source: draft-ietf-httpbis/latest/p1-messaging.xml @ 870

Last change on this file since 870 was 870, checked in by julian.reschke@…, 9 years ago

add a pointer to issue #221 to the inline comment

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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 "July">
16  <!ENTITY ID-YEAR "2010">
17  <!ENTITY caching-overview       "<xref target='Part6' x:rel='#caching.overview' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY cache-incomplete       "<xref target='Part6' x:rel='#errors.or.incomplete.response.cache.behavior' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY payload                "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY media-types            "<xref target='Part3' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY content-codings        "<xref target='Part3' x:rel='#content.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY diff-mime              "<xref target='Part3' x:rel='#differences.between.http.entities.and.rfc.2045.entities' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY entity                 "<xref target='Part3' x:rel='#entity' 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-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38]>
39<?rfc toc="yes" ?>
40<?rfc symrefs="yes" ?>
41<?rfc sortrefs="yes" ?>
42<?rfc compact="yes"?>
43<?rfc subcompact="no" ?>
44<?rfc linkmailto="no" ?>
45<?rfc editing="no" ?>
46<?rfc comments="yes"?>
47<?rfc inline="yes"?>
48<?rfc rfcedstyle="yes"?>
49<?rfc-ext allow-markup-in-artwork="yes" ?>
50<?rfc-ext include-references-in-index="yes" ?>
51<rfc obsoletes="2616" updates="2817" category="std" x:maturity-level="draft"
52     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
53     xmlns:x='http://purl.org/net/xml2rfc/ext'>
54<front>
55
56  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
57
58  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
59    <organization abbrev="Day Software">Day Software</organization>
60    <address>
61      <postal>
62        <street>23 Corporate Plaza DR, Suite 280</street>
63        <city>Newport Beach</city>
64        <region>CA</region>
65        <code>92660</code>
66        <country>USA</country>
67      </postal>
68      <phone>+1-949-706-5300</phone>
69      <facsimile>+1-949-706-5305</facsimile>
70      <email>fielding@gbiv.com</email>
71      <uri>http://roy.gbiv.com/</uri>
72    </address>
73  </author>
74
75  <author initials="J." surname="Gettys" fullname="Jim Gettys">
76    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
77    <address>
78      <postal>
79        <street>21 Oak Knoll Road</street>
80        <city>Carlisle</city>
81        <region>MA</region>
82        <code>01741</code>
83        <country>USA</country>
84      </postal>
85      <email>jg@freedesktop.org</email>
86      <uri>http://gettys.wordpress.com/</uri>
87    </address>
88  </author>
89 
90  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
91    <organization abbrev="HP">Hewlett-Packard Company</organization>
92    <address>
93      <postal>
94        <street>HP Labs, Large Scale Systems Group</street>
95        <street>1501 Page Mill Road, MS 1177</street>
96        <city>Palo Alto</city>
97        <region>CA</region>
98        <code>94304</code>
99        <country>USA</country>
100      </postal>
101      <email>JeffMogul@acm.org</email>
102    </address>
103  </author>
104
105  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
106    <organization abbrev="Microsoft">Microsoft Corporation</organization>
107    <address>
108      <postal>
109        <street>1 Microsoft Way</street>
110        <city>Redmond</city>
111        <region>WA</region>
112        <code>98052</code>
113        <country>USA</country>
114      </postal>
115      <email>henrikn@microsoft.com</email>
116    </address>
117  </author>
118
119  <author initials="L." surname="Masinter" fullname="Larry Masinter">
120    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
121    <address>
122      <postal>
123        <street>345 Park Ave</street>
124        <city>San Jose</city>
125        <region>CA</region>
126        <code>95110</code>
127        <country>USA</country>
128      </postal>
129      <email>LMM@acm.org</email>
130      <uri>http://larry.masinter.net/</uri>
131    </address>
132  </author>
133 
134  <author initials="P." surname="Leach" fullname="Paul J. Leach">
135    <organization abbrev="Microsoft">Microsoft Corporation</organization>
136    <address>
137      <postal>
138        <street>1 Microsoft Way</street>
139        <city>Redmond</city>
140        <region>WA</region>
141        <code>98052</code>
142      </postal>
143      <email>paulle@microsoft.com</email>
144    </address>
145  </author>
146   
147  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
148    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
149    <address>
150      <postal>
151        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
152        <street>The Stata Center, Building 32</street>
153        <street>32 Vassar Street</street>
154        <city>Cambridge</city>
155        <region>MA</region>
156        <code>02139</code>
157        <country>USA</country>
158      </postal>
159      <email>timbl@w3.org</email>
160      <uri>http://www.w3.org/People/Berners-Lee/</uri>
161    </address>
162  </author>
163
164  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
165    <organization abbrev="W3C">World Wide Web Consortium</organization>
166    <address>
167      <postal>
168        <street>W3C / ERCIM</street>
169        <street>2004, rte des Lucioles</street>
170        <city>Sophia-Antipolis</city>
171        <region>AM</region>
172        <code>06902</code>
173        <country>France</country>
174      </postal>
175      <email>ylafon@w3.org</email>
176      <uri>http://www.raubacapeu.net/people/yves/</uri>
177    </address>
178  </author>
179
180  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
181    <organization abbrev="greenbytes">greenbytes GmbH</organization>
182    <address>
183      <postal>
184        <street>Hafenweg 16</street>
185        <city>Muenster</city><region>NW</region><code>48155</code>
186        <country>Germany</country>
187      </postal>
188      <phone>+49 251 2807760</phone>
189      <facsimile>+49 251 2807761</facsimile>
190      <email>julian.reschke@greenbytes.de</email>
191      <uri>http://greenbytes.de/tech/webdav/</uri>
192    </address>
193  </author>
194
195  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
196  <workgroup>HTTPbis Working Group</workgroup>
197
198<abstract>
199<t>
200   The Hypertext Transfer Protocol (HTTP) is an application-level
201   protocol for distributed, collaborative, hypertext information
202   systems. HTTP has been in use by the World Wide Web global information
203   initiative since 1990. This document is Part 1 of the seven-part specification
204   that defines the protocol referred to as "HTTP/1.1" and, taken together,
205   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
206   its associated terminology, defines the "http" and "https" Uniform
207   Resource Identifier (URI) schemes, defines the generic message syntax
208   and parsing requirements for HTTP message frames, and describes
209   general security concerns for implementations.
210</t>
211</abstract>
212
213<note title="Editorial Note (To be removed by RFC Editor)">
214  <t>
215    Discussion of this draft should take place on the HTTPBIS working group
216    mailing list (ietf-http-wg@w3.org). The current issues list is
217    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/>
218    and related documents (including fancy diffs) can be found at
219    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
220  </t>
221  <t>
222    The changes in this draft are summarized in <xref target="changes.since.10"/>.
223  </t>
224</note>
225</front>
226<middle>
227<section title="Introduction" anchor="introduction">
228<t>
229   The Hypertext Transfer Protocol (HTTP) is an application-level
230   request/response protocol that uses extensible semantics and MIME-like
231   message payloads for flexible interaction with network-based hypertext
232   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
233   standard <xref target="RFC3986"/> to indicate request targets and
234   relationships between resources.
235   Messages are passed in a format similar to that used by Internet mail
236   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
237   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
238   between HTTP and MIME messages).
239</t>
240<t>
241   HTTP is a generic interface protocol for information systems. It is
242   designed to hide the details of how a service is implemented by presenting
243   a uniform interface to clients that is independent of the types of
244   resources provided. Likewise, servers do not need to be aware of each
245   client's purpose: an HTTP request can be considered in isolation rather
246   than being associated with a specific type of client or a predetermined
247   sequence of application steps. The result is a protocol that can be used
248   effectively in many different contexts and for which implementations can
249   evolve independently over time.
250</t>
251<t>
252   HTTP is also designed for use as an intermediation protocol for translating
253   communication to and from non-HTTP information systems.
254   HTTP proxies and gateways can provide access to alternative information
255   services by translating their diverse protocols into a hypertext
256   format that can be viewed and manipulated by clients in the same way
257   as HTTP services.
258</t>
259<t>
260   One consequence of HTTP flexibility is that the protocol cannot be
261   defined in terms of what occurs behind the interface. Instead, we
262   are limited to defining the syntax of communication, the intent
263   of received communication, and the expected behavior of recipients.
264   If the communication is considered in isolation, then successful
265   actions should be reflected in corresponding changes to the
266   observable interface provided by servers. However, since multiple
267   clients may act in parallel and perhaps at cross-purposes, we
268   cannot require that such changes be observable beyond the scope
269   of a single response.
270</t>
271<t>
272   This document is Part 1 of the seven-part specification of HTTP,
273   defining the protocol referred to as "HTTP/1.1" and obsoleting
274   <xref target="RFC2616"/>.
275   Part 1 describes the architectural elements that are used or
276   referred to in HTTP, defines the "http" and "https" URI schemes,
277   describes overall network operation and connection management,
278   and defines HTTP message framing and forwarding requirements.
279   Our goal is to define all of the mechanisms necessary for HTTP message
280   handling that are independent of message semantics, thereby defining the
281   complete set of requirements for message parsers and
282   message-forwarding intermediaries.
283</t>
284
285<section title="Requirements" anchor="intro.requirements">
286<t>
287   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
288   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
289   document are to be interpreted as described in <xref target="RFC2119"/>.
290</t>
291<t>
292   An implementation is not compliant if it fails to satisfy one or more
293   of the "MUST" or "REQUIRED" level requirements for the protocols it
294   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
295   level and all the "SHOULD" level requirements for its protocols is said
296   to be "unconditionally compliant"; one that satisfies all the "MUST"
297   level requirements but not all the "SHOULD" level requirements for its
298   protocols is said to be "conditionally compliant".
299</t>
300</section>
301
302<section title="Syntax Notation" anchor="notation">
303<iref primary="true" item="Grammar" subitem="ALPHA"/>
304<iref primary="true" item="Grammar" subitem="CR"/>
305<iref primary="true" item="Grammar" subitem="CRLF"/>
306<iref primary="true" item="Grammar" subitem="CTL"/>
307<iref primary="true" item="Grammar" subitem="DIGIT"/>
308<iref primary="true" item="Grammar" subitem="DQUOTE"/>
309<iref primary="true" item="Grammar" subitem="HEXDIG"/>
310<iref primary="true" item="Grammar" subitem="LF"/>
311<iref primary="true" item="Grammar" subitem="OCTET"/>
312<iref primary="true" item="Grammar" subitem="SP"/>
313<iref primary="true" item="Grammar" subitem="VCHAR"/>
314<iref primary="true" item="Grammar" subitem="WSP"/>
315<t>
316   This specification uses the Augmented Backus-Naur Form (ABNF) notation
317   of <xref target="RFC5234"/>.
318</t>
319<t anchor="core.rules">
320  <x:anchor-alias value="ALPHA"/>
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="LF"/>
328  <x:anchor-alias value="OCTET"/>
329  <x:anchor-alias value="SP"/>
330  <x:anchor-alias value="VCHAR"/>
331  <x:anchor-alias value="WSP"/>
332   The following core rules are included by
333   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
334   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
335   DIGIT (decimal 0-9), DQUOTE (double quote),
336   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
337   OCTET (any 8-bit sequence of data), SP (space),
338   VCHAR (any visible <xref target="USASCII"/> character),
339   and WSP (whitespace).
340</t>
341<t>
342   As a syntactic convention, ABNF rule names prefixed with "obs-" denote
343   "obsolete" grammar rules that appear for historical reasons.
344</t>
345
346<section title="ABNF Extension: #rule" anchor="notation.abnf">
347<t>
348  The #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
349  improve readability.
350</t>
351<t>
352  A construct "#" is defined, similar to "*", for defining comma-delimited
353  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
354  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
355  comma (",") and optional whitespace (OWS,
356  <xref target="basic.rules"/>).   
357</t>
358<figure><preamble>
359  Thus,
360</preamble><artwork type="example">
361  1#element =&gt; element *( OWS "," OWS element )
362</artwork></figure>
363<figure><preamble>
364  and:
365</preamble><artwork type="example">
366  #element =&gt; [ 1#element ]
367</artwork></figure>
368<figure><preamble>
369  and for n &gt;= 1 and m &gt; 1:
370</preamble><artwork type="example">
371  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
372</artwork></figure>
373<t>
374  For compatibility with legacy list rules, recipients &SHOULD; accept empty
375  list elements. In other words, consumers would follow the list productions:
376</t>
377<figure><artwork type="example">
378  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
379 
380  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
381</artwork></figure>
382<t>
383  Note that empty elements do not contribute to the count of elements present,
384  though.
385</t>
386<t>
387  For example, given these ABNF productions:
388</t>
389<figure><artwork type="example">
390  example-list      = 1#example-list-elmt
391  example-list-elmt = token ; see <xref target="basic.rules"/> 
392</artwork></figure>
393<t>
394  Then these are valid values for example-list (not including the double
395  quotes, which are present for delimitation only):
396</t>
397<figure><artwork type="example">
398  "foo,bar"
399  " foo ,bar,"
400  "  foo , ,bar,charlie   "
401  "foo ,bar,   charlie "
402</artwork></figure>
403<t>
404  But these values would be invalid, as at least one non-empty element is
405  required:
406</t>
407<figure><artwork type="example">
408  ""
409  ","
410  ",   ,"
411</artwork></figure>
412<t>
413  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
414  expanded as explained above.
415</t>
416</section>
417
418<section title="Basic Rules" anchor="basic.rules">
419<t anchor="rule.CRLF">
420  <x:anchor-alias value="CRLF"/>
421   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
422   protocol elements other than the message-body
423   (see <xref target="tolerant.applications"/> for tolerant applications).
424</t>
425<t anchor="rule.LWS">
426   This specification uses three rules to denote the use of linear
427   whitespace: OWS (optional whitespace), RWS (required whitespace), and
428   BWS ("bad" whitespace).
429</t>
430<t>
431   The OWS rule is used where zero or more linear whitespace characters may
432   appear. OWS &SHOULD; either not be produced or be produced as a single SP
433   character. Multiple OWS characters that occur within field-content &SHOULD;
434   be replaced with a single SP before interpreting the field value or
435   forwarding the message downstream.
436</t>
437<t>
438   RWS is used when at least one linear whitespace character is required to
439   separate field tokens. RWS &SHOULD; be produced as a single SP character.
440   Multiple RWS characters that occur within field-content &SHOULD; be
441   replaced with a single SP before interpreting the field value or
442   forwarding the message downstream.
443</t>
444<t>
445   BWS is used where the grammar allows optional whitespace for historical
446   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
447   recipients &MUST; accept such bad optional whitespace and remove it before
448   interpreting the field value or forwarding the message downstream.
449</t>
450<t anchor="rule.whitespace">
451  <x:anchor-alias value="BWS"/>
452  <x:anchor-alias value="OWS"/>
453  <x:anchor-alias value="RWS"/>
454  <x:anchor-alias value="obs-fold"/>
455</t>
456<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"/>
457  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
458                 ; "optional" whitespace
459  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
460                 ; "required" whitespace
461  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
462                 ; "bad" whitespace
463  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
464                 ; see <xref target="header.fields"/>
465</artwork></figure>
466<t anchor="rule.token.separators">
467  <x:anchor-alias value="tchar"/>
468  <x:anchor-alias value="token"/>
469  <x:anchor-alias value="special"/>
470  <x:anchor-alias value="word"/>
471   Many HTTP/1.1 header field values consist of words (token or quoted-string)
472   separated by whitespace or special characters. These special characters
473   &MUST; be in a quoted string to be used within a parameter value (as defined
474   in <xref target="transfer.codings"/>).
475</t>
476<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="word"/><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/><iref primary="true" item="Grammar" subitem="special"/>
477  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
478
479  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
480<!--
481  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
482 -->
483  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
484                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
485                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
486                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
487
488  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
489                 / ";" / ":" / "\" / DQUOTE / "/" / "["
490                 / "]" / "?" / "=" / "{" / "}"
491</artwork></figure>
492<t anchor="rule.quoted-string">
493  <x:anchor-alias value="quoted-string"/>
494  <x:anchor-alias value="qdtext"/>
495  <x:anchor-alias value="obs-text"/>
496   A string of text is parsed as a single word if it is quoted using
497   double-quote marks.
498</t>
499<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/><iref primary="true" item="Grammar" subitem="obs-text"/>
500  <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>
501  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
502                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except <x:ref>DQUOTE</x:ref> and "\"&gt; / <x:ref>obs-text</x:ref> 
503  <x:ref>obs-text</x:ref>       = %x80-FF
504</artwork></figure>
505<t anchor="rule.quoted-pair">
506  <x:anchor-alias value="quoted-pair"/>
507   The backslash character ("\") can be used as a single-character
508   quoting mechanism within quoted-string constructs:
509</t>
510<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
511  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
512</artwork></figure>
513<t>
514   Producers &SHOULD-NOT; escape characters that do not require escaping
515   (i.e., other than DQUOTE and the backslash character).
516</t>
517</section>
518
519<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
520  <x:anchor-alias value="request-header"/>
521  <x:anchor-alias value="response-header"/>
522  <x:anchor-alias value="entity-header"/>
523  <x:anchor-alias value="Cache-Control"/>
524  <x:anchor-alias value="Pragma"/>
525  <x:anchor-alias value="Warning"/>
526<t>
527  The ABNF rules below are defined in other parts:
528</t>
529<figure><!-- Part2--><artwork type="abnf2616">
530  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
531  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
532</artwork></figure>
533<figure><!-- Part3--><artwork type="abnf2616">
534  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
535</artwork></figure>
536<figure><!-- Part6--><artwork type="abnf2616">
537  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
538  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
539  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
540</artwork></figure>
541</section>
542
543</section>
544</section>
545
546<section title="HTTP architecture" anchor="architecture">
547<t>
548   HTTP was created for the World Wide Web architecture
549   and has evolved over time to support the scalability needs of a worldwide
550   hypertext system. Much of that architecture is reflected in the terminology
551   and syntax productions used to define HTTP.
552</t>
553
554<section title="Client/Server Operation" anchor="operation">
555<iref item="client"/>
556<iref item="server"/>
557<iref item="connection"/>
558<t>
559   HTTP is a request/response protocol that operates by exchanging messages
560   across a reliable transport or session-layer connection. An HTTP client
561   is a program that establishes a connection to a server for the purpose
562   of sending one or more HTTP requests.  An HTTP server is a program that
563   accepts connections in order to service HTTP requests by sending HTTP
564   responses.
565</t>
566<iref item="user agent"/>
567<iref item="origin server"/>
568<t>
569   Note that the terms "client" and "server" refer only to the roles that
570   these programs perform for a particular connection.  The same program
571   may act as a client on some connections and a server on others.  We use
572   the term "user agent" to refer to the program that initiates a request,
573   such as a WWW browser, editor, or spider (web-traversing robot), and
574   the term "origin server" to refer to the program that can originate
575   authoritative responses to a request.
576</t>
577<t>
578   Most HTTP communication consists of a retrieval request (GET) for
579   a representation of some resource identified by a URI.  In the
580   simplest case, this may be accomplished via a single connection (v)
581   between the user agent (UA) and the origin server (O).
582</t>
583<figure><artwork type="drawing">
584       request chain ------------------------&gt;
585    UA -------------------v------------------- O
586       &lt;----------------------- response chain
587</artwork></figure>
588<iref item="message"/>
589<iref item="request"/>
590<iref item="response"/>
591<t>
592   A client sends an HTTP request to the server in the form of a request
593   message (<xref target="request"/>), beginning with a method, URI, and
594   protocol version, followed by MIME-like header fields containing
595   request modifiers, client information, and payload metadata, an empty
596   line to indicate the end of the header section, and finally the payload
597   body (if any).
598</t>
599<t>
600   A server responds to the client's request by sending an HTTP response
601   message (<xref target="response"/>), beginning with a status line that
602   includes the protocol version, a success or error code, and textual
603   reason phrase, followed by MIME-like header fields containing server
604   information, resource metadata, and payload metadata, an empty line to
605   indicate the end of the header section, and finally the payload body (if any).
606</t>
607<t>
608   The following example illustrates a typical message exchange for a
609   GET request on the URI "http://www.example.com/hello.txt":
610</t>
611<figure><preamble>
612client request:
613</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
614GET /hello.txt HTTP/1.1
615User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
616Host: www.example.com
617Accept: */*
618
619</artwork></figure>
620<figure><preamble>
621server response:
622</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
623HTTP/1.1 200 OK
624Date: Mon, 27 Jul 2009 12:28:53 GMT
625Server: Apache
626Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
627ETag: "34aa387-d-1568eb00"
628Accept-Ranges: bytes
629Content-Length: <x:length-of target="exbody"/>
630Vary: Accept-Encoding
631Content-Type: text/plain
632
633<x:span anchor="exbody">Hello World!
634</x:span></artwork></figure>
635</section>
636
637<section title="Intermediaries" anchor="intermediaries">
638<t>
639   A more complicated situation occurs when one or more intermediaries
640   are present in the request/response chain. There are three common
641   forms of intermediary: proxy, gateway, and tunnel.  In some cases,
642   a single intermediary may act as an origin server, proxy, gateway,
643   or tunnel, switching behavior based on the nature of each request.
644</t>
645<figure><artwork type="drawing">
646       request chain --------------------------------------&gt;
647    UA -----v----- A -----v----- B -----v----- C -----v----- O
648       &lt;------------------------------------- response chain
649</artwork></figure>
650<t>
651   The figure above shows three intermediaries (A, B, and C) between the
652   user agent and origin server. A request or response message that
653   travels the whole chain will pass through four separate connections.
654   Some HTTP communication options
655   may apply only to the connection with the nearest, non-tunnel
656   neighbor, only to the end-points of the chain, or to all connections
657   along the chain. Although the diagram is linear, each participant may
658   be engaged in multiple, simultaneous communications. For example, B
659   may be receiving requests from many clients other than A, and/or
660   forwarding requests to servers other than C, at the same time that it
661   is handling A's request.
662</t>
663<t>
664<iref item="upstream"/><iref item="downstream"/>
665<iref item="inbound"/><iref item="outbound"/>
666   We use the terms "upstream" and "downstream" to describe various
667   requirements in relation to the directional flow of a message:
668   all messages flow from upstream to downstream.
669   Likewise, we use the terms "inbound" and "outbound" to refer to
670   directions in relation to the request path: "inbound" means toward
671   the origin server and "outbound" means toward the user agent.
672</t>
673<t><iref item="proxy"/>
674   A proxy is a message forwarding agent that is selected by the
675   client, usually via local configuration rules, to receive requests
676   for some type(s) of absolute URI and attempt to satisfy those
677   requests via translation through the HTTP interface.  Some translations
678   are minimal, such as for proxy requests for "http" URIs, whereas
679   other requests may require translation to and from entirely different
680   application-layer protocols. Proxies are often used to group an
681   organization's HTTP requests through a common intermediary for the
682   sake of security, annotation services, or shared caching.
683</t>
684<t><iref item="gateway"/><iref item="reverse proxy"/>
685   A gateway (a.k.a., reverse proxy) is a receiving agent that acts
686   as a layer above some other server(s) and translates the received
687   requests to the underlying server's protocol.  Gateways are often
688   used for load balancing or partitioning HTTP services across
689   multiple machines.
690   Unlike a proxy, a gateway receives requests as if it were the
691   origin server for the requested resource; the requesting client
692   will not be aware that it is communicating with a gateway.
693   A gateway communicates with the client as if the gateway is the
694   origin server and thus is subject to all of the requirements on
695   origin servers for that connection.  A gateway communicates
696   with inbound servers using any protocol it desires, including
697   private extensions to HTTP that are outside the scope of this
698   specification.
699</t>
700<t><iref item="tunnel"/>
701   A tunnel acts as a blind relay between two connections
702   without changing the messages. Once active, a tunnel is not
703   considered a party to the HTTP communication, though the tunnel may
704   have been initiated by an HTTP request. A tunnel ceases to exist when
705   both ends of the relayed connection are closed. Tunnels are used to
706   extend a virtual connection through an intermediary, such as when
707   transport-layer security is used to establish private communication
708   through a shared firewall proxy.
709</t>
710</section>
711
712<section title="Caches" anchor="caches">
713<iref item="cache"/>
714<t>
715   Any party to HTTP communication that is not acting as a tunnel may
716   employ an internal cache for handling requests.
717   A cache is a local store of previous response messages and the
718   subsystem that controls its message storage, retrieval, and deletion.
719   A cache stores cacheable responses in order to reduce the response
720   time and network bandwidth consumption on future, equivalent
721   requests. Any client or server may include a cache, though a cache
722   cannot be used by a server while it is acting as a tunnel.
723</t>
724<t>
725   The effect of a cache is that the request/response chain is shortened
726   if one of the participants along the chain has a cached response
727   applicable to that request. The following illustrates the resulting
728   chain if B has a cached copy of an earlier response from O (via C)
729   for a request which has not been cached by UA or A.
730</t>
731<figure><artwork type="drawing">
732          request chain ----------&gt;
733       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
734          &lt;--------- response chain
735</artwork></figure>
736<t><iref item="cacheable"/>
737   A response is cacheable if a cache is allowed to store a copy of
738   the response message for use in answering subsequent requests.
739   Even when a response is cacheable, there may be additional
740   constraints placed by the client or by the origin server on when
741   that cached response can be used for a particular request. HTTP
742   requirements for cache behavior and cacheable responses are
743   defined in &caching-overview;
744</t>
745<t>
746   There are a wide variety of architectures and configurations
747   of caches and proxies deployed across the World Wide Web and
748   inside large organizations. These systems include national hierarchies
749   of proxy caches to save transoceanic bandwidth, systems that
750   broadcast or multicast cache entries, organizations that distribute
751   subsets of cached data via optical media, and so on.
752</t>
753</section>
754
755<section title="Transport Independence" anchor="transport-independence">
756<t>
757  HTTP systems are used in a wide variety of environments, from
758  corporate intranets with high-bandwidth links to long-distance
759  communication over low-power radio links and intermittent connectivity.
760</t>
761<t>
762   HTTP communication usually takes place over TCP/IP connections. The
763   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
764   not preclude HTTP from being implemented on top of any other protocol
765   on the Internet, or on other networks. HTTP only presumes a reliable
766   transport; any protocol that provides such guarantees can be used;
767   the mapping of the HTTP/1.1 request and response structures onto the
768   transport data units of the protocol in question is outside the scope
769   of this specification.
770</t>
771<t>
772   In HTTP/1.0, most implementations used a new connection for each
773   request/response exchange. In HTTP/1.1, a connection may be used for
774   one or more request/response exchanges, although connections may be
775   closed for a variety of reasons (see <xref target="persistent.connections"/>).
776</t>
777</section>
778
779<section title="HTTP Version" anchor="http.version">
780  <x:anchor-alias value="HTTP-Version"/>
781  <x:anchor-alias value="HTTP-Prot-Name"/>
782<t>
783   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
784   of the protocol. The protocol versioning policy is intended to allow
785   the sender to indicate the format of a message and its capacity for
786   understanding further HTTP communication, rather than the features
787   obtained via that communication. No change is made to the version
788   number for the addition of message components which do not affect
789   communication behavior or which only add to extensible field values.
790   The &lt;minor&gt; number is incremented when the changes made to the
791   protocol add features which do not change the general message parsing
792   algorithm, but which may add to the message semantics and imply
793   additional capabilities of the sender. The &lt;major&gt; number is
794   incremented when the format of a message within the protocol is
795   changed. See <xref target="RFC2145"/> for a fuller explanation.
796</t>
797<t>
798   The version of an HTTP message is indicated by an HTTP-Version field
799   in the first line of the message. HTTP-Version is case-sensitive.
800</t>
801<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
802  <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>
803  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
804</artwork></figure>
805<t>
806   Note that the major and minor numbers &MUST; be treated as separate
807   integers and that each &MAY; be incremented higher than a single digit.
808   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
809   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
810   &MUST-NOT; be sent.
811</t>
812<t>
813   An application that sends a request or response message that includes
814   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
815   with this specification. Applications that are at least conditionally
816   compliant with this specification &SHOULD; use an HTTP-Version of
817   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
818   not compatible with HTTP/1.0. For more details on when to send
819   specific HTTP-Version values, see <xref target="RFC2145"/>.
820</t>
821<t>
822   The HTTP version of an application is the highest HTTP version for
823   which the application is at least conditionally compliant.
824</t>
825<t>
826   Proxy and gateway applications need to be careful when forwarding
827   messages in protocol versions different from that of the application.
828   Since the protocol version indicates the protocol capability of the
829   sender, a proxy/gateway &MUST-NOT; send a message with a version
830   indicator which is greater than its actual version. If a higher
831   version request is received, the proxy/gateway &MUST; either downgrade
832   the request version, or respond with an error, or switch to tunnel
833   behavior.
834</t>
835<t>
836   Due to interoperability problems with HTTP/1.0 proxies discovered
837   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
838   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
839   they support. The proxy/gateway's response to that request &MUST; be in
840   the same major version as the request.
841</t>
842<x:note>
843  <t>
844    <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
845    of header fields required or forbidden by the versions involved.
846  </t>
847</x:note>
848</section>
849
850<section title="Uniform Resource Identifiers" anchor="uri">
851<iref primary="true" item="resource"/>
852<t>
853   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
854   throughout HTTP as the means for identifying resources. URI references
855   are used to target requests, indicate redirects, and define relationships.
856   HTTP does not limit what a resource may be; it merely defines an interface
857   that can be used to interact with a resource via HTTP. More information on
858   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
859</t>
860  <x:anchor-alias value="URI-reference"/>
861  <x:anchor-alias value="absolute-URI"/>
862  <x:anchor-alias value="relative-part"/>
863  <x:anchor-alias value="authority"/>
864  <x:anchor-alias value="path-abempty"/>
865  <x:anchor-alias value="path-absolute"/>
866  <x:anchor-alias value="port"/>
867  <x:anchor-alias value="query"/>
868  <x:anchor-alias value="uri-host"/>
869  <x:anchor-alias value="partial-URI"/>
870<t>
871   This specification adopts the definitions of "URI-reference",
872   "absolute-URI", "relative-part", "port", "host",
873   "path-abempty", "path-absolute", "query", and "authority" from
874   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
875   protocol elements that allow a relative URI without a fragment.
876</t>
877<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"/>
878  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
879  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
880  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
881  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
882  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
883  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
884  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
885  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
886  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
887 
888  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
889</artwork></figure>
890<t>
891   Each protocol element in HTTP that allows a URI reference will indicate in
892   its ABNF production whether the element allows only a URI in absolute form
893   (absolute-URI), any relative reference (relative-ref), or some other subset
894   of the URI-reference grammar. Unless otherwise indicated, URI references
895   are parsed relative to the request target (the default base URI for both
896   the request and its corresponding response).
897</t>
898
899<section title="http URI scheme" anchor="http.uri">
900  <x:anchor-alias value="http-URI"/>
901  <iref item="http URI scheme" primary="true"/>
902  <iref item="URI scheme" subitem="http" primary="true"/>
903<t>
904   The "http" URI scheme is hereby defined for the purpose of minting
905   identifiers according to their association with the hierarchical
906   namespace governed by a potential HTTP origin server listening for
907   TCP connections on a given port.
908   The HTTP server is identified via the generic syntax's
909   <x:ref>authority</x:ref> component, which includes a host
910   identifier and optional TCP port, and the remainder of the URI is
911   considered to be identifying data corresponding to a resource for
912   which that server might provide an HTTP interface.
913</t>
914<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
915  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
916</artwork></figure>
917<t>
918   The host identifier within an <x:ref>authority</x:ref> component is
919   defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>.  If host is
920   provided as an IP literal or IPv4 address, then the HTTP server is any
921   listener on the indicated TCP port at that IP address. If host is a
922   registered name, then that name is considered an indirect identifier
923   and the recipient might use a name resolution service, such as DNS,
924   to find the address of a listener for that host.
925   The host &MUST-NOT; be empty; if an "http" URI is received with an
926   empty host, then it &MUST; be rejected as invalid.
927   If the port subcomponent is empty or not given, then TCP port 80 is
928   assumed (the default reserved port for WWW services).
929</t>
930<t>
931   Regardless of the form of host identifier, access to that host is not
932   implied by the mere presence of its name or address. The host may or may
933   not exist and, even when it does exist, may or may not be running an
934   HTTP server or listening to the indicated port. The "http" URI scheme
935   makes use of the delegated nature of Internet names and addresses to
936   establish a naming authority (whatever entity has the ability to place
937   an HTTP server at that Internet name or address) and allows that
938   authority to determine which names are valid and how they might be used.
939</t>
940<t>
941   When an "http" URI is used within a context that calls for access to the
942   indicated resource, a client &MAY; attempt access by resolving
943   the host to an IP address, establishing a TCP connection to that address
944   on the indicated port, and sending an HTTP request message to the server
945   containing the URI's identifying data as described in <xref target="request"/>.
946   If the server responds to that request with a non-interim HTTP response
947   message, as described in <xref target="response"/>, then that response
948   is considered an authoritative answer to the client's request.
949</t>
950<t>
951   Although HTTP is independent of the transport protocol, the "http"
952   scheme is specific to TCP-based services because the name delegation
953   process depends on TCP for establishing authority.
954   An HTTP service based on some other underlying connection protocol
955   would presumably be identified using a different URI scheme, just as
956   the "https" scheme (below) is used for servers that require an SSL/TLS
957   transport layer on a connection. Other protocols may also be used to
958   provide access to "http" identified resources --- it is only the
959   authoritative interface used for mapping the namespace that is
960   specific to TCP.
961</t>
962</section>
963
964<section title="https URI scheme" anchor="https.uri">
965   <x:anchor-alias value="https-URI"/>
966   <iref item="https URI scheme"/>
967   <iref item="URI scheme" subitem="https"/>
968<t>
969   The "https" URI scheme is hereby defined for the purpose of minting
970   identifiers according to their association with the hierarchical
971   namespace governed by a potential HTTP origin server listening for
972   SSL/TLS-secured connections on a given TCP port.
973   The host and port are determined in the same way
974   as for the "http" scheme, except that a default TCP port of 443
975   is assumed if the port subcomponent is empty or not given.
976</t>
977<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
978  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
979</artwork></figure>
980<t>
981   The primary difference between the "http" and "https" schemes is
982   that interaction with the latter is required to be secured for
983   privacy through the use of strong encryption. The URI cannot be
984   sent in a request until the connection is secure. Likewise, the
985   default for caching is that each response that would be considered
986   "public" under the "http" scheme is instead treated as "private"
987   and thus not eligible for shared caching.
988</t>
989<t>
990   The process for authoritative access to an "https" identified
991   resource is defined in <xref target="RFC2818"/>.
992</t>
993</section>
994
995<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
996<t>
997   Since the "http" and "https" schemes conform to the URI generic syntax,
998   such URIs are normalized and compared according to the algorithm defined
999   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1000   described above for each scheme.
1001</t>
1002<t>
1003   If the port is equal to the default port for a scheme, the normal
1004   form is to elide the port subcomponent. Likewise, an empty path
1005   component is equivalent to an absolute path of "/", so the normal
1006   form is to provide a path of "/" instead. The scheme and host
1007   are case-insensitive and normally provided in lowercase; all
1008   other components are compared in a case-sensitive manner.
1009   Characters other than those in the "reserved" set are equivalent
1010   to their percent-encoded octets (see <xref target="RFC3986"
1011   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1012</t>
1013<t>
1014   For example, the following three URIs are equivalent:
1015</t>
1016<figure><artwork type="example">
1017   http://example.com:80/~smith/home.html
1018   http://EXAMPLE.com/%7Esmith/home.html
1019   http://EXAMPLE.com:/%7esmith/home.html
1020</artwork></figure>
1021<t>
1022   <cref anchor="TODO-not-here" source="roy">This paragraph does not belong here.</cref>
1023   If path-abempty is the empty string (i.e., there is no slash "/"
1024   path separator following the authority), then the "http" URI
1025   &MUST; be given as "/" when
1026   used as a request-target (<xref target="request-target"/>). If a proxy
1027   receives a host name which is not a fully qualified domain name, it
1028   &MAY; add its domain to the host name it received. If a proxy receives
1029   a fully qualified domain name, the proxy &MUST-NOT; change the host
1030   name.
1031</t>
1032</section>
1033</section>
1034</section>
1035
1036<section title="HTTP Message" anchor="http.message">
1037<x:anchor-alias value="generic-message"/>
1038<x:anchor-alias value="message.types"/>
1039<x:anchor-alias value="HTTP-message"/>
1040<x:anchor-alias value="start-line"/>
1041<iref item="header section"/>
1042<iref item="headers"/>
1043<iref item="header field"/>
1044<t>
1045   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1046   characters in a format similar to the Internet Message Format
1047   <xref target="RFC5322"/>: zero or more header fields (collectively
1048   referred to as the "headers" or the "header section"), an empty line
1049   indicating the end of the header section, and an optional message-body.
1050</t>
1051<t>
1052   An HTTP message can either be a request from client to server or a
1053   response from server to client.  Syntactically, the two types of message
1054   differ only in the start-line, which is either a Request-Line (for requests)
1055   or a Status-Line (for responses), and in the algorithm for determining
1056   the length of the message-body (<xref target="message.body"/>).
1057   In theory, a client could receive requests and a server could receive
1058   responses, distinguishing them by their different start-line formats,
1059   but in practice servers are implemented to only expect a request
1060   (a response is interpreted as an unknown or invalid request method)
1061   and clients are implemented to only expect a response.
1062</t>
1063<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1064  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1065                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1066                    <x:ref>CRLF</x:ref>
1067                    [ <x:ref>message-body</x:ref> ]
1068  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1069</artwork></figure>
1070<t>
1071   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1072   header field. The presence of whitespace might be an attempt to trick a
1073   noncompliant implementation of HTTP into ignoring that field or processing
1074   the next line as a new request, either of which may result in security
1075   issues when implementations within the request chain interpret the
1076   same message differently. HTTP/1.1 servers &MUST; reject such a message
1077   with a 400 (Bad Request) response.
1078</t>
1079
1080<section title="Message Parsing Robustness" anchor="message.robustness">
1081<t>
1082   In the interest of robustness, servers &SHOULD; ignore at least one
1083   empty line received where a Request-Line is expected. In other words, if
1084   the server is reading the protocol stream at the beginning of a
1085   message and receives a CRLF first, it should ignore the CRLF.
1086</t>
1087<t>
1088   Some old HTTP/1.0 client implementations generate an extra CRLF
1089   after a POST request as a lame workaround for some early server
1090   applications that failed to read message-body content that was
1091   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1092   preface or follow a request with an extra CRLF.  If terminating
1093   the request message-body with a line-ending is desired, then the
1094   client &MUST; include the terminating CRLF octets as part of the
1095   message-body length.
1096</t>
1097<t>
1098   The normal procedure for parsing an HTTP message is to read the
1099   start-line into a structure, read each header field into a hash
1100   table by field name until the empty line, and then use the parsed
1101   data to determine if a message-body is expected.  If a message-body
1102   has been indicated, then it is read as a stream until an amount
1103   of octets equal to the message-body length is read or the connection
1104   is closed.  Care must be taken to parse an HTTP message as a sequence
1105   of octets in an encoding that is a superset of US-ASCII.  Attempting
1106   to parse HTTP as a stream of Unicode characters in a character encoding
1107   like UTF-16 may introduce security flaws due to the differing ways
1108   that such parsers interpret invalid characters.
1109</t>
1110</section>
1111
1112<section title="Header Fields" anchor="header.fields">
1113  <x:anchor-alias value="header-field"/>
1114  <x:anchor-alias value="field-content"/>
1115  <x:anchor-alias value="field-name"/>
1116  <x:anchor-alias value="field-value"/>
1117  <x:anchor-alias value="OWS"/>
1118<t>
1119   Each HTTP header field consists of a case-insensitive field name
1120   followed by a colon (":"), optional whitespace, and the field value.
1121</t>
1122<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="header-field"/><iref primary="true" item="Grammar" subitem="field-name"/><iref primary="true" item="Grammar" subitem="field-value"/><iref primary="true" item="Grammar" subitem="field-content"/>
1123  <x:ref>header-field</x:ref>   = <x:ref>field-name</x:ref> ":" <x:ref>OWS</x:ref> [ <x:ref>field-value</x:ref> ] <x:ref>OWS</x:ref>
1124  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1125  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1126  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1127</artwork></figure>
1128<t>
1129   No whitespace is allowed between the header field name and colon. For
1130   security reasons, any request message received containing such whitespace
1131   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1132   &MUST; remove any such whitespace from a response message before
1133   forwarding the message downstream.
1134</t>
1135<t>
1136   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1137   preferred. The field value does not include any leading or trailing white
1138   space: OWS occurring before the first non-whitespace character of the
1139   field value or after the last non-whitespace character of the field value
1140   is ignored and &SHOULD; be removed before further processing (as this does
1141   not change the meaning of the header field).
1142</t>
1143<t>
1144   The order in which header fields with differing field names are
1145   received is not significant. However, it is "good practice" to send
1146   header fields that contain control data first, such as Host on
1147   requests and Date on responses, so that implementations can decide
1148   when not to handle a message as early as possible.  A server &MUST;
1149   wait until the entire header section is received before interpreting
1150   a request message, since later header fields might include conditionals,
1151   authentication credentials, or deliberately misleading duplicate
1152   header fields that would impact request processing.
1153</t>
1154<t>
1155   Multiple header fields with the same field name &MUST-NOT; be
1156   sent in a message unless the entire field value for that
1157   header field is defined as a comma-separated list [i.e., #(values)].
1158   Multiple header fields with the same field name can be combined into
1159   one "field-name: field-value" pair, without changing the semantics of the
1160   message, by appending each subsequent field value to the combined
1161   field value in order, separated by a comma. The order in which
1162   header fields with the same field name are received is therefore
1163   significant to the interpretation of the combined field value;
1164   a proxy &MUST-NOT; change the order of these field values when
1165   forwarding a message.
1166</t>
1167<x:note>
1168  <t>
1169   <x:h>Note:</x:h> The "Set-Cookie" header as implemented in
1170   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1171   can occur multiple times, but does not use the list syntax, and thus cannot
1172   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1173   for details.) Also note that the Set-Cookie2 header specified in
1174   <xref target="RFC2965"/> does not share this problem.
1175  </t>
1176</x:note>
1177<t>
1178   Historically, HTTP header field values could be extended over multiple
1179   lines by preceding each extra line with at least one space or horizontal
1180   tab character (line folding). This specification deprecates such line
1181   folding except within the message/http media type
1182   (<xref target="internet.media.type.message.http"/>).
1183   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1184   (i.e., that contain any field-content that matches the obs-fold rule) unless
1185   the message is intended for packaging within the message/http media type.
1186   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1187   obs-fold whitespace with a single SP prior to interpreting the field value
1188   or forwarding the message downstream.
1189</t>
1190<t>
1191   Historically, HTTP has allowed field content with text in the ISO-8859-1
1192   <xref target="ISO-8859-1"/> character encoding and supported other
1193   character sets only through use of <xref target="RFC2047"/> encoding.
1194   In practice, most HTTP header field values use only a subset of the
1195   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1196   header fields &SHOULD; limit their field values to US-ASCII characters.
1197   Recipients &SHOULD; treat other (obs-text) octets in field content as
1198   opaque data.
1199</t>
1200<t anchor="rule.comment">
1201  <x:anchor-alias value="comment"/>
1202  <x:anchor-alias value="ctext"/>
1203   Comments can be included in some HTTP header fields by surrounding
1204   the comment text with parentheses. Comments are only allowed in
1205   fields containing "comment" as part of their field value definition.
1206</t>
1207<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1208  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1209  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1210                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1211</artwork></figure>
1212<t anchor="rule.quoted-cpair">
1213  <x:anchor-alias value="quoted-cpair"/>
1214   The backslash character ("\") can be used as a single-character
1215   quoting mechanism within comment constructs:
1216</t>
1217<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1218  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1219</artwork></figure>
1220<t>
1221   Producers &SHOULD-NOT; escape characters that do not require escaping
1222   (i.e., other than the backslash character "\" and the parentheses "(" and
1223   ")").
1224</t>
1225</section>
1226
1227<section title="Message Body" anchor="message.body">
1228  <x:anchor-alias value="message-body"/>
1229<t>
1230   The message-body (if any) of an HTTP message is used to carry the
1231   payload body associated with the request or response. The message-body
1232   differs from the payload body only when a transfer-coding has been
1233   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1234</t>
1235<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1236  <x:ref>message-body</x:ref> = *OCTET
1237</artwork></figure>
1238<t>
1239   When one or more transfer-codings are applied to a payload body,
1240   usually for the sake of stream-delimiting or data compression, the
1241   Transfer-Encoding header field &MUST; be provided with the list of
1242   transfer-codings applied. Transfer-Encoding is a property of the message,
1243   not of the payload, and thus &MAY; be added or removed by any implementation
1244   along the request/response chain under the constraints found in
1245   <xref target="transfer.codings"/>.
1246</t>
1247<t>
1248   The rules for when a message-body is allowed in a message differ for
1249   requests and responses.
1250</t>
1251<t>
1252   The presence of a message-body in a request is signaled by the
1253   inclusion of a Content-Length or Transfer-Encoding header field in
1254   the request's header fields, even if the request method does not
1255   define any use for a message-body.  This allows the request
1256   message framing algorithm to be independent of method semantics.
1257   A server &MUST; read the entire request message-body or close
1258   the connection after sending its response.
1259</t>
1260<t>
1261   For response messages, whether or not a message-body is included with
1262   a message is dependent on both the request method and the response
1263   status code (<xref target="status.code.and.reason.phrase"/>).
1264   Responses to the HEAD request method never include a message-body
1265   because the associated response header fields (e.g., Transfer-Encoding,
1266   Content-Length, etc.) only indicate what their values would have been
1267   if the method had been GET.  All 1xx (Informational), 204 (No Content),
1268   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1269   All other responses do include a message-body, although the body
1270   &MAY; be of zero length.
1271</t>
1272<t>
1273   The length of the message-body is determined by one of the following
1274   (in order of precedence):
1275</t>
1276<t>
1277  <list style="numbers">
1278    <x:lt><t>
1279     Any response to a HEAD request and any response with a status
1280     code of 100-199, 204, or 304 is always terminated by the first
1281     empty line after the header fields, regardless of the header
1282     fields present in the message, and thus cannot contain a message-body.
1283    </t></x:lt>
1284    <x:lt><t>
1285     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1286     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1287     is used, the message-body length is determined by reading and decoding the
1288     chunked data until the transfer-coding indicates the data is complete.
1289    </t>
1290    <t>
1291     If a message is received with both a Transfer-Encoding header field and a
1292     Content-Length header field, the Transfer-Encoding overrides the Content-Length.
1293     Such a message may indicate an attempt to perform request or response
1294     smuggling (bypass of security-related checks on message routing or content)
1295     and thus should be handled as an error.  The provided Content-Length &MUST;
1296     be removed, prior to forwarding the message downstream, or replaced with
1297     the real message-body length after the transfer-coding is decoded.
1298    </t>
1299    <t>
1300     If a Transfer-Encoding header field is present in a response and the
1301     "chunked" transfer-coding is not present, the message-body length is
1302     determined by reading the connection until it is closed.
1303     If a Transfer-Encoding header field is present in a request and the
1304     "chunked" transfer-coding is not present, the message-body length cannot
1305     be determined reliably; the server &MUST; respond with 400 (Bad Request)
1306     and then close the connection.
1307    </t></x:lt>
1308    <x:lt><t>
1309     If a valid Content-Length header field (<xref target="header.content-length"/>)
1310     is present without Transfer-Encoding, its decimal value in octets defines
1311     the message-body length.  If the actual number of octets sent in the message
1312     is less than the indicated Content-Length, the recipient &MUST; consider
1313     the message to be incomplete and treat the connection as no longer usable.
1314     If the actual number of octets sent in the message is less than the indicated
1315     Content-Length, the recipient &MUST; only process the message-body up to the
1316     field value's number of octets; the remainder of the message &MUST; either
1317     be discarded or treated as the next message in a pipeline.  For the sake of
1318     robustness, a user-agent &MAY; attempt to detect and correct such an error
1319     in message framing if it is parsing the response to the last request on
1320     on a connection and the connection has been closed by the server.
1321    </t>
1322    <t>
1323     If a message is received with multiple Content-Length header fields or a
1324     Content-Length header field with an invalid value, the message framing
1325     is invalid and &MUST; be treated as an error to prevent request or
1326     response smuggling.
1327     If this is a request message, the server &MUST; respond with
1328     a 400 (Bad Request) status and then close the connection.
1329     If this is a response message received by a proxy or gateway, the proxy
1330     or gateway &MUST; discard the received response, send a 502 (Bad Gateway)
1331     status as its downstream response, and then close the connection.
1332     If this is a response message received by a user-agent, the message-body
1333     length is determined by reading the connection until it is closed;
1334     an error &SHOULD; be indicated to the user.
1335    </t></x:lt>
1336    <x:lt><t>
1337     If this is a request message and none of the above are true, then the
1338     message-body length is zero (no message-body is present).
1339    </t></x:lt>
1340    <x:lt><t>
1341     Otherwise, this is a response message without a declared message-body
1342     length, so the message-body length is determined by the number of octets
1343     received prior to the server closing the connection.
1344    </t></x:lt>
1345  </list>
1346</t>
1347<t>
1348   Since there is no way to distinguish a successfully completed,
1349   close-delimited message from a partially-received message interrupted
1350   by network failure, implementations &SHOULD; use encoding or
1351   length-delimited messages whenever possible.  The close-delimiting
1352   feature exists primarily for backwards compatibility with HTTP/1.0.
1353</t>
1354<t>
1355   A server &MAY; reject a request that contains a message-body but
1356   not a Content-Length by responding with 411 (Length Required).
1357</t>
1358<t>
1359   A client that sends a request containing a message-body &SHOULD;
1360   include a valid Content-Length header field if the message-body length
1361   is known in advance, since many existing services will otherwise respond
1362   with a 411 (Length Required) status code though they can handle the
1363   chunked encoding.  This is typically because such services are
1364   implemented via a gateway that requires a content-length in
1365   advance of being called and the server is unable or unwilling
1366   to buffer the entire request before processing.
1367</t>
1368<t>
1369   A client that sends a request containing a message-body &MUST; include a
1370   valid Content-Length header field if it does not know the server will
1371   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1372   of specific user configuration or by remembering the version of a prior
1373   received response.
1374</t>
1375<t>
1376   Request messages that are prematurely terminated, possibly due to a
1377   cancelled connection or a server-imposed time-out exception, &MUST;
1378   result in closure of the connection; sending an HTTP/1.1 error response
1379   prior to closing the connection is &OPTIONAL;.
1380   Response messages that are prematurely terminated, usually by closure
1381   of the connection prior to receiving the given number of octets or by
1382   failure to decode a transfer-encoded message-body, &MUST; be recorded
1383   as incomplete.  A user agent &MUST-NOT; render an incomplete response
1384   message-body as if it were complete (i.e., some indication must be given
1385   to the user that an error occurred).  Cache requirements for incomplete
1386   responses are defined in &cache-incomplete;.
1387</t>
1388</section>
1389
1390<section title="General Header Fields" anchor="general.header.fields">
1391  <x:anchor-alias value="general-header"/>
1392<t>
1393   There are a few header fields which have general applicability for
1394   both request and response messages, but which do not apply to the
1395   payload being transferred. These header fields apply only to the
1396   message being transmitted.
1397</t>
1398<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1399  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1400                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1401                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1402                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1403                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1404                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1405                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1406                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1407                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1408</artwork></figure>
1409<t>
1410   General-header field names can be extended reliably only in
1411   combination with a change in the protocol version. However, new or
1412   experimental header fields may be given the semantics of general
1413   header fields if all parties in the communication recognize them to
1414   be general-header fields. Unrecognized header fields are treated as
1415   entity-header fields.
1416</t>
1417</section>
1418</section>
1419
1420<section title="Request" anchor="request">
1421  <x:anchor-alias value="Request"/>
1422<t>
1423   A request message from a client to a server includes, within the
1424   first line of that message, the method to be applied to the resource,
1425   the identifier of the resource, and the protocol version in use.
1426</t>
1427<!--                 Host                      ; should be moved here eventually -->
1428<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1429  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1430                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1431                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1432                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> ) ; &entity-header-fields;
1433                  <x:ref>CRLF</x:ref>
1434                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1435</artwork></figure>
1436
1437<section title="Request-Line" anchor="request-line">
1438  <x:anchor-alias value="Request-Line"/>
1439<t>
1440   The Request-Line begins with a method token, followed by the
1441   request-target and the protocol version, and ending with CRLF. The
1442   elements are separated by SP characters. No CR or LF is allowed
1443   except in the final CRLF sequence.
1444</t>
1445<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1446  <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>
1447</artwork></figure>
1448
1449<section title="Method" anchor="method">
1450  <x:anchor-alias value="Method"/>
1451<t>
1452   The Method  token indicates the method to be performed on the
1453   resource identified by the request-target. The method is case-sensitive.
1454</t>
1455<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1456  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1457</artwork></figure>
1458</section>
1459
1460<section title="request-target" anchor="request-target">
1461  <x:anchor-alias value="request-target"/>
1462<t>
1463   The request-target
1464   identifies the resource upon which to apply the request.
1465</t>
1466<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1467  <x:ref>request-target</x:ref> = "*"
1468                 / <x:ref>absolute-URI</x:ref>
1469                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1470                 / <x:ref>authority</x:ref>
1471</artwork></figure>
1472<t>
1473   The four options for request-target are dependent on the nature of the
1474   request.
1475</t>   
1476<t>
1477   The asterisk "*" means that the request does not apply to a
1478   particular resource, but to the server itself, and is only allowed
1479   when the method used does not necessarily apply to a resource. One
1480   example would be
1481</t>
1482<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1483OPTIONS * HTTP/1.1
1484</artwork></figure>
1485<t>
1486   The absolute-URI form is &REQUIRED; when the request is being made to a
1487   proxy. The proxy is requested to forward the request or service it
1488   from a valid cache, and return the response. Note that the proxy &MAY;
1489   forward the request on to another proxy or directly to the server
1490   specified by the absolute-URI. In order to avoid request loops, a
1491   proxy &MUST; be able to recognize all of its server names, including
1492   any aliases, local variations, and the numeric IP address. An example
1493   Request-Line would be:
1494</t>
1495<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1496GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1497</artwork></figure>
1498<t>
1499   To allow for transition to absolute-URIs in all requests in future
1500   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1501   form in requests, even though HTTP/1.1 clients will only generate
1502   them in requests to proxies.
1503</t>
1504<t>
1505   The authority form is only used by the CONNECT method (&CONNECT;).
1506</t>
1507<t>
1508   The most common form of request-target is that used to identify a
1509   resource on an origin server or gateway. In this case the absolute
1510   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1511   the request-target, and the network location of the URI (authority) &MUST;
1512   be transmitted in a Host header field. For example, a client wishing
1513   to retrieve the resource above directly from the origin server would
1514   create a TCP connection to port 80 of the host "www.example.org" and send
1515   the lines:
1516</t>
1517<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1518GET /pub/WWW/TheProject.html HTTP/1.1
1519Host: www.example.org
1520</artwork></figure>
1521<t>
1522   followed by the remainder of the Request. Note that the absolute path
1523   cannot be empty; if none is present in the original URI, it &MUST; be
1524   given as "/" (the server root).
1525</t>
1526<t>
1527   If a proxy receives a request without any path in the request-target and
1528   the method specified is capable of supporting the asterisk form of
1529   request-target, then the last proxy on the request chain &MUST; forward the
1530   request with "*" as the final request-target.
1531</t>
1532<figure><preamble>   
1533   For example, the request
1534</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1535OPTIONS http://www.example.org:8001 HTTP/1.1
1536</artwork></figure>
1537<figure><preamble>   
1538  would be forwarded by the proxy as
1539</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1540OPTIONS * HTTP/1.1
1541Host: www.example.org:8001
1542</artwork>
1543<postamble>
1544   after connecting to port 8001 of host "www.example.org".
1545</postamble>
1546</figure>
1547<t>
1548   The request-target is transmitted in the format specified in
1549   <xref target="http.uri"/>. If the request-target is percent-encoded
1550   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1551   &MUST; decode the request-target in order to
1552   properly interpret the request. Servers &SHOULD; respond to invalid
1553   request-targets with an appropriate status code.
1554</t>
1555<t>
1556   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1557   received request-target when forwarding it to the next inbound server,
1558   except as noted above to replace a null path-absolute with "/" or "*".
1559</t>
1560<x:note>
1561  <t>
1562    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1563    meaning of the request when the origin server is improperly using
1564    a non-reserved URI character for a reserved purpose.  Implementors
1565    should be aware that some pre-HTTP/1.1 proxies have been known to
1566    rewrite the request-target.
1567  </t>
1568</x:note>
1569<t>
1570   HTTP does not place a pre-defined limit on the length of a request-target.
1571   A server &MUST; be prepared to receive URIs of unbounded length and
1572   respond with the 414 (URI Too Long) status if the received
1573   request-target would be longer than the server wishes to handle
1574   (see &status-414;).
1575</t>
1576<t>
1577   Various ad-hoc limitations on request-target length are found in practice.
1578   It is &RECOMMENDED; that all HTTP senders and recipients support
1579   request-target lengths of 8000 or more octets.
1580</t>
1581<x:note>
1582  <t>
1583    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1584    are not part of the request-target and thus will not be transmitted
1585    in an HTTP request.
1586  </t>
1587</x:note>
1588</section>
1589</section>
1590
1591<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1592<t>
1593   The exact resource identified by an Internet request is determined by
1594   examining both the request-target and the Host header field.
1595</t>
1596<t>
1597   An origin server that does not allow resources to differ by the
1598   requested host &MAY; ignore the Host header field value when
1599   determining the resource identified by an HTTP/1.1 request. (But see
1600   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1601   for other requirements on Host support in HTTP/1.1.)
1602</t>
1603<t>
1604   An origin server that does differentiate resources based on the host
1605   requested (sometimes referred to as virtual hosts or vanity host
1606   names) &MUST; use the following rules for determining the requested
1607   resource on an HTTP/1.1 request:
1608  <list style="numbers">
1609    <t>If request-target is an absolute-URI, the host is part of the
1610     request-target. Any Host header field value in the request &MUST; be
1611     ignored.</t>
1612    <t>If the request-target is not an absolute-URI, and the request includes
1613     a Host header field, the host is determined by the Host header
1614     field value.</t>
1615    <t>If the host as determined by rule 1 or 2 is not a valid host on
1616     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1617  </list>
1618</t>
1619<t>
1620   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1621   attempt to use heuristics (e.g., examination of the URI path for
1622   something unique to a particular host) in order to determine what
1623   exact resource is being requested.
1624</t>
1625</section>
1626
1627<section title="Effective Request URI" anchor="effective.request.uri">
1628  <iref primary="true" item="Effective Request URI"/>
1629<t>
1630   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1631   for the resource they are intended for; instead, the value needs to be inferred from the
1632   request-target, Host header and other context. The result of this process is
1633   the "Effective Request URI".
1634</t>
1635<t>
1636   If the request-target is an absolute-URI, then the Effective Request URI is
1637   the request-target.
1638</t>
1639<t>
1640   If the request-target uses the path-absolute (plus optional query) syntax
1641   or if it is just the asterisk "*", then the Effective Request URI is
1642   constructed by concatenating
1643</t>
1644<t>
1645  <list style="symbols">
1646    <t>
1647      the scheme name: "http" if the request was received over an insecure
1648      TCP connection, or "https" when received over SSL/TLS-secured TCP
1649      connection,
1650    </t>
1651    <t>
1652      the character sequence "://",
1653    </t>
1654    <t>
1655      the authority component, as specified in the Host header
1656      (<xref target="header.host"/>) and determined by the rules in
1657      <xref target="the.resource.identified.by.a.request"/>,
1658      <cref anchor="effrequri-nohost" source="jre">Do we need to include the handling of missing hosts in HTTP/1.0 messages, as
1659      described in <xref target="the.resource.identified.by.a.request"/>? -- See <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/></cref>
1660      and
1661    </t>
1662    <t>
1663      the request-target obtained from the Request-Line, unless the
1664      request-target is just the asterisk "*".
1665    </t>
1666  </list>
1667</t>
1668<t>
1669   Otherwise, when request-target uses the authority form, the Effective
1670   Request URI is undefined.
1671</t>
1672<figure>
1673<preamble>
1674   Example 1: the Effective Request URI for the message
1675</preamble> 
1676<artwork type="example" x:indent-with="  ">
1677GET /pub/WWW/TheProject.html HTTP/1.1
1678Host: www.example.org:8080
1679</artwork>
1680<postamble>
1681  (received over an insecure TCP connection) is "http", plus "://", plus the
1682  authority component "www.example.org:8080", plus the request-target
1683  "/pub/WWW/TheProject.html", thus
1684  "http://www.example.org:8080/pub/WWW/TheProject.html".
1685</postamble>
1686</figure>
1687<figure>
1688<preamble>
1689   Example 2: the Effective Request URI for the message
1690</preamble> 
1691<artwork type="example" x:indent-with="  ">
1692GET * HTTP/1.1
1693Host: www.example.org
1694</artwork>
1695<postamble>
1696  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1697  authority component "www.example.org", thus "https://www.example.org".
1698</postamble>
1699</figure>
1700<t>
1701   Effective Request URIs are compared using the rules described in
1702   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
1703   be treated as equivalent to an absolute path of "/".
1704</t> 
1705</section>
1706
1707</section>
1708
1709
1710<section title="Response" anchor="response">
1711  <x:anchor-alias value="Response"/>
1712<t>
1713   After receiving and interpreting a request message, a server responds
1714   with an HTTP response message.
1715</t>
1716<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1717  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1718                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1719                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1720                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> ) ; &entity-header-fields;
1721                  <x:ref>CRLF</x:ref>
1722                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1723</artwork></figure>
1724
1725<section title="Status-Line" anchor="status-line">
1726  <x:anchor-alias value="Status-Line"/>
1727<t>
1728   The first line of a Response message is the Status-Line, consisting
1729   of the protocol version followed by a numeric status code and its
1730   associated textual phrase, with each element separated by SP
1731   characters. No CR or LF is allowed except in the final CRLF sequence.
1732</t>
1733<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1734  <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>
1735</artwork></figure>
1736
1737<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1738  <x:anchor-alias value="Reason-Phrase"/>
1739  <x:anchor-alias value="Status-Code"/>
1740<t>
1741   The Status-Code element is a 3-digit integer result code of the
1742   attempt to understand and satisfy the request. These codes are fully
1743   defined in &status-codes;.  The Reason Phrase exists for the sole
1744   purpose of providing a textual description associated with the numeric
1745   status code, out of deference to earlier Internet application protocols
1746   that were more frequently used with interactive text clients.
1747   A client &SHOULD; ignore the content of the Reason Phrase.
1748</t>
1749<t>
1750   The first digit of the Status-Code defines the class of response. The
1751   last two digits do not have any categorization role. There are 5
1752   values for the first digit:
1753  <list style="symbols">
1754    <t>
1755      1xx: Informational - Request received, continuing process
1756    </t>
1757    <t>
1758      2xx: Success - The action was successfully received,
1759        understood, and accepted
1760    </t>
1761    <t>
1762      3xx: Redirection - Further action must be taken in order to
1763        complete the request
1764    </t>
1765    <t>
1766      4xx: Client Error - The request contains bad syntax or cannot
1767        be fulfilled
1768    </t>
1769    <t>
1770      5xx: Server Error - The server failed to fulfill an apparently
1771        valid request
1772    </t>
1773  </list>
1774</t>
1775<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"/>
1776  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1777  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1778</artwork></figure>
1779</section>
1780</section>
1781
1782</section>
1783
1784
1785<section title="Protocol Parameters" anchor="protocol.parameters">
1786
1787<section title="Date/Time Formats: Full Date" anchor="date.time.formats.full.date">
1788  <x:anchor-alias value="HTTP-date"/>
1789<t>
1790   HTTP applications have historically allowed three different formats
1791   for date/time stamps.
1792   However, the preferred format is
1793   a fixed-length subset of that defined by <xref target="RFC1123"/>:
1794</t>
1795<figure><artwork type="example" x:indent-with="  ">
1796Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1797</artwork></figure>
1798<t>
1799   The other formats are described here only for compatibility with obsolete
1800   implementations.
1801</t>
1802<figure><artwork type="example" x:indent-with="  ">
1803Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1804Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1805</artwork></figure>
1806<t>
1807   HTTP/1.1 clients and servers that parse a date value &MUST; accept
1808   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1809   only generate the RFC 1123 format for representing HTTP-date values
1810   in header fields. See <xref target="tolerant.applications"/> for further information.
1811</t>
1812<t>
1813   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1814   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1815   equal to UTC (Coordinated Universal Time). This is indicated in the
1816   first two formats by the inclusion of "GMT" as the three-letter
1817   abbreviation for time zone, and &MUST; be assumed when reading the
1818   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1819   additional whitespace beyond that specifically included as SP in the
1820   grammar.
1821</t>
1822<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1823  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1824</artwork></figure>
1825<t anchor="preferred.date.format">
1826  <x:anchor-alias value="rfc1123-date"/>
1827  <x:anchor-alias value="time-of-day"/>
1828  <x:anchor-alias value="hour"/>
1829  <x:anchor-alias value="minute"/>
1830  <x:anchor-alias value="second"/>
1831  <x:anchor-alias value="day-name"/>
1832  <x:anchor-alias value="day"/>
1833  <x:anchor-alias value="month"/>
1834  <x:anchor-alias value="year"/>
1835  <x:anchor-alias value="GMT"/>
1836  Preferred format:
1837</t>
1838<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc1123-date"/><iref primary="true" item="Grammar" subitem="date1"/><iref primary="true" item="Grammar" subitem="time-of-day"/><iref primary="true" item="Grammar" subitem="hour"/><iref primary="true" item="Grammar" subitem="minute"/><iref primary="true" item="Grammar" subitem="second"/><iref primary="true" item="Grammar" subitem="day-name"/><iref primary="true" item="Grammar" subitem="day-name-l"/><iref primary="true" item="Grammar" subitem="day"/><iref primary="true" item="Grammar" subitem="month"/><iref primary="true" item="Grammar" subitem="year"/><iref primary="true" item="Grammar" subitem="GMT"/>
1839  <x:ref>rfc1123-date</x:ref> = <x:ref>day-name</x:ref> "," <x:ref>SP</x:ref> date1 <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>GMT</x:ref>
1840
1841  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1842               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1843               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1844               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
1845               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
1846               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
1847               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
1848               
1849  <x:ref>date1</x:ref>        = <x:ref>day</x:ref> <x:ref>SP</x:ref> <x:ref>month</x:ref> <x:ref>SP</x:ref> <x:ref>year</x:ref>
1850               ; e.g., 02 Jun 1982
1851
1852  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
1853  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
1854               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
1855               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
1856               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
1857               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
1858               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
1859               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
1860               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
1861               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
1862               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
1863               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
1864               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
1865  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
1866
1867  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
1868
1869  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
1870                 ; 00:00:00 - 23:59:59
1871                 
1872  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
1873  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1874  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1875</artwork></figure>
1876<t>
1877  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
1878  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
1879  same as those defined for the RFC 5322 constructs
1880  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
1881</t>
1882<t anchor="obsolete.date.formats">
1883  <x:anchor-alias value="obs-date"/>
1884  <x:anchor-alias value="rfc850-date"/>
1885  <x:anchor-alias value="asctime-date"/>
1886  <x:anchor-alias value="date1"/>
1887  <x:anchor-alias value="date2"/>
1888  <x:anchor-alias value="date3"/>
1889  <x:anchor-alias value="rfc1123-date"/>
1890  <x:anchor-alias value="day-name-l"/>
1891  Obsolete formats:
1892</t>
1893<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
1894  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
1895</artwork></figure>
1896<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
1897  <x:ref>rfc850-date</x:ref>  = <x:ref>day-name-l</x:ref> "," <x:ref>SP</x:ref> <x:ref>date2</x:ref> <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>GMT</x:ref>
1898  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
1899                 ; day-month-year (e.g., 02-Jun-82)
1900
1901  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
1902         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
1903         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
1904         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
1905         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
1906         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
1907         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
1908</artwork></figure>
1909<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
1910  <x:ref>asctime-date</x:ref> = <x:ref>day-name</x:ref> <x:ref>SP</x:ref> <x:ref>date3</x:ref> <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>year</x:ref>
1911  <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> ))
1912                 ; month day (e.g., Jun  2)
1913</artwork></figure>
1914<x:note>
1915  <t>
1916    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
1917    accepting date values that may have been sent by non-HTTP
1918    applications, as is sometimes the case when retrieving or posting
1919    messages via proxies/gateways to SMTP or NNTP.
1920  </t>
1921</x:note>
1922<x:note>
1923  <t>
1924    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
1925    to their usage within the protocol stream. Clients and servers are
1926    not required to use these formats for user presentation, request
1927    logging, etc.
1928  </t>
1929</x:note>
1930</section>
1931
1932<section title="Transfer Codings" anchor="transfer.codings">
1933  <x:anchor-alias value="transfer-coding"/>
1934  <x:anchor-alias value="transfer-extension"/>
1935<t>
1936   Transfer-coding values are used to indicate an encoding
1937   transformation that has been, can be, or may need to be applied to a
1938   payload body in order to ensure "safe transport" through the network.
1939   This differs from a content coding in that the transfer-coding is a
1940   property of the message rather than a property of the representation
1941   that is being transferred.
1942</t>
1943<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1944  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
1945                          / "compress" ; <xref target="compress.coding"/>
1946                          / "deflate" ; <xref target="deflate.coding"/>
1947                          / "gzip" ; <xref target="gzip.coding"/>
1948                          / <x:ref>transfer-extension</x:ref>
1949  <x:ref>transfer-extension</x:ref>      = <x:ref>token</x:ref> *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>transfer-parameter</x:ref> )
1950</artwork></figure>
1951<t anchor="rule.parameter">
1952  <x:anchor-alias value="attribute"/>
1953  <x:anchor-alias value="transfer-parameter"/>
1954  <x:anchor-alias value="value"/>
1955   Parameters are in the form of attribute/value pairs.
1956</t>
1957<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/><iref primary="true" item="Grammar" subitem="date2"/><iref primary="true" item="Grammar" subitem="date3"/>
1958  <x:ref>transfer-parameter</x:ref>      = <x:ref>attribute</x:ref> <x:ref>BWS</x:ref> "=" <x:ref>BWS</x:ref> <x:ref>value</x:ref>
1959  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
1960  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
1961</artwork></figure>
1962<t>
1963   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1964   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1965   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1966</t>
1967<t>
1968   Whenever a transfer-coding is applied to a payload body, the set of
1969   transfer-codings &MUST; include "chunked", unless the message indicates it
1970   is terminated by closing the connection. When the "chunked" transfer-coding
1971   is used, it &MUST; be the last transfer-coding applied to form the
1972   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
1973   than once to a message-body.
1974</t>
1975<t>
1976   Transfer-codings are analogous to the Content-Transfer-Encoding values of
1977   MIME, which were designed to enable safe transport of binary data over a
1978   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1979   However, safe transport
1980   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1981   the only unsafe characteristic of message-bodies is the difficulty in
1982   determining the exact message body length (<xref target="message.body"/>),
1983   or the desire to encrypt data over a shared transport.
1984</t>
1985<t>
1986   A server that receives a request message with a transfer-coding it does
1987   not understand &SHOULD; respond with 501 (Not Implemented) and then
1988   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1989   client.
1990</t>
1991
1992<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1993  <iref item="chunked (Coding Format)"/>
1994  <iref item="Coding Format" subitem="chunked"/>
1995  <x:anchor-alias value="chunk"/>
1996  <x:anchor-alias value="Chunked-Body"/>
1997  <x:anchor-alias value="chunk-data"/>
1998  <x:anchor-alias value="chunk-ext"/>
1999  <x:anchor-alias value="chunk-ext-name"/>
2000  <x:anchor-alias value="chunk-ext-val"/>
2001  <x:anchor-alias value="chunk-size"/>
2002  <x:anchor-alias value="last-chunk"/>
2003  <x:anchor-alias value="trailer-part"/>
2004  <x:anchor-alias value="quoted-str-nf"/>
2005  <x:anchor-alias value="qdtext-nf"/>
2006<t>
2007   The chunked encoding modifies the body of a message in order to
2008   transfer it as a series of chunks, each with its own size indicator,
2009   followed by an &OPTIONAL; trailer containing entity-header fields. This
2010   allows dynamically produced content to be transferred along with the
2011   information necessary for the recipient to verify that it has
2012   received the full message.
2013</t>
2014<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"/><iref primary="true" item="Grammar" subitem="quoted-str-nf"/><iref primary="true" item="Grammar" subitem="qdtext-nf"/>
2015  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2016                   <x:ref>last-chunk</x:ref>
2017                   <x:ref>trailer-part</x:ref>
2018                   <x:ref>CRLF</x:ref>
2019 
2020  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2021                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2022  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2023  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2024 
2025  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
2026                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
2027  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2028  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2029  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2030  <x:ref>trailer-part</x:ref>   = *( <x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref> )
2031 
2032  <x:ref>quoted-str-nf</x:ref>  = <x:ref>DQUOTE</x:ref> *( <x:ref>qdtext-nf</x:ref> / <x:ref>quoted-pair</x:ref> ) <x:ref>DQUOTE</x:ref>
2033                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2034  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2035                 ; <x:ref>WSP</x:ref> / &lt;<x:ref>VCHAR</x:ref> except <x:ref>DQUOTE</x:ref> and "\"&gt; / <x:ref>obs-text</x:ref> 
2036</artwork></figure>
2037<t>
2038   The chunk-size field is a string of hex digits indicating the size of
2039   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2040   zero, followed by the trailer, which is terminated by an empty line.
2041</t>
2042<t>
2043   The trailer allows the sender to include additional HTTP header
2044   fields at the end of the message. The Trailer header field can be
2045   used to indicate which header fields are included in a trailer (see
2046   <xref target="header.trailer"/>).
2047</t>
2048<t>
2049   A server using chunked transfer-coding in a response &MUST-NOT; use the
2050   trailer for any header fields unless at least one of the following is
2051   true:
2052  <list style="numbers">
2053    <t>the request included a TE header field that indicates "trailers" is
2054     acceptable in the transfer-coding of the  response, as described in
2055     <xref target="header.te"/>; or,</t>
2056
2057    <t>the server is the origin server for the response, the trailer
2058     fields consist entirely of optional metadata, and the recipient
2059     could use the message (in a manner acceptable to the origin server)
2060     without receiving this metadata.  In other words, the origin server
2061     is willing to accept the possibility that the trailer fields might
2062     be silently discarded along the path to the client.</t>
2063  </list>
2064</t>
2065<t>
2066   This requirement prevents an interoperability failure when the
2067   message is being received by an HTTP/1.1 (or later) proxy and
2068   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2069   compliance with the protocol would have necessitated a possibly
2070   infinite buffer on the proxy.
2071</t>
2072<t>
2073   A process for decoding the "chunked" transfer-coding
2074   can be represented in pseudo-code as:
2075</t>
2076<figure><artwork type="code">
2077  length := 0
2078  read chunk-size, chunk-ext (if any) and CRLF
2079  while (chunk-size &gt; 0) {
2080     read chunk-data and CRLF
2081     append chunk-data to decoded-body
2082     length := length + chunk-size
2083     read chunk-size and CRLF
2084  }
2085  read header-field
2086  while (header-field not empty) {
2087     append header-field to existing header fields
2088     read header-field
2089  }
2090  Content-Length := length
2091  Remove "chunked" from Transfer-Encoding
2092</artwork></figure>
2093<t>
2094   All HTTP/1.1 applications &MUST; be able to receive and decode the
2095   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2096   they do not understand.
2097</t>
2098</section>
2099
2100<section title="Compression Codings" anchor="compression.codings">
2101<t>
2102   The codings defined below can be used to compress the payload of a
2103   message.
2104</t>
2105<x:note><t>
2106   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2107   is not desirable and is discouraged for future encodings. Their
2108   use here is representative of historical practice, not good
2109   design.
2110</t></x:note>
2111<x:note><t>
2112   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2113   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2114   equivalent to "gzip" and "compress" respectively.
2115</t></x:note>
2116
2117<section title="Compress Coding" anchor="compress.coding">
2118<iref item="compress (Coding Format)"/>
2119<iref item="Coding Format" subitem="compress"/>
2120<t>
2121   The "compress" format is produced by the common UNIX file compression
2122   program "compress". This format is an adaptive Lempel-Ziv-Welch
2123   coding (LZW).
2124</t>
2125</section>
2126
2127<section title="Deflate Coding" anchor="deflate.coding">
2128<iref item="deflate (Coding Format)"/>
2129<iref item="Coding Format" subitem="deflate"/>
2130<t>
2131   The "deflate" format is defined as the "deflate" compression mechanism
2132   (described in <xref target="RFC1951"/>) used inside the "zlib"
2133   data format (<xref target="RFC1950"/>).
2134</t>
2135<x:note>
2136  <t>
2137    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2138    compressed data without the zlib wrapper.
2139   </t>
2140</x:note>
2141</section>
2142
2143<section title="Gzip Coding" anchor="gzip.coding">
2144<iref item="gzip (Coding Format)"/>
2145<iref item="Coding Format" subitem="gzip"/>
2146<t>
2147   The "gzip" format is produced by the file compression program
2148   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2149   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2150</t>
2151</section>
2152
2153</section>
2154
2155<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2156<t>
2157   The HTTP Transfer Coding Registry defines the name space for the transfer
2158   coding names.
2159</t>
2160<t>
2161   Registrations &MUST; include the following fields:
2162   <list style="symbols">
2163     <t>Name</t>
2164     <t>Description</t>
2165     <t>Pointer to specification text</t>
2166   </list>
2167</t>
2168<t>
2169   Names of transfer codings &MUST-NOT; overlap with names of content codings
2170   (&content-codings;), unless the encoding transformation is identical (as it
2171   is the case for the compression codings defined in
2172   <xref target="compression.codings"/>).
2173</t>
2174<t>
2175   Values to be added to this name space require expert review and a specification
2176   (see "Expert Review" and "Specification Required" in
2177   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2178   conform to the purpose of transfer coding defined in this section.
2179</t>
2180<t>
2181   The registry itself is maintained at
2182   <eref target="http://www.iana.org/assignments/http-parameters"/>.
2183</t>
2184</section>
2185</section>
2186
2187<section title="Product Tokens" anchor="product.tokens">
2188  <x:anchor-alias value="product"/>
2189  <x:anchor-alias value="product-version"/>
2190<t>
2191   Product tokens are used to allow communicating applications to
2192   identify themselves by software name and version. Most fields using
2193   product tokens also allow sub-products which form a significant part
2194   of the application to be listed, separated by whitespace. By
2195   convention, the products are listed in order of their significance
2196   for identifying the application.
2197</t>
2198<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2199  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2200  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2201</artwork></figure>
2202<t>
2203   Examples:
2204</t>
2205<figure><artwork type="example">
2206  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2207  Server: Apache/0.8.4
2208</artwork></figure>
2209<t>
2210   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2211   used for advertising or other non-essential information. Although any
2212   token character &MAY; appear in a product-version, this token &SHOULD;
2213   only be used for a version identifier (i.e., successive versions of
2214   the same product &SHOULD; only differ in the product-version portion of
2215   the product value).
2216</t>
2217</section>
2218
2219<section title="Quality Values" anchor="quality.values">
2220  <x:anchor-alias value="qvalue"/>
2221<t>
2222   Both transfer codings (TE request header, <xref target="header.te"/>)
2223   and content negotiation (&content.negotiation;) use short "floating point"
2224   numbers to indicate the relative importance ("weight") of various
2225   negotiable parameters.  A weight is normalized to a real number in
2226   the range 0 through 1, where 0 is the minimum and 1 the maximum
2227   value. If a parameter has a quality value of 0, then content with
2228   this parameter is "not acceptable" for the client. HTTP/1.1
2229   applications &MUST-NOT; generate more than three digits after the
2230   decimal point. User configuration of these values &SHOULD; also be
2231   limited in this fashion.
2232</t>
2233<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2234  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2235                 / ( "1" [ "." 0*3("0") ] )
2236</artwork></figure>
2237<x:note>
2238  <t>
2239     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2240     relative degradation in desired quality.
2241  </t>
2242</x:note>
2243</section>
2244
2245</section>
2246
2247<section title="Connections" anchor="connections">
2248
2249<section title="Persistent Connections" anchor="persistent.connections">
2250
2251<section title="Purpose" anchor="persistent.purpose">
2252<t>
2253   Prior to persistent connections, a separate TCP connection was
2254   established to fetch each URL, increasing the load on HTTP servers
2255   and causing congestion on the Internet. The use of inline images and
2256   other associated data often requires a client to make multiple
2257   requests of the same server in a short amount of time. Analysis of
2258   these performance problems and results from a prototype
2259   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2260   measurements of actual HTTP/1.1 implementations show good
2261   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2262   T/TCP <xref target="Tou1998"/>.
2263</t>
2264<t>
2265   Persistent HTTP connections have a number of advantages:
2266  <list style="symbols">
2267      <t>
2268        By opening and closing fewer TCP connections, CPU time is saved
2269        in routers and hosts (clients, servers, proxies, gateways,
2270        tunnels, or caches), and memory used for TCP protocol control
2271        blocks can be saved in hosts.
2272      </t>
2273      <t>
2274        HTTP requests and responses can be pipelined on a connection.
2275        Pipelining allows a client to make multiple requests without
2276        waiting for each response, allowing a single TCP connection to
2277        be used much more efficiently, with much lower elapsed time.
2278      </t>
2279      <t>
2280        Network congestion is reduced by reducing the number of packets
2281        caused by TCP opens, and by allowing TCP sufficient time to
2282        determine the congestion state of the network.
2283      </t>
2284      <t>
2285        Latency on subsequent requests is reduced since there is no time
2286        spent in TCP's connection opening handshake.
2287      </t>
2288      <t>
2289        HTTP can evolve more gracefully, since errors can be reported
2290        without the penalty of closing the TCP connection. Clients using
2291        future versions of HTTP might optimistically try a new feature,
2292        but if communicating with an older server, retry with old
2293        semantics after an error is reported.
2294      </t>
2295    </list>
2296</t>
2297<t>
2298   HTTP implementations &SHOULD; implement persistent connections.
2299</t>
2300</section>
2301
2302<section title="Overall Operation" anchor="persistent.overall">
2303<t>
2304   A significant difference between HTTP/1.1 and earlier versions of
2305   HTTP is that persistent connections are the default behavior of any
2306   HTTP connection. That is, unless otherwise indicated, the client
2307   &SHOULD; assume that the server will maintain a persistent connection,
2308   even after error responses from the server.
2309</t>
2310<t>
2311   Persistent connections provide a mechanism by which a client and a
2312   server can signal the close of a TCP connection. This signaling takes
2313   place using the Connection header field (<xref target="header.connection"/>). Once a close
2314   has been signaled, the client &MUST-NOT; send any more requests on that
2315   connection.
2316</t>
2317
2318<section title="Negotiation" anchor="persistent.negotiation">
2319<t>
2320   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2321   maintain a persistent connection unless a Connection header including
2322   the connection-token "close" was sent in the request. If the server
2323   chooses to close the connection immediately after sending the
2324   response, it &SHOULD; send a Connection header including the
2325   connection-token "close".
2326</t>
2327<t>
2328   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2329   decide to keep it open based on whether the response from a server
2330   contains a Connection header with the connection-token close. In case
2331   the client does not want to maintain a connection for more than that
2332   request, it &SHOULD; send a Connection header including the
2333   connection-token close.
2334</t>
2335<t>
2336   If either the client or the server sends the close token in the
2337   Connection header, that request becomes the last one for the
2338   connection.
2339</t>
2340<t>
2341   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2342   maintained for HTTP versions less than 1.1 unless it is explicitly
2343   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2344   compatibility with HTTP/1.0 clients.
2345</t>
2346<t>
2347   In order to remain persistent, all messages on the connection &MUST;
2348   have a self-defined message length (i.e., one not defined by closure
2349   of the connection), as described in <xref target="message.body"/>.
2350</t>
2351</section>
2352
2353<section title="Pipelining" anchor="pipelining">
2354<t>
2355   A client that supports persistent connections &MAY; "pipeline" its
2356   requests (i.e., send multiple requests without waiting for each
2357   response). A server &MUST; send its responses to those requests in the
2358   same order that the requests were received.
2359</t>
2360<t>
2361   Clients which assume persistent connections and pipeline immediately
2362   after connection establishment &SHOULD; be prepared to retry their
2363   connection if the first pipelined attempt fails. If a client does
2364   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2365   persistent. Clients &MUST; also be prepared to resend their requests if
2366   the server closes the connection before sending all of the
2367   corresponding responses.
2368</t>
2369<t>
2370   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
2371   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
2372   premature termination of the transport connection could lead to
2373   indeterminate results. A client wishing to send a non-idempotent
2374   request &SHOULD; wait to send that request until it has received the
2375   response status for the previous request.
2376</t>
2377</section>
2378</section>
2379
2380<section title="Proxy Servers" anchor="persistent.proxy">
2381<t>
2382   It is especially important that proxies correctly implement the
2383   properties of the Connection header field as specified in <xref target="header.connection"/>.
2384</t>
2385<t>
2386   The proxy server &MUST; signal persistent connections separately with
2387   its clients and the origin servers (or other proxy servers) that it
2388   connects to. Each persistent connection applies to only one transport
2389   link.
2390</t>
2391<t>
2392   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2393   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2394   for information and discussion of the problems with the Keep-Alive header
2395   implemented by many HTTP/1.0 clients).
2396</t>
2397
2398<section title="End-to-end and Hop-by-hop Headers" anchor="end-to-end.and.hop-by-hop.headers">
2399<!--<t>
2400  <cref anchor="TODO-end-to-end" source="jre">
2401    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1"/>.
2402    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2403  </cref>
2404</t>-->
2405<t>
2406   For the purpose of defining the behavior of caches and non-caching
2407   proxies, we divide HTTP headers into two categories:
2408  <list style="symbols">
2409      <t>End-to-end headers, which are  transmitted to the ultimate
2410        recipient of a request or response. End-to-end headers in
2411        responses MUST be stored as part of a cache entry and &MUST; be
2412        transmitted in any response formed from a cache entry.</t>
2413
2414      <t>Hop-by-hop headers, which are meaningful only for a single
2415        transport-level connection, and are not stored by caches or
2416        forwarded by proxies.</t>
2417  </list>
2418</t>
2419<t>
2420   The following HTTP/1.1 headers are hop-by-hop headers:
2421  <list style="symbols">
2422      <t>Connection</t>
2423      <t>Keep-Alive</t>
2424      <t>Proxy-Authenticate</t>
2425      <t>Proxy-Authorization</t>
2426      <t>TE</t>
2427      <t>Trailer</t>
2428      <t>Transfer-Encoding</t>
2429      <t>Upgrade</t>
2430  </list>
2431</t>
2432<t>
2433   All other headers defined by HTTP/1.1 are end-to-end headers.
2434</t>
2435<t>
2436   Other hop-by-hop headers &MUST; be listed in a Connection header
2437   (<xref target="header.connection"/>).
2438</t>
2439</section>
2440
2441<section title="Non-modifiable Headers" anchor="non-modifiable.headers">
2442<!--<t>
2443  <cref anchor="TODO-non-mod-headers" source="jre">
2444    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2"/>.
2445    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2446  </cref>
2447</t>-->
2448<t>
2449   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2450   value of certain end-to-end headers. A transparent proxy &SHOULD-NOT;
2451   modify an end-to-end header unless the definition of that header requires
2452   or specifically allows that.
2453</t>
2454<t>
2455   A transparent proxy &MUST-NOT; modify any of the following fields in a
2456   request or response, and it &MUST-NOT; add any of these fields if not
2457   already present:
2458  <list style="symbols">
2459      <t>Content-Location</t>
2460      <t>Content-MD5</t>
2461      <t>ETag</t>
2462      <t>Last-Modified</t>
2463  </list>
2464</t>
2465<t>
2466   A transparent proxy &MUST-NOT; modify any of the following fields in a
2467   response:
2468  <list style="symbols">
2469    <t>Expires</t>
2470  </list>
2471</t>
2472<t>
2473   but it &MAY; add any of these fields if not already present. If an
2474   Expires header is added, it &MUST; be given a field-value identical to
2475   that of the Date header in that response.
2476</t>
2477<t>
2478   A proxy &MUST-NOT; modify or add any of the following fields in a
2479   message that contains the no-transform cache-control directive, or in
2480   any request:
2481  <list style="symbols">
2482    <t>Content-Encoding</t>
2483    <t>Content-Range</t>
2484    <t>Content-Type</t>
2485  </list>
2486</t>
2487<t>
2488   A non-transparent proxy &MAY; modify or add these fields to a message
2489   that does not include no-transform, but if it does so, it &MUST; add a
2490   Warning 214 (Transformation applied) if one does not already appear
2491   in the message (see &header-warning;).
2492</t>
2493<x:note>
2494  <t>
2495    <x:h>Warning:</x:h> Unnecessary modification of end-to-end headers might
2496    cause authentication failures if stronger authentication
2497    mechanisms are introduced in later versions of HTTP. Such
2498    authentication mechanisms &MAY; rely on the values of header fields
2499    not listed here.
2500  </t>
2501</x:note>
2502<t>
2503   A transparent proxy &MUST; preserve the message payload (&payload;),
2504   though it &MAY; change the message-body through application or removal
2505   of a transfer-coding (<xref target="transfer.codings"/>).
2506</t>
2507</section>
2508
2509</section>
2510
2511<section title="Practical Considerations" anchor="persistent.practical">
2512<t>
2513   Servers will usually have some time-out value beyond which they will
2514   no longer maintain an inactive connection. Proxy servers might make
2515   this a higher value since it is likely that the client will be making
2516   more connections through the same server. The use of persistent
2517   connections places no requirements on the length (or existence) of
2518   this time-out for either the client or the server.
2519</t>
2520<t>
2521   When a client or server wishes to time-out it &SHOULD; issue a graceful
2522   close on the transport connection. Clients and servers &SHOULD; both
2523   constantly watch for the other side of the transport close, and
2524   respond to it as appropriate. If a client or server does not detect
2525   the other side's close promptly it could cause unnecessary resource
2526   drain on the network.
2527</t>
2528<t>
2529   A client, server, or proxy &MAY; close the transport connection at any
2530   time. For example, a client might have started to send a new request
2531   at the same time that the server has decided to close the "idle"
2532   connection. From the server's point of view, the connection is being
2533   closed while it was idle, but from the client's point of view, a
2534   request is in progress.
2535</t>
2536<t>
2537   This means that clients, servers, and proxies &MUST; be able to recover
2538   from asynchronous close events. Client software &SHOULD; reopen the
2539   transport connection and retransmit the aborted sequence of requests
2540   without user interaction so long as the request sequence is
2541   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
2542   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2543   human operator the choice of retrying the request(s). Confirmation by
2544   user-agent software with semantic understanding of the application
2545   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2546   be repeated if the second sequence of requests fails.
2547</t>
2548<t>
2549   Servers &SHOULD; always respond to at least one request per connection,
2550   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2551   middle of transmitting a response, unless a network or client failure
2552   is suspected.
2553</t>
2554<t>
2555   Clients (including proxies) &SHOULD; limit the number of simultaneous
2556   connections that they maintain to a given server (including proxies).
2557</t>
2558<t>
2559   Previous revisions of HTTP gave a specific number of connections as a
2560   ceiling, but this was found to be impractical for many applications. As a
2561   result, this specification does not mandate a particular maximum number of
2562   connections, but instead encourages clients to be conservative when opening
2563   multiple connections.
2564</t>
2565<t>
2566   In particular, while using multiple connections avoids the "head-of-line
2567   blocking" problem (whereby a request that takes significant server-side
2568   processing and/or has a large payload can block subsequent requests on the
2569   same connection), each connection used consumes server resources (sometimes
2570   significantly), and furthermore using multiple connections can cause
2571   undesirable side effects in congested networks.
2572</t>
2573<t>
2574   Note that servers might reject traffic that they deem abusive, including an
2575   excessive number of connections from a client.
2576</t>
2577</section>
2578</section>
2579
2580<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2581
2582<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2583<t>
2584   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2585   flow control mechanisms to resolve temporary overloads, rather than
2586   terminating connections with the expectation that clients will retry.
2587   The latter technique can exacerbate network congestion.
2588</t>
2589</section>
2590
2591<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2592<t>
2593   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2594   the network connection for an error status while it is transmitting
2595   the request. If the client sees an error status, it &SHOULD;
2596   immediately cease transmitting the body. If the body is being sent
2597   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2598   empty trailer &MAY; be used to prematurely mark the end of the message.
2599   If the body was preceded by a Content-Length header, the client &MUST;
2600   close the connection.
2601</t>
2602</section>
2603
2604<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2605<t>
2606   The purpose of the 100 (Continue) status (see &status-100;) is to
2607   allow a client that is sending a request message with a request body
2608   to determine if the origin server is willing to accept the request
2609   (based on the request headers) before the client sends the request
2610   body. In some cases, it might either be inappropriate or highly
2611   inefficient for the client to send the body if the server will reject
2612   the message without looking at the body.
2613</t>
2614<t>
2615   Requirements for HTTP/1.1 clients:
2616  <list style="symbols">
2617    <t>
2618        If a client will wait for a 100 (Continue) response before
2619        sending the request body, it &MUST; send an Expect request-header
2620        field (&header-expect;) with the "100-continue" expectation.
2621    </t>
2622    <t>
2623        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2624        with the "100-continue" expectation if it does not intend
2625        to send a request body.
2626    </t>
2627  </list>
2628</t>
2629<t>
2630   Because of the presence of older implementations, the protocol allows
2631   ambiguous situations in which a client may send "Expect: 100-continue"
2632   without receiving either a 417 (Expectation Failed) status
2633   or a 100 (Continue) status. Therefore, when a client sends this
2634   header field to an origin server (possibly via a proxy) from which it
2635   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
2636   for an indefinite period before sending the request body.
2637</t>
2638<t>
2639   Requirements for HTTP/1.1 origin servers:
2640  <list style="symbols">
2641    <t> Upon receiving a request which includes an Expect request-header
2642        field with the "100-continue" expectation, an origin server &MUST;
2643        either respond with 100 (Continue) status and continue to read
2644        from the input stream, or respond with a final status code. The
2645        origin server &MUST-NOT; wait for the request body before sending
2646        the 100 (Continue) response. If it responds with a final status
2647        code, it &MAY; close the transport connection or it &MAY; continue
2648        to read and discard the rest of the request.  It &MUST-NOT;
2649        perform the requested method if it returns a final status code.
2650    </t>
2651    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2652        the request message does not include an Expect request-header
2653        field with the "100-continue" expectation, and &MUST-NOT; send a
2654        100 (Continue) response if such a request comes from an HTTP/1.0
2655        (or earlier) client. There is an exception to this rule: for
2656        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2657        status in response to an HTTP/1.1 PUT or POST request that does
2658        not include an Expect request-header field with the "100-continue"
2659        expectation. This exception, the purpose of which is
2660        to minimize any client processing delays associated with an
2661        undeclared wait for 100 (Continue) status, applies only to
2662        HTTP/1.1 requests, and not to requests with any other HTTP-version
2663        value.
2664    </t>
2665    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2666        already received some or all of the request body for the
2667        corresponding request.
2668    </t>
2669    <t> An origin server that sends a 100 (Continue) response &MUST;
2670    ultimately send a final status code, once the request body is
2671        received and processed, unless it terminates the transport
2672        connection prematurely.
2673    </t>
2674    <t> If an origin server receives a request that does not include an
2675        Expect request-header field with the "100-continue" expectation,
2676        the request includes a request body, and the server responds
2677        with a final status code before reading the entire request body
2678        from the transport connection, then the server &SHOULD-NOT;  close
2679        the transport connection until it has read the entire request,
2680        or until the client closes the connection. Otherwise, the client
2681        might not reliably receive the response message. However, this
2682        requirement is not be construed as preventing a server from
2683        defending itself against denial-of-service attacks, or from
2684        badly broken client implementations.
2685      </t>
2686    </list>
2687</t>
2688<t>
2689   Requirements for HTTP/1.1 proxies:
2690  <list style="symbols">
2691    <t> If a proxy receives a request that includes an Expect request-header
2692        field with the "100-continue" expectation, and the proxy
2693        either knows that the next-hop server complies with HTTP/1.1 or
2694        higher, or does not know the HTTP version of the next-hop
2695        server, it &MUST; forward the request, including the Expect header
2696        field.
2697    </t>
2698    <t> If the proxy knows that the version of the next-hop server is
2699        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2700        respond with a 417 (Expectation Failed) status.
2701    </t>
2702    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2703        numbers received from recently-referenced next-hop servers.
2704    </t>
2705    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2706        request message was received from an HTTP/1.0 (or earlier)
2707        client and did not include an Expect request-header field with
2708        the "100-continue" expectation. This requirement overrides the
2709        general rule for forwarding of 1xx responses (see &status-1xx;).
2710    </t>
2711  </list>
2712</t>
2713</section>
2714
2715<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2716<t>
2717   If an HTTP/1.1 client sends a request which includes a request body,
2718   but which does not include an Expect request-header field with the
2719   "100-continue" expectation, and if the client is not directly
2720   connected to an HTTP/1.1 origin server, and if the client sees the
2721   connection close before receiving any status from the server, the
2722   client &SHOULD; retry the request.  If the client does retry this
2723   request, it &MAY; use the following "binary exponential backoff"
2724   algorithm to be assured of obtaining a reliable response:
2725  <list style="numbers">
2726    <t>
2727      Initiate a new connection to the server
2728    </t>
2729    <t>
2730      Transmit the request-headers
2731    </t>
2732    <t>
2733      Initialize a variable R to the estimated round-trip time to the
2734         server (e.g., based on the time it took to establish the
2735         connection), or to a constant value of 5 seconds if the round-trip
2736         time is not available.
2737    </t>
2738    <t>
2739       Compute T = R * (2**N), where N is the number of previous
2740         retries of this request.
2741    </t>
2742    <t>
2743       Wait either for an error response from the server, or for T
2744         seconds (whichever comes first)
2745    </t>
2746    <t>
2747       If no error response is received, after T seconds transmit the
2748         body of the request.
2749    </t>
2750    <t>
2751       If client sees that the connection is closed prematurely,
2752         repeat from step 1 until the request is accepted, an error
2753         response is received, or the user becomes impatient and
2754         terminates the retry process.
2755    </t>
2756  </list>
2757</t>
2758<t>
2759   If at any point an error status is received, the client
2760  <list style="symbols">
2761      <t>&SHOULD-NOT;  continue and</t>
2762
2763      <t>&SHOULD; close the connection if it has not completed sending the
2764        request message.</t>
2765    </list>
2766</t>
2767</section>
2768</section>
2769</section>
2770
2771
2772<section title="Miscellaneous notes that may disappear" anchor="misc">
2773<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2774<t>
2775   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2776</t>
2777</section>
2778
2779<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2780<t>
2781   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2782</t>
2783</section>
2784
2785<section title="Interception of HTTP for access control" anchor="http.intercept">
2786<t>
2787   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2788</t>
2789</section>
2790
2791<section title="Use of HTTP by other protocols" anchor="http.others">
2792<t>
2793   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2794   Extensions of HTTP like WebDAV.</cref>
2795</t>
2796
2797</section>
2798<section title="Use of HTTP by media type specification" anchor="http.media">
2799<t>
2800   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2801</t>
2802</section>
2803</section>
2804
2805<section title="Header Field Definitions" anchor="header.field.definitions">
2806<t>
2807   This section defines the syntax and semantics of HTTP/1.1 header fields
2808   related to message framing and transport protocols.
2809</t>
2810<t>
2811   For entity-header fields, both sender and recipient refer to either the
2812   client or the server, depending on who sends and who receives the message.
2813</t>
2814
2815<section title="Connection" anchor="header.connection">
2816  <iref primary="true" item="Connection header" x:for-anchor=""/>
2817  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2818  <x:anchor-alias value="Connection"/>
2819  <x:anchor-alias value="connection-token"/>
2820  <x:anchor-alias value="Connection-v"/>
2821<t>
2822   The "Connection" general-header field allows the sender to specify
2823   options that are desired for that particular connection and &MUST-NOT;
2824   be communicated by proxies over further connections.
2825</t>
2826<t>
2827   The Connection header's value has the following grammar:
2828</t>
2829<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"/>
2830  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2831  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2832  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2833</artwork></figure>
2834<t>
2835   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2836   message is forwarded and, for each connection-token in this field,
2837   remove any header field(s) from the message with the same name as the
2838   connection-token. Connection options are signaled by the presence of
2839   a connection-token in the Connection header field, not by any
2840   corresponding additional header field(s), since the additional header
2841   field may not be sent if there are no parameters associated with that
2842   connection option.
2843</t>
2844<t>
2845   Message headers listed in the Connection header &MUST-NOT; include
2846   end-to-end headers, such as Cache-Control.
2847</t>
2848<t>
2849   HTTP/1.1 defines the "close" connection option for the sender to
2850   signal that the connection will be closed after completion of the
2851   response. For example,
2852</t>
2853<figure><artwork type="example">
2854  Connection: close
2855</artwork></figure>
2856<t>
2857   in either the request or the response header fields indicates that
2858   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2859   after the current request/response is complete.
2860</t>
2861<t>
2862   An HTTP/1.1 client that does not support persistent connections &MUST;
2863   include the "close" connection option in every request message.
2864</t>
2865<t>
2866   An HTTP/1.1 server that does not support persistent connections &MUST;
2867   include the "close" connection option in every response message that
2868   does not have a 1xx (Informational) status code.
2869</t>
2870<t>
2871   A system receiving an HTTP/1.0 (or lower-version) message that
2872   includes a Connection header &MUST;, for each connection-token in this
2873   field, remove and ignore any header field(s) from the message with
2874   the same name as the connection-token. This protects against mistaken
2875   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2876</t>
2877</section>
2878
2879<section title="Content-Length" anchor="header.content-length">
2880  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2881  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2882  <x:anchor-alias value="Content-Length"/>
2883  <x:anchor-alias value="Content-Length-v"/>
2884<t>
2885   The "Content-Length" header field indicates the size of the
2886   message-body, in decimal number of octets, for any message other than
2887   a response to the HEAD method or a response with a status code of 304.
2888   In the case of responses to the HEAD method, it indicates the size of
2889   the payload body (not including any potential transfer-coding) that
2890   would have been sent had the request been a GET.
2891   In the case of the 304 (Not Modified) response, it indicates the size of
2892   the payload body (not including any potential transfer-coding) that
2893   would have been sent in a 200 (OK) response.
2894</t>
2895<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2896  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2897  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2898</artwork></figure>
2899<t>
2900   An example is
2901</t>
2902<figure><artwork type="example">
2903  Content-Length: 3495
2904</artwork></figure>
2905<t>
2906   Implementations &SHOULD; use this field to indicate the message-body
2907   length when no transfer-coding is being applied and the
2908   payload's body length can be determined prior to being transferred.
2909   <xref target="message.body"/> describes how recipients determine the length
2910   of a message-body.
2911</t>
2912<t>
2913   Any Content-Length greater than or equal to zero is a valid value.
2914</t>
2915<t>
2916   Note that the use of this field in HTTP is significantly different from
2917   the corresponding definition in MIME, where it is an optional field
2918   used within the "message/external-body" content-type.
2919</t>
2920</section>
2921
2922<section title="Date" anchor="header.date">
2923  <iref primary="true" item="Date header" x:for-anchor=""/>
2924  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2925  <x:anchor-alias value="Date"/>
2926  <x:anchor-alias value="Date-v"/>
2927<t>
2928   The "Date" general-header field represents the date and time at which
2929   the message was originated, having the same semantics as the Origination
2930   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2931   The field value is an HTTP-date, as described in <xref target="date.time.formats.full.date"/>;
2932   it &MUST; be sent in rfc1123-date format.
2933</t>
2934<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2935  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2936  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2937</artwork></figure>
2938<t>
2939   An example is
2940</t>
2941<figure><artwork type="example">
2942  Date: Tue, 15 Nov 1994 08:12:31 GMT
2943</artwork></figure>
2944<t>
2945   Origin servers &MUST; include a Date header field in all responses,
2946   except in these cases:
2947  <list style="numbers">
2948      <t>If the response status code is 100 (Continue) or 101 (Switching
2949         Protocols), the response &MAY; include a Date header field, at
2950         the server's option.</t>
2951
2952      <t>If the response status code conveys a server error, e.g., 500
2953         (Internal Server Error) or 503 (Service Unavailable), and it is
2954         inconvenient or impossible to generate a valid Date.</t>
2955
2956      <t>If the server does not have a clock that can provide a
2957         reasonable approximation of the current time, its responses
2958         &MUST-NOT; include a Date header field. In this case, the rules
2959         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2960  </list>
2961</t>
2962<t>
2963   A received message that does not have a Date header field &MUST; be
2964   assigned one by the recipient if the message will be cached by that
2965   recipient or gatewayed via a protocol which requires a Date. An HTTP
2966   implementation without a clock &MUST-NOT; cache responses without
2967   revalidating them on every use. An HTTP cache, especially a shared
2968   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2969   clock with a reliable external standard.
2970</t>
2971<t>
2972   Clients &SHOULD; only send a Date header field in messages that include
2973   a payload, as is usually the case for PUT and POST requests, and even
2974   then it is optional. A client without a clock &MUST-NOT; send a Date
2975   header field in a request.
2976</t>
2977<t>
2978   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2979   time subsequent to the generation of the message. It &SHOULD; represent
2980   the best available approximation of the date and time of message
2981   generation, unless the implementation has no means of generating a
2982   reasonably accurate date and time. In theory, the date ought to
2983   represent the moment just before the payload is generated. In
2984   practice, the date can be generated at any time during the message
2985   origination without affecting its semantic value.
2986</t>
2987
2988<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2989<t>
2990   Some origin server implementations might not have a clock available.
2991   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2992   values to a response, unless these values were associated
2993   with the resource by a system or user with a reliable clock. It &MAY;
2994   assign an Expires value that is known, at or before server
2995   configuration time, to be in the past (this allows "pre-expiration"
2996   of responses without storing separate Expires values for each
2997   resource).
2998</t>
2999</section>
3000</section>
3001
3002<section title="Host" anchor="header.host">
3003  <iref primary="true" item="Host header" x:for-anchor=""/>
3004  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
3005  <x:anchor-alias value="Host"/>
3006  <x:anchor-alias value="Host-v"/>
3007<t>
3008   The "Host" request-header field specifies the Internet host and port
3009   number of the resource being requested, allowing the origin server or
3010   gateway to differentiate between internally-ambiguous URLs, such as the root
3011   "/" URL of a server for multiple host names on a single IP address.
3012</t>
3013<t>   
3014   The Host field value &MUST; represent the naming authority of the origin
3015   server or gateway given by the original URL obtained from the user or
3016   referring resource (generally an http URI, as described in
3017   <xref target="http.uri"/>).
3018</t>
3019<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
3020  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
3021  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3022</artwork></figure>
3023<t>
3024   A "host" without any trailing port information implies the default
3025   port for the service requested (e.g., "80" for an HTTP URL). For
3026   example, a request on the origin server for
3027   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
3028</t>
3029<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3030GET /pub/WWW/ HTTP/1.1
3031Host: www.example.org
3032</artwork></figure>
3033<t>
3034   A client &MUST; include a Host header field in all HTTP/1.1 request
3035   messages. If the requested URI does not include an Internet host
3036   name for the service being requested, then the Host header field &MUST;
3037   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
3038   request message it forwards does contain an appropriate Host header
3039   field that identifies the service being requested by the proxy. All
3040   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
3041   status code to any HTTP/1.1 request message which lacks a Host header
3042   field.
3043</t>
3044<t>
3045   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
3046   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
3047   for other requirements relating to Host.
3048</t>
3049</section>
3050
3051<section title="TE" anchor="header.te">
3052  <iref primary="true" item="TE header" x:for-anchor=""/>
3053  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
3054  <x:anchor-alias value="TE"/>
3055  <x:anchor-alias value="TE-v"/>
3056  <x:anchor-alias value="t-codings"/>
3057  <x:anchor-alias value="te-params"/>
3058  <x:anchor-alias value="te-ext"/>
3059<t>
3060   The "TE" request-header field indicates what extension transfer-codings
3061   it is willing to accept in the response, and whether or not it is
3062   willing to accept trailer fields in a chunked transfer-coding.
3063</t>
3064<t>
3065   Its value may consist of the keyword "trailers" and/or a comma-separated
3066   list of extension transfer-coding names with optional accept
3067   parameters (as described in <xref target="transfer.codings"/>).
3068</t>
3069<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"/><iref primary="true" item="Grammar" subitem="te-params"/><iref primary="true" item="Grammar" subitem="te-ext"/>
3070  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
3071  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
3072  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3073  <x:ref>te-params</x:ref> = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> *( <x:ref>te-ext</x:ref> )
3074  <x:ref>te-ext</x:ref>    = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref> [ "=" <x:ref>word</x:ref> ]
3075</artwork></figure>
3076<t>
3077   The presence of the keyword "trailers" indicates that the client is
3078   willing to accept trailer fields in a chunked transfer-coding, as
3079   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3080   transfer-coding values even though it does not itself represent a
3081   transfer-coding.
3082</t>
3083<t>
3084   Examples of its use are:
3085</t>
3086<figure><artwork type="example">
3087  TE: deflate
3088  TE:
3089  TE: trailers, deflate;q=0.5
3090</artwork></figure>
3091<t>
3092   The TE header field only applies to the immediate connection.
3093   Therefore, the keyword &MUST; be supplied within a Connection header
3094   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3095</t>
3096<t>
3097   A server tests whether a transfer-coding is acceptable, according to
3098   a TE field, using these rules:
3099  <list style="numbers">
3100    <x:lt>
3101      <t>The "chunked" transfer-coding is always acceptable. If the
3102         keyword "trailers" is listed, the client indicates that it is
3103         willing to accept trailer fields in the chunked response on
3104         behalf of itself and any downstream clients. The implication is
3105         that, if given, the client is stating that either all
3106         downstream clients are willing to accept trailer fields in the
3107         forwarded response, or that it will attempt to buffer the
3108         response on behalf of downstream recipients.
3109      </t><t>
3110         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3111         chunked response such that a client can be assured of buffering
3112         the entire response.</t>
3113    </x:lt>
3114    <x:lt>
3115      <t>If the transfer-coding being tested is one of the transfer-codings
3116         listed in the TE field, then it is acceptable unless it
3117         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3118         qvalue of 0 means "not acceptable.")</t>
3119    </x:lt>
3120    <x:lt>
3121      <t>If multiple transfer-codings are acceptable, then the
3122         acceptable transfer-coding with the highest non-zero qvalue is
3123         preferred.  The "chunked" transfer-coding always has a qvalue
3124         of 1.</t>
3125    </x:lt>
3126  </list>
3127</t>
3128<t>
3129   If the TE field-value is empty or if no TE field is present, the only
3130   transfer-coding is "chunked". A message with no transfer-coding is
3131   always acceptable.
3132</t>
3133</section>
3134
3135<section title="Trailer" anchor="header.trailer">
3136  <iref primary="true" item="Trailer header" x:for-anchor=""/>
3137  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
3138  <x:anchor-alias value="Trailer"/>
3139  <x:anchor-alias value="Trailer-v"/>
3140<t>
3141   The "Trailer" general-header field indicates that the given set of
3142   header fields is present in the trailer of a message encoded with
3143   chunked transfer-coding.
3144</t>
3145<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
3146  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
3147  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
3148</artwork></figure>
3149<t>
3150   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3151   message using chunked transfer-coding with a non-empty trailer. Doing
3152   so allows the recipient to know which header fields to expect in the
3153   trailer.
3154</t>
3155<t>
3156   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3157   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3158   trailer fields in a "chunked" transfer-coding.
3159</t>
3160<t>
3161   Message header fields listed in the Trailer header field &MUST-NOT;
3162   include the following header fields:
3163  <list style="symbols">
3164    <t>Transfer-Encoding</t>
3165    <t>Content-Length</t>
3166    <t>Trailer</t>
3167  </list>
3168</t>
3169</section>
3170
3171<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3172  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
3173  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
3174  <x:anchor-alias value="Transfer-Encoding"/>
3175  <x:anchor-alias value="Transfer-Encoding-v"/>
3176<t>
3177   The "Transfer-Encoding" general-header field indicates what transfer-codings
3178   (if any) have been applied to the message body. It differs from
3179   Content-Encoding (&content-codings;) in that transfer-codings are a property
3180   of the message (and therefore are removed by intermediaries), whereas
3181   content-codings are not.
3182</t>
3183<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
3184  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
3185                        <x:ref>Transfer-Encoding-v</x:ref>
3186  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3187</artwork></figure>
3188<t>
3189   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3190</t>
3191<figure><artwork type="example">
3192  Transfer-Encoding: chunked
3193</artwork></figure>
3194<t>
3195   If multiple encodings have been applied to a representation, the transfer-codings
3196   &MUST; be listed in the order in which they were applied.
3197   Additional information about the encoding parameters &MAY; be provided
3198   by other entity-header fields not defined by this specification.
3199</t>
3200<t>
3201   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3202   header.
3203</t>
3204</section>
3205
3206<section title="Upgrade" anchor="header.upgrade">
3207  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
3208  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
3209  <x:anchor-alias value="Upgrade"/>
3210  <x:anchor-alias value="Upgrade-v"/>
3211<t>
3212   The "Upgrade" general-header field allows the client to specify what
3213   additional communication protocols it would like to use, if the server
3214   chooses to switch protocols. Additionally, the server &MUST; use the Upgrade
3215   header field within a 101 (Switching Protocols) response to indicate which
3216   protocol(s) are being switched to.
3217</t>
3218<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
3219  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
3220  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
3221</artwork></figure>
3222<t>
3223   For example,
3224</t>
3225<figure><artwork type="example">
3226  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3227</artwork></figure>
3228<t>
3229   The Upgrade header field is intended to provide a simple mechanism
3230   for transition from HTTP/1.1 to some other, incompatible protocol. It
3231   does so by allowing the client to advertise its desire to use another
3232   protocol, such as a later version of HTTP with a higher major version
3233   number, even though the current request has been made using HTTP/1.1.
3234   This eases the difficult transition between incompatible protocols by
3235   allowing the client to initiate a request in the more commonly
3236   supported protocol while indicating to the server that it would like
3237   to use a "better" protocol if available (where "better" is determined
3238   by the server, possibly according to the nature of the method and/or
3239   resource being requested).
3240</t>
3241<t>
3242   The Upgrade header field only applies to switching application-layer
3243   protocols upon the existing transport-layer connection. Upgrade
3244   cannot be used to insist on a protocol change; its acceptance and use
3245   by the server is optional. The capabilities and nature of the
3246   application-layer communication after the protocol change is entirely
3247   dependent upon the new protocol chosen, although the first action
3248   after changing the protocol &MUST; be a response to the initial HTTP
3249   request containing the Upgrade header field.
3250</t>
3251<t>
3252   The Upgrade header field only applies to the immediate connection.
3253   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3254   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3255   HTTP/1.1 message.
3256</t>
3257<t>
3258   The Upgrade header field cannot be used to indicate a switch to a
3259   protocol on a different connection. For that purpose, it is more
3260   appropriate to use a 301, 302, 303, or 305 redirection response.
3261</t>
3262<t>
3263   This specification only defines the protocol name "HTTP" for use by
3264   the family of Hypertext Transfer Protocols, as defined by the HTTP
3265   version rules of <xref target="http.version"/> and future updates to this
3266   specification. Additional tokens can be registered with IANA using the
3267   registration procedure defined below. 
3268</t>
3269
3270<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3271<t>
3272   The HTTP Upgrade Token Registry defines the name space for product
3273   tokens used to identify protocols in the Upgrade header field.
3274   Each registered token should be associated with one or a set of
3275   specifications, and with contact information.
3276</t>
3277<t>
3278   Registrations should be allowed on a First Come First Served basis as
3279   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. These
3280   specifications need not be IETF documents or be subject to IESG review, but
3281   should obey the following rules:
3282  <list style="numbers">
3283    <t>A token, once registered, stays registered forever.</t>
3284    <t>The registration &MUST; name a responsible party for the
3285       registration.</t>
3286    <t>The registration &MUST; name a point of contact.</t>
3287    <t>The registration &MAY; name the documentation required for the
3288       token.</t>
3289    <t>The responsible party &MAY; change the registration at any time.
3290       The IANA will keep a record of all such changes, and make them
3291       available upon request.</t>
3292    <t>The responsible party for the first registration of a "product"
3293       token &MUST; approve later registrations of a "version" token
3294       together with that "product" token before they can be registered.</t>
3295    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3296       for a token. This will normally only be used in the case when a
3297       responsible party cannot be contacted.</t>
3298  </list>
3299</t>
3300<t>
3301   It is not required that specifications for upgrade tokens be made
3302   publicly available, but the contact information for the registration
3303   should be.
3304</t>
3305</section>
3306
3307
3308</section>
3309
3310<section title="Via" anchor="header.via">
3311  <iref primary="true" item="Via header" x:for-anchor=""/>
3312  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
3313  <x:anchor-alias value="protocol-name"/>
3314  <x:anchor-alias value="protocol-version"/>
3315  <x:anchor-alias value="pseudonym"/>
3316  <x:anchor-alias value="received-by"/>
3317  <x:anchor-alias value="received-protocol"/>
3318  <x:anchor-alias value="Via"/>
3319  <x:anchor-alias value="Via-v"/>
3320<t>
3321   The "Via" general-header field &MUST; be used by gateways and proxies to
3322   indicate the intermediate protocols and recipients between the user
3323   agent and the server on requests, and between the origin server and
3324   the client on responses. It is analogous to the "Received" field defined in
3325   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
3326   avoiding request loops, and identifying the protocol capabilities of
3327   all senders along the request/response chain.
3328</t>
3329<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"/>
3330  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
3331  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3332                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3333  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3334  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3335  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3336  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3337  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3338</artwork></figure>
3339<t>
3340   The received-protocol indicates the protocol version of the message
3341   received by the server or client along each segment of the
3342   request/response chain. The received-protocol version is appended to
3343   the Via field value when the message is forwarded so that information
3344   about the protocol capabilities of upstream applications remains
3345   visible to all recipients.
3346</t>
3347<t>
3348   The protocol-name is optional if and only if it would be "HTTP". The
3349   received-by field is normally the host and optional port number of a
3350   recipient server or client that subsequently forwarded the message.
3351   However, if the real host is considered to be sensitive information,
3352   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3353   be assumed to be the default port of the received-protocol.
3354</t>
3355<t>
3356   Multiple Via field values represent each proxy or gateway that has
3357   forwarded the message. Each recipient &MUST; append its information
3358   such that the end result is ordered according to the sequence of
3359   forwarding applications.
3360</t>
3361<t>
3362   Comments &MAY; be used in the Via header field to identify the software
3363   of the recipient proxy or gateway, analogous to the User-Agent and
3364   Server header fields. However, all comments in the Via field are
3365   optional and &MAY; be removed by any recipient prior to forwarding the
3366   message.
3367</t>
3368<t>
3369   For example, a request message could be sent from an HTTP/1.0 user
3370   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3371   forward the request to a public proxy at p.example.net, which completes
3372   the request by forwarding it to the origin server at www.example.com.
3373   The request received by www.example.com would then have the following
3374   Via header field:
3375</t>
3376<figure><artwork type="example">
3377  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
3378</artwork></figure>
3379<t>
3380   Proxies and gateways used as a portal through a network firewall
3381   &SHOULD-NOT;, by default, forward the names and ports of hosts within
3382   the firewall region. This information &SHOULD; only be propagated if
3383   explicitly enabled. If not enabled, the received-by host of any host
3384   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
3385   for that host.
3386</t>
3387<t>
3388   For organizations that have strong privacy requirements for hiding
3389   internal structures, a proxy &MAY; combine an ordered subsequence of
3390   Via header field entries with identical received-protocol values into
3391   a single such entry. For example,
3392</t>
3393<figure><artwork type="example">
3394  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3395</artwork></figure>
3396<t>
3397  could be collapsed to
3398</t>
3399<figure><artwork type="example">
3400  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3401</artwork></figure>
3402<t>
3403   Applications &SHOULD-NOT;  combine multiple entries unless they are all
3404   under the same organizational control and the hosts have already been
3405   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
3406   have different received-protocol values.
3407</t>
3408</section>
3409
3410</section>
3411
3412<section title="IANA Considerations" anchor="IANA.considerations">
3413
3414<section title="Message Header Registration" anchor="message.header.registration">
3415<t>
3416   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
3417   with the permanent registrations below (see <xref target="RFC3864"/>):
3418</t>
3419<?BEGININC p1-messaging.iana-headers ?>
3420<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3421<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3422   <ttcol>Header Field Name</ttcol>
3423   <ttcol>Protocol</ttcol>
3424   <ttcol>Status</ttcol>
3425   <ttcol>Reference</ttcol>
3426
3427   <c>Connection</c>
3428   <c>http</c>
3429   <c>standard</c>
3430   <c>
3431      <xref target="header.connection"/>
3432   </c>
3433   <c>Content-Length</c>
3434   <c>http</c>
3435   <c>standard</c>
3436   <c>
3437      <xref target="header.content-length"/>
3438   </c>
3439   <c>Date</c>
3440   <c>http</c>
3441   <c>standard</c>
3442   <c>
3443      <xref target="header.date"/>
3444   </c>
3445   <c>Host</c>
3446   <c>http</c>
3447   <c>standard</c>
3448   <c>
3449      <xref target="header.host"/>
3450   </c>
3451   <c>TE</c>
3452   <c>http</c>
3453   <c>standard</c>
3454   <c>
3455      <xref target="header.te"/>
3456   </c>
3457   <c>Trailer</c>
3458   <c>http</c>
3459   <c>standard</c>
3460   <c>
3461      <xref target="header.trailer"/>
3462   </c>
3463   <c>Transfer-Encoding</c>
3464   <c>http</c>
3465   <c>standard</c>
3466   <c>
3467      <xref target="header.transfer-encoding"/>
3468   </c>
3469   <c>Upgrade</c>
3470   <c>http</c>
3471   <c>standard</c>
3472   <c>
3473      <xref target="header.upgrade"/>
3474   </c>
3475   <c>Via</c>
3476   <c>http</c>
3477   <c>standard</c>
3478   <c>
3479      <xref target="header.via"/>
3480   </c>
3481</texttable>
3482<!--(END)-->
3483<?ENDINC p1-messaging.iana-headers ?>
3484<t>
3485   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3486</t>
3487</section>
3488
3489<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3490<t>
3491   The entries for the "http" and "https" URI Schemes in the registry located at
3492   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3493   should be updated to point to Sections <xref target="http.uri" format="counter"/>
3494   and <xref target="https.uri" format="counter"/> of this document
3495   (see <xref target="RFC4395"/>).
3496</t>
3497</section>
3498
3499<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3500<t>
3501   This document serves as the specification for the Internet media types
3502   "message/http" and "application/http". The following is to be registered with
3503   IANA (see <xref target="RFC4288"/>).
3504</t>
3505<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3506<iref item="Media Type" subitem="message/http" primary="true"/>
3507<iref item="message/http Media Type" primary="true"/>
3508<t>
3509   The message/http type can be used to enclose a single HTTP request or
3510   response message, provided that it obeys the MIME restrictions for all
3511   "message" types regarding line length and encodings.
3512</t>
3513<t>
3514  <list style="hanging" x:indent="12em">
3515    <t hangText="Type name:">
3516      message
3517    </t>
3518    <t hangText="Subtype name:">
3519      http
3520    </t>
3521    <t hangText="Required parameters:">
3522      none
3523    </t>
3524    <t hangText="Optional parameters:">
3525      version, msgtype
3526      <list style="hanging">
3527        <t hangText="version:">
3528          The HTTP-Version number of the enclosed message
3529          (e.g., "1.1"). If not present, the version can be
3530          determined from the first line of the body.
3531        </t>
3532        <t hangText="msgtype:">
3533          The message type -- "request" or "response". If not
3534          present, the type can be determined from the first
3535          line of the body.
3536        </t>
3537      </list>
3538    </t>
3539    <t hangText="Encoding considerations:">
3540      only "7bit", "8bit", or "binary" are permitted
3541    </t>
3542    <t hangText="Security considerations:">
3543      none
3544    </t>
3545    <t hangText="Interoperability considerations:">
3546      none
3547    </t>
3548    <t hangText="Published specification:">
3549      This specification (see <xref target="internet.media.type.message.http"/>).
3550    </t>
3551    <t hangText="Applications that use this media type:">
3552    </t>
3553    <t hangText="Additional information:">
3554      <list style="hanging">
3555        <t hangText="Magic number(s):">none</t>
3556        <t hangText="File extension(s):">none</t>
3557        <t hangText="Macintosh file type code(s):">none</t>
3558      </list>
3559    </t>
3560    <t hangText="Person and email address to contact for further information:">
3561      See Authors Section.
3562    </t>
3563    <t hangText="Intended usage:">
3564      COMMON
3565    </t>
3566    <t hangText="Restrictions on usage:">
3567      none
3568    </t>
3569    <t hangText="Author/Change controller:">
3570      IESG
3571    </t>
3572  </list>
3573</t>
3574</section>
3575<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3576<iref item="Media Type" subitem="application/http" primary="true"/>
3577<iref item="application/http Media Type" primary="true"/>
3578<t>
3579   The application/http type can be used to enclose a pipeline of one or more
3580   HTTP request or response messages (not intermixed).
3581</t>
3582<t>
3583  <list style="hanging" x:indent="12em">
3584    <t hangText="Type name:">
3585      application
3586    </t>
3587    <t hangText="Subtype name:">
3588      http
3589    </t>
3590    <t hangText="Required parameters:">
3591      none
3592    </t>
3593    <t hangText="Optional parameters:">
3594      version, msgtype
3595      <list style="hanging">
3596        <t hangText="version:">
3597          The HTTP-Version number of the enclosed messages
3598          (e.g., "1.1"). If not present, the version can be
3599          determined from the first line of the body.
3600        </t>
3601        <t hangText="msgtype:">
3602          The message type -- "request" or "response". If not
3603          present, the type can be determined from the first
3604          line of the body.
3605        </t>
3606      </list>
3607    </t>
3608    <t hangText="Encoding considerations:">
3609      HTTP messages enclosed by this type
3610      are in "binary" format; use of an appropriate
3611      Content-Transfer-Encoding is required when
3612      transmitted via E-mail.
3613    </t>
3614    <t hangText="Security considerations:">
3615      none
3616    </t>
3617    <t hangText="Interoperability considerations:">
3618      none
3619    </t>
3620    <t hangText="Published specification:">
3621      This specification (see <xref target="internet.media.type.application.http"/>).
3622    </t>
3623    <t hangText="Applications that use this media type:">
3624    </t>
3625    <t hangText="Additional information:">
3626      <list style="hanging">
3627        <t hangText="Magic number(s):">none</t>
3628        <t hangText="File extension(s):">none</t>
3629        <t hangText="Macintosh file type code(s):">none</t>
3630      </list>
3631    </t>
3632    <t hangText="Person and email address to contact for further information:">
3633      See Authors Section.
3634    </t>
3635    <t hangText="Intended usage:">
3636      COMMON
3637    </t>
3638    <t hangText="Restrictions on usage:">
3639      none
3640    </t>
3641    <t hangText="Author/Change controller:">
3642      IESG
3643    </t>
3644  </list>
3645</t>
3646</section>
3647</section>
3648
3649<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3650<t>
3651   The registration procedure for HTTP Transfer Codings is now defined by
3652   <xref target="transfer.coding.registry"/> of this document.
3653</t>
3654<t>
3655   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
3656   should be updated with the registrations below:
3657</t>
3658<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3659   <ttcol>Name</ttcol>
3660   <ttcol>Description</ttcol>
3661   <ttcol>Reference</ttcol>
3662   <c>chunked</c>
3663   <c>Transfer in a series of chunks</c>
3664   <c>
3665      <xref target="chunked.encoding"/>
3666   </c>
3667   <c>compress</c>
3668   <c>UNIX "compress" program method</c>
3669   <c>
3670      <xref target="compress.coding"/>
3671   </c>
3672   <c>deflate</c>
3673   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3674   the "zlib" data format (<xref target="RFC1950"/>)
3675   </c>
3676   <c>
3677      <xref target="deflate.coding"/>
3678   </c>
3679   <c>gzip</c>
3680   <c>Same as GNU zip <xref target="RFC1952"/></c>
3681   <c>
3682      <xref target="gzip.coding"/>
3683   </c>
3684</texttable>
3685</section>
3686
3687<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3688<t>
3689   The registration procedure for HTTP Upgrade Tokens -- previously defined
3690   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> -- is now defined
3691   by <xref target="upgrade.token.registry"/> of this document.
3692</t>
3693<t>
3694   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-upgrade-tokens/"/>
3695   should be updated with the registration below:
3696</t>
3697<texttable align="left" suppress-title="true">
3698   <ttcol>Value</ttcol>
3699   <ttcol>Description</ttcol>
3700   <ttcol>Reference</ttcol>
3701
3702   <c>HTTP</c>
3703   <c>Hypertext Transfer Protocol</c> 
3704   <c><xref target="http.version"/> of this specification</c>
3705<!-- IANA should add this without our instructions; emailed on June 05, 2009
3706   <c>TLS/1.0</c>
3707   <c>Transport Layer Security</c>
3708   <c><xref target="RFC2817"/></c> -->
3709
3710</texttable>
3711</section>
3712
3713</section>
3714
3715<section title="Security Considerations" anchor="security.considerations">
3716<t>
3717   This section is meant to inform application developers, information
3718   providers, and users of the security limitations in HTTP/1.1 as
3719   described by this document. The discussion does not include
3720   definitive solutions to the problems revealed, though it does make
3721   some suggestions for reducing security risks.
3722</t>
3723
3724<section title="Personal Information" anchor="personal.information">
3725<t>
3726   HTTP clients are often privy to large amounts of personal information
3727   (e.g., the user's name, location, mail address, passwords, encryption
3728   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3729   leakage of this information.
3730   We very strongly recommend that a convenient interface be provided
3731   for the user to control dissemination of such information, and that
3732   designers and implementors be particularly careful in this area.
3733   History shows that errors in this area often create serious security
3734   and/or privacy problems and generate highly adverse publicity for the
3735   implementor's company.
3736</t>
3737</section>
3738
3739<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3740<t>
3741   A server is in the position to save personal data about a user's
3742   requests which might identify their reading patterns or subjects of
3743   interest. This information is clearly confidential in nature and its
3744   handling can be constrained by law in certain countries. People using
3745   HTTP to provide data are responsible for ensuring that
3746   such material is not distributed without the permission of any
3747   individuals that are identifiable by the published results.
3748</t>
3749</section>
3750
3751<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3752<t>
3753   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3754   the documents returned by HTTP requests to be only those that were
3755   intended by the server administrators. If an HTTP server translates
3756   HTTP URIs directly into file system calls, the server &MUST; take
3757   special care not to serve files that were not intended to be
3758   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3759   other operating systems use ".." as a path component to indicate a
3760   directory level above the current one. On such a system, an HTTP
3761   server &MUST; disallow any such construct in the request-target if it
3762   would otherwise allow access to a resource outside those intended to
3763   be accessible via the HTTP server. Similarly, files intended for
3764   reference only internally to the server (such as access control
3765   files, configuration files, and script code) &MUST; be protected from
3766   inappropriate retrieval, since they might contain sensitive
3767   information. Experience has shown that minor bugs in such HTTP server
3768   implementations have turned into security risks.
3769</t>
3770</section>
3771
3772<section title="DNS Spoofing" anchor="dns.spoofing">
3773<t>
3774   Clients using HTTP rely heavily on the Domain Name Service, and are
3775   thus generally prone to security attacks based on the deliberate
3776   mis-association of IP addresses and DNS names. Clients need to be
3777   cautious in assuming the continuing validity of an IP number/DNS name
3778   association.
3779</t>
3780<t>
3781   In particular, HTTP clients &SHOULD; rely on their name resolver for
3782   confirmation of an IP number/DNS name association, rather than
3783   caching the result of previous host name lookups. Many platforms
3784   already can cache host name lookups locally when appropriate, and
3785   they &SHOULD; be configured to do so. It is proper for these lookups to
3786   be cached, however, only when the TTL (Time To Live) information
3787   reported by the name server makes it likely that the cached
3788   information will remain useful.
3789</t>
3790<t>
3791   If HTTP clients cache the results of host name lookups in order to
3792   achieve a performance improvement, they &MUST; observe the TTL
3793   information reported by DNS.
3794</t>
3795<t>
3796   If HTTP clients do not observe this rule, they could be spoofed when
3797   a previously-accessed server's IP address changes. As network
3798   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3799   possibility of this form of attack will grow. Observing this
3800   requirement thus reduces this potential security vulnerability.
3801</t>
3802<t>
3803   This requirement also improves the load-balancing behavior of clients
3804   for replicated servers using the same DNS name and reduces the
3805   likelihood of a user's experiencing failure in accessing sites which
3806   use that strategy.
3807</t>
3808</section>
3809
3810<section title="Proxies and Caching" anchor="attack.proxies">
3811<t>
3812   By their very nature, HTTP proxies are men-in-the-middle, and
3813   represent an opportunity for man-in-the-middle attacks. Compromise of
3814   the systems on which the proxies run can result in serious security
3815   and privacy problems. Proxies have access to security-related
3816   information, personal information about individual users and
3817   organizations, and proprietary information belonging to users and
3818   content providers. A compromised proxy, or a proxy implemented or
3819   configured without regard to security and privacy considerations,
3820   might be used in the commission of a wide range of potential attacks.
3821</t>
3822<t>
3823   Proxy operators should protect the systems on which proxies run as
3824   they would protect any system that contains or transports sensitive
3825   information. In particular, log information gathered at proxies often
3826   contains highly sensitive personal information, and/or information
3827   about organizations. Log information should be carefully guarded, and
3828   appropriate guidelines for use should be developed and followed.
3829   (<xref target="abuse.of.server.log.information"/>).
3830</t>
3831<t>
3832   Proxy implementors should consider the privacy and security
3833   implications of their design and coding decisions, and of the
3834   configuration options they provide to proxy operators (especially the
3835   default configuration).
3836</t>
3837<t>
3838   Users of a proxy need to be aware that proxies are no trustworthier than
3839   the people who run them; HTTP itself cannot solve this problem.
3840</t>
3841<t>
3842   The judicious use of cryptography, when appropriate, may suffice to
3843   protect against a broad range of security and privacy attacks. Such
3844   cryptography is beyond the scope of the HTTP/1.1 specification.
3845</t>
3846</section>
3847
3848<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3849<t>
3850   They exist. They are hard to defend against. Research continues.
3851   Beware.
3852</t>
3853</section>
3854</section>
3855
3856<section title="Acknowledgments" anchor="ack">
3857<t>
3858   HTTP has evolved considerably over the years. It has
3859   benefited from a large and active developer community--the many
3860   people who have participated on the www-talk mailing list--and it is
3861   that community which has been most responsible for the success of
3862   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3863   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3864   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3865   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3866   VanHeyningen deserve special recognition for their efforts in
3867   defining early aspects of the protocol.
3868</t>
3869<t>
3870   This document has benefited greatly from the comments of all those
3871   participating in the HTTP-WG. In addition to those already mentioned,
3872   the following individuals have contributed to this specification:
3873</t>
3874<t>
3875   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3876   Paul Burchard, Maurizio Codogno, Josh Cohen, Mike Cowlishaw, Roman Czyborra,
3877   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3878   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3879   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3880   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3881   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3882   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3883   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3884   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3885   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3886   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko.
3887</t>
3888<t>
3889   Thanks to the "cave men" of Palo Alto. You know who you are.
3890</t>
3891<t>
3892   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3893   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3894   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3895   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3896   Larry Masinter for their help. And thanks go particularly to Jeff
3897   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3898</t>
3899<t>
3900   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3901   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3902   discovery of many of the problems that this document attempts to
3903   rectify.
3904</t>
3905<t>
3906   This specification makes heavy use of the augmented BNF and generic
3907   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3908   reuses many of the definitions provided by Nathaniel Borenstein and
3909   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3910   specification will help reduce past confusion over the relationship
3911   between HTTP and Internet mail message formats.
3912</t>
3913</section>
3914
3915</middle>
3916<back>
3917
3918<references title="Normative References">
3919
3920<reference anchor="ISO-8859-1">
3921  <front>
3922    <title>
3923     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3924    </title>
3925    <author>
3926      <organization>International Organization for Standardization</organization>
3927    </author>
3928    <date year="1998"/>
3929  </front>
3930  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3931</reference>
3932
3933<reference anchor="Part2">
3934  <front>
3935    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3936    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3937      <organization abbrev="Day Software">Day Software</organization>
3938      <address><email>fielding@gbiv.com</email></address>
3939    </author>
3940    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3941      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3942      <address><email>jg@freedesktop.org</email></address>
3943    </author>
3944    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3945      <organization abbrev="HP">Hewlett-Packard Company</organization>
3946      <address><email>JeffMogul@acm.org</email></address>
3947    </author>
3948    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3949      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3950      <address><email>henrikn@microsoft.com</email></address>
3951    </author>
3952    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3953      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3954      <address><email>LMM@acm.org</email></address>
3955    </author>
3956    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3957      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3958      <address><email>paulle@microsoft.com</email></address>
3959    </author>
3960    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3961      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3962      <address><email>timbl@w3.org</email></address>
3963    </author>
3964    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3965      <organization abbrev="W3C">World Wide Web Consortium</organization>
3966      <address><email>ylafon@w3.org</email></address>
3967    </author>
3968    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3969      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3970      <address><email>julian.reschke@greenbytes.de</email></address>
3971    </author>
3972    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3973  </front>
3974  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3975  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3976</reference>
3977
3978<reference anchor="Part3">
3979  <front>
3980    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3981    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3982      <organization abbrev="Day Software">Day Software</organization>
3983      <address><email>fielding@gbiv.com</email></address>
3984    </author>
3985    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3986      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3987      <address><email>jg@freedesktop.org</email></address>
3988    </author>
3989    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3990      <organization abbrev="HP">Hewlett-Packard Company</organization>
3991      <address><email>JeffMogul@acm.org</email></address>
3992    </author>
3993    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3994      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3995      <address><email>henrikn@microsoft.com</email></address>
3996    </author>
3997    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3998      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3999      <address><email>LMM@acm.org</email></address>
4000    </author>
4001    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4002      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4003      <address><email>paulle@microsoft.com</email></address>
4004    </author>
4005    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4006      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4007      <address><email>timbl@w3.org</email></address>
4008    </author>
4009    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4010      <organization abbrev="W3C">World Wide Web Consortium</organization>
4011      <address><email>ylafon@w3.org</email></address>
4012    </author>
4013    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4014      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4015      <address><email>julian.reschke@greenbytes.de</email></address>
4016    </author>
4017    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4018  </front>
4019  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4020  <x:source href="p3-payload.xml" basename="p3-payload"/>
4021</reference>
4022
4023<reference anchor="Part5">
4024  <front>
4025    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
4026    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4027      <organization abbrev="Day Software">Day Software</organization>
4028      <address><email>fielding@gbiv.com</email></address>
4029    </author>
4030    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4031      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4032      <address><email>jg@freedesktop.org</email></address>
4033    </author>
4034    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4035      <organization abbrev="HP">Hewlett-Packard Company</organization>
4036      <address><email>JeffMogul@acm.org</email></address>
4037    </author>
4038    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4039      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4040      <address><email>henrikn@microsoft.com</email></address>
4041    </author>
4042    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4043      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
4044      <address><email>LMM@acm.org</email></address>
4045    </author>
4046    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4047      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4048      <address><email>paulle@microsoft.com</email></address>
4049    </author>
4050    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4051      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4052      <address><email>timbl@w3.org</email></address>
4053    </author>
4054    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4055      <organization abbrev="W3C">World Wide Web Consortium</organization>
4056      <address><email>ylafon@w3.org</email></address>
4057    </author>
4058    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4059      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4060      <address><email>julian.reschke@greenbytes.de</email></address>
4061    </author>
4062    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4063  </front>
4064  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
4065  <x:source href="p5-range.xml" basename="p5-range"/>
4066</reference>
4067
4068<reference anchor="Part6">
4069  <front>
4070    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4071    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4072      <organization abbrev="Day Software">Day Software</organization>
4073      <address><email>fielding@gbiv.com</email></address>
4074    </author>
4075    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4076      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4077      <address><email>jg@freedesktop.org</email></address>
4078    </author>
4079    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4080      <organization abbrev="HP">Hewlett-Packard Company</organization>
4081      <address><email>JeffMogul@acm.org</email></address>
4082    </author>
4083    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4084      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4085      <address><email>henrikn@microsoft.com</email></address>
4086    </author>
4087    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4088      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
4089      <address><email>LMM@acm.org</email></address>
4090    </author>
4091    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4092      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4093      <address><email>paulle@microsoft.com</email></address>
4094    </author>
4095    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4096      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4097      <address><email>timbl@w3.org</email></address>
4098    </author>
4099    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4100      <organization abbrev="W3C">World Wide Web Consortium</organization>
4101      <address><email>ylafon@w3.org</email></address>
4102    </author>
4103    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4104      <address><email>mnot@mnot.net</email></address>
4105    </author>
4106    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4107      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4108      <address><email>julian.reschke@greenbytes.de</email></address>
4109    </author>
4110    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4111  </front>
4112  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4113  <x:source href="p6-cache.xml" basename="p6-cache"/>
4114</reference>
4115
4116<reference anchor="RFC5234">
4117  <front>
4118    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4119    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4120      <organization>Brandenburg InternetWorking</organization>
4121      <address>
4122        <email>dcrocker@bbiw.net</email>
4123      </address> 
4124    </author>
4125    <author initials="P." surname="Overell" fullname="Paul Overell">
4126      <organization>THUS plc.</organization>
4127      <address>
4128        <email>paul.overell@thus.net</email>
4129      </address>
4130    </author>
4131    <date month="January" year="2008"/>
4132  </front>
4133  <seriesInfo name="STD" value="68"/>
4134  <seriesInfo name="RFC" value="5234"/>
4135</reference>
4136
4137<reference anchor="RFC2119">
4138  <front>
4139    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4140    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4141      <organization>Harvard University</organization>
4142      <address><email>sob@harvard.edu</email></address>
4143    </author>
4144    <date month="March" year="1997"/>
4145  </front>
4146  <seriesInfo name="BCP" value="14"/>
4147  <seriesInfo name="RFC" value="2119"/>
4148</reference>
4149
4150<reference anchor="RFC3986">
4151 <front>
4152  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4153  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4154    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4155    <address>
4156       <email>timbl@w3.org</email>
4157       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4158    </address>
4159  </author>
4160  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4161    <organization abbrev="Day Software">Day Software</organization>
4162    <address>
4163      <email>fielding@gbiv.com</email>
4164      <uri>http://roy.gbiv.com/</uri>
4165    </address>
4166  </author>
4167  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4168    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4169    <address>
4170      <email>LMM@acm.org</email>
4171      <uri>http://larry.masinter.net/</uri>
4172    </address>
4173  </author>
4174  <date month='January' year='2005'></date>
4175 </front>
4176 <seriesInfo name="RFC" value="3986"/>
4177 <seriesInfo name="STD" value="66"/>
4178</reference>
4179
4180<reference anchor="USASCII">
4181  <front>
4182    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4183    <author>
4184      <organization>American National Standards Institute</organization>
4185    </author>
4186    <date year="1986"/>
4187  </front>
4188  <seriesInfo name="ANSI" value="X3.4"/>
4189</reference>
4190
4191<reference anchor="RFC1950">
4192  <front>
4193    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4194    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4195      <organization>Aladdin Enterprises</organization>
4196      <address><email>ghost@aladdin.com</email></address>
4197    </author>
4198    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4199    <date month="May" year="1996"/>
4200  </front>
4201  <seriesInfo name="RFC" value="1950"/>
4202  <annotation>
4203    RFC 1950 is an Informational RFC, thus it may be less stable than
4204    this specification. On the other hand, this downward reference was
4205    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4206    therefore it is unlikely to cause problems in practice. See also
4207    <xref target="BCP97"/>.
4208  </annotation>
4209</reference>
4210
4211<reference anchor="RFC1951">
4212  <front>
4213    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4214    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4215      <organization>Aladdin Enterprises</organization>
4216      <address><email>ghost@aladdin.com</email></address>
4217    </author>
4218    <date month="May" year="1996"/>
4219  </front>
4220  <seriesInfo name="RFC" value="1951"/>
4221  <annotation>
4222    RFC 1951 is an Informational RFC, thus it may be less stable than
4223    this specification. On the other hand, this downward reference was
4224    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4225    therefore it is unlikely to cause problems in practice. See also
4226    <xref target="BCP97"/>.
4227  </annotation>
4228</reference>
4229
4230<reference anchor="RFC1952">
4231  <front>
4232    <title>GZIP file format specification version 4.3</title>
4233    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4234      <organization>Aladdin Enterprises</organization>
4235      <address><email>ghost@aladdin.com</email></address>
4236    </author>
4237    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4238      <address><email>gzip@prep.ai.mit.edu</email></address>
4239    </author>
4240    <author initials="M." surname="Adler" fullname="Mark Adler">
4241      <address><email>madler@alumni.caltech.edu</email></address>
4242    </author>
4243    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4244      <address><email>ghost@aladdin.com</email></address>
4245    </author>
4246    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4247      <address><email>randeg@alumni.rpi.edu</email></address>
4248    </author>
4249    <date month="May" year="1996"/>
4250  </front>
4251  <seriesInfo name="RFC" value="1952"/>
4252  <annotation>
4253    RFC 1952 is an Informational RFC, thus it may be less stable than
4254    this specification. On the other hand, this downward reference was
4255    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4256    therefore it is unlikely to cause problems in practice. See also
4257    <xref target="BCP97"/>.
4258  </annotation>
4259</reference>
4260
4261</references>
4262
4263<references title="Informative References">
4264
4265<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4266  <front>
4267    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4268    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4269    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4270    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4271    <author initials="H." surname="Lie" fullname="H. Lie"/>
4272    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4273    <date year="1997" month="September"/>
4274  </front>
4275  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4276</reference>
4277
4278<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4279  <front>
4280    <title>Improving HTTP Latency</title>
4281    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4282    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4283    <date year="1995" month="December"/>
4284  </front>
4285  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4286</reference>
4287
4288<reference anchor="RFC1123">
4289  <front>
4290    <title>Requirements for Internet Hosts - Application and Support</title>
4291    <author initials="R." surname="Braden" fullname="Robert Braden">
4292      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4293      <address><email>Braden@ISI.EDU</email></address>
4294    </author>
4295    <date month="October" year="1989"/>
4296  </front>
4297  <seriesInfo name="STD" value="3"/>
4298  <seriesInfo name="RFC" value="1123"/>
4299</reference>
4300
4301<reference anchor="RFC1305">
4302  <front>
4303    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
4304    <author initials="D." surname="Mills" fullname="David L. Mills">
4305      <organization>University of Delaware, Electrical Engineering Department</organization>
4306      <address><email>mills@udel.edu</email></address>
4307    </author>
4308    <date month="March" year="1992"/>
4309  </front>
4310  <seriesInfo name="RFC" value="1305"/>
4311</reference>
4312
4313<reference anchor="RFC1900">
4314  <front>
4315    <title>Renumbering Needs Work</title>
4316    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4317      <organization>CERN, Computing and Networks Division</organization>
4318      <address><email>brian@dxcoms.cern.ch</email></address>
4319    </author>
4320    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4321      <organization>cisco Systems</organization>
4322      <address><email>yakov@cisco.com</email></address>
4323    </author>
4324    <date month="February" year="1996"/>
4325  </front>
4326  <seriesInfo name="RFC" value="1900"/>
4327</reference>
4328
4329<reference anchor="RFC1945">
4330  <front>
4331    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4332    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4333      <organization>MIT, Laboratory for Computer Science</organization>
4334      <address><email>timbl@w3.org</email></address>
4335    </author>
4336    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4337      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4338      <address><email>fielding@ics.uci.edu</email></address>
4339    </author>
4340    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4341      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4342      <address><email>frystyk@w3.org</email></address>
4343    </author>
4344    <date month="May" year="1996"/>
4345  </front>
4346  <seriesInfo name="RFC" value="1945"/>
4347</reference>
4348
4349<reference anchor="RFC2045">
4350  <front>
4351    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4352    <author initials="N." surname="Freed" fullname="Ned Freed">
4353      <organization>Innosoft International, Inc.</organization>
4354      <address><email>ned@innosoft.com</email></address>
4355    </author>
4356    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4357      <organization>First Virtual Holdings</organization>
4358      <address><email>nsb@nsb.fv.com</email></address>
4359    </author>
4360    <date month="November" year="1996"/>
4361  </front>
4362  <seriesInfo name="RFC" value="2045"/>
4363</reference>
4364
4365<reference anchor="RFC2047">
4366  <front>
4367    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4368    <author initials="K." surname="Moore" fullname="Keith Moore">
4369      <organization>University of Tennessee</organization>
4370      <address><email>moore@cs.utk.edu</email></address>
4371    </author>
4372    <date month="November" year="1996"/>
4373  </front>
4374  <seriesInfo name="RFC" value="2047"/>
4375</reference>
4376
4377<reference anchor="RFC2068">
4378  <front>
4379    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4380    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4381      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4382      <address><email>fielding@ics.uci.edu</email></address>
4383    </author>
4384    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4385      <organization>MIT Laboratory for Computer Science</organization>
4386      <address><email>jg@w3.org</email></address>
4387    </author>
4388    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4389      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4390      <address><email>mogul@wrl.dec.com</email></address>
4391    </author>
4392    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4393      <organization>MIT Laboratory for Computer Science</organization>
4394      <address><email>frystyk@w3.org</email></address>
4395    </author>
4396    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4397      <organization>MIT Laboratory for Computer Science</organization>
4398      <address><email>timbl@w3.org</email></address>
4399    </author>
4400    <date month="January" year="1997"/>
4401  </front>
4402  <seriesInfo name="RFC" value="2068"/>
4403</reference>
4404
4405<reference anchor='RFC2109'>
4406  <front>
4407    <title>HTTP State Management Mechanism</title>
4408    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
4409      <organization>Bell Laboratories, Lucent Technologies</organization>
4410      <address><email>dmk@bell-labs.com</email></address>
4411    </author>
4412    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4413      <organization>Netscape Communications Corp.</organization>
4414      <address><email>montulli@netscape.com</email></address>
4415    </author>
4416    <date year='1997' month='February' />
4417  </front>
4418  <seriesInfo name='RFC' value='2109' />
4419</reference>
4420
4421<reference anchor="RFC2145">
4422  <front>
4423    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4424    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4425      <organization>Western Research Laboratory</organization>
4426      <address><email>mogul@wrl.dec.com</email></address>
4427    </author>
4428    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4429      <organization>Department of Information and Computer Science</organization>
4430      <address><email>fielding@ics.uci.edu</email></address>
4431    </author>
4432    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4433      <organization>MIT Laboratory for Computer Science</organization>
4434      <address><email>jg@w3.org</email></address>
4435    </author>
4436    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4437      <organization>W3 Consortium</organization>
4438      <address><email>frystyk@w3.org</email></address>
4439    </author>
4440    <date month="May" year="1997"/>
4441  </front>
4442  <seriesInfo name="RFC" value="2145"/>
4443</reference>
4444
4445<reference anchor="RFC2616">
4446  <front>
4447    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4448    <author initials="R." surname="Fielding" fullname="R. Fielding">
4449      <organization>University of California, Irvine</organization>
4450      <address><email>fielding@ics.uci.edu</email></address>
4451    </author>
4452    <author initials="J." surname="Gettys" fullname="J. Gettys">
4453      <organization>W3C</organization>
4454      <address><email>jg@w3.org</email></address>
4455    </author>
4456    <author initials="J." surname="Mogul" fullname="J. Mogul">
4457      <organization>Compaq Computer Corporation</organization>
4458      <address><email>mogul@wrl.dec.com</email></address>
4459    </author>
4460    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4461      <organization>MIT Laboratory for Computer Science</organization>
4462      <address><email>frystyk@w3.org</email></address>
4463    </author>
4464    <author initials="L." surname="Masinter" fullname="L. Masinter">
4465      <organization>Xerox Corporation</organization>
4466      <address><email>masinter@parc.xerox.com</email></address>
4467    </author>
4468    <author initials="P." surname="Leach" fullname="P. Leach">
4469      <organization>Microsoft Corporation</organization>
4470      <address><email>paulle@microsoft.com</email></address>
4471    </author>
4472    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4473      <organization>W3C</organization>
4474      <address><email>timbl@w3.org</email></address>
4475    </author>
4476    <date month="June" year="1999"/>
4477  </front>
4478  <seriesInfo name="RFC" value="2616"/>
4479</reference>
4480
4481<reference anchor='RFC2817'>
4482  <front>
4483    <title>Upgrading to TLS Within HTTP/1.1</title>
4484    <author initials='R.' surname='Khare' fullname='R. Khare'>
4485      <organization>4K Associates / UC Irvine</organization>
4486      <address><email>rohit@4K-associates.com</email></address>
4487    </author>
4488    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4489      <organization>Agranat Systems, Inc.</organization>
4490      <address><email>lawrence@agranat.com</email></address>
4491    </author>
4492    <date year='2000' month='May' />
4493  </front>
4494  <seriesInfo name='RFC' value='2817' />
4495</reference>
4496
4497<reference anchor='RFC2818'>
4498  <front>
4499    <title>HTTP Over TLS</title>
4500    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4501      <organization>RTFM, Inc.</organization>
4502      <address><email>ekr@rtfm.com</email></address>
4503    </author>
4504    <date year='2000' month='May' />
4505  </front>
4506  <seriesInfo name='RFC' value='2818' />
4507</reference>
4508
4509<reference anchor='RFC2965'>
4510  <front>
4511    <title>HTTP State Management Mechanism</title>
4512    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4513      <organization>Bell Laboratories, Lucent Technologies</organization>
4514      <address><email>dmk@bell-labs.com</email></address>
4515    </author>
4516    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4517      <organization>Epinions.com, Inc.</organization>
4518      <address><email>lou@montulli.org</email></address>
4519    </author>
4520    <date year='2000' month='October' />
4521  </front>
4522  <seriesInfo name='RFC' value='2965' />
4523</reference>
4524
4525<reference anchor='RFC3864'>
4526  <front>
4527    <title>Registration Procedures for Message Header Fields</title>
4528    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4529      <organization>Nine by Nine</organization>
4530      <address><email>GK-IETF@ninebynine.org</email></address>
4531    </author>
4532    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4533      <organization>BEA Systems</organization>
4534      <address><email>mnot@pobox.com</email></address>
4535    </author>
4536    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4537      <organization>HP Labs</organization>
4538      <address><email>JeffMogul@acm.org</email></address>
4539    </author>
4540    <date year='2004' month='September' />
4541  </front>
4542  <seriesInfo name='BCP' value='90' />
4543  <seriesInfo name='RFC' value='3864' />
4544</reference>
4545
4546<reference anchor="RFC4288">
4547  <front>
4548    <title>Media Type Specifications and Registration Procedures</title>
4549    <author initials="N." surname="Freed" fullname="N. Freed">
4550      <organization>Sun Microsystems</organization>
4551      <address>
4552        <email>ned.freed@mrochek.com</email>
4553      </address>
4554    </author>
4555    <author initials="J." surname="Klensin" fullname="J. Klensin">
4556      <address>
4557        <email>klensin+ietf@jck.com</email>
4558      </address>
4559    </author>
4560    <date year="2005" month="December"/>
4561  </front>
4562  <seriesInfo name="BCP" value="13"/>
4563  <seriesInfo name="RFC" value="4288"/>
4564</reference>
4565
4566<reference anchor='RFC4395'>
4567  <front>
4568    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4569    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4570      <organization>AT&amp;T Laboratories</organization>
4571      <address>
4572        <email>tony+urireg@maillennium.att.com</email>
4573      </address>
4574    </author>
4575    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4576      <organization>Qualcomm, Inc.</organization>
4577      <address>
4578        <email>hardie@qualcomm.com</email>
4579      </address>
4580    </author>
4581    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4582      <organization>Adobe Systems</organization>
4583      <address>
4584        <email>LMM@acm.org</email>
4585      </address>
4586    </author>
4587    <date year='2006' month='February' />
4588  </front>
4589  <seriesInfo name='BCP' value='115' />
4590  <seriesInfo name='RFC' value='4395' />
4591</reference>
4592
4593<reference anchor='RFC5226'>
4594  <front>
4595    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4596    <author initials='T.' surname='Narten' fullname='T. Narten'>
4597      <organization>IBM</organization>
4598      <address><email>narten@us.ibm.com</email></address>
4599    </author>
4600    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4601      <organization>Google</organization>
4602      <address><email>Harald@Alvestrand.no</email></address>
4603    </author>
4604    <date year='2008' month='May' />
4605  </front>
4606  <seriesInfo name='BCP' value='26' />
4607  <seriesInfo name='RFC' value='5226' />
4608</reference>
4609
4610<reference anchor="RFC5322">
4611  <front>
4612    <title>Internet Message Format</title>
4613    <author initials="P." surname="Resnick" fullname="P. Resnick">
4614      <organization>Qualcomm Incorporated</organization>
4615    </author>
4616    <date year="2008" month="October"/>
4617  </front> 
4618  <seriesInfo name="RFC" value="5322"/>
4619</reference>
4620
4621<reference anchor='BCP97'>
4622  <front>
4623    <title>Handling Normative References to Standards-Track Documents</title>
4624    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4625      <address>
4626        <email>klensin+ietf@jck.com</email>
4627      </address>
4628    </author>
4629    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4630      <organization>MIT</organization>
4631      <address>
4632        <email>hartmans-ietf@mit.edu</email>
4633      </address>
4634    </author>
4635    <date year='2007' month='June' />
4636  </front>
4637  <seriesInfo name='BCP' value='97' />
4638  <seriesInfo name='RFC' value='4897' />
4639</reference>
4640
4641<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4642  <front>
4643    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4644    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4645    <date year="2001" month="November"/>
4646  </front>
4647  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4648</reference>
4649
4650<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4651  <front>
4652    <title>Analysis of HTTP Performance Problems</title>
4653    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4654    <date/>
4655  </front>
4656</reference>
4657
4658<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4659  <front>
4660  <title>Analysis of HTTP Performance</title>
4661  <author initials="J." surname="Touch" fullname="Joe Touch">
4662    <organization>USC/Information Sciences Institute</organization>
4663    <address><email>touch@isi.edu</email></address>
4664  </author>
4665  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4666    <organization>USC/Information Sciences Institute</organization>
4667    <address><email>johnh@isi.edu</email></address>
4668  </author>
4669  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4670    <organization>USC/Information Sciences Institute</organization>
4671    <address><email>katia@isi.edu</email></address>
4672  </author>
4673  <date year="1998" month="Aug"/>
4674  </front>
4675  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4676  <annotation>(original report dated Aug. 1996)</annotation>
4677</reference>
4678
4679</references>
4680
4681
4682<section title="Tolerant Applications" anchor="tolerant.applications">
4683<t>
4684   Although this document specifies the requirements for the generation
4685   of HTTP/1.1 messages, not all applications will be correct in their
4686   implementation. We therefore recommend that operational applications
4687   be tolerant of deviations whenever those deviations can be
4688   interpreted unambiguously.
4689</t>
4690<t>
4691   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
4692   &SHOULD; be tolerant when parsing the Request-Line. In particular, they
4693   &SHOULD; accept any amount of WSP characters between fields, even though
4694   only a single SP is required.
4695</t>
4696<t>
4697   The line terminator for header fields is the sequence CRLF.
4698   However, we recommend that applications, when parsing such headers,
4699   recognize a single LF as a line terminator and ignore the leading CR.
4700</t>
4701<t>
4702   The character set of a representation &SHOULD; be labeled as the lowest
4703   common denominator of the character codes used within that representation, with
4704   the exception that not labeling the representation is preferred over labeling
4705   the representation with the labels US-ASCII or ISO-8859-1. See &payload;.
4706</t>
4707<t>
4708   Additional rules for requirements on parsing and encoding of dates
4709   and other potential problems with date encodings include:
4710</t>
4711<t>
4712  <list style="symbols">
4713     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4714        which appears to be more than 50 years in the future is in fact
4715        in the past (this helps solve the "year 2000" problem).</t>
4716
4717     <t>Although all date formats are specified to be case-sensitive,
4718        recipients &SHOULD; match day, week and timezone names
4719        case-insensitively.</t>
4720             
4721     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4722        Expires date as earlier than the proper value, but &MUST-NOT;
4723        internally represent a parsed Expires date as later than the
4724        proper value.</t>
4725
4726     <t>All expiration-related calculations &MUST; be done in GMT. The
4727        local time zone &MUST-NOT; influence the calculation or comparison
4728        of an age or expiration time.</t>
4729
4730     <t>If an HTTP header incorrectly carries a date value with a time
4731        zone other than GMT, it &MUST; be converted into GMT using the
4732        most conservative possible conversion.</t>
4733  </list>
4734</t>
4735</section>
4736
4737<section title="Compatibility with Previous Versions" anchor="compatibility">
4738<t>
4739   HTTP has been in use by the World-Wide Web global information initiative
4740   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4741   was a simple protocol for hypertext data transfer across the Internet
4742   with only a single method and no metadata.
4743   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4744   methods and MIME-like messaging that could include metadata about the data
4745   transferred and modifiers on the request/response semantics. However,
4746   HTTP/1.0 did not sufficiently take into consideration the effects of
4747   hierarchical proxies, caching, the need for persistent connections, or
4748   name-based virtual hosts. The proliferation of incompletely-implemented
4749   applications calling themselves "HTTP/1.0" further necessitated a
4750   protocol version change in order for two communicating applications
4751   to determine each other's true capabilities.
4752</t>
4753<t>
4754   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4755   requirements that enable reliable implementations, adding only
4756   those new features that will either be safely ignored by an HTTP/1.0
4757   recipient or only sent when communicating with a party advertising
4758   compliance with HTTP/1.1.
4759</t>
4760<t>
4761   It is beyond the scope of a protocol specification to mandate
4762   compliance with previous versions. HTTP/1.1 was deliberately
4763   designed, however, to make supporting previous versions easy. It is
4764   worth noting that, at the time of composing this specification, we would
4765   expect general-purpose HTTP/1.1 servers to:
4766  <list style="symbols">
4767     <t>understand any valid request in the format of HTTP/1.0 and
4768        1.1;</t>
4769
4770     <t>respond appropriately with a message in the same major version
4771        used by the client.</t>
4772  </list>
4773</t>
4774<t>
4775   And we would expect HTTP/1.1 clients to:
4776  <list style="symbols">
4777     <t>understand any valid response in the format of HTTP/1.0 or
4778        1.1.</t>
4779  </list>
4780</t>
4781<t>
4782   For most implementations of HTTP/1.0, each connection is established
4783   by the client prior to the request and closed by the server after
4784   sending the response. Some implementations implement the Keep-Alive
4785   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4786</t>
4787
4788<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4789<t>
4790   This section summarizes major differences between versions HTTP/1.0
4791   and HTTP/1.1.
4792</t>
4793
4794<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">
4795<t>
4796   The requirements that clients and servers support the Host request-header,
4797   report an error if the Host request-header (<xref target="header.host"/>) is
4798   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4799   are among the most important changes defined by this
4800   specification.
4801</t>
4802<t>
4803   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4804   addresses and servers; there was no other established mechanism for
4805   distinguishing the intended server of a request than the IP address
4806   to which that request was directed. The changes outlined above will
4807   allow the Internet, once older HTTP clients are no longer common, to
4808   support multiple Web sites from a single IP address, greatly
4809   simplifying large operational Web servers, where allocation of many
4810   IP addresses to a single host has created serious problems. The
4811   Internet will also be able to recover the IP addresses that have been
4812   allocated for the sole purpose of allowing special-purpose domain
4813   names to be used in root-level HTTP URLs. Given the rate of growth of
4814   the Web, and the number of servers already deployed, it is extremely
4815   important that all implementations of HTTP (including updates to
4816   existing HTTP/1.0 applications) correctly implement these
4817   requirements:
4818  <list style="symbols">
4819     <t>Both clients and servers &MUST; support the Host request-header.</t>
4820
4821     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4822
4823     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4824        request does not include a Host request-header.</t>
4825
4826     <t>Servers &MUST; accept absolute URIs.</t>
4827  </list>
4828</t>
4829</section>
4830</section>
4831
4832<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4833<t>
4834   Some clients and servers might wish to be compatible with some
4835   previous implementations of persistent connections in HTTP/1.0
4836   clients and servers. Persistent connections in HTTP/1.0 are
4837   explicitly negotiated as they are not the default behavior. HTTP/1.0
4838   experimental implementations of persistent connections are faulty,
4839   and the new facilities in HTTP/1.1 are designed to rectify these
4840   problems. The problem was that some existing HTTP/1.0 clients may be
4841   sending Keep-Alive to a proxy server that doesn't understand
4842   Connection, which would then erroneously forward it to the next
4843   inbound server, which would establish the Keep-Alive connection and
4844   result in a hung HTTP/1.0 proxy waiting for the close on the
4845   response. The result is that HTTP/1.0 clients must be prevented from
4846   using Keep-Alive when talking to proxies.
4847</t>
4848<t>
4849   However, talking to proxies is the most important use of persistent
4850   connections, so that prohibition is clearly unacceptable. Therefore,
4851   we need some other mechanism for indicating a persistent connection
4852   is desired, which is safe to use even when talking to an old proxy
4853   that ignores Connection. Persistent connections are the default for
4854   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4855   declaring non-persistence. See <xref target="header.connection"/>.
4856</t>
4857<t>
4858   The original HTTP/1.0 form of persistent connections (the Connection:
4859   Keep-Alive and Keep-Alive header) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4860</t>
4861</section>
4862
4863<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4864<t>
4865   This specification has been carefully audited to correct and
4866   disambiguate key word usage; RFC 2068 had many problems in respect to
4867   the conventions laid out in <xref target="RFC2119"/>.
4868</t>
4869<t>
4870   Transfer-coding and message lengths all interact in ways that
4871   required fixing exactly when chunked encoding is used (to allow for
4872   transfer encoding that may not be self delimiting); it was important
4873   to straighten out exactly how message lengths are computed. (Sections
4874   <xref target="transfer.codings" format="counter"/>, <xref target="message.body" format="counter"/>,
4875   <xref target="header.content-length" format="counter"/>,
4876   see also <xref target="Part5"/>)
4877</t>
4878<t>
4879   The use and interpretation of HTTP version numbers has been clarified
4880   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4881   version they support to deal with problems discovered in HTTP/1.0
4882   implementations (<xref target="http.version"/>)
4883</t>
4884<t>
4885   Quality Values of zero should indicate that "I don't want something"
4886   to allow clients to refuse a representation. (<xref target="quality.values"/>)
4887</t>
4888<t>
4889   Transfer-coding had significant problems, particularly with
4890   interactions with chunked encoding. The solution is that transfer-codings
4891   become as full fledged as content-codings. This involves
4892   adding an IANA registry for transfer-codings (separate from content
4893   codings), a new header field (TE) and enabling trailer headers in the
4894   future. Transfer encoding is a major performance benefit, so it was
4895   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4896   interoperability problem that could have occurred due to interactions
4897   between authentication trailers, chunked encoding and HTTP/1.0
4898   clients.(Section
4899   <xref target="transfer.codings" format="counter"/>,
4900   <xref target="chunked.encoding" format="counter"/>,
4901   <xref target="non-modifiable.headers" format="counter"/>,
4902   and <xref target="header.te" format="counter"/>)
4903</t>
4904<t>
4905  Proxies should be able to add Content-Length when appropriate.
4906  (<xref target="non-modifiable.headers"/>)
4907</t>
4908</section>
4909
4910<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4911<t>
4912  Empty list elements in list productions have been deprecated.
4913  (<xref target="notation.abnf"/>)
4914</t>
4915<t>
4916  Rules about implicit linear whitespace between certain grammar productions
4917  have been removed; now it's only allowed when specifically pointed out
4918  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4919  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4920  Non-ASCII content in header fields and reason phrase has been obsoleted and
4921  made opaque (the TEXT rule was removed)
4922  (<xref target="basic.rules"/>)
4923</t>
4924<t>
4925  Clarify that HTTP-Version is case sensitive.
4926  (<xref target="http.version"/>)
4927</t>
4928<t>
4929  Remove reference to non-existent identity transfer-coding value tokens.
4930  (Sections <xref format="counter" target="transfer.codings"/> and
4931  <xref format="counter" target="message.body"/>)
4932</t>
4933<t>
4934  Require that invalid whitespace around field-names be rejected.
4935  (<xref target="header.fields"/>)
4936</t>
4937<t>
4938  Update use of abs_path production from RFC1808 to the path-absolute + query
4939  components of RFC3986.
4940  (<xref target="request-target"/>)
4941</t>
4942<t>
4943  Clarification that the chunk length does not include the count of the octets
4944  in the chunk header and trailer. Furthermore disallowed line folding
4945  in chunk extensions.
4946  (<xref target="chunked.encoding"/>)
4947</t>
4948<t>
4949  Remove hard limit of two connections per server.
4950  (<xref target="persistent.practical"/>)
4951</t>
4952<t>
4953  Clarify exactly when close connection options must be sent.
4954  (<xref target="header.connection"/>)
4955</t>
4956</section>
4957</section>
4958
4959<?BEGININC p1-messaging.abnf-appendix ?>
4960<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4961<figure>
4962<artwork type="abnf" name="p1-messaging.parsed-abnf">
4963<x:ref>BWS</x:ref> = OWS
4964
4965<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
4966<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4967<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4968<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4969 connection-token ] )
4970<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4971<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4972
4973<x:ref>Date</x:ref> = "Date:" OWS Date-v
4974<x:ref>Date-v</x:ref> = HTTP-date
4975
4976<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4977
4978<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
4979<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4980<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4981<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
4982 ]
4983<x:ref>Host</x:ref> = "Host:" OWS Host-v
4984<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4985
4986<x:ref>Method</x:ref> = token
4987
4988<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4989
4990<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
4991
4992<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4993<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4994<x:ref>Request</x:ref> = Request-Line *( ( general-header / request-header /
4995 entity-header ) CRLF ) CRLF [ message-body ]
4996<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4997<x:ref>Response</x:ref> = Status-Line *( ( general-header / response-header /
4998 entity-header ) CRLF ) CRLF [ message-body ]
4999
5000<x:ref>Status-Code</x:ref> = 3DIGIT
5001<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5002
5003<x:ref>TE</x:ref> = "TE:" OWS TE-v
5004<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5005<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
5006<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5007<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
5008<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5009 transfer-coding ] )
5010
5011<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5012<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
5013<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
5014
5015<x:ref>Via</x:ref> = "Via:" OWS Via-v
5016<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
5017 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
5018 ] )
5019
5020<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
5021
5022<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5023<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
5024<x:ref>attribute</x:ref> = token
5025<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5026
5027<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
5028<x:ref>chunk-data</x:ref> = 1*OCTET
5029<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
5030<x:ref>chunk-ext-name</x:ref> = token
5031<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5032<x:ref>chunk-size</x:ref> = 1*HEXDIG
5033<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5034<x:ref>connection-token</x:ref> = token
5035<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5036 / %x2A-5B ; '*'-'['
5037 / %x5D-7E ; ']'-'~'
5038 / obs-text
5039
5040<x:ref>date1</x:ref> = day SP month SP year
5041<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
5042<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
5043<x:ref>day</x:ref> = 2DIGIT
5044<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
5045 / %x54.75.65 ; Tue
5046 / %x57.65.64 ; Wed
5047 / %x54.68.75 ; Thu
5048 / %x46.72.69 ; Fri
5049 / %x53.61.74 ; Sat
5050 / %x53.75.6E ; Sun
5051<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
5052 / %x54.75.65.73.64.61.79 ; Tuesday
5053 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
5054 / %x54.68.75.72.73.64.61.79 ; Thursday
5055 / %x46.72.69.64.61.79 ; Friday
5056 / %x53.61.74.75.72.64.61.79 ; Saturday
5057 / %x53.75.6E.64.61.79 ; Sunday
5058
5059<x:ref>entity-header</x:ref> = &lt;entity-header, defined in [Part3], Section 3.1&gt;
5060
5061<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
5062<x:ref>field-name</x:ref> = token
5063<x:ref>field-value</x:ref> = *( field-content / OWS )
5064
5065<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
5066 / Transfer-Encoding / Upgrade / Via / Warning
5067
5068<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
5069<x:ref>hour</x:ref> = 2DIGIT
5070<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5071<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5072
5073<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
5074
5075<x:ref>message-body</x:ref> = *OCTET
5076<x:ref>minute</x:ref> = 2DIGIT
5077<x:ref>month</x:ref> = %x4A.61.6E ; Jan
5078 / %x46.65.62 ; Feb
5079 / %x4D.61.72 ; Mar
5080 / %x41.70.72 ; Apr
5081 / %x4D.61.79 ; May
5082 / %x4A.75.6E ; Jun
5083 / %x4A.75.6C ; Jul
5084 / %x41.75.67 ; Aug
5085 / %x53.65.70 ; Sep
5086 / %x4F.63.74 ; Oct
5087 / %x4E.6F.76 ; Nov
5088 / %x44.65.63 ; Dec
5089
5090<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
5091<x:ref>obs-fold</x:ref> = CRLF
5092<x:ref>obs-text</x:ref> = %x80-FF
5093
5094<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5095<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5096<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5097<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5098<x:ref>product</x:ref> = token [ "/" product-version ]
5099<x:ref>product-version</x:ref> = token
5100<x:ref>protocol-name</x:ref> = token
5101<x:ref>protocol-version</x:ref> = token
5102<x:ref>pseudonym</x:ref> = token
5103
5104<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5105 / %x5D-7E ; ']'-'~'
5106 / obs-text
5107<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
5108 / %x5D-7E ; ']'-'~'
5109 / obs-text
5110<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5111<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5112<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5113<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5114<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5115<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5116
5117<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5118<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5119<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5120<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
5121<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5122 / authority
5123<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
5124<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5125<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5126
5127<x:ref>second</x:ref> = 2DIGIT
5128<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5129 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5130<x:ref>start-line</x:ref> = Request-Line / Status-Line
5131
5132<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5133<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5134 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5135<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5136<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5137<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5138<x:ref>token</x:ref> = 1*tchar
5139<x:ref>trailer-part</x:ref> = *( entity-header CRLF )
5140<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5141 transfer-extension
5142<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5143<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5144
5145<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5146
5147<x:ref>value</x:ref> = word
5148
5149<x:ref>word</x:ref> = token / quoted-string
5150
5151<x:ref>year</x:ref> = 4DIGIT
5152</artwork>
5153</figure>
5154<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5155; Chunked-Body defined but not used
5156; Content-Length defined but not used
5157; HTTP-message defined but not used
5158; Host defined but not used
5159; Request defined but not used
5160; Response defined but not used
5161; TE defined but not used
5162; URI-reference defined but not used
5163; http-URI defined but not used
5164; https-URI defined but not used
5165; partial-URI defined but not used
5166; special defined but not used
5167</artwork></figure></section>
5168<?ENDINC p1-messaging.abnf-appendix ?>
5169
5170<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5171
5172<section title="Since RFC2616">
5173<t>
5174  Extracted relevant partitions from <xref target="RFC2616"/>.
5175</t>
5176</section>
5177
5178<section title="Since draft-ietf-httpbis-p1-messaging-00">
5179<t>
5180  Closed issues:
5181  <list style="symbols"> 
5182    <t>
5183      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5184      "HTTP Version should be case sensitive"
5185      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5186    </t>
5187    <t>
5188      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5189      "'unsafe' characters"
5190      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5191    </t>
5192    <t>
5193      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5194      "Chunk Size Definition"
5195      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5196    </t>
5197    <t>
5198      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5199      "Message Length"
5200      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5201    </t>
5202    <t>
5203      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5204      "Media Type Registrations"
5205      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5206    </t>
5207    <t>
5208      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5209      "URI includes query"
5210      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5211    </t>
5212    <t>
5213      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5214      "No close on 1xx responses"
5215      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5216    </t>
5217    <t>
5218      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5219      "Remove 'identity' token references"
5220      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5221    </t>
5222    <t>
5223      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5224      "Import query BNF"
5225    </t>
5226    <t>
5227      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5228      "qdtext BNF"
5229    </t>
5230    <t>
5231      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5232      "Normative and Informative references"
5233    </t>
5234    <t>
5235      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5236      "RFC2606 Compliance"
5237    </t>
5238    <t>
5239      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5240      "RFC977 reference"
5241    </t>
5242    <t>
5243      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5244      "RFC1700 references"
5245    </t>
5246    <t>
5247      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5248      "inconsistency in date format explanation"
5249    </t>
5250    <t>
5251      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5252      "Date reference typo"
5253    </t>
5254    <t>
5255      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5256      "Informative references"
5257    </t>
5258    <t>
5259      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5260      "ISO-8859-1 Reference"
5261    </t>
5262    <t>
5263      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5264      "Normative up-to-date references"
5265    </t>
5266  </list>
5267</t>
5268<t>
5269  Other changes:
5270  <list style="symbols"> 
5271    <t>
5272      Update media type registrations to use RFC4288 template.
5273    </t>
5274    <t>
5275      Use names of RFC4234 core rules DQUOTE and WSP,
5276      fix broken ABNF for chunk-data
5277      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5278    </t>
5279  </list>
5280</t>
5281</section>
5282
5283<section title="Since draft-ietf-httpbis-p1-messaging-01">
5284<t>
5285  Closed issues:
5286  <list style="symbols"> 
5287    <t>
5288      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5289      "Bodies on GET (and other) requests"
5290    </t>
5291    <t>
5292      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5293      "Updating to RFC4288"
5294    </t>
5295    <t>
5296      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5297      "Status Code and Reason Phrase"
5298    </t>
5299    <t>
5300      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5301      "rel_path not used"
5302    </t>
5303  </list>
5304</t>
5305<t>
5306  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5307  <list style="symbols"> 
5308    <t>
5309      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5310      "trailer-part").
5311    </t>
5312    <t>
5313      Avoid underscore character in rule names ("http_URL" ->
5314      "http-URL", "abs_path" -> "path-absolute").
5315    </t>
5316    <t>
5317      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5318      "path-absolute", "port", "query", "relativeURI", "host) -- these will
5319      have to be updated when switching over to RFC3986.
5320    </t>
5321    <t>
5322      Synchronize core rules with RFC5234.
5323    </t>
5324    <t>
5325      Get rid of prose rules that span multiple lines.
5326    </t>
5327    <t>
5328      Get rid of unused rules LOALPHA and UPALPHA.
5329    </t>
5330    <t>
5331      Move "Product Tokens" section (back) into Part 1, as "token" is used
5332      in the definition of the Upgrade header.
5333    </t>
5334    <t>
5335      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5336    </t>
5337    <t>
5338      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5339    </t>
5340  </list>
5341</t>
5342</section>
5343
5344<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5345<t>
5346  Closed issues:
5347  <list style="symbols"> 
5348    <t>
5349      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5350      "HTTP-date vs. rfc1123-date"
5351    </t>
5352    <t>
5353      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5354      "WS in quoted-pair"
5355    </t>
5356  </list>
5357</t>
5358<t>
5359  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5360  <list style="symbols"> 
5361    <t>
5362      Reference RFC 3984, and update header registrations for headers defined
5363      in this document.
5364    </t>
5365  </list>
5366</t>
5367<t>
5368  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5369  <list style="symbols"> 
5370    <t>
5371      Replace string literals when the string really is case-sensitive (HTTP-Version).
5372    </t>
5373  </list>
5374</t>
5375</section>
5376
5377<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5378<t>
5379  Closed issues:
5380  <list style="symbols"> 
5381    <t>
5382      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5383      "Connection closing"
5384    </t>
5385    <t>
5386      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5387      "Move registrations and registry information to IANA Considerations"
5388    </t>
5389    <t>
5390      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5391      "need new URL for PAD1995 reference"
5392    </t>
5393    <t>
5394      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5395      "IANA Considerations: update HTTP URI scheme registration"
5396    </t>
5397    <t>
5398      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5399      "Cite HTTPS URI scheme definition"
5400    </t>
5401    <t>
5402      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5403      "List-type headers vs Set-Cookie"
5404    </t>
5405  </list>
5406</t>
5407<t>
5408  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5409  <list style="symbols"> 
5410    <t>
5411      Replace string literals when the string really is case-sensitive (HTTP-Date).
5412    </t>
5413    <t>
5414      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5415    </t>
5416  </list>
5417</t>
5418</section>
5419
5420<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5421<t>
5422  Closed issues:
5423  <list style="symbols"> 
5424    <t>
5425      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5426      "Out-of-date reference for URIs"
5427    </t>
5428    <t>
5429      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5430      "RFC 2822 is updated by RFC 5322"
5431    </t>
5432  </list>
5433</t>
5434<t>
5435  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5436  <list style="symbols"> 
5437    <t>
5438      Use "/" instead of "|" for alternatives.
5439    </t>
5440    <t>
5441      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5442    </t>
5443    <t>
5444      Only reference RFC 5234's core rules.
5445    </t>
5446    <t>
5447      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5448      whitespace ("OWS") and required whitespace ("RWS").
5449    </t>
5450    <t>
5451      Rewrite ABNFs to spell out whitespace rules, factor out
5452      header value format definitions.
5453    </t>
5454  </list>
5455</t>
5456</section>
5457
5458<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5459<t>
5460  Closed issues:
5461  <list style="symbols"> 
5462    <t>
5463      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5464      "Header LWS"
5465    </t>
5466    <t>
5467      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5468      "Sort 1.3 Terminology"
5469    </t>
5470    <t>
5471      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5472      "RFC2047 encoded words"
5473    </t>
5474    <t>
5475      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5476      "Character Encodings in TEXT"
5477    </t>
5478    <t>
5479      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5480      "Line Folding"
5481    </t>
5482    <t>
5483      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5484      "OPTIONS * and proxies"
5485    </t>
5486    <t>
5487      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5488      "Reason-Phrase BNF"
5489    </t>
5490    <t>
5491      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5492      "Use of TEXT"
5493    </t>
5494    <t>
5495      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5496      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5497    </t>
5498    <t>
5499      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5500      "RFC822 reference left in discussion of date formats"
5501    </t>
5502  </list>
5503</t>
5504<t>
5505  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5506  <list style="symbols"> 
5507    <t>
5508      Rewrite definition of list rules, deprecate empty list elements.
5509    </t>
5510    <t>
5511      Add appendix containing collected and expanded ABNF.
5512    </t>
5513  </list>
5514</t>
5515<t>
5516  Other changes:
5517  <list style="symbols"> 
5518    <t>
5519      Rewrite introduction; add mostly new Architecture Section.
5520    </t>
5521    <t>
5522      Move definition of quality values from Part 3 into Part 1;
5523      make TE request header grammar independent of accept-params (defined in Part 3).
5524    </t>
5525  </list>
5526</t>
5527</section>
5528
5529<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5530<t>
5531  Closed issues:
5532  <list style="symbols"> 
5533    <t>
5534      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5535      "base for numeric protocol elements"
5536    </t>
5537    <t>
5538      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5539      "comment ABNF"
5540    </t>
5541  </list>
5542</t>
5543<t>
5544  Partly resolved issues:
5545  <list style="symbols"> 
5546    <t>
5547      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5548      "205 Bodies" (took out language that implied that there may be
5549      methods for which a request body MUST NOT be included)
5550    </t>
5551    <t>
5552      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5553      "editorial improvements around HTTP-date"
5554    </t>
5555  </list>
5556</t>
5557</section>
5558
5559<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5560<t>
5561  Closed issues:
5562  <list style="symbols"> 
5563    <t>
5564      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5565      "Repeating single-value headers"
5566    </t>
5567    <t>
5568      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5569      "increase connection limit"
5570    </t>
5571    <t>
5572      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5573      "IP addresses in URLs"
5574    </t>
5575    <t>
5576      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5577      "take over HTTP Upgrade Token Registry"
5578    </t>
5579    <t>
5580      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5581      "CR and LF in chunk extension values"
5582    </t>
5583    <t>
5584      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5585      "HTTP/0.9 support"
5586    </t>
5587    <t>
5588      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5589      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5590    </t>
5591    <t>
5592      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5593      "move definitions of gzip/deflate/compress to part 1"
5594    </t>
5595    <t>
5596      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5597      "disallow control characters in quoted-pair"
5598    </t>
5599  </list>
5600</t>
5601<t>
5602  Partly resolved issues:
5603  <list style="symbols"> 
5604    <t>
5605      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5606      "update IANA requirements wrt Transfer-Coding values" (add the
5607      IANA Considerations subsection)
5608    </t>
5609  </list>
5610</t>
5611</section>
5612
5613<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5614<t>
5615  Closed issues:
5616  <list style="symbols"> 
5617    <t>
5618      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5619      "header parsing, treatment of leading and trailing OWS"
5620    </t>
5621  </list>
5622</t>
5623<t>
5624  Partly resolved issues:
5625  <list style="symbols"> 
5626    <t>
5627      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5628      "Placement of 13.5.1 and 13.5.2"
5629    </t>
5630    <t>
5631      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5632      "use of term "word" when talking about header structure"
5633    </t>
5634  </list>
5635</t>
5636</section>
5637
5638<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5639<t>
5640  Closed issues:
5641  <list style="symbols"> 
5642    <t>
5643      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5644      "Clarification of the term 'deflate'"
5645    </t>
5646    <t>
5647      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5648      "OPTIONS * and proxies"
5649    </t>
5650    <t>
5651      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5652      "IANA registry for content/transfer encodings"
5653    </t>
5654    <t>
5655      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5656      "Case-sensitivity of HTTP-date"
5657    </t>
5658    <t>
5659      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5660      "use of term "word" when talking about header structure"
5661    </t>
5662  </list>
5663</t>
5664<t>
5665  Partly resolved issues:
5666  <list style="symbols"> 
5667    <t>
5668      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5669      "Term for the requested resource's URI"
5670    </t>
5671  </list>
5672</t>
5673</section>
5674
5675<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5676<t>
5677  Closed issues:
5678  <list style="symbols"> 
5679    <t>
5680      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5681      "Delimiting messages with multipart/byteranges"
5682    </t>
5683    <t>
5684      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5685      "Handling multiple Content-Length headers"
5686    </t>
5687  </list>
5688</t>
5689</section>
5690
5691</section>
5692
5693</back>
5694</rfc>
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