource identified by an HTTP/1.1 request. (But see
1549   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1550   for other requirements on Host support in HTTP/1.1.)
1551</t>
1552<t>
1553   An origin server that does differentiate resources based on the host
1554   requested (sometimes referred to as virtual hosts or vanity host
1555   names) &MUST; use the following rules for determining the requested
1556   resource on an HTTP/1.1 request:
1557  <list style="numbers">
1558    <t>If Request-URI is an absoluteURI, the host is part of the
1559     Request-URI. Any Host header field value in the request &MUST; be
1560     ignored.</t>
1561    <t>If the Request-URI is not an absoluteURI, and the request includes
1562     a Host header field, the host is determined by the Host header
1563     field value.</t>
1564    <t>If the host as determined by rule 1 or 2 is not a valid host on
1565     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1566  </list>
1567</t>
1568<t>
1569   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1570   attempt to use heuristics (e.g., examination of the URI path for
1571   something unique to a particular host) in order to determine what
1572   exact resource is being requested.
1573</t>
1574</section>
1575
1576</section>
1577
1578
1579<section title="Response" anchor="response">
1580  <x:anchor-alias value="Response"/>
1581<t>
1582   After receiving and interpreting a request message, a server responds
1583   with an HTTP response message.
1584</t>
1585<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1586  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1587                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1588                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1589                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1590                  <x:ref>CRLF</x:ref>
1591                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1592</artwork></figure>
1593
1594<section title="Status-Line" anchor="status-line">
1595  <x:anchor-alias value="Status-Line"/>
1596<t>
1597   The first line of a Response message is the Status-Line, consisting
1598   of the protocol version followed by a numeric status code and its
1599   associated textual phrase, with each element separated by SP
1600   characters. No CR or LF is allowed except in the final CRLF sequence.
1601</t>
1602<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1603  <x:ref>Status-Line</x:ref> = <x:ref>HTTP-Version</x:ref> <x:ref>SP</x:ref> <x:ref>Status-Code</x:ref> <x:ref>SP</x:ref> <x:ref>Reason-Phrase</x:ref> <x:ref>CRLF</x:ref>
1604</artwork></figure>
1605
1606<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1607  <x:anchor-alias value="Reason-Phrase"/>
1608  <x:anchor-alias value="Status-Code"/>
1609<t>
1610   The Status-Code element is a 3-digit integer result code of the
1611   attempt to understand and satisfy the request. These codes are fully
1612   defined in &status-codes;.  The Reason Phrase exists for the sole
1613   purpose of providing a textual description associated with the numeric
1614   status code, out of deference to earlier Internet application protocols
1615   that were more frequently used with interactive text clients.
1616   A client &SHOULD; ignore the content of the Reason Phrase.
1617</t>
1618<t>
1619   The first digit of the Status-Code defines the class of response. The
1620   last two digits do not have any categorization role. There are 5
1621   values for the first digit:
1622  <list style="symbols">
1623    <t>
1624      1xx: Informational - Request received, continuing process
1625    </t>
1626    <t>
1627      2xx: Success - The action was successfully received,
1628        understood, and accepted
1629    </t>
1630    <t>
1631      3xx: Redirection - Further action must be taken in order to
1632        complete the request
1633    </t>
1634    <t>
1635      4xx: Client Error - The request contains bad syntax or cannot
1636        be fulfilled
1637    </t>
1638    <t>
1639      5xx: Server Error - The server failed to fulfill an apparently
1640        valid request
1641    </t>
1642  </list>
1643</t>
1644<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"/>
1645  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1646  <x:ref>Reason-Phrase</x:ref>  = *&lt;<x:ref>TEXT</x:ref>, excluding <x:ref>CR</x:ref>, <x:ref>LF</x:ref>&gt;
1647</artwork></figure>
1648</section>
1649</section>
1650
1651</section>
1652
1653
1654<section title="Connections" anchor="connections">
1655
1656<section title="Persistent Connections" anchor="persistent.connections">
1657
1658<section title="Purpose" anchor="persistent.purpose">
1659<t>
1660   Prior to persistent connections, a separate TCP connection was
1661   established to fetch each URL, increasing the load on HTTP servers
1662   and causing congestion on the Internet. The use of inline images and
1663   other associated data often require a client to make multiple
1664   requests of the same server in a short amount of time. Analysis of
1665   these performance problems and results from a prototype
1666   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1667   measurements of actual HTTP/1.1 (<xref target="RFC2068" x:fmt="none">RFC 2068</xref>) implementations show good
1668   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1669   T/TCP <xref target="Tou1998"/>.
1670</t>
1671<t>
1672   Persistent HTTP connections have a number of advantages:
1673  <list style="symbols">
1674      <t>
1675        By opening and closing fewer TCP connections, CPU time is saved
1676        in routers and hosts (clients, servers, proxies, gateways,
1677        tunnels, or caches), and memory used for TCP protocol control
1678        blocks can be saved in hosts.
1679      </t>
1680      <t>
1681        HTTP requests and responses can be pipelined on a connection.
1682        Pipelining allows a client to make multiple requests without
1683        waiting for each response, allowing a single TCP connection to
1684        be used much more efficiently, with much lower elapsed time.
1685      </t>
1686      <t>
1687        Network congestion is reduced by reducing the number of packets
1688        caused by TCP opens, and by allowing TCP sufficient time to
1689        determine the congestion state of the network.
1690      </t>
1691      <t>
1692        Latency on subsequent requests is reduced since there is no time
1693        spent in TCP's connection opening handshake.
1694      </t>
1695      <t>
1696        HTTP can evolve more gracefully, since errors can be reported
1697        without the penalty of closing the TCP connection. Clients using
1698        future versions of HTTP might optimistically try a new feature,
1699        but if communicating with an older server, retry with old
1700        semantics after an error is reported.
1701      </t>
1702    </list>
1703</t>
1704<t>
1705   HTTP implementations &SHOULD; implement persistent connections.
1706</t>
1707</section>
1708
1709<section title="Overall Operation" anchor="persistent.overall">
1710<t>
1711   A significant difference between HTTP/1.1 and earlier versions of
1712   HTTP is that persistent connections are the default behavior of any
1713   HTTP connection. That is, unless otherwise indicated, the client
1714   &SHOULD; assume that the server will maintain a persistent connection,
1715   even after error responses from the server.
1716</t>
1717<t>
1718   Persistent connections provide a mechanism by which a client and a
1719   server can signal the close of a TCP connection. This signaling takes
1720   place using the Connection header field (<xref target="header.connection"/>). Once a close
1721   has been signaled, the client &MUST-NOT; send any more requests on that
1722   connection.
1723</t>
1724
1725<section title="Negotiation" anchor="persistent.negotiation">
1726<t>
1727   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1728   maintain a persistent connection unless a Connection header including
1729   the connection-token "close" was sent in the request. If the server
1730   chooses to close the connection immediately after sending the
1731   response, it &SHOULD; send a Connection header including the
1732   connection-token close.
1733</t>
1734<t>
1735   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1736   decide to keep it open based on whether the response from a server
1737   contains a Connection header with the connection-token close. In case
1738   the client does not want to maintain a connection for more than that
1739   request, it &SHOULD; send a Connection header including the
1740   connection-token close.
1741</t>
1742<t>
1743   If either the client or the server sends the close token in the
1744   Connection header, that request becomes the last one for the
1745   connection.
1746</t>
1747<t>
1748   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1749   maintained for HTTP versions less than 1.1 unless it is explicitly
1750   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1751   compatibility with HTTP/1.0 clients.
1752</t>
1753<t>
1754   In order to remain persistent, all messages on the connection &MUST;
1755   have a self-defined message length (i.e., one not defined by closure
1756   of the connection), as described in <xref target="message.length"/>.
1757</t>
1758</section>
1759
1760<section title="Pipelining" anchor="pipelining">
1761<t>
1762   A client that supports persistent connections &MAY; "pipeline" its
1763   requests (i.e., send multiple requests without waiting for each
1764   response). A server &MUST; send its responses to those requests in the
1765   same order that the requests were received.
1766</t>
1767<t>
1768   Clients which assume persistent connections and pipeline immediately
1769   after connection establishment &SHOULD; be prepared to retry their
1770   connection if the first pipelined attempt fails. If a client does
1771   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1772   persistent. Clients &MUST; also be prepared to resend their requests if
1773   the server closes the connection before sending all of the
1774   corresponding responses.
1775</t>
1776<t>
1777   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1778   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1779   premature termination of the transport connection could lead to
1780   indeterminate results. A client wishing to send a non-idempotent
1781   request &SHOULD; wait to send that request until it has received the
1782   response status for the previous request.
1783</t>
1784</section>
1785</section>
1786
1787<section title="Proxy Servers" anchor="persistent.proxy">
1788<t>
1789   It is especially important that proxies correctly implement the
1790   properties of the Connection header field as specified in <xref target="header.connection"/>.
1791</t>
1792<t>
1793   The proxy server &MUST; signal persistent connections separately with
1794   its clients and the origin servers (or other proxy servers) that it
1795   connects to. Each persistent connection applies to only one transport
1796   link.
1797</t>
1798<t>
1799   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1800   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
1801   discussion of the problems with the Keep-Alive header implemented by
1802   many HTTP/1.0 clients).
1803</t>
1804</section>
1805
1806<section title="Practical Considerations" anchor="persistent.practical">
1807<t>
1808   Servers will usually have some time-out value beyond which they will
1809   no longer maintain an inactive connection. Proxy servers might make
1810   this a higher value since it is likely that the client will be making
1811   more connections through the same server. The use of persistent
1812   connections places no requirements on the length (or existence) of
1813   this time-out for either the client or the server.
1814</t>
1815<t>
1816   When a client or server wishes to time-out it &SHOULD; issue a graceful
1817   close on the transport connection. Clients and servers &SHOULD; both
1818   constantly watch for the other side of the transport close, and
1819   respond to it as appropriate. If a client or server does not detect
1820   the other side's close promptly it could cause unnecessary resource
1821   drain on the network.
1822</t>
1823<t>
1824   A client, server, or proxy &MAY; close the transport connection at any
1825   time. For example, a client might have started to send a new request
1826   at the same time that the server has decided to close the "idle"
1827   connection. From the server's point of view, the connection is being
1828   closed while it was idle, but from the client's point of view, a
1829   request is in progress.
1830</t>
1831<t>
1832   This means that clients, servers, and proxies &MUST; be able to recover
1833   from asynchronous close events. Client software &SHOULD; reopen the
1834   transport connection and retransmit the aborted sequence of requests
1835   without user interaction so long as the request sequence is
1836   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1837   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1838   human operator the choice of retrying the request(s). Confirmation by
1839   user-agent software with semantic understanding of the application
1840   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
1841   be repeated if the second sequence of requests fails.
1842</t>
1843<t>
1844   Servers &SHOULD; always respond to at least one request per connection,
1845   if at all possible. Servers &SHOULD-NOT;  close a connection in the
1846   middle of transmitting a response, unless a network or client failure
1847   is suspected.
1848</t>
1849<t>
1850   Clients that use persistent connections &SHOULD; limit the number of
1851   simultaneous connections that they maintain to a given server. A
1852   single-user client &SHOULD-NOT; maintain more than 2 connections with
1853   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
1854   another server or proxy, where N is the number of simultaneously
1855   active users. These guidelines are intended to improve HTTP response
1856   times and avoid congestion.
1857</t>
1858</section>
1859</section>
1860
1861<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
1862
1863<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
1864<t>
1865   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
1866   flow control mechanisms to resolve temporary overloads, rather than
1867   terminating connections with the expectation that clients will retry.
1868   The latter technique can exacerbate network congestion.
1869</t>
1870</section>
1871
1872<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
1873<t>
1874   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
1875   the network connection for an error status while it is transmitting
1876   the request. If the client sees an error status, it &SHOULD;
1877   immediately cease transmitting the body. If the body is being sent
1878   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
1879   empty trailer &MAY; be used to prematurely mark the end of the message.
1880   If the body was preceded by a Content-Length header, the client &MUST;
1881   close the connection.
1882</t>
1883</section>
1884
1885<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
1886<t>
1887   The purpose of the 100 (Continue) status (see &status-100;) is to
1888   allow a client that is sending a request message with a request body
1889   to determine if the origin server is willing to accept the request
1890   (based on the request headers) before the client sends the request
1891   body. In some cases, it might either be inappropriate or highly
1892   inefficient for the client to send the body if the server will reject
1893   the message without looking at the body.
1894</t>
1895<t>
1896   Requirements for HTTP/1.1 clients:
1897  <list style="symbols">
1898    <t>
1899        If a client will wait for a 100 (Continue) response before
1900        sending the request body, it &MUST; send an Expect request-header
1901        field (&header-expect;) with the "100-continue" expectation.
1902    </t>
1903    <t>
1904        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
1905        with the "100-continue" expectation if it does not intend
1906        to send a request body.
1907    </t>
1908  </list>
1909</t>
1910<t>
1911   Because of the presence of older implementations, the protocol allows
1912   ambiguous situations in which a client may send "Expect: 100-continue"
1913   without receiving either a 417 (Expectation Failed) status
1914   or a 100 (Continue) status. Therefore, when a client sends this
1915   header field to an origin server (possibly via a proxy) from which it
1916   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
1917   for an indefinite period before sending the request body.
1918</t>
1919<t>
1920   Requirements for HTTP/1.1 origin servers:
1921  <list style="symbols">
1922    <t> Upon receiving a request which includes an Expect request-header
1923        field with the "100-continue" expectation, an origin server &MUST;
1924        either respond with 100 (Continue) status and continue to read
1925        from the input stream, or respond with a final status code. The
1926        origin server &MUST-NOT; wait for the request body before sending
1927        the 100 (Continue) response. If it responds with a final status
1928        code, it &MAY; close the transport connection or it &MAY; continue
1929        to read and discard the rest of the request.  It &MUST-NOT;
1930        perform the requested method if it returns a final status code.
1931    </t>
1932    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
1933        the request message does not include an Expect request-header
1934        field with the "100-continue" expectation, and &MUST-NOT; send a
1935        100 (Continue) response if such a request comes from an HTTP/1.0
1936        (or earlier) client. There is an exception to this rule: for
1937        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
1938        status in response to an HTTP/1.1 PUT or POST request that does
1939        not include an Expect request-header field with the "100-continue"
1940        expectation. This exception, the purpose of which is
1941        to minimize any client processing delays associated with an
1942        undeclared wait for 100 (Continue) status, applies only to
1943        HTTP/1.1 requests, and not to requests with any other HTTP-version
1944        value.
1945    </t>
1946    <t> An origin server &MAY; omit a 100 (Continue) response if it has
1947        already received some or all of the request body for the
1948        corresponding request.
1949    </t>
1950    <t> An origin server that sends a 100 (Continue) response &MUST;
1951    ultimately send a final status code, once the request body is
1952        received and processed, unless it terminates the transport
1953        connection prematurely.
1954    </t>
1955    <t> If an origin server receives a request that does not include an
1956        Expect request-header field with the "100-continue" expectation,
1957        the request includes a request body, and the server responds
1958        with a final status code before reading the entire request body
1959        from the transport connection, then the server &SHOULD-NOT;  close
1960        the transport connection until it has read the entire request,
1961        or until the client closes the connection. Otherwise, the client
1962        might not reliably receive the response message. However, this
1963        requirement is not be construed as preventing a server from
1964        defending itself against denial-of-service attacks, or from
1965        badly broken client implementations.
1966      </t>
1967    </list>
1968</t>
1969<t>
1970   Requirements for HTTP/1.1 proxies:
1971  <list style="symbols">
1972    <t> If a proxy receives a request that includes an Expect request-header
1973        field with the "100-continue" expectation, and the proxy
1974        either knows that the next-hop server complies with HTTP/1.1 or
1975        higher, or does not know the HTTP version of the next-hop
1976        server, it &MUST; forward the request, including the Expect header
1977        field.
1978    </t>
1979    <t> If the proxy knows that the version of the next-hop server is
1980        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
1981        respond with a 417 (Expectation Failed) status.
1982    </t>
1983    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
1984        numbers received from recently-referenced next-hop servers.
1985    </t>
1986    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
1987        request message was received from an HTTP/1.0 (or earlier)
1988        client and did not include an Expect request-header field with
1989        the "100-continue" expectation. This requirement overrides the
1990        general rule for forwarding of 1xx responses (see &status-1xx;).
1991    </t>
1992  </list>
1993</t>
1994</section>
1995
1996<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
1997<t>
1998   If an HTTP/1.1 client sends a request which includes a request body,
1999   but which does not include an Expect request-header field with the
2000   "100-continue" expectation, and if the client is not directly
2001   connected to an HTTP/1.1 origin server, and if the client sees the
2002   connection close before receiving any status from the server, the
2003   client &SHOULD; retry the request.  If the client does retry this
2004   request, it &MAY; use the following "binary exponential backoff"
2005   algorithm to be assured of obtaining a reliable response:
2006  <list style="numbers">
2007    <t>
2008      Initiate a new connection to the server
2009    </t>
2010    <t>
2011      Transmit the request-headers
2012    </t>
2013    <t>
2014      Initialize a variable R to the estimated round-trip time to the
2015         server (e.g., based on the time it took to establish the
2016         connection), or to a constant value of 5 seconds if the round-trip
2017         time is not available.
2018    </t>
2019    <t>
2020       Compute T = R * (2**N), where N is the number of previous
2021         retries of this request.
2022    </t>
2023    <t>
2024       Wait either for an error response from the server, or for T
2025         seconds (whichever comes first)
2026    </t>
2027    <t>
2028       If no error response is received, after T seconds transmit the
2029         body of the request.
2030    </t>
2031    <t>
2032       If client sees that the connection is closed prematurely,
2033         repeat from step 1 until the request is accepted, an error
2034         response is received, or the user becomes impatient and
2035         terminates the retry process.
2036    </t>
2037  </list>
2038</t>
2039<t>
2040   If at any point an error status is received, the client
2041  <list style="symbols">
2042      <t>&SHOULD-NOT;  continue and</t>
2043
2044      <t>&SHOULD; close the connection if it has not completed sending the
2045        request message.</t>
2046    </list>
2047</t>
2048</section>
2049</section>
2050</section>
2051
2052
2053<section title="Header Field Definitions" anchor="header.fields">
2054<t>
2055   This section defines the syntax and semantics of HTTP/1.1 header fields
2056   related to message framing and transport protocols.
2057</t>
2058<t>
2059   For entity-header fields, both sender and recipient refer to either the
2060   client or the server, depending on who sends and who receives the entity.
2061</t>
2062
2063<section title="Connection" anchor="header.connection">
2064  <iref primary="true" item="Connection header" x:for-anchor=""/>
2065  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2066  <x:anchor-alias value="Connection"/>
2067  <x:anchor-alias value="connection-token"/>
2068  <x:anchor-alias value="Connection-v"/>
2069<t>
2070   The general-header field "Connection" allows the sender to specify
2071   options that are desired for that particular connection and &MUST-NOT;
2072   be communicated by proxies over further connections.
2073</t>
2074<t>
2075   The Connection header's value has the following grammar:
2076</t>
2077<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="Connection-v"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2078  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2079  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2080  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2081</artwork></figure>
2082<t>
2083   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2084   message is forwarded and, for each connection-token in this field,
2085   remove any header field(s) from the message with the same name as the
2086   connection-token. Connection options are signaled by the presence of
2087   a connection-token in the Connection header field, not by any
2088   corresponding additional header field(s), since the additional header
2089   field may not be sent if there are no parameters associated with that
2090   connection option.
2091</t>
2092<t>
2093   Message headers listed in the Connection header &MUST-NOT; include
2094   end-to-end headers, such as Cache-Control.
2095</t>
2096<t>
2097   HTTP/1.1 defines the "close" connection option for the sender to
2098   signal that the connection will be closed after completion of the
2099   response. For example,
2100</t>
2101<figure><artwork type="example">
2102  Connection: close
2103</artwork></figure>
2104<t>
2105   in either the request or the response header fields indicates that
2106   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2107   after the current request/response is complete.
2108</t>
2109<t>
2110   An HTTP/1.1 client that does not support persistent connections &MUST;
2111   include the "close" connection option in every request message.
2112</t>
2113<t>
2114   An HTTP/1.1 server that does not support persistent connections &MUST;
2115   include the "close" connection option in every response message that
2116   does not have a 1xx (informational) status code.
2117</t>
2118<t>
2119   A system receiving an HTTP/1.0 (or lower-version) message that
2120   includes a Connection header &MUST;, for each connection-token in this
2121   field, remove and ignore any header field(s) from the message with
2122   the same name as the connection-token. This protects against mistaken
2123   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2124</t>
2125</section>
2126
2127<section title="Content-Length" anchor="header.content-length">
2128  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2129  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2130  <x:anchor-alias value="Content-Length"/>
2131  <x:anchor-alias value="Content-Length-v"/>
2132<t>
2133   The entity-header field "Content-Length" indicates the size of the
2134   entity-body, in decimal number of OCTETs, sent to the recipient or,
2135   in the case of the HEAD method, the size of the entity-body that
2136   would have been sent had the request been a GET.
2137</t>
2138<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2139  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2140  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2141</artwork></figure>
2142<t>
2143   An example is
2144</t>
2145<figure><artwork type="example">
2146  Content-Length: 3495
2147</artwork></figure>
2148<t>
2149   Applications &SHOULD; use this field to indicate the transfer-length of
2150   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2151</t>
2152<t>
2153   Any Content-Length greater than or equal to zero is a valid value.
2154   <xref target="message.length"/> describes how to determine the length of a message-body
2155   if a Content-Length is not given.
2156</t>
2157<t>
2158   Note that the meaning of this field is significantly different from
2159   the corresponding definition in MIME, where it is an optional field
2160   used within the "message/external-body" content-type. In HTTP, it
2161   &SHOULD; be sent whenever the message's length can be determined prior
2162   to being transferred, unless this is prohibited by the rules in
2163   <xref target="message.length"/>.
2164</t>
2165</section>
2166
2167<section title="Date" anchor="header.date">
2168  <iref primary="true" item="Date header" x:for-anchor=""/>
2169  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2170  <x:anchor-alias value="Date"/>
2171  <x:anchor-alias value="Date-v"/>
2172<t>
2173   The general-header field "Date" represents the date and time at which
2174   the message was originated, having the same semantics as orig-date in
2175   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2176   HTTP-date, as described in <xref target="full.date"/>;
2177   it &MUST; be sent in rfc1123-date format.
2178</t>
2179<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2180  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2181  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2182</artwork></figure>
2183<t>
2184   An example is
2185</t>
2186<figure><artwork type="example">
2187  Date: Tue, 15 Nov 1994 08:12:31 GMT
2188</artwork></figure>
2189<t>
2190   Origin servers &MUST; include a Date header field in all responses,
2191   except in these cases:
2192  <list style="numbers">
2193      <t>If the response status code is 100 (Continue) or 101 (Switching
2194         Protocols), the response &MAY; include a Date header field, at
2195         the server's option.</t>
2196
2197      <t>If the response status code conveys a server error, e.g. 500
2198         (Internal Server Error) or 503 (Service Unavailable), and it is
2199         inconvenient or impossible to generate a valid Date.</t>
2200
2201      <t>If the server does not have a clock that can provide a
2202         reasonable approximation of the current time, its responses
2203         &MUST-NOT; include a Date header field. In this case, the rules
2204         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2205  </list>
2206</t>
2207<t>
2208   A received message that does not have a Date header field &MUST; be
2209   assigned one by the recipient if the message will be cached by that
2210   recipient or gatewayed via a protocol which requires a Date. An HTTP
2211   implementation without a clock &MUST-NOT; cache responses without
2212   revalidating them on every use. An HTTP cache, especially a shared
2213   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2214   clock with a reliable external standard.
2215</t>
2216<t>
2217   Clients &SHOULD; only send a Date header field in messages that include
2218   an entity-body, as in the case of the PUT and POST requests, and even
2219   then it is optional. A client without a clock &MUST-NOT; send a Date
2220   header field in a request.
2221</t>
2222<t>
2223   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2224   time subsequent to the generation of the message. It &SHOULD; represent
2225   the best available approximation of the date and time of message
2226   generation, unless the implementation has no means of generating a
2227   reasonably accurate date and time. In theory, the date ought to
2228   represent the moment just before the entity is generated. In
2229   practice, the date can be generated at any time during the message
2230   origination without affecting its semantic value.
2231</t>
2232
2233<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2234<t>
2235   Some origin server implementations might not have a clock available.
2236   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2237   values to a response, unless these values were associated
2238   with the resource by a system or user with a reliable clock. It &MAY;
2239   assign an Expires value that is known, at or before server
2240   configuration time, to be in the past (this allows "pre-expiration"
2241   of responses without storing separate Expires values for each
2242   resource).
2243</t>
2244</section>
2245</section>
2246
2247<section title="Host" anchor="header.host">
2248  <iref primary="true" item="Host header" x:for-anchor=""/>
2249  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2250  <x:anchor-alias value="Host"/>
2251  <x:anchor-alias value="Host-v"/>
2252<t>
2253   The request-header field "Host" specifies the Internet host and port
2254   number of the resource being requested, as obtained from the original
2255   URI given by the user or referring resource (generally an HTTP URL,
2256   as described in <xref target="http.url"/>). The Host field value &MUST; represent
2257   the naming authority of the origin server or gateway given by the
2258   original URL. This allows the origin server or gateway to
2259   differentiate between internally-ambiguous URLs, such as the root "/"
2260   URL of a server for multiple host names on a single IP address.
2261</t>
2262<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2263  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2264  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.url"/>
2265</artwork></figure>
2266<t>
2267   A "host" without any trailing port information implies the default
2268   port for the service requested (e.g., "80" for an HTTP URL). For
2269   example, a request on the origin server for
2270   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2271</t>
2272<figure><artwork type="example">
2273  GET /pub/WWW/ HTTP/1.1
2274  Host: www.example.org
2275</artwork></figure>
2276<t>
2277   A client &MUST; include a Host header field in all HTTP/1.1 request
2278   messages. If the requested URI does not include an Internet host
2279   name for the service being requested, then the Host header field &MUST;
2280   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2281   request message it forwards does contain an appropriate Host header
2282   field that identifies the service being requested by the proxy. All
2283   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2284   status code to any HTTP/1.1 request message which lacks a Host header
2285   field.
2286</t>
2287<t>
2288   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2289   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2290   for other requirements relating to Host.
2291</t>
2292</section>
2293
2294<section title="TE" anchor="header.te">
2295  <iref primary="true" item="TE header" x:for-anchor=""/>
2296  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2297  <x:anchor-alias value="TE"/>
2298  <x:anchor-alias value="TE-v"/>
2299  <x:anchor-alias value="t-codings"/>
2300<t>
2301   The request-header field "TE" indicates what extension transfer-codings
2302   it is willing to accept in the response and whether or not it is
2303   willing to accept trailer fields in a chunked transfer-coding. Its
2304   value may consist of the keyword "trailers" and/or a comma-separated
2305   list of extension transfer-coding names with optional accept
2306   parameters (as described in <xref target="transfer.codings"/>).
2307</t>
2308<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="TE-v"/><iref primary="true" item="Grammar" subitem="t-codings"/>
2309  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2310  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2311  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>accept-params</x:ref> ] )
2312</artwork></figure>
2313<t>
2314   The presence of the keyword "trailers" indicates that the client is
2315   willing to accept trailer fields in a chunked transfer-coding, as
2316   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2317   transfer-coding values even though it does not itself represent a
2318   transfer-coding.
2319</t>
2320<t>
2321   Examples of its use are:
2322</t>
2323<figure><artwork type="example">
2324  TE: deflate
2325  TE:
2326  TE: trailers, deflate;q=0.5
2327</artwork></figure>
2328<t>
2329   The TE header field only applies to the immediate connection.
2330   Therefore, the keyword &MUST; be supplied within a Connection header
2331   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2332</t>
2333<t>
2334   A server tests whether a transfer-coding is acceptable, according to
2335   a TE field, using these rules:
2336  <list style="numbers">
2337    <x:lt>
2338      <t>The "chunked" transfer-coding is always acceptable. If the
2339         keyword "trailers" is listed, the client indicates that it is
2340         willing to accept trailer fields in the chunked response on
2341         behalf of itself and any downstream clients. The implication is
2342         that, if given, the client is stating that either all
2343         downstream clients are willing to accept trailer fields in the
2344         forwarded response, or that it will attempt to buffer the
2345         response on behalf of downstream recipients.
2346      </t><t>
2347         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2348         chunked response such that a client can be assured of buffering
2349         the entire response.</t>
2350    </x:lt>
2351    <x:lt>
2352      <t>If the transfer-coding being tested is one of the transfer-codings
2353         listed in the TE field, then it is acceptable unless it
2354         is accompanied by a qvalue of 0. (As defined in &qvalue;, a
2355         qvalue of 0 means "not acceptable.")</t>
2356    </x:lt>
2357    <x:lt>
2358      <t>If multiple transfer-codings are acceptable, then the
2359         acceptable transfer-coding with the highest non-zero qvalue is
2360         preferred.  The "chunked" transfer-coding always has a qvalue
2361         of 1.</t>
2362    </x:lt>
2363  </list>
2364</t>
2365<t>
2366   If the TE field-value is empty or if no TE field is present, the only
2367   transfer-coding  is "chunked". A message with no transfer-coding is
2368   always acceptable.
2369</t>
2370</section>
2371
2372<section title="Trailer" anchor="header.trailer">
2373  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2374  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2375  <x:anchor-alias value="Trailer"/>
2376  <x:anchor-alias value="Trailer-v"/>
2377<t>
2378   The general field "Trailer" indicates that the given set of
2379   header fields is present in the trailer of a message encoded with
2380   chunked transfer-coding.
2381</t>
2382<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
2383  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
2384  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
2385</artwork></figure>
2386<t>
2387   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2388   message using chunked transfer-coding with a non-empty trailer. Doing
2389   so allows the recipient to know which header fields to expect in the
2390   trailer.
2391</t>
2392<t>
2393   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2394   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2395   trailer fields in a "chunked" transfer-coding.
2396</t>
2397<t>
2398   Message header fields listed in the Trailer header field &MUST-NOT;
2399   include the following header fields:
2400  <list style="symbols">
2401    <t>Transfer-Encoding</t>
2402    <t>Content-Length</t>
2403    <t>Trailer</t>
2404  </list>
2405</t>
2406</section>
2407
2408<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2409  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2410  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2411  <x:anchor-alias value="Transfer-Encoding"/>
2412  <x:anchor-alias value="Transfer-Encoding-v"/>
2413<t>
2414   The general-header "Transfer-Encoding" field indicates what (if any)
2415   type of transformation has been applied to the message body in order
2416   to safely transfer it between the sender and the recipient. This
2417   differs from the content-coding in that the transfer-coding is a
2418   property of the message, not of the entity.
2419</t>
2420<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
2421  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref> <x:ref>Transfer-Encoding-v</x:ref>
2422  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
2423</artwork></figure>
2424<t>
2425   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2426</t>
2427<figure><artwork type="example">
2428  Transfer-Encoding: chunked
2429</artwork></figure>
2430<t>
2431   If multiple encodings have been applied to an entity, the transfer-codings
2432   &MUST; be listed in the order in which they were applied.
2433   Additional information about the encoding parameters &MAY; be provided
2434   by other entity-header fields not defined by this specification.
2435</t>
2436<t>
2437   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2438   header.
2439</t>
2440</section>
2441
2442<section title="Upgrade" anchor="header.upgrade">
2443  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2444  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2445  <x:anchor-alias value="Upgrade"/>
2446  <x:anchor-alias value="Upgrade-v"/>
2447<t>
2448   The general-header "Upgrade" allows the client to specify what
2449   additional communication protocols it supports and would like to use
2450   if the server finds it appropriate to switch protocols. The server
2451   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2452   response to indicate which protocol(s) are being switched.
2453</t>
2454<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
2455  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
2456  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
2457</artwork></figure>
2458<t>
2459   For example,
2460</t>
2461<figure><artwork type="example">
2462  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2463</artwork></figure>
2464<t>
2465   The Upgrade header field is intended to provide a simple mechanism
2466   for transition from HTTP/1.1 to some other, incompatible protocol. It
2467   does so by allowing the client to advertise its desire to use another
2468   protocol, such as a later version of HTTP with a higher major version
2469   number, even though the current request has been made using HTTP/1.1.
2470   This eases the difficult transition between incompatible protocols by
2471   allowing the client to initiate a request in the more commonly
2472   supported protocol while indicating to the server that it would like
2473   to use a "better" protocol if available (where "better" is determined
2474   by the server, possibly according to the nature of the method and/or
2475   resource being requested).
2476</t>
2477<t>
2478   The Upgrade header field only applies to switching application-layer
2479   protocols upon the existing transport-layer connection. Upgrade
2480   cannot be used to insist on a protocol change; its acceptance and use
2481   by the server is optional. The capabilities and nature of the
2482   application-layer communication after the protocol change is entirely
2483   dependent upon the new protocol chosen, although the first action
2484   after changing the protocol &MUST; be a response to the initial HTTP
2485   request containing the Upgrade header field.
2486</t>
2487<t>
2488   The Upgrade header field only applies to the immediate connection.
2489   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2490   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2491   HTTP/1.1 message.
2492</t>
2493<t>
2494   The Upgrade header field cannot be used to indicate a switch to a
2495   protocol on a different connection. For that purpose, it is more
2496   appropriate to use a 301, 302, 303, or 305 redirection response.
2497</t>
2498<t>
2499   This specification only defines the protocol name "HTTP" for use by
2500   the family of Hypertext Transfer Protocols, as defined by the HTTP
2501   version rules of <xref target="http.version"/> and future updates to this
2502   specification. Any token can be used as a protocol name; however, it
2503   will only be useful if both the client and server associate the name
2504   with the same protocol.
2505</t>
2506</section>
2507
2508<section title="Via" anchor="header.via">
2509  <iref primary="true" item="Via header" x:for-anchor=""/>
2510  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2511  <x:anchor-alias value="protocol-name"/>
2512  <x:anchor-alias value="protocol-version"/>
2513  <x:anchor-alias value="pseudonym"/>
2514  <x:anchor-alias value="received-by"/>
2515  <x:anchor-alias value="received-protocol"/>
2516  <x:anchor-alias value="Via"/>
2517  <x:anchor-alias value="Via-v"/>
2518<t>
2519   The general-header field "Via" &MUST; be used by gateways and proxies to
2520   indicate the intermediate protocols and recipients between the user
2521   agent and the server on requests, and between the origin server and
2522   the client on responses. It is analogous to the "Received" field defined in
2523   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2524   avoiding request loops, and identifying the protocol capabilities of
2525   all senders along the request/response chain.
2526</t>
2527<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Via"/><iref primary="true" item="Grammar" subitem="Via-v"/><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"/>
2528  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
2529  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref> [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2530  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2531  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2532  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2533  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2534  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2535</artwork></figure>
2536<t>
2537   The received-protocol indicates the protocol version of the message
2538   received by the server or client along each segment of the
2539   request/response chain. The received-protocol version is appended to
2540   the Via field value when the message is forwarded so that information
2541   about the protocol capabilities of upstream applications remains
2542   visible to all recipients.
2543</t>
2544<t>
2545   The protocol-name is optional if and only if it would be "HTTP". The
2546   received-by field is normally the host and optional port number of a
2547   recipient server or client that subsequently forwarded the message.
2548   However, if the real host is considered to be sensitive information,
2549   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2550   be assumed to be the default port of the received-protocol.
2551</t>
2552<t>
2553   Multiple Via field values represents each proxy or gateway that has
2554   forwarded the message. Each recipient &MUST; append its information
2555   such that the end result is ordered according to the sequence of
2556   forwarding applications.
2557</t>
2558<t>
2559   Comments &MAY; be used in the Via header field to identify the software
2560   of the recipient proxy or gateway, analogous to the User-Agent and
2561   Server header fields. However, all comments in the Via field are
2562   optional and &MAY; be removed by any recipient prior to forwarding the
2563   message.
2564</t>
2565<t>
2566   For example, a request message could be sent from an HTTP/1.0 user
2567   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2568   forward the request to a public proxy at p.example.net, which completes
2569   the request by forwarding it to the origin server at www.example.com.
2570   The request received by www.example.com would then have the following
2571   Via header field:
2572</t>
2573<figure><artwork type="example">
2574  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2575</artwork></figure>
2576<t>
2577   Proxies and gateways used as a portal through a network firewall
2578   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2579   the firewall region. This information &SHOULD; only be propagated if
2580   explicitly enabled. If not enabled, the received-by host of any host
2581   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2582   for that host.
2583</t>
2584<t>
2585   For organizations that have strong privacy requirements for hiding
2586   internal structures, a proxy &MAY; combine an ordered subsequence of
2587   Via header field entries with identical received-protocol values into
2588   a single such entry. For example,
2589</t>
2590<figure><artwork type="example">
2591  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2592</artwork></figure>
2593<t>
2594        could be collapsed to
2595</t>
2596<figure><artwork type="example">
2597  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2598</artwork></figure>
2599<t>
2600   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2601   under the same organizational control and the hosts have already been
2602   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2603   have different received-protocol values.
2604</t>
2605</section>
2606
2607</section>
2608
2609<section title="IANA Considerations" anchor="IANA.considerations">
2610<section title="Message Header Registration" anchor="message.header.registration">
2611<t>
2612   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
2613   with the permanent registrations below (see <xref target="RFC3864"/>):
2614</t>
2615<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2616<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2617   <ttcol>Header Field Name</ttcol>
2618   <ttcol>Protocol</ttcol>
2619   <ttcol>Status</ttcol>
2620   <ttcol>Reference</ttcol>
2621
2622   <c>Connection</c>
2623   <c>http</c>
2624   <c>standard</c>
2625   <c>
2626      <xref target="header.connection"/>
2627   </c>
2628   <c>Content-Length</c>
2629   <c>http</c>
2630   <c>standard</c>
2631   <c>
2632      <xref target="header.content-length"/>
2633   </c>
2634   <c>Date</c>
2635   <c>http</c>
2636   <c>standard</c>
2637   <c>
2638      <xref target="header.date"/>
2639   </c>
2640   <c>Host</c>
2641   <c>http</c>
2642   <c>standard</c>
2643   <c>
2644      <xref target="header.host"/>
2645   </c>
2646   <c>TE</c>
2647   <c>http</c>
2648   <c>standard</c>
2649   <c>
2650      <xref target="header.te"/>
2651   </c>
2652   <c>Trailer</c>
2653   <c>http</c>
2654   <c>standard</c>
2655   <c>
2656      <xref target="header.trailer"/>
2657   </c>
2658   <c>Transfer-Encoding</c>
2659   <c>http</c>
2660   <c>standard</c>
2661   <c>
2662      <xref target="header.transfer-encoding"/>
2663   </c>
2664   <c>Upgrade</c>
2665   <c>http</c>
2666   <c>standard</c>
2667   <c>
2668      <xref target="header.upgrade"/>
2669   </c>
2670   <c>Via</c>
2671   <c>http</c>
2672   <c>standard</c>
2673   <c>
2674      <xref target="header.via"/>
2675   </c>
2676</texttable>
2677<!--(END)-->
2678<t>
2679   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2680</t>
2681</section>
2682
2683<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2684<t>
2685   The entry for the "http" URI Scheme in the registry located at
2686   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
2687   should be updated to point to <xref target="http.url"/> of this document
2688   (see <xref target="RFC4395"/>).
2689</t>
2690</section>
2691
2692<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
2693<t>
2694   This document serves as the specification for the Internet media types
2695   "message/http" and "application/http". The following is to be registered with
2696   IANA (see <xref target="RFC4288"/>).
2697</t>
2698<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
2699<iref item="Media Type" subitem="message/http" primary="true"/>
2700<iref item="message/http Media Type" primary="true"/>
2701<t>
2702   The message/http type can be used to enclose a single HTTP request or
2703   response message, provided that it obeys the MIME restrictions for all
2704   "message" types regarding line length and encodings.
2705</t>
2706<t>
2707  <list style="hanging" x:indent="12em">
2708    <t hangText="Type name:">
2709      message
2710    </t>
2711    <t hangText="Subtype name:">
2712      http
2713    </t>
2714    <t hangText="Required parameters:">
2715      none
2716    </t>
2717    <t hangText="Optional parameters:">
2718      version, msgtype
2719      <list style="hanging">
2720        <t hangText="version:">
2721          The HTTP-Version number of the enclosed message
2722          (e.g., "1.1"). If not present, the version can be
2723          determined from the first line of the body.
2724        </t>
2725        <t hangText="msgtype:">
2726          The message type -- "request" or "response". If not
2727          present, the type can be determined from the first
2728          line of the body.
2729        </t>
2730      </list>
2731    </t>
2732    <t hangText="Encoding considerations:">
2733      only "7bit", "8bit", or "binary" are permitted
2734    </t>
2735    <t hangText="Security considerations:">
2736      none
2737    </t>
2738    <t hangText="Interoperability considerations:">
2739      none
2740    </t>
2741    <t hangText="Published specification:">
2742      This specification (see <xref target="internet.media.type.message.http"/>).
2743    </t>
2744    <t hangText="Applications that use this media type:">
2745    </t>
2746    <t hangText="Additional information:">
2747      <list style="hanging">
2748        <t hangText="Magic number(s):">none</t>
2749        <t hangText="File extension(s):">none</t>
2750        <t hangText="Macintosh file type code(s):">none</t>
2751      </list>
2752    </t>
2753    <t hangText="Person and email address to contact for further information:">
2754      See Authors Section.
2755    </t>
2756                <t hangText="Intended usage:">
2757                  COMMON
2758    </t>
2759                <t hangText="Restrictions on usage:">
2760                  none
2761    </t>
2762    <t hangText="Author/Change controller:">
2763      IESG
2764    </t>
2765  </list>
2766</t>
2767</section>
2768<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
2769<iref item="Media Type" subitem="application/http" primary="true"/>
2770<iref item="application/http Media Type" primary="true"/>
2771<t>
2772   The application/http type can be used to enclose a pipeline of one or more
2773   HTTP request or response messages (not intermixed).
2774</t>
2775<t>
2776  <list style="hanging" x:indent="12em">
2777    <t hangText="Type name:">
2778      application
2779    </t>
2780    <t hangText="Subtype name:">
2781      http
2782    </t>
2783    <t hangText="Required parameters:">
2784      none
2785    </t>
2786    <t hangText="Optional parameters:">
2787      version, msgtype
2788      <list style="hanging">
2789        <t hangText="version:">
2790          The HTTP-Version number of the enclosed messages
2791          (e.g., "1.1"). If not present, the version can be
2792          determined from the first line of the body.
2793        </t>
2794        <t hangText="msgtype:">
2795          The message type -- "request" or "response". If not
2796          present, the type can be determined from the first
2797          line of the body.
2798        </t>
2799      </list>
2800    </t>
2801    <t hangText="Encoding considerations:">
2802      HTTP messages enclosed by this type
2803      are in "binary" format; use of an appropriate
2804      Content-Transfer-Encoding is required when
2805      transmitted via E-mail.
2806    </t>
2807    <t hangText="Security considerations:">
2808      none
2809    </t>
2810    <t hangText="Interoperability considerations:">
2811      none
2812    </t>
2813    <t hangText="Published specification:">
2814      This specification (see <xref target="internet.media.type.application.http"/>).
2815    </t>
2816    <t hangText="Applications that use this media type:">
2817    </t>
2818    <t hangText="Additional information:">
2819      <list style="hanging">
2820        <t hangText="Magic number(s):">none</t>
2821        <t hangText="File extension(s):">none</t>
2822        <t hangText="Macintosh file type code(s):">none</t>
2823      </list>
2824    </t>
2825    <t hangText="Person and email address to contact for further information:">
2826      See Authors Section.
2827    </t>
2828                <t hangText="Intended usage:">
2829                  COMMON
2830    </t>
2831                <t hangText="Restrictions on usage:">
2832                  none
2833    </t>
2834    <t hangText="Author/Change controller:">
2835      IESG
2836    </t>
2837  </list>
2838</t>
2839</section>
2840</section>
2841
2842</section>
2843
2844<section title="Security Considerations" anchor="security.considerations">
2845<t>
2846   This section is meant to inform application developers, information
2847   providers, and users of the security limitations in HTTP/1.1 as
2848   described by this document. The discussion does not include
2849   definitive solutions to the problems revealed, though it does make
2850   some suggestions for reducing security risks.
2851</t>
2852
2853<section title="Personal Information" anchor="personal.information">
2854<t>
2855   HTTP clients are often privy to large amounts of personal information
2856   (e.g. the user's name, location, mail address, passwords, encryption
2857   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2858   leakage of this information.
2859   We very strongly recommend that a convenient interface be provided
2860   for the user to control dissemination of such information, and that
2861   designers and implementors be particularly careful in this area.
2862   History shows that errors in this area often create serious security
2863   and/or privacy problems and generate highly adverse publicity for the
2864   implementor's company.
2865</t>
2866</section>
2867
2868<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2869<t>
2870   A server is in the position to save personal data about a user's
2871   requests which might identify their reading patterns or subjects of
2872   interest. This information is clearly confidential in nature and its
2873   handling can be constrained by law in certain countries. People using
2874   HTTP to provide data are responsible for ensuring that
2875   such material is not distributed without the permission of any
2876   individuals that are identifiable by the published results.
2877</t>
2878</section>
2879
2880<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2881<t>
2882   Implementations of HTTP origin servers &SHOULD; be careful to restrict
2883   the documents returned by HTTP requests to be only those that were
2884   intended by the server administrators. If an HTTP server translates
2885   HTTP URIs directly into file system calls, the server &MUST; take
2886   special care not to serve files that were not intended to be
2887   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
2888   other operating systems use ".." as a path component to indicate a
2889   directory level above the current one. On such a system, an HTTP
2890   server &MUST; disallow any such construct in the Request-URI if it
2891   would otherwise allow access to a resource outside those intended to
2892   be accessible via the HTTP server. Similarly, files intended for
2893   reference only internally to the server (such as access control
2894   files, configuration files, and script code) &MUST; be protected from
2895   inappropriate retrieval, since they might contain sensitive
2896   information. Experience has shown that minor bugs in such HTTP server
2897   implementations have turned into security risks.
2898</t>
2899</section>
2900
2901<section title="DNS Spoofing" anchor="dns.spoofing">
2902<t>
2903   Clients using HTTP rely heavily on the Domain Name Service, and are
2904   thus generally prone to security attacks based on the deliberate
2905   mis-association of IP addresses and DNS names. Clients need to be
2906   cautious in assuming the continuing validity of an IP number/DNS name
2907   association.
2908</t>
2909<t>
2910   In particular, HTTP clients &SHOULD; rely on their name resolver for
2911   confirmation of an IP number/DNS name association, rather than
2912   caching the result of previous host name lookups. Many platforms
2913   already can cache host name lookups locally when appropriate, and
2914   they &SHOULD; be configured to do so. It is proper for these lookups to
2915   be cached, however, only when the TTL (Time To Live) information
2916   reported by the name server makes it likely that the cached
2917   information will remain useful.
2918</t>
2919<t>
2920   If HTTP clients cache the results of host name lookups in order to
2921   achieve a performance improvement, they &MUST; observe the TTL
2922   information reported by DNS.
2923</t>
2924<t>
2925   If HTTP clients do not observe this rule, they could be spoofed when
2926   a previously-accessed server's IP address changes. As network
2927   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
2928   possibility of this form of attack will grow. Observing this
2929   requirement thus reduces this potential security vulnerability.
2930</t>
2931<t>
2932   This requirement also improves the load-balancing behavior of clients
2933   for replicated servers using the same DNS name and reduces the
2934   likelihood of a user's experiencing failure in accessing sites which
2935   use that strategy.
2936</t>
2937</section>
2938
2939<section title="Proxies and Caching" anchor="attack.proxies">
2940<t>
2941   By their very nature, HTTP proxies are men-in-the-middle, and
2942   represent an opportunity for man-in-the-middle attacks. Compromise of
2943   the systems on which the proxies run can result in serious security
2944   and privacy problems. Proxies have access to security-related
2945   information, personal information about individual users and
2946   organizations, and proprietary information belonging to users and
2947   content providers. A compromised proxy, or a proxy implemented or
2948   configured without regard to security and privacy considerations,
2949   might be used in the commission of a wide range of potential attacks.
2950</t>
2951<t>
2952   Proxy operators should protect the systems on which proxies run as
2953   they would protect any system that contains or transports sensitive
2954   information. In particular, log information gathered at proxies often
2955   contains highly sensitive personal information, and/or information
2956   about organizations. Log information should be carefully guarded, and
2957   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
2958</t>
2959<t>
2960   Proxy implementors should consider the privacy and security
2961   implications of their design and coding decisions, and of the
2962   configuration options they provide to proxy operators (especially the
2963   default configuration).
2964</t>
2965<t>
2966   Users of a proxy need to be aware that they are no trustworthier than
2967   the people who run the proxy; HTTP itself cannot solve this problem.
2968</t>
2969<t>
2970   The judicious use of cryptography, when appropriate, may suffice to
2971   protect against a broad range of security and privacy attacks. Such
2972   cryptography is beyond the scope of the HTTP/1.1 specification.
2973</t>
2974</section>
2975
2976<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
2977<t>
2978   They exist. They are hard to defend against. Research continues.
2979   Beware.
2980</t>
2981</section>
2982</section>
2983
2984<section title="Acknowledgments" anchor="ack">
2985<t>
2986   This specification makes heavy use of the augmented BNF and generic
2987   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
2988   reuses many of the definitions provided by Nathaniel Borenstein and
2989   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
2990   specification will help reduce past confusion over the relationship
2991   between HTTP and Internet mail message formats.
2992</t>
2993<t>
2994   HTTP has evolved considerably over the years. It has
2995   benefited from a large and active developer community--the many
2996   people who have participated on the www-talk mailing list--and it is
2997   that community which has been most responsible for the success of
2998   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
2999   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3000   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3001   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3002   VanHeyningen deserve special recognition for their efforts in
3003   defining early aspects of the protocol.
3004</t>
3005<t>
3006   This document has benefited greatly from the comments of all those
3007   participating in the HTTP-WG. In addition to those already mentioned,
3008   the following individuals have contributed to this specification:
3009</t>
3010<t>
3011   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3012   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3013   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3014   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3015   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3016   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3017   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3018   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3019   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3020   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3021   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3022   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3023   Josh Cohen.
3024</t>
3025<t>
3026   Thanks to the "cave men" of Palo Alto. You know who you are.
3027</t>
3028<t>
3029   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3030   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3031   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3032   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3033   Larry Masinter for their help. And thanks go particularly to Jeff
3034   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3035</t>
3036<t>
3037   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3038   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3039   discovery of many of the problems that this document attempts to
3040   rectify.
3041</t>
3042</section>
3043
3044</middle>
3045<back>
3046
3047<references title="Normative References">
3048
3049<reference anchor="ISO-8859-1">
3050  <front>
3051    <title>
3052     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3053    </title>
3054    <author>
3055      <organization>International Organization for Standardization</organization>
3056    </author>
3057    <date year="1998"/>
3058  </front>
3059  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3060</reference>
3061
3062<reference anchor="Part2">
3063  <front>
3064    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3065    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3066      <organization abbrev="Day Software">Day Software</organization>
3067      <address><email>fielding@gbiv.com</email></address>
3068    </author>
3069    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3070      <organization>One Laptop per Child</organization>
3071      <address><email>jg@laptop.org</email></address>
3072    </author>
3073    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3074      <organization abbrev="HP">Hewlett-Packard Company</organization>
3075      <address><email>JeffMogul@acm.org</email></address>
3076    </author>
3077    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3078      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3079      <address><email>henrikn@microsoft.com</email></address>
3080    </author>
3081    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3082      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3083      <address><email>LMM@acm.org</email></address>
3084    </author>
3085    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3086      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3087      <address><email>paulle@microsoft.com</email></address>
3088    </author>
3089    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3090      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3091      <address><email>timbl@w3.org</email></address>
3092    </author>
3093    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3094      <organization abbrev="W3C">World Wide Web Consortium</organization>
3095      <address><email>ylafon@w3.org</email></address>
3096    </author>
3097    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3098      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3099      <address><email>julian.reschke@greenbytes.de</email></address>
3100    </author>
3101    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3102  </front>
3103  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3104  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3105</reference>
3106
3107<reference anchor="Part3">
3108  <front>
3109    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3110    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3111      <organization abbrev="Day Software">Day Software</organization>
3112      <address><email>fielding@gbiv.com</email></address>
3113    </author>
3114    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3115      <organization>One Laptop per Child</organization>
3116      <address><email>jg@laptop.org</email></address>
3117    </author>
3118    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3119      <organization abbrev="HP">Hewlett-Packard Company</organization>
3120      <address><email>JeffMogul@acm.org</email></address>
3121    </author>
3122    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3123      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3124      <address><email>henrikn@microsoft.com</email></address>
3125    </author>
3126    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3127      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3128      <address><email>LMM@acm.org</email></address>
3129    </author>
3130    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3131      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3132      <address><email>paulle@microsoft.com</email></address>
3133    </author>
3134    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3135      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3136      <address><email>timbl@w3.org</email></address>
3137    </author>
3138    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3139      <organization abbrev="W3C">World Wide Web Consortium</organization>
3140      <address><email>ylafon@w3.org</email></address>
3141    </author>
3142    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3143      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3144      <address><email>julian.reschke@greenbytes.de</email></address>
3145    </author>
3146    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3147  </front>
3148  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3149  <x:source href="p3-payload.xml" basename="p3-payload"/>
3150</reference>
3151
3152<reference anchor="Part5">
3153  <front>
3154    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3155    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3156      <organization abbrev="Day Software">Day Software</organization>
3157      <address><email>fielding@gbiv.com</email></address>
3158    </author>
3159    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3160      <organization>One Laptop per Child</organization>
3161      <address><email>jg@laptop.org</email></address>
3162    </author>
3163    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3164      <organization abbrev="HP">Hewlett-Packard Company</organization>
3165      <address><email>JeffMogul@acm.org</email></address>
3166    </author>
3167    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3168      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3169      <address><email>henrikn@microsoft.com</email></address>
3170    </author>
3171    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3172      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3173      <address><email>LMM@acm.org</email></address>
3174    </author>
3175    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3176      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3177      <address><email>paulle@microsoft.com</email></address>
3178    </author>
3179    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3180      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3181      <address><email>timbl@w3.org</email></address>
3182    </author>
3183    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3184      <organization abbrev="W3C">World Wide Web Consortium</organization>
3185      <address><email>ylafon@w3.org</email></address>
3186    </author>
3187    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3188      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3189      <address><email>julian.reschke@greenbytes.de</email></address>
3190    </author>
3191    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3192  </front>
3193  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3194  <x:source href="p5-range.xml" basename="p5-range"/>
3195</reference>
3196
3197<reference anchor="Part6">
3198  <front>
3199    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3200    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3201      <organization abbrev="Day Software">Day Software</organization>
3202      <address><email>fielding@gbiv.com</email></address>
3203    </author>
3204    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3205      <organization>One Laptop per Child</organization>
3206      <address><email>jg@laptop.org</email></address>
3207    </author>
3208    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3209      <organization abbrev="HP">Hewlett-Packard Company</organization>
3210      <address><email>JeffMogul@acm.org</email></address>
3211    </author>
3212    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3213      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3214      <address><email>henrikn@microsoft.com</email></address>
3215    </author>
3216    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3217      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3218      <address><email>LMM@acm.org</email></address>
3219    </author>
3220    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3221      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3222      <address><email>paulle@microsoft.com</email></address>
3223    </author>
3224    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3225      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3226      <address><email>timbl@w3.org</email></address>
3227    </author>
3228    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3229      <organization abbrev="W3C">World Wide Web Consortium</organization>
3230      <address><email>ylafon@w3.org</email></address>
3231    </author>
3232    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3233      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3234      <address><email>julian.reschke@greenbytes.de</email></address>
3235    </author>
3236    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3237  </front>
3238  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3239  <x:source href="p6-cache.xml" basename="p6-cache"/>
3240</reference>
3241
3242<reference anchor="RFC5234">
3243  <front>
3244    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3245    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3246      <organization>Brandenburg InternetWorking</organization>
3247      <address>
3248      <postal>
3249      <street>675 Spruce Dr.</street>
3250      <city>Sunnyvale</city>
3251      <region>CA</region>
3252      <code>94086</code>
3253      <country>US</country></postal>
3254      <phone>+1.408.246.8253</phone>
3255      <email>dcrocker@bbiw.net</email></address> 
3256    </author>
3257    <author initials="P." surname="Overell" fullname="Paul Overell">
3258      <organization>THUS plc.</organization>
3259      <address>
3260      <postal>
3261      <street>1/2 Berkeley Square</street>
3262      <street>99 Berkely Street</street>
3263      <city>Glasgow</city>
3264      <code>G3 7HR</code>
3265      <country>UK</country></postal>
3266      <email>paul.overell@thus.net</email></address>
3267    </author>
3268    <date month="January" year="2008"/>
3269  </front>
3270  <seriesInfo name="STD" value="68"/>
3271  <seriesInfo name="RFC" value="5234"/>
3272</reference>
3273
3274<reference anchor="RFC2045">
3275  <front>
3276    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3277    <author initials="N." surname="Freed" fullname="Ned Freed">
3278      <organization>Innosoft International, Inc.</organization>
3279      <address><email>ned@innosoft.com</email></address>
3280    </author>
3281    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3282      <organization>First Virtual Holdings</organization>
3283      <address><email>nsb@nsb.fv.com</email></address>
3284    </author>
3285    <date month="November" year="1996"/>
3286  </front>
3287  <seriesInfo name="RFC" value="2045"/>
3288</reference>
3289
3290<reference anchor="RFC2047">
3291  <front>
3292    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3293    <author initials="K." surname="Moore" fullname="Keith Moore">
3294      <organization>University of Tennessee</organization>
3295      <address><email>moore@cs.utk.edu</email></address>
3296    </author>
3297    <date month="November" year="1996"/>
3298  </front>
3299  <seriesInfo name="RFC" value="2047"/>
3300</reference>
3301
3302<reference anchor="RFC2119">
3303  <front>
3304    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3305    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3306      <organization>Harvard University</organization>
3307      <address><email>sob@harvard.edu</email></address>
3308    </author>
3309    <date month="March" year="1997"/>
3310  </front>
3311  <seriesInfo name="BCP" value="14"/>
3312  <seriesInfo name="RFC" value="2119"/>
3313</reference>
3314
3315<reference anchor="RFC2396">
3316  <front>
3317    <title abbrev="URI Generic Syntax">Uniform Resource Identifiers (URI): Generic Syntax</title>
3318    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3319      <organization abbrev="MIT/LCS">World Wide Web Consortium</organization>
3320      <address><email>timbl@w3.org</email></address>
3321    </author>
3322    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3323      <organization abbrev="U.C. Irvine">Department of Information and Computer Science</organization>
3324      <address><email>fielding@ics.uci.edu</email></address>
3325    </author>
3326    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3327      <organization abbrev="Xerox Corporation">Xerox PARC</organization>
3328      <address><email>masinter@parc.xerox.com</email></address>
3329    </author>
3330    <date month="August" year="1998"/>
3331  </front>
3332  <seriesInfo name="RFC" value="2396"/>
3333</reference>
3334
3335<reference anchor="USASCII">
3336  <front>
3337    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3338    <author>
3339      <organization>American National Standards Institute</organization>
3340    </author>
3341    <date year="1986"/>
3342  </front>
3343  <seriesInfo name="ANSI" value="X3.4"/>
3344</reference>
3345
3346</references>
3347
3348<references title="Informative References">
3349
3350<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
3351  <front>
3352    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3353    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3354      <organization/>
3355    </author>
3356    <author initials="J." surname="Gettys" fullname="J. Gettys">
3357      <organization/>
3358    </author>
3359    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3360      <organization/>
3361    </author>
3362    <author initials="H." surname="Lie" fullname="H. Lie">
3363      <organization/>
3364    </author>
3365    <author initials="C." surname="Lilley" fullname="C. Lilley">
3366      <organization/>
3367    </author>
3368    <date year="1997" month="September"/>
3369  </front>
3370  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3371</reference>
3372
3373<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
3374  <front>
3375    <title>Improving HTTP Latency</title>
3376    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3377      <organization/>
3378    </author>
3379    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3380      <organization/>
3381    </author>
3382    <date year="1995" month="December"/>
3383  </front>
3384  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3385</reference>
3386
3387<reference anchor="RFC822">
3388  <front>
3389    <title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
3390    <author initials="D.H." surname="Crocker" fullname="David H. Crocker">
3391      <organization>University of Delaware, Dept. of Electrical Engineering</organization>
3392      <address><email>DCrocker@UDel-Relay</email></address>
3393    </author>
3394    <date month="August" day="13" year="1982"/>
3395  </front>
3396  <seriesInfo name="STD" value="11"/>
3397  <seriesInfo name="RFC" value="822"/>
3398</reference>
3399
3400<reference anchor="RFC959">
3401  <front>
3402    <title abbrev="File Transfer Protocol">File Transfer Protocol</title>
3403    <author initials="J." surname="Postel" fullname="J. Postel">
3404      <organization>Information Sciences Institute (ISI)</organization>
3405    </author>
3406    <author initials="J." surname="Reynolds" fullname="J. Reynolds">
3407      <organization/>
3408    </author>
3409    <date month="October" year="1985"/>
3410  </front>
3411  <seriesInfo name="STD" value="9"/>
3412  <seriesInfo name="RFC" value="959"/>
3413</reference>
3414
3415<reference anchor="RFC1123">
3416  <front>
3417    <title>Requirements for Internet Hosts - Application and Support</title>
3418    <author initials="R." surname="Braden" fullname="Robert Braden">
3419      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3420      <address><email>Braden@ISI.EDU</email></address>
3421    </author>
3422    <date month="October" year="1989"/>
3423  </front>
3424  <seriesInfo name="STD" value="3"/>
3425  <seriesInfo name="RFC" value="1123"/>
3426</reference>
3427
3428<reference anchor="RFC1305">
3429  <front>
3430    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3431    <author initials="D." surname="Mills" fullname="David L. Mills">
3432      <organization>University of Delaware, Electrical Engineering Department</organization>
3433      <address><email>mills@udel.edu</email></address>
3434    </author>
3435    <date month="March" year="1992"/>
3436  </front>
3437  <seriesInfo name="RFC" value="1305"/>
3438</reference>
3439
3440<reference anchor="RFC1436">
3441  <front>
3442    <title abbrev="Gopher">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</title>
3443    <author initials="F." surname="Anklesaria" fullname="Farhad Anklesaria">
3444      <organization>University of Minnesota, Computer and Information Services</organization>
3445      <address><email>fxa@boombox.micro.umn.edu</email></address>
3446    </author>
3447    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3448      <organization>University of Minnesota, Computer and Information Services</organization>
3449      <address><email>mpm@boombox.micro.umn.edu</email></address>
3450    </author>
3451    <author initials="P." surname="Lindner" fullname="Paul Lindner">
3452      <organization>University of Minnesota, Computer and Information Services</organization>
3453      <address><email>lindner@boombox.micro.umn.edu</email></address>
3454    </author>
3455    <author initials="D." surname="Johnson" fullname="David Johnson">
3456      <organization>University of Minnesota, Computer and Information Services</organization>
3457      <address><email>dmj@boombox.micro.umn.edu</email></address>
3458    </author>
3459    <author initials="D." surname="Torrey" fullname="Daniel Torrey">
3460      <organization>University of Minnesota, Computer and Information Services</organization>
3461      <address><email>daniel@boombox.micro.umn.edu</email></address>
3462    </author>
3463    <author initials="B." surname="Alberti" fullname="Bob Alberti">
3464      <organization>University of Minnesota, Computer and Information Services</organization>
3465      <address><email>alberti@boombox.micro.umn.edu</email></address>
3466    </author>
3467    <date month="March" year="1993"/>
3468  </front>
3469  <seriesInfo name="RFC" value="1436"/>
3470</reference>
3471
3472<reference anchor="RFC1630">
3473  <front>
3474    <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>
3475    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3476      <organization>CERN, World-Wide Web project</organization>
3477      <address><email>timbl@info.cern.ch</email></address>
3478    </author>
3479    <date month="June" year="1994"/>
3480  </front>
3481  <seriesInfo name="RFC" value="1630"/>
3482</reference>
3483
3484<reference anchor="RFC1737">
3485  <front>
3486    <title abbrev="Requirements for Uniform Resource Names">Functional Requirements for Uniform Resource Names</title>
3487    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3488      <organization>Xerox Palo Alto Research Center</organization>
3489      <address><email>masinter@parc.xerox.com</email></address>
3490    </author>
3491    <author initials="K." surname="Sollins" fullname="Karen Sollins">
3492      <organization>MIT Laboratory for Computer Science</organization>
3493      <address><email>sollins@lcs.mit.edu</email></address>
3494    </author>
3495    <date month="December" year="1994"/>
3496  </front>
3497  <seriesInfo name="RFC" value="1737"/>
3498</reference>
3499
3500<reference anchor="RFC1738">
3501  <front>
3502    <title>Uniform Resource Locators (URL)</title>
3503    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3504      <organization>CERN, World-Wide Web project</organization>
3505      <address><email>timbl@info.cern.ch</email></address>
3506    </author>
3507    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3508      <organization>Xerox PARC</organization>
3509      <address><email>masinter@parc.xerox.com</email></address>
3510    </author>
3511    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3512      <organization>University of Minnesota, Computer and Information Services</organization>
3513      <address><email>mpm@boombox.micro.umn.edu</email></address>
3514    </author>
3515    <date month="December" year="1994"/>
3516  </front>
3517  <seriesInfo name="RFC" value="1738"/>
3518</reference>
3519
3520<reference anchor="RFC1808">
3521  <front>
3522    <title>Relative Uniform Resource Locators</title>
3523    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3524      <organization>University of California Irvine, Department of Information and Computer Science</organization>
3525      <address><email>fielding@ics.uci.edu</email></address>
3526    </author>
3527    <date month="June" year="1995"/>
3528  </front>
3529  <seriesInfo name="RFC" value="1808"/>
3530</reference>
3531
3532<reference anchor="RFC1900">
3533  <front>
3534    <title>Renumbering Needs Work</title>
3535    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3536      <organization>CERN, Computing and Networks Division</organization>
3537      <address><email>brian@dxcoms.cern.ch</email></address>
3538    </author>
3539    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3540      <organization>cisco Systems</organization>
3541      <address><email>yakov@cisco.com</email></address>
3542    </author>
3543    <date month="February" year="1996"/>
3544  </front>
3545  <seriesInfo name="RFC" value="1900"/>
3546</reference>
3547
3548<reference anchor="RFC1945">
3549  <front>
3550    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3551    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3552      <organization>MIT, Laboratory for Computer Science</organization>
3553      <address><email>timbl@w3.org</email></address>
3554    </author>
3555    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3556      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3557      <address><email>fielding@ics.uci.edu</email></address>
3558    </author>
3559    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3560      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3561      <address><email>frystyk@w3.org</email></address>
3562    </author>
3563    <date month="May" year="1996"/>
3564  </front>
3565  <seriesInfo name="RFC" value="1945"/>
3566</reference>
3567
3568<reference anchor="RFC2068">
3569  <front>
3570    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3571    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3572      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3573      <address><email>fielding@ics.uci.edu</email></address>
3574    </author>
3575    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3576      <organization>MIT Laboratory for Computer Science</organization>
3577      <address><email>jg@w3.org</email></address>
3578    </author>
3579    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3580      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3581      <address><email>mogul@wrl.dec.com</email></address>
3582    </author>
3583    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3584      <organization>MIT Laboratory for Computer Science</organization>
3585      <address><email>frystyk@w3.org</email></address>
3586    </author>
3587    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3588      <organization>MIT Laboratory for Computer Science</organization>
3589      <address><email>timbl@w3.org</email></address>
3590    </author>
3591    <date month="January" year="1997"/>
3592  </front>
3593  <seriesInfo name="RFC" value="2068"/>
3594</reference>
3595
3596<reference anchor='RFC2109'>
3597  <front>
3598    <title>HTTP State Management Mechanism</title>
3599    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3600      <organization>Bell Laboratories, Lucent Technologies</organization>
3601      <address><email>dmk@bell-labs.com</email></address>
3602    </author>
3603    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3604      <organization>Netscape Communications Corp.</organization>
3605      <address><email>montulli@netscape.com</email></address>
3606    </author>
3607    <date year='1997' month='February' />
3608  </front>
3609  <seriesInfo name='RFC' value='2109' />
3610</reference>
3611
3612<reference anchor="RFC2145">
3613  <front>
3614    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3615    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3616      <organization>Western Research Laboratory</organization>
3617      <address><email>mogul@wrl.dec.com</email></address>
3618    </author>
3619    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3620      <organization>Department of Information and Computer Science</organization>
3621      <address><email>fielding@ics.uci.edu</email></address>
3622    </author>
3623    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3624      <organization>MIT Laboratory for Computer Science</organization>
3625      <address><email>jg@w3.org</email></address>
3626    </author>
3627    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3628      <organization>W3 Consortium</organization>
3629      <address><email>frystyk@w3.org</email></address>
3630    </author>
3631    <date month="May" year="1997"/>
3632  </front>
3633  <seriesInfo name="RFC" value="2145"/>
3634</reference>
3635
3636<reference anchor="RFC2324">
3637  <front>
3638    <title abbrev="HTCPCP/1.0">Hyper Text Coffee Pot Control Protocol (HTCPCP/1.0)</title>
3639    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3640      <organization>Xerox Palo Alto Research Center</organization>
3641      <address><email>masinter@parc.xerox.com</email></address>
3642    </author>
3643    <date month="April" day="1" year="1998"/>
3644  </front>
3645  <seriesInfo name="RFC" value="2324"/>
3646</reference>
3647
3648<reference anchor="RFC2616">
3649  <front>
3650    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3651    <author initials="R." surname="Fielding" fullname="R. Fielding">
3652      <organization>University of California, Irvine</organization>
3653      <address><email>fielding@ics.uci.edu</email></address>
3654    </author>
3655    <author initials="J." surname="Gettys" fullname="J. Gettys">
3656      <organization>W3C</organization>
3657      <address><email>jg@w3.org</email></address>
3658    </author>
3659    <author initials="J." surname="Mogul" fullname="J. Mogul">
3660      <organization>Compaq Computer Corporation</organization>
3661      <address><email>mogul@wrl.dec.com</email></address>
3662    </author>
3663    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3664      <organization>MIT Laboratory for Computer Science</organization>
3665      <address><email>frystyk@w3.org</email></address>
3666    </author>
3667    <author initials="L." surname="Masinter" fullname="L. Masinter">
3668      <organization>Xerox Corporation</organization>
3669      <address><email>masinter@parc.xerox.com</email></address>
3670    </author>
3671    <author initials="P." surname="Leach" fullname="P. Leach">
3672      <organization>Microsoft Corporation</organization>
3673      <address><email>paulle@microsoft.com</email></address>
3674    </author>
3675    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3676      <organization>W3C</organization>
3677      <address><email>timbl@w3.org</email></address>
3678    </author>
3679    <date month="June" year="1999"/>
3680  </front>
3681  <seriesInfo name="RFC" value="2616"/>
3682</reference>
3683
3684<reference anchor='RFC2818'>
3685  <front>
3686    <title>HTTP Over TLS</title>
3687    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3688      <organization>RTFM, Inc.</organization>
3689      <address><email>ekr@rtfm.com</email></address>
3690    </author>
3691    <date year='2000' month='May' />
3692  </front>
3693  <seriesInfo name='RFC' value='2818' />
3694</reference>
3695
3696<reference anchor="RFC2821">
3697  <front>
3698    <title>Simple Mail Transfer Protocol</title>
3699    <author initials="J." surname="Klensin" fullname="J. Klensin">
3700      <organization>AT&amp;T Laboratories</organization>
3701      <address><email>klensin@research.att.com</email></address>
3702    </author>
3703    <date year="2001" month="April"/>
3704  </front>
3705  <seriesInfo name="RFC" value="2821"/>
3706</reference>
3707
3708<reference anchor='RFC2965'>
3709  <front>
3710    <title>HTTP State Management Mechanism</title>
3711    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3712      <organization>Bell Laboratories, Lucent Technologies</organization>
3713      <address><email>dmk@bell-labs.com</email></address>
3714    </author>
3715    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3716      <organization>Epinions.com, Inc.</organization>
3717      <address><email>lou@montulli.org</email></address>
3718    </author>
3719    <date year='2000' month='October' />
3720  </front>
3721  <seriesInfo name='RFC' value='2965' />
3722</reference>
3723
3724<reference anchor='RFC3864'>
3725  <front>
3726    <title>Registration Procedures for Message Header Fields</title>
3727    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3728      <organization>Nine by Nine</organization>
3729      <address><email>GK-IETF@ninebynine.org</email></address>
3730    </author>
3731    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3732      <organization>BEA Systems</organization>
3733      <address><email>mnot@pobox.com</email></address>
3734    </author>
3735    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3736      <organization>HP Labs</organization>
3737      <address><email>JeffMogul@acm.org</email></address>
3738    </author>
3739    <date year='2004' month='September' />
3740  </front>
3741  <seriesInfo name='BCP' value='90' />
3742  <seriesInfo name='RFC' value='3864' />
3743</reference>
3744
3745<reference anchor='RFC3977'>
3746  <front>
3747    <title>Network News Transfer Protocol (NNTP)</title>
3748    <author initials='C.' surname='Feather' fullname='C. Feather'>
3749      <organization>THUS plc</organization>
3750      <address><email>clive@demon.net</email></address>
3751    </author>
3752    <date year='2006' month='October' />
3753  </front>
3754  <seriesInfo name="RFC" value="3977"/>
3755</reference>
3756
3757<reference anchor="RFC4288">
3758  <front>
3759    <title>Media Type Specifications and Registration Procedures</title>
3760    <author initials="N." surname="Freed" fullname="N. Freed">
3761      <organization>Sun Microsystems</organization>
3762      <address>
3763        <email>ned.freed@mrochek.com</email>
3764      </address>
3765    </author>
3766    <author initials="J." surname="Klensin" fullname="J. Klensin">
3767      <organization/>
3768      <address>
3769        <email>klensin+ietf@jck.com</email>
3770      </address>
3771    </author>
3772    <date year="2005" month="December"/>
3773  </front>
3774  <seriesInfo name="BCP" value="13"/>
3775  <seriesInfo name="RFC" value="4288"/>
3776</reference>
3777
3778<reference anchor='RFC4395'>
3779  <front>
3780    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3781    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3782      <organization>AT&amp;T Laboratories</organization>
3783      <address>
3784        <email>tony+urireg@maillennium.att.com</email>
3785      </address>
3786    </author>
3787    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3788      <organization>Qualcomm, Inc.</organization>
3789      <address>
3790        <email>hardie@qualcomm.com</email>
3791      </address>
3792    </author>
3793    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3794      <organization>Adobe Systems</organization>
3795      <address>
3796        <email>LMM@acm.org</email>
3797      </address>
3798    </author>
3799    <date year='2006' month='February' />
3800  </front>
3801  <seriesInfo name='BCP' value='115' />
3802  <seriesInfo name='RFC' value='4395' />
3803</reference>
3804
3805<reference anchor="RFC5322">
3806  <front>
3807    <title>Internet Message Format</title>
3808    <author initials="P." surname="Resnick" fullname="P. Resnick">
3809      <organization>Qualcomm Incorporated</organization>
3810    </author>
3811    <date year="2008" month="October"/>
3812  </front> 
3813  <seriesInfo name="RFC" value="5322"/>
3814</reference>
3815
3816<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
3817  <front>
3818    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3819    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3820      <organization/>
3821    </author>
3822    <date year="2001" month="November"/>
3823  </front>
3824  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3825</reference>
3826
3827<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
3828  <front>
3829  <title>Analysis of HTTP Performance Problems</title>
3830  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3831    <organization/>
3832  </author>
3833  <date/>
3834  </front>
3835</reference>
3836
3837<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
3838  <front>
3839  <title>Analysis of HTTP Performance</title>
3840  <author initials="J." surname="Touch" fullname="Joe Touch">
3841    <organization>USC/Information Sciences Institute</organization>
3842    <address><email>touch@isi.edu</email></address>
3843  </author>
3844  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3845    <organization>USC/Information Sciences Institute</organization>
3846    <address><email>johnh@isi.edu</email></address>
3847  </author>
3848  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3849    <organization>USC/Information Sciences Institute</organization>
3850    <address><email>katia@isi.edu</email></address>
3851  </author>
3852  <date year="1998" month="Aug"/>
3853  </front>
3854  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3855  <annotation>(original report dated Aug. 1996)</annotation>
3856</reference>
3857
3858<reference anchor="WAIS">
3859  <front>
3860    <title>WAIS Interface Protocol Prototype Functional Specification (v1.5)</title>
3861    <author initials="F." surname="Davis" fullname="F. Davis">
3862      <organization>Thinking Machines Corporation</organization>
3863    </author>
3864    <author initials="B." surname="Kahle" fullname="B. Kahle">
3865      <organization>Thinking Machines Corporation</organization>
3866    </author>
3867    <author initials="H." surname="Morris" fullname="H. Morris">
3868      <organization>Thinking Machines Corporation</organization>
3869    </author>
3870    <author initials="J." surname="Salem" fullname="J. Salem">
3871      <organization>Thinking Machines Corporation</organization>
3872    </author>
3873    <author initials="T." surname="Shen" fullname="T. Shen">
3874      <organization>Thinking Machines Corporation</organization>
3875    </author>
3876    <author initials="R." surname="Wang" fullname="R. Wang">
3877      <organization>Thinking Machines Corporation</organization>
3878    </author>
3879    <author initials="J." surname="Sui" fullname="J. Sui">
3880      <organization>Thinking Machines Corporation</organization>
3881    </author>
3882    <author initials="M." surname="Grinbaum" fullname="M. Grinbaum">
3883      <organization>Thinking Machines Corporation</organization>
3884    </author>
3885    <date month="April" year="1990"/>
3886  </front>
3887  <seriesInfo name="Thinking Machines Corporation" value=""/>
3888</reference>
3889
3890</references>
3891
3892
3893<section title="Tolerant Applications" anchor="tolerant.applications">
3894<t>
3895   Although this document specifies the requirements for the generation
3896   of HTTP/1.1 messages, not all applications will be correct in their
3897   implementation. We therefore recommend that operational applications
3898   be tolerant of deviations whenever those deviations can be
3899   interpreted unambiguously.
3900</t>
3901<t>
3902   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3903   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3904   accept any amount of SP or HTAB characters between fields, even though
3905   only a single SP is required.
3906</t>
3907<t>
3908   The line terminator for message-header fields is the sequence CRLF.
3909   However, we recommend that applications, when parsing such headers,
3910   recognize a single LF as a line terminator and ignore the leading CR.
3911</t>
3912<t>
3913   The character set of an entity-body &SHOULD; be labeled as the lowest
3914   common denominator of the character codes used within that body, with
3915   the exception that not labeling the entity is preferred over labeling
3916   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3917</t>
3918<t>
3919   Additional rules for requirements on parsing and encoding of dates
3920   and other potential problems with date encodings include:
3921</t>
3922<t>
3923  <list style="symbols">
3924     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3925        which appears to be more than 50 years in the future is in fact
3926        in the past (this helps solve the "year 2000" problem).</t>
3927
3928     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3929        Expires date as earlier than the proper value, but &MUST-NOT;
3930        internally represent a parsed Expires date as later than the
3931        proper value.</t>
3932
3933     <t>All expiration-related calculations &MUST; be done in GMT. The
3934        local time zone &MUST-NOT; influence the calculation or comparison
3935        of an age or expiration time.</t>
3936
3937     <t>If an HTTP header incorrectly carries a date value with a time
3938        zone other than GMT, it &MUST; be converted into GMT using the
3939        most conservative possible conversion.</t>
3940  </list>
3941</t>
3942</section>
3943
3944<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
3945<t>
3946   HTTP/1.1 uses a restricted set of date formats (<xref target="full.date"/>) to
3947   simplify the process of date comparison. Proxies and gateways from
3948   other protocols &SHOULD; ensure that any Date header field present in a
3949   message conforms to one of the HTTP/1.1 formats and rewrite the date
3950   if necessary.
3951</t>
3952</section>
3953
3954<section title="Compatibility with Previous Versions" anchor="compatibility">
3955<t>
3956   It is beyond the scope of a protocol specification to mandate
3957   compliance with previous versions. HTTP/1.1 was deliberately
3958   designed, however, to make supporting previous versions easy. It is
3959   worth noting that, at the time of composing this specification
3960   (1996), we would expect commercial HTTP/1.1 servers to:
3961  <list style="symbols">
3962     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3963        1.1 requests;</t>
3964
3965     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3966        1.1;</t>
3967
3968     <t>respond appropriately with a message in the same major version
3969        used by the client.</t>
3970  </list>
3971</t>
3972<t>
3973   And we would expect HTTP/1.1 clients to:
3974  <list style="symbols">
3975     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3976        responses;</t>
3977
3978     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3979        1.1.</t>
3980  </list>
3981</t>
3982<t>
3983   For most implementations of HTTP/1.0, each connection is established
3984   by the client prior to the request and closed by the server after
3985   sending the response. Some implementations implement the Keep-Alive
3986   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3987</t>
3988
3989<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3990<t>
3991   This section summarizes major differences between versions HTTP/1.0
3992   and HTTP/1.1.
3993</t>
3994
3995<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">
3996<t>
3997   The requirements that clients and servers support the Host request-header,
3998   report an error if the Host request-header (<xref target="header.host"/>) is
3999   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-uri"/>)
4000   are among the most important changes defined by this
4001   specification.
4002</t>
4003<t>
4004   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4005   addresses and servers; there was no other established mechanism for
4006   distinguishing the intended server of a request than the IP address
4007   to which that request was directed. The changes outlined above will
4008   allow the Internet, once older HTTP clients are no longer common, to
4009   support multiple Web sites from a single IP address, greatly
4010   simplifying large operational Web servers, where allocation of many
4011   IP addresses to a single host has created serious problems. The
4012   Internet will also be able to recover the IP addresses that have been
4013   allocated for the sole purpose of allowing special-purpose domain
4014   names to be used in root-level HTTP URLs. Given the rate of growth of
4015   the Web, and the number of servers already deployed, it is extremely
4016   important that all implementations of HTTP (including updates to
4017   existing HTTP/1.0 applications) correctly implement these
4018   requirements:
4019  <list style="symbols">
4020     <t>Both clients and servers &MUST; support the Host request-header.</t>
4021
4022     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4023
4024     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4025        request does not include a Host request-header.</t>
4026
4027     <t>Servers &MUST; accept absolute URIs.</t>
4028  </list>
4029</t>
4030</section>
4031</section>
4032
4033<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4034<t>
4035   Some clients and servers might wish to be compatible with some
4036   previous implementations of persistent connections in HTTP/1.0
4037   clients and servers. Persistent connections in HTTP/1.0 are
4038   explicitly negotiated as they are not the default behavior. HTTP/1.0
4039   experimental implementations of persistent connections are faulty,
4040   and the new facilities in HTTP/1.1 are designed to rectify these
4041   problems. The problem was that some existing 1.0 clients may be
4042   sending Keep-Alive to a proxy server that doesn't understand
4043   Connection, which would then erroneously forward it to the next
4044   inbound server, which would establish the Keep-Alive connection and
4045   result in a hung HTTP/1.0 proxy waiting for the close on the
4046   response. The result is that HTTP/1.0 clients must be prevented from
4047   using Keep-Alive when talking to proxies.
4048</t>
4049<t>
4050   However, talking to proxies is the most important use of persistent
4051   connections, so that prohibition is clearly unacceptable. Therefore,
4052   we need some other mechanism for indicating a persistent connection
4053   is desired, which is safe to use even when talking to an old proxy
4054   that ignores Connection. Persistent connections are the default for
4055   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4056   declaring non-persistence. See <xref target="header.connection"/>.
4057</t>
4058<t>
4059   The original HTTP/1.0 form of persistent connections (the Connection:
4060   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
4061</t>
4062</section>
4063
4064<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4065<t>
4066   This specification has been carefully audited to correct and
4067   disambiguate key word usage; RFC 2068 had many problems in respect to
4068   the conventions laid out in <xref target="RFC2119"/>.
4069</t>
4070<t>
4071   Transfer-coding and message lengths all interact in ways that
4072   required fixing exactly when chunked encoding is used (to allow for
4073   transfer encoding that may not be self delimiting); it was important
4074   to straighten out exactly how message lengths are computed. (Sections
4075   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4076   <xref target="header.content-length" format="counter"/>,
4077   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4078</t>
4079<t>
4080   The use and interpretation of HTTP version numbers has been clarified
4081   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4082   version they support to deal with problems discovered in HTTP/1.0
4083   implementations (<xref target="http.version"/>)
4084</t>
4085<t>
4086   Transfer-coding had significant problems, particularly with
4087   interactions with chunked encoding. The solution is that transfer-codings
4088   become as full fledged as content-codings. This involves
4089   adding an IANA registry for transfer-codings (separate from content
4090   codings), a new header field (TE) and enabling trailer headers in the
4091   future. Transfer encoding is a major performance benefit, so it was
4092   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4093   interoperability problem that could have occurred due to interactions
4094   between authentication trailers, chunked encoding and HTTP/1.0
4095   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4096   and <xref target="header.te" format="counter"/>)
4097</t>
4098</section>
4099
4100<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4101<t>
4102  The CHAR rule does not allow the NUL character anymore (this affects
4103  the comment and quoted-string rules).  Furthermore, the quoted-pair
4104  rule does not allow escaping NUL, CR or LF anymore.
4105  (<xref target="basic.rules"/>)
4106</t>
4107<t>
4108  Clarify that HTTP-Version is case sensitive.
4109  (<xref target="http.version"/>)
4110</t>
4111<t>
4112  Remove reference to non-existant identity transfer-coding value tokens.
4113  (Sections <xref format="counter" target="transfer.codings"/> and
4114  <xref format="counter" target="message.length"/>)
4115</t>
4116<t>
4117  Clarification that the chunk length does not include
4118  the count of the octets in the chunk header and trailer.
4119  (<xref target="chunked.transfer.encoding"/>)
4120</t>
4121<t>
4122  Fix BNF to add query, as the abs_path production in
4123  <xref x:sec="3" x:fmt="of" target="RFC2396"/> doesn't define it.
4124  (<xref target="request-uri"/>)
4125</t>
4126<t>
4127  Clarify exactly when close connection options must be sent.
4128  (<xref target="header.connection"/>)
4129</t>
4130</section>
4131</section>
4132
4133<section title="Terminology" anchor="terminology">
4134<t>
4135   This specification uses a number of terms to refer to the roles
4136   played by participants in, and objects of, the HTTP communication.
4137</t>
4138<t>
4139  <iref item="connection"/>
4140  <x:dfn>connection</x:dfn>
4141  <list>
4142    <t>
4143      A transport layer virtual circuit established between two programs
4144      for the purpose of communication.
4145    </t>
4146  </list>
4147</t>
4148<t>
4149  <iref item="message"/>
4150  <x:dfn>message</x:dfn>
4151  <list>
4152    <t>
4153      The basic unit of HTTP communication, consisting of a structured
4154      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4155      transmitted via the connection.
4156    </t>
4157  </list>
4158</t>
4159<t>
4160  <iref item="request"/>
4161  <x:dfn>request</x:dfn>
4162  <list>
4163    <t>
4164      An HTTP request message, as defined in <xref target="request"/>.
4165    </t>
4166  </list>
4167</t>
4168<t>
4169  <iref item="response"/>
4170  <x:dfn>response</x:dfn>
4171  <list>
4172    <t>
4173      An HTTP response message, as defined in <xref target="response"/>.
4174    </t>
4175  </list>
4176</t>
4177<t>
4178  <iref item="resource"/>
4179  <x:dfn>resource</x:dfn>
4180  <list>
4181    <t>
4182      A network data object or service that can be identified by a URI,
4183      as defined in <xref target="uri"/>. Resources may be available in multiple
4184      representations (e.g. multiple languages, data formats, size, and
4185      resolutions) or vary in other ways.
4186    </t>
4187  </list>
4188</t>
4189<t>
4190  <iref item="entity"/>
4191  <x:dfn>entity</x:dfn>
4192  <list>
4193    <t>
4194      The information transferred as the payload of a request or
4195      response. An entity consists of metainformation in the form of
4196      entity-header fields and content in the form of an entity-body, as
4197      described in &entity;.
4198    </t>
4199  </list>
4200</t>
4201<t>
4202  <iref item="representation"/>
4203  <x:dfn>representation</x:dfn>
4204  <list>
4205    <t>
4206      An entity included with a response that is subject to content
4207      negotiation, as described in &content.negotiation;. There may exist multiple
4208      representations associated with a particular response status.
4209    </t>
4210  </list>
4211</t>
4212<t>
4213  <iref item="content negotiation"/>
4214  <x:dfn>content negotiation</x:dfn>
4215  <list>
4216    <t>
4217      The mechanism for selecting the appropriate representation when
4218      servicing a request, as described in &content.negotiation;. The
4219      representation of entities in any response can be negotiated
4220      (including error responses).
4221    </t>
4222  </list>
4223</t>
4224<t>
4225  <iref item="variant"/>
4226  <x:dfn>variant</x:dfn>
4227  <list>
4228    <t>
4229      A resource may have one, or more than one, representation(s)
4230      associated with it at any given instant. Each of these
4231      representations is termed a `variant'.  Use of the term `variant'
4232      does not necessarily imply that the resource is subject to content
4233      negotiation.
4234    </t>
4235  </list>
4236</t>
4237<t>
4238  <iref item="client"/>
4239  <x:dfn>client</x:dfn>
4240  <list>
4241    <t>
4242      A program that establishes connections for the purpose of sending
4243      requests.
4244    </t>
4245  </list>
4246</t>
4247<t>
4248  <iref item="user agent"/>
4249  <x:dfn>user agent</x:dfn>
4250  <list>
4251    <t>
4252      The client which initiates a request. These are often browsers,
4253      editors, spiders (web-traversing robots), or other end user tools.
4254    </t>
4255  </list>
4256</t>
4257<t>
4258  <iref item="server"/>
4259  <x:dfn>server</x:dfn>
4260  <list>
4261    <t>
4262      An application program that accepts connections in order to
4263      service requests by sending back responses. Any given program may
4264      be capable of being both a client and a server; our use of these
4265      terms refers only to the role being performed by the program for a
4266      particular connection, rather than to the program's capabilities
4267      in general. Likewise, any server may act as an origin server,
4268      proxy, gateway, or tunnel, switching behavior based on the nature
4269      of each request.
4270    </t>
4271  </list>
4272</t>
4273<t>
4274  <iref item="origin server"/>
4275  <x:dfn>origin server</x:dfn>
4276  <list>
4277    <t>
4278      The server on which a given resource resides or is to be created.
4279    </t>
4280  </list>
4281</t>
4282<t>
4283  <iref item="proxy"/>
4284  <x:dfn>proxy</x:dfn>
4285  <list>
4286    <t>
4287      An intermediary program which acts as both a server and a client
4288      for the purpose of making requests on behalf of other clients.
4289      Requests are serviced internally or by passing them on, with
4290      possible translation, to other servers. A proxy &MUST; implement
4291      both the client and server requirements of this specification. A
4292      "transparent proxy" is a proxy that does not modify the request or
4293      response beyond what is required for proxy authentication and
4294      identification. A "non-transparent proxy" is a proxy that modifies
4295      the request or response in order to provide some added service to
4296      the user agent, such as group annotation services, media type
4297      transformation, protocol reduction, or anonymity filtering. Except
4298      where either transparent or non-transparent behavior is explicitly
4299      stated, the HTTP proxy requirements apply to both types of
4300      proxies.
4301    </t>
4302  </list>
4303</t>
4304<t>
4305  <iref item="gateway"/>
4306  <x:dfn>gateway</x:dfn>
4307  <list>
4308    <t>
4309      A server which acts as an intermediary for some other server.
4310      Unlike a proxy, a gateway receives requests as if it were the
4311      origin server for the requested resource; the requesting client
4312      may not be aware that it is communicating with a gateway.
4313    </t>
4314  </list>
4315</t>
4316<t>
4317  <iref item="tunnel"/>
4318  <x:dfn>tunnel</x:dfn>
4319  <list>
4320    <t>
4321      An intermediary program which is acting as a blind relay between
4322      two connections. Once active, a tunnel is not considered a party
4323      to the HTTP communication, though the tunnel may have been
4324      initiated by an HTTP request. The tunnel ceases to exist when both
4325      ends of the relayed connections are closed.
4326    </t>
4327  </list>
4328</t>
4329<t>
4330  <iref item="cache"/>
4331  <x:dfn>cache</x:dfn>
4332  <list>
4333    <t>
4334      A program's local store of response messages and the subsystem
4335      that controls its message storage, retrieval, and deletion. A
4336      cache stores cacheable responses in order to reduce the response
4337      time and network bandwidth consumption on future, equivalent
4338      requests. Any client or server may include a cache, though a cache
4339      cannot be used by a server that is acting as a tunnel.
4340    </t>
4341  </list>
4342</t>
4343<t>
4344  <iref item="cacheable"/>
4345  <x:dfn>cacheable</x:dfn>
4346  <list>
4347    <t>
4348      A response is cacheable if a cache is allowed to store a copy of
4349      the response message for use in answering subsequent requests. The
4350      rules for determining the cacheability of HTTP responses are
4351      defined in &caching;. Even if a resource is cacheable, there may
4352      be additional constraints on whether a cache can use the cached
4353      copy for a particular request.
4354    </t>
4355  </list>
4356</t>
4357<t>
4358  <iref item="upstream"/>
4359  <iref item="downstream"/>
4360  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
4361  <list>
4362    <t>
4363      Upstream and downstream describe the flow of a message: all
4364      messages flow from upstream to downstream.
4365    </t>
4366  </list>
4367</t>
4368<t>
4369  <iref item="inbound"/>
4370  <iref item="outbound"/>
4371  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
4372  <list>
4373    <t>
4374      Inbound and outbound refer to the request and response paths for
4375      messages: "inbound" means "traveling toward the origin server",
4376      and "outbound" means "traveling toward the user agent"
4377    </t>
4378  </list>
4379</t>
4380</section>
4381
4382<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4383
4384<section title="Since RFC2616">
4385<t>
4386  Extracted relevant partitions from <xref target="RFC2616"/>.
4387</t>
4388</section>
4389
4390<section title="Since draft-ietf-httpbis-p1-messaging-00">
4391<t>
4392  Closed issues:
4393  <list style="symbols"> 
4394    <t>
4395      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
4396      "HTTP Version should be case sensitive"
4397      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
4398    </t>
4399    <t>
4400      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
4401      "'unsafe' characters"
4402      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
4403    </t>
4404    <t>
4405      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
4406      "Chunk Size Definition"
4407      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
4408    </t>
4409    <t>
4410      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
4411      "Message Length"
4412      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
4413    </t>
4414    <t>
4415      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
4416      "Media Type Registrations"
4417      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
4418    </t>
4419    <t>
4420      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
4421      "URI includes query"
4422      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
4423    </t>
4424    <t>
4425      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
4426      "No close on 1xx responses"
4427      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
4428    </t>
4429    <t>
4430      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
4431      "Remove 'identity' token references"
4432      (<eref target="http://purl.org/NET/http-errata#identity"/>)
4433    </t>
4434    <t>
4435      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
4436      "Import query BNF"
4437    </t>
4438    <t>
4439      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
4440      "qdtext BNF"
4441    </t>
4442    <t>
4443      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4444      "Normative and Informative references"
4445    </t>
4446    <t>
4447      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4448      "RFC2606 Compliance"
4449    </t>
4450    <t>
4451      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
4452      "RFC977 reference"
4453    </t>
4454    <t>
4455      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
4456      "RFC1700 references"
4457    </t>
4458    <t>
4459      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
4460      "inconsistency in date format explanation"
4461    </t>
4462    <t>
4463      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
4464      "Date reference typo"
4465    </t>
4466    <t>
4467      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4468      "Informative references"
4469    </t>
4470    <t>
4471      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
4472      "ISO-8859-1 Reference"
4473    </t>
4474    <t>
4475      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
4476      "Normative up-to-date references"
4477    </t>
4478  </list>
4479</t>
4480<t>
4481  Other changes:
4482  <list style="symbols"> 
4483    <t>
4484      Update media type registrations to use RFC4288 template.
4485    </t>
4486    <t>
4487      Use names of RFC4234 core rules DQUOTE and HTAB,
4488      fix broken ABNF for chunk-data
4489      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
4490    </t>
4491  </list>
4492</t>
4493</section>
4494
4495<section title="Since draft-ietf-httpbis-p1-messaging-01">
4496<t>
4497  Closed issues:
4498  <list style="symbols"> 
4499    <t>
4500      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
4501      "Bodies on GET (and other) requests"
4502    </t>
4503    <t>
4504      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
4505      "Updating to RFC4288"
4506    </t>
4507    <t>
4508      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
4509      "Status Code and Reason Phrase"
4510    </t>
4511    <t>
4512      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
4513      "rel_path not used"
4514    </t>
4515  </list>
4516</t>
4517<t>
4518  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4519  <list style="symbols"> 
4520    <t>
4521      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4522      "trailer-part").
4523    </t>
4524    <t>
4525      Avoid underscore character in rule names ("http_URL" ->
4526      "http-URL", "abs_path" -> "path-absolute").
4527    </t>
4528    <t>
4529      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4530      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4531      have to be updated when switching over to RFC3986.
4532    </t>
4533    <t>
4534      Synchronize core rules with RFC5234 (this includes a change to CHAR
4535      which now excludes NUL).
4536    </t>
4537    <t>
4538      Get rid of prose rules that span multiple lines.
4539    </t>
4540    <t>
4541      Get rid of unused rules LOALPHA and UPALPHA.
4542    </t>
4543    <t>
4544      Move "Product Tokens" section (back) into Part 1, as "token" is used
4545      in the definition of the Upgrade header.
4546    </t>
4547    <t>
4548      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4549    </t>
4550    <t>
4551      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4552    </t>
4553  </list>
4554</t>
4555</section>
4556
4557<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4558<t>
4559  Closed issues:
4560  <list style="symbols"> 
4561    <t>
4562      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
4563      "HTTP-date vs. rfc1123-date"
4564    </t>
4565    <t>
4566      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
4567      "WS in quoted-pair"
4568    </t>
4569  </list>
4570</t>
4571<t>
4572  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4573  <list style="symbols"> 
4574    <t>
4575      Reference RFC 3984, and update header registrations for headers defined
4576      in this document.
4577    </t>
4578  </list>
4579</t>
4580<t>
4581  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4582  <list style="symbols"> 
4583    <t>
4584      Replace string literals when the string really is case-sensitive (HTTP-Version).
4585    </t>
4586  </list>
4587</t>
4588</section>
4589
4590<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4591<t>
4592  Closed issues:
4593  <list style="symbols"> 
4594    <t>
4595      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
4596      "Connection closing"
4597    </t>
4598    <t>
4599      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
4600      "Move registrations and registry information to IANA Considerations"
4601    </t>
4602    <t>
4603      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
4604      "need new URL for PAD1995 reference"
4605    </t>
4606    <t>
4607      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
4608      "IANA Considerations: update HTTP URI scheme registration"
4609    </t>
4610    <t>
4611      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
4612      "Cite HTTPS URI scheme definition"
4613    </t>
4614    <t>
4615      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
4616      "List-type headers vs Set-Cookie"
4617    </t>
4618  </list>
4619</t>
4620<t>
4621  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4622  <list style="symbols"> 
4623    <t>
4624      Replace string literals when the string really is case-sensitive (HTTP-Date).
4625    </t>
4626    <t>
4627      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4628    </t>
4629  </list>
4630</t>
4631</section>
4632
4633<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4634<t>
4635  Closed issues:
4636  <list style="symbols"> 
4637    <t>
4638      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4639      "RFC 2822 is updated by RFC 5322"
4640    </t>
4641  </list>
4642</t>
4643<t>
4644  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4645  <list style="symbols"> 
4646    <t>
4647      Use "/" instead of "|" for alternatives.
4648    </t>
4649    <t>
4650      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4651    </t>
4652    <t>
4653      Only reference RFC 5234's core rules.
4654    </t>
4655    <t>
4656      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4657      whitespace ("OWS") and required whitespace ("RWS").
4658    </t>
4659    <t>
4660      Rewrite ABNFs to spell out whitespace rules, factor out
4661      header value format definitions.
4662    </t>
4663  </list>
4664</t>
4665</section>
4666
4667</section>
4668
4669</back>
4670</rfc>
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