source: draft-ietf-httpbis/latest/p1-messaging.xml @ 391

Last change on this file since 391 was 391, checked in by julian.reschke@…, 11 years ago

Merge in Roy's changes wrt Introduction and HTTP Architecture, replace Request-URI by request-target and relative-URI by partial-URI throughout.

  • Property svn:eol-style set to native
File size: 200.7 KB
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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.05"/>.
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   request/response protocol that uses extensible semantics and MIME-like
232   message payloads for flexible interaction with network-based hypertext
233   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
234   standard <xref target="RFC3986"/> to indicate resource targets and
235   relationships between resources.
236   Messages are passed in a format similar to that used by Internet mail
237   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
238   (MIME) <xref target="RFC2045"/> (see &diff2045entity; for the differences
239   between HTTP and MIME messages).
240</t>
241<t>
242   HTTP is a generic interface protocol for informations systems. It is
243   designed to hide the details of how a service is implemented by presenting
244   a uniform interface to clients that is independent of the types of
245   resources provided. Likewise, servers do not need to be aware of each
246   client's purpose: an HTTP request can be considered in isolation rather
247   than being associated with a specific type of client or a predetermined
248   sequence of application steps. The result is a protocol that can be used
249   effectively in many different contexts and for which implementations can
250   evolve independently over time.
251</t>
252<t>
253   HTTP is also designed for use as a generic protocol for translating
254   communication to and from other Internet information systems, such as
255   USENET news services via NNTP <xref target="RFC3977"/>,
256   file services via FTP <xref target="RFC959"/>,
257   Gopher <xref target="RFC1436"/>, and WAIS <xref target="WAIS"/>.
258   HTTP proxies and gateways provide access to alternative information
259   services by translating their diverse protocols into a hypermedia
260   format that can be viewed and manipulated by clients in the same way
261   as HTTP services.
262</t>
263<t>
264   One consequence of HTTP flexibility is that we cannot define the protocol
265   in terms of how to implement it behind the interface. Instead, we are
266   limited to restricting the syntax of communication, defining the intent
267   of received communication, and the expected behavior of recipients. If
268   the communication is considered in isolation, then successful actions
269   should be reflected in the observable interface provided by servers.
270   However, since many clients are potentially acting in parallel and
271   perhaps at cross-purposes, it would be meaningless to require that such
272   behavior be observable.
273</t>
274<t>
275   This document is Part 1 of the seven-part specification of HTTP,
276   defining the protocol referred to as "HTTP/1.1" and obsoleting
277   <xref target="RFC2616"/>.
278   Part 1 defines the URI schemes specific to HTTP-based resources, overall
279   network operation, transport protocol connection management, and HTTP
280   message framing and forwarding requirements.
281   Our goal is to define all of the mechanisms necessary for HTTP message
282   handling that are independent of message semantics, thereby defining the
283   complete set of requirements for a message parser and transparent
284   message-forwarding intermediaries.
285</t>
286
287<section title="Requirements" anchor="intro.requirements">
288<t>
289   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
290   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
291   document are to be interpreted as described in <xref target="RFC2119"/>.
292</t>
293<t>
294   An implementation is not compliant if it fails to satisfy one or more
295   of the &MUST; or &REQUIRED; level requirements for the protocols it
296   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
297   level and all the &SHOULD; level requirements for its protocols is said
298   to be "unconditionally compliant"; one that satisfies all the &MUST;
299   level requirements but not all the &SHOULD; level requirements for its
300   protocols is said to be "conditionally compliant."
301</t>
302</section>
303
304<section title="Syntax Notation" anchor="notation">
305<iref primary="true" item="Grammar" subitem="ALPHA"/>
306<iref primary="true" item="Grammar" subitem="CHAR"/>
307<iref primary="true" item="Grammar" subitem="CR"/>
308<iref primary="true" item="Grammar" subitem="CRLF"/>
309<iref primary="true" item="Grammar" subitem="CTL"/>
310<iref primary="true" item="Grammar" subitem="DIGIT"/>
311<iref primary="true" item="Grammar" subitem="DQUOTE"/>
312<iref primary="true" item="Grammar" subitem="HEXDIG"/>
313<iref primary="true" item="Grammar" subitem="HTAB"/>
314<iref primary="true" item="Grammar" subitem="LF"/>
315<iref primary="true" item="Grammar" subitem="OCTET"/>
316<iref primary="true" item="Grammar" subitem="SP"/>
317<iref primary="true" item="Grammar" subitem="WSP"/>
318<t anchor="core.rules">
319  <x:anchor-alias value="ALPHA"/>
320  <x:anchor-alias value="CHAR"/>
321  <x:anchor-alias value="CTL"/>
322  <x:anchor-alias value="CR"/>
323  <x:anchor-alias value="CRLF"/>
324  <x:anchor-alias value="DIGIT"/>
325  <x:anchor-alias value="DQUOTE"/>
326  <x:anchor-alias value="HEXDIG"/>
327  <x:anchor-alias value="HTAB"/>
328  <x:anchor-alias value="LF"/>
329  <x:anchor-alias value="OCTET"/>
330  <x:anchor-alias value="SP"/>
331  <x:anchor-alias value="WSP"/>
332   This specification uses the Augmented Backus-Naur Form (ABNF) notation
333   of <xref target="RFC5234"/>.  The following core rules are included by
334   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
335   ALPHA (letters), CHAR (any <xref target="USASCII"/> character,
336   excluding NUL), CR (carriage return), CRLF (CR LF), CTL (controls),
337   DIGIT (decimal 0-9), DQUOTE (double quote),
338   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab),
339   LF (line feed), OCTET (any 8-bit sequence of data), SP (space)
340   and WSP (white space).
341</t>
342
343<section title="ABNF Extension: #rule" anchor="notation.abnf">
344  <t>
345    One extension to the ABNF rules of <xref target="RFC5234"/> is used to
346    improve readability.
347  </t>
348  <t>
349    A construct "#" is defined, similar to "*", for defining lists of
350    elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at least
351    &lt;n&gt; and at most &lt;m&gt; elements, each separated by one or more commas
352    (",") and &OPTIONAL; linear white space (OWS). This makes the usual
353    form of lists very easy; a rule such as
354    <figure><artwork type="example">
355 ( *<x:ref>OWS</x:ref> element *( *<x:ref>OWS</x:ref> "," *<x:ref>OWS</x:ref> element ))</artwork></figure>
356  </t>
357  <t>
358    can be shown as
359    <figure><artwork type="example">
360 1#element</artwork></figure>
361  </t>
362  <t>
363    Wherever this construct is used, null elements are allowed, but do
364    not contribute to the count of elements present. That is,
365    "(element), , (element) " is permitted, but counts as only two
366    elements. Therefore, where at least one element is required, at
367    least one non-null element &MUST; be present. Default values are 0
368    and infinity so that "#element" allows any number, including zero;
369    "1#element" requires at least one; and "1#2element" allows one or
370    two.
371  </t>
372  <t>
373    <cref anchor="abnf.list">
374      At a later point of time, we may want to add an appendix containing
375      the whole ABNF, with the list rules expanded to strict RFC 5234
376      notation.
377    </cref>
378  </t>
379</section>
380
381<section title="Basic Rules" anchor="basic.rules">
382<t anchor="rule.CRLF">
383  <x:anchor-alias value="CRLF"/>
384   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
385   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
386   tolerant applications). The end-of-line marker within an entity-body
387   is defined by its associated media type, as described in &media-types;.
388</t>
389<t anchor="rule.LWS">
390   All linear white space (LWS) in header field-values has the same semantics as SP. A
391   recipient &MAY; replace any such linear white space with a single SP before
392   interpreting the field value or forwarding the message downstream.
393</t>
394<t>
395   Historically, HTTP/1.1 header field values allow linear white space folding across
396   multiple lines. However, this specification deprecates its use; senders &MUST-NOT; 
397   produce messages that include LWS folding (i.e., use the obs-fold rule), except
398   within the message/http media type (<xref target="internet.media.type.message.http"/>).
399   Receivers &SHOULD; still parse folded linear white space.
400</t>
401<t>
402   This specification uses three rules to denote the use of linear white space;
403   BWS ("Bad" White Space), OWS (Optional White Space), and RWS (Required White Space).
404</t>
405<t>
406   "Bad" white space is allowed by the BNF, but senders &SHOULD-NOT; produce it in messages.
407   Receivers &MUST; accept it in incoming messages.
408</t>
409<t>
410   Required white space is used when at least one linear white space character
411   is required to separate field tokens. In all such cases, a single SP character
412   &SHOULD; be used.
413</t>
414<t anchor="rule.whitespace">
415  <x:anchor-alias value="BWS"/>
416  <x:anchor-alias value="OWS"/>
417  <x:anchor-alias value="RWS"/>
418  <x:anchor-alias value="obs-fold"/>
419</t>
420<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"/>
421  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
422                 ; "optional" white space
423  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
424                 ; "required" white space
425  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
426                 ; "bad" white space
427  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
428</artwork></figure>
429<t anchor="rule.TEXT">
430  <x:anchor-alias value="TEXT"/>
431   The TEXT rule is only used for descriptive field contents and values
432   that are not intended to be interpreted by the message parser. Words
433   of *TEXT &MAY; contain characters from character sets other than ISO-8859-1
434   <xref target="ISO-8859-1"/> only when encoded according to the rules of
435   <xref target="RFC2047"/>.
436</t>
437<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TEXT"/>
438  <x:ref>TEXT</x:ref>           = %x20-7E / %x80-FF / <x:ref>OWS</x:ref>
439                 ; any <x:ref>OCTET</x:ref> except <x:ref>CTL</x:ref>s, but including <x:ref>OWS</x:ref>
440</artwork></figure>
441<t>
442   A CRLF is allowed in the definition of TEXT only as part of a header
443   field continuation. It is expected that the folding LWS will be
444   replaced with a single SP before interpretation of the TEXT value.
445</t>
446<t anchor="rule.token.separators">
447  <x:anchor-alias value="tchar"/>
448  <x:anchor-alias value="token"/>
449   Many HTTP/1.1 header field values consist of words separated by LWS
450   or special characters. These special characters &MUST; be in a quoted
451   string to be used within a parameter value (as defined in
452   <xref target="transfer.codings"/>).
453</t>
454<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/>
455  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
456                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
457                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
458                 
459  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
460</artwork></figure>
461<t anchor="rule.comment">
462  <x:anchor-alias value="comment"/>
463  <x:anchor-alias value="ctext"/>
464   Comments can be included in some HTTP header fields by surrounding
465   the comment text with parentheses. Comments are only allowed in
466   fields containing "comment" as part of their field value definition.
467   In all other fields, parentheses are considered part of the field
468   value.
469</t>
470<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
471  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
472  <x:ref>ctext</x:ref>          = &lt;any <x:ref>TEXT</x:ref> excluding "(" and ")"&gt;
473</artwork></figure>
474<t anchor="rule.quoted-string">
475  <x:anchor-alias value="quoted-string"/>
476  <x:anchor-alias value="qdtext"/>
477   A string of text is parsed as a single word if it is quoted using
478   double-quote marks.
479</t>
480<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/>
481  <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>
482  <x:ref>qdtext</x:ref>         = &lt;any <x:ref>TEXT</x:ref> excluding <x:ref>DQUOTE</x:ref> and "\">
483</artwork></figure>
484<t anchor="rule.quoted-pair">
485  <x:anchor-alias value="quoted-pair"/>
486  <x:anchor-alias value="quoted-text"/>
487   The backslash character ("\") &MAY; be used as a single-character
488   quoting mechanism only within quoted-string and comment constructs.
489</t>
490<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-text"/><iref primary="true" item="Grammar" subitem="quoted-pair"/>
491  <x:ref>quoted-text</x:ref>    = %x01-09 /
492                   %x0B-0C /
493                   %x0E-FF ; Characters excluding NUL, <x:ref>CR</x:ref> and <x:ref>LF</x:ref>
494  <x:ref>quoted-pair</x:ref>    = "\" <x:ref>quoted-text</x:ref>
495</artwork></figure>
496</section>
497
498<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
499  <x:anchor-alias value="request-header"/>
500  <x:anchor-alias value="response-header"/>
501  <x:anchor-alias value="accept-params"/>
502  <x:anchor-alias value="entity-body"/>
503  <x:anchor-alias value="entity-header"/>
504  <x:anchor-alias value="Cache-Control"/>
505  <x:anchor-alias value="Pragma"/>
506  <x:anchor-alias value="Warning"/>
507<t>
508  The ABNF rules below are defined in other parts:
509</t>
510<figure><!-- Part2--><artwork type="abnf2616">
511  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
512  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
513</artwork></figure>
514<figure><!-- Part3--><artwork type="abnf2616">
515  <x:ref>accept-params</x:ref>   = &lt;accept-params, defined in &header-accept;&gt;
516  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
517  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
518</artwork></figure>
519<figure><!-- Part6--><artwork type="abnf2616">
520  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
521  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
522  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
523</artwork></figure>
524</section>
525
526</section>
527</section>
528
529<section title="HTTP architecture" anchor="architecture">
530<t>
531   HTTP was created with a specific architecture in mind, the World Wide Web,
532   and has evolved over time to support the scalability needs of a worldwide
533   hypertext system. Much of that architecture is reflected in the terminology
534   and syntax productions used to define HTTP.
535</t>
536
537<section title="Uniform Resource Identifiers" anchor="uri">
538<t>
539   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
540   throughout HTTP as the means for identifying resources. URI references
541   are used to target requests, redirect responses, and define relationships.
542   HTTP does not limit what a resource may be; it merely defines an interface
543   that can be used to interact with a resource via HTTP. More information on
544   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
545</t>
546  <x:anchor-alias value="URI"/>
547  <x:anchor-alias value="URI-reference"/>
548  <x:anchor-alias value="absolute-URI"/>
549  <x:anchor-alias value="relative-part"/>
550  <x:anchor-alias value="authority"/>
551  <x:anchor-alias value="fragment"/>
552  <x:anchor-alias value="path-abempty"/>
553  <x:anchor-alias value="path-absolute"/>
554  <x:anchor-alias value="port"/>
555  <x:anchor-alias value="query"/>
556  <x:anchor-alias value="uri-host"/>
557  <x:anchor-alias value="partial-URI"/>
558<t>
559   This specification adopts the definitions of "URI-reference",
560   "absolute-URI", "relative-part", "fragment", "port", "host",
561   "path-abempty", "path-absolute", "query", and "authority" from
562   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
563   protocol elements that allow a relative URI without a fragment.
564</t>
565<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="URI-reference"/><iref primary="true" item="Grammar" subitem="absolute-URI"/><iref primary="true" item="Grammar" subitem="authority"/><iref primary="true" item="Grammar" subitem="path-absolute"/><iref primary="true" item="Grammar" subitem="port"/><iref primary="true" item="Grammar" subitem="query"/><iref primary="true" item="Grammar" subitem="uri-host"/>
566  <x:ref>URI</x:ref>           = &lt;URI, defined in <xref target="RFC3986" x:fmt="," x:sec="3"/>>
567  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>>
568  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>>
569  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>>
570  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>>
571  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC3986" x:fmt="," x:sec="3.5"/>>
572  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>>
573  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>>
574  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>>
575  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>>
576  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>>
577 
578  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
579</artwork></figure>
580<t>
581   Each protocol element in HTTP that allows a URI reference will indicate in
582   its ABNF production whether the element allows only a URI in absolute form
583   (absolute-URI), any relative reference (relative-ref), or some other subset
584   of the URI-reference grammar. Unless otherwise indicated, URI references
585   are parsed relative to the request target (the default base URI for both
586   the request and its corresponding response).
587</t>
588
589<section title="http URI scheme" anchor="http.uri">
590  <x:anchor-alias value="http-URI"/>
591  <iref item="http URI scheme" primary="true"/>
592  <iref item="URI scheme" subitem="http" primary="true"/>
593<t>
594   The "http" scheme is used to locate network resources via the HTTP
595   protocol. This section defines the syntax and semantics for identifiers
596   using the http or https URI schemes.
597</t>
598<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
599  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
600</artwork></figure>
601<t>
602   If the port is empty or not given, port 80 is assumed. The semantics
603   are that the identified resource is located at the server listening
604   for TCP connections on that port of that host, and the request-target
605   for the resource is path-absolute (<xref target="request-target"/>). The use of IP addresses
606   in URLs &SHOULD; be avoided whenever possible (see <xref target="RFC1900"/>). If
607   the path-absolute is not present in the URL, it &MUST; be given as "/" when
608   used as a request-target for a resource (<xref target="request-target"/>). If a proxy
609   receives a host name which is not a fully qualified domain name, it
610   &MAY; add its domain to the host name it received. If a proxy receives
611   a fully qualified domain name, the proxy &MUST-NOT; change the host
612   name.
613</t>
614<t><list><t>
615  <iref item="https URI scheme"/>
616  <iref item="URI scheme" subitem="https"/>
617  <x:h>Note:</x:h> the "https" scheme is defined in <xref target="RFC2818"/>.
618</t></list></t>
619</section>
620
621<section title="URI Comparison" anchor="uri.comparison">
622<t>
623   When comparing two URIs to decide if they match or not, a client
624   &SHOULD; use a case-sensitive octet-by-octet comparison of the entire
625   URIs, with these exceptions:
626  <list style="symbols">
627    <t>A port that is empty or not given is equivalent to the default
628        port for that URI-reference;</t>
629    <t>Comparisons of host names &MUST; be case-insensitive;</t>
630    <t>Comparisons of scheme names &MUST; be case-insensitive;</t>
631    <t>An empty path-absolute is equivalent to an path-absolute of "/".</t>
632  </list>
633</t>
634<t>
635   Characters other than those in the "reserved" set (see
636   <xref target="RFC3986" x:fmt="," x:sec="2.2"/>) are equivalent to their
637   ""%" <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding.
638</t>
639<t>
640   For example, the following three URIs are equivalent:
641</t>
642<figure><artwork type="example">
643   http://example.com:80/~smith/home.html
644   http://EXAMPLE.com/%7Esmith/home.html
645   http://EXAMPLE.com:/%7esmith/home.html
646</artwork></figure>
647</section>
648
649<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
650<t>
651</t>
652</section>
653</section>
654
655<section title="Overall Operation" anchor="intro.overall.operation">
656<t>
657   HTTP is a request/response protocol. A client sends a
658   request to the server in the form of a request method, URI, and
659   protocol version, followed by a MIME-like message containing request
660   modifiers, client information, and possible body content over a
661   connection with a server. The server responds with a status line,
662   including the message's protocol version and a success or error code,
663   followed by a MIME-like message containing server information, entity
664   metainformation, and possible entity-body content.
665</t>
666<t>
667   Most HTTP communication is initiated by a user agent and consists of
668   a request to be applied to a resource on some origin server. In the
669   simplest case, this may be accomplished via a single connection (v)
670   between the user agent (UA) and the origin server (O).
671</t>
672<figure><artwork type="drawing">
673       request chain ------------------------&gt;
674    UA -------------------v------------------- O
675       &lt;----------------------- response chain
676</artwork></figure>
677<t>
678   A more complicated situation occurs when one or more intermediaries
679   are present in the request/response chain. There are three common
680   forms of intermediary: proxy, gateway, and tunnel. A proxy is a
681   forwarding agent, receiving requests for a URI in its absolute form,
682   rewriting all or part of the message, and forwarding the reformatted
683   request toward the server identified by the URI. A gateway is a
684   receiving agent, acting as a layer above some other server(s) and, if
685   necessary, translating the requests to the underlying server's
686   protocol. A tunnel acts as a relay point between two connections
687   without changing the messages; tunnels are used when the
688   communication needs to pass through an intermediary (such as a
689   firewall) even when the intermediary cannot understand the contents
690   of the messages.
691</t>
692<figure><artwork type="drawing">
693       request chain --------------------------------------&gt;
694    UA -----v----- A -----v----- B -----v----- C -----v----- O
695       &lt;------------------------------------- response chain
696</artwork></figure>
697<t>
698   The figure above shows three intermediaries (A, B, and C) between the
699   user agent and origin server. A request or response message that
700   travels the whole chain will pass through four separate connections.
701   This distinction is important because some HTTP communication options
702   may apply only to the connection with the nearest, non-tunnel
703   neighbor, only to the end-points of the chain, or to all connections
704   along the chain. Although the diagram is linear, each participant may
705   be engaged in multiple, simultaneous communications. For example, B
706   may be receiving requests from many clients other than A, and/or
707   forwarding requests to servers other than C, at the same time that it
708   is handling A's request.
709</t>
710<t>
711   Any party to the communication which is not acting as a tunnel may
712   employ an internal cache for handling requests. The effect of a cache
713   is that the request/response chain is shortened if one of the
714   participants along the chain has a cached response applicable to that
715   request. The following illustrates the resulting chain if B has a
716   cached copy of an earlier response from O (via C) for a request which
717   has not been cached by UA or A.
718</t>
719<figure><artwork type="drawing">
720          request chain ----------&gt;
721       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
722          &lt;--------- response chain
723</artwork></figure>
724<t>
725   Not all responses are usefully cacheable, and some requests may
726   contain modifiers which place special requirements on cache behavior.
727   HTTP requirements for cache behavior and cacheable responses are
728   defined in &caching;.
729</t>
730<t>
731   In fact, there are a wide variety of architectures and configurations
732   of caches and proxies currently being experimented with or deployed
733   across the World Wide Web. These systems include national hierarchies
734   of proxy caches to save transoceanic bandwidth, systems that
735   broadcast or multicast cache entries, organizations that distribute
736   subsets of cached data via CD-ROM, and so on. HTTP systems are used
737   in corporate intranets over high-bandwidth links, and for access via
738   PDAs with low-power radio links and intermittent connectivity. The
739   goal of HTTP/1.1 is to support the wide diversity of configurations
740   already deployed while introducing protocol constructs that meet the
741   needs of those who build web applications that require high
742   reliability and, failing that, at least reliable indications of
743   failure.
744</t>
745<t>
746   HTTP communication usually takes place over TCP/IP connections. The
747   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
748   not preclude HTTP from being implemented on top of any other protocol
749   on the Internet, or on other networks. HTTP only presumes a reliable
750   transport; any protocol that provides such guarantees can be used;
751   the mapping of the HTTP/1.1 request and response structures onto the
752   transport data units of the protocol in question is outside the scope
753   of this specification.
754</t>
755<t>
756   In HTTP/1.0, most implementations used a new connection for each
757   request/response exchange. In HTTP/1.1, a connection may be used for
758   one or more request/response exchanges, although connections may be
759   closed for a variety of reasons (see <xref target="persistent.connections"/>).
760</t>
761</section>
762
763<section title="Use of HTTP for proxy communication" anchor="http.proxy">
764<t>
765   Configured to use HTTP to proxy HTTP or other protocols.
766</t>
767</section>
768<section title="Interception of HTTP for access control" anchor="http.intercept">
769<t>
770   Interception of HTTP traffic for initiating access control.
771</t>
772</section>
773<section title="Use of HTTP by other protocols" anchor="http.others">
774<t>
775   Profiles of HTTP defined by other protocol.
776   Extensions of HTTP like WebDAV.
777</t>
778</section>
779<section title="Use of HTTP by media type specification" anchor="http.media">
780<t>
781   Instructions on composing HTTP requests via hypertext formats.
782</t>
783</section>
784</section>
785
786<section title="Protocol Parameters" anchor="protocol.parameters">
787
788<section title="HTTP Version" anchor="http.version">
789  <x:anchor-alias value="HTTP-Version"/>
790  <x:anchor-alias value="HTTP-Prot-Name"/>
791<t>
792   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
793   of the protocol. The protocol versioning policy is intended to allow
794   the sender to indicate the format of a message and its capacity for
795   understanding further HTTP communication, rather than the features
796   obtained via that communication. No change is made to the version
797   number for the addition of message components which do not affect
798   communication behavior or which only add to extensible field values.
799   The &lt;minor&gt; number is incremented when the changes made to the
800   protocol add features which do not change the general message parsing
801   algorithm, but which may add to the message semantics and imply
802   additional capabilities of the sender. The &lt;major&gt; number is
803   incremented when the format of a message within the protocol is
804   changed. See <xref target="RFC2145"/> for a fuller explanation.
805</t>
806<t>
807   The version of an HTTP message is indicated by an HTTP-Version field
808   in the first line of the message. HTTP-Version is case-sensitive.
809</t>
810<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
811  <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>
812  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
813</artwork></figure>
814<t>
815   Note that the major and minor numbers &MUST; be treated as separate
816   integers and that each &MAY; be incremented higher than a single digit.
817   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
818   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
819   &MUST-NOT; be sent.
820</t>
821<t>
822   An application that sends a request or response message that includes
823   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
824   with this specification. Applications that are at least conditionally
825   compliant with this specification &SHOULD; use an HTTP-Version of
826   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
827   not compatible with HTTP/1.0. For more details on when to send
828   specific HTTP-Version values, see <xref target="RFC2145"/>.
829</t>
830<t>
831   The HTTP version of an application is the highest HTTP version for
832   which the application is at least conditionally compliant.
833</t>
834<t>
835   Proxy and gateway applications need to be careful when forwarding
836   messages in protocol versions different from that of the application.
837   Since the protocol version indicates the protocol capability of the
838   sender, a proxy/gateway &MUST-NOT; send a message with a version
839   indicator which is greater than its actual version. If a higher
840   version request is received, the proxy/gateway &MUST; either downgrade
841   the request version, or respond with an error, or switch to tunnel
842   behavior.
843</t>
844<t>
845   Due to interoperability problems with HTTP/1.0 proxies discovered
846   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
847   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
848   they support. The proxy/gateway's response to that request &MUST; be in
849   the same major version as the request.
850</t>
851<t>
852  <list>
853    <t>
854      <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
855      of header fields required or forbidden by the versions involved.
856    </t>
857  </list>
858</t>
859</section>
860
861<section title="Date/Time Formats" anchor="date.time.formats">
862<section title="Full Date" anchor="full.date">
863  <x:anchor-alias value="HTTP-date"/>
864  <x:anchor-alias value="obsolete-date"/>
865  <x:anchor-alias value="rfc1123-date"/>
866  <x:anchor-alias value="rfc850-date"/>
867  <x:anchor-alias value="asctime-date"/>
868  <x:anchor-alias value="date1"/>
869  <x:anchor-alias value="date2"/>
870  <x:anchor-alias value="date3"/>
871  <x:anchor-alias value="rfc1123-date"/>
872  <x:anchor-alias value="time"/>
873  <x:anchor-alias value="wkday"/>
874  <x:anchor-alias value="weekday"/>
875  <x:anchor-alias value="month"/>
876<t>
877   HTTP applications have historically allowed three different formats
878   for the representation of date/time stamps:
879</t>
880<figure><artwork type="example">
881   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
882   Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
883   Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
884</artwork></figure>
885<t>
886   The first format is preferred as an Internet standard and represents
887   a fixed-length subset of that defined by <xref target="RFC1123"/>. The
888   other formats are described here only for
889   compatibility with obsolete implementations.
890   HTTP/1.1 clients and servers that parse the date value &MUST; accept
891   all three formats (for compatibility with HTTP/1.0), though they &MUST;
892   only generate the RFC 1123 format for representing HTTP-date values
893   in header fields. See <xref target="tolerant.applications"/> for further information.
894</t>
895<t><list><t>
896      <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
897      accepting date values that may have been sent by non-HTTP
898      applications, as is sometimes the case when retrieving or posting
899      messages via proxies/gateways to SMTP or NNTP.
900</t></list></t>
901<t>
902   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
903   (GMT), without exception. For the purposes of HTTP, GMT is exactly
904   equal to UTC (Coordinated Universal Time). This is indicated in the
905   first two formats by the inclusion of "GMT" as the three-letter
906   abbreviation for time zone, and &MUST; be assumed when reading the
907   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
908   additional LWS beyond that specifically included as SP in the
909   grammar.
910</t>
911<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"/>
912  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obsolete-date</x:ref>
913  <x:ref>obsolete-date</x:ref> = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
914  <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
915  <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
916  <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>
917  <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>
918                 ; day month year (e.g., 02 Jun 1982)
919  <x:ref>date2</x:ref>        = 2<x:ref>DIGIT</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
920                 ; day-month-year (e.g., 02-Jun-82)
921  <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> ))
922                 ; month day (e.g., Jun  2)
923  <x:ref>time</x:ref>         = 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref>
924                 ; 00:00:00 - 23:59:59
925  <x:ref>wkday</x:ref>        = s-Mon / s-Tue / s-Wed
926               / s-Thu / s-Fri / s-Sat / s-Sun
927  <x:ref>weekday</x:ref>      = l-Mon / l-Tue / l-Wed
928               / l-Thu / l-Fri / l-Sat / l-Sun
929  <x:ref>month</x:ref>        = s-Jan / s-Feb / s-Mar / s-Apr
930               / s-May / s-Jun / s-Jul / s-Aug
931               / s-Sep / s-Oct / s-Nov / s-Dec
932               
933  GMT   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
934
935  s-Mon = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
936  s-Tue = <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
937  s-Wed = <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
938  s-Thu = <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
939  s-Fri = <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
940  s-Sat = <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
941  s-Sun = <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
942
943  l-Mon = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence>          ; "Monday", case-sensitive
944  l-Tue = <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence>       ; "Tuesday", case-sensitive
945  l-Wed = <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
946  l-Thu = <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence>    ; "Thursday", case-sensitive
947  l-Fri = <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence>          ; "Friday", case-sensitive
948  l-Sat = <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence>    ; "Saturday", case-sensitive
949  l-Sun = <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence>          ; "Sunday", case-sensitive
950
951  s-Jan = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
952  s-Feb = <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
953  s-Mar = <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
954  s-Apr = <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
955  s-May = <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
956  s-Jun = <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
957  s-Jul = <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
958  s-Aug = <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
959  s-Sep = <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
960  s-Oct = <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
961  s-Nov = <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
962  s-Dec = <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
963</artwork></figure>
964<t>
965      <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
966      to their usage within the protocol stream. Clients and servers are
967      not required to use these formats for user presentation, request
968      logging, etc.
969</t>
970</section>
971</section>
972
973<section title="Transfer Codings" anchor="transfer.codings">
974  <x:anchor-alias value="parameter"/>
975  <x:anchor-alias value="transfer-coding"/>
976  <x:anchor-alias value="transfer-extension"/>
977<t>
978   Transfer-coding values are used to indicate an encoding
979   transformation that has been, can be, or may need to be applied to an
980   entity-body in order to ensure "safe transport" through the network.
981   This differs from a content coding in that the transfer-coding is a
982   property of the message, not of the original entity.
983</t>
984<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
985  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
986  <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> )
987</artwork></figure>
988<t anchor="rule.parameter">
989  <x:anchor-alias value="attribute"/>
990  <x:anchor-alias value="parameter"/>
991  <x:anchor-alias value="value"/>
992   Parameters are in  the form of attribute/value pairs.
993</t>
994<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"/>
995  <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>
996  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
997  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
998</artwork></figure>
999<t>
1000   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1001   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1002   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1003</t>
1004<t>
1005   Whenever a transfer-coding is applied to a message-body, the set of
1006   transfer-codings &MUST; include "chunked", unless the message indicates it
1007   is terminated by closing the connection. When the "chunked" transfer-coding
1008   is used, it &MUST; be the last transfer-coding applied to the
1009   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
1010   than once to a message-body. These rules allow the recipient to
1011   determine the transfer-length of the message (<xref target="message.length"/>).
1012</t>
1013<t>
1014   Transfer-codings are analogous to the Content-Transfer-Encoding
1015   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
1016   binary data over a 7-bit transport service. However, safe transport
1017   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1018   the only unsafe characteristic of message-bodies is the difficulty in
1019   determining the exact body length (<xref target="message.length"/>), or the desire to
1020   encrypt data over a shared transport.
1021</t>
1022<t>
1023   The Internet Assigned Numbers Authority (IANA) acts as a registry for
1024   transfer-coding value tokens. Initially, the registry contains the
1025   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
1026   "gzip", "compress", and "deflate" (&content-codings;).
1027</t>
1028<t>
1029   New transfer-coding value tokens &SHOULD; be registered in the same way
1030   as new content-coding value tokens (&content-codings;).
1031</t>
1032<t>
1033   A server which receives an entity-body with a transfer-coding it does
1034   not understand &SHOULD; return 501 (Not Implemented), and close the
1035   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1036   client.
1037</t>
1038
1039<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1040  <x:anchor-alias value="chunk"/>
1041  <x:anchor-alias value="Chunked-Body"/>
1042  <x:anchor-alias value="chunk-data"/>
1043  <x:anchor-alias value="chunk-ext"/>
1044  <x:anchor-alias value="chunk-ext-name"/>
1045  <x:anchor-alias value="chunk-ext-val"/>
1046  <x:anchor-alias value="chunk-size"/>
1047  <x:anchor-alias value="last-chunk"/>
1048  <x:anchor-alias value="trailer-part"/>
1049<t>
1050   The chunked encoding modifies the body of a message in order to
1051   transfer it as a series of chunks, each with its own size indicator,
1052   followed by an &OPTIONAL; trailer containing entity-header fields. This
1053   allows dynamically produced content to be transferred along with the
1054   information necessary for the recipient to verify that it has
1055   received the full message.
1056</t>
1057<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"/>
1058  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1059                   <x:ref>last-chunk</x:ref>
1060                   <x:ref>trailer-part</x:ref>
1061                   <x:ref>CRLF</x:ref>
1062 
1063  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1064                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1065  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1066  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1067 
1068  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
1069                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
1070  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1071  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1072  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1073  <x:ref>trailer-part</x:ref>   = *(<x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref>)
1074</artwork></figure>
1075<t>
1076   The chunk-size field is a string of hex digits indicating the size of
1077   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1078   zero, followed by the trailer, which is terminated by an empty line.
1079</t>
1080<t>
1081   The trailer allows the sender to include additional HTTP header
1082   fields at the end of the message. The Trailer header field can be
1083   used to indicate which header fields are included in a trailer (see
1084   <xref target="header.trailer"/>).
1085</t>
1086<t>
1087   A server using chunked transfer-coding in a response &MUST-NOT; use the
1088   trailer for any header fields unless at least one of the following is
1089   true:
1090  <list style="numbers">
1091    <t>the request included a TE header field that indicates "trailers" is
1092     acceptable in the transfer-coding of the  response, as described in
1093     <xref target="header.te"/>; or,</t>
1094
1095    <t>the server is the origin server for the response, the trailer
1096     fields consist entirely of optional metadata, and the recipient
1097     could use the message (in a manner acceptable to the origin server)
1098     without receiving this metadata.  In other words, the origin server
1099     is willing to accept the possibility that the trailer fields might
1100     be silently discarded along the path to the client.</t>
1101  </list>
1102</t>
1103<t>
1104   This requirement prevents an interoperability failure when the
1105   message is being received by an HTTP/1.1 (or later) proxy and
1106   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1107   compliance with the protocol would have necessitated a possibly
1108   infinite buffer on the proxy.
1109</t>
1110<t>
1111   A process for decoding the "chunked" transfer-coding
1112   can be represented in pseudo-code as:
1113</t>
1114<figure><artwork type="code">
1115  length := 0
1116  read chunk-size, chunk-ext (if any) and CRLF
1117  while (chunk-size &gt; 0) {
1118     read chunk-data and CRLF
1119     append chunk-data to entity-body
1120     length := length + chunk-size
1121     read chunk-size and CRLF
1122  }
1123  read entity-header
1124  while (entity-header not empty) {
1125     append entity-header to existing header fields
1126     read entity-header
1127  }
1128  Content-Length := length
1129  Remove "chunked" from Transfer-Encoding
1130</artwork></figure>
1131<t>
1132   All HTTP/1.1 applications &MUST; be able to receive and decode the
1133   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1134   they do not understand.
1135</t>
1136</section>
1137</section>
1138
1139<section title="Product Tokens" anchor="product.tokens">
1140  <x:anchor-alias value="product"/>
1141  <x:anchor-alias value="product-version"/>
1142<t>
1143   Product tokens are used to allow communicating applications to
1144   identify themselves by software name and version. Most fields using
1145   product tokens also allow sub-products which form a significant part
1146   of the application to be listed, separated by white space. By
1147   convention, the products are listed in order of their significance
1148   for identifying the application.
1149</t>
1150<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1151  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1152  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1153</artwork></figure>
1154<t>
1155   Examples:
1156</t>
1157<figure><artwork type="example">
1158    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1159    Server: Apache/0.8.4
1160</artwork></figure>
1161<t>
1162   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1163   used for advertising or other non-essential information. Although any
1164   token character &MAY; appear in a product-version, this token &SHOULD;
1165   only be used for a version identifier (i.e., successive versions of
1166   the same product &SHOULD; only differ in the product-version portion of
1167   the product value).
1168</t>
1169</section>
1170
1171</section>
1172
1173<section title="HTTP Message" anchor="http.message">
1174
1175<section title="Message Types" anchor="message.types">
1176  <x:anchor-alias value="generic-message"/>
1177  <x:anchor-alias value="HTTP-message"/>
1178  <x:anchor-alias value="start-line"/>
1179<t>
1180   HTTP messages consist of requests from client to server and responses
1181   from server to client.
1182</t>
1183<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1184  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1185</artwork></figure>
1186<t>
1187   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1188   message format of <xref target="RFC5322"/> for transferring entities (the payload
1189   of the message). Both types of message consist of a start-line, zero
1190   or more header fields (also known as "headers"), an empty line (i.e.,
1191   a line with nothing preceding the CRLF) indicating the end of the
1192   header fields, and possibly a message-body.
1193</t>
1194<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1195  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1196                    *(<x:ref>message-header</x:ref> <x:ref>CRLF</x:ref>)
1197                    <x:ref>CRLF</x:ref>
1198                    [ <x:ref>message-body</x:ref> ]
1199  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1200</artwork></figure>
1201<t>
1202   In the interest of robustness, servers &SHOULD; ignore any empty
1203   line(s) received where a Request-Line is expected. In other words, if
1204   the server is reading the protocol stream at the beginning of a
1205   message and receives a CRLF first, it should ignore the CRLF.
1206</t>
1207<t>
1208   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1209   after a POST request. To restate what is explicitly forbidden by the
1210   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1211   extra CRLF.
1212</t>
1213</section>
1214
1215<section title="Message Headers" anchor="message.headers">
1216  <x:anchor-alias value="field-content"/>
1217  <x:anchor-alias value="field-name"/>
1218  <x:anchor-alias value="field-value"/>
1219  <x:anchor-alias value="message-header"/>
1220<t>
1221   HTTP header fields, which include general-header (<xref target="general.header.fields"/>),
1222   request-header (&request-header-fields;), response-header (&response-header-fields;), and
1223   entity-header (&entity-header-fields;) fields, follow the same generic format as
1224   that given in <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1225   of a name followed by a colon (":") and the field value. Field names
1226   are case-insensitive. The field value &MAY; be preceded by any amount
1227   of LWS, though a single SP is preferred. Header fields can be
1228   extended over multiple lines by preceding each extra line with at
1229   least one SP or HTAB. Applications ought to follow "common form", where
1230   one is known or indicated, when generating HTTP constructs, since
1231   there might exist some implementations that fail to accept anything
1232   beyond the common forms.
1233</t>
1234<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"/>
1235  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" [ <x:ref>field-value</x:ref> ]
1236  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1237  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1238  <x:ref>field-content</x:ref>  = &lt;field content&gt;
1239</artwork></figure>
1240<t>
1241  <cref>whitespace between field-name and colon is an error and MUST NOT be accepted</cref>
1242</t>
1243<t>
1244   The field-content does not include any leading or trailing LWS:
1245   linear white space occurring before the first non-whitespace
1246   character of the field-value or after the last non-whitespace
1247   character of the field-value. Such leading or trailing LWS &MAY; be
1248   removed without changing the semantics of the field value. Any LWS
1249   that occurs between field-content &MAY; be replaced with a single SP
1250   before interpreting the field value or forwarding the message
1251   downstream.
1252</t>
1253<t>
1254   The order in which header fields with differing field names are
1255   received is not significant. However, it is "good practice" to send
1256   general-header fields first, followed by request-header or response-header
1257   fields, and ending with the entity-header fields.
1258</t>
1259<t>
1260   Multiple message-header fields with the same field-name &MAY; be
1261   present in a message if and only if the entire field-value for that
1262   header field is defined as a comma-separated list [i.e., #(values)].
1263   It &MUST; be possible to combine the multiple header fields into one
1264   "field-name: field-value" pair, without changing the semantics of the
1265   message, by appending each subsequent field-value to the first, each
1266   separated by a comma. The order in which header fields with the same
1267   field-name are received is therefore significant to the
1268   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1269   change the order of these field values when a message is forwarded.
1270</t>
1271<t>
1272  <list><t>
1273   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1274   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1275   can occur multiple times, but does not use the list syntax, and thus cannot
1276   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1277   for details.) Also note that the Set-Cookie2 header specified in
1278   <xref target="RFC2965"/> does not share this problem.
1279  </t></list>
1280</t>
1281 
1282</section>
1283
1284<section title="Message Body" anchor="message.body">
1285  <x:anchor-alias value="message-body"/>
1286<t>
1287   The message-body (if any) of an HTTP message is used to carry the
1288   entity-body associated with the request or response. The message-body
1289   differs from the entity-body only when a transfer-coding has been
1290   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1291</t>
1292<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1293  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1294               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1295</artwork></figure>
1296<t>
1297   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1298   applied by an application to ensure safe and proper transfer of the
1299   message. Transfer-Encoding is a property of the message, not of the
1300   entity, and thus &MAY; be added or removed by any application along the
1301   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1302   when certain transfer-codings may be used.)
1303</t>
1304<t>
1305   The rules for when a message-body is allowed in a message differ for
1306   requests and responses.
1307</t>
1308<t>
1309   The presence of a message-body in a request is signaled by the
1310   inclusion of a Content-Length or Transfer-Encoding header field in
1311   the request's message-headers. A message-body &MUST-NOT; be included in
1312   a request if the specification of the request method (&method;)
1313   explicitly disallows an entity-body in requests.
1314   When a request message contains both a message-body of non-zero
1315   length and a method that does not define any semantics for that
1316   request message-body, then an origin server &SHOULD; either ignore
1317   the message-body or respond with an appropriate error message
1318   (e.g., 413).  A proxy or gateway, when presented the same request,
1319   &SHOULD; either forward the request inbound with the message-body or
1320   ignore the message-body when determining a response.
1321</t>
1322<t>
1323   For response messages, whether or not a message-body is included with
1324   a message is dependent on both the request method and the response
1325   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1326   &MUST-NOT; include a message-body, even though the presence of entity-header
1327   fields might lead one to believe they do. All 1xx
1328   (informational), 204 (No Content), and 304 (Not Modified) responses
1329   &MUST-NOT; include a message-body. All other responses do include a
1330   message-body, although it &MAY; be of zero length.
1331</t>
1332</section>
1333
1334<section title="Message Length" anchor="message.length">
1335<t>
1336   The transfer-length of a message is the length of the message-body as
1337   it appears in the message; that is, after any transfer-codings have
1338   been applied. When a message-body is included with a message, the
1339   transfer-length of that body is determined by one of the following
1340   (in order of precedence):
1341</t>
1342<t>
1343  <list style="numbers">
1344    <x:lt><t>
1345     Any response message which "&MUST-NOT;" include a message-body (such
1346     as the 1xx, 204, and 304 responses and any response to a HEAD
1347     request) is always terminated by the first empty line after the
1348     header fields, regardless of the entity-header fields present in
1349     the message.
1350    </t></x:lt>
1351    <x:lt><t>
1352     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1353     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1354     is used, the transfer-length is defined by the use of this transfer-coding.
1355     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1356     is not present, the transfer-length is defined by the sender closing the connection.
1357    </t></x:lt>
1358    <x:lt><t>
1359     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1360     decimal value in OCTETs represents both the entity-length and the
1361     transfer-length. The Content-Length header field &MUST-NOT; be sent
1362     if these two lengths are different (i.e., if a Transfer-Encoding
1363     header field is present). If a message is received with both a
1364     Transfer-Encoding header field and a Content-Length header field,
1365     the latter &MUST; be ignored.
1366    </t></x:lt>
1367    <x:lt><t>
1368     If the message uses the media type "multipart/byteranges", and the
1369     transfer-length is not otherwise specified, then this self-delimiting
1370     media type defines the transfer-length. This media type
1371     &MUST-NOT; be used unless the sender knows that the recipient can parse
1372     it; the presence in a request of a Range header with multiple byte-range
1373     specifiers from a 1.1 client implies that the client can parse
1374     multipart/byteranges responses.
1375    <list style="empty"><t>
1376       A range header might be forwarded by a 1.0 proxy that does not
1377       understand multipart/byteranges; in this case the server &MUST;
1378       delimit the message using methods defined in items 1, 3 or 5 of
1379       this section.
1380    </t></list>
1381    </t></x:lt>
1382    <x:lt><t>
1383     By the server closing the connection. (Closing the connection
1384     cannot be used to indicate the end of a request body, since that
1385     would leave no possibility for the server to send back a response.)
1386    </t></x:lt>
1387  </list>
1388</t>
1389<t>
1390   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1391   containing a message-body &MUST; include a valid Content-Length header
1392   field unless the server is known to be HTTP/1.1 compliant. If a
1393   request contains a message-body and a Content-Length is not given,
1394   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1395   determine the length of the message, or with 411 (Length Required) if
1396   it wishes to insist on receiving a valid Content-Length.
1397</t>
1398<t>
1399   All HTTP/1.1 applications that receive entities &MUST; accept the
1400   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1401   to be used for messages when the message length cannot be determined
1402   in advance.
1403</t>
1404<t>
1405   Messages &MUST-NOT; include both a Content-Length header field and a
1406   transfer-coding. If the message does include a
1407   transfer-coding, the Content-Length &MUST; be ignored.
1408</t>
1409<t>
1410   When a Content-Length is given in a message where a message-body is
1411   allowed, its field value &MUST; exactly match the number of OCTETs in
1412   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1413   invalid length is received and detected.
1414</t>
1415</section>
1416
1417<section title="General Header Fields" anchor="general.header.fields">
1418  <x:anchor-alias value="general-header"/>
1419<t>
1420   There are a few header fields which have general applicability for
1421   both request and response messages, but which do not apply to the
1422   entity being transferred. These header fields apply only to the
1423   message being transmitted.
1424</t>
1425<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1426  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1427                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1428                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1429                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1430                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1431                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1432                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1433                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1434                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1435</artwork></figure>
1436<t>
1437   General-header field names can be extended reliably only in
1438   combination with a change in the protocol version. However, new or
1439   experimental header fields may be given the semantics of general
1440   header fields if all parties in the communication recognize them to
1441   be general-header fields. Unrecognized header fields are treated as
1442   entity-header fields.
1443</t>
1444</section>
1445</section>
1446
1447<section title="Request" anchor="request">
1448  <x:anchor-alias value="Request"/>
1449<t>
1450   A request message from a client to a server includes, within the
1451   first line of that message, the method to be applied to the resource,
1452   the identifier of the resource, and the protocol version in use.
1453</t>
1454<!--                 Host                      ; should be moved here eventually -->
1455<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1456  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1457                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1458                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1459                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1460                  <x:ref>CRLF</x:ref>
1461                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1462</artwork></figure>
1463
1464<section title="Request-Line" anchor="request-line">
1465  <x:anchor-alias value="Request-Line"/>
1466<t>
1467   The Request-Line begins with a method token, followed by the
1468   request-target and the protocol version, and ending with CRLF. The
1469   elements are separated by SP characters. No CR or LF is allowed
1470   except in the final CRLF sequence.
1471</t>
1472<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1473  <x:ref>Request-Line</x:ref>   = <x:ref>Method</x:ref> <x:ref>SP</x:ref> <x:ref>request-target</x:ref> <x:ref>SP</x:ref> <x:ref>HTTP-Version</x:ref> <x:ref>CRLF</x:ref>
1474</artwork></figure>
1475
1476<section title="Method" anchor="method">
1477  <x:anchor-alias value="Method"/>
1478<t>
1479   The Method  token indicates the method to be performed on the
1480   resource identified by the request-target. The method is case-sensitive.
1481</t>
1482<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1483  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1484</artwork></figure>
1485</section>
1486
1487<section title="request-target" anchor="request-target">
1488  <x:anchor-alias value="request-target"/>
1489<t>
1490   The request-target is a Uniform Resource Identifier (<xref target="uri"/>) and
1491   identifies the resource upon which to apply the request.
1492</t>
1493<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1494  <x:ref>request-target</x:ref>    = "*"
1495                 / <x:ref>absolute-URI</x:ref>
1496                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1497                 / <x:ref>authority</x:ref>
1498</artwork></figure>
1499<t>
1500   The four options for request-target are dependent on the nature of the
1501   request. The asterisk "*" means that the request does not apply to a
1502   particular resource, but to the server itself, and is only allowed
1503   when the method used does not necessarily apply to a resource. One
1504   example would be
1505</t>
1506<figure><artwork type="example">
1507    OPTIONS * HTTP/1.1
1508</artwork></figure>
1509<t>
1510   The absolute-URI form is &REQUIRED; when the request is being made to a
1511   proxy. The proxy is requested to forward the request or service it
1512   from a valid cache, and return the response. Note that the proxy &MAY;
1513   forward the request on to another proxy or directly to the server
1514   specified by the absolute-URI. In order to avoid request loops, a
1515   proxy &MUST; be able to recognize all of its server names, including
1516   any aliases, local variations, and the numeric IP address. An example
1517   Request-Line would be:
1518</t>
1519<figure><artwork type="example">
1520    GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1521</artwork></figure>
1522<t>
1523   To allow for transition to absolute-URIs in all requests in future
1524   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1525   form in requests, even though HTTP/1.1 clients will only generate
1526   them in requests to proxies.
1527</t>
1528<t>
1529   The authority form is only used by the CONNECT method (&CONNECT;).
1530</t>
1531<t>
1532   The most common form of request-target is that used to identify a
1533   resource on an origin server or gateway. In this case the absolute
1534   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1535   the request-target, and the network location of the URI (authority) &MUST;
1536   be transmitted in a Host header field. For example, a client wishing
1537   to retrieve the resource above directly from the origin server would
1538   create a TCP connection to port 80 of the host "www.example.org" and send
1539   the lines:
1540</t>
1541<figure><artwork type="example">
1542    GET /pub/WWW/TheProject.html HTTP/1.1
1543    Host: www.example.org
1544</artwork></figure>
1545<t>
1546   followed by the remainder of the Request. Note that the absolute path
1547   cannot be empty; if none is present in the original URI, it &MUST; be
1548   given as "/" (the server root).
1549</t>
1550<t>
1551   The request-target is transmitted in the format specified in
1552   <xref target="http.uri"/>. If the request-target is encoded using the
1553   "% <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding
1554   (<xref target="RFC3986" x:fmt="," x:sec="2.4"/>), the origin server
1555   &MUST; decode the request-target in order to
1556   properly interpret the request. Servers &SHOULD; respond to invalid
1557   request-targets with an appropriate status code.
1558</t>
1559<t>
1560   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1561   received request-target when forwarding it to the next inbound server,
1562   except as noted above to replace a null path-absolute with "/".
1563</t>
1564<t>
1565  <list><t>
1566      <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1567      meaning of the request when the origin server is improperly using
1568      a non-reserved URI character for a reserved purpose.  Implementors
1569      should be aware that some pre-HTTP/1.1 proxies have been known to
1570      rewrite the request-target.
1571  </t></list>
1572</t>
1573<t>
1574   HTTP does not place a pre-defined limit on the length of a request-target.
1575   A server &MUST; be prepared to receive URIs of unbounded length and
1576   respond with the 414 (URI too long) status if the received
1577   request-target would be longer than the server wishes to handle
1578   (see &status-414;).
1579</t>
1580<t>
1581   Various ad-hoc limitations on request-target length are found in practice.
1582   It is &RECOMMENDED; that all HTTP senders and recipients support
1583   request-target lengths of 8000 or more OCTETs.
1584</t>
1585</section>
1586</section>
1587
1588<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1589<t>
1590   The exact resource identified by an Internet request is determined by
1591   examining both the request-target and the Host header field.
1592</t>
1593<t>
1594   An origin server that does not allow resources to differ by the
1595   requested host &MAY; ignore the Host header field value when
1596   determining the resource identified by an HTTP/1.1 request. (But see
1597   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1598   for other requirements on Host support in HTTP/1.1.)
1599</t>
1600<t>
1601   An origin server that does differentiate resources based on the host
1602   requested (sometimes referred to as virtual hosts or vanity host
1603   names) &MUST; use the following rules for determining the requested
1604   resource on an HTTP/1.1 request:
1605  <list style="numbers">
1606    <t>If request-target is an absolute-URI, the host is part of the
1607     request-target. Any Host header field value in the request &MUST; be
1608     ignored.</t>
1609    <t>If the request-target is not an absolute-URI, and the request includes
1610     a Host header field, the host is determined by the Host header
1611     field value.</t>
1612    <t>If the host as determined by rule 1 or 2 is not a valid host on
1613     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1614  </list>
1615</t>
1616<t>
1617   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1618   attempt to use heuristics (e.g., examination of the URI path for
1619   something unique to a particular host) in order to determine what
1620   exact resource is being requested.
1621</t>
1622</section>
1623
1624</section>
1625
1626
1627<section title="Response" anchor="response">
1628  <x:anchor-alias value="Response"/>
1629<t>
1630   After receiving and interpreting a request message, a server responds
1631   with an HTTP response message.
1632</t>
1633<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1634  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1635                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1636                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1637                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1638                  <x:ref>CRLF</x:ref>
1639                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1640</artwork></figure>
1641
1642<section title="Status-Line" anchor="status-line">
1643  <x:anchor-alias value="Status-Line"/>
1644<t>
1645   The first line of a Response message is the Status-Line, consisting
1646   of the protocol version followed by a numeric status code and its
1647   associated textual phrase, with each element separated by SP
1648   characters. No CR or LF is allowed except in the final CRLF sequence.
1649</t>
1650<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1651  <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>
1652</artwork></figure>
1653
1654<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1655  <x:anchor-alias value="Reason-Phrase"/>
1656  <x:anchor-alias value="Status-Code"/>
1657<t>
1658   The Status-Code element is a 3-digit integer result code of the
1659   attempt to understand and satisfy the request. These codes are fully
1660   defined in &status-codes;.  The Reason Phrase exists for the sole
1661   purpose of providing a textual description associated with the numeric
1662   status code, out of deference to earlier Internet application protocols
1663   that were more frequently used with interactive text clients.
1664   A client &SHOULD; ignore the content of the Reason Phrase.
1665</t>
1666<t>
1667   The first digit of the Status-Code defines the class of response. The
1668   last two digits do not have any categorization role. There are 5
1669   values for the first digit:
1670  <list style="symbols">
1671    <t>
1672      1xx: Informational - Request received, continuing process
1673    </t>
1674    <t>
1675      2xx: Success - The action was successfully received,
1676        understood, and accepted
1677    </t>
1678    <t>
1679      3xx: Redirection - Further action must be taken in order to
1680        complete the request
1681    </t>
1682    <t>
1683      4xx: Client Error - The request contains bad syntax or cannot
1684        be fulfilled
1685    </t>
1686    <t>
1687      5xx: Server Error - The server failed to fulfill an apparently
1688        valid request
1689    </t>
1690  </list>
1691</t>
1692<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"/>
1693  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1694  <x:ref>Reason-Phrase</x:ref>  = *&lt;<x:ref>TEXT</x:ref>, excluding <x:ref>CR</x:ref>, <x:ref>LF</x:ref>&gt;
1695</artwork></figure>
1696</section>
1697</section>
1698
1699</section>
1700
1701
1702<section title="Connections" anchor="connections">
1703
1704<section title="Persistent Connections" anchor="persistent.connections">
1705
1706<section title="Purpose" anchor="persistent.purpose">
1707<t>
1708   Prior to persistent connections, a separate TCP connection was
1709   established to fetch each URL, increasing the load on HTTP servers
1710   and causing congestion on the Internet. The use of inline images and
1711   other associated data often require a client to make multiple
1712   requests of the same server in a short amount of time. Analysis of
1713   these performance problems and results from a prototype
1714   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1715   measurements of actual HTTP/1.1 (<xref target="RFC2068" x:fmt="none">RFC 2068</xref>) implementations show good
1716   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1717   T/TCP <xref target="Tou1998"/>.
1718</t>
1719<t>
1720   Persistent HTTP connections have a number of advantages:
1721  <list style="symbols">
1722      <t>
1723        By opening and closing fewer TCP connections, CPU time is saved
1724        in routers and hosts (clients, servers, proxies, gateways,
1725        tunnels, or caches), and memory used for TCP protocol control
1726        blocks can be saved in hosts.
1727      </t>
1728      <t>
1729        HTTP requests and responses can be pipelined on a connection.
1730        Pipelining allows a client to make multiple requests without
1731        waiting for each response, allowing a single TCP connection to
1732        be used much more efficiently, with much lower elapsed time.
1733      </t>
1734      <t>
1735        Network congestion is reduced by reducing the number of packets
1736        caused by TCP opens, and by allowing TCP sufficient time to
1737        determine the congestion state of the network.
1738      </t>
1739      <t>
1740        Latency on subsequent requests is reduced since there is no time
1741        spent in TCP's connection opening handshake.
1742      </t>
1743      <t>
1744        HTTP can evolve more gracefully, since errors can be reported
1745        without the penalty of closing the TCP connection. Clients using
1746        future versions of HTTP might optimistically try a new feature,
1747        but if communicating with an older server, retry with old
1748        semantics after an error is reported.
1749      </t>
1750    </list>
1751</t>
1752<t>
1753   HTTP implementations &SHOULD; implement persistent connections.
1754</t>
1755</section>
1756
1757<section title="Overall Operation" anchor="persistent.overall">
1758<t>
1759   A significant difference between HTTP/1.1 and earlier versions of
1760   HTTP is that persistent connections are the default behavior of any
1761   HTTP connection. That is, unless otherwise indicated, the client
1762   &SHOULD; assume that the server will maintain a persistent connection,
1763   even after error responses from the server.
1764</t>
1765<t>
1766   Persistent connections provide a mechanism by which a client and a
1767   server can signal the close of a TCP connection. This signaling takes
1768   place using the Connection header field (<xref target="header.connection"/>). Once a close
1769   has been signaled, the client &MUST-NOT; send any more requests on that
1770   connection.
1771</t>
1772
1773<section title="Negotiation" anchor="persistent.negotiation">
1774<t>
1775   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1776   maintain a persistent connection unless a Connection header including
1777   the connection-token "close" was sent in the request. If the server
1778   chooses to close the connection immediately after sending the
1779   response, it &SHOULD; send a Connection header including the
1780   connection-token close.
1781</t>
1782<t>
1783   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1784   decide to keep it open based on whether the response from a server
1785   contains a Connection header with the connection-token close. In case
1786   the client does not want to maintain a connection for more than that
1787   request, it &SHOULD; send a Connection header including the
1788   connection-token close.
1789</t>
1790<t>
1791   If either the client or the server sends the close token in the
1792   Connection header, that request becomes the last one for the
1793   connection.
1794</t>
1795<t>
1796   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1797   maintained for HTTP versions less than 1.1 unless it is explicitly
1798   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1799   compatibility with HTTP/1.0 clients.
1800</t>
1801<t>
1802   In order to remain persistent, all messages on the connection &MUST;
1803   have a self-defined message length (i.e., one not defined by closure
1804   of the connection), as described in <xref target="message.length"/>.
1805</t>
1806</section>
1807
1808<section title="Pipelining" anchor="pipelining">
1809<t>
1810   A client that supports persistent connections &MAY; "pipeline" its
1811   requests (i.e., send multiple requests without waiting for each
1812   response). A server &MUST; send its responses to those requests in the
1813   same order that the requests were received.
1814</t>
1815<t>
1816   Clients which assume persistent connections and pipeline immediately
1817   after connection establishment &SHOULD; be prepared to retry their
1818   connection if the first pipelined attempt fails. If a client does
1819   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1820   persistent. Clients &MUST; also be prepared to resend their requests if
1821   the server closes the connection before sending all of the
1822   corresponding responses.
1823</t>
1824<t>
1825   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1826   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1827   premature termination of the transport connection could lead to
1828   indeterminate results. A client wishing to send a non-idempotent
1829   request &SHOULD; wait to send that request until it has received the
1830   response status for the previous request.
1831</t>
1832</section>
1833</section>
1834
1835<section title="Proxy Servers" anchor="persistent.proxy">
1836<t>
1837   It is especially important that proxies correctly implement the
1838   properties of the Connection header field as specified in <xref target="header.connection"/>.
1839</t>
1840<t>
1841   The proxy server &MUST; signal persistent connections separately with
1842   its clients and the origin servers (or other proxy servers) that it
1843   connects to. Each persistent connection applies to only one transport
1844   link.
1845</t>
1846<t>
1847   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1848   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
1849   discussion of the problems with the Keep-Alive header implemented by
1850   many HTTP/1.0 clients).
1851</t>
1852</section>
1853
1854<section title="Practical Considerations" anchor="persistent.practical">
1855<t>
1856   Servers will usually have some time-out value beyond which they will
1857   no longer maintain an inactive connection. Proxy servers might make
1858   this a higher value since it is likely that the client will be making
1859   more connections through the same server. The use of persistent
1860   connections places no requirements on the length (or existence) of
1861   this time-out for either the client or the server.
1862</t>
1863<t>
1864   When a client or server wishes to time-out it &SHOULD; issue a graceful
1865   close on the transport connection. Clients and servers &SHOULD; both
1866   constantly watch for the other side of the transport close, and
1867   respond to it as appropriate. If a client or server does not detect
1868   the other side's close promptly it could cause unnecessary resource
1869   drain on the network.
1870</t>
1871<t>
1872   A client, server, or proxy &MAY; close the transport connection at any
1873   time. For example, a client might have started to send a new request
1874   at the same time that the server has decided to close the "idle"
1875   connection. From the server's point of view, the connection is being
1876   closed while it was idle, but from the client's point of view, a
1877   request is in progress.
1878</t>
1879<t>
1880   This means that clients, servers, and proxies &MUST; be able to recover
1881   from asynchronous close events. Client software &SHOULD; reopen the
1882   transport connection and retransmit the aborted sequence of requests
1883   without user interaction so long as the request sequence is
1884   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1885   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1886   human operator the choice of retrying the request(s). Confirmation by
1887   user-agent software with semantic understanding of the application
1888   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
1889   be repeated if the second sequence of requests fails.
1890</t>
1891<t>
1892   Servers &SHOULD; always respond to at least one request per connection,
1893   if at all possible. Servers &SHOULD-NOT;  close a connection in the
1894   middle of transmitting a response, unless a network or client failure
1895   is suspected.
1896</t>
1897<t>
1898   Clients that use persistent connections &SHOULD; limit the number of
1899   simultaneous connections that they maintain to a given server. A
1900   single-user client &SHOULD-NOT; maintain more than 2 connections with
1901   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
1902   another server or proxy, where N is the number of simultaneously
1903   active users. These guidelines are intended to improve HTTP response
1904   times and avoid congestion.
1905</t>
1906</section>
1907</section>
1908
1909<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
1910
1911<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
1912<t>
1913   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
1914   flow control mechanisms to resolve temporary overloads, rather than
1915   terminating connections with the expectation that clients will retry.
1916   The latter technique can exacerbate network congestion.
1917</t>
1918</section>
1919
1920<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
1921<t>
1922   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
1923   the network connection for an error status while it is transmitting
1924   the request. If the client sees an error status, it &SHOULD;
1925   immediately cease transmitting the body. If the body is being sent
1926   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
1927   empty trailer &MAY; be used to prematurely mark the end of the message.
1928   If the body was preceded by a Content-Length header, the client &MUST;
1929   close the connection.
1930</t>
1931</section>
1932
1933<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
1934<t>
1935   The purpose of the 100 (Continue) status (see &status-100;) is to
1936   allow a client that is sending a request message with a request body
1937   to determine if the origin server is willing to accept the request
1938   (based on the request headers) before the client sends the request
1939   body. In some cases, it might either be inappropriate or highly
1940   inefficient for the client to send the body if the server will reject
1941   the message without looking at the body.
1942</t>
1943<t>
1944   Requirements for HTTP/1.1 clients:
1945  <list style="symbols">
1946    <t>
1947        If a client will wait for a 100 (Continue) response before
1948        sending the request body, it &MUST; send an Expect request-header
1949        field (&header-expect;) with the "100-continue" expectation.
1950    </t>
1951    <t>
1952        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
1953        with the "100-continue" expectation if it does not intend
1954        to send a request body.
1955    </t>
1956  </list>
1957</t>
1958<t>
1959   Because of the presence of older implementations, the protocol allows
1960   ambiguous situations in which a client may send "Expect: 100-continue"
1961   without receiving either a 417 (Expectation Failed) status
1962   or a 100 (Continue) status. Therefore, when a client sends this
1963   header field to an origin server (possibly via a proxy) from which it
1964   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
1965   for an indefinite period before sending the request body.
1966</t>
1967<t>
1968   Requirements for HTTP/1.1 origin servers:
1969  <list style="symbols">
1970    <t> Upon receiving a request which includes an Expect request-header
1971        field with the "100-continue" expectation, an origin server &MUST;
1972        either respond with 100 (Continue) status and continue to read
1973        from the input stream, or respond with a final status code. The
1974        origin server &MUST-NOT; wait for the request body before sending
1975        the 100 (Continue) response. If it responds with a final status
1976        code, it &MAY; close the transport connection or it &MAY; continue
1977        to read and discard the rest of the request.  It &MUST-NOT;
1978        perform the requested method if it returns a final status code.
1979    </t>
1980    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
1981        the request message does not include an Expect request-header
1982        field with the "100-continue" expectation, and &MUST-NOT; send a
1983        100 (Continue) response if such a request comes from an HTTP/1.0
1984        (or earlier) client. There is an exception to this rule: for
1985        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
1986        status in response to an HTTP/1.1 PUT or POST request that does
1987        not include an Expect request-header field with the "100-continue"
1988        expectation. This exception, the purpose of which is
1989        to minimize any client processing delays associated with an
1990        undeclared wait for 100 (Continue) status, applies only to
1991        HTTP/1.1 requests, and not to requests with any other HTTP-version
1992        value.
1993    </t>
1994    <t> An origin server &MAY; omit a 100 (Continue) response if it has
1995        already received some or all of the request body for the
1996        corresponding request.
1997    </t>
1998    <t> An origin server that sends a 100 (Continue) response &MUST;
1999    ultimately send a final status code, once the request body is
2000        received and processed, unless it terminates the transport
2001        connection prematurely.
2002    </t>
2003    <t> If an origin server receives a request that does not include an
2004        Expect request-header field with the "100-continue" expectation,
2005        the request includes a request body, and the server responds
2006        with a final status code before reading the entire request body
2007        from the transport connection, then the server &SHOULD-NOT;  close
2008        the transport connection until it has read the entire request,
2009        or until the client closes the connection. Otherwise, the client
2010        might not reliably receive the response message. However, this
2011        requirement is not be construed as preventing a server from
2012        defending itself against denial-of-service attacks, or from
2013        badly broken client implementations.
2014      </t>
2015    </list>
2016</t>
2017<t>
2018   Requirements for HTTP/1.1 proxies:
2019  <list style="symbols">
2020    <t> If a proxy receives a request that includes an Expect request-header
2021        field with the "100-continue" expectation, and the proxy
2022        either knows that the next-hop server complies with HTTP/1.1 or
2023        higher, or does not know the HTTP version of the next-hop
2024        server, it &MUST; forward the request, including the Expect header
2025        field.
2026    </t>
2027    <t> If the proxy knows that the version of the next-hop server is
2028        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2029        respond with a 417 (Expectation Failed) status.
2030    </t>
2031    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2032        numbers received from recently-referenced next-hop servers.
2033    </t>
2034    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2035        request message was received from an HTTP/1.0 (or earlier)
2036        client and did not include an Expect request-header field with
2037        the "100-continue" expectation. This requirement overrides the
2038        general rule for forwarding of 1xx responses (see &status-1xx;).
2039    </t>
2040  </list>
2041</t>
2042</section>
2043
2044<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2045<t>
2046   If an HTTP/1.1 client sends a request which includes a request body,
2047   but which does not include an Expect request-header field with the
2048   "100-continue" expectation, and if the client is not directly
2049   connected to an HTTP/1.1 origin server, and if the client sees the
2050   connection close before receiving any status from the server, the
2051   client &SHOULD; retry the request.  If the client does retry this
2052   request, it &MAY; use the following "binary exponential backoff"
2053   algorithm to be assured of obtaining a reliable response:
2054  <list style="numbers">
2055    <t>
2056      Initiate a new connection to the server
2057    </t>
2058    <t>
2059      Transmit the request-headers
2060    </t>
2061    <t>
2062      Initialize a variable R to the estimated round-trip time to the
2063         server (e.g., based on the time it took to establish the
2064         connection), or to a constant value of 5 seconds if the round-trip
2065         time is not available.
2066    </t>
2067    <t>
2068       Compute T = R * (2**N), where N is the number of previous
2069         retries of this request.
2070    </t>
2071    <t>
2072       Wait either for an error response from the server, or for T
2073         seconds (whichever comes first)
2074    </t>
2075    <t>
2076       If no error response is received, after T seconds transmit the
2077         body of the request.
2078    </t>
2079    <t>
2080       If client sees that the connection is closed prematurely,
2081         repeat from step 1 until the request is accepted, an error
2082         response is received, or the user becomes impatient and
2083         terminates the retry process.
2084    </t>
2085  </list>
2086</t>
2087<t>
2088   If at any point an error status is received, the client
2089  <list style="symbols">
2090      <t>&SHOULD-NOT;  continue and</t>
2091
2092      <t>&SHOULD; close the connection if it has not completed sending the
2093        request message.</t>
2094    </list>
2095</t>
2096</section>
2097</section>
2098</section>
2099
2100
2101<section title="Header Field Definitions" anchor="header.fields">
2102<t>
2103   This section defines the syntax and semantics of HTTP/1.1 header fields
2104   related to message framing and transport protocols.
2105</t>
2106<t>
2107   For entity-header fields, both sender and recipient refer to either the
2108   client or the server, depending on who sends and who receives the entity.
2109</t>
2110
2111<section title="Connection" anchor="header.connection">
2112  <iref primary="true" item="Connection header" x:for-anchor=""/>
2113  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2114  <x:anchor-alias value="Connection"/>
2115  <x:anchor-alias value="connection-token"/>
2116  <x:anchor-alias value="Connection-v"/>
2117<t>
2118   The general-header field "Connection" allows the sender to specify
2119   options that are desired for that particular connection and &MUST-NOT;
2120   be communicated by proxies over further connections.
2121</t>
2122<t>
2123   The Connection header's value has the following grammar:
2124</t>
2125<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"/>
2126  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2127  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2128  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2129</artwork></figure>
2130<t>
2131   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2132   message is forwarded and, for each connection-token in this field,
2133   remove any header field(s) from the message with the same name as the
2134   connection-token. Connection options are signaled by the presence of
2135   a connection-token in the Connection header field, not by any
2136   corresponding additional header field(s), since the additional header
2137   field may not be sent if there are no parameters associated with that
2138   connection option.
2139</t>
2140<t>
2141   Message headers listed in the Connection header &MUST-NOT; include
2142   end-to-end headers, such as Cache-Control.
2143</t>
2144<t>
2145   HTTP/1.1 defines the "close" connection option for the sender to
2146   signal that the connection will be closed after completion of the
2147   response. For example,
2148</t>
2149<figure><artwork type="example">
2150  Connection: close
2151</artwork></figure>
2152<t>
2153   in either the request or the response header fields indicates that
2154   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2155   after the current request/response is complete.
2156</t>
2157<t>
2158   An HTTP/1.1 client that does not support persistent connections &MUST;
2159   include the "close" connection option in every request message.
2160</t>
2161<t>
2162   An HTTP/1.1 server that does not support persistent connections &MUST;
2163   include the "close" connection option in every response message that
2164   does not have a 1xx (informational) status code.
2165</t>
2166<t>
2167   A system receiving an HTTP/1.0 (or lower-version) message that
2168   includes a Connection header &MUST;, for each connection-token in this
2169   field, remove and ignore any header field(s) from the message with
2170   the same name as the connection-token. This protects against mistaken
2171   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2172</t>
2173</section>
2174
2175<section title="Content-Length" anchor="header.content-length">
2176  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2177  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2178  <x:anchor-alias value="Content-Length"/>
2179  <x:anchor-alias value="Content-Length-v"/>
2180<t>
2181   The entity-header field "Content-Length" indicates the size of the
2182   entity-body, in decimal number of OCTETs, sent to the recipient or,
2183   in the case of the HEAD method, the size of the entity-body that
2184   would have been sent had the request been a GET.
2185</t>
2186<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2187  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2188  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2189</artwork></figure>
2190<t>
2191   An example is
2192</t>
2193<figure><artwork type="example">
2194  Content-Length: 3495
2195</artwork></figure>
2196<t>
2197   Applications &SHOULD; use this field to indicate the transfer-length of
2198   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2199</t>
2200<t>
2201   Any Content-Length greater than or equal to zero is a valid value.
2202   <xref target="message.length"/> describes how to determine the length of a message-body
2203   if a Content-Length is not given.
2204</t>
2205<t>
2206   Note that the meaning of this field is significantly different from
2207   the corresponding definition in MIME, where it is an optional field
2208   used within the "message/external-body" content-type. In HTTP, it
2209   &SHOULD; be sent whenever the message's length can be determined prior
2210   to being transferred, unless this is prohibited by the rules in
2211   <xref target="message.length"/>.
2212</t>
2213</section>
2214
2215<section title="Date" anchor="header.date">
2216  <iref primary="true" item="Date header" x:for-anchor=""/>
2217  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2218  <x:anchor-alias value="Date"/>
2219  <x:anchor-alias value="Date-v"/>
2220<t>
2221   The general-header field "Date" represents the date and time at which
2222   the message was originated, having the same semantics as orig-date in
2223   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2224   HTTP-date, as described in <xref target="full.date"/>;
2225   it &MUST; be sent in rfc1123-date format.
2226</t>
2227<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2228  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2229  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2230</artwork></figure>
2231<t>
2232   An example is
2233</t>
2234<figure><artwork type="example">
2235  Date: Tue, 15 Nov 1994 08:12:31 GMT
2236</artwork></figure>
2237<t>
2238   Origin servers &MUST; include a Date header field in all responses,
2239   except in these cases:
2240  <list style="numbers">
2241      <t>If the response status code is 100 (Continue) or 101 (Switching
2242         Protocols), the response &MAY; include a Date header field, at
2243         the server's option.</t>
2244
2245      <t>If the response status code conveys a server error, e.g. 500
2246         (Internal Server Error) or 503 (Service Unavailable), and it is
2247         inconvenient or impossible to generate a valid Date.</t>
2248
2249      <t>If the server does not have a clock that can provide a
2250         reasonable approximation of the current time, its responses
2251         &MUST-NOT; include a Date header field. In this case, the rules
2252         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2253  </list>
2254</t>
2255<t>
2256   A received message that does not have a Date header field &MUST; be
2257   assigned one by the recipient if the message will be cached by that
2258   recipient or gatewayed via a protocol which requires a Date. An HTTP
2259   implementation without a clock &MUST-NOT; cache responses without
2260   revalidating them on every use. An HTTP cache, especially a shared
2261   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2262   clock with a reliable external standard.
2263</t>
2264<t>
2265   Clients &SHOULD; only send a Date header field in messages that include
2266   an entity-body, as in the case of the PUT and POST requests, and even
2267   then it is optional. A client without a clock &MUST-NOT; send a Date
2268   header field in a request.
2269</t>
2270<t>
2271   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2272   time subsequent to the generation of the message. It &SHOULD; represent
2273   the best available approximation of the date and time of message
2274   generation, unless the implementation has no means of generating a
2275   reasonably accurate date and time. In theory, the date ought to
2276   represent the moment just before the entity is generated. In
2277   practice, the date can be generated at any time during the message
2278   origination without affecting its semantic value.
2279</t>
2280
2281<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2282<t>
2283   Some origin server implementations might not have a clock available.
2284   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2285   values to a response, unless these values were associated
2286   with the resource by a system or user with a reliable clock. It &MAY;
2287   assign an Expires value that is known, at or before server
2288   configuration time, to be in the past (this allows "pre-expiration"
2289   of responses without storing separate Expires values for each
2290   resource).
2291</t>
2292</section>
2293</section>
2294
2295<section title="Host" anchor="header.host">
2296  <iref primary="true" item="Host header" x:for-anchor=""/>
2297  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2298  <x:anchor-alias value="Host"/>
2299  <x:anchor-alias value="Host-v"/>
2300<t>
2301   The request-header field "Host" specifies the Internet host and port
2302   number of the resource being requested, as obtained from the original
2303   URI given by the user or referring resource (generally an http URI,
2304   as described in <xref target="http.uri"/>). The Host field value &MUST; represent
2305   the naming authority of the origin server or gateway given by the
2306   original URL. This allows the origin server or gateway to
2307   differentiate between internally-ambiguous URLs, such as the root "/"
2308   URL of a server for multiple host names on a single IP address.
2309</t>
2310<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2311  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2312  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2313</artwork></figure>
2314<t>
2315   A "host" without any trailing port information implies the default
2316   port for the service requested (e.g., "80" for an HTTP URL). For
2317   example, a request on the origin server for
2318   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2319</t>
2320<figure><artwork type="example">
2321  GET /pub/WWW/ HTTP/1.1
2322  Host: www.example.org
2323</artwork></figure>
2324<t>
2325   A client &MUST; include a Host header field in all HTTP/1.1 request
2326   messages. If the requested URI does not include an Internet host
2327   name for the service being requested, then the Host header field &MUST;
2328   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2329   request message it forwards does contain an appropriate Host header
2330   field that identifies the service being requested by the proxy. All
2331   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2332   status code to any HTTP/1.1 request message which lacks a Host header
2333   field.
2334</t>
2335<t>
2336   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2337   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2338   for other requirements relating to Host.
2339</t>
2340</section>
2341
2342<section title="TE" anchor="header.te">
2343  <iref primary="true" item="TE header" x:for-anchor=""/>
2344  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2345  <x:anchor-alias value="TE"/>
2346  <x:anchor-alias value="TE-v"/>
2347  <x:anchor-alias value="t-codings"/>
2348<t>
2349   The request-header field "TE" indicates what extension transfer-codings
2350   it is willing to accept in the response and whether or not it is
2351   willing to accept trailer fields in a chunked transfer-coding. Its
2352   value may consist of the keyword "trailers" and/or a comma-separated
2353   list of extension transfer-coding names with optional accept
2354   parameters (as described in <xref target="transfer.codings"/>).
2355</t>
2356<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"/>
2357  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2358  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2359  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>accept-params</x:ref> ] )
2360</artwork></figure>
2361<t>
2362   The presence of the keyword "trailers" indicates that the client is
2363   willing to accept trailer fields in a chunked transfer-coding, as
2364   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2365   transfer-coding values even though it does not itself represent a
2366   transfer-coding.
2367</t>
2368<t>
2369   Examples of its use are:
2370</t>
2371<figure><artwork type="example">
2372  TE: deflate
2373  TE:
2374  TE: trailers, deflate;q=0.5
2375</artwork></figure>
2376<t>
2377   The TE header field only applies to the immediate connection.
2378   Therefore, the keyword &MUST; be supplied within a Connection header
2379   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2380</t>
2381<t>
2382   A server tests whether a transfer-coding is acceptable, according to
2383   a TE field, using these rules:
2384  <list style="numbers">
2385    <x:lt>
2386      <t>The "chunked" transfer-coding is always acceptable. If the
2387         keyword "trailers" is listed, the client indicates that it is
2388         willing to accept trailer fields in the chunked response on
2389         behalf of itself and any downstream clients. The implication is
2390         that, if given, the client is stating that either all
2391         downstream clients are willing to accept trailer fields in the
2392         forwarded response, or that it will attempt to buffer the
2393         response on behalf of downstream recipients.
2394      </t><t>
2395         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2396         chunked response such that a client can be assured of buffering
2397         the entire response.</t>
2398    </x:lt>
2399    <x:lt>
2400      <t>If the transfer-coding being tested is one of the transfer-codings
2401         listed in the TE field, then it is acceptable unless it
2402         is accompanied by a qvalue of 0. (As defined in &qvalue;, a
2403         qvalue of 0 means "not acceptable.")</t>
2404    </x:lt>
2405    <x:lt>
2406      <t>If multiple transfer-codings are acceptable, then the
2407         acceptable transfer-coding with the highest non-zero qvalue is
2408         preferred.  The "chunked" transfer-coding always has a qvalue
2409         of 1.</t>
2410    </x:lt>
2411  </list>
2412</t>
2413<t>
2414   If the TE field-value is empty or if no TE field is present, the only
2415   transfer-coding  is "chunked". A message with no transfer-coding is
2416   always acceptable.
2417</t>
2418</section>
2419
2420<section title="Trailer" anchor="header.trailer">
2421  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2422  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2423  <x:anchor-alias value="Trailer"/>
2424  <x:anchor-alias value="Trailer-v"/>
2425<t>
2426   The general field "Trailer" indicates that the given set of
2427   header fields is present in the trailer of a message encoded with
2428   chunked transfer-coding.
2429</t>
2430<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
2431  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
2432  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
2433</artwork></figure>
2434<t>
2435   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2436   message using chunked transfer-coding with a non-empty trailer. Doing
2437   so allows the recipient to know which header fields to expect in the
2438   trailer.
2439</t>
2440<t>
2441   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2442   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2443   trailer fields in a "chunked" transfer-coding.
2444</t>
2445<t>
2446   Message header fields listed in the Trailer header field &MUST-NOT;
2447   include the following header fields:
2448  <list style="symbols">
2449    <t>Transfer-Encoding</t>
2450    <t>Content-Length</t>
2451    <t>Trailer</t>
2452  </list>
2453</t>
2454</section>
2455
2456<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2457  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2458  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2459  <x:anchor-alias value="Transfer-Encoding"/>
2460  <x:anchor-alias value="Transfer-Encoding-v"/>
2461<t>
2462   The general-header "Transfer-Encoding" field indicates what (if any)
2463   type of transformation has been applied to the message body in order
2464   to safely transfer it between the sender and the recipient. This
2465   differs from the content-coding in that the transfer-coding is a
2466   property of the message, not of the entity.
2467</t>
2468<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
2469  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
2470                        <x:ref>Transfer-Encoding-v</x:ref>
2471  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
2472</artwork></figure>
2473<t>
2474   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2475</t>
2476<figure><artwork type="example">
2477  Transfer-Encoding: chunked
2478</artwork></figure>
2479<t>
2480   If multiple encodings have been applied to an entity, the transfer-codings
2481   &MUST; be listed in the order in which they were applied.
2482   Additional information about the encoding parameters &MAY; be provided
2483   by other entity-header fields not defined by this specification.
2484</t>
2485<t>
2486   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2487   header.
2488</t>
2489</section>
2490
2491<section title="Upgrade" anchor="header.upgrade">
2492  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2493  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2494  <x:anchor-alias value="Upgrade"/>
2495  <x:anchor-alias value="Upgrade-v"/>
2496<t>
2497   The general-header "Upgrade" allows the client to specify what
2498   additional communication protocols it supports and would like to use
2499   if the server finds it appropriate to switch protocols. The server
2500   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2501   response to indicate which protocol(s) are being switched.
2502</t>
2503<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
2504  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
2505  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
2506</artwork></figure>
2507<t>
2508   For example,
2509</t>
2510<figure><artwork type="example">
2511  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2512</artwork></figure>
2513<t>
2514   The Upgrade header field is intended to provide a simple mechanism
2515   for transition from HTTP/1.1 to some other, incompatible protocol. It
2516   does so by allowing the client to advertise its desire to use another
2517   protocol, such as a later version of HTTP with a higher major version
2518   number, even though the current request has been made using HTTP/1.1.
2519   This eases the difficult transition between incompatible protocols by
2520   allowing the client to initiate a request in the more commonly
2521   supported protocol while indicating to the server that it would like
2522   to use a "better" protocol if available (where "better" is determined
2523   by the server, possibly according to the nature of the method and/or
2524   resource being requested).
2525</t>
2526<t>
2527   The Upgrade header field only applies to switching application-layer
2528   protocols upon the existing transport-layer connection. Upgrade
2529   cannot be used to insist on a protocol change; its acceptance and use
2530   by the server is optional. The capabilities and nature of the
2531   application-layer communication after the protocol change is entirely
2532   dependent upon the new protocol chosen, although the first action
2533   after changing the protocol &MUST; be a response to the initial HTTP
2534   request containing the Upgrade header field.
2535</t>
2536<t>
2537   The Upgrade header field only applies to the immediate connection.
2538   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2539   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2540   HTTP/1.1 message.
2541</t>
2542<t>
2543   The Upgrade header field cannot be used to indicate a switch to a
2544   protocol on a different connection. For that purpose, it is more
2545   appropriate to use a 301, 302, 303, or 305 redirection response.
2546</t>
2547<t>
2548   This specification only defines the protocol name "HTTP" for use by
2549   the family of Hypertext Transfer Protocols, as defined by the HTTP
2550   version rules of <xref target="http.version"/> and future updates to this
2551   specification. Any token can be used as a protocol name; however, it
2552   will only be useful if both the client and server associate the name
2553   with the same protocol.
2554</t>
2555</section>
2556
2557<section title="Via" anchor="header.via">
2558  <iref primary="true" item="Via header" x:for-anchor=""/>
2559  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2560  <x:anchor-alias value="protocol-name"/>
2561  <x:anchor-alias value="protocol-version"/>
2562  <x:anchor-alias value="pseudonym"/>
2563  <x:anchor-alias value="received-by"/>
2564  <x:anchor-alias value="received-protocol"/>
2565  <x:anchor-alias value="Via"/>
2566  <x:anchor-alias value="Via-v"/>
2567<t>
2568   The general-header field "Via" &MUST; be used by gateways and proxies to
2569   indicate the intermediate protocols and recipients between the user
2570   agent and the server on requests, and between the origin server and
2571   the client on responses. It is analogous to the "Received" field defined in
2572   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2573   avoiding request loops, and identifying the protocol capabilities of
2574   all senders along the request/response chain.
2575</t>
2576<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"/>
2577  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
2578  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2579                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2580  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2581  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2582  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2583  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2584  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2585</artwork></figure>
2586<t>
2587   The received-protocol indicates the protocol version of the message
2588   received by the server or client along each segment of the
2589   request/response chain. The received-protocol version is appended to
2590   the Via field value when the message is forwarded so that information
2591   about the protocol capabilities of upstream applications remains
2592   visible to all recipients.
2593</t>
2594<t>
2595   The protocol-name is optional if and only if it would be "HTTP". The
2596   received-by field is normally the host and optional port number of a
2597   recipient server or client that subsequently forwarded the message.
2598   However, if the real host is considered to be sensitive information,
2599   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2600   be assumed to be the default port of the received-protocol.
2601</t>
2602<t>
2603   Multiple Via field values represents each proxy or gateway that has
2604   forwarded the message. Each recipient &MUST; append its information
2605   such that the end result is ordered according to the sequence of
2606   forwarding applications.
2607</t>
2608<t>
2609   Comments &MAY; be used in the Via header field to identify the software
2610   of the recipient proxy or gateway, analogous to the User-Agent and
2611   Server header fields. However, all comments in the Via field are
2612   optional and &MAY; be removed by any recipient prior to forwarding the
2613   message.
2614</t>
2615<t>
2616   For example, a request message could be sent from an HTTP/1.0 user
2617   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2618   forward the request to a public proxy at p.example.net, which completes
2619   the request by forwarding it to the origin server at www.example.com.
2620   The request received by www.example.com would then have the following
2621   Via header field:
2622</t>
2623<figure><artwork type="example">
2624  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2625</artwork></figure>
2626<t>
2627   Proxies and gateways used as a portal through a network firewall
2628   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2629   the firewall region. This information &SHOULD; only be propagated if
2630   explicitly enabled. If not enabled, the received-by host of any host
2631   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2632   for that host.
2633</t>
2634<t>
2635   For organizations that have strong privacy requirements for hiding
2636   internal structures, a proxy &MAY; combine an ordered subsequence of
2637   Via header field entries with identical received-protocol values into
2638   a single such entry. For example,
2639</t>
2640<figure><artwork type="example">
2641  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2642</artwork></figure>
2643<t>
2644        could be collapsed to
2645</t>
2646<figure><artwork type="example">
2647  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2648</artwork></figure>
2649<t>
2650   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2651   under the same organizational control and the hosts have already been
2652   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2653   have different received-protocol values.
2654</t>
2655</section>
2656
2657</section>
2658
2659<section title="IANA Considerations" anchor="IANA.considerations">
2660<section title="Message Header Registration" anchor="message.header.registration">
2661<t>
2662   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
2663   with the permanent registrations below (see <xref target="RFC3864"/>):
2664</t>
2665<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2666<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2667   <ttcol>Header Field Name</ttcol>
2668   <ttcol>Protocol</ttcol>
2669   <ttcol>Status</ttcol>
2670   <ttcol>Reference</ttcol>
2671
2672   <c>Connection</c>
2673   <c>http</c>
2674   <c>standard</c>
2675   <c>
2676      <xref target="header.connection"/>
2677   </c>
2678   <c>Content-Length</c>
2679   <c>http</c>
2680   <c>standard</c>
2681   <c>
2682      <xref target="header.content-length"/>
2683   </c>
2684   <c>Date</c>
2685   <c>http</c>
2686   <c>standard</c>
2687   <c>
2688      <xref target="header.date"/>
2689   </c>
2690   <c>Host</c>
2691   <c>http</c>
2692   <c>standard</c>
2693   <c>
2694      <xref target="header.host"/>
2695   </c>
2696   <c>TE</c>
2697   <c>http</c>
2698   <c>standard</c>
2699   <c>
2700      <xref target="header.te"/>
2701   </c>
2702   <c>Trailer</c>
2703   <c>http</c>
2704   <c>standard</c>
2705   <c>
2706      <xref target="header.trailer"/>
2707   </c>
2708   <c>Transfer-Encoding</c>
2709   <c>http</c>
2710   <c>standard</c>
2711   <c>
2712      <xref target="header.transfer-encoding"/>
2713   </c>
2714   <c>Upgrade</c>
2715   <c>http</c>
2716   <c>standard</c>
2717   <c>
2718      <xref target="header.upgrade"/>
2719   </c>
2720   <c>Via</c>
2721   <c>http</c>
2722   <c>standard</c>
2723   <c>
2724      <xref target="header.via"/>
2725   </c>
2726</texttable>
2727<!--(END)-->
2728<t>
2729   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2730</t>
2731</section>
2732
2733<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2734<t>
2735   The entry for the "http" URI Scheme in the registry located at
2736   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
2737   should be updated to point to <xref target="http.uri"/> of this document
2738   (see <xref target="RFC4395"/>).
2739</t>
2740</section>
2741
2742<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
2743<t>
2744   This document serves as the specification for the Internet media types
2745   "message/http" and "application/http". The following is to be registered with
2746   IANA (see <xref target="RFC4288"/>).
2747</t>
2748<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
2749<iref item="Media Type" subitem="message/http" primary="true"/>
2750<iref item="message/http Media Type" primary="true"/>
2751<t>
2752   The message/http type can be used to enclose a single HTTP request or
2753   response message, provided that it obeys the MIME restrictions for all
2754   "message" types regarding line length and encodings.
2755</t>
2756<t>
2757  <list style="hanging" x:indent="12em">
2758    <t hangText="Type name:">
2759      message
2760    </t>
2761    <t hangText="Subtype name:">
2762      http
2763    </t>
2764    <t hangText="Required parameters:">
2765      none
2766    </t>
2767    <t hangText="Optional parameters:">
2768      version, msgtype
2769      <list style="hanging">
2770        <t hangText="version:">
2771          The HTTP-Version number of the enclosed message
2772          (e.g., "1.1"). If not present, the version can be
2773          determined from the first line of the body.
2774        </t>
2775        <t hangText="msgtype:">
2776          The message type -- "request" or "response". If not
2777          present, the type can be determined from the first
2778          line of the body.
2779        </t>
2780      </list>
2781    </t>
2782    <t hangText="Encoding considerations:">
2783      only "7bit", "8bit", or "binary" are permitted
2784    </t>
2785    <t hangText="Security considerations:">
2786      none
2787    </t>
2788    <t hangText="Interoperability considerations:">
2789      none
2790    </t>
2791    <t hangText="Published specification:">
2792      This specification (see <xref target="internet.media.type.message.http"/>).
2793    </t>
2794    <t hangText="Applications that use this media type:">
2795    </t>
2796    <t hangText="Additional information:">
2797      <list style="hanging">
2798        <t hangText="Magic number(s):">none</t>
2799        <t hangText="File extension(s):">none</t>
2800        <t hangText="Macintosh file type code(s):">none</t>
2801      </list>
2802    </t>
2803    <t hangText="Person and email address to contact for further information:">
2804      See Authors Section.
2805    </t>
2806                <t hangText="Intended usage:">
2807                  COMMON
2808    </t>
2809                <t hangText="Restrictions on usage:">
2810                  none
2811    </t>
2812    <t hangText="Author/Change controller:">
2813      IESG
2814    </t>
2815  </list>
2816</t>
2817</section>
2818<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
2819<iref item="Media Type" subitem="application/http" primary="true"/>
2820<iref item="application/http Media Type" primary="true"/>
2821<t>
2822   The application/http type can be used to enclose a pipeline of one or more
2823   HTTP request or response messages (not intermixed).
2824</t>
2825<t>
2826  <list style="hanging" x:indent="12em">
2827    <t hangText="Type name:">
2828      application
2829    </t>
2830    <t hangText="Subtype name:">
2831      http
2832    </t>
2833    <t hangText="Required parameters:">
2834      none
2835    </t>
2836    <t hangText="Optional parameters:">
2837      version, msgtype
2838      <list style="hanging">
2839        <t hangText="version:">
2840          The HTTP-Version number of the enclosed messages
2841          (e.g., "1.1"). If not present, the version can be
2842          determined from the first line of the body.
2843        </t>
2844        <t hangText="msgtype:">
2845          The message type -- "request" or "response". If not
2846          present, the type can be determined from the first
2847          line of the body.
2848        </t>
2849      </list>
2850    </t>
2851    <t hangText="Encoding considerations:">
2852      HTTP messages enclosed by this type
2853      are in "binary" format; use of an appropriate
2854      Content-Transfer-Encoding is required when
2855      transmitted via E-mail.
2856    </t>
2857    <t hangText="Security considerations:">
2858      none
2859    </t>
2860    <t hangText="Interoperability considerations:">
2861      none
2862    </t>
2863    <t hangText="Published specification:">
2864      This specification (see <xref target="internet.media.type.application.http"/>).
2865    </t>
2866    <t hangText="Applications that use this media type:">
2867    </t>
2868    <t hangText="Additional information:">
2869      <list style="hanging">
2870        <t hangText="Magic number(s):">none</t>
2871        <t hangText="File extension(s):">none</t>
2872        <t hangText="Macintosh file type code(s):">none</t>
2873      </list>
2874    </t>
2875    <t hangText="Person and email address to contact for further information:">
2876      See Authors Section.
2877    </t>
2878                <t hangText="Intended usage:">
2879                  COMMON
2880    </t>
2881                <t hangText="Restrictions on usage:">
2882                  none
2883    </t>
2884    <t hangText="Author/Change controller:">
2885      IESG
2886    </t>
2887  </list>
2888</t>
2889</section>
2890</section>
2891
2892</section>
2893
2894<section title="Security Considerations" anchor="security.considerations">
2895<t>
2896   This section is meant to inform application developers, information
2897   providers, and users of the security limitations in HTTP/1.1 as
2898   described by this document. The discussion does not include
2899   definitive solutions to the problems revealed, though it does make
2900   some suggestions for reducing security risks.
2901</t>
2902
2903<section title="Personal Information" anchor="personal.information">
2904<t>
2905   HTTP clients are often privy to large amounts of personal information
2906   (e.g. the user's name, location, mail address, passwords, encryption
2907   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2908   leakage of this information.
2909   We very strongly recommend that a convenient interface be provided
2910   for the user to control dissemination of such information, and that
2911   designers and implementors be particularly careful in this area.
2912   History shows that errors in this area often create serious security
2913   and/or privacy problems and generate highly adverse publicity for the
2914   implementor's company.
2915</t>
2916</section>
2917
2918<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2919<t>
2920   A server is in the position to save personal data about a user's
2921   requests which might identify their reading patterns or subjects of
2922   interest. This information is clearly confidential in nature and its
2923   handling can be constrained by law in certain countries. People using
2924   HTTP to provide data are responsible for ensuring that
2925   such material is not distributed without the permission of any
2926   individuals that are identifiable by the published results.
2927</t>
2928</section>
2929
2930<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2931<t>
2932   Implementations of HTTP origin servers &SHOULD; be careful to restrict
2933   the documents returned by HTTP requests to be only those that were
2934   intended by the server administrators. If an HTTP server translates
2935   HTTP URIs directly into file system calls, the server &MUST; take
2936   special care not to serve files that were not intended to be
2937   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
2938   other operating systems use ".." as a path component to indicate a
2939   directory level above the current one. On such a system, an HTTP
2940   server &MUST; disallow any such construct in the request-target if it
2941   would otherwise allow access to a resource outside those intended to
2942   be accessible via the HTTP server. Similarly, files intended for
2943   reference only internally to the server (such as access control
2944   files, configuration files, and script code) &MUST; be protected from
2945   inappropriate retrieval, since they might contain sensitive
2946   information. Experience has shown that minor bugs in such HTTP server
2947   implementations have turned into security risks.
2948</t>
2949</section>
2950
2951<section title="DNS Spoofing" anchor="dns.spoofing">
2952<t>
2953   Clients using HTTP rely heavily on the Domain Name Service, and are
2954   thus generally prone to security attacks based on the deliberate
2955   mis-association of IP addresses and DNS names. Clients need to be
2956   cautious in assuming the continuing validity of an IP number/DNS name
2957   association.
2958</t>
2959<t>
2960   In particular, HTTP clients &SHOULD; rely on their name resolver for
2961   confirmation of an IP number/DNS name association, rather than
2962   caching the result of previous host name lookups. Many platforms
2963   already can cache host name lookups locally when appropriate, and
2964   they &SHOULD; be configured to do so. It is proper for these lookups to
2965   be cached, however, only when the TTL (Time To Live) information
2966   reported by the name server makes it likely that the cached
2967   information will remain useful.
2968</t>
2969<t>
2970   If HTTP clients cache the results of host name lookups in order to
2971   achieve a performance improvement, they &MUST; observe the TTL
2972   information reported by DNS.
2973</t>
2974<t>
2975   If HTTP clients do not observe this rule, they could be spoofed when
2976   a previously-accessed server's IP address changes. As network
2977   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
2978   possibility of this form of attack will grow. Observing this
2979   requirement thus reduces this potential security vulnerability.
2980</t>
2981<t>
2982   This requirement also improves the load-balancing behavior of clients
2983   for replicated servers using the same DNS name and reduces the
2984   likelihood of a user's experiencing failure in accessing sites which
2985   use that strategy.
2986</t>
2987</section>
2988
2989<section title="Proxies and Caching" anchor="attack.proxies">
2990<t>
2991   By their very nature, HTTP proxies are men-in-the-middle, and
2992   represent an opportunity for man-in-the-middle attacks. Compromise of
2993   the systems on which the proxies run can result in serious security
2994   and privacy problems. Proxies have access to security-related
2995   information, personal information about individual users and
2996   organizations, and proprietary information belonging to users and
2997   content providers. A compromised proxy, or a proxy implemented or
2998   configured without regard to security and privacy considerations,
2999   might be used in the commission of a wide range of potential attacks.
3000</t>
3001<t>
3002   Proxy operators should protect the systems on which proxies run as
3003   they would protect any system that contains or transports sensitive
3004   information. In particular, log information gathered at proxies often
3005   contains highly sensitive personal information, and/or information
3006   about organizations. Log information should be carefully guarded, and
3007   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
3008</t>
3009<t>
3010   Proxy implementors should consider the privacy and security
3011   implications of their design and coding decisions, and of the
3012   configuration options they provide to proxy operators (especially the
3013   default configuration).
3014</t>
3015<t>
3016   Users of a proxy need to be aware that they are no trustworthier than
3017   the people who run the proxy; HTTP itself cannot solve this problem.
3018</t>
3019<t>
3020   The judicious use of cryptography, when appropriate, may suffice to
3021   protect against a broad range of security and privacy attacks. Such
3022   cryptography is beyond the scope of the HTTP/1.1 specification.
3023</t>
3024</section>
3025
3026<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3027<t>
3028   They exist. They are hard to defend against. Research continues.
3029   Beware.
3030</t>
3031</section>
3032</section>
3033
3034<section title="Acknowledgments" anchor="ack">
3035<t>
3036   HTTP has evolved considerably over the years. It has
3037   benefited from a large and active developer community--the many
3038   people who have participated on the www-talk mailing list--and it is
3039   that community which has been most responsible for the success of
3040   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3041   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3042   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3043   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3044   VanHeyningen deserve special recognition for their efforts in
3045   defining early aspects of the protocol.
3046</t>
3047<t>
3048   This document has benefited greatly from the comments of all those
3049   participating in the HTTP-WG. In addition to those already mentioned,
3050   the following individuals have contributed to this specification:
3051</t>
3052<t>
3053   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3054   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3055   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3056   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3057   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3058   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3059   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3060   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3061   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3062   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3063   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3064   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3065   Josh Cohen.
3066</t>
3067<t>
3068   Thanks to the "cave men" of Palo Alto. You know who you are.
3069</t>
3070<t>
3071   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3072   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3073   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3074   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3075   Larry Masinter for their help. And thanks go particularly to Jeff
3076   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3077</t>
3078<t>
3079   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3080   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3081   discovery of many of the problems that this document attempts to
3082   rectify.
3083</t>
3084<t>
3085   This specification makes heavy use of the augmented BNF and generic
3086   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3087   reuses many of the definitions provided by Nathaniel Borenstein and
3088   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3089   specification will help reduce past confusion over the relationship
3090   between HTTP and Internet mail message formats.
3091</t>
3092</section>
3093
3094</middle>
3095<back>
3096
3097<references title="Normative References">
3098
3099<reference anchor="ISO-8859-1">
3100  <front>
3101    <title>
3102     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3103    </title>
3104    <author>
3105      <organization>International Organization for Standardization</organization>
3106    </author>
3107    <date year="1998"/>
3108  </front>
3109  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3110</reference>
3111
3112<reference anchor="Part2">
3113  <front>
3114    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3115    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3116      <organization abbrev="Day Software">Day Software</organization>
3117      <address><email>fielding@gbiv.com</email></address>
3118    </author>
3119    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3120      <organization>One Laptop per Child</organization>
3121      <address><email>jg@laptop.org</email></address>
3122    </author>
3123    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3124      <organization abbrev="HP">Hewlett-Packard Company</organization>
3125      <address><email>JeffMogul@acm.org</email></address>
3126    </author>
3127    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3128      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3129      <address><email>henrikn@microsoft.com</email></address>
3130    </author>
3131    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3132      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3133      <address><email>LMM@acm.org</email></address>
3134    </author>
3135    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3136      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3137      <address><email>paulle@microsoft.com</email></address>
3138    </author>
3139    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3140      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3141      <address><email>timbl@w3.org</email></address>
3142    </author>
3143    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3144      <organization abbrev="W3C">World Wide Web Consortium</organization>
3145      <address><email>ylafon@w3.org</email></address>
3146    </author>
3147    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3148      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3149      <address><email>julian.reschke@greenbytes.de</email></address>
3150    </author>
3151    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3152  </front>
3153  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3154  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3155</reference>
3156
3157<reference anchor="Part3">
3158  <front>
3159    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3160    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3161      <organization abbrev="Day Software">Day Software</organization>
3162      <address><email>fielding@gbiv.com</email></address>
3163    </author>
3164    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3165      <organization>One Laptop per Child</organization>
3166      <address><email>jg@laptop.org</email></address>
3167    </author>
3168    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3169      <organization abbrev="HP">Hewlett-Packard Company</organization>
3170      <address><email>JeffMogul@acm.org</email></address>
3171    </author>
3172    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3173      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3174      <address><email>henrikn@microsoft.com</email></address>
3175    </author>
3176    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3177      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3178      <address><email>LMM@acm.org</email></address>
3179    </author>
3180    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3181      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3182      <address><email>paulle@microsoft.com</email></address>
3183    </author>
3184    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3185      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3186      <address><email>timbl@w3.org</email></address>
3187    </author>
3188    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3189      <organization abbrev="W3C">World Wide Web Consortium</organization>
3190      <address><email>ylafon@w3.org</email></address>
3191    </author>
3192    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3193      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3194      <address><email>julian.reschke@greenbytes.de</email></address>
3195    </author>
3196    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3197  </front>
3198  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3199  <x:source href="p3-payload.xml" basename="p3-payload"/>
3200</reference>
3201
3202<reference anchor="Part5">
3203  <front>
3204    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3205    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3206      <organization abbrev="Day Software">Day Software</organization>
3207      <address><email>fielding@gbiv.com</email></address>
3208    </author>
3209    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3210      <organization>One Laptop per Child</organization>
3211      <address><email>jg@laptop.org</email></address>
3212    </author>
3213    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3214      <organization abbrev="HP">Hewlett-Packard Company</organization>
3215      <address><email>JeffMogul@acm.org</email></address>
3216    </author>
3217    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3218      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3219      <address><email>henrikn@microsoft.com</email></address>
3220    </author>
3221    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3222      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3223      <address><email>LMM@acm.org</email></address>
3224    </author>
3225    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3226      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3227      <address><email>paulle@microsoft.com</email></address>
3228    </author>
3229    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3230      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3231      <address><email>timbl@w3.org</email></address>
3232    </author>
3233    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3234      <organization abbrev="W3C">World Wide Web Consortium</organization>
3235      <address><email>ylafon@w3.org</email></address>
3236    </author>
3237    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3238      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3239      <address><email>julian.reschke@greenbytes.de</email></address>
3240    </author>
3241    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3242  </front>
3243  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3244  <x:source href="p5-range.xml" basename="p5-range"/>
3245</reference>
3246
3247<reference anchor="Part6">
3248  <front>
3249    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3250    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3251      <organization abbrev="Day Software">Day Software</organization>
3252      <address><email>fielding@gbiv.com</email></address>
3253    </author>
3254    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3255      <organization>One Laptop per Child</organization>
3256      <address><email>jg@laptop.org</email></address>
3257    </author>
3258    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3259      <organization abbrev="HP">Hewlett-Packard Company</organization>
3260      <address><email>JeffMogul@acm.org</email></address>
3261    </author>
3262    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3263      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3264      <address><email>henrikn@microsoft.com</email></address>
3265    </author>
3266    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3267      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3268      <address><email>LMM@acm.org</email></address>
3269    </author>
3270    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3271      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3272      <address><email>paulle@microsoft.com</email></address>
3273    </author>
3274    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3275      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3276      <address><email>timbl@w3.org</email></address>
3277    </author>
3278    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3279      <organization abbrev="W3C">World Wide Web Consortium</organization>
3280      <address><email>ylafon@w3.org</email></address>
3281    </author>
3282    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3283      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3284      <address><email>julian.reschke@greenbytes.de</email></address>
3285    </author>
3286    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3287  </front>
3288  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3289  <x:source href="p6-cache.xml" basename="p6-cache"/>
3290</reference>
3291
3292<reference anchor="RFC5234">
3293  <front>
3294    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3295    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3296      <organization>Brandenburg InternetWorking</organization>
3297      <address>
3298      <postal>
3299      <street>675 Spruce Dr.</street>
3300      <city>Sunnyvale</city>
3301      <region>CA</region>
3302      <code>94086</code>
3303      <country>US</country></postal>
3304      <phone>+1.408.246.8253</phone>
3305      <email>dcrocker@bbiw.net</email></address> 
3306    </author>
3307    <author initials="P." surname="Overell" fullname="Paul Overell">
3308      <organization>THUS plc.</organization>
3309      <address>
3310      <postal>
3311      <street>1/2 Berkeley Square</street>
3312      <street>99 Berkely Street</street>
3313      <city>Glasgow</city>
3314      <code>G3 7HR</code>
3315      <country>UK</country></postal>
3316      <email>paul.overell@thus.net</email></address>
3317    </author>
3318    <date month="January" year="2008"/>
3319  </front>
3320  <seriesInfo name="STD" value="68"/>
3321  <seriesInfo name="RFC" value="5234"/>
3322</reference>
3323
3324<reference anchor="RFC2045">
3325  <front>
3326    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3327    <author initials="N." surname="Freed" fullname="Ned Freed">
3328      <organization>Innosoft International, Inc.</organization>
3329      <address><email>ned@innosoft.com</email></address>
3330    </author>
3331    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3332      <organization>First Virtual Holdings</organization>
3333      <address><email>nsb@nsb.fv.com</email></address>
3334    </author>
3335    <date month="November" year="1996"/>
3336  </front>
3337  <seriesInfo name="RFC" value="2045"/>
3338</reference>
3339
3340<reference anchor="RFC2047">
3341  <front>
3342    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3343    <author initials="K." surname="Moore" fullname="Keith Moore">
3344      <organization>University of Tennessee</organization>
3345      <address><email>moore@cs.utk.edu</email></address>
3346    </author>
3347    <date month="November" year="1996"/>
3348  </front>
3349  <seriesInfo name="RFC" value="2047"/>
3350</reference>
3351
3352<reference anchor="RFC2119">
3353  <front>
3354    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3355    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3356      <organization>Harvard University</organization>
3357      <address><email>sob@harvard.edu</email></address>
3358    </author>
3359    <date month="March" year="1997"/>
3360  </front>
3361  <seriesInfo name="BCP" value="14"/>
3362  <seriesInfo name="RFC" value="2119"/>
3363</reference>
3364
3365<reference anchor="RFC3986">
3366 <front>
3367  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3368  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3369    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3370    <address>
3371       <email>timbl@w3.org</email>
3372       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3373    </address>
3374  </author>
3375  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3376    <organization abbrev="Day Software">Day Software</organization>
3377    <address>
3378      <email>fielding@gbiv.com</email>
3379      <uri>http://roy.gbiv.com/</uri>
3380    </address>
3381  </author>
3382  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3383    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3384    <address>
3385      <email>LMM@acm.org</email>
3386      <uri>http://larry.masinter.net/</uri>
3387    </address>
3388  </author>
3389  <date month='January' year='2005'></date>
3390 </front>
3391 <seriesInfo name="RFC" value="3986"/>
3392 <seriesInfo name="STD" value="66"/>
3393</reference>
3394
3395<reference anchor="USASCII">
3396  <front>
3397    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3398    <author>
3399      <organization>American National Standards Institute</organization>
3400    </author>
3401    <date year="1986"/>
3402  </front>
3403  <seriesInfo name="ANSI" value="X3.4"/>
3404</reference>
3405
3406</references>
3407
3408<references title="Informative References">
3409
3410<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
3411  <front>
3412    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3413    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3414      <organization/>
3415    </author>
3416    <author initials="J." surname="Gettys" fullname="J. Gettys">
3417      <organization/>
3418    </author>
3419    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3420      <organization/>
3421    </author>
3422    <author initials="H." surname="Lie" fullname="H. Lie">
3423      <organization/>
3424    </author>
3425    <author initials="C." surname="Lilley" fullname="C. Lilley">
3426      <organization/>
3427    </author>
3428    <date year="1997" month="September"/>
3429  </front>
3430  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3431</reference>
3432
3433<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
3434  <front>
3435    <title>Improving HTTP Latency</title>
3436    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3437      <organization/>
3438    </author>
3439    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3440      <organization/>
3441    </author>
3442    <date year="1995" month="December"/>
3443  </front>
3444  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3445</reference>
3446
3447<reference anchor="RFC959">
3448  <front>
3449    <title abbrev="File Transfer Protocol">File Transfer Protocol</title>
3450    <author initials="J." surname="Postel" fullname="J. Postel">
3451      <organization>Information Sciences Institute (ISI)</organization>
3452    </author>
3453    <author initials="J." surname="Reynolds" fullname="J. Reynolds">
3454      <organization/>
3455    </author>
3456    <date month="October" year="1985"/>
3457  </front>
3458  <seriesInfo name="STD" value="9"/>
3459  <seriesInfo name="RFC" value="959"/>
3460</reference>
3461
3462<reference anchor="RFC1123">
3463  <front>
3464    <title>Requirements for Internet Hosts - Application and Support</title>
3465    <author initials="R." surname="Braden" fullname="Robert Braden">
3466      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3467      <address><email>Braden@ISI.EDU</email></address>
3468    </author>
3469    <date month="October" year="1989"/>
3470  </front>
3471  <seriesInfo name="STD" value="3"/>
3472  <seriesInfo name="RFC" value="1123"/>
3473</reference>
3474
3475<reference anchor="RFC1305">
3476  <front>
3477    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3478    <author initials="D." surname="Mills" fullname="David L. Mills">
3479      <organization>University of Delaware, Electrical Engineering Department</organization>
3480      <address><email>mills@udel.edu</email></address>
3481    </author>
3482    <date month="March" year="1992"/>
3483  </front>
3484  <seriesInfo name="RFC" value="1305"/>
3485</reference>
3486
3487<reference anchor="RFC1436">
3488  <front>
3489    <title abbrev="Gopher">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</title>
3490    <author initials="F." surname="Anklesaria" fullname="Farhad Anklesaria">
3491      <organization>University of Minnesota, Computer and Information Services</organization>
3492      <address><email>fxa@boombox.micro.umn.edu</email></address>
3493    </author>
3494    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3495      <organization>University of Minnesota, Computer and Information Services</organization>
3496      <address><email>mpm@boombox.micro.umn.edu</email></address>
3497    </author>
3498    <author initials="P." surname="Lindner" fullname="Paul Lindner">
3499      <organization>University of Minnesota, Computer and Information Services</organization>
3500      <address><email>lindner@boombox.micro.umn.edu</email></address>
3501    </author>
3502    <author initials="D." surname="Johnson" fullname="David Johnson">
3503      <organization>University of Minnesota, Computer and Information Services</organization>
3504      <address><email>dmj@boombox.micro.umn.edu</email></address>
3505    </author>
3506    <author initials="D." surname="Torrey" fullname="Daniel Torrey">
3507      <organization>University of Minnesota, Computer and Information Services</organization>
3508      <address><email>daniel@boombox.micro.umn.edu</email></address>
3509    </author>
3510    <author initials="B." surname="Alberti" fullname="Bob Alberti">
3511      <organization>University of Minnesota, Computer and Information Services</organization>
3512      <address><email>alberti@boombox.micro.umn.edu</email></address>
3513    </author>
3514    <date month="March" year="1993"/>
3515  </front>
3516  <seriesInfo name="RFC" value="1436"/>
3517</reference>
3518
3519<reference anchor="RFC1900">
3520  <front>
3521    <title>Renumbering Needs Work</title>
3522    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3523      <organization>CERN, Computing and Networks Division</organization>
3524      <address><email>brian@dxcoms.cern.ch</email></address>
3525    </author>
3526    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3527      <organization>cisco Systems</organization>
3528      <address><email>yakov@cisco.com</email></address>
3529    </author>
3530    <date month="February" year="1996"/>
3531  </front>
3532  <seriesInfo name="RFC" value="1900"/>
3533</reference>
3534
3535<reference anchor="RFC1945">
3536  <front>
3537    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3538    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3539      <organization>MIT, Laboratory for Computer Science</organization>
3540      <address><email>timbl@w3.org</email></address>
3541    </author>
3542    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3543      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3544      <address><email>fielding@ics.uci.edu</email></address>
3545    </author>
3546    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3547      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3548      <address><email>frystyk@w3.org</email></address>
3549    </author>
3550    <date month="May" year="1996"/>
3551  </front>
3552  <seriesInfo name="RFC" value="1945"/>
3553</reference>
3554
3555<reference anchor="RFC2068">
3556  <front>
3557    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3558    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3559      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3560      <address><email>fielding@ics.uci.edu</email></address>
3561    </author>
3562    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3563      <organization>MIT Laboratory for Computer Science</organization>
3564      <address><email>jg@w3.org</email></address>
3565    </author>
3566    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3567      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3568      <address><email>mogul@wrl.dec.com</email></address>
3569    </author>
3570    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3571      <organization>MIT Laboratory for Computer Science</organization>
3572      <address><email>frystyk@w3.org</email></address>
3573    </author>
3574    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3575      <organization>MIT Laboratory for Computer Science</organization>
3576      <address><email>timbl@w3.org</email></address>
3577    </author>
3578    <date month="January" year="1997"/>
3579  </front>
3580  <seriesInfo name="RFC" value="2068"/>
3581</reference>
3582
3583<reference anchor='RFC2109'>
3584  <front>
3585    <title>HTTP State Management Mechanism</title>
3586    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3587      <organization>Bell Laboratories, Lucent Technologies</organization>
3588      <address><email>dmk@bell-labs.com</email></address>
3589    </author>
3590    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3591      <organization>Netscape Communications Corp.</organization>
3592      <address><email>montulli@netscape.com</email></address>
3593    </author>
3594    <date year='1997' month='February' />
3595  </front>
3596  <seriesInfo name='RFC' value='2109' />
3597</reference>
3598
3599<reference anchor="RFC2145">
3600  <front>
3601    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3602    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3603      <organization>Western Research Laboratory</organization>
3604      <address><email>mogul@wrl.dec.com</email></address>
3605    </author>
3606    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3607      <organization>Department of Information and Computer Science</organization>
3608      <address><email>fielding@ics.uci.edu</email></address>
3609    </author>
3610    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3611      <organization>MIT Laboratory for Computer Science</organization>
3612      <address><email>jg@w3.org</email></address>
3613    </author>
3614    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3615      <organization>W3 Consortium</organization>
3616      <address><email>frystyk@w3.org</email></address>
3617    </author>
3618    <date month="May" year="1997"/>
3619  </front>
3620  <seriesInfo name="RFC" value="2145"/>
3621</reference>
3622
3623<reference anchor="RFC2616">
3624  <front>
3625    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3626    <author initials="R." surname="Fielding" fullname="R. Fielding">
3627      <organization>University of California, Irvine</organization>
3628      <address><email>fielding@ics.uci.edu</email></address>
3629    </author>
3630    <author initials="J." surname="Gettys" fullname="J. Gettys">
3631      <organization>W3C</organization>
3632      <address><email>jg@w3.org</email></address>
3633    </author>
3634    <author initials="J." surname="Mogul" fullname="J. Mogul">
3635      <organization>Compaq Computer Corporation</organization>
3636      <address><email>mogul@wrl.dec.com</email></address>
3637    </author>
3638    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3639      <organization>MIT Laboratory for Computer Science</organization>
3640      <address><email>frystyk@w3.org</email></address>
3641    </author>
3642    <author initials="L." surname="Masinter" fullname="L. Masinter">
3643      <organization>Xerox Corporation</organization>
3644      <address><email>masinter@parc.xerox.com</email></address>
3645    </author>
3646    <author initials="P." surname="Leach" fullname="P. Leach">
3647      <organization>Microsoft Corporation</organization>
3648      <address><email>paulle@microsoft.com</email></address>
3649    </author>
3650    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3651      <organization>W3C</organization>
3652      <address><email>timbl@w3.org</email></address>
3653    </author>
3654    <date month="June" year="1999"/>
3655  </front>
3656  <seriesInfo name="RFC" value="2616"/>
3657</reference>
3658
3659<reference anchor='RFC2818'>
3660  <front>
3661    <title>HTTP Over TLS</title>
3662    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3663      <organization>RTFM, Inc.</organization>
3664      <address><email>ekr@rtfm.com</email></address>
3665    </author>
3666    <date year='2000' month='May' />
3667  </front>
3668  <seriesInfo name='RFC' value='2818' />
3669</reference>
3670
3671<reference anchor='RFC2965'>
3672  <front>
3673    <title>HTTP State Management Mechanism</title>
3674    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3675      <organization>Bell Laboratories, Lucent Technologies</organization>
3676      <address><email>dmk@bell-labs.com</email></address>
3677    </author>
3678    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3679      <organization>Epinions.com, Inc.</organization>
3680      <address><email>lou@montulli.org</email></address>
3681    </author>
3682    <date year='2000' month='October' />
3683  </front>
3684  <seriesInfo name='RFC' value='2965' />
3685</reference>
3686
3687<reference anchor='RFC3864'>
3688  <front>
3689    <title>Registration Procedures for Message Header Fields</title>
3690    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3691      <organization>Nine by Nine</organization>
3692      <address><email>GK-IETF@ninebynine.org</email></address>
3693    </author>
3694    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3695      <organization>BEA Systems</organization>
3696      <address><email>mnot@pobox.com</email></address>
3697    </author>
3698    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3699      <organization>HP Labs</organization>
3700      <address><email>JeffMogul@acm.org</email></address>
3701    </author>
3702    <date year='2004' month='September' />
3703  </front>
3704  <seriesInfo name='BCP' value='90' />
3705  <seriesInfo name='RFC' value='3864' />
3706</reference>
3707
3708<reference anchor='RFC3977'>
3709  <front>
3710    <title>Network News Transfer Protocol (NNTP)</title>
3711    <author initials='C.' surname='Feather' fullname='C. Feather'>
3712      <organization>THUS plc</organization>
3713      <address><email>clive@demon.net</email></address>
3714    </author>
3715    <date year='2006' month='October' />
3716  </front>
3717  <seriesInfo name="RFC" value="3977"/>
3718</reference>
3719
3720<reference anchor="RFC4288">
3721  <front>
3722    <title>Media Type Specifications and Registration Procedures</title>
3723    <author initials="N." surname="Freed" fullname="N. Freed">
3724      <organization>Sun Microsystems</organization>
3725      <address>
3726        <email>ned.freed@mrochek.com</email>
3727      </address>
3728    </author>
3729    <author initials="J." surname="Klensin" fullname="J. Klensin">
3730      <organization/>
3731      <address>
3732        <email>klensin+ietf@jck.com</email>
3733      </address>
3734    </author>
3735    <date year="2005" month="December"/>
3736  </front>
3737  <seriesInfo name="BCP" value="13"/>
3738  <seriesInfo name="RFC" value="4288"/>
3739</reference>
3740
3741<reference anchor='RFC4395'>
3742  <front>
3743    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3744    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3745      <organization>AT&amp;T Laboratories</organization>
3746      <address>
3747        <email>tony+urireg@maillennium.att.com</email>
3748      </address>
3749    </author>
3750    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3751      <organization>Qualcomm, Inc.</organization>
3752      <address>
3753        <email>hardie@qualcomm.com</email>
3754      </address>
3755    </author>
3756    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3757      <organization>Adobe Systems</organization>
3758      <address>
3759        <email>LMM@acm.org</email>
3760      </address>
3761    </author>
3762    <date year='2006' month='February' />
3763  </front>
3764  <seriesInfo name='BCP' value='115' />
3765  <seriesInfo name='RFC' value='4395' />
3766</reference>
3767
3768<reference anchor="RFC5322">
3769  <front>
3770    <title>Internet Message Format</title>
3771    <author initials="P." surname="Resnick" fullname="P. Resnick">
3772      <organization>Qualcomm Incorporated</organization>
3773    </author>
3774    <date year="2008" month="October"/>
3775  </front> 
3776  <seriesInfo name="RFC" value="5322"/>
3777</reference>
3778
3779<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
3780  <front>
3781    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3782    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3783      <organization/>
3784    </author>
3785    <date year="2001" month="November"/>
3786  </front>
3787  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3788</reference>
3789
3790<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
3791  <front>
3792  <title>Analysis of HTTP Performance Problems</title>
3793  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3794    <organization/>
3795  </author>
3796  <date/>
3797  </front>
3798</reference>
3799
3800<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
3801  <front>
3802  <title>Analysis of HTTP Performance</title>
3803  <author initials="J." surname="Touch" fullname="Joe Touch">
3804    <organization>USC/Information Sciences Institute</organization>
3805    <address><email>touch@isi.edu</email></address>
3806  </author>
3807  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3808    <organization>USC/Information Sciences Institute</organization>
3809    <address><email>johnh@isi.edu</email></address>
3810  </author>
3811  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3812    <organization>USC/Information Sciences Institute</organization>
3813    <address><email>katia@isi.edu</email></address>
3814  </author>
3815  <date year="1998" month="Aug"/>
3816  </front>
3817  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3818  <annotation>(original report dated Aug. 1996)</annotation>
3819</reference>
3820
3821<reference anchor="WAIS">
3822  <front>
3823    <title>WAIS Interface Protocol Prototype Functional Specification (v1.5)</title>
3824    <author initials="F." surname="Davis" fullname="F. Davis">
3825      <organization>Thinking Machines Corporation</organization>
3826    </author>
3827    <author initials="B." surname="Kahle" fullname="B. Kahle">
3828      <organization>Thinking Machines Corporation</organization>
3829    </author>
3830    <author initials="H." surname="Morris" fullname="H. Morris">
3831      <organization>Thinking Machines Corporation</organization>
3832    </author>
3833    <author initials="J." surname="Salem" fullname="J. Salem">
3834      <organization>Thinking Machines Corporation</organization>
3835    </author>
3836    <author initials="T." surname="Shen" fullname="T. Shen">
3837      <organization>Thinking Machines Corporation</organization>
3838    </author>
3839    <author initials="R." surname="Wang" fullname="R. Wang">
3840      <organization>Thinking Machines Corporation</organization>
3841    </author>
3842    <author initials="J." surname="Sui" fullname="J. Sui">
3843      <organization>Thinking Machines Corporation</organization>
3844    </author>
3845    <author initials="M." surname="Grinbaum" fullname="M. Grinbaum">
3846      <organization>Thinking Machines Corporation</organization>
3847    </author>
3848    <date month="April" year="1990"/>
3849  </front>
3850  <seriesInfo name="Thinking Machines Corporation" value=""/>
3851</reference>
3852
3853</references>
3854
3855
3856<section title="Tolerant Applications" anchor="tolerant.applications">
3857<t>
3858   Although this document specifies the requirements for the generation
3859   of HTTP/1.1 messages, not all applications will be correct in their
3860   implementation. We therefore recommend that operational applications
3861   be tolerant of deviations whenever those deviations can be
3862   interpreted unambiguously.
3863</t>
3864<t>
3865   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3866   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3867   accept any amount of SP or HTAB characters between fields, even though
3868   only a single SP is required.
3869</t>
3870<t>
3871   The line terminator for message-header fields is the sequence CRLF.
3872   However, we recommend that applications, when parsing such headers,
3873   recognize a single LF as a line terminator and ignore the leading CR.
3874</t>
3875<t>
3876   The character set of an entity-body &SHOULD; be labeled as the lowest
3877   common denominator of the character codes used within that body, with
3878   the exception that not labeling the entity is preferred over labeling
3879   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3880</t>
3881<t>
3882   Additional rules for requirements on parsing and encoding of dates
3883   and other potential problems with date encodings include:
3884</t>
3885<t>
3886  <list style="symbols">
3887     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3888        which appears to be more than 50 years in the future is in fact
3889        in the past (this helps solve the "year 2000" problem).</t>
3890
3891     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3892        Expires date as earlier than the proper value, but &MUST-NOT;
3893        internally represent a parsed Expires date as later than the
3894        proper value.</t>
3895
3896     <t>All expiration-related calculations &MUST; be done in GMT. The
3897        local time zone &MUST-NOT; influence the calculation or comparison
3898        of an age or expiration time.</t>
3899
3900     <t>If an HTTP header incorrectly carries a date value with a time
3901        zone other than GMT, it &MUST; be converted into GMT using the
3902        most conservative possible conversion.</t>
3903  </list>
3904</t>
3905</section>
3906
3907<section title="Compatibility with Previous Versions" anchor="compatibility">
3908<t>
3909   HTTP has been in use by the World-Wide Web global information initiative
3910   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
3911   was a simple protocol for hypertext data transfer across the Internet
3912   with only a single method and no metadata.
3913   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
3914   methods and MIME-like messaging that could include metadata about the data
3915   transferred and modifiers on the request/response semantics. However,
3916   HTTP/1.0 did not sufficiently take into consideration the effects of
3917   hierarchical proxies, caching, the need for persistent connections, or
3918   name-based virtual hosts. The proliferation of incompletely-implemented
3919   applications calling themselves "HTTP/1.0" further necessitated a
3920   protocol version change in order for two communicating applications
3921   to determine each other's true capabilities.
3922</t>
3923<t>
3924   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
3925   requirements that enable reliable implementations, adding only
3926   those new features that will either be safely ignored by an HTTP/1.0
3927   recipient or only sent when communicating with a party advertising
3928   compliance with HTTP/1.1.
3929</t>
3930<t>
3931   It is beyond the scope of a protocol specification to mandate
3932   compliance with previous versions. HTTP/1.1 was deliberately
3933   designed, however, to make supporting previous versions easy. It is
3934   worth noting that, at the time of composing this specification
3935   (1996), we would expect commercial HTTP/1.1 servers to:
3936  <list style="symbols">
3937     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3938        1.1 requests;</t>
3939
3940     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3941        1.1;</t>
3942
3943     <t>respond appropriately with a message in the same major version
3944        used by the client.</t>
3945  </list>
3946</t>
3947<t>
3948   And we would expect HTTP/1.1 clients to:
3949  <list style="symbols">
3950     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3951        responses;</t>
3952
3953     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3954        1.1.</t>
3955  </list>
3956</t>
3957<t>
3958   For most implementations of HTTP/1.0, each connection is established
3959   by the client prior to the request and closed by the server after
3960   sending the response. Some implementations implement the Keep-Alive
3961   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3962</t>
3963
3964<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3965<t>
3966   This section summarizes major differences between versions HTTP/1.0
3967   and HTTP/1.1.
3968</t>
3969
3970<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">
3971<t>
3972   The requirements that clients and servers support the Host request-header,
3973   report an error if the Host request-header (<xref target="header.host"/>) is
3974   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
3975   are among the most important changes defined by this
3976   specification.
3977</t>
3978<t>
3979   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
3980   addresses and servers; there was no other established mechanism for
3981   distinguishing the intended server of a request than the IP address
3982   to which that request was directed. The changes outlined above will
3983   allow the Internet, once older HTTP clients are no longer common, to
3984   support multiple Web sites from a single IP address, greatly
3985   simplifying large operational Web servers, where allocation of many
3986   IP addresses to a single host has created serious problems. The
3987   Internet will also be able to recover the IP addresses that have been
3988   allocated for the sole purpose of allowing special-purpose domain
3989   names to be used in root-level HTTP URLs. Given the rate of growth of
3990   the Web, and the number of servers already deployed, it is extremely
3991   important that all implementations of HTTP (including updates to
3992   existing HTTP/1.0 applications) correctly implement these
3993   requirements:
3994  <list style="symbols">
3995     <t>Both clients and servers &MUST; support the Host request-header.</t>
3996
3997     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
3998
3999     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4000        request does not include a Host request-header.</t>
4001
4002     <t>Servers &MUST; accept absolute URIs.</t>
4003  </list>
4004</t>
4005</section>
4006</section>
4007
4008<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4009<t>
4010   Some clients and servers might wish to be compatible with some
4011   previous implementations of persistent connections in HTTP/1.0
4012   clients and servers. Persistent connections in HTTP/1.0 are
4013   explicitly negotiated as they are not the default behavior. HTTP/1.0
4014   experimental implementations of persistent connections are faulty,
4015   and the new facilities in HTTP/1.1 are designed to rectify these
4016   problems. The problem was that some existing 1.0 clients may be
4017   sending Keep-Alive to a proxy server that doesn't understand
4018   Connection, which would then erroneously forward it to the next
4019   inbound server, which would establish the Keep-Alive connection and
4020   result in a hung HTTP/1.0 proxy waiting for the close on the
4021   response. The result is that HTTP/1.0 clients must be prevented from
4022   using Keep-Alive when talking to proxies.
4023</t>
4024<t>
4025   However, talking to proxies is the most important use of persistent
4026   connections, so that prohibition is clearly unacceptable. Therefore,
4027   we need some other mechanism for indicating a persistent connection
4028   is desired, which is safe to use even when talking to an old proxy
4029   that ignores Connection. Persistent connections are the default for
4030   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4031   declaring non-persistence. See <xref target="header.connection"/>.
4032</t>
4033<t>
4034   The original HTTP/1.0 form of persistent connections (the Connection:
4035   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
4036</t>
4037</section>
4038
4039<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4040<t>
4041   This specification has been carefully audited to correct and
4042   disambiguate key word usage; RFC 2068 had many problems in respect to
4043   the conventions laid out in <xref target="RFC2119"/>.
4044</t>
4045<t>
4046   Transfer-coding and message lengths all interact in ways that
4047   required fixing exactly when chunked encoding is used (to allow for
4048   transfer encoding that may not be self delimiting); it was important
4049   to straighten out exactly how message lengths are computed. (Sections
4050   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4051   <xref target="header.content-length" format="counter"/>,
4052   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4053</t>
4054<t>
4055   The use and interpretation of HTTP version numbers has been clarified
4056   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4057   version they support to deal with problems discovered in HTTP/1.0
4058   implementations (<xref target="http.version"/>)
4059</t>
4060<t>
4061   Transfer-coding had significant problems, particularly with
4062   interactions with chunked encoding. The solution is that transfer-codings
4063   become as full fledged as content-codings. This involves
4064   adding an IANA registry for transfer-codings (separate from content
4065   codings), a new header field (TE) and enabling trailer headers in the
4066   future. Transfer encoding is a major performance benefit, so it was
4067   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4068   interoperability problem that could have occurred due to interactions
4069   between authentication trailers, chunked encoding and HTTP/1.0
4070   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4071   and <xref target="header.te" format="counter"/>)
4072</t>
4073</section>
4074
4075<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4076<t>
4077  Rules about implicit linear white space between certain grammar productions
4078  have been removed; now it's only allowed when specifically pointed out
4079  in the ABNF.
4080  The CHAR rule does not allow the NUL character anymore (this affects
4081  the comment and quoted-string rules).  Furthermore, the quoted-pair
4082  rule does not allow escaping NUL, CR or LF anymore.
4083  (<xref target="basic.rules"/>)
4084</t>
4085<t>
4086  Clarify that HTTP-Version is case sensitive.
4087  (<xref target="http.version"/>)
4088</t>
4089<t>
4090  Remove reference to non-existant identity transfer-coding value tokens.
4091  (Sections <xref format="counter" target="transfer.codings"/> and
4092  <xref format="counter" target="message.length"/>)
4093</t>
4094<t>
4095  Clarification that the chunk length does not include
4096  the count of the octets in the chunk header and trailer.
4097  (<xref target="chunked.transfer.encoding"/>)
4098</t>
4099<t>
4100  Update use of abs_path production from RFC1808 to the path-absolute + query
4101  components of RFC3986.
4102  (<xref target="request-target"/>)
4103</t>
4104<t>
4105  Clarify exactly when close connection options must be sent.
4106  (<xref target="header.connection"/>)
4107</t>
4108</section>
4109</section>
4110
4111<section title="Terminology" anchor="terminology">
4112<t>
4113   This specification uses a number of terms to refer to the roles
4114   played by participants in, and objects of, the HTTP communication.
4115</t>
4116<t>
4117  <iref item="connection"/>
4118  <x:dfn>connection</x:dfn>
4119  <list>
4120    <t>
4121      A transport layer virtual circuit established between two programs
4122      for the purpose of communication.
4123    </t>
4124  </list>
4125</t>
4126<t>
4127  <iref item="message"/>
4128  <x:dfn>message</x:dfn>
4129  <list>
4130    <t>
4131      The basic unit of HTTP communication, consisting of a structured
4132      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4133      transmitted via the connection.
4134    </t>
4135  </list>
4136</t>
4137<t>
4138  <iref item="request"/>
4139  <x:dfn>request</x:dfn>
4140  <list>
4141    <t>
4142      An HTTP request message, as defined in <xref target="request"/>.
4143    </t>
4144  </list>
4145</t>
4146<t>
4147  <iref item="response"/>
4148  <x:dfn>response</x:dfn>
4149  <list>
4150    <t>
4151      An HTTP response message, as defined in <xref target="response"/>.
4152    </t>
4153  </list>
4154</t>
4155<t>
4156  <iref item="resource"/>
4157  <x:dfn>resource</x:dfn>
4158  <list>
4159    <t>
4160      A network data object or service that can be identified by a URI,
4161      as defined in <xref target="uri"/>. Resources may be available in multiple
4162      representations (e.g. multiple languages, data formats, size, and
4163      resolutions) or vary in other ways.
4164    </t>
4165  </list>
4166</t>
4167<t>
4168  <iref item="entity"/>
4169  <x:dfn>entity</x:dfn>
4170  <list>
4171    <t>
4172      The information transferred as the payload of a request or
4173      response. An entity consists of metainformation in the form of
4174      entity-header fields and content in the form of an entity-body, as
4175      described in &entity;.
4176    </t>
4177  </list>
4178</t>
4179<t>
4180  <iref item="representation"/>
4181  <x:dfn>representation</x:dfn>
4182  <list>
4183    <t>
4184      An entity included with a response that is subject to content
4185      negotiation, as described in &content.negotiation;. There may exist multiple
4186      representations associated with a particular response status.
4187    </t>
4188  </list>
4189</t>
4190<t>
4191  <iref item="content negotiation"/>
4192  <x:dfn>content negotiation</x:dfn>
4193  <list>
4194    <t>
4195      The mechanism for selecting the appropriate representation when
4196      servicing a request, as described in &content.negotiation;. The
4197      representation of entities in any response can be negotiated
4198      (including error responses).
4199    </t>
4200  </list>
4201</t>
4202<t>
4203  <iref item="variant"/>
4204  <x:dfn>variant</x:dfn>
4205  <list>
4206    <t>
4207      A resource may have one, or more than one, representation(s)
4208      associated with it at any given instant. Each of these
4209      representations is termed a `variant'.  Use of the term `variant'
4210      does not necessarily imply that the resource is subject to content
4211      negotiation.
4212    </t>
4213  </list>
4214</t>
4215<t>
4216  <iref item="client"/>
4217  <x:dfn>client</x:dfn>
4218  <list>
4219    <t>
4220      A program that establishes connections for the purpose of sending
4221      requests.
4222    </t>
4223  </list>
4224</t>
4225<t>
4226  <iref item="user agent"/>
4227  <x:dfn>user agent</x:dfn>
4228  <list>
4229    <t>
4230      The client which initiates a request. These are often browsers,
4231      editors, spiders (web-traversing robots), or other end user tools.
4232    </t>
4233  </list>
4234</t>
4235<t>
4236  <iref item="server"/>
4237  <x:dfn>server</x:dfn>
4238  <list>
4239    <t>
4240      An application program that accepts connections in order to
4241      service requests by sending back responses. Any given program may
4242      be capable of being both a client and a server; our use of these
4243      terms refers only to the role being performed by the program for a
4244      particular connection, rather than to the program's capabilities
4245      in general. Likewise, any server may act as an origin server,
4246      proxy, gateway, or tunnel, switching behavior based on the nature
4247      of each request.
4248    </t>
4249  </list>
4250</t>
4251<t>
4252  <iref item="origin server"/>
4253  <x:dfn>origin server</x:dfn>
4254  <list>
4255    <t>
4256      The server on which a given resource resides or is to be created.
4257    </t>
4258  </list>
4259</t>
4260<t>
4261  <iref item="proxy"/>
4262  <x:dfn>proxy</x:dfn>
4263  <list>
4264    <t>
4265      An intermediary program which acts as both a server and a client
4266      for the purpose of making requests on behalf of other clients.
4267      Requests are serviced internally or by passing them on, with
4268      possible translation, to other servers. A proxy &MUST; implement
4269      both the client and server requirements of this specification. A
4270      "transparent proxy" is a proxy that does not modify the request or
4271      response beyond what is required for proxy authentication and
4272      identification. A "non-transparent proxy" is a proxy that modifies
4273      the request or response in order to provide some added service to
4274      the user agent, such as group annotation services, media type
4275      transformation, protocol reduction, or anonymity filtering. Except
4276      where either transparent or non-transparent behavior is explicitly
4277      stated, the HTTP proxy requirements apply to both types of
4278      proxies.
4279    </t>
4280  </list>
4281</t>
4282<t>
4283  <iref item="gateway"/>
4284  <x:dfn>gateway</x:dfn>
4285  <list>
4286    <t>
4287      A server which acts as an intermediary for some other server.
4288      Unlike a proxy, a gateway receives requests as if it were the
4289      origin server for the requested resource; the requesting client
4290      may not be aware that it is communicating with a gateway.
4291    </t>
4292  </list>
4293</t>
4294<t>
4295  <iref item="tunnel"/>
4296  <x:dfn>tunnel</x:dfn>
4297  <list>
4298    <t>
4299      An intermediary program which is acting as a blind relay between
4300      two connections. Once active, a tunnel is not considered a party
4301      to the HTTP communication, though the tunnel may have been
4302      initiated by an HTTP request. The tunnel ceases to exist when both
4303      ends of the relayed connections are closed.
4304    </t>
4305  </list>
4306</t>
4307<t>
4308  <iref item="cache"/>
4309  <x:dfn>cache</x:dfn>
4310  <list>
4311    <t>
4312      A program's local store of response messages and the subsystem
4313      that controls its message storage, retrieval, and deletion. A
4314      cache stores cacheable responses in order to reduce the response
4315      time and network bandwidth consumption on future, equivalent
4316      requests. Any client or server may include a cache, though a cache
4317      cannot be used by a server that is acting as a tunnel.
4318    </t>
4319  </list>
4320</t>
4321<t>
4322  <iref item="cacheable"/>
4323  <x:dfn>cacheable</x:dfn>
4324  <list>
4325    <t>
4326      A response is cacheable if a cache is allowed to store a copy of
4327      the response message for use in answering subsequent requests. The
4328      rules for determining the cacheability of HTTP responses are
4329      defined in &caching;. Even if a resource is cacheable, there may
4330      be additional constraints on whether a cache can use the cached
4331      copy for a particular request.
4332    </t>
4333  </list>
4334</t>
4335<t>
4336  <iref item="upstream"/>
4337  <iref item="downstream"/>
4338  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
4339  <list>
4340    <t>
4341      Upstream and downstream describe the flow of a message: all
4342      messages flow from upstream to downstream.
4343    </t>
4344  </list>
4345</t>
4346<t>
4347  <iref item="inbound"/>
4348  <iref item="outbound"/>
4349  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
4350  <list>
4351    <t>
4352      Inbound and outbound refer to the request and response paths for
4353      messages: "inbound" means "traveling toward the origin server",
4354      and "outbound" means "traveling toward the user agent"
4355    </t>
4356  </list>
4357</t>
4358</section>
4359
4360<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4361
4362<section title="Since RFC2616">
4363<t>
4364  Extracted relevant partitions from <xref target="RFC2616"/>.
4365</t>
4366</section>
4367
4368<section title="Since draft-ietf-httpbis-p1-messaging-00">
4369<t>
4370  Closed issues:
4371  <list style="symbols"> 
4372    <t>
4373      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
4374      "HTTP Version should be case sensitive"
4375      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
4376    </t>
4377    <t>
4378      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
4379      "'unsafe' characters"
4380      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
4381    </t>
4382    <t>
4383      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
4384      "Chunk Size Definition"
4385      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
4386    </t>
4387    <t>
4388      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
4389      "Message Length"
4390      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
4391    </t>
4392    <t>
4393      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
4394      "Media Type Registrations"
4395      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
4396    </t>
4397    <t>
4398      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
4399      "URI includes query"
4400      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
4401    </t>
4402    <t>
4403      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
4404      "No close on 1xx responses"
4405      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
4406    </t>
4407    <t>
4408      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
4409      "Remove 'identity' token references"
4410      (<eref target="http://purl.org/NET/http-errata#identity"/>)
4411    </t>
4412    <t>
4413      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
4414      "Import query BNF"
4415    </t>
4416    <t>
4417      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
4418      "qdtext BNF"
4419    </t>
4420    <t>
4421      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4422      "Normative and Informative references"
4423    </t>
4424    <t>
4425      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4426      "RFC2606 Compliance"
4427    </t>
4428    <t>
4429      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
4430      "RFC977 reference"
4431    </t>
4432    <t>
4433      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
4434      "RFC1700 references"
4435    </t>
4436    <t>
4437      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
4438      "inconsistency in date format explanation"
4439    </t>
4440    <t>
4441      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
4442      "Date reference typo"
4443    </t>
4444    <t>
4445      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4446      "Informative references"
4447    </t>
4448    <t>
4449      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
4450      "ISO-8859-1 Reference"
4451    </t>
4452    <t>
4453      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
4454      "Normative up-to-date references"
4455    </t>
4456  </list>
4457</t>
4458<t>
4459  Other changes:
4460  <list style="symbols"> 
4461    <t>
4462      Update media type registrations to use RFC4288 template.
4463    </t>
4464    <t>
4465      Use names of RFC4234 core rules DQUOTE and HTAB,
4466      fix broken ABNF for chunk-data
4467      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
4468    </t>
4469  </list>
4470</t>
4471</section>
4472
4473<section title="Since draft-ietf-httpbis-p1-messaging-01">
4474<t>
4475  Closed issues:
4476  <list style="symbols"> 
4477    <t>
4478      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
4479      "Bodies on GET (and other) requests"
4480    </t>
4481    <t>
4482      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
4483      "Updating to RFC4288"
4484    </t>
4485    <t>
4486      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
4487      "Status Code and Reason Phrase"
4488    </t>
4489    <t>
4490      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
4491      "rel_path not used"
4492    </t>
4493  </list>
4494</t>
4495<t>
4496  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4497  <list style="symbols"> 
4498    <t>
4499      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4500      "trailer-part").
4501    </t>
4502    <t>
4503      Avoid underscore character in rule names ("http_URL" ->
4504      "http-URL", "abs_path" -> "path-absolute").
4505    </t>
4506    <t>
4507      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4508      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4509      have to be updated when switching over to RFC3986.
4510    </t>
4511    <t>
4512      Synchronize core rules with RFC5234 (this includes a change to CHAR
4513      which now excludes NUL).
4514    </t>
4515    <t>
4516      Get rid of prose rules that span multiple lines.
4517    </t>
4518    <t>
4519      Get rid of unused rules LOALPHA and UPALPHA.
4520    </t>
4521    <t>
4522      Move "Product Tokens" section (back) into Part 1, as "token" is used
4523      in the definition of the Upgrade header.
4524    </t>
4525    <t>
4526      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4527    </t>
4528    <t>
4529      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4530    </t>
4531  </list>
4532</t>
4533</section>
4534
4535<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4536<t>
4537  Closed issues:
4538  <list style="symbols"> 
4539    <t>
4540      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
4541      "HTTP-date vs. rfc1123-date"
4542    </t>
4543    <t>
4544      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
4545      "WS in quoted-pair"
4546    </t>
4547  </list>
4548</t>
4549<t>
4550  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4551  <list style="symbols"> 
4552    <t>
4553      Reference RFC 3984, and update header registrations for headers defined
4554      in this document.
4555    </t>
4556  </list>
4557</t>
4558<t>
4559  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4560  <list style="symbols"> 
4561    <t>
4562      Replace string literals when the string really is case-sensitive (HTTP-Version).
4563    </t>
4564  </list>
4565</t>
4566</section>
4567
4568<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4569<t>
4570  Closed issues:
4571  <list style="symbols"> 
4572    <t>
4573      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
4574      "Connection closing"
4575    </t>
4576    <t>
4577      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
4578      "Move registrations and registry information to IANA Considerations"
4579    </t>
4580    <t>
4581      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
4582      "need new URL for PAD1995 reference"
4583    </t>
4584    <t>
4585      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
4586      "IANA Considerations: update HTTP URI scheme registration"
4587    </t>
4588    <t>
4589      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
4590      "Cite HTTPS URI scheme definition"
4591    </t>
4592    <t>
4593      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
4594      "List-type headers vs Set-Cookie"
4595    </t>
4596  </list>
4597</t>
4598<t>
4599  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4600  <list style="symbols"> 
4601    <t>
4602      Replace string literals when the string really is case-sensitive (HTTP-Date).
4603    </t>
4604    <t>
4605      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4606    </t>
4607  </list>
4608</t>
4609</section>
4610
4611<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4612<t>
4613  Closed issues:
4614  <list style="symbols"> 
4615    <t>
4616      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
4617      "Out-of-date reference for URIs"
4618    </t>
4619    <t>
4620      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4621      "RFC 2822 is updated by RFC 5322"
4622    </t>
4623  </list>
4624</t>
4625<t>
4626  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4627  <list style="symbols"> 
4628    <t>
4629      Use "/" instead of "|" for alternatives.
4630    </t>
4631    <t>
4632      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4633    </t>
4634    <t>
4635      Only reference RFC 5234's core rules.
4636    </t>
4637    <t>
4638      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4639      whitespace ("OWS") and required whitespace ("RWS").
4640    </t>
4641    <t>
4642      Rewrite ABNFs to spell out whitespace rules, factor out
4643      header value format definitions.
4644    </t>
4645  </list>
4646</t>
4647</section>
4648
4649<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
4650<t>
4651  Closed issues:
4652  <list style="symbols"> 
4653    <t>
4654      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
4655      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
4656    </t>
4657    <t>
4658      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
4659      "RFC822 reference left in discussion of date formats"
4660    </t>
4661  </list>
4662</t>
4663<t>
4664  Other changes:
4665  <list style="symbols"> 
4666    <t>
4667      Rewrite introduction; add mostly new Architecture Section.
4668    </t>
4669  </list>
4670</t>
4671</section>
4672
4673</section>
4674
4675</back>
4676</rfc>
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