source: draft-ietf-httpbis/latest/p1-messaging.xml @ 738

Last change on this file since 738 was 738, checked in by julian.reschke@…, 10 years ago

Syntax notation: mention "obs-" prefix convention. List rule: clarify intro, add note about how empty list elements contribute to the total number of elements, add examples. Related to #36.

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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "December">
16  <!ENTITY ID-YEAR "2009">
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 header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38]>
39<?rfc toc="yes" ?>
40<?rfc symrefs="yes" ?>
41<?rfc sortrefs="yes" ?>
42<?rfc compact="yes"?>
43<?rfc subcompact="no" ?>
44<?rfc linkmailto="no" ?>
45<?rfc editing="no" ?>
46<?rfc comments="yes"?>
47<?rfc inline="yes"?>
48<?rfc-ext allow-markup-in-artwork="yes" ?>
49<?rfc-ext include-references-in-index="yes" ?>
50<rfc obsoletes="2616" updates="2817" category="std" x:maturity-level="draft"
51     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
52     xmlns:x='http://purl.org/net/xml2rfc/ext'>
53<front>
54
55  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
56
57  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
58    <organization abbrev="Day Software">Day Software</organization>
59    <address>
60      <postal>
61        <street>23 Corporate Plaza DR, Suite 280</street>
62        <city>Newport Beach</city>
63        <region>CA</region>
64        <code>92660</code>
65        <country>USA</country>
66      </postal>
67      <phone>+1-949-706-5300</phone>
68      <facsimile>+1-949-706-5305</facsimile>
69      <email>fielding@gbiv.com</email>
70      <uri>http://roy.gbiv.com/</uri>
71    </address>
72  </author>
73
74  <author initials="J." surname="Gettys" fullname="Jim Gettys">
75    <organization>One Laptop per Child</organization>
76    <address>
77      <postal>
78        <street>21 Oak Knoll Road</street>
79        <city>Carlisle</city>
80        <region>MA</region>
81        <code>01741</code>
82        <country>USA</country>
83      </postal>
84      <email>jg@laptop.org</email>
85      <uri>http://www.laptop.org/</uri>
86    </address>
87  </author>
88 
89  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
90    <organization abbrev="HP">Hewlett-Packard Company</organization>
91    <address>
92      <postal>
93        <street>HP Labs, Large Scale Systems Group</street>
94        <street>1501 Page Mill Road, MS 1177</street>
95        <city>Palo Alto</city>
96        <region>CA</region>
97        <code>94304</code>
98        <country>USA</country>
99      </postal>
100      <email>JeffMogul@acm.org</email>
101    </address>
102  </author>
103
104  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
105    <organization abbrev="Microsoft">Microsoft Corporation</organization>
106    <address>
107      <postal>
108        <street>1 Microsoft Way</street>
109        <city>Redmond</city>
110        <region>WA</region>
111        <code>98052</code>
112        <country>USA</country>
113      </postal>
114      <email>henrikn@microsoft.com</email>
115    </address>
116  </author>
117
118  <author initials="L." surname="Masinter" fullname="Larry Masinter">
119    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
120    <address>
121      <postal>
122        <street>345 Park Ave</street>
123        <city>San Jose</city>
124        <region>CA</region>
125        <code>95110</code>
126        <country>USA</country>
127      </postal>
128      <email>LMM@acm.org</email>
129      <uri>http://larry.masinter.net/</uri>
130    </address>
131  </author>
132 
133  <author initials="P." surname="Leach" fullname="Paul J. Leach">
134    <organization abbrev="Microsoft">Microsoft Corporation</organization>
135    <address>
136      <postal>
137        <street>1 Microsoft Way</street>
138        <city>Redmond</city>
139        <region>WA</region>
140        <code>98052</code>
141      </postal>
142      <email>paulle@microsoft.com</email>
143    </address>
144  </author>
145   
146  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
147    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
148    <address>
149      <postal>
150        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
151        <street>The Stata Center, Building 32</street>
152        <street>32 Vassar Street</street>
153        <city>Cambridge</city>
154        <region>MA</region>
155        <code>02139</code>
156        <country>USA</country>
157      </postal>
158      <email>timbl@w3.org</email>
159      <uri>http://www.w3.org/People/Berners-Lee/</uri>
160    </address>
161  </author>
162
163  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
164    <organization abbrev="W3C">World Wide Web Consortium</organization>
165    <address>
166      <postal>
167        <street>W3C / ERCIM</street>
168        <street>2004, rte des Lucioles</street>
169        <city>Sophia-Antipolis</city>
170        <region>AM</region>
171        <code>06902</code>
172        <country>France</country>
173      </postal>
174      <email>ylafon@w3.org</email>
175      <uri>http://www.raubacapeu.net/people/yves/</uri>
176    </address>
177  </author>
178
179  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
180    <organization abbrev="greenbytes">greenbytes GmbH</organization>
181    <address>
182      <postal>
183        <street>Hafenweg 16</street>
184        <city>Muenster</city><region>NW</region><code>48155</code>
185        <country>Germany</country>
186      </postal>
187      <phone>+49 251 2807760</phone>
188      <facsimile>+49 251 2807761</facsimile>
189      <email>julian.reschke@greenbytes.de</email>
190      <uri>http://greenbytes.de/tech/webdav/</uri>
191    </address>
192  </author>
193
194  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
195  <workgroup>HTTPbis Working Group</workgroup>
196
197<abstract>
198<t>
199   The Hypertext Transfer Protocol (HTTP) is an application-level
200   protocol for distributed, collaborative, hypertext information
201   systems. HTTP has been in use by the World Wide Web global information
202   initiative since 1990. This document is Part 1 of the seven-part specification
203   that defines the protocol referred to as "HTTP/1.1" and, taken together,
204   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
205   its associated terminology, defines the "http" and "https" Uniform
206   Resource Identifier (URI) schemes, defines the generic message syntax
207   and parsing requirements for HTTP message frames, and describes
208   general security concerns for implementations.
209</t>
210</abstract>
211
212<note title="Editorial Note (To be removed by RFC Editor)">
213  <t>
214    Discussion of this draft should take place on the HTTPBIS working group
215    mailing list (ietf-http-wg@w3.org). The current issues list is
216    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
217    and related documents (including fancy diffs) can be found at
218    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
219  </t>
220  <t>
221    The changes in this draft are summarized in <xref target="changes.since.08"/>.
222  </t>
223</note>
224</front>
225<middle>
226<section title="Introduction" anchor="introduction">
227<t>
228   The Hypertext Transfer Protocol (HTTP) is an application-level
229   request/response protocol that uses extensible semantics and MIME-like
230   message payloads for flexible interaction with network-based hypertext
231   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
232   standard <xref target="RFC3986"/> to indicate request targets and
233   relationships between resources.
234   Messages are passed in a format similar to that used by Internet mail
235   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
236   (MIME) <xref target="RFC2045"/> (see &diff2045entity; for the differences
237   between HTTP and MIME messages).
238</t>
239<t>
240   HTTP is a generic interface protocol for information systems. It is
241   designed to hide the details of how a service is implemented by presenting
242   a uniform interface to clients that is independent of the types of
243   resources provided. Likewise, servers do not need to be aware of each
244   client's purpose: an HTTP request can be considered in isolation rather
245   than being associated with a specific type of client or a predetermined
246   sequence of application steps. The result is a protocol that can be used
247   effectively in many different contexts and for which implementations can
248   evolve independently over time.
249</t>
250<t>
251   HTTP is also designed for use as a generic protocol for translating
252   communication to and from other Internet information systems.
253   HTTP proxies and gateways provide access to alternative information
254   services by translating their diverse protocols into a hypertext
255   format that can be viewed and manipulated by clients in the same way
256   as HTTP services.
257</t>
258<t>
259   One consequence of HTTP flexibility is that the protocol cannot be
260   defined in terms of what occurs behind the interface. Instead, we
261   are limited to defining the syntax of communication, the intent
262   of received communication, and the expected behavior of recipients.
263   If the communication is considered in isolation, then successful
264   actions should be reflected in corresponding changes to the
265   observable interface provided by servers. However, since multiple
266   clients may act in parallel and perhaps at cross-purposes, we
267   cannot require that such changes be observable beyond the scope
268   of a single response.
269</t>
270<t>
271   This document is Part 1 of the seven-part specification of HTTP,
272   defining the protocol referred to as "HTTP/1.1" and obsoleting
273   <xref target="RFC2616"/>.
274   Part 1 describes the architectural elements that are used or
275   referred to in HTTP, defines the "http" and "https" URI schemes,
276   describes overall network operation and connection management,
277   and defines HTTP message framing and forwarding requirements.
278   Our goal is to define all of the mechanisms necessary for HTTP message
279   handling that are independent of message semantics, thereby defining the
280   complete set of requirements for message parsers and
281   message-forwarding intermediaries.
282</t>
283
284<section title="Requirements" anchor="intro.requirements">
285<t>
286   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
287   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
288   document are to be interpreted as described in <xref target="RFC2119"/>.
289</t>
290<t>
291   An implementation is not compliant if it fails to satisfy one or more
292   of the &MUST; or &REQUIRED; level requirements for the protocols it
293   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
294   level and all the &SHOULD; level requirements for its protocols is said
295   to be "unconditionally compliant"; one that satisfies all the &MUST;
296   level requirements but not all the &SHOULD; level requirements for its
297   protocols is said to be "conditionally compliant."
298</t>
299</section>
300
301<section title="Syntax Notation" anchor="notation">
302<iref primary="true" item="Grammar" subitem="ALPHA"/>
303<iref primary="true" item="Grammar" subitem="CR"/>
304<iref primary="true" item="Grammar" subitem="CRLF"/>
305<iref primary="true" item="Grammar" subitem="CTL"/>
306<iref primary="true" item="Grammar" subitem="DIGIT"/>
307<iref primary="true" item="Grammar" subitem="DQUOTE"/>
308<iref primary="true" item="Grammar" subitem="HEXDIG"/>
309<iref primary="true" item="Grammar" subitem="LF"/>
310<iref primary="true" item="Grammar" subitem="OCTET"/>
311<iref primary="true" item="Grammar" subitem="SP"/>
312<iref primary="true" item="Grammar" subitem="VCHAR"/>
313<iref primary="true" item="Grammar" subitem="WSP"/>
314<t>
315   This specification uses the Augmented Backus-Naur Form (ABNF) notation
316   of <xref target="RFC5234"/>.
317</t>
318<t anchor="core.rules">
319  <x:anchor-alias value="ALPHA"/>
320  <x:anchor-alias value="CTL"/>
321  <x:anchor-alias value="CR"/>
322  <x:anchor-alias value="CRLF"/>
323  <x:anchor-alias value="DIGIT"/>
324  <x:anchor-alias value="DQUOTE"/>
325  <x:anchor-alias value="HEXDIG"/>
326  <x:anchor-alias value="LF"/>
327  <x:anchor-alias value="OCTET"/>
328  <x:anchor-alias value="SP"/>
329  <x:anchor-alias value="VCHAR"/>
330  <x:anchor-alias value="WSP"/>
331   The following core rules are included by
332   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
333   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
334   DIGIT (decimal 0-9), DQUOTE (double quote),
335   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
336   OCTET (any 8-bit sequence of data), SP (space),
337   VCHAR (any visible <xref target="USASCII"/> character),
338   and WSP (whitespace).
339</t>
340<t>
341   As a syntactical convention, ABNF rule names prefixed with "obs-" denote
342   "obsolete" grammar rules that appear for historical reasons.
343</t>
344
345<section title="ABNF Extension: #rule" anchor="notation.abnf">
346<t>
347  The #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
348  improve readability.
349</t>
350<t>
351  A construct "#" is defined, similar to "*", for defining comma-delimited
352  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
353  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
354  comma (",") and optional whitespace (OWS,
355  <xref target="basic.rules"/>).   
356</t>
357<figure><preamble>
358  Thus,
359</preamble><artwork type="example">
360  1#element =&gt; element *( OWS "," OWS element )
361</artwork></figure>
362<figure><preamble>
363  and:
364</preamble><artwork type="example">
365  #element =&gt; [ 1#element ]
366</artwork></figure>
367<figure><preamble>
368  and for n &gt;= 1 and m &gt; 1:
369</preamble><artwork type="example">
370  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
371</artwork></figure>
372<t>
373  For compatibility with legacy list rules, recipients &SHOULD; accept empty
374  list elements. In other words, consumers would follow the list productions:
375</t>
376<figure><artwork type="example">
377  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
378 
379  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
380</artwork></figure>
381<t>
382  Note that empty elements do not contribute to the count of elements present,
383  though.
384</t>
385<t>
386  For example, given these ABNF productions:
387</t>
388<figure><artwork type="example">
389  example-list      = 1#example-list-elmt
390  example-list-elmt = token ; see <xref target="basic.rules"/> 
391</artwork></figure>
392<t>
393  Then these are valid values for example-list (not including the double
394  quotes, which are present for delimitation only):
395</t>
396<figure><artwork type="example">
397  "foo,bar"
398  " foo ,bar,"
399  "  foo , ,bar,charlie   "
400  "foo ,bar,   charlie "
401</artwork></figure>
402<t>
403  But these values would be invalid, as at least one non-empty element is
404  required:
405</t>
406<figure><artwork type="example">
407  ""
408  ","
409  ",   ,"
410</artwork></figure>
411<t>
412  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
413  expanded as explained above.
414</t>
415</section>
416
417<section title="Basic Rules" anchor="basic.rules">
418<t anchor="rule.CRLF">
419  <x:anchor-alias value="CRLF"/>
420   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
421   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
422   tolerant applications). The end-of-line marker within an entity-body
423   is defined by its associated media type, as described in &media-types;.
424</t>
425<t anchor="rule.LWS">
426   This specification uses three rules to denote the use of linear
427   whitespace: OWS (optional whitespace), RWS (required whitespace), and
428   BWS ("bad" whitespace).
429</t>
430<t>
431   The OWS rule is used where zero or more linear whitespace characters may
432   appear. OWS &SHOULD; either not be produced or be produced as a single SP
433   character. Multiple OWS characters that occur within field-content &SHOULD;
434   be replaced with a single SP before interpreting the field value or
435   forwarding the message downstream.
436</t>
437<t>
438   RWS is used when at least one linear whitespace character is required to
439   separate field tokens. RWS &SHOULD; be produced as a single SP character.
440   Multiple RWS characters that occur within field-content &SHOULD; be
441   replaced with a single SP before interpreting the field value or
442   forwarding the message downstream.
443</t>
444<t>
445   BWS is used where the grammar allows optional whitespace for historical
446   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
447   recipients &MUST; accept such bad optional whitespace and remove it before
448   interpreting the field value or forwarding the message downstream.
449</t>
450<t anchor="rule.whitespace">
451  <x:anchor-alias value="BWS"/>
452  <x:anchor-alias value="OWS"/>
453  <x:anchor-alias value="RWS"/>
454  <x:anchor-alias value="obs-fold"/>
455</t>
456<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="OWS"/><iref primary="true" item="Grammar" subitem="RWS"/><iref primary="true" item="Grammar" subitem="BWS"/>
457  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
458                 ; "optional" whitespace
459  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
460                 ; "required" whitespace
461  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
462                 ; "bad" whitespace
463  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
464                 ; see <xref target="header.fields"/>
465</artwork></figure>
466<t anchor="rule.token.separators">
467  <x:anchor-alias value="tchar"/>
468  <x:anchor-alias value="token"/>
469   Many HTTP/1.1 header field values consist of words separated by whitespace
470   or special characters. These special characters &MUST; be in a quoted
471   string to be used within a parameter value (as defined in
472   <xref target="transfer.codings"/>).
473</t>
474<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/>
475  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
476                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
477                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
478                 
479  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
480</artwork></figure>
481<t anchor="rule.quoted-string">
482  <x:anchor-alias value="quoted-string"/>
483  <x:anchor-alias value="qdtext"/>
484  <x:anchor-alias value="obs-text"/>
485   A string of text is parsed as a single word if it is quoted using
486   double-quote marks.
487</t>
488<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"/>
489  <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>
490  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
491                 ; <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> 
492  <x:ref>obs-text</x:ref>       = %x80-FF
493</artwork></figure>
494<t anchor="rule.quoted-pair">
495  <x:anchor-alias value="quoted-pair"/>
496   The backslash character ("\") can be used as a single-character
497   quoting mechanism within quoted-string constructs:
498</t>
499<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
500  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
501</artwork></figure>
502<t>
503   Producers &SHOULD-NOT; escape characters that do not require escaping
504   (i.e., other than DQUOTE and the backslash character).
505</t>
506</section>
507
508<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
509  <x:anchor-alias value="request-header"/>
510  <x:anchor-alias value="response-header"/>
511  <x:anchor-alias value="entity-body"/>
512  <x:anchor-alias value="entity-header"/>
513  <x:anchor-alias value="Cache-Control"/>
514  <x:anchor-alias value="Pragma"/>
515  <x:anchor-alias value="Warning"/>
516<t>
517  The ABNF rules below are defined in other parts:
518</t>
519<figure><!-- Part2--><artwork type="abnf2616">
520  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
521  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
522</artwork></figure>
523<figure><!-- Part3--><artwork type="abnf2616">
524  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
525  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
526</artwork></figure>
527<figure><!-- Part6--><artwork type="abnf2616">
528  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
529  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
530  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
531</artwork></figure>
532</section>
533
534</section>
535</section>
536
537<section title="HTTP architecture" anchor="architecture">
538<t>
539   HTTP was created for the World Wide Web architecture
540   and has evolved over time to support the scalability needs of a worldwide
541   hypertext system. Much of that architecture is reflected in the terminology
542   and syntax productions used to define HTTP.
543</t>
544
545<section title="Client/Server Operation" anchor="operation">
546<iref item="client"/>
547<iref item="server"/>
548<iref item="connection"/>
549<t>
550   HTTP is a request/response protocol that operates by exchanging messages
551   across a reliable transport or session-layer connection. An HTTP client
552   is a program that establishes a connection to a server for the purpose
553   of sending one or more HTTP requests.  An HTTP server is a program that
554   accepts connections in order to service HTTP requests by sending HTTP
555   responses.
556</t>
557<iref item="user agent"/>
558<iref item="origin server"/>
559<t>
560   Note that the terms "client" and "server" refer only to the roles that
561   these programs perform for a particular connection.  The same program
562   may act as a client on some connections and a server on others.  We use
563   the term "user agent" to refer to the program that initiates a request,
564   such as a WWW browser, editor, or spider (web-traversing robot), and
565   the term "origin server" to refer to the program that can originate
566   authoritative responses to a request.
567</t>
568<t>
569   Most HTTP communication consists of a retrieval request (GET) for
570   a representation of some resource identified by a URI.  In the
571   simplest case, this may be accomplished via a single connection (v)
572   between the user agent (UA) and the origin server (O).
573</t>
574<figure><artwork type="drawing">
575       request chain ------------------------&gt;
576    UA -------------------v------------------- O
577       &lt;----------------------- response chain
578</artwork></figure>
579<iref item="message"/>
580<iref item="request"/>
581<iref item="response"/>
582<t>
583   A client sends an HTTP request to the server in the form of a request
584   message (<xref target="request"/>), beginning with a method, URI, and
585   protocol version, followed by MIME-like header fields containing
586   request modifiers, client information, and payload metadata, an empty
587   line to indicate the end of the header section, and finally the payload
588   body (if any).
589</t>
590<t>
591   A server responds to the client's request by sending an HTTP response
592   message (<xref target="response"/>), beginning with a status line that
593   includes the protocol version, a success or error code, and textual
594   reason phrase, followed by MIME-like header fields containing server
595   information, resource metadata, and payload metadata, an empty line to
596   indicate the end of the header section, and finally the payload body (if any).
597</t>
598<t>
599   The following example illustrates a typical message exchange for a
600   GET request on the URI "http://www.example.com/hello.txt":
601</t>
602<figure><preamble>
603client request:
604</preamble><artwork  type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
605GET /hello.txt HTTP/1.1
606User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
607Host: www.example.com
608Accept: */*
609
610</artwork></figure>
611<figure><preamble>
612server response:
613</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
614HTTP/1.1 200 OK
615Date: Mon, 27 Jul 2009 12:28:53 GMT
616Server: Apache
617Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
618ETag: "34aa387-d-1568eb00"
619Accept-Ranges: bytes
620Content-Length: <x:length-of target="exbody"/>
621Vary: Accept-Encoding
622Content-Type: text/plain
623
624<x:span anchor="exbody">Hello World!
625</x:span></artwork></figure>
626</section>
627
628<section title="Intermediaries" anchor="intermediaries">
629<t>
630   A more complicated situation occurs when one or more intermediaries
631   are present in the request/response chain. There are three common
632   forms of intermediary: proxy, gateway, and tunnel.  In some cases,
633   a single intermediary may act as an origin server, proxy, gateway,
634   or tunnel, switching behavior based on the nature of each request.
635</t>
636<figure><artwork type="drawing">
637       request chain --------------------------------------&gt;
638    UA -----v----- A -----v----- B -----v----- C -----v----- O
639       &lt;------------------------------------- response chain
640</artwork></figure>
641<t>
642   The figure above shows three intermediaries (A, B, and C) between the
643   user agent and origin server. A request or response message that
644   travels the whole chain will pass through four separate connections.
645   Some HTTP communication options
646   may apply only to the connection with the nearest, non-tunnel
647   neighbor, only to the end-points of the chain, or to all connections
648   along the chain. Although the diagram is linear, each participant may
649   be engaged in multiple, simultaneous communications. For example, B
650   may be receiving requests from many clients other than A, and/or
651   forwarding requests to servers other than C, at the same time that it
652   is handling A's request.
653</t>
654<t>
655<iref item="upstream"/><iref item="downstream"/>
656<iref item="inbound"/><iref item="outbound"/>
657   We use the terms "upstream" and "downstream" to describe various
658   requirements in relation to the directional flow of a message:
659   all messages flow from upstream to downstream.
660   Likewise, we use the terms "inbound" and "outbound" to refer to
661   directions in relation to the request path: "inbound" means toward
662   the origin server and "outbound" means toward the user agent.
663</t>
664<t><iref item="proxy"/>
665   A proxy is a message forwarding agent that is selected by the
666   client, usually via local configuration rules, to receive requests
667   for some type(s) of absolute URI and attempt to satisfy those
668   requests via translation through the HTTP interface.  Some translations
669   are minimal, such as for proxy requests for "http" URIs, whereas
670   other requests may require translation to and from entirely different
671   application-layer protocols. Proxies are often used to group an
672   organization's HTTP requests through a common intermediary for the
673   sake of security, annotation services, or shared caching.
674</t>
675<t><iref item="gateway"/><iref item="reverse proxy"/>
676   A gateway (a.k.a., reverse proxy) is a receiving agent that acts
677   as a layer above some other server(s) and translates the received
678   requests to the underlying server's protocol.  Gateways are often
679   used for load balancing or partitioning HTTP services across
680   multiple machines.
681   Unlike a proxy, a gateway receives requests as if it were the
682   origin server for the requested resource; the requesting client
683   will not be aware that it is communicating with a gateway.
684   A gateway communicates with the client as if the gateway is the
685   origin server and thus is subject to all of the requirements on
686   origin servers for that connection.  A gateway communicates
687   with inbound servers using any protocol it desires, including
688   private extensions to HTTP that are outside the scope of this
689   specification.
690</t>
691<t><iref item="tunnel"/>
692   A tunnel acts as a blind relay between two connections
693   without changing the messages. Once active, a tunnel is not
694   considered a party to the HTTP communication, though the tunnel may
695   have been initiated by an HTTP request. A tunnel ceases to exist when
696   both ends of the relayed connection are closed. Tunnels are used to
697   extend a virtual connection through an intermediary, such as when
698   transport-layer security is used to establish private communication
699   through a shared firewall proxy.
700</t>
701</section>
702
703<section title="Caches" anchor="caches">
704<iref item="cache"/>
705<t>
706   Any party to HTTP communication that is not acting as a tunnel may
707   employ an internal cache for handling requests.
708   A cache is a local store of previous response messages and the
709   subsystem that controls its message storage, retrieval, and deletion.
710   A cache stores cacheable responses in order to reduce the response
711   time and network bandwidth consumption on future, equivalent
712   requests. Any client or server may include a cache, though a cache
713   cannot be used by a server while it is acting as a tunnel.
714</t>
715<t>
716   The effect of a cache is that the request/response chain is shortened
717   if one of the participants along the chain has a cached response
718   applicable to that request. The following illustrates the resulting
719   chain if B has a cached copy of an earlier response from O (via C)
720   for a request which has not been cached by UA or A.
721</t>
722<figure><artwork type="drawing">
723          request chain ----------&gt;
724       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
725          &lt;--------- response chain
726</artwork></figure>
727<t><iref item="cacheable"/>
728   A response is cacheable if a cache is allowed to store a copy of
729   the response message for use in answering subsequent requests.
730   Even when a response is cacheable, there may be additional
731   constraints placed by the client or by the origin server on when
732   that cached response can be used for a particular request. HTTP
733   requirements for cache behavior and cacheable responses are
734   defined in &caching-overview;
735</t>
736<t>
737   There are a wide variety of architectures and configurations
738   of caches and proxies deployed across the World Wide Web and
739   inside large organizations. These systems include national hierarchies
740   of proxy caches to save transoceanic bandwidth, systems that
741   broadcast or multicast cache entries, organizations that distribute
742   subsets of cached data via optical media, and so on.
743</t>
744</section>
745
746<section title="Transport Independence" anchor="transport-independence">
747<t>
748  HTTP systems are used in a wide variety of environments, from
749  corporate intranets with high-bandwidth links to long-distance
750  communication over low-power radio links and intermittent connectivity.
751</t>
752<t>
753   HTTP communication usually takes place over TCP/IP connections. The
754   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
755   not preclude HTTP from being implemented on top of any other protocol
756   on the Internet, or on other networks. HTTP only presumes a reliable
757   transport; any protocol that provides such guarantees can be used;
758   the mapping of the HTTP/1.1 request and response structures onto the
759   transport data units of the protocol in question is outside the scope
760   of this specification.
761</t>
762<t>
763   In HTTP/1.0, most implementations used a new connection for each
764   request/response exchange. In HTTP/1.1, a connection may be used for
765   one or more request/response exchanges, although connections may be
766   closed for a variety of reasons (see <xref target="persistent.connections"/>).
767</t>
768</section>
769
770<section title="HTTP Version" anchor="http.version">
771  <x:anchor-alias value="HTTP-Version"/>
772  <x:anchor-alias value="HTTP-Prot-Name"/>
773<t>
774   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
775   of the protocol. The protocol versioning policy is intended to allow
776   the sender to indicate the format of a message and its capacity for
777   understanding further HTTP communication, rather than the features
778   obtained via that communication. No change is made to the version
779   number for the addition of message components which do not affect
780   communication behavior or which only add to extensible field values.
781   The &lt;minor&gt; number is incremented when the changes made to the
782   protocol add features which do not change the general message parsing
783   algorithm, but which may add to the message semantics and imply
784   additional capabilities of the sender. The &lt;major&gt; number is
785   incremented when the format of a message within the protocol is
786   changed. See <xref target="RFC2145"/> for a fuller explanation.
787</t>
788<t>
789   The version of an HTTP message is indicated by an HTTP-Version field
790   in the first line of the message. HTTP-Version is case-sensitive.
791</t>
792<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
793  <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>
794  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
795</artwork></figure>
796<t>
797   Note that the major and minor numbers &MUST; be treated as separate
798   integers and that each &MAY; be incremented higher than a single digit.
799   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
800   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
801   &MUST-NOT; be sent.
802</t>
803<t>
804   An application that sends a request or response message that includes
805   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
806   with this specification. Applications that are at least conditionally
807   compliant with this specification &SHOULD; use an HTTP-Version of
808   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
809   not compatible with HTTP/1.0. For more details on when to send
810   specific HTTP-Version values, see <xref target="RFC2145"/>.
811</t>
812<t>
813   The HTTP version of an application is the highest HTTP version for
814   which the application is at least conditionally compliant.
815</t>
816<t>
817   Proxy and gateway applications need to be careful when forwarding
818   messages in protocol versions different from that of the application.
819   Since the protocol version indicates the protocol capability of the
820   sender, a proxy/gateway &MUST-NOT; send a message with a version
821   indicator which is greater than its actual version. If a higher
822   version request is received, the proxy/gateway &MUST; either downgrade
823   the request version, or respond with an error, or switch to tunnel
824   behavior.
825</t>
826<t>
827   Due to interoperability problems with HTTP/1.0 proxies discovered
828   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
829   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
830   they support. The proxy/gateway's response to that request &MUST; be in
831   the same major version as the request.
832</t>
833<x:note>
834  <t>
835    <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
836    of header fields required or forbidden by the versions involved.
837  </t>
838</x:note>
839</section>
840
841<section title="Uniform Resource Identifiers" anchor="uri">
842<iref primary="true" item="resource"/>
843<t>
844   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
845   throughout HTTP as the means for identifying resources. URI references
846   are used to target requests, indicate redirects, and define relationships.
847   HTTP does not limit what a resource may be; it merely defines an interface
848   that can be used to interact with a resource via HTTP. More information on
849   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
850</t>
851  <x:anchor-alias value="URI"/>
852  <x:anchor-alias value="URI-reference"/>
853  <x:anchor-alias value="absolute-URI"/>
854  <x:anchor-alias value="relative-part"/>
855  <x:anchor-alias value="authority"/>
856  <x:anchor-alias value="path-abempty"/>
857  <x:anchor-alias value="path-absolute"/>
858  <x:anchor-alias value="port"/>
859  <x:anchor-alias value="query"/>
860  <x:anchor-alias value="uri-host"/>
861  <x:anchor-alias value="partial-URI"/>
862<t>
863   This specification adopts the definitions of "URI-reference",
864   "absolute-URI", "relative-part", "port", "host",
865   "path-abempty", "path-absolute", "query", and "authority" from
866   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
867   protocol elements that allow a relative URI without a fragment.
868</t>
869<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"/>
870  <x:ref>URI</x:ref>           = &lt;URI, defined in <xref target="RFC3986" x:fmt="," x:sec="3"/>&gt;
871  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
872  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
873  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
874  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
875  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
876  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
877  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
878  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
879  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
880 
881  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
882</artwork></figure>
883<t>
884   Each protocol element in HTTP that allows a URI reference will indicate in
885   its ABNF production whether the element allows only a URI in absolute form
886   (absolute-URI), any relative reference (relative-ref), or some other subset
887   of the URI-reference grammar. Unless otherwise indicated, URI references
888   are parsed relative to the request target (the default base URI for both
889   the request and its corresponding response).
890</t>
891
892<section title="http URI scheme" anchor="http.uri">
893  <x:anchor-alias value="http-URI"/>
894  <iref item="http URI scheme" primary="true"/>
895  <iref item="URI scheme" subitem="http" primary="true"/>
896<t>
897   The "http" URI scheme is hereby defined for the purpose of minting
898   identifiers according to their association with the hierarchical
899   namespace governed by a potential HTTP origin server listening for
900   TCP connections on a given port.
901   The HTTP server is identified via the generic syntax's
902   <x:ref>authority</x:ref> component, which includes a host
903   identifier and optional TCP port, and the remainder of the URI is
904   considered to be identifying data corresponding to a resource for
905   which that server might provide an HTTP interface.
906</t>
907<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
908  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
909</artwork></figure>
910<t>
911   The host identifier within an <x:ref>authority</x:ref> component is
912   defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>.  If host is
913   provided as an IP literal or IPv4 address, then the HTTP server is any
914   listener on the indicated TCP port at that IP address. If host is a
915   registered name, then that name is considered an indirect identifier
916   and the recipient might use a name resolution service, such as DNS,
917   to find the address of a listener for that host.
918   The host &MUST-NOT; be empty; if an "http" URI is received with an
919   empty host, then it &MUST; be rejected as invalid.
920   If the port subcomponent is empty or not given, then TCP port 80 is
921   assumed (the default reserved port for WWW services).
922</t>
923<t>
924   Regardless of the form of host identifier, access to that host is not
925   implied by the mere presence of its name or address. The host may or may
926   not exist and, even when it does exist, may or may not be running an
927   HTTP server or listening to the indicated port. The "http" URI scheme
928   makes use of the delegated nature of Internet names and addresses to
929   establish a naming authority (whatever entity has the ability to place
930   an HTTP server at that Internet name or address) and allows that
931   authority to determine which names are valid and how they might be used.
932</t>
933<t>
934   When an "http" URI is used within a context that calls for access to the
935   indicated resource, a client &MAY; attempt access by resolving
936   the host to an IP address, establishing a TCP connection to that address
937   on the indicated port, and sending an HTTP request message to the server
938   containing the URI's identifying data as described in <xref target="request"/>.
939   If the server responds to that request with a non-interim HTTP response
940   message, as described in <xref target="response"/>, then that response
941   is considered an authoritative answer to the client's request.
942</t>
943<t>
944   Although HTTP is independent of the transport protocol, the "http"
945   scheme is specific to TCP-based services because the name delegation
946   process depends on TCP for establishing authority.
947   An HTTP service based on some other underlying connection protocol
948   would presumably be identified using a different URI scheme, just as
949   the "https" scheme (below) is used for servers that require an SSL/TLS
950   transport layer on a connection. Other protocols may also be used to
951   provide access to "http" identified resources --- it is only the
952   authoritative interface used for mapping the namespace that is
953   specific to TCP.
954</t>
955</section>
956
957<section title="https URI scheme" anchor="https.uri">
958   <x:anchor-alias value="https-URI"/>
959   <iref item="https URI scheme"/>
960   <iref item="URI scheme" subitem="https"/>
961<t>
962   The "https" URI scheme is hereby defined for the purpose of minting
963   identifiers according to their association with the hierarchical
964   namespace governed by a potential HTTP origin server listening for
965   SSL/TLS-secured connections on a given TCP port.
966   The host and port are determined in the same way
967   as for the "http" scheme, except that a default TCP port of 443
968   is assumed if the port subcomponent is empty or not given.
969</t>
970<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
971  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
972</artwork></figure>
973<t>
974   The primary difference between the "http" and "https" schemes is
975   that interaction with the latter is required to be secured for
976   privacy through the use of strong encryption. The URI cannot be
977   sent in a request until the connection is secure. Likewise, the
978   default for caching is that each response that would be considered
979   "public" under the "http" scheme is instead treated as "private"
980   and thus not eligible for shared caching.
981</t>
982<t>
983   The process for authoritative access to an "https" identified
984   resource is defined in <xref target="RFC2818"/>.
985</t>
986</section>
987
988<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
989<t>
990   Since the "http" and "https" schemes conform to the URI generic syntax,
991   such URIs are normalized and compared according to the algorithm defined
992   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
993   described above for each scheme.
994</t>
995<t>
996   If the port is equal to the default port for a scheme, the normal
997   form is to elide the port subcomponent. Likewise, an empty path
998   component is equivalent to an absolute path of "/", so the normal
999   form is to provide a path of "/" instead. The scheme and host
1000   are case-insensitive and normally provided in lowercase; all
1001   other components are compared in a case-sensitive manner.
1002   Characters other than those in the "reserved" set are equivalent
1003   to their percent-encoded octets (see <xref target="RFC3986"
1004   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1005</t>
1006<t>
1007   For example, the following three URIs are equivalent:
1008</t>
1009<figure><artwork type="example">
1010   http://example.com:80/~smith/home.html
1011   http://EXAMPLE.com/%7Esmith/home.html
1012   http://EXAMPLE.com:/%7esmith/home.html
1013</artwork></figure>
1014<t>
1015   <cref>[[This paragraph does not belong here. --Roy]]</cref>
1016   If path-abempty is the empty string (i.e., there is no slash "/"
1017   path separator following the authority), then the "http" URI
1018   &MUST; be given as "/" when
1019   used as a request-target (<xref target="request-target"/>). If a proxy
1020   receives a host name which is not a fully qualified domain name, it
1021   &MAY; add its domain to the host name it received. If a proxy receives
1022   a fully qualified domain name, the proxy &MUST-NOT; change the host
1023   name.
1024</t>
1025</section>
1026</section>
1027</section>
1028
1029<section title="HTTP Message" anchor="http.message">
1030<x:anchor-alias value="generic-message"/>
1031<x:anchor-alias value="message.types"/>
1032<x:anchor-alias value="HTTP-message"/>
1033<x:anchor-alias value="start-line"/>
1034<iref item="header section"/>
1035<iref item="headers"/>
1036<iref item="header field"/>
1037<t>
1038   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1039   characters in a format similar to the Internet Message Format
1040   <xref target="RFC5322"/>: zero or more header fields (collectively
1041   referred to as the "headers" or the "header section"), an empty line
1042   indicating the end of the header section, and an optional message-body.
1043</t>
1044<t>
1045   An HTTP message can either be a request from client to server or a
1046   response from server to client.  Syntactically, the two types of message
1047   differ only in the start-line, which is either a Request-Line (for requests)
1048   or a Status-Line (for responses), and in the algorithm for determining
1049   the length of the message-body (<xref target="message.length"/>).
1050   In theory, a client could receive requests and a server could receive
1051   responses, distinguishing them by their different start-line formats,
1052   but in practice servers are implemented to only expect a request
1053   (a response is interpreted as an unknown or invalid request method)
1054   and clients are implemented to only expect a response.
1055</t>
1056<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1057  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1058                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1059                    <x:ref>CRLF</x:ref>
1060                    [ <x:ref>message-body</x:ref> ]
1061  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1062</artwork></figure>
1063<t>
1064   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1065   header field. The presence of whitespace might be an attempt to trick a
1066   noncompliant implementation of HTTP into ignoring that field or processing
1067   the next line as a new request, either of which may result in security
1068   issues when implementations within the request chain interpret the
1069   same message differently. HTTP/1.1 servers &MUST; reject such a message
1070   with a 400 (Bad Request) response.
1071</t>
1072
1073<section title="Message Parsing Robustness" anchor="message.robustness">
1074<t>
1075   In the interest of robustness, servers &SHOULD; ignore at least one
1076   empty line received where a Request-Line is expected. In other words, if
1077   the server is reading the protocol stream at the beginning of a
1078   message and receives a CRLF first, it should ignore the CRLF.
1079</t>
1080<t>
1081   Some old HTTP/1.0 client implementations generate an extra CRLF
1082   after a POST request as a lame workaround for some early server
1083   applications that failed to read message-body content that was
1084   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1085   preface or follow a request with an extra CRLF.  If terminating
1086   the request message-body with a line-ending is desired, then the
1087   client &MUST; include the terminating CRLF octets as part of the
1088   message-body length.
1089</t>
1090<t>
1091   The normal procedure for parsing an HTTP message is to read the
1092   start-line into a structure, read each header field into a hash
1093   table by field name until the empty line, and then use the parsed
1094   data to determine if a message-body is expected.  If a message-body
1095   has been indicated, then it is read as a stream until an amount
1096   of OCTETs equal to the message-length is read or the connection
1097   is closed.  Care must be taken to parse an HTTP message as a sequence
1098   of OCTETs in an encoding that is a superset of US-ASCII.  Attempting
1099   to parse HTTP as a stream of Unicode characters in a character encoding
1100   like UTF-16 may introduce security flaws due to the differing ways
1101   that such parsers interpret invalid characters.
1102</t>
1103</section>
1104
1105<section title="Header Fields" anchor="header.fields">
1106  <x:anchor-alias value="header-field"/>
1107  <x:anchor-alias value="field-content"/>
1108  <x:anchor-alias value="field-name"/>
1109  <x:anchor-alias value="field-value"/>
1110  <x:anchor-alias value="OWS"/>
1111<t>
1112   Each HTTP header field consists of a case-insensitive field name
1113   followed by a colon (":"), optional whitespace, and the field value.
1114</t>
1115<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"/>
1116  <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>
1117  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1118  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1119  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1120</artwork></figure>
1121<t>
1122   No whitespace is allowed between the header field name and colon. For
1123   security reasons, any request message received containing such whitespace
1124   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1125   &MUST; remove any such whitespace from a response message before
1126   forwarding the message downstream.
1127</t>
1128<t>
1129   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1130   preferred. The field value does not include any leading or trailing white
1131   space: OWS occurring before the first non-whitespace character of the
1132   field value or after the last non-whitespace character of the field value
1133   is ignored and &SHOULD; be removed without changing the meaning of the header
1134   field.
1135</t>
1136<t>
1137   The order in which header fields with differing field names are
1138   received is not significant. However, it is "good practice" to send
1139   header fields that contain control data first, such as Host on
1140   requests and Date on responses, so that implementations can decide
1141   when not to handle a message as early as possible.  A server &MUST;
1142   wait until the entire header section is received before interpreting
1143   a request message, since later header fields might include conditionals,
1144   authentication credentials, or deliberately misleading duplicate
1145   header fields that would impact request processing.
1146</t>
1147<t>
1148   Multiple header fields with the same field name &MUST-NOT; be
1149   sent in a message unless the entire field value for that
1150   header field is defined as a comma-separated list [i.e., #(values)].
1151   Multiple header fields with the same field name can be combined into
1152   one "field-name: field-value" pair, without changing the semantics of the
1153   message, by appending each subsequent field value to the combined
1154   field value in order, separated by a comma. The order in which
1155   header fields with the same field name are received is therefore
1156   significant to the interpretation of the combined field value;
1157   a proxy &MUST-NOT; change the order of these field values when
1158   forwarding a message.
1159</t>
1160<x:note>
1161  <t>
1162   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1163   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1164   can occur multiple times, but does not use the list syntax, and thus cannot
1165   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1166   for details.) Also note that the Set-Cookie2 header specified in
1167   <xref target="RFC2965"/> does not share this problem.
1168  </t>
1169</x:note>
1170<t>
1171   Historically, HTTP header field values could be extended over multiple
1172   lines by preceding each extra line with at least one space or horizontal
1173   tab character (line folding). This specification deprecates such line
1174   folding except within the message/http media type
1175   (<xref target="internet.media.type.message.http"/>).
1176   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1177   (i.e., that contain any field-content that matches the obs-fold rule) unless
1178   the message is intended for packaging within the message/http media type.
1179   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1180   obs-fold whitespace with a single SP prior to interpreting the field value
1181   or forwarding the message downstream.
1182</t>
1183<t>
1184   Historically, HTTP has allowed field content with text in the ISO-8859-1
1185   <xref target="ISO-8859-1"/> character encoding and supported other
1186   character sets only through use of <xref target="RFC2047"/> encoding.
1187   In practice, most HTTP header field values use only a subset of the
1188   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1189   header fields &SHOULD; limit their field values to US-ASCII characters.
1190   Recipients &SHOULD; treat other (obs-text) octets in field content as
1191   opaque data.
1192</t>
1193<t anchor="rule.comment">
1194  <x:anchor-alias value="comment"/>
1195  <x:anchor-alias value="ctext"/>
1196   Comments can be included in some HTTP header fields by surrounding
1197   the comment text with parentheses. Comments are only allowed in
1198   fields containing "comment" as part of their field value definition.
1199</t>
1200<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1201  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1202  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1203                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1204</artwork></figure>
1205<t anchor="rule.quoted-cpair">
1206  <x:anchor-alias value="quoted-cpair"/>
1207   The backslash character ("\") can be used as a single-character
1208   quoting mechanism within comment constructs:
1209</t>
1210<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1211  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1212</artwork></figure>
1213<t>
1214   Producers &SHOULD-NOT; escape characters that do not require escaping
1215   (i.e., other than the backslash character "\" and the parentheses "(" and
1216   ")").
1217</t>
1218</section>
1219
1220<section title="Message Body" anchor="message.body">
1221  <x:anchor-alias value="message-body"/>
1222<t>
1223   The message-body (if any) of an HTTP message is used to carry the
1224   entity-body associated with the request or response. The message-body
1225   differs from the entity-body only when a transfer-coding has been
1226   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1227</t>
1228<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1229  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1230               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1231</artwork></figure>
1232<t>
1233   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1234   applied by an application to ensure safe and proper transfer of the
1235   message. Transfer-Encoding is a property of the message, not of the
1236   entity, and thus &MAY; be added or removed by any application along the
1237   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1238   when certain transfer-codings may be used.)
1239</t>
1240<t>
1241   The rules for when a message-body is allowed in a message differ for
1242   requests and responses.
1243</t>
1244<t>
1245   The presence of a message-body in a request is signaled by the
1246   inclusion of a Content-Length or Transfer-Encoding header field in
1247   the request's header fields.
1248   When a request message contains both a message-body of non-zero
1249   length and a method that does not define any semantics for that
1250   request message-body, then an origin server &SHOULD; either ignore
1251   the message-body or respond with an appropriate error message
1252   (e.g., 413).  A proxy or gateway, when presented the same request,
1253   &SHOULD; either forward the request inbound with the message-body or
1254   ignore the message-body when determining a response.
1255</t>
1256<t>
1257   For response messages, whether or not a message-body is included with
1258   a message is dependent on both the request method and the response
1259   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1260   &MUST-NOT; include a message-body, even though the presence of entity-header
1261   fields might lead one to believe they do. All 1xx
1262   (informational), 204 (No Content), and 304 (Not Modified) responses
1263   &MUST-NOT; include a message-body. All other responses do include a
1264   message-body, although it &MAY; be of zero length.
1265</t>
1266</section>
1267
1268<section title="Message Length" anchor="message.length">
1269<t>
1270   The transfer-length of a message is the length of the message-body as
1271   it appears in the message; that is, after any transfer-codings have
1272   been applied. When a message-body is included with a message, the
1273   transfer-length of that body is determined by one of the following
1274   (in order of precedence):
1275</t>
1276<t>
1277  <list style="numbers">
1278    <x:lt><t>
1279     Any response message which "&MUST-NOT;" include a message-body (such
1280     as the 1xx, 204, and 304 responses and any response to a HEAD
1281     request) is always terminated by the first empty line after the
1282     header fields, regardless of the entity-header fields present in
1283     the message.
1284    </t></x:lt>
1285    <x:lt><t>
1286     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1287     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1288     is used, the transfer-length is defined by the use of this transfer-coding.
1289     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1290     is not present, the transfer-length is defined by the sender closing the connection.
1291    </t></x:lt>
1292    <x:lt><t>
1293     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1294     value in OCTETs represents both the entity-length and the
1295     transfer-length. The Content-Length header field &MUST-NOT; be sent
1296     if these two lengths are different (i.e., if a Transfer-Encoding
1297     header field is present). If a message is received with both a
1298     Transfer-Encoding header field and a Content-Length header field,
1299     the latter &MUST; be ignored.
1300    </t></x:lt>
1301    <x:lt><t>
1302     If the message uses the media type "multipart/byteranges", and the
1303     transfer-length is not otherwise specified, then this self-delimiting
1304     media type defines the transfer-length. This media type
1305     &MUST-NOT; be used unless the sender knows that the recipient can parse
1306     it; the presence in a request of a Range header with multiple byte-range
1307     specifiers from a 1.1 client implies that the client can parse
1308     multipart/byteranges responses.
1309    <list style="empty"><t>
1310       A range header might be forwarded by a 1.0 proxy that does not
1311       understand multipart/byteranges; in this case the server &MUST;
1312       delimit the message using methods defined in items 1, 3 or 5 of
1313       this section.
1314    </t></list>
1315    </t></x:lt>
1316    <x:lt><t>
1317     By the server closing the connection. (Closing the connection
1318     cannot be used to indicate the end of a request body, since that
1319     would leave no possibility for the server to send back a response.)
1320    </t></x:lt>
1321  </list>
1322</t>
1323<t>
1324   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1325   containing a message-body &MUST; include a valid Content-Length header
1326   field unless the server is known to be HTTP/1.1 compliant. If a
1327   request contains a message-body and a Content-Length is not given,
1328   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1329   determine the length of the message, or with 411 (Length Required) if
1330   it wishes to insist on receiving a valid Content-Length.
1331</t>
1332<t>
1333   All HTTP/1.1 applications that receive entities &MUST; accept the
1334   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1335   to be used for messages when the message length cannot be determined
1336   in advance.
1337</t>
1338<t>
1339   Messages &MUST-NOT; include both a Content-Length header field and a
1340   transfer-coding. If the message does include a
1341   transfer-coding, the Content-Length &MUST; be ignored.
1342</t>
1343<t>
1344   When a Content-Length is given in a message where a message-body is
1345   allowed, its field value &MUST; exactly match the number of OCTETs in
1346   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1347   invalid length is received and detected.
1348</t>
1349</section>
1350
1351<section title="General Header Fields" anchor="general.header.fields">
1352  <x:anchor-alias value="general-header"/>
1353<t>
1354   There are a few header fields which have general applicability for
1355   both request and response messages, but which do not apply to the
1356   entity being transferred. These header fields apply only to the
1357   message being transmitted.
1358</t>
1359<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1360  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1361                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1362                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1363                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1364                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1365                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1366                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1367                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1368                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1369</artwork></figure>
1370<t>
1371   General-header field names can be extended reliably only in
1372   combination with a change in the protocol version. However, new or
1373   experimental header fields may be given the semantics of general
1374   header fields if all parties in the communication recognize them to
1375   be general-header fields. Unrecognized header fields are treated as
1376   entity-header fields.
1377</t>
1378</section>
1379</section>
1380
1381<section title="Request" anchor="request">
1382  <x:anchor-alias value="Request"/>
1383<t>
1384   A request message from a client to a server includes, within the
1385   first line of that message, the method to be applied to the resource,
1386   the identifier of the resource, and the protocol version in use.
1387</t>
1388<!--                 Host                      ; should be moved here eventually -->
1389<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1390  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1391                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1392                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1393                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> ) ; &entity-header-fields;
1394                  <x:ref>CRLF</x:ref>
1395                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1396</artwork></figure>
1397
1398<section title="Request-Line" anchor="request-line">
1399  <x:anchor-alias value="Request-Line"/>
1400<t>
1401   The Request-Line begins with a method token, followed by the
1402   request-target and the protocol version, and ending with CRLF. The
1403   elements are separated by SP characters. No CR or LF is allowed
1404   except in the final CRLF sequence.
1405</t>
1406<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1407  <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>
1408</artwork></figure>
1409
1410<section title="Method" anchor="method">
1411  <x:anchor-alias value="Method"/>
1412<t>
1413   The Method  token indicates the method to be performed on the
1414   resource identified by the request-target. The method is case-sensitive.
1415</t>
1416<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1417  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1418</artwork></figure>
1419</section>
1420
1421<section title="request-target" anchor="request-target">
1422  <x:anchor-alias value="request-target"/>
1423<t>
1424   The request-target
1425   identifies the resource upon which to apply the request.
1426</t>
1427<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1428  <x:ref>request-target</x:ref> = "*"
1429                 / <x:ref>absolute-URI</x:ref>
1430                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1431                 / <x:ref>authority</x:ref>
1432</artwork></figure>
1433<t>
1434   The four options for request-target are dependent on the nature of the
1435   request. The asterisk "*" means that the request does not apply to a
1436   particular resource, but to the server itself, and is only allowed
1437   when the method used does not necessarily apply to a resource. One
1438   example would be
1439</t>
1440<figure><artwork type="example">
1441  OPTIONS * HTTP/1.1
1442</artwork></figure>
1443<t>
1444   The absolute-URI form is &REQUIRED; when the request is being made to a
1445   proxy. The proxy is requested to forward the request or service it
1446   from a valid cache, and return the response. Note that the proxy &MAY;
1447   forward the request on to another proxy or directly to the server
1448   specified by the absolute-URI. In order to avoid request loops, a
1449   proxy &MUST; be able to recognize all of its server names, including
1450   any aliases, local variations, and the numeric IP address. An example
1451   Request-Line would be:
1452</t>
1453<figure><artwork type="example">
1454  GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1455</artwork></figure>
1456<t>
1457   To allow for transition to absolute-URIs in all requests in future
1458   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1459   form in requests, even though HTTP/1.1 clients will only generate
1460   them in requests to proxies.
1461</t>
1462<t>
1463   The authority form is only used by the CONNECT method (&CONNECT;).
1464</t>
1465<t>
1466   The most common form of request-target is that used to identify a
1467   resource on an origin server or gateway. In this case the absolute
1468   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1469   the request-target, and the network location of the URI (authority) &MUST;
1470   be transmitted in a Host header field. For example, a client wishing
1471   to retrieve the resource above directly from the origin server would
1472   create a TCP connection to port 80 of the host "www.example.org" and send
1473   the lines:
1474</t>
1475<figure><artwork type="example">
1476  GET /pub/WWW/TheProject.html HTTP/1.1
1477  Host: www.example.org
1478</artwork></figure>
1479<t>
1480   followed by the remainder of the Request. Note that the absolute path
1481   cannot be empty; if none is present in the original URI, it &MUST; be
1482   given as "/" (the server root).
1483</t>
1484<t>
1485   If a proxy receives a request without any path in the request-target and
1486   the method specified is capable of supporting the asterisk form of
1487   request-target, then the last proxy on the request chain &MUST; forward the
1488   request with "*" as the final request-target.
1489</t>
1490<figure><preamble>   
1491   For example, the request
1492</preamble><artwork type="example">
1493  OPTIONS http://www.example.org:8001 HTTP/1.1
1494</artwork></figure>
1495<figure><preamble>   
1496  would be forwarded by the proxy as
1497</preamble><artwork type="example">
1498  OPTIONS * HTTP/1.1
1499  Host: www.example.org:8001
1500</artwork>
1501<postamble>
1502   after connecting to port 8001 of host "www.example.org".
1503</postamble>
1504</figure>
1505<t>
1506   The request-target is transmitted in the format specified in
1507   <xref target="http.uri"/>. If the request-target is percent-encoded
1508   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1509   &MUST; decode the request-target in order to
1510   properly interpret the request. Servers &SHOULD; respond to invalid
1511   request-targets with an appropriate status code.
1512</t>
1513<t>
1514   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1515   received request-target when forwarding it to the next inbound server,
1516   except as noted above to replace a null path-absolute with "/".
1517</t>
1518<x:note>
1519  <t>
1520    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1521    meaning of the request when the origin server is improperly using
1522    a non-reserved URI character for a reserved purpose.  Implementors
1523    should be aware that some pre-HTTP/1.1 proxies have been known to
1524    rewrite the request-target.
1525  </t>
1526</x:note>
1527<t>
1528   HTTP does not place a pre-defined limit on the length of a request-target.
1529   A server &MUST; be prepared to receive URIs of unbounded length and
1530   respond with the 414 (URI Too Long) status if the received
1531   request-target would be longer than the server wishes to handle
1532   (see &status-414;).
1533</t>
1534<t>
1535   Various ad-hoc limitations on request-target length are found in practice.
1536   It is &RECOMMENDED; that all HTTP senders and recipients support
1537   request-target lengths of 8000 or more OCTETs.
1538</t>
1539</section>
1540</section>
1541
1542<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1543<t>
1544   The exact resource identified by an Internet request is determined by
1545   examining both the request-target and the Host header field.
1546</t>
1547<t>
1548   An origin server that does not allow resources to differ by the
1549   requested host &MAY; ignore the Host header field value when
1550   determining the resource identified by an HTTP/1.1 request. (But see
1551   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1552   for other requirements on Host support in HTTP/1.1.)
1553</t>
1554<t>
1555   An origin server that does differentiate resources based on the host
1556   requested (sometimes referred to as virtual hosts or vanity host
1557   names) &MUST; use the following rules for determining the requested
1558   resource on an HTTP/1.1 request:
1559  <list style="numbers">
1560    <t>If request-target is an absolute-URI, the host is part of the
1561     request-target. Any Host header field value in the request &MUST; be
1562     ignored.</t>
1563    <t>If the request-target is not an absolute-URI, and the request includes
1564     a Host header field, the host is determined by the Host header
1565     field value.</t>
1566    <t>If the host as determined by rule 1 or 2 is not a valid host on
1567     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1568  </list>
1569</t>
1570<t>
1571   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1572   attempt to use heuristics (e.g., examination of the URI path for
1573   something unique to a particular host) in order to determine what
1574   exact resource is being requested.
1575</t>
1576</section>
1577
1578</section>
1579
1580
1581<section title="Response" anchor="response">
1582  <x:anchor-alias value="Response"/>
1583<t>
1584   After receiving and interpreting a request message, a server responds
1585   with an HTTP response message.
1586</t>
1587<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1588  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1589                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1590                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1591                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> ) ; &entity-header-fields;
1592                  <x:ref>CRLF</x:ref>
1593                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1594</artwork></figure>
1595
1596<section title="Status-Line" anchor="status-line">
1597  <x:anchor-alias value="Status-Line"/>
1598<t>
1599   The first line of a Response message is the Status-Line, consisting
1600   of the protocol version followed by a numeric status code and its
1601   associated textual phrase, with each element separated by SP
1602   characters. No CR or LF is allowed except in the final CRLF sequence.
1603</t>
1604<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1605  <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>
1606</artwork></figure>
1607
1608<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1609  <x:anchor-alias value="Reason-Phrase"/>
1610  <x:anchor-alias value="Status-Code"/>
1611<t>
1612   The Status-Code element is a 3-digit integer result code of the
1613   attempt to understand and satisfy the request. These codes are fully
1614   defined in &status-codes;.  The Reason Phrase exists for the sole
1615   purpose of providing a textual description associated with the numeric
1616   status code, out of deference to earlier Internet application protocols
1617   that were more frequently used with interactive text clients.
1618   A client &SHOULD; ignore the content of the Reason Phrase.
1619</t>
1620<t>
1621   The first digit of the Status-Code defines the class of response. The
1622   last two digits do not have any categorization role. There are 5
1623   values for the first digit:
1624  <list style="symbols">
1625    <t>
1626      1xx: Informational - Request received, continuing process
1627    </t>
1628    <t>
1629      2xx: Success - The action was successfully received,
1630        understood, and accepted
1631    </t>
1632    <t>
1633      3xx: Redirection - Further action must be taken in order to
1634        complete the request
1635    </t>
1636    <t>
1637      4xx: Client Error - The request contains bad syntax or cannot
1638        be fulfilled
1639    </t>
1640    <t>
1641      5xx: Server Error - The server failed to fulfill an apparently
1642        valid request
1643    </t>
1644  </list>
1645</t>
1646<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"/>
1647  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1648  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1649</artwork></figure>
1650</section>
1651</section>
1652
1653</section>
1654
1655
1656<section title="Protocol Parameters" anchor="protocol.parameters">
1657
1658<section title="Date/Time Formats: Full Date" anchor="date.time.formats.full.date">
1659  <x:anchor-alias value="HTTP-date"/>
1660<t>
1661   HTTP applications have historically allowed three different formats
1662   for the representation of date/time stamps:
1663</t>
1664<figure><artwork type="example">
1665  Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1666  Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1667  Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1668</artwork></figure>
1669<t>
1670   The first format is preferred as an Internet standard and represents
1671   a fixed-length subset of that defined by <xref target="RFC1123"/>. The
1672   other formats are described here only for
1673   compatibility with obsolete implementations.
1674   HTTP/1.1 clients and servers that parse the date value &MUST; accept
1675   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1676   only generate the RFC 1123 format for representing HTTP-date values
1677   in header fields. See <xref target="tolerant.applications"/> for further information.
1678</t>
1679<t>
1680   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1681   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1682   equal to UTC (Coordinated Universal Time). This is indicated in the
1683   first two formats by the inclusion of "GMT" as the three-letter
1684   abbreviation for time zone, and &MUST; be assumed when reading the
1685   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1686   additional whitespace beyond that specifically included as SP in the
1687   grammar.
1688</t>
1689<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1690  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1691</artwork></figure>
1692<t anchor="preferred.date.format">
1693  <x:anchor-alias value="rfc1123-date"/>
1694  <x:anchor-alias value="time-of-day"/>
1695  <x:anchor-alias value="hour"/>
1696  <x:anchor-alias value="minute"/>
1697  <x:anchor-alias value="second"/>
1698  <x:anchor-alias value="day-name"/>
1699  <x:anchor-alias value="day"/>
1700  <x:anchor-alias value="month"/>
1701  <x:anchor-alias value="year"/>
1702  <x:anchor-alias value="GMT"/>
1703  Preferred format:
1704</t>
1705<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"/>
1706  <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>
1707
1708  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1709               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1710               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1711               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
1712               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
1713               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
1714               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
1715               
1716  <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>
1717               ; e.g., 02 Jun 1982
1718
1719  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
1720  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
1721               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
1722               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
1723               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
1724               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
1725               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
1726               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
1727               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
1728               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
1729               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
1730               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
1731               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
1732  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
1733
1734  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
1735
1736  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
1737                 ; 00:00:00 - 23:59:59
1738                 
1739  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
1740  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1741  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1742</artwork></figure>
1743<t>
1744  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
1745  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
1746  same as those defined for the RFC 5322 constructs
1747  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
1748</t>
1749<t anchor="obsolete.date.formats">
1750  <x:anchor-alias value="obs-date"/>
1751  <x:anchor-alias value="rfc850-date"/>
1752  <x:anchor-alias value="asctime-date"/>
1753  <x:anchor-alias value="date1"/>
1754  <x:anchor-alias value="date2"/>
1755  <x:anchor-alias value="date3"/>
1756  <x:anchor-alias value="rfc1123-date"/>
1757  <x:anchor-alias value="day-name-l"/>
1758  Obsolete formats:
1759</t>
1760<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
1761  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
1762</artwork></figure>
1763<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
1764  <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>
1765  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
1766                 ; day-month-year (e.g., 02-Jun-82)
1767
1768  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
1769         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
1770         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
1771         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
1772         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
1773         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
1774         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
1775</artwork></figure>
1776<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
1777  <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>
1778  <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> ))
1779                 ; month day (e.g., Jun  2)
1780</artwork></figure>
1781<x:note>
1782  <t>
1783    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
1784    accepting date values that may have been sent by non-HTTP
1785    applications, as is sometimes the case when retrieving or posting
1786    messages via proxies/gateways to SMTP or NNTP.
1787  </t>
1788</x:note>
1789<x:note>
1790  <t>
1791    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
1792    to their usage within the protocol stream. Clients and servers are
1793    not required to use these formats for user presentation, request
1794    logging, etc.
1795  </t>
1796</x:note>
1797</section>
1798
1799<section title="Transfer Codings" anchor="transfer.codings">
1800  <x:anchor-alias value="transfer-coding"/>
1801  <x:anchor-alias value="transfer-extension"/>
1802<t>
1803   Transfer-coding values are used to indicate an encoding
1804   transformation that has been, can be, or may need to be applied to an
1805   entity-body in order to ensure "safe transport" through the network.
1806   This differs from a content coding in that the transfer-coding is a
1807   property of the message, not of the original entity.
1808</t>
1809<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1810  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
1811                          / "compress" ; <xref target="compress.coding"/>
1812                          / "deflate" ; <xref target="deflate.coding"/>
1813                          / "gzip" ; <xref target="gzip.coding"/>
1814                          / <x:ref>transfer-extension</x:ref>
1815  <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> )
1816</artwork></figure>
1817<t anchor="rule.parameter">
1818  <x:anchor-alias value="attribute"/>
1819  <x:anchor-alias value="transfer-parameter"/>
1820  <x:anchor-alias value="value"/>
1821   Parameters are in  the form of attribute/value pairs.
1822</t>
1823<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"/>
1824  <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>
1825  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
1826  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1827</artwork></figure>
1828<t>
1829   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1830   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1831   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1832</t>
1833<t>
1834   Whenever a transfer-coding is applied to a message-body, the set of
1835   transfer-codings &MUST; include "chunked", unless the message indicates it
1836   is terminated by closing the connection. When the "chunked" transfer-coding
1837   is used, it &MUST; be the last transfer-coding applied to the
1838   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
1839   than once to a message-body. These rules allow the recipient to
1840   determine the transfer-length of the message (<xref target="message.length"/>).
1841</t>
1842<t>
1843   Transfer-codings are analogous to the Content-Transfer-Encoding values of
1844   MIME, which were designed to enable safe transport of binary data over a
1845   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1846   However, safe transport
1847   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1848   the only unsafe characteristic of message-bodies is the difficulty in
1849   determining the exact body length (<xref target="message.length"/>), or the desire to
1850   encrypt data over a shared transport.
1851</t>
1852<t>
1853   A server which receives an entity-body with a transfer-coding it does
1854   not understand &SHOULD; return 501 (Not Implemented), and close the
1855   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1856   client.
1857</t>
1858
1859<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1860  <iref item="chunked (Coding Format)"/>
1861  <iref item="Coding Format" subitem="chunked"/>
1862  <x:anchor-alias value="chunk"/>
1863  <x:anchor-alias value="Chunked-Body"/>
1864  <x:anchor-alias value="chunk-data"/>
1865  <x:anchor-alias value="chunk-ext"/>
1866  <x:anchor-alias value="chunk-ext-name"/>
1867  <x:anchor-alias value="chunk-ext-val"/>
1868  <x:anchor-alias value="chunk-size"/>
1869  <x:anchor-alias value="last-chunk"/>
1870  <x:anchor-alias value="trailer-part"/>
1871  <x:anchor-alias value="quoted-str-nf"/>
1872  <x:anchor-alias value="qdtext-nf"/>
1873<t>
1874   The chunked encoding modifies the body of a message in order to
1875   transfer it as a series of chunks, each with its own size indicator,
1876   followed by an &OPTIONAL; trailer containing entity-header fields. This
1877   allows dynamically produced content to be transferred along with the
1878   information necessary for the recipient to verify that it has
1879   received the full message.
1880</t>
1881<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"/>
1882  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1883                   <x:ref>last-chunk</x:ref>
1884                   <x:ref>trailer-part</x:ref>
1885                   <x:ref>CRLF</x:ref>
1886 
1887  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1888                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1889  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1890  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1891 
1892  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
1893                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
1894  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1895  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
1896  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1897  <x:ref>trailer-part</x:ref>   = *( <x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref> )
1898 
1899  <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>
1900                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
1901  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1902                 ; <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> 
1903</artwork></figure>
1904<t>
1905   The chunk-size field is a string of hex digits indicating the size of
1906   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1907   zero, followed by the trailer, which is terminated by an empty line.
1908</t>
1909<t>
1910   The trailer allows the sender to include additional HTTP header
1911   fields at the end of the message. The Trailer header field can be
1912   used to indicate which header fields are included in a trailer (see
1913   <xref target="header.trailer"/>).
1914</t>
1915<t>
1916   A server using chunked transfer-coding in a response &MUST-NOT; use the
1917   trailer for any header fields unless at least one of the following is
1918   true:
1919  <list style="numbers">
1920    <t>the request included a TE header field that indicates "trailers" is
1921     acceptable in the transfer-coding of the  response, as described in
1922     <xref target="header.te"/>; or,</t>
1923
1924    <t>the server is the origin server for the response, the trailer
1925     fields consist entirely of optional metadata, and the recipient
1926     could use the message (in a manner acceptable to the origin server)
1927     without receiving this metadata.  In other words, the origin server
1928     is willing to accept the possibility that the trailer fields might
1929     be silently discarded along the path to the client.</t>
1930  </list>
1931</t>
1932<t>
1933   This requirement prevents an interoperability failure when the
1934   message is being received by an HTTP/1.1 (or later) proxy and
1935   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1936   compliance with the protocol would have necessitated a possibly
1937   infinite buffer on the proxy.
1938</t>
1939<t>
1940   A process for decoding the "chunked" transfer-coding
1941   can be represented in pseudo-code as:
1942</t>
1943<figure><artwork type="code">
1944  length := 0
1945  read chunk-size, chunk-ext (if any) and CRLF
1946  while (chunk-size &gt; 0) {
1947     read chunk-data and CRLF
1948     append chunk-data to entity-body
1949     length := length + chunk-size
1950     read chunk-size and CRLF
1951  }
1952  read entity-header
1953  while (entity-header not empty) {
1954     append entity-header to existing header fields
1955     read entity-header
1956  }
1957  Content-Length := length
1958  Remove "chunked" from Transfer-Encoding
1959</artwork></figure>
1960<t>
1961   All HTTP/1.1 applications &MUST; be able to receive and decode the
1962   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1963   they do not understand.
1964</t>
1965</section>
1966
1967<section title="Compression Codings" anchor="compression.codings">
1968<t>
1969   The codings defined below can be used to compress the payload of a
1970   message.
1971</t>
1972<x:note><t>
1973   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
1974   is not desirable and is discouraged for future encodings. Their
1975   use here is representative of historical practice, not good
1976   design.
1977</t></x:note>
1978<x:note><t>
1979   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
1980   applications &SHOULD; consider "x-gzip" and "x-compress" to be
1981   equivalent to "gzip" and "compress" respectively.
1982</t></x:note>
1983
1984<section title="Compress Coding" anchor="compress.coding">
1985<iref item="compress (Coding Format)"/>
1986<iref item="Coding Format" subitem="compress"/>
1987<t>
1988   The "compress" format is produced by the common UNIX file compression
1989   program "compress". This format is an adaptive Lempel-Ziv-Welch
1990   coding (LZW).
1991</t>
1992</section>
1993
1994<section title="Deflate Coding" anchor="deflate.coding">
1995<iref item="deflate (Coding Format)"/>
1996<iref item="Coding Format" subitem="deflate"/>
1997<t>
1998   The "zlib" format is defined in <xref target="RFC1950"/> in combination with
1999   the "deflate" compression mechanism described in <xref target="RFC1951"/>.
2000</t>
2001</section>
2002
2003<section title="Gzip Coding" anchor="gzip.coding">
2004<iref item="gzip (Coding Format)"/>
2005<iref item="Coding Format" subitem="gzip"/>
2006<t>
2007   The "gzip" format is produced by the file compression program
2008   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2009   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2010</t>
2011</section>
2012
2013</section>
2014
2015<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2016<t>
2017   The HTTP Transfer Coding Registry defines the name space for the transfer
2018   coding names.
2019</t>
2020<t>
2021   Registrations &MUST; include the following fields:
2022   <list style="symbols">
2023     <t>Name</t>
2024     <t>Description</t>
2025     <t>Pointer to specification text</t>
2026   </list>
2027</t>
2028<t>
2029   Values to be added to this name space require expert review and a specification
2030   (see "Expert Review" and "Specification Required" in
2031   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2032   conform to the purpose of transfer coding defined in this section.
2033</t>
2034<t>
2035   The registry itself is maintained at
2036   <eref target="http://www.iana.org/assignments/http-parameters"/>.
2037</t>
2038</section>
2039</section>
2040
2041<section title="Product Tokens" anchor="product.tokens">
2042  <x:anchor-alias value="product"/>
2043  <x:anchor-alias value="product-version"/>
2044<t>
2045   Product tokens are used to allow communicating applications to
2046   identify themselves by software name and version. Most fields using
2047   product tokens also allow sub-products which form a significant part
2048   of the application to be listed, separated by whitespace. By
2049   convention, the products are listed in order of their significance
2050   for identifying the application.
2051</t>
2052<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2053  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2054  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2055</artwork></figure>
2056<t>
2057   Examples:
2058</t>
2059<figure><artwork type="example">
2060  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2061  Server: Apache/0.8.4
2062</artwork></figure>
2063<t>
2064   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2065   used for advertising or other non-essential information. Although any
2066   token character &MAY; appear in a product-version, this token &SHOULD;
2067   only be used for a version identifier (i.e., successive versions of
2068   the same product &SHOULD; only differ in the product-version portion of
2069   the product value).
2070</t>
2071</section>
2072
2073<section title="Quality Values" anchor="quality.values">
2074  <x:anchor-alias value="qvalue"/>
2075<t>
2076   Both transfer codings (TE request header, <xref target="header.te"/>)
2077   and content negotiation (&content.negotiation;) use short "floating point"
2078   numbers to indicate the relative importance ("weight") of various
2079   negotiable parameters.  A weight is normalized to a real number in
2080   the range 0 through 1, where 0 is the minimum and 1 the maximum
2081   value. If a parameter has a quality value of 0, then content with
2082   this parameter is `not acceptable' for the client. HTTP/1.1
2083   applications &MUST-NOT; generate more than three digits after the
2084   decimal point. User configuration of these values &SHOULD; also be
2085   limited in this fashion.
2086</t>
2087<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2088  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2089                 / ( "1" [ "." 0*3("0") ] )
2090</artwork></figure>
2091<x:note>
2092  <t>
2093     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2094     relative degradation in desired quality.
2095  </t>
2096</x:note>
2097</section>
2098
2099</section>
2100
2101<section title="Connections" anchor="connections">
2102
2103<section title="Persistent Connections" anchor="persistent.connections">
2104
2105<section title="Purpose" anchor="persistent.purpose">
2106<t>
2107   Prior to persistent connections, a separate TCP connection was
2108   established to fetch each URL, increasing the load on HTTP servers
2109   and causing congestion on the Internet. The use of inline images and
2110   other associated data often require a client to make multiple
2111   requests of the same server in a short amount of time. Analysis of
2112   these performance problems and results from a prototype
2113   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2114   measurements of actual HTTP/1.1 implementations show good
2115   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2116   T/TCP <xref target="Tou1998"/>.
2117</t>
2118<t>
2119   Persistent HTTP connections have a number of advantages:
2120  <list style="symbols">
2121      <t>
2122        By opening and closing fewer TCP connections, CPU time is saved
2123        in routers and hosts (clients, servers, proxies, gateways,
2124        tunnels, or caches), and memory used for TCP protocol control
2125        blocks can be saved in hosts.
2126      </t>
2127      <t>
2128        HTTP requests and responses can be pipelined on a connection.
2129        Pipelining allows a client to make multiple requests without
2130        waiting for each response, allowing a single TCP connection to
2131        be used much more efficiently, with much lower elapsed time.
2132      </t>
2133      <t>
2134        Network congestion is reduced by reducing the number of packets
2135        caused by TCP opens, and by allowing TCP sufficient time to
2136        determine the congestion state of the network.
2137      </t>
2138      <t>
2139        Latency on subsequent requests is reduced since there is no time
2140        spent in TCP's connection opening handshake.
2141      </t>
2142      <t>
2143        HTTP can evolve more gracefully, since errors can be reported
2144        without the penalty of closing the TCP connection. Clients using
2145        future versions of HTTP might optimistically try a new feature,
2146        but if communicating with an older server, retry with old
2147        semantics after an error is reported.
2148      </t>
2149    </list>
2150</t>
2151<t>
2152   HTTP implementations &SHOULD; implement persistent connections.
2153</t>
2154</section>
2155
2156<section title="Overall Operation" anchor="persistent.overall">
2157<t>
2158   A significant difference between HTTP/1.1 and earlier versions of
2159   HTTP is that persistent connections are the default behavior of any
2160   HTTP connection. That is, unless otherwise indicated, the client
2161   &SHOULD; assume that the server will maintain a persistent connection,
2162   even after error responses from the server.
2163</t>
2164<t>
2165   Persistent connections provide a mechanism by which a client and a
2166   server can signal the close of a TCP connection. This signaling takes
2167   place using the Connection header field (<xref target="header.connection"/>). Once a close
2168   has been signaled, the client &MUST-NOT; send any more requests on that
2169   connection.
2170</t>
2171
2172<section title="Negotiation" anchor="persistent.negotiation">
2173<t>
2174   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2175   maintain a persistent connection unless a Connection header including
2176   the connection-token "close" was sent in the request. If the server
2177   chooses to close the connection immediately after sending the
2178   response, it &SHOULD; send a Connection header including the
2179   connection-token close.
2180</t>
2181<t>
2182   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2183   decide to keep it open based on whether the response from a server
2184   contains a Connection header with the connection-token close. In case
2185   the client does not want to maintain a connection for more than that
2186   request, it &SHOULD; send a Connection header including the
2187   connection-token close.
2188</t>
2189<t>
2190   If either the client or the server sends the close token in the
2191   Connection header, that request becomes the last one for the
2192   connection.
2193</t>
2194<t>
2195   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2196   maintained for HTTP versions less than 1.1 unless it is explicitly
2197   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2198   compatibility with HTTP/1.0 clients.
2199</t>
2200<t>
2201   In order to remain persistent, all messages on the connection &MUST;
2202   have a self-defined message length (i.e., one not defined by closure
2203   of the connection), as described in <xref target="message.length"/>.
2204</t>
2205</section>
2206
2207<section title="Pipelining" anchor="pipelining">
2208<t>
2209   A client that supports persistent connections &MAY; "pipeline" its
2210   requests (i.e., send multiple requests without waiting for each
2211   response). A server &MUST; send its responses to those requests in the
2212   same order that the requests were received.
2213</t>
2214<t>
2215   Clients which assume persistent connections and pipeline immediately
2216   after connection establishment &SHOULD; be prepared to retry their
2217   connection if the first pipelined attempt fails. If a client does
2218   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2219   persistent. Clients &MUST; also be prepared to resend their requests if
2220   the server closes the connection before sending all of the
2221   corresponding responses.
2222</t>
2223<t>
2224   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
2225   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
2226   premature termination of the transport connection could lead to
2227   indeterminate results. A client wishing to send a non-idempotent
2228   request &SHOULD; wait to send that request until it has received the
2229   response status for the previous request.
2230</t>
2231</section>
2232</section>
2233
2234<section title="Proxy Servers" anchor="persistent.proxy">
2235<t>
2236   It is especially important that proxies correctly implement the
2237   properties of the Connection header field as specified in <xref target="header.connection"/>.
2238</t>
2239<t>
2240   The proxy server &MUST; signal persistent connections separately with
2241   its clients and the origin servers (or other proxy servers) that it
2242   connects to. Each persistent connection applies to only one transport
2243   link.
2244</t>
2245<t>
2246   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2247   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2248   for information and discussion of the problems with the Keep-Alive header
2249   implemented by many HTTP/1.0 clients).
2250</t>
2251</section>
2252
2253<section title="Practical Considerations" anchor="persistent.practical">
2254<t>
2255   Servers will usually have some time-out value beyond which they will
2256   no longer maintain an inactive connection. Proxy servers might make
2257   this a higher value since it is likely that the client will be making
2258   more connections through the same server. The use of persistent
2259   connections places no requirements on the length (or existence) of
2260   this time-out for either the client or the server.
2261</t>
2262<t>
2263   When a client or server wishes to time-out it &SHOULD; issue a graceful
2264   close on the transport connection. Clients and servers &SHOULD; both
2265   constantly watch for the other side of the transport close, and
2266   respond to it as appropriate. If a client or server does not detect
2267   the other side's close promptly it could cause unnecessary resource
2268   drain on the network.
2269</t>
2270<t>
2271   A client, server, or proxy &MAY; close the transport connection at any
2272   time. For example, a client might have started to send a new request
2273   at the same time that the server has decided to close the "idle"
2274   connection. From the server's point of view, the connection is being
2275   closed while it was idle, but from the client's point of view, a
2276   request is in progress.
2277</t>
2278<t>
2279   This means that clients, servers, and proxies &MUST; be able to recover
2280   from asynchronous close events. Client software &SHOULD; reopen the
2281   transport connection and retransmit the aborted sequence of requests
2282   without user interaction so long as the request sequence is
2283   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
2284   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2285   human operator the choice of retrying the request(s). Confirmation by
2286   user-agent software with semantic understanding of the application
2287   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2288   be repeated if the second sequence of requests fails.
2289</t>
2290<t>
2291   Servers &SHOULD; always respond to at least one request per connection,
2292   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2293   middle of transmitting a response, unless a network or client failure
2294   is suspected.
2295</t>
2296<t>
2297   Clients (including proxies) &SHOULD; limit the number of simultaneous
2298   connections that they maintain to a given server (including proxies).
2299</t>
2300<t>
2301   Previous revisions of HTTP gave a specific number of connections as a
2302   ceiling, but this was found to be impractical for many applications. As a
2303   result, this specification does not mandate a particular maximum number of
2304   connections, but instead encourages clients to be conservative when opening
2305   multiple connections.
2306</t>
2307<t>
2308   In particular, while using multiple connections avoids the "head-of-line
2309   blocking" problem (whereby a request that takes significant server-side
2310   processing and/or has a large payload can block subsequent requests on the
2311   same connection), each connection used consumes server resources (sometimes
2312   significantly), and furthermore using multiple connections can cause
2313   undesirable side effects in congested networks.
2314</t>
2315<t>
2316   Note that servers might reject traffic that they deem abusive, including an
2317   excessive number of connections from a client.
2318</t>
2319</section>
2320</section>
2321
2322<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2323
2324<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2325<t>
2326   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2327   flow control mechanisms to resolve temporary overloads, rather than
2328   terminating connections with the expectation that clients will retry.
2329   The latter technique can exacerbate network congestion.
2330</t>
2331</section>
2332
2333<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2334<t>
2335   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2336   the network connection for an error status while it is transmitting
2337   the request. If the client sees an error status, it &SHOULD;
2338   immediately cease transmitting the body. If the body is being sent
2339   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2340   empty trailer &MAY; be used to prematurely mark the end of the message.
2341   If the body was preceded by a Content-Length header, the client &MUST;
2342   close the connection.
2343</t>
2344</section>
2345
2346<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2347<t>
2348   The purpose of the 100 (Continue) status (see &status-100;) is to
2349   allow a client that is sending a request message with a request body
2350   to determine if the origin server is willing to accept the request
2351   (based on the request headers) before the client sends the request
2352   body. In some cases, it might either be inappropriate or highly
2353   inefficient for the client to send the body if the server will reject
2354   the message without looking at the body.
2355</t>
2356<t>
2357   Requirements for HTTP/1.1 clients:
2358  <list style="symbols">
2359    <t>
2360        If a client will wait for a 100 (Continue) response before
2361        sending the request body, it &MUST; send an Expect request-header
2362        field (&header-expect;) with the "100-continue" expectation.
2363    </t>
2364    <t>
2365        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2366        with the "100-continue" expectation if it does not intend
2367        to send a request body.
2368    </t>
2369  </list>
2370</t>
2371<t>
2372   Because of the presence of older implementations, the protocol allows
2373   ambiguous situations in which a client may send "Expect: 100-continue"
2374   without receiving either a 417 (Expectation Failed) status
2375   or a 100 (Continue) status. Therefore, when a client sends this
2376   header field to an origin server (possibly via a proxy) from which it
2377   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
2378   for an indefinite period before sending the request body.
2379</t>
2380<t>
2381   Requirements for HTTP/1.1 origin servers:
2382  <list style="symbols">
2383    <t> Upon receiving a request which includes an Expect request-header
2384        field with the "100-continue" expectation, an origin server &MUST;
2385        either respond with 100 (Continue) status and continue to read
2386        from the input stream, or respond with a final status code. The
2387        origin server &MUST-NOT; wait for the request body before sending
2388        the 100 (Continue) response. If it responds with a final status
2389        code, it &MAY; close the transport connection or it &MAY; continue
2390        to read and discard the rest of the request.  It &MUST-NOT;
2391        perform the requested method if it returns a final status code.
2392    </t>
2393    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2394        the request message does not include an Expect request-header
2395        field with the "100-continue" expectation, and &MUST-NOT; send a
2396        100 (Continue) response if such a request comes from an HTTP/1.0
2397        (or earlier) client. There is an exception to this rule: for
2398        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2399        status in response to an HTTP/1.1 PUT or POST request that does
2400        not include an Expect request-header field with the "100-continue"
2401        expectation. This exception, the purpose of which is
2402        to minimize any client processing delays associated with an
2403        undeclared wait for 100 (Continue) status, applies only to
2404        HTTP/1.1 requests, and not to requests with any other HTTP-version
2405        value.
2406    </t>
2407    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2408        already received some or all of the request body for the
2409        corresponding request.
2410    </t>
2411    <t> An origin server that sends a 100 (Continue) response &MUST;
2412    ultimately send a final status code, once the request body is
2413        received and processed, unless it terminates the transport
2414        connection prematurely.
2415    </t>
2416    <t> If an origin server receives a request that does not include an
2417        Expect request-header field with the "100-continue" expectation,
2418        the request includes a request body, and the server responds
2419        with a final status code before reading the entire request body
2420        from the transport connection, then the server &SHOULD-NOT;  close
2421        the transport connection until it has read the entire request,
2422        or until the client closes the connection. Otherwise, the client
2423        might not reliably receive the response message. However, this
2424        requirement is not be construed as preventing a server from
2425        defending itself against denial-of-service attacks, or from
2426        badly broken client implementations.
2427      </t>
2428    </list>
2429</t>
2430<t>
2431   Requirements for HTTP/1.1 proxies:
2432  <list style="symbols">
2433    <t> If a proxy receives a request that includes an Expect request-header
2434        field with the "100-continue" expectation, and the proxy
2435        either knows that the next-hop server complies with HTTP/1.1 or
2436        higher, or does not know the HTTP version of the next-hop
2437        server, it &MUST; forward the request, including the Expect header
2438        field.
2439    </t>
2440    <t> If the proxy knows that the version of the next-hop server is
2441        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2442        respond with a 417 (Expectation Failed) status.
2443    </t>
2444    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2445        numbers received from recently-referenced next-hop servers.
2446    </t>
2447    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2448        request message was received from an HTTP/1.0 (or earlier)
2449        client and did not include an Expect request-header field with
2450        the "100-continue" expectation. This requirement overrides the
2451        general rule for forwarding of 1xx responses (see &status-1xx;).
2452    </t>
2453  </list>
2454</t>
2455</section>
2456
2457<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2458<t>
2459   If an HTTP/1.1 client sends a request which includes a request body,
2460   but which does not include an Expect request-header field with the
2461   "100-continue" expectation, and if the client is not directly
2462   connected to an HTTP/1.1 origin server, and if the client sees the
2463   connection close before receiving any status from the server, the
2464   client &SHOULD; retry the request.  If the client does retry this
2465   request, it &MAY; use the following "binary exponential backoff"
2466   algorithm to be assured of obtaining a reliable response:
2467  <list style="numbers">
2468    <t>
2469      Initiate a new connection to the server
2470    </t>
2471    <t>
2472      Transmit the request-headers
2473    </t>
2474    <t>
2475      Initialize a variable R to the estimated round-trip time to the
2476         server (e.g., based on the time it took to establish the
2477         connection), or to a constant value of 5 seconds if the round-trip
2478         time is not available.
2479    </t>
2480    <t>
2481       Compute T = R * (2**N), where N is the number of previous
2482         retries of this request.
2483    </t>
2484    <t>
2485       Wait either for an error response from the server, or for T
2486         seconds (whichever comes first)
2487    </t>
2488    <t>
2489       If no error response is received, after T seconds transmit the
2490         body of the request.
2491    </t>
2492    <t>
2493       If client sees that the connection is closed prematurely,
2494         repeat from step 1 until the request is accepted, an error
2495         response is received, or the user becomes impatient and
2496         terminates the retry process.
2497    </t>
2498  </list>
2499</t>
2500<t>
2501   If at any point an error status is received, the client
2502  <list style="symbols">
2503      <t>&SHOULD-NOT;  continue and</t>
2504
2505      <t>&SHOULD; close the connection if it has not completed sending the
2506        request message.</t>
2507    </list>
2508</t>
2509</section>
2510</section>
2511</section>
2512
2513
2514<section title="Miscellaneous notes that may disappear" anchor="misc">
2515<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2516<t>
2517   <cref>TBS: describe why aliases like webcal are harmful.</cref>
2518</t>
2519</section>
2520
2521<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2522<t>
2523   <cref>TBD: Configured to use HTTP to proxy HTTP or other protocols.</cref>
2524</t>
2525</section>
2526
2527<section title="Interception of HTTP for access control" anchor="http.intercept">
2528<t>
2529   <cref>TBD: Interception of HTTP traffic for initiating access control.</cref>
2530</t>
2531</section>
2532
2533<section title="Use of HTTP by other protocols" anchor="http.others">
2534<t>
2535   <cref>TBD: Profiles of HTTP defined by other protocol.
2536   Extensions of HTTP like WebDAV.</cref>
2537</t>
2538
2539</section>
2540<section title="Use of HTTP by media type specification" anchor="http.media">
2541<t>
2542   <cref>TBD: Instructions on composing HTTP requests via hypertext formats.</cref>
2543</t>
2544</section>
2545</section>
2546
2547<section title="Header Field Definitions" anchor="header.field.definitions">
2548<t>
2549   This section defines the syntax and semantics of HTTP/1.1 header fields
2550   related to message framing and transport protocols.
2551</t>
2552<t>
2553   For entity-header fields, both sender and recipient refer to either the
2554   client or the server, depending on who sends and who receives the entity.
2555</t>
2556
2557<section title="Connection" anchor="header.connection">
2558  <iref primary="true" item="Connection header" x:for-anchor=""/>
2559  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2560  <x:anchor-alias value="Connection"/>
2561  <x:anchor-alias value="connection-token"/>
2562  <x:anchor-alias value="Connection-v"/>
2563<t>
2564   The "Connection" general-header field allows the sender to specify
2565   options that are desired for that particular connection and &MUST-NOT;
2566   be communicated by proxies over further connections.
2567</t>
2568<t>
2569   The Connection header's value has the following grammar:
2570</t>
2571<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"/>
2572  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2573  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2574  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2575</artwork></figure>
2576<t>
2577   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2578   message is forwarded and, for each connection-token in this field,
2579   remove any header field(s) from the message with the same name as the
2580   connection-token. Connection options are signaled by the presence of
2581   a connection-token in the Connection header field, not by any
2582   corresponding additional header field(s), since the additional header
2583   field may not be sent if there are no parameters associated with that
2584   connection option.
2585</t>
2586<t>
2587   Message headers listed in the Connection header &MUST-NOT; include
2588   end-to-end headers, such as Cache-Control.
2589</t>
2590<t>
2591   HTTP/1.1 defines the "close" connection option for the sender to
2592   signal that the connection will be closed after completion of the
2593   response. For example,
2594</t>
2595<figure><artwork type="example">
2596  Connection: close
2597</artwork></figure>
2598<t>
2599   in either the request or the response header fields indicates that
2600   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2601   after the current request/response is complete.
2602</t>
2603<t>
2604   An HTTP/1.1 client that does not support persistent connections &MUST;
2605   include the "close" connection option in every request message.
2606</t>
2607<t>
2608   An HTTP/1.1 server that does not support persistent connections &MUST;
2609   include the "close" connection option in every response message that
2610   does not have a 1xx (informational) status code.
2611</t>
2612<t>
2613   A system receiving an HTTP/1.0 (or lower-version) message that
2614   includes a Connection header &MUST;, for each connection-token in this
2615   field, remove and ignore any header field(s) from the message with
2616   the same name as the connection-token. This protects against mistaken
2617   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2618</t>
2619</section>
2620
2621<section title="Content-Length" anchor="header.content-length">
2622  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2623  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2624  <x:anchor-alias value="Content-Length"/>
2625  <x:anchor-alias value="Content-Length-v"/>
2626<t>
2627   The "Content-Length" entity-header field indicates the size of the
2628   entity-body, in number of OCTETs. In the case of responses to the HEAD
2629   method, it indicates the size of the entity-body that would have been sent
2630   had the request been a GET.
2631</t>
2632<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2633  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2634  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2635</artwork></figure>
2636<t>
2637   An example is
2638</t>
2639<figure><artwork type="example">
2640  Content-Length: 3495
2641</artwork></figure>
2642<t>
2643   Applications &SHOULD; use this field to indicate the transfer-length of
2644   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2645</t>
2646<t>
2647   Any Content-Length greater than or equal to zero is a valid value.
2648   <xref target="message.length"/> describes how to determine the length of a message-body
2649   if a Content-Length is not given.
2650</t>
2651<t>
2652   Note that the meaning of this field is significantly different from
2653   the corresponding definition in MIME, where it is an optional field
2654   used within the "message/external-body" content-type. In HTTP, it
2655   &SHOULD; be sent whenever the message's length can be determined prior
2656   to being transferred, unless this is prohibited by the rules in
2657   <xref target="message.length"/>.
2658</t>
2659</section>
2660
2661<section title="Date" anchor="header.date">
2662  <iref primary="true" item="Date header" x:for-anchor=""/>
2663  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2664  <x:anchor-alias value="Date"/>
2665  <x:anchor-alias value="Date-v"/>
2666<t>
2667   The "Date" general-header field represents the date and time at which
2668   the message was originated, having the same semantics as the Origination
2669   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2670   The field value is an HTTP-date, as described in <xref target="date.time.formats.full.date"/>;
2671   it &MUST; be sent in rfc1123-date format.
2672</t>
2673<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2674  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2675  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2676</artwork></figure>
2677<t>
2678   An example is
2679</t>
2680<figure><artwork type="example">
2681  Date: Tue, 15 Nov 1994 08:12:31 GMT
2682</artwork></figure>
2683<t>
2684   Origin servers &MUST; include a Date header field in all responses,
2685   except in these cases:
2686  <list style="numbers">
2687      <t>If the response status code is 100 (Continue) or 101 (Switching
2688         Protocols), the response &MAY; include a Date header field, at
2689         the server's option.</t>
2690
2691      <t>If the response status code conveys a server error, e.g. 500
2692         (Internal Server Error) or 503 (Service Unavailable), and it is
2693         inconvenient or impossible to generate a valid Date.</t>
2694
2695      <t>If the server does not have a clock that can provide a
2696         reasonable approximation of the current time, its responses
2697         &MUST-NOT; include a Date header field. In this case, the rules
2698         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2699  </list>
2700</t>
2701<t>
2702   A received message that does not have a Date header field &MUST; be
2703   assigned one by the recipient if the message will be cached by that
2704   recipient or gatewayed via a protocol which requires a Date. An HTTP
2705   implementation without a clock &MUST-NOT; cache responses without
2706   revalidating them on every use. An HTTP cache, especially a shared
2707   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2708   clock with a reliable external standard.
2709</t>
2710<t>
2711   Clients &SHOULD; only send a Date header field in messages that include
2712   an entity-body, as in the case of the PUT and POST requests, and even
2713   then it is optional. A client without a clock &MUST-NOT; send a Date
2714   header field in a request.
2715</t>
2716<t>
2717   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2718   time subsequent to the generation of the message. It &SHOULD; represent
2719   the best available approximation of the date and time of message
2720   generation, unless the implementation has no means of generating a
2721   reasonably accurate date and time. In theory, the date ought to
2722   represent the moment just before the entity is generated. In
2723   practice, the date can be generated at any time during the message
2724   origination without affecting its semantic value.
2725</t>
2726
2727<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2728<t>
2729   Some origin server implementations might not have a clock available.
2730   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2731   values to a response, unless these values were associated
2732   with the resource by a system or user with a reliable clock. It &MAY;
2733   assign an Expires value that is known, at or before server
2734   configuration time, to be in the past (this allows "pre-expiration"
2735   of responses without storing separate Expires values for each
2736   resource).
2737</t>
2738</section>
2739</section>
2740
2741<section title="Host" anchor="header.host">
2742  <iref primary="true" item="Host header" x:for-anchor=""/>
2743  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2744  <x:anchor-alias value="Host"/>
2745  <x:anchor-alias value="Host-v"/>
2746<t>
2747   The "Host" request-header field specifies the Internet host and port
2748   number of the resource being requested, allowing the origin server or
2749   gateway to differentiate between internally-ambiguous URLs, such as the root
2750   "/" URL of a server for multiple host names on a single IP address.
2751</t>
2752<t>   
2753   The Host field value &MUST; represent the naming authority of the origin
2754   server or gateway given by the original URL obtained from the user or
2755   referring resource (generally an http URI, as described in
2756   <xref target="http.uri"/>).
2757</t>
2758<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2759  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2760  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2761</artwork></figure>
2762<t>
2763   A "host" without any trailing port information implies the default
2764   port for the service requested (e.g., "80" for an HTTP URL). For
2765   example, a request on the origin server for
2766   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2767</t>
2768<figure><artwork type="example">
2769  GET /pub/WWW/ HTTP/1.1
2770  Host: www.example.org
2771</artwork></figure>
2772<t>
2773   A client &MUST; include a Host header field in all HTTP/1.1 request
2774   messages. If the requested URI does not include an Internet host
2775   name for the service being requested, then the Host header field &MUST;
2776   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2777   request message it forwards does contain an appropriate Host header
2778   field that identifies the service being requested by the proxy. All
2779   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2780   status code to any HTTP/1.1 request message which lacks a Host header
2781   field.
2782</t>
2783<t>
2784   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2785   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2786   for other requirements relating to Host.
2787</t>
2788</section>
2789
2790<section title="TE" anchor="header.te">
2791  <iref primary="true" item="TE header" x:for-anchor=""/>
2792  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2793  <x:anchor-alias value="TE"/>
2794  <x:anchor-alias value="TE-v"/>
2795  <x:anchor-alias value="t-codings"/>
2796  <x:anchor-alias value="te-params"/>
2797  <x:anchor-alias value="te-ext"/>
2798<t>
2799   The "TE" request-header field indicates what extension transfer-codings
2800   it is willing to accept in the response, and whether or not it is
2801   willing to accept trailer fields in a chunked transfer-coding.
2802</t>
2803<t>
2804   Its value may consist of the keyword "trailers" and/or a comma-separated
2805   list of extension transfer-coding names with optional accept
2806   parameters (as described in <xref target="transfer.codings"/>).
2807</t>
2808<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"/>
2809  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2810  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2811  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
2812  <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> )
2813  <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> ) ]
2814</artwork></figure>
2815<t>
2816   The presence of the keyword "trailers" indicates that the client is
2817   willing to accept trailer fields in a chunked transfer-coding, as
2818   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
2819   transfer-coding values even though it does not itself represent a
2820   transfer-coding.
2821</t>
2822<t>
2823   Examples of its use are:
2824</t>
2825<figure><artwork type="example">
2826  TE: deflate
2827  TE:
2828  TE: trailers, deflate;q=0.5
2829</artwork></figure>
2830<t>
2831   The TE header field only applies to the immediate connection.
2832   Therefore, the keyword &MUST; be supplied within a Connection header
2833   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2834</t>
2835<t>
2836   A server tests whether a transfer-coding is acceptable, according to
2837   a TE field, using these rules:
2838  <list style="numbers">
2839    <x:lt>
2840      <t>The "chunked" transfer-coding is always acceptable. If the
2841         keyword "trailers" is listed, the client indicates that it is
2842         willing to accept trailer fields in the chunked response on
2843         behalf of itself and any downstream clients. The implication is
2844         that, if given, the client is stating that either all
2845         downstream clients are willing to accept trailer fields in the
2846         forwarded response, or that it will attempt to buffer the
2847         response on behalf of downstream recipients.
2848      </t><t>
2849         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2850         chunked response such that a client can be assured of buffering
2851         the entire response.</t>
2852    </x:lt>
2853    <x:lt>
2854      <t>If the transfer-coding being tested is one of the transfer-codings
2855         listed in the TE field, then it is acceptable unless it
2856         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
2857         qvalue of 0 means "not acceptable.")</t>
2858    </x:lt>
2859    <x:lt>
2860      <t>If multiple transfer-codings are acceptable, then the
2861         acceptable transfer-coding with the highest non-zero qvalue is
2862         preferred.  The "chunked" transfer-coding always has a qvalue
2863         of 1.</t>
2864    </x:lt>
2865  </list>
2866</t>
2867<t>
2868   If the TE field-value is empty or if no TE field is present, the only
2869   transfer-coding is "chunked". A message with no transfer-coding is
2870   always acceptable.
2871</t>
2872</section>
2873
2874<section title="Trailer" anchor="header.trailer">
2875  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2876  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2877  <x:anchor-alias value="Trailer"/>
2878  <x:anchor-alias value="Trailer-v"/>
2879<t>
2880   The "Trailer" general-header field indicates that the given set of
2881   header fields is present in the trailer of a message encoded with
2882   chunked transfer-coding.
2883</t>
2884<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
2885  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
2886  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
2887</artwork></figure>
2888<t>
2889   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2890   message using chunked transfer-coding with a non-empty trailer. Doing
2891   so allows the recipient to know which header fields to expect in the
2892   trailer.
2893</t>
2894<t>
2895   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2896   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
2897   trailer fields in a "chunked" transfer-coding.
2898</t>
2899<t>
2900   Message header fields listed in the Trailer header field &MUST-NOT;
2901   include the following header fields:
2902  <list style="symbols">
2903    <t>Transfer-Encoding</t>
2904    <t>Content-Length</t>
2905    <t>Trailer</t>
2906  </list>
2907</t>
2908</section>
2909
2910<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2911  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2912  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2913  <x:anchor-alias value="Transfer-Encoding"/>
2914  <x:anchor-alias value="Transfer-Encoding-v"/>
2915<t>
2916   The "Transfer-Encoding" general-header field indicates what transfer-codings
2917   (if any) have been applied to the message body. It differs from
2918   Content-Encoding (&content-codings;) in that transfer-codings are a property
2919   of the message (and therefore are removed by intermediaries), whereas
2920   content-codings are not.
2921</t>
2922<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
2923  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
2924                        <x:ref>Transfer-Encoding-v</x:ref>
2925  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
2926</artwork></figure>
2927<t>
2928   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2929</t>
2930<figure><artwork type="example">
2931  Transfer-Encoding: chunked
2932</artwork></figure>
2933<t>
2934   If multiple encodings have been applied to an entity, the transfer-codings
2935   &MUST; be listed in the order in which they were applied.
2936   Additional information about the encoding parameters &MAY; be provided
2937   by other entity-header fields not defined by this specification.
2938</t>
2939<t>
2940   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2941   header.
2942</t>
2943</section>
2944
2945<section title="Upgrade" anchor="header.upgrade">
2946  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2947  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2948  <x:anchor-alias value="Upgrade"/>
2949  <x:anchor-alias value="Upgrade-v"/>
2950<t>
2951   The "Upgrade" general-header field allows the client to specify what
2952   additional communication protocols it would like to use, if the server
2953   chooses to switch protocols. Additionally, the server &MUST; use the Upgrade
2954   header field within a 101 (Switching Protocols) response to indicate which
2955   protocol(s) are being switched to.
2956</t>
2957<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
2958  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
2959  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
2960</artwork></figure>
2961<t>
2962   For example,
2963</t>
2964<figure><artwork type="example">
2965  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2966</artwork></figure>
2967<t>
2968   The Upgrade header field is intended to provide a simple mechanism
2969   for transition from HTTP/1.1 to some other, incompatible protocol. It
2970   does so by allowing the client to advertise its desire to use another
2971   protocol, such as a later version of HTTP with a higher major version
2972   number, even though the current request has been made using HTTP/1.1.
2973   This eases the difficult transition between incompatible protocols by
2974   allowing the client to initiate a request in the more commonly
2975   supported protocol while indicating to the server that it would like
2976   to use a "better" protocol if available (where "better" is determined
2977   by the server, possibly according to the nature of the method and/or
2978   resource being requested).
2979</t>
2980<t>
2981   The Upgrade header field only applies to switching application-layer
2982   protocols upon the existing transport-layer connection. Upgrade
2983   cannot be used to insist on a protocol change; its acceptance and use
2984   by the server is optional. The capabilities and nature of the
2985   application-layer communication after the protocol change is entirely
2986   dependent upon the new protocol chosen, although the first action
2987   after changing the protocol &MUST; be a response to the initial HTTP
2988   request containing the Upgrade header field.
2989</t>
2990<t>
2991   The Upgrade header field only applies to the immediate connection.
2992   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2993   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2994   HTTP/1.1 message.
2995</t>
2996<t>
2997   The Upgrade header field cannot be used to indicate a switch to a
2998   protocol on a different connection. For that purpose, it is more
2999   appropriate to use a 301, 302, 303, or 305 redirection response.
3000</t>
3001<t>
3002   This specification only defines the protocol name "HTTP" for use by
3003   the family of Hypertext Transfer Protocols, as defined by the HTTP
3004   version rules of <xref target="http.version"/> and future updates to this
3005   specification. Additional tokens can be registered with IANA using the
3006   registration procedure defined below. 
3007</t>
3008
3009<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3010<t>
3011   The HTTP Upgrade Token Registry defines the name space for product
3012   tokens used to identify protocols in the Upgrade header field.
3013   Each registered token should be associated with one or a set of
3014   specifications, and with contact information.
3015</t>
3016<t>
3017   Registrations should be allowed on a First Come First Served basis as
3018   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. These
3019   specifications need not be IETF documents or be subject to IESG review, but
3020   should obey the following rules:
3021  <list style="numbers">
3022    <t>A token, once registered, stays registered forever.</t>
3023    <t>The registration &MUST; name a responsible party for the
3024       registration.</t>
3025    <t>The registration &MUST; name a point of contact.</t>
3026    <t>The registration &MAY; name the documentation required for the
3027       token.</t>
3028    <t>The responsible party &MAY; change the registration at any time.
3029       The IANA will keep a record of all such changes, and make them
3030       available upon request.</t>
3031    <t>The responsible party for the first registration of a "product"
3032       token &MUST; approve later registrations of a "version" token
3033       together with that "product" token before they can be registered.</t>
3034    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3035       for a token. This will normally only be used in the case when a
3036       responsible party cannot be contacted.</t>
3037  </list>
3038</t>
3039<t>
3040   It is not required that specifications for upgrade tokens be made
3041   publicly available, but the contact information for the registration
3042   should be.
3043</t>
3044</section>
3045
3046
3047</section>
3048
3049<section title="Via" anchor="header.via">
3050  <iref primary="true" item="Via header" x:for-anchor=""/>
3051  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
3052  <x:anchor-alias value="protocol-name"/>
3053  <x:anchor-alias value="protocol-version"/>
3054  <x:anchor-alias value="pseudonym"/>
3055  <x:anchor-alias value="received-by"/>
3056  <x:anchor-alias value="received-protocol"/>
3057  <x:anchor-alias value="Via"/>
3058  <x:anchor-alias value="Via-v"/>
3059<t>
3060   The "Via" general-header field &MUST; be used by gateways and proxies to
3061   indicate the intermediate protocols and recipients between the user
3062   agent and the server on requests, and between the origin server and
3063   the client on responses. It is analogous to the "Received" field defined in
3064   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
3065   avoiding request loops, and identifying the protocol capabilities of
3066   all senders along the request/response chain.
3067</t>
3068<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"/>
3069  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
3070  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3071                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3072  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3073  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3074  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3075  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3076  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3077</artwork></figure>
3078<t>
3079   The received-protocol indicates the protocol version of the message
3080   received by the server or client along each segment of the
3081   request/response chain. The received-protocol version is appended to
3082   the Via field value when the message is forwarded so that information
3083   about the protocol capabilities of upstream applications remains
3084   visible to all recipients.
3085</t>
3086<t>
3087   The protocol-name is optional if and only if it would be "HTTP". The
3088   received-by field is normally the host and optional port number of a
3089   recipient server or client that subsequently forwarded the message.
3090   However, if the real host is considered to be sensitive information,
3091   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3092   be assumed to be the default port of the received-protocol.
3093</t>
3094<t>
3095   Multiple Via field values represents each proxy or gateway that has
3096   forwarded the message. Each recipient &MUST; append its information
3097   such that the end result is ordered according to the sequence of
3098   forwarding applications.
3099</t>
3100<t>
3101   Comments &MAY; be used in the Via header field to identify the software
3102   of the recipient proxy or gateway, analogous to the User-Agent and
3103   Server header fields. However, all comments in the Via field are
3104   optional and &MAY; be removed by any recipient prior to forwarding the
3105   message.
3106</t>
3107<t>
3108   For example, a request message could be sent from an HTTP/1.0 user
3109   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3110   forward the request to a public proxy at p.example.net, which completes
3111   the request by forwarding it to the origin server at www.example.com.
3112   The request received by www.example.com would then have the following
3113   Via header field:
3114</t>
3115<figure><artwork type="example">
3116  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
3117</artwork></figure>
3118<t>
3119   Proxies and gateways used as a portal through a network firewall
3120   &SHOULD-NOT;, by default, forward the names and ports of hosts within
3121   the firewall region. This information &SHOULD; only be propagated if
3122   explicitly enabled. If not enabled, the received-by host of any host
3123   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
3124   for that host.
3125</t>
3126<t>
3127   For organizations that have strong privacy requirements for hiding
3128   internal structures, a proxy &MAY; combine an ordered subsequence of
3129   Via header field entries with identical received-protocol values into
3130   a single such entry. For example,
3131</t>
3132<figure><artwork type="example">
3133  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3134</artwork></figure>
3135<t>
3136        could be collapsed to
3137</t>
3138<figure><artwork type="example">
3139  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3140</artwork></figure>
3141<t>
3142   Applications &SHOULD-NOT;  combine multiple entries unless they are all
3143   under the same organizational control and the hosts have already been
3144   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
3145   have different received-protocol values.
3146</t>
3147</section>
3148
3149</section>
3150
3151<section title="IANA Considerations" anchor="IANA.considerations">
3152
3153<section title="Message Header Registration" anchor="message.header.registration">
3154<t>
3155   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
3156   with the permanent registrations below (see <xref target="RFC3864"/>):
3157</t>
3158<?BEGININC p1-messaging.iana-headers ?>
3159<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3160<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3161   <ttcol>Header Field Name</ttcol>
3162   <ttcol>Protocol</ttcol>
3163   <ttcol>Status</ttcol>
3164   <ttcol>Reference</ttcol>
3165
3166   <c>Connection</c>
3167   <c>http</c>
3168   <c>standard</c>
3169   <c>
3170      <xref target="header.connection"/>
3171   </c>
3172   <c>Content-Length</c>
3173   <c>http</c>
3174   <c>standard</c>
3175   <c>
3176      <xref target="header.content-length"/>
3177   </c>
3178   <c>Date</c>
3179   <c>http</c>
3180   <c>standard</c>
3181   <c>
3182      <xref target="header.date"/>
3183   </c>
3184   <c>Host</c>
3185   <c>http</c>
3186   <c>standard</c>
3187   <c>
3188      <xref target="header.host"/>
3189   </c>
3190   <c>TE</c>
3191   <c>http</c>
3192   <c>standard</c>
3193   <c>
3194      <xref target="header.te"/>
3195   </c>
3196   <c>Trailer</c>
3197   <c>http</c>
3198   <c>standard</c>
3199   <c>
3200      <xref target="header.trailer"/>
3201   </c>
3202   <c>Transfer-Encoding</c>
3203   <c>http</c>
3204   <c>standard</c>
3205   <c>
3206      <xref target="header.transfer-encoding"/>
3207   </c>
3208   <c>Upgrade</c>
3209   <c>http</c>
3210   <c>standard</c>
3211   <c>
3212      <xref target="header.upgrade"/>
3213   </c>
3214   <c>Via</c>
3215   <c>http</c>
3216   <c>standard</c>
3217   <c>
3218      <xref target="header.via"/>
3219   </c>
3220</texttable>
3221<!--(END)-->
3222<?ENDINC p1-messaging.iana-headers ?>
3223<t>
3224   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3225</t>
3226</section>
3227
3228<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3229<t>
3230   The entries for the "http" and "https" URI Schemes in the registry located at
3231   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3232   should be updated to point to Sections <xref target="http.uri" format="counter"/>
3233   and <xref target="https.uri" format="counter"/> of this document
3234   (see <xref target="RFC4395"/>).
3235</t>
3236</section>
3237
3238<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3239<t>
3240   This document serves as the specification for the Internet media types
3241   "message/http" and "application/http". The following is to be registered with
3242   IANA (see <xref target="RFC4288"/>).
3243</t>
3244<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3245<iref item="Media Type" subitem="message/http" primary="true"/>
3246<iref item="message/http Media Type" primary="true"/>
3247<t>
3248   The message/http type can be used to enclose a single HTTP request or
3249   response message, provided that it obeys the MIME restrictions for all
3250   "message" types regarding line length and encodings.
3251</t>
3252<t>
3253  <list style="hanging" x:indent="12em">
3254    <t hangText="Type name:">
3255      message
3256    </t>
3257    <t hangText="Subtype name:">
3258      http
3259    </t>
3260    <t hangText="Required parameters:">
3261      none
3262    </t>
3263    <t hangText="Optional parameters:">
3264      version, msgtype
3265      <list style="hanging">
3266        <t hangText="version:">
3267          The HTTP-Version number of the enclosed message
3268          (e.g., "1.1"). If not present, the version can be
3269          determined from the first line of the body.
3270        </t>
3271        <t hangText="msgtype:">
3272          The message type -- "request" or "response". If not
3273          present, the type can be determined from the first
3274          line of the body.
3275        </t>
3276      </list>
3277    </t>
3278    <t hangText="Encoding considerations:">
3279      only "7bit", "8bit", or "binary" are permitted
3280    </t>
3281    <t hangText="Security considerations:">
3282      none
3283    </t>
3284    <t hangText="Interoperability considerations:">
3285      none
3286    </t>
3287    <t hangText="Published specification:">
3288      This specification (see <xref target="internet.media.type.message.http"/>).
3289    </t>
3290    <t hangText="Applications that use this media type:">
3291    </t>
3292    <t hangText="Additional information:">
3293      <list style="hanging">
3294        <t hangText="Magic number(s):">none</t>
3295        <t hangText="File extension(s):">none</t>
3296        <t hangText="Macintosh file type code(s):">none</t>
3297      </list>
3298    </t>
3299    <t hangText="Person and email address to contact for further information:">
3300      See Authors Section.
3301    </t>
3302    <t hangText="Intended usage:">
3303      COMMON
3304    </t>
3305    <t hangText="Restrictions on usage:">
3306      none
3307    </t>
3308    <t hangText="Author/Change controller:">
3309      IESG
3310    </t>
3311  </list>
3312</t>
3313</section>
3314<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3315<iref item="Media Type" subitem="application/http" primary="true"/>
3316<iref item="application/http Media Type" primary="true"/>
3317<t>
3318   The application/http type can be used to enclose a pipeline of one or more
3319   HTTP request or response messages (not intermixed).
3320</t>
3321<t>
3322  <list style="hanging" x:indent="12em">
3323    <t hangText="Type name:">
3324      application
3325    </t>
3326    <t hangText="Subtype name:">
3327      http
3328    </t>
3329    <t hangText="Required parameters:">
3330      none
3331    </t>
3332    <t hangText="Optional parameters:">
3333      version, msgtype
3334      <list style="hanging">
3335        <t hangText="version:">
3336          The HTTP-Version number of the enclosed messages
3337          (e.g., "1.1"). If not present, the version can be
3338          determined from the first line of the body.
3339        </t>
3340        <t hangText="msgtype:">
3341          The message type -- "request" or "response". If not
3342          present, the type can be determined from the first
3343          line of the body.
3344        </t>
3345      </list>
3346    </t>
3347    <t hangText="Encoding considerations:">
3348      HTTP messages enclosed by this type
3349      are in "binary" format; use of an appropriate
3350      Content-Transfer-Encoding is required when
3351      transmitted via E-mail.
3352    </t>
3353    <t hangText="Security considerations:">
3354      none
3355    </t>
3356    <t hangText="Interoperability considerations:">
3357      none
3358    </t>
3359    <t hangText="Published specification:">
3360      This specification (see <xref target="internet.media.type.application.http"/>).
3361    </t>
3362    <t hangText="Applications that use this media type:">
3363    </t>
3364    <t hangText="Additional information:">
3365      <list style="hanging">
3366        <t hangText="Magic number(s):">none</t>
3367        <t hangText="File extension(s):">none</t>
3368        <t hangText="Macintosh file type code(s):">none</t>
3369      </list>
3370    </t>
3371    <t hangText="Person and email address to contact for further information:">
3372      See Authors Section.
3373    </t>
3374    <t hangText="Intended usage:">
3375      COMMON
3376    </t>
3377    <t hangText="Restrictions on usage:">
3378      none
3379    </t>
3380    <t hangText="Author/Change controller:">
3381      IESG
3382    </t>
3383  </list>
3384</t>
3385</section>
3386</section>
3387
3388<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3389<t>
3390   The registration procedure for HTTP Transfer Codings is now defined by
3391   <xref target="transfer.coding.registry"/> of this document.
3392</t>
3393<t>
3394   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
3395   should be updated with the registrations below:
3396</t>
3397<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3398   <ttcol>Name</ttcol>
3399   <ttcol>Description</ttcol>
3400   <ttcol>Reference</ttcol>
3401   <c>chunked</c>
3402   <c>Transfer in a series of chunks</c>
3403   <c>
3404      <xref target="chunked.encoding"/>
3405   </c>
3406   <c>compress</c>
3407   <c>UNIX "compress" program method</c>
3408   <c>
3409      <xref target="compress.coding"/>
3410   </c>
3411   <c>deflate</c>
3412   <c>"zlib" format <xref target="RFC1950"/> with "deflate" compression</c>
3413   <c>
3414      <xref target="deflate.coding"/>
3415   </c>
3416   <c>gzip</c>
3417   <c>Same as GNU zip <xref target="RFC1952"/></c>
3418   <c>
3419      <xref target="gzip.coding"/>
3420   </c>
3421</texttable>
3422</section>
3423
3424<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3425<t>
3426   The registration procedure for HTTP Upgrade Tokens -- previously defined
3427   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> -- is now defined
3428   by <xref target="upgrade.token.registry"/> of this document.
3429</t>
3430<t>
3431   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-upgrade-tokens/"/>
3432   should be updated with the registration below:
3433</t>
3434<texttable align="left" suppress-title="true">
3435   <ttcol>Value</ttcol>
3436   <ttcol>Description</ttcol>
3437   <ttcol>Reference</ttcol>
3438
3439   <c>HTTP</c>
3440   <c>Hypertext Transfer Protocol</c> 
3441   <c><xref target="http.version"/> of this specification</c>
3442<!-- IANA should add this without our instructions; emailed on June 05, 2009
3443   <c>TLS/1.0</c>
3444   <c>Transport Layer Security</c>
3445   <c><xref target="RFC2817"/></c> -->
3446
3447</texttable>
3448</section>
3449
3450</section>
3451
3452<section title="Security Considerations" anchor="security.considerations">
3453<t>
3454   This section is meant to inform application developers, information
3455   providers, and users of the security limitations in HTTP/1.1 as
3456   described by this document. The discussion does not include
3457   definitive solutions to the problems revealed, though it does make
3458   some suggestions for reducing security risks.
3459</t>
3460
3461<section title="Personal Information" anchor="personal.information">
3462<t>
3463   HTTP clients are often privy to large amounts of personal information
3464   (e.g. the user's name, location, mail address, passwords, encryption
3465   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3466   leakage of this information.
3467   We very strongly recommend that a convenient interface be provided
3468   for the user to control dissemination of such information, and that
3469   designers and implementors be particularly careful in this area.
3470   History shows that errors in this area often create serious security
3471   and/or privacy problems and generate highly adverse publicity for the
3472   implementor's company.
3473</t>
3474</section>
3475
3476<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3477<t>
3478   A server is in the position to save personal data about a user's
3479   requests which might identify their reading patterns or subjects of
3480   interest. This information is clearly confidential in nature and its
3481   handling can be constrained by law in certain countries. People using
3482   HTTP to provide data are responsible for ensuring that
3483   such material is not distributed without the permission of any
3484   individuals that are identifiable by the published results.
3485</t>
3486</section>
3487
3488<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3489<t>
3490   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3491   the documents returned by HTTP requests to be only those that were
3492   intended by the server administrators. If an HTTP server translates
3493   HTTP URIs directly into file system calls, the server &MUST; take
3494   special care not to serve files that were not intended to be
3495   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3496   other operating systems use ".." as a path component to indicate a
3497   directory level above the current one. On such a system, an HTTP
3498   server &MUST; disallow any such construct in the request-target if it
3499   would otherwise allow access to a resource outside those intended to
3500   be accessible via the HTTP server. Similarly, files intended for
3501   reference only internally to the server (such as access control
3502   files, configuration files, and script code) &MUST; be protected from
3503   inappropriate retrieval, since they might contain sensitive
3504   information. Experience has shown that minor bugs in such HTTP server
3505   implementations have turned into security risks.
3506</t>
3507</section>
3508
3509<section title="DNS Spoofing" anchor="dns.spoofing">
3510<t>
3511   Clients using HTTP rely heavily on the Domain Name Service, and are
3512   thus generally prone to security attacks based on the deliberate
3513   mis-association of IP addresses and DNS names. Clients need to be
3514   cautious in assuming the continuing validity of an IP number/DNS name
3515   association.
3516</t>
3517<t>
3518   In particular, HTTP clients &SHOULD; rely on their name resolver for
3519   confirmation of an IP number/DNS name association, rather than
3520   caching the result of previous host name lookups. Many platforms
3521   already can cache host name lookups locally when appropriate, and
3522   they &SHOULD; be configured to do so. It is proper for these lookups to
3523   be cached, however, only when the TTL (Time To Live) information
3524   reported by the name server makes it likely that the cached
3525   information will remain useful.
3526</t>
3527<t>
3528   If HTTP clients cache the results of host name lookups in order to
3529   achieve a performance improvement, they &MUST; observe the TTL
3530   information reported by DNS.
3531</t>
3532<t>
3533   If HTTP clients do not observe this rule, they could be spoofed when
3534   a previously-accessed server's IP address changes. As network
3535   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3536   possibility of this form of attack will grow. Observing this
3537   requirement thus reduces this potential security vulnerability.
3538</t>
3539<t>
3540   This requirement also improves the load-balancing behavior of clients
3541   for replicated servers using the same DNS name and reduces the
3542   likelihood of a user's experiencing failure in accessing sites which
3543   use that strategy.
3544</t>
3545</section>
3546
3547<section title="Proxies and Caching" anchor="attack.proxies">
3548<t>
3549   By their very nature, HTTP proxies are men-in-the-middle, and
3550   represent an opportunity for man-in-the-middle attacks. Compromise of
3551   the systems on which the proxies run can result in serious security
3552   and privacy problems. Proxies have access to security-related
3553   information, personal information about individual users and
3554   organizations, and proprietary information belonging to users and
3555   content providers. A compromised proxy, or a proxy implemented or
3556   configured without regard to security and privacy considerations,
3557   might be used in the commission of a wide range of potential attacks.
3558</t>
3559<t>
3560   Proxy operators should protect the systems on which proxies run as
3561   they would protect any system that contains or transports sensitive
3562   information. In particular, log information gathered at proxies often
3563   contains highly sensitive personal information, and/or information
3564   about organizations. Log information should be carefully guarded, and
3565   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
3566</t>
3567<t>
3568   Proxy implementors should consider the privacy and security
3569   implications of their design and coding decisions, and of the
3570   configuration options they provide to proxy operators (especially the
3571   default configuration).
3572</t>
3573<t>
3574   Users of a proxy need to be aware that they are no trustworthier than
3575   the people who run the proxy; HTTP itself cannot solve this problem.
3576</t>
3577<t>
3578   The judicious use of cryptography, when appropriate, may suffice to
3579   protect against a broad range of security and privacy attacks. Such
3580   cryptography is beyond the scope of the HTTP/1.1 specification.
3581</t>
3582</section>
3583
3584<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3585<t>
3586   They exist. They are hard to defend against. Research continues.
3587   Beware.
3588</t>
3589</section>
3590</section>
3591
3592<section title="Acknowledgments" anchor="ack">
3593<t>
3594   HTTP has evolved considerably over the years. It has
3595   benefited from a large and active developer community--the many
3596   people who have participated on the www-talk mailing list--and it is
3597   that community which has been most responsible for the success of
3598   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3599   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3600   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3601   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3602   VanHeyningen deserve special recognition for their efforts in
3603   defining early aspects of the protocol.
3604</t>
3605<t>
3606   This document has benefited greatly from the comments of all those
3607   participating in the HTTP-WG. In addition to those already mentioned,
3608   the following individuals have contributed to this specification:
3609</t>
3610<t>
3611   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3612   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3613   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3614   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3615   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3616   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3617   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3618   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3619   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3620   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3621   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3622   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3623   Josh Cohen.
3624</t>
3625<t>
3626   Thanks to the "cave men" of Palo Alto. You know who you are.
3627</t>
3628<t>
3629   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3630   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3631   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3632   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3633   Larry Masinter for their help. And thanks go particularly to Jeff
3634   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3635</t>
3636<t>
3637   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3638   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3639   discovery of many of the problems that this document attempts to
3640   rectify.
3641</t>
3642<t>
3643   This specification makes heavy use of the augmented BNF and generic
3644   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3645   reuses many of the definitions provided by Nathaniel Borenstein and
3646   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3647   specification will help reduce past confusion over the relationship
3648   between HTTP and Internet mail message formats.
3649</t>
3650</section>
3651
3652</middle>
3653<back>
3654
3655<references title="Normative References">
3656
3657<reference anchor="ISO-8859-1">
3658  <front>
3659    <title>
3660     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3661    </title>
3662    <author>
3663      <organization>International Organization for Standardization</organization>
3664    </author>
3665    <date year="1998"/>
3666  </front>
3667  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3668</reference>
3669
3670<reference anchor="Part2">
3671  <front>
3672    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3673    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3674      <organization abbrev="Day Software">Day Software</organization>
3675      <address><email>fielding@gbiv.com</email></address>
3676    </author>
3677    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3678      <organization>One Laptop per Child</organization>
3679      <address><email>jg@laptop.org</email></address>
3680    </author>
3681    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3682      <organization abbrev="HP">Hewlett-Packard Company</organization>
3683      <address><email>JeffMogul@acm.org</email></address>
3684    </author>
3685    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3686      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3687      <address><email>henrikn@microsoft.com</email></address>
3688    </author>
3689    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3690      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3691      <address><email>LMM@acm.org</email></address>
3692    </author>
3693    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3694      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3695      <address><email>paulle@microsoft.com</email></address>
3696    </author>
3697    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3698      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3699      <address><email>timbl@w3.org</email></address>
3700    </author>
3701    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3702      <organization abbrev="W3C">World Wide Web Consortium</organization>
3703      <address><email>ylafon@w3.org</email></address>
3704    </author>
3705    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3706      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3707      <address><email>julian.reschke@greenbytes.de</email></address>
3708    </author>
3709    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3710  </front>
3711  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3712  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3713</reference>
3714
3715<reference anchor="Part3">
3716  <front>
3717    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3718    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3719      <organization abbrev="Day Software">Day Software</organization>
3720      <address><email>fielding@gbiv.com</email></address>
3721    </author>
3722    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3723      <organization>One Laptop per Child</organization>
3724      <address><email>jg@laptop.org</email></address>
3725    </author>
3726    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3727      <organization abbrev="HP">Hewlett-Packard Company</organization>
3728      <address><email>JeffMogul@acm.org</email></address>
3729    </author>
3730    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3731      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3732      <address><email>henrikn@microsoft.com</email></address>
3733    </author>
3734    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3735      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3736      <address><email>LMM@acm.org</email></address>
3737    </author>
3738    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3739      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3740      <address><email>paulle@microsoft.com</email></address>
3741    </author>
3742    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3743      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3744      <address><email>timbl@w3.org</email></address>
3745    </author>
3746    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3747      <organization abbrev="W3C">World Wide Web Consortium</organization>
3748      <address><email>ylafon@w3.org</email></address>
3749    </author>
3750    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3751      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3752      <address><email>julian.reschke@greenbytes.de</email></address>
3753    </author>
3754    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3755  </front>
3756  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3757  <x:source href="p3-payload.xml" basename="p3-payload"/>
3758</reference>
3759
3760<reference anchor="Part5">
3761  <front>
3762    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3763    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3764      <organization abbrev="Day Software">Day Software</organization>
3765      <address><email>fielding@gbiv.com</email></address>
3766    </author>
3767    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3768      <organization>One Laptop per Child</organization>
3769      <address><email>jg@laptop.org</email></address>
3770    </author>
3771    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3772      <organization abbrev="HP">Hewlett-Packard Company</organization>
3773      <address><email>JeffMogul@acm.org</email></address>
3774    </author>
3775    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3776      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3777      <address><email>henrikn@microsoft.com</email></address>
3778    </author>
3779    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3780      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3781      <address><email>LMM@acm.org</email></address>
3782    </author>
3783    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3784      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3785      <address><email>paulle@microsoft.com</email></address>
3786    </author>
3787    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3788      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3789      <address><email>timbl@w3.org</email></address>
3790    </author>
3791    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3792      <organization abbrev="W3C">World Wide Web Consortium</organization>
3793      <address><email>ylafon@w3.org</email></address>
3794    </author>
3795    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3796      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3797      <address><email>julian.reschke@greenbytes.de</email></address>
3798    </author>
3799    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3800  </front>
3801  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3802  <x:source href="p5-range.xml" basename="p5-range"/>
3803</reference>
3804
3805<reference anchor="Part6">
3806  <front>
3807    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3808    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3809      <organization abbrev="Day Software">Day Software</organization>
3810      <address><email>fielding@gbiv.com</email></address>
3811    </author>
3812    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3813      <organization>One Laptop per Child</organization>
3814      <address><email>jg@laptop.org</email></address>
3815    </author>
3816    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3817      <organization abbrev="HP">Hewlett-Packard Company</organization>
3818      <address><email>JeffMogul@acm.org</email></address>
3819    </author>
3820    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3821      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3822      <address><email>henrikn@microsoft.com</email></address>
3823    </author>
3824    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3825      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3826      <address><email>LMM@acm.org</email></address>
3827    </author>
3828    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3829      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3830      <address><email>paulle@microsoft.com</email></address>
3831    </author>
3832    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3833      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3834      <address><email>timbl@w3.org</email></address>
3835    </author>
3836    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3837      <organization abbrev="W3C">World Wide Web Consortium</organization>
3838      <address><email>ylafon@w3.org</email></address>
3839    </author>
3840    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3841      <address><email>mnot@mnot.net</email></address>
3842    </author>
3843    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3844      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3845      <address><email>julian.reschke@greenbytes.de</email></address>
3846    </author>
3847    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3848  </front>
3849  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3850  <x:source href="p6-cache.xml" basename="p6-cache"/>
3851</reference>
3852
3853<reference anchor="RFC5234">
3854  <front>
3855    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3856    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3857      <organization>Brandenburg InternetWorking</organization>
3858      <address>
3859        <email>dcrocker@bbiw.net</email>
3860      </address> 
3861    </author>
3862    <author initials="P." surname="Overell" fullname="Paul Overell">
3863      <organization>THUS plc.</organization>
3864      <address>
3865        <email>paul.overell@thus.net</email>
3866      </address>
3867    </author>
3868    <date month="January" year="2008"/>
3869  </front>
3870  <seriesInfo name="STD" value="68"/>
3871  <seriesInfo name="RFC" value="5234"/>
3872</reference>
3873
3874<reference anchor="RFC2119">
3875  <front>
3876    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3877    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3878      <organization>Harvard University</organization>
3879      <address><email>sob@harvard.edu</email></address>
3880    </author>
3881    <date month="March" year="1997"/>
3882  </front>
3883  <seriesInfo name="BCP" value="14"/>
3884  <seriesInfo name="RFC" value="2119"/>
3885</reference>
3886
3887<reference anchor="RFC3986">
3888 <front>
3889  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3890  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3891    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3892    <address>
3893       <email>timbl@w3.org</email>
3894       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3895    </address>
3896  </author>
3897  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3898    <organization abbrev="Day Software">Day Software</organization>
3899    <address>
3900      <email>fielding@gbiv.com</email>
3901      <uri>http://roy.gbiv.com/</uri>
3902    </address>
3903  </author>
3904  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3905    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3906    <address>
3907      <email>LMM@acm.org</email>
3908      <uri>http://larry.masinter.net/</uri>
3909    </address>
3910  </author>
3911  <date month='January' year='2005'></date>
3912 </front>
3913 <seriesInfo name="RFC" value="3986"/>
3914 <seriesInfo name="STD" value="66"/>
3915</reference>
3916
3917<reference anchor="USASCII">
3918  <front>
3919    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3920    <author>
3921      <organization>American National Standards Institute</organization>
3922    </author>
3923    <date year="1986"/>
3924  </front>
3925  <seriesInfo name="ANSI" value="X3.4"/>
3926</reference>
3927
3928<reference anchor="RFC1950">
3929  <front>
3930    <title>ZLIB Compressed Data Format Specification version 3.3</title>
3931    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
3932      <organization>Aladdin Enterprises</organization>
3933      <address><email>ghost@aladdin.com</email></address>
3934    </author>
3935    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
3936    <date month="May" year="1996"/>
3937  </front>
3938  <seriesInfo name="RFC" value="1950"/>
3939  <annotation>
3940    RFC 1950 is an Informational RFC, thus it may be less stable than
3941    this specification. On the other hand, this downward reference was
3942    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
3943    therefore it is unlikely to cause problems in practice. See also
3944    <xref target="BCP97"/>.
3945  </annotation>
3946</reference>
3947
3948<reference anchor="RFC1951">
3949  <front>
3950    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
3951    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
3952      <organization>Aladdin Enterprises</organization>
3953      <address><email>ghost@aladdin.com</email></address>
3954    </author>
3955    <date month="May" year="1996"/>
3956  </front>
3957  <seriesInfo name="RFC" value="1951"/>
3958  <annotation>
3959    RFC 1951 is an Informational RFC, thus it may be less stable than
3960    this specification. On the other hand, this downward reference was
3961    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
3962    therefore it is unlikely to cause problems in practice. See also
3963    <xref target="BCP97"/>.
3964  </annotation>
3965</reference>
3966
3967<reference anchor="RFC1952">
3968  <front>
3969    <title>GZIP file format specification version 4.3</title>
3970    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
3971      <organization>Aladdin Enterprises</organization>
3972      <address><email>ghost@aladdin.com</email></address>
3973    </author>
3974    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
3975      <address><email>gzip@prep.ai.mit.edu</email></address>
3976    </author>
3977    <author initials="M." surname="Adler" fullname="Mark Adler">
3978      <address><email>madler@alumni.caltech.edu</email></address>
3979    </author>
3980    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
3981      <address><email>ghost@aladdin.com</email></address>
3982    </author>
3983    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
3984      <address><email>randeg@alumni.rpi.edu</email></address>
3985    </author>
3986    <date month="May" year="1996"/>
3987  </front>
3988  <seriesInfo name="RFC" value="1952"/>
3989  <annotation>
3990    RFC 1952 is an Informational RFC, thus it may be less stable than
3991    this specification. On the other hand, this downward reference was
3992    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
3993    therefore it is unlikely to cause problems in practice. See also
3994    <xref target="BCP97"/>.
3995  </annotation>
3996</reference>
3997
3998</references>
3999
4000<references title="Informative References">
4001
4002<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4003  <front>
4004    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4005    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen"/>
4006    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4007    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4008    <author initials="H." surname="Lie" fullname="H. Lie"/>
4009    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4010    <date year="1997" month="September"/>
4011  </front>
4012  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4013</reference>
4014
4015<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4016  <front>
4017    <title>Improving HTTP Latency</title>
4018    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4019    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4020    <date year="1995" month="December"/>
4021  </front>
4022  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4023</reference>
4024
4025<reference anchor="RFC1123">
4026  <front>
4027    <title>Requirements for Internet Hosts - Application and Support</title>
4028    <author initials="R." surname="Braden" fullname="Robert Braden">
4029      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4030      <address><email>Braden@ISI.EDU</email></address>
4031    </author>
4032    <date month="October" year="1989"/>
4033  </front>
4034  <seriesInfo name="STD" value="3"/>
4035  <seriesInfo name="RFC" value="1123"/>
4036</reference>
4037
4038<reference anchor="RFC1305">
4039  <front>
4040    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
4041    <author initials="D." surname="Mills" fullname="David L. Mills">
4042      <organization>University of Delaware, Electrical Engineering Department</organization>
4043      <address><email>mills@udel.edu</email></address>
4044    </author>
4045    <date month="March" year="1992"/>
4046  </front>
4047  <seriesInfo name="RFC" value="1305"/>
4048</reference>
4049
4050<reference anchor="RFC1900">
4051  <front>
4052    <title>Renumbering Needs Work</title>
4053    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4054      <organization>CERN, Computing and Networks Division</organization>
4055      <address><email>brian@dxcoms.cern.ch</email></address>
4056    </author>
4057    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4058      <organization>cisco Systems</organization>
4059      <address><email>yakov@cisco.com</email></address>
4060    </author>
4061    <date month="February" year="1996"/>
4062  </front>
4063  <seriesInfo name="RFC" value="1900"/>
4064</reference>
4065
4066<reference anchor="RFC1945">
4067  <front>
4068    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4069    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4070      <organization>MIT, Laboratory for Computer Science</organization>
4071      <address><email>timbl@w3.org</email></address>
4072    </author>
4073    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4074      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4075      <address><email>fielding@ics.uci.edu</email></address>
4076    </author>
4077    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4078      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4079      <address><email>frystyk@w3.org</email></address>
4080    </author>
4081    <date month="May" year="1996"/>
4082  </front>
4083  <seriesInfo name="RFC" value="1945"/>
4084</reference>
4085
4086<reference anchor="RFC2045">
4087  <front>
4088    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4089    <author initials="N." surname="Freed" fullname="Ned Freed">
4090      <organization>Innosoft International, Inc.</organization>
4091      <address><email>ned@innosoft.com</email></address>
4092    </author>
4093    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4094      <organization>First Virtual Holdings</organization>
4095      <address><email>nsb@nsb.fv.com</email></address>
4096    </author>
4097    <date month="November" year="1996"/>
4098  </front>
4099  <seriesInfo name="RFC" value="2045"/>
4100</reference>
4101
4102<reference anchor="RFC2047">
4103  <front>
4104    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4105    <author initials="K." surname="Moore" fullname="Keith Moore">
4106      <organization>University of Tennessee</organization>
4107      <address><email>moore@cs.utk.edu</email></address>
4108    </author>
4109    <date month="November" year="1996"/>
4110  </front>
4111  <seriesInfo name="RFC" value="2047"/>
4112</reference>
4113
4114<reference anchor="RFC2068">
4115  <front>
4116    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4117    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4118      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4119      <address><email>fielding@ics.uci.edu</email></address>
4120    </author>
4121    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4122      <organization>MIT Laboratory for Computer Science</organization>
4123      <address><email>jg@w3.org</email></address>
4124    </author>
4125    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4126      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4127      <address><email>mogul@wrl.dec.com</email></address>
4128    </author>
4129    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4130      <organization>MIT Laboratory for Computer Science</organization>
4131      <address><email>frystyk@w3.org</email></address>
4132    </author>
4133    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4134      <organization>MIT Laboratory for Computer Science</organization>
4135      <address><email>timbl@w3.org</email></address>
4136    </author>
4137    <date month="January" year="1997"/>
4138  </front>
4139  <seriesInfo name="RFC" value="2068"/>
4140</reference>
4141
4142<reference anchor='RFC2109'>
4143  <front>
4144    <title>HTTP State Management Mechanism</title>
4145    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
4146      <organization>Bell Laboratories, Lucent Technologies</organization>
4147      <address><email>dmk@bell-labs.com</email></address>
4148    </author>
4149    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4150      <organization>Netscape Communications Corp.</organization>
4151      <address><email>montulli@netscape.com</email></address>
4152    </author>
4153    <date year='1997' month='February' />
4154  </front>
4155  <seriesInfo name='RFC' value='2109' />
4156</reference>
4157
4158<reference anchor="RFC2145">
4159  <front>
4160    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4161    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4162      <organization>Western Research Laboratory</organization>
4163      <address><email>mogul@wrl.dec.com</email></address>
4164    </author>
4165    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4166      <organization>Department of Information and Computer Science</organization>
4167      <address><email>fielding@ics.uci.edu</email></address>
4168    </author>
4169    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4170      <organization>MIT Laboratory for Computer Science</organization>
4171      <address><email>jg@w3.org</email></address>
4172    </author>
4173    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4174      <organization>W3 Consortium</organization>
4175      <address><email>frystyk@w3.org</email></address>
4176    </author>
4177    <date month="May" year="1997"/>
4178  </front>
4179  <seriesInfo name="RFC" value="2145"/>
4180</reference>
4181
4182<reference anchor="RFC2616">
4183  <front>
4184    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4185    <author initials="R." surname="Fielding" fullname="R. Fielding">
4186      <organization>University of California, Irvine</organization>
4187      <address><email>fielding@ics.uci.edu</email></address>
4188    </author>
4189    <author initials="J." surname="Gettys" fullname="J. Gettys">
4190      <organization>W3C</organization>
4191      <address><email>jg@w3.org</email></address>
4192    </author>
4193    <author initials="J." surname="Mogul" fullname="J. Mogul">
4194      <organization>Compaq Computer Corporation</organization>
4195      <address><email>mogul@wrl.dec.com</email></address>
4196    </author>
4197    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4198      <organization>MIT Laboratory for Computer Science</organization>
4199      <address><email>frystyk@w3.org</email></address>
4200    </author>
4201    <author initials="L." surname="Masinter" fullname="L. Masinter">
4202      <organization>Xerox Corporation</organization>
4203      <address><email>masinter@parc.xerox.com</email></address>
4204    </author>
4205    <author initials="P." surname="Leach" fullname="P. Leach">
4206      <organization>Microsoft Corporation</organization>
4207      <address><email>paulle@microsoft.com</email></address>
4208    </author>
4209    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4210      <organization>W3C</organization>
4211      <address><email>timbl@w3.org</email></address>
4212    </author>
4213    <date month="June" year="1999"/>
4214  </front>
4215  <seriesInfo name="RFC" value="2616"/>
4216</reference>
4217
4218<reference anchor='RFC2817'>
4219  <front>
4220    <title>Upgrading to TLS Within HTTP/1.1</title>
4221    <author initials='R.' surname='Khare' fullname='R. Khare'>
4222      <organization>4K Associates / UC Irvine</organization>
4223      <address><email>rohit@4K-associates.com</email></address>
4224    </author>
4225    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4226      <organization>Agranat Systems, Inc.</organization>
4227      <address><email>lawrence@agranat.com</email></address>
4228    </author>
4229    <date year='2000' month='May' />
4230  </front>
4231  <seriesInfo name='RFC' value='2817' />
4232</reference>
4233
4234<reference anchor='RFC2818'>
4235  <front>
4236    <title>HTTP Over TLS</title>
4237    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4238      <organization>RTFM, Inc.</organization>
4239      <address><email>ekr@rtfm.com</email></address>
4240    </author>
4241    <date year='2000' month='May' />
4242  </front>
4243  <seriesInfo name='RFC' value='2818' />
4244</reference>
4245
4246<reference anchor='RFC2965'>
4247  <front>
4248    <title>HTTP State Management Mechanism</title>
4249    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4250      <organization>Bell Laboratories, Lucent Technologies</organization>
4251      <address><email>dmk@bell-labs.com</email></address>
4252    </author>
4253    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4254      <organization>Epinions.com, Inc.</organization>
4255      <address><email>lou@montulli.org</email></address>
4256    </author>
4257    <date year='2000' month='October' />
4258  </front>
4259  <seriesInfo name='RFC' value='2965' />
4260</reference>
4261
4262<reference anchor='RFC3864'>
4263  <front>
4264    <title>Registration Procedures for Message Header Fields</title>
4265    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4266      <organization>Nine by Nine</organization>
4267      <address><email>GK-IETF@ninebynine.org</email></address>
4268    </author>
4269    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4270      <organization>BEA Systems</organization>
4271      <address><email>mnot@pobox.com</email></address>
4272    </author>
4273    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4274      <organization>HP Labs</organization>
4275      <address><email>JeffMogul@acm.org</email></address>
4276    </author>
4277    <date year='2004' month='September' />
4278  </front>
4279  <seriesInfo name='BCP' value='90' />
4280  <seriesInfo name='RFC' value='3864' />
4281</reference>
4282
4283<reference anchor="RFC4288">
4284  <front>
4285    <title>Media Type Specifications and Registration Procedures</title>
4286    <author initials="N." surname="Freed" fullname="N. Freed">
4287      <organization>Sun Microsystems</organization>
4288      <address>
4289        <email>ned.freed@mrochek.com</email>
4290      </address>
4291    </author>
4292    <author initials="J." surname="Klensin" fullname="J. Klensin">
4293      <address>
4294        <email>klensin+ietf@jck.com</email>
4295      </address>
4296    </author>
4297    <date year="2005" month="December"/>
4298  </front>
4299  <seriesInfo name="BCP" value="13"/>
4300  <seriesInfo name="RFC" value="4288"/>
4301</reference>
4302
4303<reference anchor='RFC4395'>
4304  <front>
4305    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4306    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4307      <organization>AT&amp;T Laboratories</organization>
4308      <address>
4309        <email>tony+urireg@maillennium.att.com</email>
4310      </address>
4311    </author>
4312    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4313      <organization>Qualcomm, Inc.</organization>
4314      <address>
4315        <email>hardie@qualcomm.com</email>
4316      </address>
4317    </author>
4318    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4319      <organization>Adobe Systems</organization>
4320      <address>
4321        <email>LMM@acm.org</email>
4322      </address>
4323    </author>
4324    <date year='2006' month='February' />
4325  </front>
4326  <seriesInfo name='BCP' value='115' />
4327  <seriesInfo name='RFC' value='4395' />
4328</reference>
4329
4330<reference anchor='RFC5226'>
4331  <front>
4332    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4333    <author initials='T.' surname='Narten' fullname='T. Narten'>
4334      <organization>IBM</organization>
4335      <address><email>narten@us.ibm.com</email></address>
4336    </author>
4337    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4338      <organization>Google</organization>
4339      <address><email>Harald@Alvestrand.no</email></address>
4340    </author>
4341    <date year='2008' month='May' />
4342  </front>
4343  <seriesInfo name='BCP' value='26' />
4344  <seriesInfo name='RFC' value='5226' />
4345</reference>
4346
4347<reference anchor="RFC5322">
4348  <front>
4349    <title>Internet Message Format</title>
4350    <author initials="P." surname="Resnick" fullname="P. Resnick">
4351      <organization>Qualcomm Incorporated</organization>
4352    </author>
4353    <date year="2008" month="October"/>
4354  </front> 
4355  <seriesInfo name="RFC" value="5322"/>
4356</reference>
4357
4358<reference anchor='BCP97'>
4359  <front>
4360    <title>Handling Normative References to Standards-Track Documents</title>
4361    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4362      <address>
4363        <email>klensin+ietf@jck.com</email>
4364      </address>
4365    </author>
4366    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4367      <organization>MIT</organization>
4368      <address>
4369        <email>hartmans-ietf@mit.edu</email>
4370      </address>
4371    </author>
4372    <date year='2007' month='June' />
4373  </front>
4374  <seriesInfo name='BCP' value='97' />
4375  <seriesInfo name='RFC' value='4897' />
4376</reference>
4377
4378<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4379  <front>
4380    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4381    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4382    <date year="2001" month="November"/>
4383  </front>
4384  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4385</reference>
4386
4387<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4388  <front>
4389    <title>Analysis of HTTP Performance Problems</title>
4390    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4391    <date/>
4392  </front>
4393</reference>
4394
4395<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4396  <front>
4397  <title>Analysis of HTTP Performance</title>
4398  <author initials="J." surname="Touch" fullname="Joe Touch">
4399    <organization>USC/Information Sciences Institute</organization>
4400    <address><email>touch@isi.edu</email></address>
4401  </author>
4402  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4403    <organization>USC/Information Sciences Institute</organization>
4404    <address><email>johnh@isi.edu</email></address>
4405  </author>
4406  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4407    <organization>USC/Information Sciences Institute</organization>
4408    <address><email>katia@isi.edu</email></address>
4409  </author>
4410  <date year="1998" month="Aug"/>
4411  </front>
4412  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4413  <annotation>(original report dated Aug. 1996)</annotation>
4414</reference>
4415
4416</references>
4417
4418
4419<section title="Tolerant Applications" anchor="tolerant.applications">
4420<t>
4421   Although this document specifies the requirements for the generation
4422   of HTTP/1.1 messages, not all applications will be correct in their
4423   implementation. We therefore recommend that operational applications
4424   be tolerant of deviations whenever those deviations can be
4425   interpreted unambiguously.
4426</t>
4427<t>
4428   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
4429   tolerant when parsing the Request-Line. In particular, they &SHOULD;
4430   accept any amount of WSP characters between fields, even though
4431   only a single SP is required.
4432</t>
4433<t>
4434   The line terminator for header fields is the sequence CRLF.
4435   However, we recommend that applications, when parsing such headers,
4436   recognize a single LF as a line terminator and ignore the leading CR.
4437</t>
4438<t>
4439   The character set of an entity-body &SHOULD; be labeled as the lowest
4440   common denominator of the character codes used within that body, with
4441   the exception that not labeling the entity is preferred over labeling
4442   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
4443</t>
4444<t>
4445   Additional rules for requirements on parsing and encoding of dates
4446   and other potential problems with date encodings include:
4447</t>
4448<t>
4449  <list style="symbols">
4450     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4451        which appears to be more than 50 years in the future is in fact
4452        in the past (this helps solve the "year 2000" problem).</t>
4453
4454     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4455        Expires date as earlier than the proper value, but &MUST-NOT;
4456        internally represent a parsed Expires date as later than the
4457        proper value.</t>
4458
4459     <t>All expiration-related calculations &MUST; be done in GMT. The
4460        local time zone &MUST-NOT; influence the calculation or comparison
4461        of an age or expiration time.</t>
4462
4463     <t>If an HTTP header incorrectly carries a date value with a time
4464        zone other than GMT, it &MUST; be converted into GMT using the
4465        most conservative possible conversion.</t>
4466  </list>
4467</t>
4468</section>
4469
4470<section title="Compatibility with Previous Versions" anchor="compatibility">
4471<t>
4472   HTTP has been in use by the World-Wide Web global information initiative
4473   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4474   was a simple protocol for hypertext data transfer across the Internet
4475   with only a single method and no metadata.
4476   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4477   methods and MIME-like messaging that could include metadata about the data
4478   transferred and modifiers on the request/response semantics. However,
4479   HTTP/1.0 did not sufficiently take into consideration the effects of
4480   hierarchical proxies, caching, the need for persistent connections, or
4481   name-based virtual hosts. The proliferation of incompletely-implemented
4482   applications calling themselves "HTTP/1.0" further necessitated a
4483   protocol version change in order for two communicating applications
4484   to determine each other's true capabilities.
4485</t>
4486<t>
4487   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4488   requirements that enable reliable implementations, adding only
4489   those new features that will either be safely ignored by an HTTP/1.0
4490   recipient or only sent when communicating with a party advertising
4491   compliance with HTTP/1.1.
4492</t>
4493<t>
4494   It is beyond the scope of a protocol specification to mandate
4495   compliance with previous versions. HTTP/1.1 was deliberately
4496   designed, however, to make supporting previous versions easy. It is
4497   worth noting that, at the time of composing this specification, we would
4498   expect general-purpose HTTP/1.1 servers to:
4499  <list style="symbols">
4500     <t>understand any valid request in the format of HTTP/1.0 and
4501        1.1;</t>
4502
4503     <t>respond appropriately with a message in the same major version
4504        used by the client.</t>
4505  </list>
4506</t>
4507<t>
4508   And we would expect HTTP/1.1 clients to:
4509  <list style="symbols">
4510     <t>understand any valid response in the format of HTTP/1.0 or
4511        1.1.</t>
4512  </list>
4513</t>
4514<t>
4515   For most implementations of HTTP/1.0, each connection is established
4516   by the client prior to the request and closed by the server after
4517   sending the response. Some implementations implement the Keep-Alive
4518   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4519</t>
4520
4521<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4522<t>
4523   This section summarizes major differences between versions HTTP/1.0
4524   and HTTP/1.1.
4525</t>
4526
4527<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">
4528<t>
4529   The requirements that clients and servers support the Host request-header,
4530   report an error if the Host request-header (<xref target="header.host"/>) is
4531   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4532   are among the most important changes defined by this
4533   specification.
4534</t>
4535<t>
4536   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4537   addresses and servers; there was no other established mechanism for
4538   distinguishing the intended server of a request than the IP address
4539   to which that request was directed. The changes outlined above will
4540   allow the Internet, once older HTTP clients are no longer common, to
4541   support multiple Web sites from a single IP address, greatly
4542   simplifying large operational Web servers, where allocation of many
4543   IP addresses to a single host has created serious problems. The
4544   Internet will also be able to recover the IP addresses that have been
4545   allocated for the sole purpose of allowing special-purpose domain
4546   names to be used in root-level HTTP URLs. Given the rate of growth of
4547   the Web, and the number of servers already deployed, it is extremely
4548   important that all implementations of HTTP (including updates to
4549   existing HTTP/1.0 applications) correctly implement these
4550   requirements:
4551  <list style="symbols">
4552     <t>Both clients and servers &MUST; support the Host request-header.</t>
4553
4554     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4555
4556     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4557        request does not include a Host request-header.</t>
4558
4559     <t>Servers &MUST; accept absolute URIs.</t>
4560  </list>
4561</t>
4562</section>
4563</section>
4564
4565<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4566<t>
4567   Some clients and servers might wish to be compatible with some
4568   previous implementations of persistent connections in HTTP/1.0
4569   clients and servers. Persistent connections in HTTP/1.0 are
4570   explicitly negotiated as they are not the default behavior. HTTP/1.0
4571   experimental implementations of persistent connections are faulty,
4572   and the new facilities in HTTP/1.1 are designed to rectify these
4573   problems. The problem was that some existing 1.0 clients may be
4574   sending Keep-Alive to a proxy server that doesn't understand
4575   Connection, which would then erroneously forward it to the next
4576   inbound server, which would establish the Keep-Alive connection and
4577   result in a hung HTTP/1.0 proxy waiting for the close on the
4578   response. The result is that HTTP/1.0 clients must be prevented from
4579   using Keep-Alive when talking to proxies.
4580</t>
4581<t>
4582   However, talking to proxies is the most important use of persistent
4583   connections, so that prohibition is clearly unacceptable. Therefore,
4584   we need some other mechanism for indicating a persistent connection
4585   is desired, which is safe to use even when talking to an old proxy
4586   that ignores Connection. Persistent connections are the default for
4587   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4588   declaring non-persistence. See <xref target="header.connection"/>.
4589</t>
4590<t>
4591   The original HTTP/1.0 form of persistent connections (the Connection:
4592   Keep-Alive and Keep-Alive header) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4593</t>
4594</section>
4595
4596<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4597<t>
4598   This specification has been carefully audited to correct and
4599   disambiguate key word usage; RFC 2068 had many problems in respect to
4600   the conventions laid out in <xref target="RFC2119"/>.
4601</t>
4602<t>
4603   Transfer-coding and message lengths all interact in ways that
4604   required fixing exactly when chunked encoding is used (to allow for
4605   transfer encoding that may not be self delimiting); it was important
4606   to straighten out exactly how message lengths are computed. (Sections
4607   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4608   <xref target="header.content-length" format="counter"/>,
4609   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4610</t>
4611<t>
4612   The use and interpretation of HTTP version numbers has been clarified
4613   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4614   version they support to deal with problems discovered in HTTP/1.0
4615   implementations (<xref target="http.version"/>)
4616</t>
4617<t>
4618   Quality Values of zero should indicate that "I don't want something"
4619   to allow clients to refuse a representation. (<xref target="quality.values"/>)
4620</t>
4621<t>
4622   Transfer-coding had significant problems, particularly with
4623   interactions with chunked encoding. The solution is that transfer-codings
4624   become as full fledged as content-codings. This involves
4625   adding an IANA registry for transfer-codings (separate from content
4626   codings), a new header field (TE) and enabling trailer headers in the
4627   future. Transfer encoding is a major performance benefit, so it was
4628   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4629   interoperability problem that could have occurred due to interactions
4630   between authentication trailers, chunked encoding and HTTP/1.0
4631   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.encoding" format="counter"/>,
4632   and <xref target="header.te" format="counter"/>)
4633</t>
4634</section>
4635
4636<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4637<t>
4638  Empty list elements in list productions have been deprecated.
4639  (<xref target="notation.abnf"/>)
4640</t>
4641<t>
4642  Rules about implicit linear whitespace between certain grammar productions
4643  have been removed; now it's only allowed when specifically pointed out
4644  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4645  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4646  Non-ASCII content in header fields and reason phrase has been obsoleted and
4647  made opaque (the TEXT rule was removed)
4648  (<xref target="basic.rules"/>)
4649</t>
4650<t>
4651  Clarify that HTTP-Version is case sensitive.
4652  (<xref target="http.version"/>)
4653</t>
4654<t>
4655  Remove reference to non-existant identity transfer-coding value tokens.
4656  (Sections <xref format="counter" target="transfer.codings"/> and
4657  <xref format="counter" target="message.length"/>)
4658</t>
4659<t>
4660  Require that invalid whitespace around field-names be rejected.
4661  (<xref target="header.fields"/>)
4662</t>
4663<t>
4664  Update use of abs_path production from RFC1808 to the path-absolute + query
4665  components of RFC3986.
4666  (<xref target="request-target"/>)
4667</t>
4668<t>
4669  Clarification that the chunk length does not include the count of the octets
4670  in the chunk header and trailer. Furthermore disallowed line folding
4671  in chunk extensions.
4672  (<xref target="chunked.encoding"/>)
4673</t>
4674<t>
4675  Remove hard limit of two connections per server.
4676  (<xref target="persistent.practical"/>)
4677</t>
4678<t>
4679  Clarify exactly when close connection options must be sent.
4680  (<xref target="header.connection"/>)
4681</t>
4682</section>
4683</section>
4684
4685<?BEGININC p1-messaging.abnf-appendix ?>
4686<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4687<figure>
4688<artwork type="abnf" name="p1-messaging.parsed-abnf">
4689<x:ref>BWS</x:ref> = OWS
4690
4691<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
4692<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4693<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4694<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4695 connection-token ] )
4696<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4697<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4698
4699<x:ref>Date</x:ref> = "Date:" OWS Date-v
4700<x:ref>Date-v</x:ref> = HTTP-date
4701
4702<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4703
4704<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
4705<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4706<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4707<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
4708 ]
4709<x:ref>Host</x:ref> = "Host:" OWS Host-v
4710<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4711
4712<x:ref>Method</x:ref> = token
4713
4714<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4715
4716<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
4717
4718<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4719<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4720<x:ref>Request</x:ref> = Request-Line *( ( general-header / request-header /
4721 entity-header ) CRLF ) CRLF [ message-body ]
4722<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4723<x:ref>Response</x:ref> = Status-Line *( ( general-header / response-header /
4724 entity-header ) CRLF ) CRLF [ message-body ]
4725
4726<x:ref>Status-Code</x:ref> = 3DIGIT
4727<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4728
4729<x:ref>TE</x:ref> = "TE:" OWS TE-v
4730<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4731<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
4732<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4733<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
4734<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4735 transfer-coding ] )
4736
4737<x:ref>URI</x:ref> = &lt;URI, defined in [RFC3986], Section 3&gt;
4738<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4739<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
4740<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
4741
4742<x:ref>Via</x:ref> = "Via:" OWS Via-v
4743<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4744 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4745 ] )
4746
4747<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
4748
4749<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4750<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4751<x:ref>attribute</x:ref> = token
4752<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4753
4754<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4755<x:ref>chunk-data</x:ref> = 1*OCTET
4756<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4757<x:ref>chunk-ext-name</x:ref> = token
4758<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
4759<x:ref>chunk-size</x:ref> = 1*HEXDIG
4760<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
4761<x:ref>connection-token</x:ref> = token
4762<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4763 / %x2A-5B ; '*'-'['
4764 / %x5D-7E ; ']'-'~'
4765 / obs-text
4766
4767<x:ref>date1</x:ref> = day SP month SP year
4768<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4769<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4770<x:ref>day</x:ref> = 2DIGIT
4771<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4772 / %x54.75.65 ; Tue
4773 / %x57.65.64 ; Wed
4774 / %x54.68.75 ; Thu
4775 / %x46.72.69 ; Fri
4776 / %x53.61.74 ; Sat
4777 / %x53.75.6E ; Sun
4778<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
4779 / %x54.75.65.73.64.61.79 ; Tuesday
4780 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
4781 / %x54.68.75.72.73.64.61.79 ; Thursday
4782 / %x46.72.69.64.61.79 ; Friday
4783 / %x53.61.74.75.72.64.61.79 ; Saturday
4784 / %x53.75.6E.64.61.79 ; Sunday
4785
4786<x:ref>entity-body</x:ref> = &lt;entity-body, defined in [Part3], Section 3.2&gt;
4787<x:ref>entity-header</x:ref> = &lt;entity-header, defined in [Part3], Section 3.1&gt;
4788
4789<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
4790<x:ref>field-name</x:ref> = token
4791<x:ref>field-value</x:ref> = *( field-content / OWS )
4792
4793<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
4794 / Transfer-Encoding / Upgrade / Via / Warning
4795
4796<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
4797<x:ref>hour</x:ref> = 2DIGIT
4798<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4799<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
4800
4801<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
4802
4803<x:ref>message-body</x:ref> = entity-body /
4804 &lt;entity-body encoded as per Transfer-Encoding&gt;
4805<x:ref>minute</x:ref> = 2DIGIT
4806<x:ref>month</x:ref> = %x4A.61.6E ; Jan
4807 / %x46.65.62 ; Feb
4808 / %x4D.61.72 ; Mar
4809 / %x41.70.72 ; Apr
4810 / %x4D.61.79 ; May
4811 / %x4A.75.6E ; Jun
4812 / %x4A.75.6C ; Jul
4813 / %x41.75.67 ; Aug
4814 / %x53.65.70 ; Sep
4815 / %x4F.63.74 ; Oct
4816 / %x4E.6F.76 ; Nov
4817 / %x44.65.63 ; Dec
4818
4819<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
4820<x:ref>obs-fold</x:ref> = CRLF
4821<x:ref>obs-text</x:ref> = %x80-FF
4822
4823<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4824<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4825<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4826<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4827<x:ref>product</x:ref> = token [ "/" product-version ]
4828<x:ref>product-version</x:ref> = token
4829<x:ref>protocol-name</x:ref> = token
4830<x:ref>protocol-version</x:ref> = token
4831<x:ref>pseudonym</x:ref> = token
4832
4833<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
4834 / %x5D-7E ; ']'-'~'
4835 / obs-text
4836<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
4837 / %x5D-7E ; ']'-'~'
4838 / obs-text
4839<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
4840<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
4841<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
4842<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
4843<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
4844<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
4845
4846<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
4847<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
4848<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
4849<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
4850<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
4851 / authority
4852<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
4853<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
4854<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
4855
4856<x:ref>second</x:ref> = 2DIGIT
4857<x:ref>start-line</x:ref> = Request-Line / Status-Line
4858
4859<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
4860<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
4861 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
4862<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
4863<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
4864<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
4865<x:ref>token</x:ref> = 1*tchar
4866<x:ref>trailer-part</x:ref> = *( entity-header CRLF )
4867<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
4868 transfer-extension
4869<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
4870<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
4871
4872<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
4873
4874<x:ref>value</x:ref> = token / quoted-string
4875
4876<x:ref>year</x:ref> = 4DIGIT
4877</artwork>
4878</figure>
4879<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
4880; Chunked-Body defined but not used
4881; Content-Length defined but not used
4882; HTTP-message defined but not used
4883; Host defined but not used
4884; Request defined but not used
4885; Response defined but not used
4886; TE defined but not used
4887; URI defined but not used
4888; URI-reference defined but not used
4889; http-URI defined but not used
4890; https-URI defined but not used
4891; partial-URI defined but not used
4892</artwork></figure></section>
4893<?ENDINC p1-messaging.abnf-appendix ?>
4894
4895<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4896
4897<section title="Since RFC2616">
4898<t>
4899  Extracted relevant partitions from <xref target="RFC2616"/>.
4900</t>
4901</section>
4902
4903<section title="Since draft-ietf-httpbis-p1-messaging-00">
4904<t>
4905  Closed issues:
4906  <list style="symbols"> 
4907    <t>
4908      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
4909      "HTTP Version should be case sensitive"
4910      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
4911    </t>
4912    <t>
4913      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
4914      "'unsafe' characters"
4915      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
4916    </t>
4917    <t>
4918      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
4919      "Chunk Size Definition"
4920      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
4921    </t>
4922    <t>
4923      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
4924      "Message Length"
4925      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
4926    </t>
4927    <t>
4928      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
4929      "Media Type Registrations"
4930      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
4931    </t>
4932    <t>
4933      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
4934      "URI includes query"
4935      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
4936    </t>
4937    <t>
4938      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
4939      "No close on 1xx responses"
4940      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
4941    </t>
4942    <t>
4943      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
4944      "Remove 'identity' token references"
4945      (<eref target="http://purl.org/NET/http-errata#identity"/>)
4946    </t>
4947    <t>
4948      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
4949      "Import query BNF"
4950    </t>
4951    <t>
4952      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
4953      "qdtext BNF"
4954    </t>
4955    <t>
4956      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4957      "Normative and Informative references"
4958    </t>
4959    <t>
4960      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4961      "RFC2606 Compliance"
4962    </t>
4963    <t>
4964      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
4965      "RFC977 reference"
4966    </t>
4967    <t>
4968      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
4969      "RFC1700 references"
4970    </t>
4971    <t>
4972      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
4973      "inconsistency in date format explanation"
4974    </t>
4975    <t>
4976      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
4977      "Date reference typo"
4978    </t>
4979    <t>
4980      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4981      "Informative references"
4982    </t>
4983    <t>
4984      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
4985      "ISO-8859-1 Reference"
4986    </t>
4987    <t>
4988      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
4989      "Normative up-to-date references"
4990    </t>
4991  </list>
4992</t>
4993<t>
4994  Other changes:
4995  <list style="symbols"> 
4996    <t>
4997      Update media type registrations to use RFC4288 template.
4998    </t>
4999    <t>
5000      Use names of RFC4234 core rules DQUOTE and WSP,
5001      fix broken ABNF for chunk-data
5002      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5003    </t>
5004  </list>
5005</t>
5006</section>
5007
5008<section title="Since draft-ietf-httpbis-p1-messaging-01">
5009<t>
5010  Closed issues:
5011  <list style="symbols"> 
5012    <t>
5013      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5014      "Bodies on GET (and other) requests"
5015    </t>
5016    <t>
5017      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5018      "Updating to RFC4288"
5019    </t>
5020    <t>
5021      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5022      "Status Code and Reason Phrase"
5023    </t>
5024    <t>
5025      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5026      "rel_path not used"
5027    </t>
5028  </list>
5029</t>
5030<t>
5031  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5032  <list style="symbols"> 
5033    <t>
5034      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5035      "trailer-part").
5036    </t>
5037    <t>
5038      Avoid underscore character in rule names ("http_URL" ->
5039      "http-URL", "abs_path" -> "path-absolute").
5040    </t>
5041    <t>
5042      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5043      "path-absolute", "port", "query", "relativeURI", "host) -- these will
5044      have to be updated when switching over to RFC3986.
5045    </t>
5046    <t>
5047      Synchronize core rules with RFC5234.
5048    </t>
5049    <t>
5050      Get rid of prose rules that span multiple lines.
5051    </t>
5052    <t>
5053      Get rid of unused rules LOALPHA and UPALPHA.
5054    </t>
5055    <t>
5056      Move "Product Tokens" section (back) into Part 1, as "token" is used
5057      in the definition of the Upgrade header.
5058    </t>
5059    <t>
5060      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5061    </t>
5062    <t>
5063      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5064    </t>
5065  </list>
5066</t>
5067</section>
5068
5069<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5070<t>
5071  Closed issues:
5072  <list style="symbols"> 
5073    <t>
5074      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5075      "HTTP-date vs. rfc1123-date"
5076    </t>
5077    <t>
5078      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5079      "WS in quoted-pair"
5080    </t>
5081  </list>
5082</t>
5083<t>
5084  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5085  <list style="symbols"> 
5086    <t>
5087      Reference RFC 3984, and update header registrations for headers defined
5088      in this document.
5089    </t>
5090  </list>
5091</t>
5092<t>
5093  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5094  <list style="symbols"> 
5095    <t>
5096      Replace string literals when the string really is case-sensitive (HTTP-Version).
5097    </t>
5098  </list>
5099</t>
5100</section>
5101
5102<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5103<t>
5104  Closed issues:
5105  <list style="symbols"> 
5106    <t>
5107      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5108      "Connection closing"
5109    </t>
5110    <t>
5111      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5112      "Move registrations and registry information to IANA Considerations"
5113    </t>
5114    <t>
5115      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5116      "need new URL for PAD1995 reference"
5117    </t>
5118    <t>
5119      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5120      "IANA Considerations: update HTTP URI scheme registration"
5121    </t>
5122    <t>
5123      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5124      "Cite HTTPS URI scheme definition"
5125    </t>
5126    <t>
5127      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5128      "List-type headers vs Set-Cookie"
5129    </t>
5130  </list>
5131</t>
5132<t>
5133  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5134  <list style="symbols"> 
5135    <t>
5136      Replace string literals when the string really is case-sensitive (HTTP-Date).
5137    </t>
5138    <t>
5139      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5140    </t>
5141  </list>
5142</t>
5143</section>
5144
5145<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5146<t>
5147  Closed issues:
5148  <list style="symbols"> 
5149    <t>
5150      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5151      "Out-of-date reference for URIs"
5152    </t>
5153    <t>
5154      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5155      "RFC 2822 is updated by RFC 5322"
5156    </t>
5157  </list>
5158</t>
5159<t>
5160  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5161  <list style="symbols"> 
5162    <t>
5163      Use "/" instead of "|" for alternatives.
5164    </t>
5165    <t>
5166      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5167    </t>
5168    <t>
5169      Only reference RFC 5234's core rules.
5170    </t>
5171    <t>
5172      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5173      whitespace ("OWS") and required whitespace ("RWS").
5174    </t>
5175    <t>
5176      Rewrite ABNFs to spell out whitespace rules, factor out
5177      header value format definitions.
5178    </t>
5179  </list>
5180</t>
5181</section>
5182
5183<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5184<t>
5185  Closed issues:
5186  <list style="symbols"> 
5187    <t>
5188      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5189      "Header LWS"
5190    </t>
5191    <t>
5192      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5193      "Sort 1.3 Terminology"
5194    </t>
5195    <t>
5196      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5197      "RFC2047 encoded words"
5198    </t>
5199    <t>
5200      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5201      "Character Encodings in TEXT"
5202    </t>
5203    <t>
5204      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5205      "Line Folding"
5206    </t>
5207    <t>
5208      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5209      "OPTIONS * and proxies"
5210    </t>
5211    <t>
5212      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5213      "Reason-Phrase BNF"
5214    </t>
5215    <t>
5216      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5217      "Use of TEXT"
5218    </t>
5219    <t>
5220      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5221      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5222    </t>
5223    <t>
5224      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5225      "RFC822 reference left in discussion of date formats"
5226    </t>
5227  </list>
5228</t>
5229<t>
5230  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5231  <list style="symbols"> 
5232    <t>
5233      Rewrite definition of list rules, deprecate empty list elements.
5234    </t>
5235    <t>
5236      Add appendix containing collected and expanded ABNF.
5237    </t>
5238  </list>
5239</t>
5240<t>
5241  Other changes:
5242  <list style="symbols"> 
5243    <t>
5244      Rewrite introduction; add mostly new Architecture Section.
5245    </t>
5246    <t>
5247      Move definition of quality values from Part 3 into Part 1;
5248      make TE request header grammar independent of accept-params (defined in Part 3).
5249    </t>
5250  </list>
5251</t>
5252</section>
5253
5254<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5255<t>
5256  Closed issues:
5257  <list style="symbols"> 
5258    <t>
5259      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5260      "base for numeric protocol elements"
5261    </t>
5262    <t>
5263      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5264      "comment ABNF"
5265    </t>
5266  </list>
5267</t>
5268<t>
5269  Partly resolved issues:
5270  <list style="symbols"> 
5271    <t>
5272      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5273      "205 Bodies" (took out language that implied that there may be
5274      methods for which a request body MUST NOT be included)
5275    </t>
5276    <t>
5277      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5278      "editorial improvements around HTTP-date"
5279    </t>
5280  </list>
5281</t>
5282</section>
5283
5284<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5285<t>
5286  Closed issues:
5287  <list style="symbols"> 
5288    <t>
5289      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5290      "Repeating single-value headers"
5291    </t>
5292    <t>
5293      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5294      "increase connection limit"
5295    </t>
5296    <t>
5297      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5298      "IP addresses in URLs"
5299    </t>
5300    <t>
5301      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5302      "take over HTTP Upgrade Token Registry"
5303    </t>
5304    <t>
5305      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5306      "CR and LF in chunk extension values"
5307    </t>
5308    <t>
5309      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5310      "HTTP/0.9 support"
5311    </t>
5312    <t>
5313      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5314      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5315    </t>
5316    <t>
5317      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5318      "move definitions of gzip/deflate/compress to part 1"
5319    </t>
5320    <t>
5321      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5322      "disallow control characters in quoted-pair"
5323    </t>
5324  </list>
5325</t>
5326<t>
5327  Partly resolved issues:
5328  <list style="symbols"> 
5329    <t>
5330      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5331      "update IANA requirements wrt Transfer-Coding values" (add the
5332      IANA Considerations subsection)
5333    </t>
5334  </list>
5335</t>
5336</section>
5337
5338<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5339<t>
5340  None yet.
5341</t>
5342</section>
5343
5344</section>
5345
5346</back>
5347</rfc>
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