source: draft-ietf-httpbis/09/p1-messaging.xml @ 847

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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 "09">
15  <!ENTITY ID-MONTH "March">
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 payload                "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY media-types            "<xref target='Part3' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY content-codings        "<xref target='Part3' x:rel='#content.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY diff2045entity         "<xref target='Part3' x:rel='#differences.between.http.entities.and.rfc.2045.entities' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY entity                 "<xref target='Part3' x:rel='#entity' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY entity-body            "<xref target='Part3' x:rel='#entity.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY entity-header-fields   "<xref target='Part3' x:rel='#entity.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY entity-length          "<xref target='Part3' x:rel='#entity.length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39]>
40<?rfc toc="yes" ?>
41<?rfc symrefs="yes" ?>
42<?rfc sortrefs="yes" ?>
43<?rfc compact="yes"?>
44<?rfc subcompact="no" ?>
45<?rfc linkmailto="no" ?>
46<?rfc editing="no" ?>
47<?rfc comments="yes"?>
48<?rfc inline="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>One Laptop per Child</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@laptop.org</email>
86      <uri>http://www.laptop.org/</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;" day="8"/>
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/11"/>
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.08"/>.
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 &diff2045entity; 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 a generic protocol for translating
253   communication to and from other Internet information systems.
254   HTTP proxies and gateways 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 syntactical 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 except the entity-body (see <xref target="tolerant.applications"/> for
423   tolerant applications). The end-of-line marker within an entity-body
424   is defined by its associated media type, as described in &media-types;.
425</t>
426<t anchor="rule.LWS">
427   This specification uses three rules to denote the use of linear
428   whitespace: OWS (optional whitespace), RWS (required whitespace), and
429   BWS ("bad" whitespace).
430</t>
431<t>
432   The OWS rule is used where zero or more linear whitespace characters may
433   appear. OWS &SHOULD; either not be produced or be produced as a single SP
434   character. Multiple OWS characters that occur within field-content &SHOULD;
435   be replaced with a single SP before interpreting the field value or
436   forwarding the message downstream.
437</t>
438<t>
439   RWS is used when at least one linear whitespace character is required to
440   separate field tokens. RWS &SHOULD; be produced as a single SP character.
441   Multiple RWS characters that occur within field-content &SHOULD; be
442   replaced with a single SP before interpreting the field value or
443   forwarding the message downstream.
444</t>
445<t>
446   BWS is used where the grammar allows optional whitespace for historical
447   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
448   recipients &MUST; accept such bad optional whitespace and remove it before
449   interpreting the field value or forwarding the message downstream.
450</t>
451<t anchor="rule.whitespace">
452  <x:anchor-alias value="BWS"/>
453  <x:anchor-alias value="OWS"/>
454  <x:anchor-alias value="RWS"/>
455  <x:anchor-alias value="obs-fold"/>
456</t>
457<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"/>
458  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
459                 ; "optional" whitespace
460  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
461                 ; "required" whitespace
462  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
463                 ; "bad" whitespace
464  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
465                 ; see <xref target="header.fields"/>
466</artwork></figure>
467<t anchor="rule.token.separators">
468  <x:anchor-alias value="tchar"/>
469  <x:anchor-alias value="token"/>
470  <x:anchor-alias value="special"/>
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="token"/><iref primary="true" item="Grammar" subitem="tchar"/><iref primary="true" item="Grammar" subitem="special"/>
477  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
478<!--
479  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
480 -->
481  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
482                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
483                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
484                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
485
486  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
487                 / ";" / ":" / "\" / DQUOTE / "/" / "["
488                 / "]" / "?" / "=" / "{" / "}"
489</artwork></figure>
490<t anchor="rule.quoted-string">
491  <x:anchor-alias value="quoted-string"/>
492  <x:anchor-alias value="qdtext"/>
493  <x:anchor-alias value="obs-text"/>
494   A string of text is parsed as a single word if it is quoted using
495   double-quote marks.
496</t>
497<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"/>
498  <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>
499  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
500                 ; <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> 
501  <x:ref>obs-text</x:ref>       = %x80-FF
502</artwork></figure>
503<t anchor="rule.quoted-pair">
504  <x:anchor-alias value="quoted-pair"/>
505   The backslash character ("\") can be used as a single-character
506   quoting mechanism within quoted-string constructs:
507</t>
508<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
509  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
510</artwork></figure>
511<t>
512   Producers &SHOULD-NOT; escape characters that do not require escaping
513   (i.e., other than DQUOTE and the backslash character).
514</t>
515</section>
516
517<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
518  <x:anchor-alias value="request-header"/>
519  <x:anchor-alias value="response-header"/>
520  <x:anchor-alias value="entity-body"/>
521  <x:anchor-alias value="entity-header"/>
522  <x:anchor-alias value="Cache-Control"/>
523  <x:anchor-alias value="Pragma"/>
524  <x:anchor-alias value="Warning"/>
525<t>
526  The ABNF rules below are defined in other parts:
527</t>
528<figure><!-- Part2--><artwork type="abnf2616">
529  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
530  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
531</artwork></figure>
532<figure><!-- Part3--><artwork type="abnf2616">
533  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
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"/>
861  <x:anchor-alias value="URI-reference"/>
862  <x:anchor-alias value="absolute-URI"/>
863  <x:anchor-alias value="relative-part"/>
864  <x:anchor-alias value="authority"/>
865  <x:anchor-alias value="path-abempty"/>
866  <x:anchor-alias value="path-absolute"/>
867  <x:anchor-alias value="port"/>
868  <x:anchor-alias value="query"/>
869  <x:anchor-alias value="uri-host"/>
870  <x:anchor-alias value="partial-URI"/>
871<t>
872   This specification adopts the definitions of "URI-reference",
873   "absolute-URI", "relative-part", "port", "host",
874   "path-abempty", "path-absolute", "query", and "authority" from
875   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
876   protocol elements that allow a relative URI without a fragment.
877</t>
878<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"/>
879  <x:ref>URI</x:ref>           = &lt;URI, defined in <xref target="RFC3986" x:fmt="," x:sec="3"/>&gt;
880  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
881  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
882  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
883  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
884  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
885  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
886  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
887  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
888  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
889 
890  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
891</artwork></figure>
892<t>
893   Each protocol element in HTTP that allows a URI reference will indicate in
894   its ABNF production whether the element allows only a URI in absolute form
895   (absolute-URI), any relative reference (relative-ref), or some other subset
896   of the URI-reference grammar. Unless otherwise indicated, URI references
897   are parsed relative to the request target (the default base URI for both
898   the request and its corresponding response).
899</t>
900
901<section title="http URI scheme" anchor="http.uri">
902  <x:anchor-alias value="http-URI"/>
903  <iref item="http URI scheme" primary="true"/>
904  <iref item="URI scheme" subitem="http" primary="true"/>
905<t>
906   The "http" URI scheme is hereby defined for the purpose of minting
907   identifiers according to their association with the hierarchical
908   namespace governed by a potential HTTP origin server listening for
909   TCP connections on a given port.
910   The HTTP server is identified via the generic syntax's
911   <x:ref>authority</x:ref> component, which includes a host
912   identifier and optional TCP port, and the remainder of the URI is
913   considered to be identifying data corresponding to a resource for
914   which that server might provide an HTTP interface.
915</t>
916<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
917  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
918</artwork></figure>
919<t>
920   The host identifier within an <x:ref>authority</x:ref> component is
921   defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>.  If host is
922   provided as an IP literal or IPv4 address, then the HTTP server is any
923   listener on the indicated TCP port at that IP address. If host is a
924   registered name, then that name is considered an indirect identifier
925   and the recipient might use a name resolution service, such as DNS,
926   to find the address of a listener for that host.
927   The host &MUST-NOT; be empty; if an "http" URI is received with an
928   empty host, then it &MUST; be rejected as invalid.
929   If the port subcomponent is empty or not given, then TCP port 80 is
930   assumed (the default reserved port for WWW services).
931</t>
932<t>
933   Regardless of the form of host identifier, access to that host is not
934   implied by the mere presence of its name or address. The host may or may
935   not exist and, even when it does exist, may or may not be running an
936   HTTP server or listening to the indicated port. The "http" URI scheme
937   makes use of the delegated nature of Internet names and addresses to
938   establish a naming authority (whatever entity has the ability to place
939   an HTTP server at that Internet name or address) and allows that
940   authority to determine which names are valid and how they might be used.
941</t>
942<t>
943   When an "http" URI is used within a context that calls for access to the
944   indicated resource, a client &MAY; attempt access by resolving
945   the host to an IP address, establishing a TCP connection to that address
946   on the indicated port, and sending an HTTP request message to the server
947   containing the URI's identifying data as described in <xref target="request"/>.
948   If the server responds to that request with a non-interim HTTP response
949   message, as described in <xref target="response"/>, then that response
950   is considered an authoritative answer to the client's request.
951</t>
952<t>
953   Although HTTP is independent of the transport protocol, the "http"
954   scheme is specific to TCP-based services because the name delegation
955   process depends on TCP for establishing authority.
956   An HTTP service based on some other underlying connection protocol
957   would presumably be identified using a different URI scheme, just as
958   the "https" scheme (below) is used for servers that require an SSL/TLS
959   transport layer on a connection. Other protocols may also be used to
960   provide access to "http" identified resources --- it is only the
961   authoritative interface used for mapping the namespace that is
962   specific to TCP.
963</t>
964</section>
965
966<section title="https URI scheme" anchor="https.uri">
967   <x:anchor-alias value="https-URI"/>
968   <iref item="https URI scheme"/>
969   <iref item="URI scheme" subitem="https"/>
970<t>
971   The "https" URI scheme is hereby defined for the purpose of minting
972   identifiers according to their association with the hierarchical
973   namespace governed by a potential HTTP origin server listening for
974   SSL/TLS-secured connections on a given TCP port.
975   The host and port are determined in the same way
976   as for the "http" scheme, except that a default TCP port of 443
977   is assumed if the port subcomponent is empty or not given.
978</t>
979<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
980  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
981</artwork></figure>
982<t>
983   The primary difference between the "http" and "https" schemes is
984   that interaction with the latter is required to be secured for
985   privacy through the use of strong encryption. The URI cannot be
986   sent in a request until the connection is secure. Likewise, the
987   default for caching is that each response that would be considered
988   "public" under the "http" scheme is instead treated as "private"
989   and thus not eligible for shared caching.
990</t>
991<t>
992   The process for authoritative access to an "https" identified
993   resource is defined in <xref target="RFC2818"/>.
994</t>
995</section>
996
997<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
998<t>
999   Since the "http" and "https" schemes conform to the URI generic syntax,
1000   such URIs are normalized and compared according to the algorithm defined
1001   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1002   described above for each scheme.
1003</t>
1004<t>
1005   If the port is equal to the default port for a scheme, the normal
1006   form is to elide the port subcomponent. Likewise, an empty path
1007   component is equivalent to an absolute path of "/", so the normal
1008   form is to provide a path of "/" instead. The scheme and host
1009   are case-insensitive and normally provided in lowercase; all
1010   other components are compared in a case-sensitive manner.
1011   Characters other than those in the "reserved" set are equivalent
1012   to their percent-encoded octets (see <xref target="RFC3986"
1013   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1014</t>
1015<t>
1016   For example, the following three URIs are equivalent:
1017</t>
1018<figure><artwork type="example">
1019   http://example.com:80/~smith/home.html
1020   http://EXAMPLE.com/%7Esmith/home.html
1021   http://EXAMPLE.com:/%7esmith/home.html
1022</artwork></figure>
1023<t>
1024   <cref anchor="TODO-not-here" source="roy">This paragraph does not belong here.</cref>
1025   If path-abempty is the empty string (i.e., there is no slash "/"
1026   path separator following the authority), then the "http" URI
1027   &MUST; be given as "/" when
1028   used as a request-target (<xref target="request-target"/>). If a proxy
1029   receives a host name which is not a fully qualified domain name, it
1030   &MAY; add its domain to the host name it received. If a proxy receives
1031   a fully qualified domain name, the proxy &MUST-NOT; change the host
1032   name.
1033</t>
1034</section>
1035</section>
1036</section>
1037
1038<section title="HTTP Message" anchor="http.message">
1039<x:anchor-alias value="generic-message"/>
1040<x:anchor-alias value="message.types"/>
1041<x:anchor-alias value="HTTP-message"/>
1042<x:anchor-alias value="start-line"/>
1043<iref item="header section"/>
1044<iref item="headers"/>
1045<iref item="header field"/>
1046<t>
1047   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1048   characters in a format similar to the Internet Message Format
1049   <xref target="RFC5322"/>: zero or more header fields (collectively
1050   referred to as the "headers" or the "header section"), an empty line
1051   indicating the end of the header section, and an optional message-body.
1052</t>
1053<t>
1054   An HTTP message can either be a request from client to server or a
1055   response from server to client.  Syntactically, the two types of message
1056   differ only in the start-line, which is either a Request-Line (for requests)
1057   or a Status-Line (for responses), and in the algorithm for determining
1058   the length of the message-body (<xref target="message.length"/>).
1059   In theory, a client could receive requests and a server could receive
1060   responses, distinguishing them by their different start-line formats,
1061   but in practice servers are implemented to only expect a request
1062   (a response is interpreted as an unknown or invalid request method)
1063   and clients are implemented to only expect a response.
1064</t>
1065<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1066  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1067                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1068                    <x:ref>CRLF</x:ref>
1069                    [ <x:ref>message-body</x:ref> ]
1070  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1071</artwork></figure>
1072<t>
1073   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1074   header field. The presence of whitespace might be an attempt to trick a
1075   noncompliant implementation of HTTP into ignoring that field or processing
1076   the next line as a new request, either of which may result in security
1077   issues when implementations within the request chain interpret the
1078   same message differently. HTTP/1.1 servers &MUST; reject such a message
1079   with a 400 (Bad Request) response.
1080</t>
1081
1082<section title="Message Parsing Robustness" anchor="message.robustness">
1083<t>
1084   In the interest of robustness, servers &SHOULD; ignore at least one
1085   empty line received where a Request-Line is expected. In other words, if
1086   the server is reading the protocol stream at the beginning of a
1087   message and receives a CRLF first, it should ignore the CRLF.
1088</t>
1089<t>
1090   Some old HTTP/1.0 client implementations generate an extra CRLF
1091   after a POST request as a lame workaround for some early server
1092   applications that failed to read message-body content that was
1093   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1094   preface or follow a request with an extra CRLF.  If terminating
1095   the request message-body with a line-ending is desired, then the
1096   client &MUST; include the terminating CRLF octets as part of the
1097   message-body length.
1098</t>
1099<t>
1100   The normal procedure for parsing an HTTP message is to read the
1101   start-line into a structure, read each header field into a hash
1102   table by field name until the empty line, and then use the parsed
1103   data to determine if a message-body is expected.  If a message-body
1104   has been indicated, then it is read as a stream until an amount
1105   of OCTETs equal to the message-length is read or the connection
1106   is closed.  Care must be taken to parse an HTTP message as a sequence
1107   of OCTETs in an encoding that is a superset of US-ASCII.  Attempting
1108   to parse HTTP as a stream of Unicode characters in a character encoding
1109   like UTF-16 may introduce security flaws due to the differing ways
1110   that such parsers interpret invalid characters.
1111</t>
1112</section>
1113
1114<section title="Header Fields" anchor="header.fields">
1115  <x:anchor-alias value="header-field"/>
1116  <x:anchor-alias value="field-content"/>
1117  <x:anchor-alias value="field-name"/>
1118  <x:anchor-alias value="field-value"/>
1119  <x:anchor-alias value="OWS"/>
1120<t>
1121   Each HTTP header field consists of a case-insensitive field name
1122   followed by a colon (":"), optional whitespace, and the field value.
1123</t>
1124<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"/>
1125  <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>
1126  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1127  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1128  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1129</artwork></figure>
1130<t>
1131   No whitespace is allowed between the header field name and colon. For
1132   security reasons, any request message received containing such whitespace
1133   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1134   &MUST; remove any such whitespace from a response message before
1135   forwarding the message downstream.
1136</t>
1137<t>
1138   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1139   preferred. The field value does not include any leading or trailing white
1140   space: OWS occurring before the first non-whitespace character of the
1141   field value or after the last non-whitespace character of the field value
1142   is ignored and &SHOULD; be removed before further processing (as this does
1143   not change the meaning of the header field).
1144</t>
1145<t>
1146   The order in which header fields with differing field names are
1147   received is not significant. However, it is "good practice" to send
1148   header fields that contain control data first, such as Host on
1149   requests and Date on responses, so that implementations can decide
1150   when not to handle a message as early as possible.  A server &MUST;
1151   wait until the entire header section is received before interpreting
1152   a request message, since later header fields might include conditionals,
1153   authentication credentials, or deliberately misleading duplicate
1154   header fields that would impact request processing.
1155</t>
1156<t>
1157   Multiple header fields with the same field name &MUST-NOT; be
1158   sent in a message unless the entire field value for that
1159   header field is defined as a comma-separated list [i.e., #(values)].
1160   Multiple header fields with the same field name can be combined into
1161   one "field-name: field-value" pair, without changing the semantics of the
1162   message, by appending each subsequent field value to the combined
1163   field value in order, separated by a comma. The order in which
1164   header fields with the same field name are received is therefore
1165   significant to the interpretation of the combined field value;
1166   a proxy &MUST-NOT; change the order of these field values when
1167   forwarding a message.
1168</t>
1169<x:note>
1170  <t>
1171   <x:h>Note:</x:h> The "Set-Cookie" header as implemented in
1172   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1173   can occur multiple times, but does not use the list syntax, and thus cannot
1174   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1175   for details.) Also note that the Set-Cookie2 header specified in
1176   <xref target="RFC2965"/> does not share this problem.
1177  </t>
1178</x:note>
1179<t>
1180   Historically, HTTP header field values could be extended over multiple
1181   lines by preceding each extra line with at least one space or horizontal
1182   tab character (line folding). This specification deprecates such line
1183   folding except within the message/http media type
1184   (<xref target="internet.media.type.message.http"/>).
1185   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1186   (i.e., that contain any field-content that matches the obs-fold rule) unless
1187   the message is intended for packaging within the message/http media type.
1188   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1189   obs-fold whitespace with a single SP prior to interpreting the field value
1190   or forwarding the message downstream.
1191</t>
1192<t>
1193   Historically, HTTP has allowed field content with text in the ISO-8859-1
1194   <xref target="ISO-8859-1"/> character encoding and supported other
1195   character sets only through use of <xref target="RFC2047"/> encoding.
1196   In practice, most HTTP header field values use only a subset of the
1197   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1198   header fields &SHOULD; limit their field values to US-ASCII characters.
1199   Recipients &SHOULD; treat other (obs-text) octets in field content as
1200   opaque data.
1201</t>
1202<t anchor="rule.comment">
1203  <x:anchor-alias value="comment"/>
1204  <x:anchor-alias value="ctext"/>
1205   Comments can be included in some HTTP header fields by surrounding
1206   the comment text with parentheses. Comments are only allowed in
1207   fields containing "comment" as part of their field value definition.
1208</t>
1209<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1210  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1211  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1212                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1213</artwork></figure>
1214<t anchor="rule.quoted-cpair">
1215  <x:anchor-alias value="quoted-cpair"/>
1216   The backslash character ("\") can be used as a single-character
1217   quoting mechanism within comment constructs:
1218</t>
1219<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1220  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1221</artwork></figure>
1222<t>
1223   Producers &SHOULD-NOT; escape characters that do not require escaping
1224   (i.e., other than the backslash character "\" and the parentheses "(" and
1225   ")").
1226</t>
1227</section>
1228
1229<section title="Message Body" anchor="message.body">
1230  <x:anchor-alias value="message-body"/>
1231<t>
1232   The message-body (if any) of an HTTP message is used to carry the
1233   entity-body associated with the request or response. The message-body
1234   differs from the entity-body only when a transfer-coding has been
1235   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1236</t>
1237<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1238  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1239               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1240</artwork></figure>
1241<t>
1242   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1243   applied by an application to ensure safe and proper transfer of the
1244   message. Transfer-Encoding is a property of the message, not of the
1245   entity, and thus &MAY; be added or removed by any application along the
1246   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1247   when certain transfer-codings may be used.)
1248</t>
1249<t>
1250   The rules for when a message-body is allowed in a message differ for
1251   requests and responses.
1252</t>
1253<t>
1254   The presence of a message-body in a request is signaled by the
1255   inclusion of a Content-Length or Transfer-Encoding header field in
1256   the request's header fields.
1257   When a request message contains both a message-body of non-zero
1258   length and a method that does not define any semantics for that
1259   request message-body, then an origin server &SHOULD; either ignore
1260   the message-body or respond with an appropriate error message
1261   (e.g., 413).  A proxy or gateway, when presented the same request,
1262   &SHOULD; either forward the request inbound with the message-body or
1263   ignore the message-body when determining a response.
1264</t>
1265<t>
1266   For response messages, whether or not a message-body is included with
1267   a message is dependent on both the request method and the response
1268   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1269   &MUST-NOT; include a message-body, even though the presence of entity-header
1270   fields might lead one to believe they do. All 1xx
1271   (Informational), 204 (No Content), and 304 (Not Modified) responses
1272   &MUST-NOT; include a message-body. All other responses do include a
1273   message-body, although it &MAY; be of zero length.
1274</t>
1275</section>
1276
1277<section title="Message Length" anchor="message.length">
1278<t>
1279   The transfer-length of a message is the length of the message-body as
1280   it appears in the message; that is, after any transfer-codings have
1281   been applied. When a message-body is included with a message, the
1282   transfer-length of that body is determined by one of the following
1283   (in order of precedence):
1284</t>
1285<t>
1286  <list style="numbers">
1287    <x:lt><t>
1288     Any response message which "&MUST-NOT;" include a message-body (such
1289     as the 1xx, 204, and 304 responses and any response to a HEAD
1290     request) is always terminated by the first empty line after the
1291     header fields, regardless of the entity-header fields present in
1292     the message.
1293    </t></x:lt>
1294    <x:lt><t>
1295     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1296     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1297     is used, the transfer-length is defined by the use of this transfer-coding.
1298     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1299     is not present, the transfer-length is defined by the sender closing the connection.
1300    </t></x:lt>
1301    <x:lt><t>
1302     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1303     value in OCTETs represents both the entity-length and the
1304     transfer-length. The Content-Length header field &MUST-NOT; be sent
1305     if these two lengths are different (i.e., if a Transfer-Encoding
1306     header field is present). If a message is received with both a
1307     Transfer-Encoding header field and a Content-Length header field,
1308     the latter &MUST; be ignored.
1309    </t></x:lt>
1310    <x:lt><t>
1311     If the message uses the media type "multipart/byteranges", and the
1312     transfer-length is not otherwise specified, then this self-delimiting
1313     media type defines the transfer-length. This media type
1314     &MUST-NOT; be used unless the sender knows that the recipient can parse
1315     it; the presence in a request of a Range header with multiple byte-range
1316     specifiers from a HTTP/1.1 client implies that the client can parse
1317     multipart/byteranges responses.
1318    <list style="empty"><t>
1319       A range header might be forwarded by a HTTP/1.0 proxy that does not
1320       understand multipart/byteranges; in this case the server &MUST;
1321       delimit the message using methods defined in items 1, 3 or 5 of
1322       this section.
1323    </t></list>
1324    </t></x:lt>
1325    <x:lt><t>
1326     By the server closing the connection. (Closing the connection
1327     cannot be used to indicate the end of a request body, since that
1328     would leave no possibility for the server to send back a response.)
1329    </t></x:lt>
1330  </list>
1331</t>
1332<t>
1333   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1334   containing a message-body &MUST; include a valid Content-Length header
1335   field unless the server is known to be HTTP/1.1 compliant. If a
1336   request contains a message-body and a Content-Length is not given,
1337   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1338   determine the length of the message, or with 411 (Length Required) if
1339   it wishes to insist on receiving a valid Content-Length.
1340</t>
1341<t>
1342   All HTTP/1.1 applications that receive entities &MUST; accept the
1343   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1344   to be used for messages when the message length cannot be determined
1345   in advance.
1346</t>
1347<t>
1348   Messages &MUST-NOT; include both a Content-Length header field and a
1349   transfer-coding. If the message does include a
1350   transfer-coding, the Content-Length &MUST; be ignored.
1351</t>
1352<t>
1353   When a Content-Length is given in a message where a message-body is
1354   allowed, its field value &MUST; exactly match the number of OCTETs in
1355   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1356   invalid length is received and detected.
1357</t>
1358</section>
1359
1360<section title="General Header Fields" anchor="general.header.fields">
1361  <x:anchor-alias value="general-header"/>
1362<t>
1363   There are a few header fields which have general applicability for
1364   both request and response messages, but which do not apply to the
1365   entity being transferred. These header fields apply only to the
1366   message being transmitted.
1367</t>
1368<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1369  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1370                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1371                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1372                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1373                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1374                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1375                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1376                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1377                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1378</artwork></figure>
1379<t>
1380   General-header field names can be extended reliably only in
1381   combination with a change in the protocol version. However, new or
1382   experimental header fields may be given the semantics of general
1383   header fields if all parties in the communication recognize them to
1384   be general-header fields. Unrecognized header fields are treated as
1385   entity-header fields.
1386</t>
1387</section>
1388</section>
1389
1390<section title="Request" anchor="request">
1391  <x:anchor-alias value="Request"/>
1392<t>
1393   A request message from a client to a server includes, within the
1394   first line of that message, the method to be applied to the resource,
1395   the identifier of the resource, and the protocol version in use.
1396</t>
1397<!--                 Host                      ; should be moved here eventually -->
1398<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1399  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1400                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1401                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1402                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> ) ; &entity-header-fields;
1403                  <x:ref>CRLF</x:ref>
1404                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1405</artwork></figure>
1406
1407<section title="Request-Line" anchor="request-line">
1408  <x:anchor-alias value="Request-Line"/>
1409<t>
1410   The Request-Line begins with a method token, followed by the
1411   request-target and the protocol version, and ending with CRLF. The
1412   elements are separated by SP characters. No CR or LF is allowed
1413   except in the final CRLF sequence.
1414</t>
1415<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1416  <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>
1417</artwork></figure>
1418
1419<section title="Method" anchor="method">
1420  <x:anchor-alias value="Method"/>
1421<t>
1422   The Method  token indicates the method to be performed on the
1423   resource identified by the request-target. The method is case-sensitive.
1424</t>
1425<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1426  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1427</artwork></figure>
1428</section>
1429
1430<section title="request-target" anchor="request-target">
1431  <x:anchor-alias value="request-target"/>
1432<t>
1433   The request-target
1434   identifies the resource upon which to apply the request.
1435</t>
1436<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1437  <x:ref>request-target</x:ref> = "*"
1438                 / <x:ref>absolute-URI</x:ref>
1439                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1440                 / <x:ref>authority</x:ref>
1441</artwork></figure>
1442<t>
1443   The four options for request-target are dependent on the nature of the
1444   request. The asterisk "*" means that the request does not apply to a
1445   particular resource, but to the server itself, and is only allowed
1446   when the method used does not necessarily apply to a resource. One
1447   example would be
1448</t>
1449<figure><artwork type="example">
1450  OPTIONS * HTTP/1.1
1451</artwork></figure>
1452<t>
1453   The absolute-URI form is &REQUIRED; when the request is being made to a
1454   proxy. The proxy is requested to forward the request or service it
1455   from a valid cache, and return the response. Note that the proxy &MAY;
1456   forward the request on to another proxy or directly to the server
1457   specified by the absolute-URI. In order to avoid request loops, a
1458   proxy &MUST; be able to recognize all of its server names, including
1459   any aliases, local variations, and the numeric IP address. An example
1460   Request-Line would be:
1461</t>
1462<figure><artwork type="example">
1463  GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1464</artwork></figure>
1465<t>
1466   To allow for transition to absolute-URIs in all requests in future
1467   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1468   form in requests, even though HTTP/1.1 clients will only generate
1469   them in requests to proxies.
1470</t>
1471<t>
1472   The authority form is only used by the CONNECT method (&CONNECT;).
1473</t>
1474<t>
1475   The most common form of request-target is that used to identify a
1476   resource on an origin server or gateway. In this case the absolute
1477   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1478   the request-target, and the network location of the URI (authority) &MUST;
1479   be transmitted in a Host header field. For example, a client wishing
1480   to retrieve the resource above directly from the origin server would
1481   create a TCP connection to port 80 of the host "www.example.org" and send
1482   the lines:
1483</t>
1484<figure><artwork type="example">
1485  GET /pub/WWW/TheProject.html HTTP/1.1
1486  Host: www.example.org
1487</artwork></figure>
1488<t>
1489   followed by the remainder of the Request. Note that the absolute path
1490   cannot be empty; if none is present in the original URI, it &MUST; be
1491   given as "/" (the server root).
1492</t>
1493<t>
1494   If a proxy receives a request without any path in the request-target and
1495   the method specified is capable of supporting the asterisk form of
1496   request-target, then the last proxy on the request chain &MUST; forward the
1497   request with "*" as the final request-target.
1498</t>
1499<figure><preamble>   
1500   For example, the request
1501</preamble><artwork type="example">
1502  OPTIONS http://www.example.org:8001 HTTP/1.1
1503</artwork></figure>
1504<figure><preamble>   
1505  would be forwarded by the proxy as
1506</preamble><artwork type="example">
1507  OPTIONS * HTTP/1.1
1508  Host: www.example.org:8001
1509</artwork>
1510<postamble>
1511   after connecting to port 8001 of host "www.example.org".
1512</postamble>
1513</figure>
1514<t>
1515   The request-target is transmitted in the format specified in
1516   <xref target="http.uri"/>. If the request-target is percent-encoded
1517   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1518   &MUST; decode the request-target in order to
1519   properly interpret the request. Servers &SHOULD; respond to invalid
1520   request-targets with an appropriate status code.
1521</t>
1522<t>
1523   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1524   received request-target when forwarding it to the next inbound server,
1525   except as noted above to replace a null path-absolute with "/".
1526</t>
1527<x:note>
1528  <t>
1529    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1530    meaning of the request when the origin server is improperly using
1531    a non-reserved URI character for a reserved purpose.  Implementors
1532    should be aware that some pre-HTTP/1.1 proxies have been known to
1533    rewrite the request-target.
1534  </t>
1535</x:note>
1536<t>
1537   HTTP does not place a pre-defined limit on the length of a request-target.
1538   A server &MUST; be prepared to receive URIs of unbounded length and
1539   respond with the 414 (URI Too Long) status if the received
1540   request-target would be longer than the server wishes to handle
1541   (see &status-414;).
1542</t>
1543<t>
1544   Various ad-hoc limitations on request-target length are found in practice.
1545   It is &RECOMMENDED; that all HTTP senders and recipients support
1546   request-target lengths of 8000 or more OCTETs.
1547</t>
1548</section>
1549</section>
1550
1551<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1552<t>
1553   The exact resource identified by an Internet request is determined by
1554   examining both the request-target and the Host header field.
1555</t>
1556<t>
1557   An origin server that does not allow resources to differ by the
1558   requested host &MAY; ignore the Host header field value when
1559   determining the resource identified by an HTTP/1.1 request. (But see
1560   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1561   for other requirements on Host support in HTTP/1.1.)
1562</t>
1563<t>
1564   An origin server that does differentiate resources based on the host
1565   requested (sometimes referred to as virtual hosts or vanity host
1566   names) &MUST; use the following rules for determining the requested
1567   resource on an HTTP/1.1 request:
1568  <list style="numbers">
1569    <t>If request-target is an absolute-URI, the host is part of the
1570     request-target. Any Host header field value in the request &MUST; be
1571     ignored.</t>
1572    <t>If the request-target is not an absolute-URI, and the request includes
1573     a Host header field, the host is determined by the Host header
1574     field value.</t>
1575    <t>If the host as determined by rule 1 or 2 is not a valid host on
1576     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1577  </list>
1578</t>
1579<t>
1580   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1581   attempt to use heuristics (e.g., examination of the URI path for
1582   something unique to a particular host) in order to determine what
1583   exact resource is being requested.
1584</t>
1585</section>
1586
1587</section>
1588
1589
1590<section title="Response" anchor="response">
1591  <x:anchor-alias value="Response"/>
1592<t>
1593   After receiving and interpreting a request message, a server responds
1594   with an HTTP response message.
1595</t>
1596<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1597  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1598                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1599                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1600                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> ) ; &entity-header-fields;
1601                  <x:ref>CRLF</x:ref>
1602                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1603</artwork></figure>
1604
1605<section title="Status-Line" anchor="status-line">
1606  <x:anchor-alias value="Status-Line"/>
1607<t>
1608   The first line of a Response message is the Status-Line, consisting
1609   of the protocol version followed by a numeric status code and its
1610   associated textual phrase, with each element separated by SP
1611   characters. No CR or LF is allowed except in the final CRLF sequence.
1612</t>
1613<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1614  <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>
1615</artwork></figure>
1616
1617<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1618  <x:anchor-alias value="Reason-Phrase"/>
1619  <x:anchor-alias value="Status-Code"/>
1620<t>
1621   The Status-Code element is a 3-digit integer result code of the
1622   attempt to understand and satisfy the request. These codes are fully
1623   defined in &status-codes;.  The Reason Phrase exists for the sole
1624   purpose of providing a textual description associated with the numeric
1625   status code, out of deference to earlier Internet application protocols
1626   that were more frequently used with interactive text clients.
1627   A client &SHOULD; ignore the content of the Reason Phrase.
1628</t>
1629<t>
1630   The first digit of the Status-Code defines the class of response. The
1631   last two digits do not have any categorization role. There are 5
1632   values for the first digit:
1633  <list style="symbols">
1634    <t>
1635      1xx: Informational - Request received, continuing process
1636    </t>
1637    <t>
1638      2xx: Success - The action was successfully received,
1639        understood, and accepted
1640    </t>
1641    <t>
1642      3xx: Redirection - Further action must be taken in order to
1643        complete the request
1644    </t>
1645    <t>
1646      4xx: Client Error - The request contains bad syntax or cannot
1647        be fulfilled
1648    </t>
1649    <t>
1650      5xx: Server Error - The server failed to fulfill an apparently
1651        valid request
1652    </t>
1653  </list>
1654</t>
1655<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"/>
1656  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1657  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1658</artwork></figure>
1659</section>
1660</section>
1661
1662</section>
1663
1664
1665<section title="Protocol Parameters" anchor="protocol.parameters">
1666
1667<section title="Date/Time Formats: Full Date" anchor="date.time.formats.full.date">
1668  <x:anchor-alias value="HTTP-date"/>
1669<t>
1670   HTTP applications have historically allowed three different formats
1671   for the representation of date/time stamps:
1672</t>
1673<figure><artwork type="example">
1674  Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1675  Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1676  Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1677</artwork></figure>
1678<t>
1679   The first format is preferred as an Internet standard and represents
1680   a fixed-length subset of that defined by <xref target="RFC1123"/>. The
1681   other formats are described here only for
1682   compatibility with obsolete implementations.
1683   HTTP/1.1 clients and servers that parse the date value &MUST; accept
1684   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1685   only generate the RFC 1123 format for representing HTTP-date values
1686   in header fields. See <xref target="tolerant.applications"/> for further information.
1687</t>
1688<t>
1689   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1690   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1691   equal to UTC (Coordinated Universal Time). This is indicated in the
1692   first two formats by the inclusion of "GMT" as the three-letter
1693   abbreviation for time zone, and &MUST; be assumed when reading the
1694   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1695   additional whitespace beyond that specifically included as SP in the
1696   grammar.
1697</t>
1698<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1699  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1700</artwork></figure>
1701<t anchor="preferred.date.format">
1702  <x:anchor-alias value="rfc1123-date"/>
1703  <x:anchor-alias value="time-of-day"/>
1704  <x:anchor-alias value="hour"/>
1705  <x:anchor-alias value="minute"/>
1706  <x:anchor-alias value="second"/>
1707  <x:anchor-alias value="day-name"/>
1708  <x:anchor-alias value="day"/>
1709  <x:anchor-alias value="month"/>
1710  <x:anchor-alias value="year"/>
1711  <x:anchor-alias value="GMT"/>
1712  Preferred format:
1713</t>
1714<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"/>
1715  <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>
1716
1717  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1718               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1719               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1720               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
1721               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
1722               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
1723               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
1724               
1725  <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>
1726               ; e.g., 02 Jun 1982
1727
1728  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
1729  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
1730               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
1731               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
1732               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
1733               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
1734               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
1735               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
1736               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
1737               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
1738               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
1739               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
1740               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
1741  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
1742
1743  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
1744
1745  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
1746                 ; 00:00:00 - 23:59:59
1747                 
1748  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
1749  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1750  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1751</artwork></figure>
1752<t>
1753  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
1754  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
1755  same as those defined for the RFC 5322 constructs
1756  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
1757</t>
1758<t anchor="obsolete.date.formats">
1759  <x:anchor-alias value="obs-date"/>
1760  <x:anchor-alias value="rfc850-date"/>
1761  <x:anchor-alias value="asctime-date"/>
1762  <x:anchor-alias value="date1"/>
1763  <x:anchor-alias value="date2"/>
1764  <x:anchor-alias value="date3"/>
1765  <x:anchor-alias value="rfc1123-date"/>
1766  <x:anchor-alias value="day-name-l"/>
1767  Obsolete formats:
1768</t>
1769<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
1770  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
1771</artwork></figure>
1772<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
1773  <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>
1774  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
1775                 ; day-month-year (e.g., 02-Jun-82)
1776
1777  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
1778         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
1779         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
1780         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
1781         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
1782         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
1783         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
1784</artwork></figure>
1785<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
1786  <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>
1787  <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> ))
1788                 ; month day (e.g., Jun  2)
1789</artwork></figure>
1790<x:note>
1791  <t>
1792    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
1793    accepting date values that may have been sent by non-HTTP
1794    applications, as is sometimes the case when retrieving or posting
1795    messages via proxies/gateways to SMTP or NNTP.
1796  </t>
1797</x:note>
1798<x:note>
1799  <t>
1800    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
1801    to their usage within the protocol stream. Clients and servers are
1802    not required to use these formats for user presentation, request
1803    logging, etc.
1804  </t>
1805</x:note>
1806</section>
1807
1808<section title="Transfer Codings" anchor="transfer.codings">
1809  <x:anchor-alias value="transfer-coding"/>
1810  <x:anchor-alias value="transfer-extension"/>
1811<t>
1812   Transfer-coding values are used to indicate an encoding
1813   transformation that has been, can be, or may need to be applied to an
1814   entity-body in order to ensure "safe transport" through the network.
1815   This differs from a content coding in that the transfer-coding is a
1816   property of the message, not of the original entity.
1817</t>
1818<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1819  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
1820                          / "compress" ; <xref target="compress.coding"/>
1821                          / "deflate" ; <xref target="deflate.coding"/>
1822                          / "gzip" ; <xref target="gzip.coding"/>
1823                          / <x:ref>transfer-extension</x:ref>
1824  <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> )
1825</artwork></figure>
1826<t anchor="rule.parameter">
1827  <x:anchor-alias value="attribute"/>
1828  <x:anchor-alias value="transfer-parameter"/>
1829  <x:anchor-alias value="value"/>
1830   Parameters are in  the form of attribute/value pairs.
1831</t>
1832<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"/>
1833  <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>
1834  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
1835  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1836</artwork></figure>
1837<t>
1838   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1839   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1840   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1841</t>
1842<t>
1843   Whenever a transfer-coding is applied to a message-body, the set of
1844   transfer-codings &MUST; include "chunked", unless the message indicates it
1845   is terminated by closing the connection. When the "chunked" transfer-coding
1846   is used, it &MUST; be the last transfer-coding applied to the
1847   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
1848   than once to a message-body. These rules allow the recipient to
1849   determine the transfer-length of the message (<xref target="message.length"/>).
1850</t>
1851<t>
1852   Transfer-codings are analogous to the Content-Transfer-Encoding values of
1853   MIME, which were designed to enable safe transport of binary data over a
1854   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1855   However, safe transport
1856   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1857   the only unsafe characteristic of message-bodies is the difficulty in
1858   determining the exact body length (<xref target="message.length"/>), or the desire to
1859   encrypt data over a shared transport.
1860</t>
1861<t>
1862   A server which receives an entity-body with a transfer-coding it does
1863   not understand &SHOULD; return 501 (Not Implemented), and close the
1864   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1865   client.
1866</t>
1867
1868<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1869  <iref item="chunked (Coding Format)"/>
1870  <iref item="Coding Format" subitem="chunked"/>
1871  <x:anchor-alias value="chunk"/>
1872  <x:anchor-alias value="Chunked-Body"/>
1873  <x:anchor-alias value="chunk-data"/>
1874  <x:anchor-alias value="chunk-ext"/>
1875  <x:anchor-alias value="chunk-ext-name"/>
1876  <x:anchor-alias value="chunk-ext-val"/>
1877  <x:anchor-alias value="chunk-size"/>
1878  <x:anchor-alias value="last-chunk"/>
1879  <x:anchor-alias value="trailer-part"/>
1880  <x:anchor-alias value="quoted-str-nf"/>
1881  <x:anchor-alias value="qdtext-nf"/>
1882<t>
1883   The chunked encoding modifies the body of a message in order to
1884   transfer it as a series of chunks, each with its own size indicator,
1885   followed by an &OPTIONAL; trailer containing entity-header fields. This
1886   allows dynamically produced content to be transferred along with the
1887   information necessary for the recipient to verify that it has
1888   received the full message.
1889</t>
1890<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"/>
1891  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1892                   <x:ref>last-chunk</x:ref>
1893                   <x:ref>trailer-part</x:ref>
1894                   <x:ref>CRLF</x:ref>
1895 
1896  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1897                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1898  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1899  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1900 
1901  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
1902                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
1903  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1904  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
1905  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1906  <x:ref>trailer-part</x:ref>   = *( <x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref> )
1907 
1908  <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>
1909                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
1910  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1911                 ; <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> 
1912</artwork></figure>
1913<t>
1914   The chunk-size field is a string of hex digits indicating the size of
1915   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1916   zero, followed by the trailer, which is terminated by an empty line.
1917</t>
1918<t>
1919   The trailer allows the sender to include additional HTTP header
1920   fields at the end of the message. The Trailer header field can be
1921   used to indicate which header fields are included in a trailer (see
1922   <xref target="header.trailer"/>).
1923</t>
1924<t>
1925   A server using chunked transfer-coding in a response &MUST-NOT; use the
1926   trailer for any header fields unless at least one of the following is
1927   true:
1928  <list style="numbers">
1929    <t>the request included a TE header field that indicates "trailers" is
1930     acceptable in the transfer-coding of the  response, as described in
1931     <xref target="header.te"/>; or,</t>
1932
1933    <t>the server is the origin server for the response, the trailer
1934     fields consist entirely of optional metadata, and the recipient
1935     could use the message (in a manner acceptable to the origin server)
1936     without receiving this metadata.  In other words, the origin server
1937     is willing to accept the possibility that the trailer fields might
1938     be silently discarded along the path to the client.</t>
1939  </list>
1940</t>
1941<t>
1942   This requirement prevents an interoperability failure when the
1943   message is being received by an HTTP/1.1 (or later) proxy and
1944   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1945   compliance with the protocol would have necessitated a possibly
1946   infinite buffer on the proxy.
1947</t>
1948<t>
1949   A process for decoding the "chunked" transfer-coding
1950   can be represented in pseudo-code as:
1951</t>
1952<figure><artwork type="code">
1953  length := 0
1954  read chunk-size, chunk-ext (if any) and CRLF
1955  while (chunk-size &gt; 0) {
1956     read chunk-data and CRLF
1957     append chunk-data to entity-body
1958     length := length + chunk-size
1959     read chunk-size and CRLF
1960  }
1961  read entity-header
1962  while (entity-header not empty) {
1963     append entity-header to existing header fields
1964     read entity-header
1965  }
1966  Content-Length := length
1967  Remove "chunked" from Transfer-Encoding
1968</artwork></figure>
1969<t>
1970   All HTTP/1.1 applications &MUST; be able to receive and decode the
1971   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1972   they do not understand.
1973</t>
1974</section>
1975
1976<section title="Compression Codings" anchor="compression.codings">
1977<t>
1978   The codings defined below can be used to compress the payload of a
1979   message.
1980</t>
1981<x:note><t>
1982   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
1983   is not desirable and is discouraged for future encodings. Their
1984   use here is representative of historical practice, not good
1985   design.
1986</t></x:note>
1987<x:note><t>
1988   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
1989   applications &SHOULD; consider "x-gzip" and "x-compress" to be
1990   equivalent to "gzip" and "compress" respectively.
1991</t></x:note>
1992
1993<section title="Compress Coding" anchor="compress.coding">
1994<iref item="compress (Coding Format)"/>
1995<iref item="Coding Format" subitem="compress"/>
1996<t>
1997   The "compress" format is produced by the common UNIX file compression
1998   program "compress". This format is an adaptive Lempel-Ziv-Welch
1999   coding (LZW).
2000</t>
2001</section>
2002
2003<section title="Deflate Coding" anchor="deflate.coding">
2004<iref item="deflate (Coding Format)"/>
2005<iref item="Coding Format" subitem="deflate"/>
2006<t>
2007   The "zlib" format is defined in <xref target="RFC1950"/> in combination with
2008   the "deflate" compression mechanism described in <xref target="RFC1951"/>.
2009</t>
2010</section>
2011
2012<section title="Gzip Coding" anchor="gzip.coding">
2013<iref item="gzip (Coding Format)"/>
2014<iref item="Coding Format" subitem="gzip"/>
2015<t>
2016   The "gzip" format is produced by the file compression program
2017   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2018   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2019</t>
2020</section>
2021
2022</section>
2023
2024<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2025<t>
2026   The HTTP Transfer Coding Registry defines the name space for the transfer
2027   coding names.
2028</t>
2029<t>
2030   Registrations &MUST; include the following fields:
2031   <list style="symbols">
2032     <t>Name</t>
2033     <t>Description</t>
2034     <t>Pointer to specification text</t>
2035   </list>
2036</t>
2037<t>
2038   Values to be added to this name space require expert review and a specification
2039   (see "Expert Review" and "Specification Required" in
2040   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2041   conform to the purpose of transfer coding defined in this section.
2042</t>
2043<t>
2044   The registry itself is maintained at
2045   <eref target="http://www.iana.org/assignments/http-parameters"/>.
2046</t>
2047</section>
2048</section>
2049
2050<section title="Product Tokens" anchor="product.tokens">
2051  <x:anchor-alias value="product"/>
2052  <x:anchor-alias value="product-version"/>
2053<t>
2054   Product tokens are used to allow communicating applications to
2055   identify themselves by software name and version. Most fields using
2056   product tokens also allow sub-products which form a significant part
2057   of the application to be listed, separated by whitespace. By
2058   convention, the products are listed in order of their significance
2059   for identifying the application.
2060</t>
2061<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2062  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2063  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2064</artwork></figure>
2065<t>
2066   Examples:
2067</t>
2068<figure><artwork type="example">
2069  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2070  Server: Apache/0.8.4
2071</artwork></figure>
2072<t>
2073   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2074   used for advertising or other non-essential information. Although any
2075   token character &MAY; appear in a product-version, this token &SHOULD;
2076   only be used for a version identifier (i.e., successive versions of
2077   the same product &SHOULD; only differ in the product-version portion of
2078   the product value).
2079</t>
2080</section>
2081
2082<section title="Quality Values" anchor="quality.values">
2083  <x:anchor-alias value="qvalue"/>
2084<t>
2085   Both transfer codings (TE request header, <xref target="header.te"/>)
2086   and content negotiation (&content.negotiation;) use short "floating point"
2087   numbers to indicate the relative importance ("weight") of various
2088   negotiable parameters.  A weight is normalized to a real number in
2089   the range 0 through 1, where 0 is the minimum and 1 the maximum
2090   value. If a parameter has a quality value of 0, then content with
2091   this parameter is "not acceptable" for the client. HTTP/1.1
2092   applications &MUST-NOT; generate more than three digits after the
2093   decimal point. User configuration of these values &SHOULD; also be
2094   limited in this fashion.
2095</t>
2096<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2097  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2098                 / ( "1" [ "." 0*3("0") ] )
2099</artwork></figure>
2100<x:note>
2101  <t>
2102     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2103     relative degradation in desired quality.
2104  </t>
2105</x:note>
2106</section>
2107
2108</section>
2109
2110<section title="Connections" anchor="connections">
2111
2112<section title="Persistent Connections" anchor="persistent.connections">
2113
2114<section title="Purpose" anchor="persistent.purpose">
2115<t>
2116   Prior to persistent connections, a separate TCP connection was
2117   established to fetch each URL, increasing the load on HTTP servers
2118   and causing congestion on the Internet. The use of inline images and
2119   other associated data often requires a client to make multiple
2120   requests of the same server in a short amount of time. Analysis of
2121   these performance problems and results from a prototype
2122   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2123   measurements of actual HTTP/1.1 implementations show good
2124   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2125   T/TCP <xref target="Tou1998"/>.
2126</t>
2127<t>
2128   Persistent HTTP connections have a number of advantages:
2129  <list style="symbols">
2130      <t>
2131        By opening and closing fewer TCP connections, CPU time is saved
2132        in routers and hosts (clients, servers, proxies, gateways,
2133        tunnels, or caches), and memory used for TCP protocol control
2134        blocks can be saved in hosts.
2135      </t>
2136      <t>
2137        HTTP requests and responses can be pipelined on a connection.
2138        Pipelining allows a client to make multiple requests without
2139        waiting for each response, allowing a single TCP connection to
2140        be used much more efficiently, with much lower elapsed time.
2141      </t>
2142      <t>
2143        Network congestion is reduced by reducing the number of packets
2144        caused by TCP opens, and by allowing TCP sufficient time to
2145        determine the congestion state of the network.
2146      </t>
2147      <t>
2148        Latency on subsequent requests is reduced since there is no time
2149        spent in TCP's connection opening handshake.
2150      </t>
2151      <t>
2152        HTTP can evolve more gracefully, since errors can be reported
2153        without the penalty of closing the TCP connection. Clients using
2154        future versions of HTTP might optimistically try a new feature,
2155        but if communicating with an older server, retry with old
2156        semantics after an error is reported.
2157      </t>
2158    </list>
2159</t>
2160<t>
2161   HTTP implementations &SHOULD; implement persistent connections.
2162</t>
2163</section>
2164
2165<section title="Overall Operation" anchor="persistent.overall">
2166<t>
2167   A significant difference between HTTP/1.1 and earlier versions of
2168   HTTP is that persistent connections are the default behavior of any
2169   HTTP connection. That is, unless otherwise indicated, the client
2170   &SHOULD; assume that the server will maintain a persistent connection,
2171   even after error responses from the server.
2172</t>
2173<t>
2174   Persistent connections provide a mechanism by which a client and a
2175   server can signal the close of a TCP connection. This signaling takes
2176   place using the Connection header field (<xref target="header.connection"/>). Once a close
2177   has been signaled, the client &MUST-NOT; send any more requests on that
2178   connection.
2179</t>
2180
2181<section title="Negotiation" anchor="persistent.negotiation">
2182<t>
2183   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2184   maintain a persistent connection unless a Connection header including
2185   the connection-token "close" was sent in the request. If the server
2186   chooses to close the connection immediately after sending the
2187   response, it &SHOULD; send a Connection header including the
2188   connection-token "close".
2189</t>
2190<t>
2191   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2192   decide to keep it open based on whether the response from a server
2193   contains a Connection header with the connection-token close. In case
2194   the client does not want to maintain a connection for more than that
2195   request, it &SHOULD; send a Connection header including the
2196   connection-token close.
2197</t>
2198<t>
2199   If either the client or the server sends the close token in the
2200   Connection header, that request becomes the last one for the
2201   connection.
2202</t>
2203<t>
2204   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2205   maintained for HTTP versions less than 1.1 unless it is explicitly
2206   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2207   compatibility with HTTP/1.0 clients.
2208</t>
2209<t>
2210   In order to remain persistent, all messages on the connection &MUST;
2211   have a self-defined message length (i.e., one not defined by closure
2212   of the connection), as described in <xref target="message.length"/>.
2213</t>
2214</section>
2215
2216<section title="Pipelining" anchor="pipelining">
2217<t>
2218   A client that supports persistent connections &MAY; "pipeline" its
2219   requests (i.e., send multiple requests without waiting for each
2220   response). A server &MUST; send its responses to those requests in the
2221   same order that the requests were received.
2222</t>
2223<t>
2224   Clients which assume persistent connections and pipeline immediately
2225   after connection establishment &SHOULD; be prepared to retry their
2226   connection if the first pipelined attempt fails. If a client does
2227   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2228   persistent. Clients &MUST; also be prepared to resend their requests if
2229   the server closes the connection before sending all of the
2230   corresponding responses.
2231</t>
2232<t>
2233   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
2234   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
2235   premature termination of the transport connection could lead to
2236   indeterminate results. A client wishing to send a non-idempotent
2237   request &SHOULD; wait to send that request until it has received the
2238   response status for the previous request.
2239</t>
2240</section>
2241</section>
2242
2243<section title="Proxy Servers" anchor="persistent.proxy">
2244<t>
2245   It is especially important that proxies correctly implement the
2246   properties of the Connection header field as specified in <xref target="header.connection"/>.
2247</t>
2248<t>
2249   The proxy server &MUST; signal persistent connections separately with
2250   its clients and the origin servers (or other proxy servers) that it
2251   connects to. Each persistent connection applies to only one transport
2252   link.
2253</t>
2254<t>
2255   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2256   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2257   for information and discussion of the problems with the Keep-Alive header
2258   implemented by many HTTP/1.0 clients).
2259</t>
2260
2261<section title="End-to-end and Hop-by-hop Headers" anchor="end-to-end.and.hop-by-hop.headers">
2262<t>
2263  <cref anchor="TODO-end-to-end" source="jre">
2264    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1"/>.
2265    See also <eref target="http://trac.tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2266  </cref>
2267</t>
2268<t>
2269   For the purpose of defining the behavior of caches and non-caching
2270   proxies, we divide HTTP headers into two categories:
2271  <list style="symbols">
2272      <t>End-to-end headers, which are  transmitted to the ultimate
2273        recipient of a request or response. End-to-end headers in
2274        responses MUST be stored as part of a cache entry and &MUST; be
2275        transmitted in any response formed from a cache entry.</t>
2276
2277      <t>Hop-by-hop headers, which are meaningful only for a single
2278        transport-level connection, and are not stored by caches or
2279        forwarded by proxies.</t>
2280  </list>
2281</t>
2282<t>
2283   The following HTTP/1.1 headers are hop-by-hop headers:
2284  <list style="symbols">
2285      <t>Connection</t>
2286      <t>Keep-Alive</t>
2287      <t>Proxy-Authenticate</t>
2288      <t>Proxy-Authorization</t>
2289      <t>TE</t>
2290      <t>Trailer</t>
2291      <t>Transfer-Encoding</t>
2292      <t>Upgrade</t>
2293  </list>
2294</t>
2295<t>
2296   All other headers defined by HTTP/1.1 are end-to-end headers.
2297</t>
2298<t>
2299   Other hop-by-hop headers &MUST; be listed in a Connection header
2300   (<xref target="header.connection"/>).
2301</t>
2302</section>
2303
2304<section title="Non-modifiable Headers" anchor="non-modifiable.headers">
2305<t>
2306  <cref anchor="TODO-non-mod-headers" source="jre">
2307    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2"/>.
2308    See also <eref target="http://trac.tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2309  </cref>
2310</t>
2311<t>
2312   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2313   value of certain end-to-end headers. A transparent proxy &SHOULD-NOT;
2314   modify an end-to-end header unless the definition of that header requires
2315   or specifically allows that.
2316</t>
2317<t>
2318   A transparent proxy &MUST-NOT; modify any of the following fields in a
2319   request or response, and it &MUST-NOT; add any of these fields if not
2320   already present:
2321  <list style="symbols">
2322      <t>Content-Location</t>
2323      <t>Content-MD5</t>
2324      <t>ETag</t>
2325      <t>Last-Modified</t>
2326  </list>
2327</t>
2328<t>
2329   A transparent proxy &MUST-NOT; modify any of the following fields in a
2330   response:
2331  <list style="symbols">
2332    <t>Expires</t>
2333  </list>
2334</t>
2335<t>
2336   but it &MAY; add any of these fields if not already present. If an
2337   Expires header is added, it &MUST; be given a field-value identical to
2338   that of the Date header in that response.
2339</t>
2340<t>
2341   A proxy &MUST-NOT; modify or add any of the following fields in a
2342   message that contains the no-transform cache-control directive, or in
2343   any request:
2344  <list style="symbols">
2345    <t>Content-Encoding</t>
2346    <t>Content-Range</t>
2347    <t>Content-Type</t>
2348  </list>
2349</t>
2350<t>
2351   A non-transparent proxy &MAY; modify or add these fields to a message
2352   that does not include no-transform, but if it does so, it &MUST; add a
2353   Warning 214 (Transformation applied) if one does not already appear
2354   in the message (see &header-warning;).
2355</t>
2356<x:note>
2357  <t>
2358    <x:h>Warning:</x:h> Unnecessary modification of end-to-end headers might
2359    cause authentication failures if stronger authentication
2360    mechanisms are introduced in later versions of HTTP. Such
2361    authentication mechanisms &MAY; rely on the values of header fields
2362    not listed here.
2363  </t>
2364</x:note>
2365<t>
2366   The Content-Length field of a request or response is added or deleted
2367   according to the rules in <xref target="message.length"/>. A transparent proxy &MUST;
2368   preserve the entity-length (&entity-length;) of the entity-body,
2369   although it &MAY; change the transfer-length (<xref target="message.length"/>).
2370</t>
2371</section>
2372
2373</section>
2374
2375<section title="Practical Considerations" anchor="persistent.practical">
2376<t>
2377   Servers will usually have some time-out value beyond which they will
2378   no longer maintain an inactive connection. Proxy servers might make
2379   this a higher value since it is likely that the client will be making
2380   more connections through the same server. The use of persistent
2381   connections places no requirements on the length (or existence) of
2382   this time-out for either the client or the server.
2383</t>
2384<t>
2385   When a client or server wishes to time-out it &SHOULD; issue a graceful
2386   close on the transport connection. Clients and servers &SHOULD; both
2387   constantly watch for the other side of the transport close, and
2388   respond to it as appropriate. If a client or server does not detect
2389   the other side's close promptly it could cause unnecessary resource
2390   drain on the network.
2391</t>
2392<t>
2393   A client, server, or proxy &MAY; close the transport connection at any
2394   time. For example, a client might have started to send a new request
2395   at the same time that the server has decided to close the "idle"
2396   connection. From the server's point of view, the connection is being
2397   closed while it was idle, but from the client's point of view, a
2398   request is in progress.
2399</t>
2400<t>
2401   This means that clients, servers, and proxies &MUST; be able to recover
2402   from asynchronous close events. Client software &SHOULD; reopen the
2403   transport connection and retransmit the aborted sequence of requests
2404   without user interaction so long as the request sequence is
2405   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
2406   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2407   human operator the choice of retrying the request(s). Confirmation by
2408   user-agent software with semantic understanding of the application
2409   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2410   be repeated if the second sequence of requests fails.
2411</t>
2412<t>
2413   Servers &SHOULD; always respond to at least one request per connection,
2414   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2415   middle of transmitting a response, unless a network or client failure
2416   is suspected.
2417</t>
2418<t>
2419   Clients (including proxies) &SHOULD; limit the number of simultaneous
2420   connections that they maintain to a given server (including proxies).
2421</t>
2422<t>
2423   Previous revisions of HTTP gave a specific number of connections as a
2424   ceiling, but this was found to be impractical for many applications. As a
2425   result, this specification does not mandate a particular maximum number of
2426   connections, but instead encourages clients to be conservative when opening
2427   multiple connections.
2428</t>
2429<t>
2430   In particular, while using multiple connections avoids the "head-of-line
2431   blocking" problem (whereby a request that takes significant server-side
2432   processing and/or has a large payload can block subsequent requests on the
2433   same connection), each connection used consumes server resources (sometimes
2434   significantly), and furthermore using multiple connections can cause
2435   undesirable side effects in congested networks.
2436</t>
2437<t>
2438   Note that servers might reject traffic that they deem abusive, including an
2439   excessive number of connections from a client.
2440</t>
2441</section>
2442</section>
2443
2444<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2445
2446<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2447<t>
2448   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2449   flow control mechanisms to resolve temporary overloads, rather than
2450   terminating connections with the expectation that clients will retry.
2451   The latter technique can exacerbate network congestion.
2452</t>
2453</section>
2454
2455<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2456<t>
2457   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2458   the network connection for an error status while it is transmitting
2459   the request. If the client sees an error status, it &SHOULD;
2460   immediately cease transmitting the body. If the body is being sent
2461   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2462   empty trailer &MAY; be used to prematurely mark the end of the message.
2463   If the body was preceded by a Content-Length header, the client &MUST;
2464   close the connection.
2465</t>
2466</section>
2467
2468<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2469<t>
2470   The purpose of the 100 (Continue) status (see &status-100;) is to
2471   allow a client that is sending a request message with a request body
2472   to determine if the origin server is willing to accept the request
2473   (based on the request headers) before the client sends the request
2474   body. In some cases, it might either be inappropriate or highly
2475   inefficient for the client to send the body if the server will reject
2476   the message without looking at the body.
2477</t>
2478<t>
2479   Requirements for HTTP/1.1 clients:
2480  <list style="symbols">
2481    <t>
2482        If a client will wait for a 100 (Continue) response before
2483        sending the request body, it &MUST; send an Expect request-header
2484        field (&header-expect;) with the "100-continue" expectation.
2485    </t>
2486    <t>
2487        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2488        with the "100-continue" expectation if it does not intend
2489        to send a request body.
2490    </t>
2491  </list>
2492</t>
2493<t>
2494   Because of the presence of older implementations, the protocol allows
2495   ambiguous situations in which a client may send "Expect: 100-continue"
2496   without receiving either a 417 (Expectation Failed) status
2497   or a 100 (Continue) status. Therefore, when a client sends this
2498   header field to an origin server (possibly via a proxy) from which it
2499   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
2500   for an indefinite period before sending the request body.
2501</t>
2502<t>
2503   Requirements for HTTP/1.1 origin servers:
2504  <list style="symbols">
2505    <t> Upon receiving a request which includes an Expect request-header
2506        field with the "100-continue" expectation, an origin server &MUST;
2507        either respond with 100 (Continue) status and continue to read
2508        from the input stream, or respond with a final status code. The
2509        origin server &MUST-NOT; wait for the request body before sending
2510        the 100 (Continue) response. If it responds with a final status
2511        code, it &MAY; close the transport connection or it &MAY; continue
2512        to read and discard the rest of the request.  It &MUST-NOT;
2513        perform the requested method if it returns a final status code.
2514    </t>
2515    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2516        the request message does not include an Expect request-header
2517        field with the "100-continue" expectation, and &MUST-NOT; send a
2518        100 (Continue) response if such a request comes from an HTTP/1.0
2519        (or earlier) client. There is an exception to this rule: for
2520        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2521        status in response to an HTTP/1.1 PUT or POST request that does
2522        not include an Expect request-header field with the "100-continue"
2523        expectation. This exception, the purpose of which is
2524        to minimize any client processing delays associated with an
2525        undeclared wait for 100 (Continue) status, applies only to
2526        HTTP/1.1 requests, and not to requests with any other HTTP-version
2527        value.
2528    </t>
2529    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2530        already received some or all of the request body for the
2531        corresponding request.
2532    </t>
2533    <t> An origin server that sends a 100 (Continue) response &MUST;
2534    ultimately send a final status code, once the request body is
2535        received and processed, unless it terminates the transport
2536        connection prematurely.
2537    </t>
2538    <t> If an origin server receives a request that does not include an
2539        Expect request-header field with the "100-continue" expectation,
2540        the request includes a request body, and the server responds
2541        with a final status code before reading the entire request body
2542        from the transport connection, then the server &SHOULD-NOT;  close
2543        the transport connection until it has read the entire request,
2544        or until the client closes the connection. Otherwise, the client
2545        might not reliably receive the response message. However, this
2546        requirement is not be construed as preventing a server from
2547        defending itself against denial-of-service attacks, or from
2548        badly broken client implementations.
2549      </t>
2550    </list>
2551</t>
2552<t>
2553   Requirements for HTTP/1.1 proxies:
2554  <list style="symbols">
2555    <t> If a proxy receives a request that includes an Expect request-header
2556        field with the "100-continue" expectation, and the proxy
2557        either knows that the next-hop server complies with HTTP/1.1 or
2558        higher, or does not know the HTTP version of the next-hop
2559        server, it &MUST; forward the request, including the Expect header
2560        field.
2561    </t>
2562    <t> If the proxy knows that the version of the next-hop server is
2563        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2564        respond with a 417 (Expectation Failed) status.
2565    </t>
2566    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2567        numbers received from recently-referenced next-hop servers.
2568    </t>
2569    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2570        request message was received from an HTTP/1.0 (or earlier)
2571        client and did not include an Expect request-header field with
2572        the "100-continue" expectation. This requirement overrides the
2573        general rule for forwarding of 1xx responses (see &status-1xx;).
2574    </t>
2575  </list>
2576</t>
2577</section>
2578
2579<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2580<t>
2581   If an HTTP/1.1 client sends a request which includes a request body,
2582   but which does not include an Expect request-header field with the
2583   "100-continue" expectation, and if the client is not directly
2584   connected to an HTTP/1.1 origin server, and if the client sees the
2585   connection close before receiving any status from the server, the
2586   client &SHOULD; retry the request.  If the client does retry this
2587   request, it &MAY; use the following "binary exponential backoff"
2588   algorithm to be assured of obtaining a reliable response:
2589  <list style="numbers">
2590    <t>
2591      Initiate a new connection to the server
2592    </t>
2593    <t>
2594      Transmit the request-headers
2595    </t>
2596    <t>
2597      Initialize a variable R to the estimated round-trip time to the
2598         server (e.g., based on the time it took to establish the
2599         connection), or to a constant value of 5 seconds if the round-trip
2600         time is not available.
2601    </t>
2602    <t>
2603       Compute T = R * (2**N), where N is the number of previous
2604         retries of this request.
2605    </t>
2606    <t>
2607       Wait either for an error response from the server, or for T
2608         seconds (whichever comes first)
2609    </t>
2610    <t>
2611       If no error response is received, after T seconds transmit the
2612         body of the request.
2613    </t>
2614    <t>
2615       If client sees that the connection is closed prematurely,
2616         repeat from step 1 until the request is accepted, an error
2617         response is received, or the user becomes impatient and
2618         terminates the retry process.
2619    </t>
2620  </list>
2621</t>
2622<t>
2623   If at any point an error status is received, the client
2624  <list style="symbols">
2625      <t>&SHOULD-NOT;  continue and</t>
2626
2627      <t>&SHOULD; close the connection if it has not completed sending the
2628        request message.</t>
2629    </list>
2630</t>
2631</section>
2632</section>
2633</section>
2634
2635
2636<section title="Miscellaneous notes that may disappear" anchor="misc">
2637<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2638<t>
2639   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2640</t>
2641</section>
2642
2643<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2644<t>
2645   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2646</t>
2647</section>
2648
2649<section title="Interception of HTTP for access control" anchor="http.intercept">
2650<t>
2651   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2652</t>
2653</section>
2654
2655<section title="Use of HTTP by other protocols" anchor="http.others">
2656<t>
2657   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2658   Extensions of HTTP like WebDAV.</cref>
2659</t>
2660
2661</section>
2662<section title="Use of HTTP by media type specification" anchor="http.media">
2663<t>
2664   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2665</t>
2666</section>
2667</section>
2668
2669<section title="Header Field Definitions" anchor="header.field.definitions">
2670<t>
2671   This section defines the syntax and semantics of HTTP/1.1 header fields
2672   related to message framing and transport protocols.
2673</t>
2674<t>
2675   For entity-header fields, both sender and recipient refer to either the
2676   client or the server, depending on who sends and who receives the entity.
2677</t>
2678
2679<section title="Connection" anchor="header.connection">
2680  <iref primary="true" item="Connection header" x:for-anchor=""/>
2681  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2682  <x:anchor-alias value="Connection"/>
2683  <x:anchor-alias value="connection-token"/>
2684  <x:anchor-alias value="Connection-v"/>
2685<t>
2686   The "Connection" general-header field allows the sender to specify
2687   options that are desired for that particular connection and &MUST-NOT;
2688   be communicated by proxies over further connections.
2689</t>
2690<t>
2691   The Connection header's value has the following grammar:
2692</t>
2693<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"/>
2694  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2695  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2696  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2697</artwork></figure>
2698<t>
2699   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2700   message is forwarded and, for each connection-token in this field,
2701   remove any header field(s) from the message with the same name as the
2702   connection-token. Connection options are signaled by the presence of
2703   a connection-token in the Connection header field, not by any
2704   corresponding additional header field(s), since the additional header
2705   field may not be sent if there are no parameters associated with that
2706   connection option.
2707</t>
2708<t>
2709   Message headers listed in the Connection header &MUST-NOT; include
2710   end-to-end headers, such as Cache-Control.
2711</t>
2712<t>
2713   HTTP/1.1 defines the "close" connection option for the sender to
2714   signal that the connection will be closed after completion of the
2715   response. For example,
2716</t>
2717<figure><artwork type="example">
2718  Connection: close
2719</artwork></figure>
2720<t>
2721   in either the request or the response header fields indicates that
2722   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2723   after the current request/response is complete.
2724</t>
2725<t>
2726   An HTTP/1.1 client that does not support persistent connections &MUST;
2727   include the "close" connection option in every request message.
2728</t>
2729<t>
2730   An HTTP/1.1 server that does not support persistent connections &MUST;
2731   include the "close" connection option in every response message that
2732   does not have a 1xx (Informational) status code.
2733</t>
2734<t>
2735   A system receiving an HTTP/1.0 (or lower-version) message that
2736   includes a Connection header &MUST;, for each connection-token in this
2737   field, remove and ignore any header field(s) from the message with
2738   the same name as the connection-token. This protects against mistaken
2739   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2740</t>
2741</section>
2742
2743<section title="Content-Length" anchor="header.content-length">
2744  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2745  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2746  <x:anchor-alias value="Content-Length"/>
2747  <x:anchor-alias value="Content-Length-v"/>
2748<t>
2749   The "Content-Length" entity-header field indicates the size of the
2750   entity-body, in number of OCTETs. In the case of responses to the HEAD
2751   method, it indicates the size of the entity-body that would have been sent
2752   had the request been a GET.
2753</t>
2754<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2755  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2756  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2757</artwork></figure>
2758<t>
2759   An example is
2760</t>
2761<figure><artwork type="example">
2762  Content-Length: 3495
2763</artwork></figure>
2764<t>
2765   Applications &SHOULD; use this field to indicate the transfer-length of
2766   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2767</t>
2768<t>
2769   Any Content-Length greater than or equal to zero is a valid value.
2770   <xref target="message.length"/> describes how to determine the length of a message-body
2771   if a Content-Length is not given.
2772</t>
2773<t>
2774   Note that the meaning of this field is significantly different from
2775   the corresponding definition in MIME, where it is an optional field
2776   used within the "message/external-body" content-type. In HTTP, it
2777   &SHOULD; be sent whenever the message's length can be determined prior
2778   to being transferred, unless this is prohibited by the rules in
2779   <xref target="message.length"/>.
2780</t>
2781</section>
2782
2783<section title="Date" anchor="header.date">
2784  <iref primary="true" item="Date header" x:for-anchor=""/>
2785  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2786  <x:anchor-alias value="Date"/>
2787  <x:anchor-alias value="Date-v"/>
2788<t>
2789   The "Date" general-header field represents the date and time at which
2790   the message was originated, having the same semantics as the Origination
2791   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2792   The field value is an HTTP-date, as described in <xref target="date.time.formats.full.date"/>;
2793   it &MUST; be sent in rfc1123-date format.
2794</t>
2795<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2796  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2797  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2798</artwork></figure>
2799<t>
2800   An example is
2801</t>
2802<figure><artwork type="example">
2803  Date: Tue, 15 Nov 1994 08:12:31 GMT
2804</artwork></figure>
2805<t>
2806   Origin servers &MUST; include a Date header field in all responses,
2807   except in these cases:
2808  <list style="numbers">
2809      <t>If the response status code is 100 (Continue) or 101 (Switching
2810         Protocols), the response &MAY; include a Date header field, at
2811         the server's option.</t>
2812
2813      <t>If the response status code conveys a server error, e.g., 500
2814         (Internal Server Error) or 503 (Service Unavailable), and it is
2815         inconvenient or impossible to generate a valid Date.</t>
2816
2817      <t>If the server does not have a clock that can provide a
2818         reasonable approximation of the current time, its responses
2819         &MUST-NOT; include a Date header field. In this case, the rules
2820         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2821  </list>
2822</t>
2823<t>
2824   A received message that does not have a Date header field &MUST; be
2825   assigned one by the recipient if the message will be cached by that
2826   recipient or gatewayed via a protocol which requires a Date. An HTTP
2827   implementation without a clock &MUST-NOT; cache responses without
2828   revalidating them on every use. An HTTP cache, especially a shared
2829   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2830   clock with a reliable external standard.
2831</t>
2832<t>
2833   Clients &SHOULD; only send a Date header field in messages that include
2834   an entity-body, as in the case of the PUT and POST requests, and even
2835   then it is optional. A client without a clock &MUST-NOT; send a Date
2836   header field in a request.
2837</t>
2838<t>
2839   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2840   time subsequent to the generation of the message. It &SHOULD; represent
2841   the best available approximation of the date and time of message
2842   generation, unless the implementation has no means of generating a
2843   reasonably accurate date and time. In theory, the date ought to
2844   represent the moment just before the entity is generated. In
2845   practice, the date can be generated at any time during the message
2846   origination without affecting its semantic value.
2847</t>
2848
2849<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2850<t>
2851   Some origin server implementations might not have a clock available.
2852   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2853   values to a response, unless these values were associated
2854   with the resource by a system or user with a reliable clock. It &MAY;
2855   assign an Expires value that is known, at or before server
2856   configuration time, to be in the past (this allows "pre-expiration"
2857   of responses without storing separate Expires values for each
2858   resource).
2859</t>
2860</section>
2861</section>
2862
2863<section title="Host" anchor="header.host">
2864  <iref primary="true" item="Host header" x:for-anchor=""/>
2865  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2866  <x:anchor-alias value="Host"/>
2867  <x:anchor-alias value="Host-v"/>
2868<t>
2869   The "Host" request-header field specifies the Internet host and port
2870   number of the resource being requested, allowing the origin server or
2871   gateway to differentiate between internally-ambiguous URLs, such as the root
2872   "/" URL of a server for multiple host names on a single IP address.
2873</t>
2874<t>   
2875   The Host field value &MUST; represent the naming authority of the origin
2876   server or gateway given by the original URL obtained from the user or
2877   referring resource (generally an http URI, as described in
2878   <xref target="http.uri"/>).
2879</t>
2880<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2881  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2882  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2883</artwork></figure>
2884<t>
2885   A "host" without any trailing port information implies the default
2886   port for the service requested (e.g., "80" for an HTTP URL). For
2887   example, a request on the origin server for
2888   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2889</t>
2890<figure><artwork type="example">
2891  GET /pub/WWW/ HTTP/1.1
2892  Host: www.example.org
2893</artwork></figure>
2894<t>
2895   A client &MUST; include a Host header field in all HTTP/1.1 request
2896   messages. If the requested URI does not include an Internet host
2897   name for the service being requested, then the Host header field &MUST;
2898   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2899   request message it forwards does contain an appropriate Host header
2900   field that identifies the service being requested by the proxy. All
2901   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2902   status code to any HTTP/1.1 request message which lacks a Host header
2903   field.
2904</t>
2905<t>
2906   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2907   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2908   for other requirements relating to Host.
2909</t>
2910</section>
2911
2912<section title="TE" anchor="header.te">
2913  <iref primary="true" item="TE header" x:for-anchor=""/>
2914  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2915  <x:anchor-alias value="TE"/>
2916  <x:anchor-alias value="TE-v"/>
2917  <x:anchor-alias value="t-codings"/>
2918  <x:anchor-alias value="te-params"/>
2919  <x:anchor-alias value="te-ext"/>
2920<t>
2921   The "TE" request-header field indicates what extension transfer-codings
2922   it is willing to accept in the response, and whether or not it is
2923   willing to accept trailer fields in a chunked transfer-coding.
2924</t>
2925<t>
2926   Its value may consist of the keyword "trailers" and/or a comma-separated
2927   list of extension transfer-coding names with optional accept
2928   parameters (as described in <xref target="transfer.codings"/>).
2929</t>
2930<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"/>
2931  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2932  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2933  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
2934  <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> )
2935  <x:ref>te-ext</x:ref>    = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> ) ]
2936</artwork></figure>
2937<t>
2938   The presence of the keyword "trailers" indicates that the client is
2939   willing to accept trailer fields in a chunked transfer-coding, as
2940   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
2941   transfer-coding values even though it does not itself represent a
2942   transfer-coding.
2943</t>
2944<t>
2945   Examples of its use are:
2946</t>
2947<figure><artwork type="example">
2948  TE: deflate
2949  TE:
2950  TE: trailers, deflate;q=0.5
2951</artwork></figure>
2952<t>
2953   The TE header field only applies to the immediate connection.
2954   Therefore, the keyword &MUST; be supplied within a Connection header
2955   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2956</t>
2957<t>
2958   A server tests whether a transfer-coding is acceptable, according to
2959   a TE field, using these rules:
2960  <list style="numbers">
2961    <x:lt>
2962      <t>The "chunked" transfer-coding is always acceptable. If the
2963         keyword "trailers" is listed, the client indicates that it is
2964         willing to accept trailer fields in the chunked response on
2965         behalf of itself and any downstream clients. The implication is
2966         that, if given, the client is stating that either all
2967         downstream clients are willing to accept trailer fields in the
2968         forwarded response, or that it will attempt to buffer the
2969         response on behalf of downstream recipients.
2970      </t><t>
2971         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2972         chunked response such that a client can be assured of buffering
2973         the entire response.</t>
2974    </x:lt>
2975    <x:lt>
2976      <t>If the transfer-coding being tested is one of the transfer-codings
2977         listed in the TE field, then it is acceptable unless it
2978         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
2979         qvalue of 0 means "not acceptable.")</t>
2980    </x:lt>
2981    <x:lt>
2982      <t>If multiple transfer-codings are acceptable, then the
2983         acceptable transfer-coding with the highest non-zero qvalue is
2984         preferred.  The "chunked" transfer-coding always has a qvalue
2985         of 1.</t>
2986    </x:lt>
2987  </list>
2988</t>
2989<t>
2990   If the TE field-value is empty or if no TE field is present, the only
2991   transfer-coding is "chunked". A message with no transfer-coding is
2992   always acceptable.
2993</t>
2994</section>
2995
2996<section title="Trailer" anchor="header.trailer">
2997  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2998  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2999  <x:anchor-alias value="Trailer"/>
3000  <x:anchor-alias value="Trailer-v"/>
3001<t>
3002   The "Trailer" general-header field indicates that the given set of
3003   header fields is present in the trailer of a message encoded with
3004   chunked transfer-coding.
3005</t>
3006<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
3007  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
3008  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
3009</artwork></figure>
3010<t>
3011   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3012   message using chunked transfer-coding with a non-empty trailer. Doing
3013   so allows the recipient to know which header fields to expect in the
3014   trailer.
3015</t>
3016<t>
3017   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3018   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3019   trailer fields in a "chunked" transfer-coding.
3020</t>
3021<t>
3022   Message header fields listed in the Trailer header field &MUST-NOT;
3023   include the following header fields:
3024  <list style="symbols">
3025    <t>Transfer-Encoding</t>
3026    <t>Content-Length</t>
3027    <t>Trailer</t>
3028  </list>
3029</t>
3030</section>
3031
3032<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3033  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
3034  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
3035  <x:anchor-alias value="Transfer-Encoding"/>
3036  <x:anchor-alias value="Transfer-Encoding-v"/>
3037<t>
3038   The "Transfer-Encoding" general-header field indicates what transfer-codings
3039   (if any) have been applied to the message body. It differs from
3040   Content-Encoding (&content-codings;) in that transfer-codings are a property
3041   of the message (and therefore are removed by intermediaries), whereas
3042   content-codings are not.
3043</t>
3044<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
3045  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
3046                        <x:ref>Transfer-Encoding-v</x:ref>
3047  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3048</artwork></figure>
3049<t>
3050   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3051</t>
3052<figure><artwork type="example">
3053  Transfer-Encoding: chunked
3054</artwork></figure>
3055<t>
3056   If multiple encodings have been applied to an entity, the transfer-codings
3057   &MUST; be listed in the order in which they were applied.
3058   Additional information about the encoding parameters &MAY; be provided
3059   by other entity-header fields not defined by this specification.
3060</t>
3061<t>
3062   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3063   header.
3064</t>
3065</section>
3066
3067<section title="Upgrade" anchor="header.upgrade">
3068  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
3069  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
3070  <x:anchor-alias value="Upgrade"/>
3071  <x:anchor-alias value="Upgrade-v"/>
3072<t>
3073   The "Upgrade" general-header field allows the client to specify what
3074   additional communication protocols it would like to use, if the server
3075   chooses to switch protocols. Additionally, the server &MUST; use the Upgrade
3076   header field within a 101 (Switching Protocols) response to indicate which
3077   protocol(s) are being switched to.
3078</t>
3079<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
3080  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
3081  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
3082</artwork></figure>
3083<t>
3084   For example,
3085</t>
3086<figure><artwork type="example">
3087  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3088</artwork></figure>
3089<t>
3090   The Upgrade header field is intended to provide a simple mechanism
3091   for transition from HTTP/1.1 to some other, incompatible protocol. It
3092   does so by allowing the client to advertise its desire to use another
3093   protocol, such as a later version of HTTP with a higher major version
3094   number, even though the current request has been made using HTTP/1.1.
3095   This eases the difficult transition between incompatible protocols by
3096   allowing the client to initiate a request in the more commonly
3097   supported protocol while indicating to the server that it would like
3098   to use a "better" protocol if available (where "better" is determined
3099   by the server, possibly according to the nature of the method and/or
3100   resource being requested).
3101</t>
3102<t>
3103   The Upgrade header field only applies to switching application-layer
3104   protocols upon the existing transport-layer connection. Upgrade
3105   cannot be used to insist on a protocol change; its acceptance and use
3106   by the server is optional. The capabilities and nature of the
3107   application-layer communication after the protocol change is entirely
3108   dependent upon the new protocol chosen, although the first action
3109   after changing the protocol &MUST; be a response to the initial HTTP
3110   request containing the Upgrade header field.
3111</t>
3112<t>
3113   The Upgrade header field only applies to the immediate connection.
3114   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3115   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3116   HTTP/1.1 message.
3117</t>
3118<t>
3119   The Upgrade header field cannot be used to indicate a switch to a
3120   protocol on a different connection. For that purpose, it is more
3121   appropriate to use a 301, 302, 303, or 305 redirection response.
3122</t>
3123<t>
3124   This specification only defines the protocol name "HTTP" for use by
3125   the family of Hypertext Transfer Protocols, as defined by the HTTP
3126   version rules of <xref target="http.version"/> and future updates to this
3127   specification. Additional tokens can be registered with IANA using the
3128   registration procedure defined below. 
3129</t>
3130
3131<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3132<t>
3133   The HTTP Upgrade Token Registry defines the name space for product
3134   tokens used to identify protocols in the Upgrade header field.
3135   Each registered token should be associated with one or a set of
3136   specifications, and with contact information.
3137</t>
3138<t>
3139   Registrations should be allowed on a First Come First Served basis as
3140   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. These
3141   specifications need not be IETF documents or be subject to IESG review, but
3142   should obey the following rules:
3143  <list style="numbers">
3144    <t>A token, once registered, stays registered forever.</t>
3145    <t>The registration &MUST; name a responsible party for the
3146       registration.</t>
3147    <t>The registration &MUST; name a point of contact.</t>
3148    <t>The registration &MAY; name the documentation required for the
3149       token.</t>
3150    <t>The responsible party &MAY; change the registration at any time.
3151       The IANA will keep a record of all such changes, and make them
3152       available upon request.</t>
3153    <t>The responsible party for the first registration of a "product"
3154       token &MUST; approve later registrations of a "version" token
3155       together with that "product" token before they can be registered.</t>
3156    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3157       for a token. This will normally only be used in the case when a
3158       responsible party cannot be contacted.</t>
3159  </list>
3160</t>
3161<t>
3162   It is not required that specifications for upgrade tokens be made
3163   publicly available, but the contact information for the registration
3164   should be.
3165</t>
3166</section>
3167
3168
3169</section>
3170
3171<section title="Via" anchor="header.via">
3172  <iref primary="true" item="Via header" x:for-anchor=""/>
3173  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
3174  <x:anchor-alias value="protocol-name"/>
3175  <x:anchor-alias value="protocol-version"/>
3176  <x:anchor-alias value="pseudonym"/>
3177  <x:anchor-alias value="received-by"/>
3178  <x:anchor-alias value="received-protocol"/>
3179  <x:anchor-alias value="Via"/>
3180  <x:anchor-alias value="Via-v"/>
3181<t>
3182   The "Via" general-header field &MUST; be used by gateways and proxies to
3183   indicate the intermediate protocols and recipients between the user
3184   agent and the server on requests, and between the origin server and
3185   the client on responses. It is analogous to the "Received" field defined in
3186   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
3187   avoiding request loops, and identifying the protocol capabilities of
3188   all senders along the request/response chain.
3189</t>
3190<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"/>
3191  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
3192  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3193                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3194  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3195  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3196  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3197  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3198  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3199</artwork></figure>
3200<t>
3201   The received-protocol indicates the protocol version of the message
3202   received by the server or client along each segment of the
3203   request/response chain. The received-protocol version is appended to
3204   the Via field value when the message is forwarded so that information
3205   about the protocol capabilities of upstream applications remains
3206   visible to all recipients.
3207</t>
3208<t>
3209   The protocol-name is optional if and only if it would be "HTTP". The
3210   received-by field is normally the host and optional port number of a
3211   recipient server or client that subsequently forwarded the message.
3212   However, if the real host is considered to be sensitive information,
3213   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3214   be assumed to be the default port of the received-protocol.
3215</t>
3216<t>
3217   Multiple Via field values represent each proxy or gateway that has
3218   forwarded the message. Each recipient &MUST; append its information
3219   such that the end result is ordered according to the sequence of
3220   forwarding applications.
3221</t>
3222<t>
3223   Comments &MAY; be used in the Via header field to identify the software
3224   of the recipient proxy or gateway, analogous to the User-Agent and
3225   Server header fields. However, all comments in the Via field are
3226   optional and &MAY; be removed by any recipient prior to forwarding the
3227   message.
3228</t>
3229<t>
3230   For example, a request message could be sent from an HTTP/1.0 user
3231   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3232   forward the request to a public proxy at p.example.net, which completes
3233   the request by forwarding it to the origin server at www.example.com.
3234   The request received by www.example.com would then have the following
3235   Via header field:
3236</t>
3237<figure><artwork type="example">
3238  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
3239</artwork></figure>
3240<t>
3241   Proxies and gateways used as a portal through a network firewall
3242   &SHOULD-NOT;, by default, forward the names and ports of hosts within
3243   the firewall region. This information &SHOULD; only be propagated if
3244   explicitly enabled. If not enabled, the received-by host of any host
3245   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
3246   for that host.
3247</t>
3248<t>
3249   For organizations that have strong privacy requirements for hiding
3250   internal structures, a proxy &MAY; combine an ordered subsequence of
3251   Via header field entries with identical received-protocol values into
3252   a single such entry. For example,
3253</t>
3254<figure><artwork type="example">
3255  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3256</artwork></figure>
3257<t>
3258        could be collapsed to
3259</t>
3260<figure><artwork type="example">
3261  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3262</artwork></figure>
3263<t>
3264   Applications &SHOULD-NOT;  combine multiple entries unless they are all
3265   under the same organizational control and the hosts have already been
3266   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
3267   have different received-protocol values.
3268</t>
3269</section>
3270
3271</section>
3272
3273<section title="IANA Considerations" anchor="IANA.considerations">
3274
3275<section title="Message Header Registration" anchor="message.header.registration">
3276<t>
3277   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
3278   with the permanent registrations below (see <xref target="RFC3864"/>):
3279</t>
3280<?BEGININC p1-messaging.iana-headers ?>
3281<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3282<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3283   <ttcol>Header Field Name</ttcol>
3284   <ttcol>Protocol</ttcol>
3285   <ttcol>Status</ttcol>
3286   <ttcol>Reference</ttcol>
3287
3288   <c>Connection</c>
3289   <c>http</c>
3290   <c>standard</c>
3291   <c>
3292      <xref target="header.connection"/>
3293   </c>
3294   <c>Content-Length</c>
3295   <c>http</c>
3296   <c>standard</c>
3297   <c>
3298      <xref target="header.content-length"/>
3299   </c>
3300   <c>Date</c>
3301   <c>http</c>
3302   <c>standard</c>
3303   <c>
3304      <xref target="header.date"/>
3305   </c>
3306   <c>Host</c>
3307   <c>http</c>
3308   <c>standard</c>
3309   <c>
3310      <xref target="header.host"/>
3311   </c>
3312   <c>TE</c>
3313   <c>http</c>
3314   <c>standard</c>
3315   <c>
3316      <xref target="header.te"/>
3317   </c>
3318   <c>Trailer</c>
3319   <c>http</c>
3320   <c>standard</c>
3321   <c>
3322      <xref target="header.trailer"/>
3323   </c>
3324   <c>Transfer-Encoding</c>
3325   <c>http</c>
3326   <c>standard</c>
3327   <c>
3328      <xref target="header.transfer-encoding"/>
3329   </c>
3330   <c>Upgrade</c>
3331   <c>http</c>
3332   <c>standard</c>
3333   <c>
3334      <xref target="header.upgrade"/>
3335   </c>
3336   <c>Via</c>
3337   <c>http</c>
3338   <c>standard</c>
3339   <c>
3340      <xref target="header.via"/>
3341   </c>
3342</texttable>
3343<!--(END)-->
3344<?ENDINC p1-messaging.iana-headers ?>
3345<t>
3346   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3347</t>
3348</section>
3349
3350<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3351<t>
3352   The entries for the "http" and "https" URI Schemes in the registry located at
3353   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3354   should be updated to point to Sections <xref target="http.uri" format="counter"/>
3355   and <xref target="https.uri" format="counter"/> of this document
3356   (see <xref target="RFC4395"/>).
3357</t>
3358</section>
3359
3360<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3361<t>
3362   This document serves as the specification for the Internet media types
3363   "message/http" and "application/http". The following is to be registered with
3364   IANA (see <xref target="RFC4288"/>).
3365</t>
3366<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3367<iref item="Media Type" subitem="message/http" primary="true"/>
3368<iref item="message/http Media Type" primary="true"/>
3369<t>
3370   The message/http type can be used to enclose a single HTTP request or
3371   response message, provided that it obeys the MIME restrictions for all
3372   "message" types regarding line length and encodings.
3373</t>
3374<t>
3375  <list style="hanging" x:indent="12em">
3376    <t hangText="Type name:">
3377      message
3378    </t>
3379    <t hangText="Subtype name:">
3380      http
3381    </t>
3382    <t hangText="Required parameters:">
3383      none
3384    </t>
3385    <t hangText="Optional parameters:">
3386      version, msgtype
3387      <list style="hanging">
3388        <t hangText="version:">
3389          The HTTP-Version number of the enclosed message
3390          (e.g., "1.1"). If not present, the version can be
3391          determined from the first line of the body.
3392        </t>
3393        <t hangText="msgtype:">
3394          The message type -- "request" or "response". If not
3395          present, the type can be determined from the first
3396          line of the body.
3397        </t>
3398      </list>
3399    </t>
3400    <t hangText="Encoding considerations:">
3401      only "7bit", "8bit", or "binary" are permitted
3402    </t>
3403    <t hangText="Security considerations:">
3404      none
3405    </t>
3406    <t hangText="Interoperability considerations:">
3407      none
3408    </t>
3409    <t hangText="Published specification:">
3410      This specification (see <xref target="internet.media.type.message.http"/>).
3411    </t>
3412    <t hangText="Applications that use this media type:">
3413    </t>
3414    <t hangText="Additional information:">
3415      <list style="hanging">
3416        <t hangText="Magic number(s):">none</t>
3417        <t hangText="File extension(s):">none</t>
3418        <t hangText="Macintosh file type code(s):">none</t>
3419      </list>
3420    </t>
3421    <t hangText="Person and email address to contact for further information:">
3422      See Authors Section.
3423    </t>
3424    <t hangText="Intended usage:">
3425      COMMON
3426    </t>
3427    <t hangText="Restrictions on usage:">
3428      none
3429    </t>
3430    <t hangText="Author/Change controller:">
3431      IESG
3432    </t>
3433  </list>
3434</t>
3435</section>
3436<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3437<iref item="Media Type" subitem="application/http" primary="true"/>
3438<iref item="application/http Media Type" primary="true"/>
3439<t>
3440   The application/http type can be used to enclose a pipeline of one or more
3441   HTTP request or response messages (not intermixed).
3442</t>
3443<t>
3444  <list style="hanging" x:indent="12em">
3445    <t hangText="Type name:">
3446      application
3447    </t>
3448    <t hangText="Subtype name:">
3449      http
3450    </t>
3451    <t hangText="Required parameters:">
3452      none
3453    </t>
3454    <t hangText="Optional parameters:">
3455      version, msgtype
3456      <list style="hanging">
3457        <t hangText="version:">
3458          The HTTP-Version number of the enclosed messages
3459          (e.g., "1.1"). If not present, the version can be
3460          determined from the first line of the body.
3461        </t>
3462        <t hangText="msgtype:">
3463          The message type -- "request" or "response". If not
3464          present, the type can be determined from the first
3465          line of the body.
3466        </t>
3467      </list>
3468    </t>
3469    <t hangText="Encoding considerations:">
3470      HTTP messages enclosed by this type
3471      are in "binary" format; use of an appropriate
3472      Content-Transfer-Encoding is required when
3473      transmitted via E-mail.
3474    </t>
3475    <t hangText="Security considerations:">
3476      none
3477    </t>
3478    <t hangText="Interoperability considerations:">
3479      none
3480    </t>
3481    <t hangText="Published specification:">
3482      This specification (see <xref target="internet.media.type.application.http"/>).
3483    </t>
3484    <t hangText="Applications that use this media type:">
3485    </t>
3486    <t hangText="Additional information:">
3487      <list style="hanging">
3488        <t hangText="Magic number(s):">none</t>
3489        <t hangText="File extension(s):">none</t>
3490        <t hangText="Macintosh file type code(s):">none</t>
3491      </list>
3492    </t>
3493    <t hangText="Person and email address to contact for further information:">
3494      See Authors Section.
3495    </t>
3496    <t hangText="Intended usage:">
3497      COMMON
3498    </t>
3499    <t hangText="Restrictions on usage:">
3500      none
3501    </t>
3502    <t hangText="Author/Change controller:">
3503      IESG
3504    </t>
3505  </list>
3506</t>
3507</section>
3508</section>
3509
3510<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3511<t>
3512   The registration procedure for HTTP Transfer Codings is now defined by
3513   <xref target="transfer.coding.registry"/> of this document.
3514</t>
3515<t>
3516   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
3517   should be updated with the registrations below:
3518</t>
3519<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3520   <ttcol>Name</ttcol>
3521   <ttcol>Description</ttcol>
3522   <ttcol>Reference</ttcol>
3523   <c>chunked</c>
3524   <c>Transfer in a series of chunks</c>
3525   <c>
3526      <xref target="chunked.encoding"/>
3527   </c>
3528   <c>compress</c>
3529   <c>UNIX "compress" program method</c>
3530   <c>
3531      <xref target="compress.coding"/>
3532   </c>
3533   <c>deflate</c>
3534   <c>"zlib" format <xref target="RFC1950"/> with "deflate" compression</c>
3535   <c>
3536      <xref target="deflate.coding"/>
3537   </c>
3538   <c>gzip</c>
3539   <c>Same as GNU zip <xref target="RFC1952"/></c>
3540   <c>
3541      <xref target="gzip.coding"/>
3542   </c>
3543</texttable>
3544</section>
3545
3546<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3547<t>
3548   The registration procedure for HTTP Upgrade Tokens -- previously defined
3549   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> -- is now defined
3550   by <xref target="upgrade.token.registry"/> of this document.
3551</t>
3552<t>
3553   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-upgrade-tokens/"/>
3554   should be updated with the registration below:
3555</t>
3556<texttable align="left" suppress-title="true">
3557   <ttcol>Value</ttcol>
3558   <ttcol>Description</ttcol>
3559   <ttcol>Reference</ttcol>
3560
3561   <c>HTTP</c>
3562   <c>Hypertext Transfer Protocol</c> 
3563   <c><xref target="http.version"/> of this specification</c>
3564<!-- IANA should add this without our instructions; emailed on June 05, 2009
3565   <c>TLS/1.0</c>
3566   <c>Transport Layer Security</c>
3567   <c><xref target="RFC2817"/></c> -->
3568
3569</texttable>
3570</section>
3571
3572</section>
3573
3574<section title="Security Considerations" anchor="security.considerations">
3575<t>
3576   This section is meant to inform application developers, information
3577   providers, and users of the security limitations in HTTP/1.1 as
3578   described by this document. The discussion does not include
3579   definitive solutions to the problems revealed, though it does make
3580   some suggestions for reducing security risks.
3581</t>
3582
3583<section title="Personal Information" anchor="personal.information">
3584<t>
3585   HTTP clients are often privy to large amounts of personal information
3586   (e.g., the user's name, location, mail address, passwords, encryption
3587   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3588   leakage of this information.
3589   We very strongly recommend that a convenient interface be provided
3590   for the user to control dissemination of such information, and that
3591   designers and implementors be particularly careful in this area.
3592   History shows that errors in this area often create serious security
3593   and/or privacy problems and generate highly adverse publicity for the
3594   implementor's company.
3595</t>
3596</section>
3597
3598<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3599<t>
3600   A server is in the position to save personal data about a user's
3601   requests which might identify their reading patterns or subjects of
3602   interest. This information is clearly confidential in nature and its
3603   handling can be constrained by law in certain countries. People using
3604   HTTP to provide data are responsible for ensuring that
3605   such material is not distributed without the permission of any
3606   individuals that are identifiable by the published results.
3607</t>
3608</section>
3609
3610<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3611<t>
3612   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3613   the documents returned by HTTP requests to be only those that were
3614   intended by the server administrators. If an HTTP server translates
3615   HTTP URIs directly into file system calls, the server &MUST; take
3616   special care not to serve files that were not intended to be
3617   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3618   other operating systems use ".." as a path component to indicate a
3619   directory level above the current one. On such a system, an HTTP
3620   server &MUST; disallow any such construct in the request-target if it
3621   would otherwise allow access to a resource outside those intended to
3622   be accessible via the HTTP server. Similarly, files intended for
3623   reference only internally to the server (such as access control
3624   files, configuration files, and script code) &MUST; be protected from
3625   inappropriate retrieval, since they might contain sensitive
3626   information. Experience has shown that minor bugs in such HTTP server
3627   implementations have turned into security risks.
3628</t>
3629</section>
3630
3631<section title="DNS Spoofing" anchor="dns.spoofing">
3632<t>
3633   Clients using HTTP rely heavily on the Domain Name Service, and are
3634   thus generally prone to security attacks based on the deliberate
3635   mis-association of IP addresses and DNS names. Clients need to be
3636   cautious in assuming the continuing validity of an IP number/DNS name
3637   association.
3638</t>
3639<t>
3640   In particular, HTTP clients &SHOULD; rely on their name resolver for
3641   confirmation of an IP number/DNS name association, rather than
3642   caching the result of previous host name lookups. Many platforms
3643   already can cache host name lookups locally when appropriate, and
3644   they &SHOULD; be configured to do so. It is proper for these lookups to
3645   be cached, however, only when the TTL (Time To Live) information
3646   reported by the name server makes it likely that the cached
3647   information will remain useful.
3648</t>
3649<t>
3650   If HTTP clients cache the results of host name lookups in order to
3651   achieve a performance improvement, they &MUST; observe the TTL
3652   information reported by DNS.
3653</t>
3654<t>
3655   If HTTP clients do not observe this rule, they could be spoofed when
3656   a previously-accessed server's IP address changes. As network
3657   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3658   possibility of this form of attack will grow. Observing this
3659   requirement thus reduces this potential security vulnerability.
3660</t>
3661<t>
3662   This requirement also improves the load-balancing behavior of clients
3663   for replicated servers using the same DNS name and reduces the
3664   likelihood of a user's experiencing failure in accessing sites which
3665   use that strategy.
3666</t>
3667</section>
3668
3669<section title="Proxies and Caching" anchor="attack.proxies">
3670<t>
3671   By their very nature, HTTP proxies are men-in-the-middle, and
3672   represent an opportunity for man-in-the-middle attacks. Compromise of
3673   the systems on which the proxies run can result in serious security
3674   and privacy problems. Proxies have access to security-related
3675   information, personal information about individual users and
3676   organizations, and proprietary information belonging to users and
3677   content providers. A compromised proxy, or a proxy implemented or
3678   configured without regard to security and privacy considerations,
3679   might be used in the commission of a wide range of potential attacks.
3680</t>
3681<t>
3682   Proxy operators should protect the systems on which proxies run as
3683   they would protect any system that contains or transports sensitive
3684   information. In particular, log information gathered at proxies often
3685   contains highly sensitive personal information, and/or information
3686   about organizations. Log information should be carefully guarded, and
3687   appropriate guidelines for use should be developed and followed.
3688   (<xref target="abuse.of.server.log.information"/>).
3689</t>
3690<t>
3691   Proxy implementors should consider the privacy and security
3692   implications of their design and coding decisions, and of the
3693   configuration options they provide to proxy operators (especially the
3694   default configuration).
3695</t>
3696<t>
3697   Users of a proxy need to be aware that proxies are no trustworthier than
3698   the people who run them; HTTP itself cannot solve this problem.
3699</t>
3700<t>
3701   The judicious use of cryptography, when appropriate, may suffice to
3702   protect against a broad range of security and privacy attacks. Such
3703   cryptography is beyond the scope of the HTTP/1.1 specification.
3704</t>
3705</section>
3706
3707<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3708<t>
3709   They exist. They are hard to defend against. Research continues.
3710   Beware.
3711</t>
3712</section>
3713</section>
3714
3715<section title="Acknowledgments" anchor="ack">
3716<t>
3717   HTTP has evolved considerably over the years. It has
3718   benefited from a large and active developer community--the many
3719   people who have participated on the www-talk mailing list--and it is
3720   that community which has been most responsible for the success of
3721   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3722   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3723   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3724   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3725   VanHeyningen deserve special recognition for their efforts in
3726   defining early aspects of the protocol.
3727</t>
3728<t>
3729   This document has benefited greatly from the comments of all those
3730   participating in the HTTP-WG. In addition to those already mentioned,
3731   the following individuals have contributed to this specification:
3732</t>
3733<t>
3734   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3735   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3736   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3737   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3738   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3739   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3740   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3741   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3742   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3743   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3744   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3745   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3746   Josh Cohen.
3747</t>
3748<t>
3749   Thanks to the "cave men" of Palo Alto. You know who you are.
3750</t>
3751<t>
3752   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3753   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3754   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3755   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3756   Larry Masinter for their help. And thanks go particularly to Jeff
3757   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3758</t>
3759<t>
3760   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3761   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3762   discovery of many of the problems that this document attempts to
3763   rectify.
3764</t>
3765<t>
3766   This specification makes heavy use of the augmented BNF and generic
3767   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3768   reuses many of the definitions provided by Nathaniel Borenstein and
3769   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3770   specification will help reduce past confusion over the relationship
3771   between HTTP and Internet mail message formats.
3772</t>
3773</section>
3774
3775</middle>
3776<back>
3777
3778<references title="Normative References">
3779
3780<reference anchor="ISO-8859-1">
3781  <front>
3782    <title>
3783     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3784    </title>
3785    <author>
3786      <organization>International Organization for Standardization</organization>
3787    </author>
3788    <date year="1998"/>
3789  </front>
3790  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3791</reference>
3792
3793<reference anchor="Part2">
3794  <front>
3795    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3796    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3797      <organization abbrev="Day Software">Day Software</organization>
3798      <address><email>fielding@gbiv.com</email></address>
3799    </author>
3800    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3801      <organization>One Laptop per Child</organization>
3802      <address><email>jg@laptop.org</email></address>
3803    </author>
3804    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3805      <organization abbrev="HP">Hewlett-Packard Company</organization>
3806      <address><email>JeffMogul@acm.org</email></address>
3807    </author>
3808    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3809      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3810      <address><email>henrikn@microsoft.com</email></address>
3811    </author>
3812    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3813      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3814      <address><email>LMM@acm.org</email></address>
3815    </author>
3816    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3817      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3818      <address><email>paulle@microsoft.com</email></address>
3819    </author>
3820    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3821      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3822      <address><email>timbl@w3.org</email></address>
3823    </author>
3824    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3825      <organization abbrev="W3C">World Wide Web Consortium</organization>
3826      <address><email>ylafon@w3.org</email></address>
3827    </author>
3828    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3829      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3830      <address><email>julian.reschke@greenbytes.de</email></address>
3831    </author>
3832    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3833  </front>
3834  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3835  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3836</reference>
3837
3838<reference anchor="Part3">
3839  <front>
3840    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3841    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3842      <organization abbrev="Day Software">Day Software</organization>
3843      <address><email>fielding@gbiv.com</email></address>
3844    </author>
3845    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3846      <organization>One Laptop per Child</organization>
3847      <address><email>jg@laptop.org</email></address>
3848    </author>
3849    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3850      <organization abbrev="HP">Hewlett-Packard Company</organization>
3851      <address><email>JeffMogul@acm.org</email></address>
3852    </author>
3853    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3854      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3855      <address><email>henrikn@microsoft.com</email></address>
3856    </author>
3857    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3858      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3859      <address><email>LMM@acm.org</email></address>
3860    </author>
3861    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3862      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3863      <address><email>paulle@microsoft.com</email></address>
3864    </author>
3865    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3866      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3867      <address><email>timbl@w3.org</email></address>
3868    </author>
3869    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3870      <organization abbrev="W3C">World Wide Web Consortium</organization>
3871      <address><email>ylafon@w3.org</email></address>
3872    </author>
3873    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3874      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3875      <address><email>julian.reschke@greenbytes.de</email></address>
3876    </author>
3877    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3878  </front>
3879  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3880  <x:source href="p3-payload.xml" basename="p3-payload"/>
3881</reference>
3882
3883<reference anchor="Part5">
3884  <front>
3885    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3886    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3887      <organization abbrev="Day Software">Day Software</organization>
3888      <address><email>fielding@gbiv.com</email></address>
3889    </author>
3890    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3891      <organization>One Laptop per Child</organization>
3892      <address><email>jg@laptop.org</email></address>
3893    </author>
3894    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3895      <organization abbrev="HP">Hewlett-Packard Company</organization>
3896      <address><email>JeffMogul@acm.org</email></address>
3897    </author>
3898    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3899      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3900      <address><email>henrikn@microsoft.com</email></address>
3901    </author>
3902    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3903      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3904      <address><email>LMM@acm.org</email></address>
3905    </author>
3906    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3907      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3908      <address><email>paulle@microsoft.com</email></address>
3909    </author>
3910    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3911      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3912      <address><email>timbl@w3.org</email></address>
3913    </author>
3914    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3915      <organization abbrev="W3C">World Wide Web Consortium</organization>
3916      <address><email>ylafon@w3.org</email></address>
3917    </author>
3918    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3919      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3920      <address><email>julian.reschke@greenbytes.de</email></address>
3921    </author>
3922    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3923  </front>
3924  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3925  <x:source href="p5-range.xml" basename="p5-range"/>
3926</reference>
3927
3928<reference anchor="Part6">
3929  <front>
3930    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3931    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3932      <organization abbrev="Day Software">Day Software</organization>
3933      <address><email>fielding@gbiv.com</email></address>
3934    </author>
3935    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3936      <organization>One Laptop per Child</organization>
3937      <address><email>jg@laptop.org</email></address>
3938    </author>
3939    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3940      <organization abbrev="HP">Hewlett-Packard Company</organization>
3941      <address><email>JeffMogul@acm.org</email></address>
3942    </author>
3943    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3944      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3945      <address><email>henrikn@microsoft.com</email></address>
3946    </author>
3947    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3948      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3949      <address><email>LMM@acm.org</email></address>
3950    </author>
3951    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3952      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3953      <address><email>paulle@microsoft.com</email></address>
3954    </author>
3955    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3956      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3957      <address><email>timbl@w3.org</email></address>
3958    </author>
3959    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3960      <organization abbrev="W3C">World Wide Web Consortium</organization>
3961      <address><email>ylafon@w3.org</email></address>
3962    </author>
3963    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3964      <address><email>mnot@mnot.net</email></address>
3965    </author>
3966    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3967      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3968      <address><email>julian.reschke@greenbytes.de</email></address>
3969    </author>
3970    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3971  </front>
3972  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3973  <x:source href="p6-cache.xml" basename="p6-cache"/>
3974</reference>
3975
3976<reference anchor="RFC5234">
3977  <front>
3978    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3979    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3980      <organization>Brandenburg InternetWorking</organization>
3981      <address>
3982        <email>dcrocker@bbiw.net</email>
3983      </address> 
3984    </author>
3985    <author initials="P." surname="Overell" fullname="Paul Overell">
3986      <organization>THUS plc.</organization>
3987      <address>
3988        <email>paul.overell@thus.net</email>
3989      </address>
3990    </author>
3991    <date month="January" year="2008"/>
3992  </front>
3993  <seriesInfo name="STD" value="68"/>
3994  <seriesInfo name="RFC" value="5234"/>
3995</reference>
3996
3997<reference anchor="RFC2119">
3998  <front>
3999    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4000    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4001      <organization>Harvard University</organization>
4002      <address><email>sob@harvard.edu</email></address>
4003    </author>
4004    <date month="March" year="1997"/>
4005  </front>
4006  <seriesInfo name="BCP" value="14"/>
4007  <seriesInfo name="RFC" value="2119"/>
4008</reference>
4009
4010<reference anchor="RFC3986">
4011 <front>
4012  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4013  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4014    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4015    <address>
4016       <email>timbl@w3.org</email>
4017       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4018    </address>
4019  </author>
4020  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4021    <organization abbrev="Day Software">Day Software</organization>
4022    <address>
4023      <email>fielding@gbiv.com</email>
4024      <uri>http://roy.gbiv.com/</uri>
4025    </address>
4026  </author>
4027  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4028    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4029    <address>
4030      <email>LMM@acm.org</email>
4031      <uri>http://larry.masinter.net/</uri>
4032    </address>
4033  </author>
4034  <date month='January' year='2005'></date>
4035 </front>
4036 <seriesInfo name="RFC" value="3986"/>
4037 <seriesInfo name="STD" value="66"/>
4038</reference>
4039
4040<reference anchor="USASCII">
4041  <front>
4042    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4043    <author>
4044      <organization>American National Standards Institute</organization>
4045    </author>
4046    <date year="1986"/>
4047  </front>
4048  <seriesInfo name="ANSI" value="X3.4"/>
4049</reference>
4050
4051<reference anchor="RFC1950">
4052  <front>
4053    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4054    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4055      <organization>Aladdin Enterprises</organization>
4056      <address><email>ghost@aladdin.com</email></address>
4057    </author>
4058    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4059    <date month="May" year="1996"/>
4060  </front>
4061  <seriesInfo name="RFC" value="1950"/>
4062  <annotation>
4063    RFC 1950 is an Informational RFC, thus it may be less stable than
4064    this specification. On the other hand, this downward reference was
4065    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4066    therefore it is unlikely to cause problems in practice. See also
4067    <xref target="BCP97"/>.
4068  </annotation>
4069</reference>
4070
4071<reference anchor="RFC1951">
4072  <front>
4073    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4074    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4075      <organization>Aladdin Enterprises</organization>
4076      <address><email>ghost@aladdin.com</email></address>
4077    </author>
4078    <date month="May" year="1996"/>
4079  </front>
4080  <seriesInfo name="RFC" value="1951"/>
4081  <annotation>
4082    RFC 1951 is an Informational RFC, thus it may be less stable than
4083    this specification. On the other hand, this downward reference was
4084    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4085    therefore it is unlikely to cause problems in practice. See also
4086    <xref target="BCP97"/>.
4087  </annotation>
4088</reference>
4089
4090<reference anchor="RFC1952">
4091  <front>
4092    <title>GZIP file format specification version 4.3</title>
4093    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4094      <organization>Aladdin Enterprises</organization>
4095      <address><email>ghost@aladdin.com</email></address>
4096    </author>
4097    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4098      <address><email>gzip@prep.ai.mit.edu</email></address>
4099    </author>
4100    <author initials="M." surname="Adler" fullname="Mark Adler">
4101      <address><email>madler@alumni.caltech.edu</email></address>
4102    </author>
4103    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4104      <address><email>ghost@aladdin.com</email></address>
4105    </author>
4106    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4107      <address><email>randeg@alumni.rpi.edu</email></address>
4108    </author>
4109    <date month="May" year="1996"/>
4110  </front>
4111  <seriesInfo name="RFC" value="1952"/>
4112  <annotation>
4113    RFC 1952 is an Informational RFC, thus it may be less stable than
4114    this specification. On the other hand, this downward reference was
4115    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4116    therefore it is unlikely to cause problems in practice. See also
4117    <xref target="BCP97"/>.
4118  </annotation>
4119</reference>
4120
4121</references>
4122
4123<references title="Informative References">
4124
4125<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4126  <front>
4127    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4128    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen"/>
4129    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4130    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4131    <author initials="H." surname="Lie" fullname="H. Lie"/>
4132    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4133    <date year="1997" month="September"/>
4134  </front>
4135  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4136</reference>
4137
4138<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4139  <front>
4140    <title>Improving HTTP Latency</title>
4141    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4142    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4143    <date year="1995" month="December"/>
4144  </front>
4145  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4146</reference>
4147
4148<reference anchor="RFC1123">
4149  <front>
4150    <title>Requirements for Internet Hosts - Application and Support</title>
4151    <author initials="R." surname="Braden" fullname="Robert Braden">
4152      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4153      <address><email>Braden@ISI.EDU</email></address>
4154    </author>
4155    <date month="October" year="1989"/>
4156  </front>
4157  <seriesInfo name="STD" value="3"/>
4158  <seriesInfo name="RFC" value="1123"/>
4159</reference>
4160
4161<reference anchor="RFC1305">
4162  <front>
4163    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
4164    <author initials="D." surname="Mills" fullname="David L. Mills">
4165      <organization>University of Delaware, Electrical Engineering Department</organization>
4166      <address><email>mills@udel.edu</email></address>
4167    </author>
4168    <date month="March" year="1992"/>
4169  </front>
4170  <seriesInfo name="RFC" value="1305"/>
4171</reference>
4172
4173<reference anchor="RFC1900">
4174  <front>
4175    <title>Renumbering Needs Work</title>
4176    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4177      <organization>CERN, Computing and Networks Division</organization>
4178      <address><email>brian@dxcoms.cern.ch</email></address>
4179    </author>
4180    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4181      <organization>cisco Systems</organization>
4182      <address><email>yakov@cisco.com</email></address>
4183    </author>
4184    <date month="February" year="1996"/>
4185  </front>
4186  <seriesInfo name="RFC" value="1900"/>
4187</reference>
4188
4189<reference anchor="RFC1945">
4190  <front>
4191    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4192    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4193      <organization>MIT, Laboratory for Computer Science</organization>
4194      <address><email>timbl@w3.org</email></address>
4195    </author>
4196    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4197      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4198      <address><email>fielding@ics.uci.edu</email></address>
4199    </author>
4200    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4201      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4202      <address><email>frystyk@w3.org</email></address>
4203    </author>
4204    <date month="May" year="1996"/>
4205  </front>
4206  <seriesInfo name="RFC" value="1945"/>
4207</reference>
4208
4209<reference anchor="RFC2045">
4210  <front>
4211    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4212    <author initials="N." surname="Freed" fullname="Ned Freed">
4213      <organization>Innosoft International, Inc.</organization>
4214      <address><email>ned@innosoft.com</email></address>
4215    </author>
4216    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4217      <organization>First Virtual Holdings</organization>
4218      <address><email>nsb@nsb.fv.com</email></address>
4219    </author>
4220    <date month="November" year="1996"/>
4221  </front>
4222  <seriesInfo name="RFC" value="2045"/>
4223</reference>
4224
4225<reference anchor="RFC2047">
4226  <front>
4227    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4228    <author initials="K." surname="Moore" fullname="Keith Moore">
4229      <organization>University of Tennessee</organization>
4230      <address><email>moore@cs.utk.edu</email></address>
4231    </author>
4232    <date month="November" year="1996"/>
4233  </front>
4234  <seriesInfo name="RFC" value="2047"/>
4235</reference>
4236
4237<reference anchor="RFC2068">
4238  <front>
4239    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4240    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4241      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4242      <address><email>fielding@ics.uci.edu</email></address>
4243    </author>
4244    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4245      <organization>MIT Laboratory for Computer Science</organization>
4246      <address><email>jg@w3.org</email></address>
4247    </author>
4248    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4249      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4250      <address><email>mogul@wrl.dec.com</email></address>
4251    </author>
4252    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4253      <organization>MIT Laboratory for Computer Science</organization>
4254      <address><email>frystyk@w3.org</email></address>
4255    </author>
4256    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4257      <organization>MIT Laboratory for Computer Science</organization>
4258      <address><email>timbl@w3.org</email></address>
4259    </author>
4260    <date month="January" year="1997"/>
4261  </front>
4262  <seriesInfo name="RFC" value="2068"/>
4263</reference>
4264
4265<reference anchor='RFC2109'>
4266  <front>
4267    <title>HTTP State Management Mechanism</title>
4268    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
4269      <organization>Bell Laboratories, Lucent Technologies</organization>
4270      <address><email>dmk@bell-labs.com</email></address>
4271    </author>
4272    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4273      <organization>Netscape Communications Corp.</organization>
4274      <address><email>montulli@netscape.com</email></address>
4275    </author>
4276    <date year='1997' month='February' />
4277  </front>
4278  <seriesInfo name='RFC' value='2109' />
4279</reference>
4280
4281<reference anchor="RFC2145">
4282  <front>
4283    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4284    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4285      <organization>Western Research Laboratory</organization>
4286      <address><email>mogul@wrl.dec.com</email></address>
4287    </author>
4288    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4289      <organization>Department of Information and Computer Science</organization>
4290      <address><email>fielding@ics.uci.edu</email></address>
4291    </author>
4292    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4293      <organization>MIT Laboratory for Computer Science</organization>
4294      <address><email>jg@w3.org</email></address>
4295    </author>
4296    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4297      <organization>W3 Consortium</organization>
4298      <address><email>frystyk@w3.org</email></address>
4299    </author>
4300    <date month="May" year="1997"/>
4301  </front>
4302  <seriesInfo name="RFC" value="2145"/>
4303</reference>
4304
4305<reference anchor="RFC2616">
4306  <front>
4307    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4308    <author initials="R." surname="Fielding" fullname="R. Fielding">
4309      <organization>University of California, Irvine</organization>
4310      <address><email>fielding@ics.uci.edu</email></address>
4311    </author>
4312    <author initials="J." surname="Gettys" fullname="J. Gettys">
4313      <organization>W3C</organization>
4314      <address><email>jg@w3.org</email></address>
4315    </author>
4316    <author initials="J." surname="Mogul" fullname="J. Mogul">
4317      <organization>Compaq Computer Corporation</organization>
4318      <address><email>mogul@wrl.dec.com</email></address>
4319    </author>
4320    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4321      <organization>MIT Laboratory for Computer Science</organization>
4322      <address><email>frystyk@w3.org</email></address>
4323    </author>
4324    <author initials="L." surname="Masinter" fullname="L. Masinter">
4325      <organization>Xerox Corporation</organization>
4326      <address><email>masinter@parc.xerox.com</email></address>
4327    </author>
4328    <author initials="P." surname="Leach" fullname="P. Leach">
4329      <organization>Microsoft Corporation</organization>
4330      <address><email>paulle@microsoft.com</email></address>
4331    </author>
4332    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4333      <organization>W3C</organization>
4334      <address><email>timbl@w3.org</email></address>
4335    </author>
4336    <date month="June" year="1999"/>
4337  </front>
4338  <seriesInfo name="RFC" value="2616"/>
4339</reference>
4340
4341<reference anchor='RFC2817'>
4342  <front>
4343    <title>Upgrading to TLS Within HTTP/1.1</title>
4344    <author initials='R.' surname='Khare' fullname='R. Khare'>
4345      <organization>4K Associates / UC Irvine</organization>
4346      <address><email>rohit@4K-associates.com</email></address>
4347    </author>
4348    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4349      <organization>Agranat Systems, Inc.</organization>
4350      <address><email>lawrence@agranat.com</email></address>
4351    </author>
4352    <date year='2000' month='May' />
4353  </front>
4354  <seriesInfo name='RFC' value='2817' />
4355</reference>
4356
4357<reference anchor='RFC2818'>
4358  <front>
4359    <title>HTTP Over TLS</title>
4360    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4361      <organization>RTFM, Inc.</organization>
4362      <address><email>ekr@rtfm.com</email></address>
4363    </author>
4364    <date year='2000' month='May' />
4365  </front>
4366  <seriesInfo name='RFC' value='2818' />
4367</reference>
4368
4369<reference anchor='RFC2965'>
4370  <front>
4371    <title>HTTP State Management Mechanism</title>
4372    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4373      <organization>Bell Laboratories, Lucent Technologies</organization>
4374      <address><email>dmk@bell-labs.com</email></address>
4375    </author>
4376    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4377      <organization>Epinions.com, Inc.</organization>
4378      <address><email>lou@montulli.org</email></address>
4379    </author>
4380    <date year='2000' month='October' />
4381  </front>
4382  <seriesInfo name='RFC' value='2965' />
4383</reference>
4384
4385<reference anchor='RFC3864'>
4386  <front>
4387    <title>Registration Procedures for Message Header Fields</title>
4388    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4389      <organization>Nine by Nine</organization>
4390      <address><email>GK-IETF@ninebynine.org</email></address>
4391    </author>
4392    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4393      <organization>BEA Systems</organization>
4394      <address><email>mnot@pobox.com</email></address>
4395    </author>
4396    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4397      <organization>HP Labs</organization>
4398      <address><email>JeffMogul@acm.org</email></address>
4399    </author>
4400    <date year='2004' month='September' />
4401  </front>
4402  <seriesInfo name='BCP' value='90' />
4403  <seriesInfo name='RFC' value='3864' />
4404</reference>
4405
4406<reference anchor="RFC4288">
4407  <front>
4408    <title>Media Type Specifications and Registration Procedures</title>
4409    <author initials="N." surname="Freed" fullname="N. Freed">
4410      <organization>Sun Microsystems</organization>
4411      <address>
4412        <email>ned.freed@mrochek.com</email>
4413      </address>
4414    </author>
4415    <author initials="J." surname="Klensin" fullname="J. Klensin">
4416      <address>
4417        <email>klensin+ietf@jck.com</email>
4418      </address>
4419    </author>
4420    <date year="2005" month="December"/>
4421  </front>
4422  <seriesInfo name="BCP" value="13"/>
4423  <seriesInfo name="RFC" value="4288"/>
4424</reference>
4425
4426<reference anchor='RFC4395'>
4427  <front>
4428    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4429    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4430      <organization>AT&amp;T Laboratories</organization>
4431      <address>
4432        <email>tony+urireg@maillennium.att.com</email>
4433      </address>
4434    </author>
4435    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4436      <organization>Qualcomm, Inc.</organization>
4437      <address>
4438        <email>hardie@qualcomm.com</email>
4439      </address>
4440    </author>
4441    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4442      <organization>Adobe Systems</organization>
4443      <address>
4444        <email>LMM@acm.org</email>
4445      </address>
4446    </author>
4447    <date year='2006' month='February' />
4448  </front>
4449  <seriesInfo name='BCP' value='115' />
4450  <seriesInfo name='RFC' value='4395' />
4451</reference>
4452
4453<reference anchor='RFC5226'>
4454  <front>
4455    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4456    <author initials='T.' surname='Narten' fullname='T. Narten'>
4457      <organization>IBM</organization>
4458      <address><email>narten@us.ibm.com</email></address>
4459    </author>
4460    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4461      <organization>Google</organization>
4462      <address><email>Harald@Alvestrand.no</email></address>
4463    </author>
4464    <date year='2008' month='May' />
4465  </front>
4466  <seriesInfo name='BCP' value='26' />
4467  <seriesInfo name='RFC' value='5226' />
4468</reference>
4469
4470<reference anchor="RFC5322">
4471  <front>
4472    <title>Internet Message Format</title>
4473    <author initials="P." surname="Resnick" fullname="P. Resnick">
4474      <organization>Qualcomm Incorporated</organization>
4475    </author>
4476    <date year="2008" month="October"/>
4477  </front> 
4478  <seriesInfo name="RFC" value="5322"/>
4479</reference>
4480
4481<reference anchor='BCP97'>
4482  <front>
4483    <title>Handling Normative References to Standards-Track Documents</title>
4484    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4485      <address>
4486        <email>klensin+ietf@jck.com</email>
4487      </address>
4488    </author>
4489    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4490      <organization>MIT</organization>
4491      <address>
4492        <email>hartmans-ietf@mit.edu</email>
4493      </address>
4494    </author>
4495    <date year='2007' month='June' />
4496  </front>
4497  <seriesInfo name='BCP' value='97' />
4498  <seriesInfo name='RFC' value='4897' />
4499</reference>
4500
4501<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4502  <front>
4503    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4504    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4505    <date year="2001" month="November"/>
4506  </front>
4507  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4508</reference>
4509
4510<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4511  <front>
4512    <title>Analysis of HTTP Performance Problems</title>
4513    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4514    <date/>
4515  </front>
4516</reference>
4517
4518<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4519  <front>
4520  <title>Analysis of HTTP Performance</title>
4521  <author initials="J." surname="Touch" fullname="Joe Touch">
4522    <organization>USC/Information Sciences Institute</organization>
4523    <address><email>touch@isi.edu</email></address>
4524  </author>
4525  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4526    <organization>USC/Information Sciences Institute</organization>
4527    <address><email>johnh@isi.edu</email></address>
4528  </author>
4529  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4530    <organization>USC/Information Sciences Institute</organization>
4531    <address><email>katia@isi.edu</email></address>
4532  </author>
4533  <date year="1998" month="Aug"/>
4534  </front>
4535  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4536  <annotation>(original report dated Aug. 1996)</annotation>
4537</reference>
4538
4539</references>
4540
4541
4542<section title="Tolerant Applications" anchor="tolerant.applications">
4543<t>
4544   Although this document specifies the requirements for the generation
4545   of HTTP/1.1 messages, not all applications will be correct in their
4546   implementation. We therefore recommend that operational applications
4547   be tolerant of deviations whenever those deviations can be
4548   interpreted unambiguously.
4549</t>
4550<t>
4551   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
4552   &SHOULD; be tolerant when parsing the Request-Line. In particular, they
4553   &SHOULD; accept any amount of WSP characters between fields, even though
4554   only a single SP is required.
4555</t>
4556<t>
4557   The line terminator for header fields is the sequence CRLF.
4558   However, we recommend that applications, when parsing such headers,
4559   recognize a single LF as a line terminator and ignore the leading CR.
4560</t>
4561<t>
4562   The character set of an entity-body &SHOULD; be labeled as the lowest
4563   common denominator of the character codes used within that body, with
4564   the exception that not labeling the entity is preferred over labeling
4565   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
4566</t>
4567<t>
4568   Additional rules for requirements on parsing and encoding of dates
4569   and other potential problems with date encodings include:
4570</t>
4571<t>
4572  <list style="symbols">
4573     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4574        which appears to be more than 50 years in the future is in fact
4575        in the past (this helps solve the "year 2000" problem).</t>
4576
4577     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4578        Expires date as earlier than the proper value, but &MUST-NOT;
4579        internally represent a parsed Expires date as later than the
4580        proper value.</t>
4581
4582     <t>All expiration-related calculations &MUST; be done in GMT. The
4583        local time zone &MUST-NOT; influence the calculation or comparison
4584        of an age or expiration time.</t>
4585
4586     <t>If an HTTP header incorrectly carries a date value with a time
4587        zone other than GMT, it &MUST; be converted into GMT using the
4588        most conservative possible conversion.</t>
4589  </list>
4590</t>
4591</section>
4592
4593<section title="Compatibility with Previous Versions" anchor="compatibility">
4594<t>
4595   HTTP has been in use by the World-Wide Web global information initiative
4596   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4597   was a simple protocol for hypertext data transfer across the Internet
4598   with only a single method and no metadata.
4599   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4600   methods and MIME-like messaging that could include metadata about the data
4601   transferred and modifiers on the request/response semantics. However,
4602   HTTP/1.0 did not sufficiently take into consideration the effects of
4603   hierarchical proxies, caching, the need for persistent connections, or
4604   name-based virtual hosts. The proliferation of incompletely-implemented
4605   applications calling themselves "HTTP/1.0" further necessitated a
4606   protocol version change in order for two communicating applications
4607   to determine each other's true capabilities.
4608</t>
4609<t>
4610   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4611   requirements that enable reliable implementations, adding only
4612   those new features that will either be safely ignored by an HTTP/1.0
4613   recipient or only sent when communicating with a party advertising
4614   compliance with HTTP/1.1.
4615</t>
4616<t>
4617   It is beyond the scope of a protocol specification to mandate
4618   compliance with previous versions. HTTP/1.1 was deliberately
4619   designed, however, to make supporting previous versions easy. It is
4620   worth noting that, at the time of composing this specification, we would
4621   expect general-purpose HTTP/1.1 servers to:
4622  <list style="symbols">
4623     <t>understand any valid request in the format of HTTP/1.0 and
4624        1.1;</t>
4625
4626     <t>respond appropriately with a message in the same major version
4627        used by the client.</t>
4628  </list>
4629</t>
4630<t>
4631   And we would expect HTTP/1.1 clients to:
4632  <list style="symbols">
4633     <t>understand any valid response in the format of HTTP/1.0 or
4634        1.1.</t>
4635  </list>
4636</t>
4637<t>
4638   For most implementations of HTTP/1.0, each connection is established
4639   by the client prior to the request and closed by the server after
4640   sending the response. Some implementations implement the Keep-Alive
4641   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4642</t>
4643
4644<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4645<t>
4646   This section summarizes major differences between versions HTTP/1.0
4647   and HTTP/1.1.
4648</t>
4649
4650<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">
4651<t>
4652   The requirements that clients and servers support the Host request-header,
4653   report an error if the Host request-header (<xref target="header.host"/>) is
4654   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4655   are among the most important changes defined by this
4656   specification.
4657</t>
4658<t>
4659   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4660   addresses and servers; there was no other established mechanism for
4661   distinguishing the intended server of a request than the IP address
4662   to which that request was directed. The changes outlined above will
4663   allow the Internet, once older HTTP clients are no longer common, to
4664   support multiple Web sites from a single IP address, greatly
4665   simplifying large operational Web servers, where allocation of many
4666   IP addresses to a single host has created serious problems. The
4667   Internet will also be able to recover the IP addresses that have been
4668   allocated for the sole purpose of allowing special-purpose domain
4669   names to be used in root-level HTTP URLs. Given the rate of growth of
4670   the Web, and the number of servers already deployed, it is extremely
4671   important that all implementations of HTTP (including updates to
4672   existing HTTP/1.0 applications) correctly implement these
4673   requirements:
4674  <list style="symbols">
4675     <t>Both clients and servers &MUST; support the Host request-header.</t>
4676
4677     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4678
4679     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4680        request does not include a Host request-header.</t>
4681
4682     <t>Servers &MUST; accept absolute URIs.</t>
4683  </list>
4684</t>
4685</section>
4686</section>
4687
4688<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4689<t>
4690   Some clients and servers might wish to be compatible with some
4691   previous implementations of persistent connections in HTTP/1.0
4692   clients and servers. Persistent connections in HTTP/1.0 are
4693   explicitly negotiated as they are not the default behavior. HTTP/1.0
4694   experimental implementations of persistent connections are faulty,
4695   and the new facilities in HTTP/1.1 are designed to rectify these
4696   problems. The problem was that some existing HTTP/1.0 clients may be
4697   sending Keep-Alive to a proxy server that doesn't understand
4698   Connection, which would then erroneously forward it to the next
4699   inbound server, which would establish the Keep-Alive connection and
4700   result in a hung HTTP/1.0 proxy waiting for the close on the
4701   response. The result is that HTTP/1.0 clients must be prevented from
4702   using Keep-Alive when talking to proxies.
4703</t>
4704<t>
4705   However, talking to proxies is the most important use of persistent
4706   connections, so that prohibition is clearly unacceptable. Therefore,
4707   we need some other mechanism for indicating a persistent connection
4708   is desired, which is safe to use even when talking to an old proxy
4709   that ignores Connection. Persistent connections are the default for
4710   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4711   declaring non-persistence. See <xref target="header.connection"/>.
4712</t>
4713<t>
4714   The original HTTP/1.0 form of persistent connections (the Connection:
4715   Keep-Alive and Keep-Alive header) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4716</t>
4717</section>
4718
4719<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4720<t>
4721   This specification has been carefully audited to correct and
4722   disambiguate key word usage; RFC 2068 had many problems in respect to
4723   the conventions laid out in <xref target="RFC2119"/>.
4724</t>
4725<t>
4726   Transfer-coding and message lengths all interact in ways that
4727   required fixing exactly when chunked encoding is used (to allow for
4728   transfer encoding that may not be self delimiting); it was important
4729   to straighten out exactly how message lengths are computed. (Sections
4730   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4731   <xref target="header.content-length" format="counter"/>,
4732   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4733</t>
4734<t>
4735   The use and interpretation of HTTP version numbers has been clarified
4736   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4737   version they support to deal with problems discovered in HTTP/1.0
4738   implementations (<xref target="http.version"/>)
4739</t>
4740<t>
4741   Quality Values of zero should indicate that "I don't want something"
4742   to allow clients to refuse a representation. (<xref target="quality.values"/>)
4743</t>
4744<t>
4745   Transfer-coding had significant problems, particularly with
4746   interactions with chunked encoding. The solution is that transfer-codings
4747   become as full fledged as content-codings. This involves
4748   adding an IANA registry for transfer-codings (separate from content
4749   codings), a new header field (TE) and enabling trailer headers in the
4750   future. Transfer encoding is a major performance benefit, so it was
4751   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4752   interoperability problem that could have occurred due to interactions
4753   between authentication trailers, chunked encoding and HTTP/1.0
4754   clients.(Section
4755   <xref target="transfer.codings" format="counter"/>,
4756   <xref target="chunked.encoding" format="counter"/>,
4757   <xref target="non-modifiable.headers" format="counter"/>,
4758   and <xref target="header.te" format="counter"/>)
4759</t>
4760<t>
4761  Proxies should be able to add Content-Length when appropriate.
4762  (<xref target="non-modifiable.headers"/>)
4763</t>
4764</section>
4765
4766<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4767<t>
4768  Empty list elements in list productions have been deprecated.
4769  (<xref target="notation.abnf"/>)
4770</t>
4771<t>
4772  Rules about implicit linear whitespace between certain grammar productions
4773  have been removed; now it's only allowed when specifically pointed out
4774  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4775  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4776  Non-ASCII content in header fields and reason phrase has been obsoleted and
4777  made opaque (the TEXT rule was removed)
4778  (<xref target="basic.rules"/>)
4779</t>
4780<t>
4781  Clarify that HTTP-Version is case sensitive.
4782  (<xref target="http.version"/>)
4783</t>
4784<t>
4785  Remove reference to non-existent identity transfer-coding value tokens.
4786  (Sections <xref format="counter" target="transfer.codings"/> and
4787  <xref format="counter" target="message.length"/>)
4788</t>
4789<t>
4790  Require that invalid whitespace around field-names be rejected.
4791  (<xref target="header.fields"/>)
4792</t>
4793<t>
4794  Update use of abs_path production from RFC1808 to the path-absolute + query
4795  components of RFC3986.
4796  (<xref target="request-target"/>)
4797</t>
4798<t>
4799  Clarification that the chunk length does not include the count of the octets
4800  in the chunk header and trailer. Furthermore disallowed line folding
4801  in chunk extensions.
4802  (<xref target="chunked.encoding"/>)
4803</t>
4804<t>
4805  Remove hard limit of two connections per server.
4806  (<xref target="persistent.practical"/>)
4807</t>
4808<t>
4809  Clarify exactly when close connection options must be sent.
4810  (<xref target="header.connection"/>)
4811</t>
4812</section>
4813</section>
4814
4815<?BEGININC p1-messaging.abnf-appendix ?>
4816<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4817<figure>
4818<artwork type="abnf" name="p1-messaging.parsed-abnf">
4819<x:ref>BWS</x:ref> = OWS
4820
4821<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
4822<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4823<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4824<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4825 connection-token ] )
4826<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4827<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4828
4829<x:ref>Date</x:ref> = "Date:" OWS Date-v
4830<x:ref>Date-v</x:ref> = HTTP-date
4831
4832<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4833
4834<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
4835<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4836<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4837<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
4838 ]
4839<x:ref>Host</x:ref> = "Host:" OWS Host-v
4840<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4841
4842<x:ref>Method</x:ref> = token
4843
4844<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4845
4846<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
4847
4848<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4849<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4850<x:ref>Request</x:ref> = Request-Line *( ( general-header / request-header /
4851 entity-header ) CRLF ) CRLF [ message-body ]
4852<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4853<x:ref>Response</x:ref> = Status-Line *( ( general-header / response-header /
4854 entity-header ) CRLF ) CRLF [ message-body ]
4855
4856<x:ref>Status-Code</x:ref> = 3DIGIT
4857<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4858
4859<x:ref>TE</x:ref> = "TE:" OWS TE-v
4860<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4861<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
4862<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4863<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
4864<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4865 transfer-coding ] )
4866
4867<x:ref>URI</x:ref> = &lt;URI, defined in [RFC3986], Section 3&gt;
4868<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4869<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
4870<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
4871
4872<x:ref>Via</x:ref> = "Via:" OWS Via-v
4873<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4874 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4875 ] )
4876
4877<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
4878
4879<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4880<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4881<x:ref>attribute</x:ref> = token
4882<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4883
4884<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4885<x:ref>chunk-data</x:ref> = 1*OCTET
4886<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4887<x:ref>chunk-ext-name</x:ref> = token
4888<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
4889<x:ref>chunk-size</x:ref> = 1*HEXDIG
4890<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
4891<x:ref>connection-token</x:ref> = token
4892<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4893 / %x2A-5B ; '*'-'['
4894 / %x5D-7E ; ']'-'~'
4895 / obs-text
4896
4897<x:ref>date1</x:ref> = day SP month SP year
4898<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4899<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4900<x:ref>day</x:ref> = 2DIGIT
4901<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4902 / %x54.75.65 ; Tue
4903 / %x57.65.64 ; Wed
4904 / %x54.68.75 ; Thu
4905 / %x46.72.69 ; Fri
4906 / %x53.61.74 ; Sat
4907 / %x53.75.6E ; Sun
4908<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
4909 / %x54.75.65.73.64.61.79 ; Tuesday
4910 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
4911 / %x54.68.75.72.73.64.61.79 ; Thursday
4912 / %x46.72.69.64.61.79 ; Friday
4913 / %x53.61.74.75.72.64.61.79 ; Saturday
4914 / %x53.75.6E.64.61.79 ; Sunday
4915
4916<x:ref>entity-body</x:ref> = &lt;entity-body, defined in [Part3], Section 3.2&gt;
4917<x:ref>entity-header</x:ref> = &lt;entity-header, defined in [Part3], Section 3.1&gt;
4918
4919<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
4920<x:ref>field-name</x:ref> = token
4921<x:ref>field-value</x:ref> = *( field-content / OWS )
4922
4923<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
4924 / Transfer-Encoding / Upgrade / Via / Warning
4925
4926<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
4927<x:ref>hour</x:ref> = 2DIGIT
4928<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4929<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
4930
4931<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
4932
4933<x:ref>message-body</x:ref> = entity-body /
4934 &lt;entity-body encoded as per Transfer-Encoding&gt;
4935<x:ref>minute</x:ref> = 2DIGIT
4936<x:ref>month</x:ref> = %x4A.61.6E ; Jan
4937 / %x46.65.62 ; Feb
4938 / %x4D.61.72 ; Mar
4939 / %x41.70.72 ; Apr
4940 / %x4D.61.79 ; May
4941 / %x4A.75.6E ; Jun
4942 / %x4A.75.6C ; Jul
4943 / %x41.75.67 ; Aug
4944 / %x53.65.70 ; Sep
4945 / %x4F.63.74 ; Oct
4946 / %x4E.6F.76 ; Nov
4947 / %x44.65.63 ; Dec
4948
4949<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
4950<x:ref>obs-fold</x:ref> = CRLF
4951<x:ref>obs-text</x:ref> = %x80-FF
4952
4953<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4954<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4955<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4956<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4957<x:ref>product</x:ref> = token [ "/" product-version ]
4958<x:ref>product-version</x:ref> = token
4959<x:ref>protocol-name</x:ref> = token
4960<x:ref>protocol-version</x:ref> = token
4961<x:ref>pseudonym</x:ref> = token
4962
4963<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
4964 / %x5D-7E ; ']'-'~'
4965 / obs-text
4966<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
4967 / %x5D-7E ; ']'-'~'
4968 / obs-text
4969<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
4970<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
4971<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
4972<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
4973<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
4974<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
4975
4976<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
4977<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
4978<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
4979<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
4980<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
4981 / authority
4982<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
4983<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
4984<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
4985
4986<x:ref>second</x:ref> = 2DIGIT
4987<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
4988 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
4989<x:ref>start-line</x:ref> = Request-Line / Status-Line
4990
4991<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
4992<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
4993 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
4994<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
4995<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
4996<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
4997<x:ref>token</x:ref> = 1*tchar
4998<x:ref>trailer-part</x:ref> = *( entity-header CRLF )
4999<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5000 transfer-extension
5001<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5002<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5003
5004<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5005
5006<x:ref>value</x:ref> = token / quoted-string
5007
5008<x:ref>year</x:ref> = 4DIGIT
5009</artwork>
5010</figure>
5011<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5012; Chunked-Body defined but not used
5013; Content-Length defined but not used
5014; HTTP-message defined but not used
5015; Host defined but not used
5016; Request defined but not used
5017; Response defined but not used
5018; TE defined but not used
5019; URI defined but not used
5020; URI-reference defined but not used
5021; http-URI defined but not used
5022; https-URI defined but not used
5023; partial-URI defined but not used
5024; special defined but not used
5025</artwork></figure></section>
5026<?ENDINC p1-messaging.abnf-appendix ?>
5027
5028<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5029
5030<section title="Since RFC2616">
5031<t>
5032  Extracted relevant partitions from <xref target="RFC2616"/>.
5033</t>
5034</section>
5035
5036<section title="Since draft-ietf-httpbis-p1-messaging-00">
5037<t>
5038  Closed issues:
5039  <list style="symbols"> 
5040    <t>
5041      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5042      "HTTP Version should be case sensitive"
5043      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5044    </t>
5045    <t>
5046      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5047      "'unsafe' characters"
5048      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5049    </t>
5050    <t>
5051      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5052      "Chunk Size Definition"
5053      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5054    </t>
5055    <t>
5056      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5057      "Message Length"
5058      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5059    </t>
5060    <t>
5061      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5062      "Media Type Registrations"
5063      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5064    </t>
5065    <t>
5066      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5067      "URI includes query"
5068      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5069    </t>
5070    <t>
5071      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5072      "No close on 1xx responses"
5073      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5074    </t>
5075    <t>
5076      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5077      "Remove 'identity' token references"
5078      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5079    </t>
5080    <t>
5081      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5082      "Import query BNF"
5083    </t>
5084    <t>
5085      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5086      "qdtext BNF"
5087    </t>
5088    <t>
5089      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5090      "Normative and Informative references"
5091    </t>
5092    <t>
5093      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5094      "RFC2606 Compliance"
5095    </t>
5096    <t>
5097      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5098      "RFC977 reference"
5099    </t>
5100    <t>
5101      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5102      "RFC1700 references"
5103    </t>
5104    <t>
5105      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5106      "inconsistency in date format explanation"
5107    </t>
5108    <t>
5109      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5110      "Date reference typo"
5111    </t>
5112    <t>
5113      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5114      "Informative references"
5115    </t>
5116    <t>
5117      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5118      "ISO-8859-1 Reference"
5119    </t>
5120    <t>
5121      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5122      "Normative up-to-date references"
5123    </t>
5124  </list>
5125</t>
5126<t>
5127  Other changes:
5128  <list style="symbols"> 
5129    <t>
5130      Update media type registrations to use RFC4288 template.
5131    </t>
5132    <t>
5133      Use names of RFC4234 core rules DQUOTE and WSP,
5134      fix broken ABNF for chunk-data
5135      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5136    </t>
5137  </list>
5138</t>
5139</section>
5140
5141<section title="Since draft-ietf-httpbis-p1-messaging-01">
5142<t>
5143  Closed issues:
5144  <list style="symbols"> 
5145    <t>
5146      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5147      "Bodies on GET (and other) requests"
5148    </t>
5149    <t>
5150      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5151      "Updating to RFC4288"
5152    </t>
5153    <t>
5154      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5155      "Status Code and Reason Phrase"
5156    </t>
5157    <t>
5158      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5159      "rel_path not used"
5160    </t>
5161  </list>
5162</t>
5163<t>
5164  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5165  <list style="symbols"> 
5166    <t>
5167      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5168      "trailer-part").
5169    </t>
5170    <t>
5171      Avoid underscore character in rule names ("http_URL" ->
5172      "http-URL", "abs_path" -> "path-absolute").
5173    </t>
5174    <t>
5175      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5176      "path-absolute", "port", "query", "relativeURI", "host) -- these will
5177      have to be updated when switching over to RFC3986.
5178    </t>
5179    <t>
5180      Synchronize core rules with RFC5234.
5181    </t>
5182    <t>
5183      Get rid of prose rules that span multiple lines.
5184    </t>
5185    <t>
5186      Get rid of unused rules LOALPHA and UPALPHA.
5187    </t>
5188    <t>
5189      Move "Product Tokens" section (back) into Part 1, as "token" is used
5190      in the definition of the Upgrade header.
5191    </t>
5192    <t>
5193      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5194    </t>
5195    <t>
5196      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5197    </t>
5198  </list>
5199</t>
5200</section>
5201
5202<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5203<t>
5204  Closed issues:
5205  <list style="symbols"> 
5206    <t>
5207      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5208      "HTTP-date vs. rfc1123-date"
5209    </t>
5210    <t>
5211      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5212      "WS in quoted-pair"
5213    </t>
5214  </list>
5215</t>
5216<t>
5217  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5218  <list style="symbols"> 
5219    <t>
5220      Reference RFC 3984, and update header registrations for headers defined
5221      in this document.
5222    </t>
5223  </list>
5224</t>
5225<t>
5226  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5227  <list style="symbols"> 
5228    <t>
5229      Replace string literals when the string really is case-sensitive (HTTP-Version).
5230    </t>
5231  </list>
5232</t>
5233</section>
5234
5235<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5236<t>
5237  Closed issues:
5238  <list style="symbols"> 
5239    <t>
5240      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5241      "Connection closing"
5242    </t>
5243    <t>
5244      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5245      "Move registrations and registry information to IANA Considerations"
5246    </t>
5247    <t>
5248      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5249      "need new URL for PAD1995 reference"
5250    </t>
5251    <t>
5252      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5253      "IANA Considerations: update HTTP URI scheme registration"
5254    </t>
5255    <t>
5256      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5257      "Cite HTTPS URI scheme definition"
5258    </t>
5259    <t>
5260      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5261      "List-type headers vs Set-Cookie"
5262    </t>
5263  </list>
5264</t>
5265<t>
5266  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5267  <list style="symbols"> 
5268    <t>
5269      Replace string literals when the string really is case-sensitive (HTTP-Date).
5270    </t>
5271    <t>
5272      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5273    </t>
5274  </list>
5275</t>
5276</section>
5277
5278<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5279<t>
5280  Closed issues:
5281  <list style="symbols"> 
5282    <t>
5283      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5284      "Out-of-date reference for URIs"
5285    </t>
5286    <t>
5287      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5288      "RFC 2822 is updated by RFC 5322"
5289    </t>
5290  </list>
5291</t>
5292<t>
5293  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5294  <list style="symbols"> 
5295    <t>
5296      Use "/" instead of "|" for alternatives.
5297    </t>
5298    <t>
5299      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5300    </t>
5301    <t>
5302      Only reference RFC 5234's core rules.
5303    </t>
5304    <t>
5305      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5306      whitespace ("OWS") and required whitespace ("RWS").
5307    </t>
5308    <t>
5309      Rewrite ABNFs to spell out whitespace rules, factor out
5310      header value format definitions.
5311    </t>
5312  </list>
5313</t>
5314</section>
5315
5316<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5317<t>
5318  Closed issues:
5319  <list style="symbols"> 
5320    <t>
5321      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5322      "Header LWS"
5323    </t>
5324    <t>
5325      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5326      "Sort 1.3 Terminology"
5327    </t>
5328    <t>
5329      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5330      "RFC2047 encoded words"
5331    </t>
5332    <t>
5333      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5334      "Character Encodings in TEXT"
5335    </t>
5336    <t>
5337      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5338      "Line Folding"
5339    </t>
5340    <t>
5341      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5342      "OPTIONS * and proxies"
5343    </t>
5344    <t>
5345      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5346      "Reason-Phrase BNF"
5347    </t>
5348    <t>
5349      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5350      "Use of TEXT"
5351    </t>
5352    <t>
5353      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5354      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5355    </t>
5356    <t>
5357      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5358      "RFC822 reference left in discussion of date formats"
5359    </t>
5360  </list>
5361</t>
5362<t>
5363  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5364  <list style="symbols"> 
5365    <t>
5366      Rewrite definition of list rules, deprecate empty list elements.
5367    </t>
5368    <t>
5369      Add appendix containing collected and expanded ABNF.
5370    </t>
5371  </list>
5372</t>
5373<t>
5374  Other changes:
5375  <list style="symbols"> 
5376    <t>
5377      Rewrite introduction; add mostly new Architecture Section.
5378    </t>
5379    <t>
5380      Move definition of quality values from Part 3 into Part 1;
5381      make TE request header grammar independent of accept-params (defined in Part 3).
5382    </t>
5383  </list>
5384</t>
5385</section>
5386
5387<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5388<t>
5389  Closed issues:
5390  <list style="symbols"> 
5391    <t>
5392      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5393      "base for numeric protocol elements"
5394    </t>
5395    <t>
5396      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5397      "comment ABNF"
5398    </t>
5399  </list>
5400</t>
5401<t>
5402  Partly resolved issues:
5403  <list style="symbols"> 
5404    <t>
5405      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5406      "205 Bodies" (took out language that implied that there may be
5407      methods for which a request body MUST NOT be included)
5408    </t>
5409    <t>
5410      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5411      "editorial improvements around HTTP-date"
5412    </t>
5413  </list>
5414</t>
5415</section>
5416
5417<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5418<t>
5419  Closed issues:
5420  <list style="symbols"> 
5421    <t>
5422      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5423      "Repeating single-value headers"
5424    </t>
5425    <t>
5426      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5427      "increase connection limit"
5428    </t>
5429    <t>
5430      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5431      "IP addresses in URLs"
5432    </t>
5433    <t>
5434      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5435      "take over HTTP Upgrade Token Registry"
5436    </t>
5437    <t>
5438      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5439      "CR and LF in chunk extension values"
5440    </t>
5441    <t>
5442      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5443      "HTTP/0.9 support"
5444    </t>
5445    <t>
5446      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5447      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5448    </t>
5449    <t>
5450      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5451      "move definitions of gzip/deflate/compress to part 1"
5452    </t>
5453    <t>
5454      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5455      "disallow control characters in quoted-pair"
5456    </t>
5457  </list>
5458</t>
5459<t>
5460  Partly resolved issues:
5461  <list style="symbols"> 
5462    <t>
5463      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5464      "update IANA requirements wrt Transfer-Coding values" (add the
5465      IANA Considerations subsection)
5466    </t>
5467  </list>
5468</t>
5469</section>
5470
5471<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5472<t>
5473  Closed issues:
5474  <list style="symbols"> 
5475    <t>
5476      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5477      "header parsing, treatment of leading and trailing OWS"
5478    </t>
5479  </list>
5480</t>
5481<t>
5482  Partly resolved issues:
5483  <list style="symbols"> 
5484    <t>
5485      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5486      "Placement of 13.5.1 and 13.5.2"
5487    </t>
5488    <t>
5489      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5490      "use of term "word" when talking about header structure"
5491    </t>
5492  </list>
5493</t>
5494</section>
5495
5496</section>
5497
5498</back>
5499</rfc>
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