source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1910

Last change on this file since 1910 was 1910, checked in by fielding@…, 7 years ago

(editorial) be more consistent when referring to a "body", preferring the
defined terms for message (body), payload (body), and representation (data).

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
File size: 243.4 KB
Line 
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 "September">
16  <!ENTITY ID-YEAR "2012">
17  <!ENTITY mdash "&#8212;">
18  <!ENTITY Note "<x:h xmlns:x='http://purl.org/net/xml2rfc/ext'>Note:</x:h>">
19  <!ENTITY caching-overview       "<xref target='Part6' x:rel='#caching.overview' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY cache-incomplete       "<xref target='Part6' x:rel='#response.cacheability' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY payload                "<xref target='Part2' x:rel='#payload' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY media-types            "<xref target='Part2' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY content-codings        "<xref target='Part2' x:rel='#content.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY content.negotiation    "<xref target='Part2' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY diff-mime              "<xref target='Part2' x:rel='#differences.between.http.and.mime' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY representation         "<xref target='Part2' x:rel='#representation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY HEAD                   "<xref target='Part2' x:rel='#HEAD' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-allow           "<xref target='Part2' x:rel='#header.allow' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-content-encoding    "<xref target='Part2' x:rel='#header.content-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY header-content-location    "<xref target='Part2' x:rel='#header.content-location' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY header-content-range   "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY header-content-type    "<xref target='Part2' x:rel='#header.content-type' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY header-date            "<xref target='Part2' x:rel='#header.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY header-etag            "<xref target='Part4' x:rel='#header.etag' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY header-expires         "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY header-last-modified   "<xref target='Part4' x:rel='#header.last-modified' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY header-mime-version    "<xref target='Part2' x:rel='#mime-version' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41  <!ENTITY header-proxy-authenticate  "<xref target='Part7' x:rel='#header.proxy-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
42  <!ENTITY header-proxy-authorization "<xref target='Part7' x:rel='#header.proxy-authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
43  <!ENTITY header-server          "<xref target='Part2' x:rel='#header.server' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
44  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
45  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
46  <!ENTITY methods                "<xref target='Part2' x:rel='#methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
47  <!ENTITY OPTIONS                "<xref target='Part2' x:rel='#OPTIONS' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
48  <!ENTITY qvalue                 "<xref target='Part2' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
49  <!ENTITY resource               "<xref target='Part2' x:rel='#resource' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
50  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
51  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
52  <!ENTITY status-203             "<xref target='Part2' x:rel='#status.203' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
53  <!ENTITY status-3xx             "<xref target='Part2' x:rel='#status.3xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
54  <!ENTITY status-304             "<xref target='Part4' x:rel='#status.304' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
55  <!ENTITY status-4xx             "<xref target='Part2' x:rel='#status.4xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
56  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
57  <!ENTITY iana-header-registry   "<xref target='Part2' x:rel='#header.field.registry' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
58]>
59<?rfc toc="yes" ?>
60<?rfc symrefs="yes" ?>
61<?rfc sortrefs="yes" ?>
62<?rfc compact="yes"?>
63<?rfc subcompact="no" ?>
64<?rfc linkmailto="no" ?>
65<?rfc editing="no" ?>
66<?rfc comments="yes"?>
67<?rfc inline="yes"?>
68<?rfc rfcedstyle="yes"?>
69<?rfc-ext allow-markup-in-artwork="yes" ?>
70<?rfc-ext include-references-in-index="yes" ?>
71<rfc obsoletes="2145,2616" updates="2817" category="std" x:maturity-level="proposed"
72     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
73     xmlns:x='http://purl.org/net/xml2rfc/ext'>
74<x:link rel="next" basename="p2-semantics"/>
75<x:feedback template="mailto:ietf-http-wg@w3.org?subject={docname},%20%22{section}%22&amp;body=&lt;{ref}&gt;:"/>
76<front>
77
78  <title abbrev="HTTP/1.1 Message Syntax and Routing">Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing</title>
79
80  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
81    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
82    <address>
83      <postal>
84        <street>345 Park Ave</street>
85        <city>San Jose</city>
86        <region>CA</region>
87        <code>95110</code>
88        <country>USA</country>
89      </postal>
90      <email>fielding@gbiv.com</email>
91      <uri>http://roy.gbiv.com/</uri>
92    </address>
93  </author>
94
95  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
96    <organization abbrev="W3C">World Wide Web Consortium</organization>
97    <address>
98      <postal>
99        <street>W3C / ERCIM</street>
100        <street>2004, rte des Lucioles</street>
101        <city>Sophia-Antipolis</city>
102        <region>AM</region>
103        <code>06902</code>
104        <country>France</country>
105      </postal>
106      <email>ylafon@w3.org</email>
107      <uri>http://www.raubacapeu.net/people/yves/</uri>
108    </address>
109  </author>
110
111  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
112    <organization abbrev="greenbytes">greenbytes GmbH</organization>
113    <address>
114      <postal>
115        <street>Hafenweg 16</street>
116        <city>Muenster</city><region>NW</region><code>48155</code>
117        <country>Germany</country>
118      </postal>
119      <email>julian.reschke@greenbytes.de</email>
120      <uri>http://greenbytes.de/tech/webdav/</uri>
121    </address>
122  </author>
123
124  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
125  <workgroup>HTTPbis Working Group</workgroup>
126
127<abstract>
128<t>
129   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
130   distributed, collaborative, hypertext information systems. HTTP has been in
131   use by the World Wide Web global information initiative since 1990.
132   This document provides an overview of HTTP architecture and its associated
133   terminology, defines the "http" and "https" Uniform Resource Identifier
134   (URI) schemes, defines the HTTP/1.1 message syntax and parsing requirements,
135   and describes general security concerns for implementations.
136</t>   
137</abstract>
138
139<note title="Editorial Note (To be removed by RFC Editor)">
140  <t>
141    Discussion of this draft takes place on the HTTPBIS working group
142    mailing list (ietf-http-wg@w3.org), which is archived at
143    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
144  </t>
145  <t>
146    The current issues list is at
147    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
148    documents (including fancy diffs) can be found at
149    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
150  </t>
151  <t>
152    The changes in this draft are summarized in <xref target="changes.since.20"/>.
153  </t>
154</note>
155</front>
156<middle>
157<section title="Introduction" anchor="introduction">
158<t>
159   The Hypertext Transfer Protocol (HTTP) is an application-level
160   request/response protocol that uses extensible semantics and MIME-like
161   message payloads for flexible interaction with network-based hypertext
162   information systems. This document is the first in a series of documents
163   that collectively form the HTTP/1.1 specification:
164   <list style="empty">
165    <t>RFC xxx1: Message Syntax and Routing</t>
166    <t><xref target="Part2" x:fmt="none">RFC xxx2</xref>: Semantics and Content</t>
167    <t><xref target="Part4" x:fmt="none">RFC xxx3</xref>: Conditional Requests</t>
168    <t><xref target="Part5" x:fmt="none">RFC xxx4</xref>: Range Requests</t>
169    <t><xref target="Part6" x:fmt="none">RFC xxx5</xref>: Caching</t>
170    <t><xref target="Part7" x:fmt="none">RFC xxx6</xref>: Authentication</t>
171   </list>
172</t>
173<t>
174   This HTTP/1.1 specification obsoletes and moves to historic status
175   <xref target="RFC2616" x:fmt="none">RFC 2616</xref>, its predecessor
176   <xref target="RFC2068" x:fmt="none">RFC 2068</xref>,
177   <xref target="RFC2145" x:fmt="none">RFC 2145</xref> (on HTTP versioning),
178   and <xref target="RFC2817" x:fmt="none">RFC 2817</xref> (on using CONNECT
179   for TLS upgrades).
180</t>
181<t>
182   HTTP is a generic interface protocol for information systems. It is
183   designed to hide the details of how a service is implemented by presenting
184   a uniform interface to clients that is independent of the types of
185   resources provided. Likewise, servers do not need to be aware of each
186   client's purpose: an HTTP request can be considered in isolation rather
187   than being associated with a specific type of client or a predetermined
188   sequence of application steps. The result is a protocol that can be used
189   effectively in many different contexts and for which implementations can
190   evolve independently over time.
191</t>
192<t>
193   HTTP is also designed for use as an intermediation protocol for translating
194   communication to and from non-HTTP information systems.
195   HTTP proxies and gateways can provide access to alternative information
196   services by translating their diverse protocols into a hypertext
197   format that can be viewed and manipulated by clients in the same way
198   as HTTP services.
199</t>
200<t>
201   One consequence of HTTP flexibility is that the protocol cannot be
202   defined in terms of what occurs behind the interface. Instead, we
203   are limited to defining the syntax of communication, the intent
204   of received communication, and the expected behavior of recipients.
205   If the communication is considered in isolation, then successful
206   actions ought to be reflected in corresponding changes to the
207   observable interface provided by servers. However, since multiple
208   clients might act in parallel and perhaps at cross-purposes, we
209   cannot require that such changes be observable beyond the scope
210   of a single response.
211</t>
212<t>
213   This document describes the architectural elements that are used or
214   referred to in HTTP, defines the "http" and "https" URI schemes,
215   describes overall network operation and connection management,
216   and defines HTTP message framing and forwarding requirements.
217   Our goal is to define all of the mechanisms necessary for HTTP message
218   handling that are independent of message semantics, thereby defining the
219   complete set of requirements for message parsers and
220   message-forwarding intermediaries.
221</t>
222
223
224<section title="Requirement Notation" anchor="intro.requirements">
225<t>
226   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
227   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
228   document are to be interpreted as described in <xref target="RFC2119"/>.
229</t>
230<t>
231   Conformance criteria and considerations regarding error handling
232   are defined in <xref target="conformance"/>.
233</t>
234</section>
235
236<section title="Syntax Notation" anchor="notation">
237<iref primary="true" item="Grammar" subitem="ALPHA"/>
238<iref primary="true" item="Grammar" subitem="CR"/>
239<iref primary="true" item="Grammar" subitem="CRLF"/>
240<iref primary="true" item="Grammar" subitem="CTL"/>
241<iref primary="true" item="Grammar" subitem="DIGIT"/>
242<iref primary="true" item="Grammar" subitem="DQUOTE"/>
243<iref primary="true" item="Grammar" subitem="HEXDIG"/>
244<iref primary="true" item="Grammar" subitem="HTAB"/>
245<iref primary="true" item="Grammar" subitem="LF"/>
246<iref primary="true" item="Grammar" subitem="OCTET"/>
247<iref primary="true" item="Grammar" subitem="SP"/>
248<iref primary="true" item="Grammar" subitem="VCHAR"/>
249<t>
250   This specification uses the Augmented Backus-Naur Form (ABNF) notation
251   of <xref target="RFC5234"/> with the list rule extension defined in
252   <xref target="abnf.extension"/><xref target="collected.abnf"/> shows
253   the collected ABNF with the list rule expanded.
254</t>
255<t anchor="core.rules">
256  <x:anchor-alias value="ALPHA"/>
257  <x:anchor-alias value="CTL"/>
258  <x:anchor-alias value="CR"/>
259  <x:anchor-alias value="CRLF"/>
260  <x:anchor-alias value="DIGIT"/>
261  <x:anchor-alias value="DQUOTE"/>
262  <x:anchor-alias value="HEXDIG"/>
263  <x:anchor-alias value="HTAB"/>
264  <x:anchor-alias value="LF"/>
265  <x:anchor-alias value="OCTET"/>
266  <x:anchor-alias value="SP"/>
267  <x:anchor-alias value="VCHAR"/>
268   The following core rules are included by
269   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
270   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
271   DIGIT (decimal 0-9), DQUOTE (double quote),
272   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
273   OCTET (any 8-bit sequence of data), SP (space), and
274   VCHAR (any visible <xref target="USASCII"/> character).
275</t>
276<t>
277   As a convention, ABNF rule names prefixed with "obs-" denote
278   "obsolete" grammar rules that appear for historical reasons.
279</t>
280</section>
281</section>
282
283<section title="Architecture" anchor="architecture">
284<t>
285   HTTP was created for the World Wide Web architecture
286   and has evolved over time to support the scalability needs of a worldwide
287   hypertext system. Much of that architecture is reflected in the terminology
288   and syntax productions used to define HTTP.
289</t>
290
291<section title="Client/Server Messaging" anchor="operation">
292<iref primary="true" item="client"/>
293<iref primary="true" item="server"/>
294<iref primary="true" item="connection"/>
295<t>
296   HTTP is a stateless request/response protocol that operates by exchanging
297   <x:dfn>messages</x:dfn> (<xref target="http.message"/>) across a reliable
298   transport or session-layer
299   "<x:dfn>connection</x:dfn>" (<xref target="connection.management"/>).
300   An HTTP "<x:dfn>client</x:dfn>" is a program that establishes a connection
301   to a server for the purpose of sending one or more HTTP requests.
302   An HTTP "<x:dfn>server</x:dfn>" is a program that accepts connections
303   in order to service HTTP requests by sending HTTP responses.
304</t>
305<iref primary="true" item="user agent"/>
306<iref primary="true" item="origin server"/>
307<iref primary="true" item="browser"/>
308<iref primary="true" item="spider"/>
309<iref primary="true" item="sender"/>
310<iref primary="true" item="recipient"/>
311<t>
312   The terms client and server refer only to the roles that
313   these programs perform for a particular connection.  The same program
314   might act as a client on some connections and a server on others.  We use
315   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
316   such as a WWW browser, editor, or spider (web-traversing robot), and
317   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
318   authoritative responses to a request.  For general requirements, we use
319   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
320   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
321   message.
322</t>
323<t>
324   HTTP relies upon the Uniform Resource Identifier (URI)
325   standard <xref target="RFC3986"/> to indicate the target resource
326   (<xref target="target-resource"/>) and relationships between resources.
327   Messages are passed in a format similar to that used by Internet mail
328   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
329   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
330   between HTTP and MIME messages).
331</t>
332<t>
333   Most HTTP communication consists of a retrieval request (GET) for
334   a representation of some resource identified by a URI.  In the
335   simplest case, this might be accomplished via a single bidirectional
336   connection (===) between the user agent (UA) and the origin server (O).
337</t>
338<figure><artwork type="drawing">
339         request   &gt;
340    <x:highlight>UA</x:highlight> ======================================= <x:highlight>O</x:highlight>
341                                &lt;   response
342</artwork></figure>
343<iref primary="true" item="message"/>
344<iref primary="true" item="request"/>
345<iref primary="true" item="response"/>
346<t>
347   A client sends an HTTP request to a server in the form of a <x:dfn>request</x:dfn>
348   message, beginning with a request-line that includes a method, URI, and
349   protocol version (<xref target="request.line"/>),
350   followed by header fields containing
351   request modifiers, client information, and representation metadata
352   (<xref target="header.fields"/>),
353   an empty line to indicate the end of the header section, and finally
354   a message body containing the payload body (if any,
355   <xref target="message.body"/>).
356</t>
357<t>
358   A server responds to a client's request by sending one or more HTTP
359   <x:dfn>response</x:dfn>
360   messages, each beginning with a status line that
361   includes the protocol version, a success or error code, and textual
362   reason phrase (<xref target="status.line"/>),
363   possibly followed by header fields containing server
364   information, resource metadata, and representation metadata
365   (<xref target="header.fields"/>),
366   an empty line to indicate the end of the header section, and finally
367   a message body containing the payload body (if any,
368   <xref target="message.body"/>).
369</t>
370<t>
371   A connection might be used for multiple request/response exchanges,
372   as defined in <xref target="persistent.connections"/>.
373</t>
374<t>
375   The following example illustrates a typical message exchange for a
376   GET request on the URI "http://www.example.com/hello.txt":
377</t>
378<figure><preamble>
379client request:
380</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
381GET /hello.txt HTTP/1.1
382User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
383Host: www.example.com
384Accept-Language: en, mi
385
386</artwork></figure>
387<figure><preamble>
388server response:
389</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
390HTTP/1.1 200 OK
391Date: Mon, 27 Jul 2009 12:28:53 GMT
392Server: Apache
393Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
394ETag: "34aa387-d-1568eb00"
395Accept-Ranges: bytes
396Content-Length: <x:length-of target="exbody"/>
397Vary: Accept-Encoding
398Content-Type: text/plain
399
400<x:span anchor="exbody">Hello World!
401</x:span></artwork></figure>
402</section>
403
404<section title="Implementation Diversity" anchor="implementation-diversity">
405<t>
406   When considering the design of HTTP, it is easy to fall into a trap of
407   thinking that all user agents are general-purpose browsers and all origin
408   servers are large public websites. That is not the case in practice.
409   Common HTTP user agents include household appliances, stereos, scales,
410   firmware update scripts, command-line programs, mobile apps,
411   and communication devices in a multitude of shapes and sizes.  Likewise,
412   common HTTP origin servers include home automation units, configurable
413   networking components, office machines, autonomous robots, news feeds,
414   traffic cameras, ad selectors, and video delivery platforms.
415</t>
416<t>
417   The term "user agent" does not imply that there is a human user directly
418   interacting with the software agent at the time of a request. In many
419   cases, a user agent is installed or configured to run in the background
420   and save its results for later inspection (or save only a subset of those
421   results that might be interesting or erroneous). Spiders, for example, are
422   typically given a start URI and configured to follow certain behavior while
423   crawling the Web as a hypertext graph.
424</t>
425<t>
426   The implementation diversity of HTTP means that we cannot assume the
427   user agent can make interactive suggestions to a user or provide adequate
428   warning for security or privacy options.  In the few cases where this
429   specification requires reporting of errors to the user, it is acceptable
430   for such reporting to only be observable in an error console or log file.
431   Likewise, requirements that an automated action be confirmed by the user
432   before proceeding can me met via advance configuration choices,
433   run-time options, or simply not proceeding with the unsafe action.
434</t>
435</section>
436
437<section title="Intermediaries" anchor="intermediaries">
438<iref primary="true" item="intermediary"/>
439<t>
440   HTTP enables the use of intermediaries to satisfy requests through
441   a chain of connections.  There are three common forms of HTTP
442   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
443   a single intermediary might act as an origin server, proxy, gateway,
444   or tunnel, switching behavior based on the nature of each request.
445</t>
446<figure><artwork type="drawing">
447         &gt;             &gt;             &gt;             &gt;
448    <x:highlight>UA</x:highlight> =========== <x:highlight>A</x:highlight> =========== <x:highlight>B</x:highlight> =========== <x:highlight>C</x:highlight> =========== <x:highlight>O</x:highlight>
449               &lt;             &lt;             &lt;             &lt;
450</artwork></figure>
451<t>
452   The figure above shows three intermediaries (A, B, and C) between the
453   user agent and origin server. A request or response message that
454   travels the whole chain will pass through four separate connections.
455   Some HTTP communication options
456   might apply only to the connection with the nearest, non-tunnel
457   neighbor, only to the end-points of the chain, or to all connections
458   along the chain. Although the diagram is linear, each participant might
459   be engaged in multiple, simultaneous communications. For example, B
460   might be receiving requests from many clients other than A, and/or
461   forwarding requests to servers other than C, at the same time that it
462   is handling A's request.
463</t>
464<t>
465<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
466<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
467   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
468   to describe various requirements in relation to the directional flow of a
469   message: all messages flow from upstream to downstream.
470   Likewise, we use the terms inbound and outbound to refer to
471   directions in relation to the request path:
472   "<x:dfn>inbound</x:dfn>" means toward the origin server and
473   "<x:dfn>outbound</x:dfn>" means toward the user agent.
474</t>
475<t><iref primary="true" item="proxy"/>
476   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
477   client, usually via local configuration rules, to receive requests
478   for some type(s) of absolute URI and attempt to satisfy those
479   requests via translation through the HTTP interface.  Some translations
480   are minimal, such as for proxy requests for "http" URIs, whereas
481   other requests might require translation to and from entirely different
482   application-level protocols. Proxies are often used to group an
483   organization's HTTP requests through a common intermediary for the
484   sake of security, annotation services, or shared caching.
485</t>
486<t>
487<iref primary="true" item="transforming proxy"/>
488<iref primary="true" item="non-transforming proxy"/>
489   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
490   or configured to modify request or response messages in a semantically
491   meaningful way (i.e., modifications, beyond those required by normal
492   HTTP processing, that change the message in a way that would be
493   significant to the original sender or potentially significant to
494   downstream recipients).  For example, a transforming proxy might be
495   acting as a shared annotation server (modifying responses to include
496   references to a local annotation database), a malware filter, a
497   format transcoder, or an intranet-to-Internet privacy filter.  Such
498   transformations are presumed to be desired by the client (or client
499   organization) that selected the proxy and are beyond the scope of
500   this specification.  However, when a proxy is not intended to transform
501   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
502   requirements that preserve HTTP message semantics. See &status-203; and
503   &header-warning; for status and warning codes related to transformations.
504</t>
505<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
506<iref primary="true" item="accelerator"/>
507   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
508   is a receiving agent that acts
509   as a layer above some other server(s) and translates the received
510   requests to the underlying server's protocol.  Gateways are often
511   used to encapsulate legacy or untrusted information services, to
512   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
513   enable partitioning or load-balancing of HTTP services across
514   multiple machines.
515</t>
516<t>
517   A gateway behaves as an origin server on its outbound connection and
518   as a user agent on its inbound connection.
519   All HTTP requirements applicable to an origin server
520   also apply to the outbound communication of a gateway.
521   A gateway communicates with inbound servers using any protocol that
522   it desires, including private extensions to HTTP that are outside
523   the scope of this specification.  However, an HTTP-to-HTTP gateway
524   that wishes to interoperate with third-party HTTP servers &MUST;
525   conform to HTTP user agent requirements on the gateway's inbound
526   connection and &MUST; implement the <x:ref>Connection</x:ref>
527   (<xref target="header.connection"/>) and <x:ref>Via</x:ref>
528   (<xref target="header.via"/>) header fields for both connections.
529</t>
530<t><iref primary="true" item="tunnel"/>
531   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
532   without changing the messages. Once active, a tunnel is not
533   considered a party to the HTTP communication, though the tunnel might
534   have been initiated by an HTTP request. A tunnel ceases to exist when
535   both ends of the relayed connection are closed. Tunnels are used to
536   extend a virtual connection through an intermediary, such as when
537   Transport Layer Security (TLS, <xref target="RFC5246"/>) is used to
538   establish confidential communication through a shared firewall proxy.
539</t>
540<t><iref primary="true" item="interception proxy"/>
541<iref primary="true" item="transparent proxy"/>
542<iref primary="true" item="captive portal"/>
543   The above categories for intermediary only consider those acting as
544   participants in the HTTP communication.  There are also intermediaries
545   that can act on lower layers of the network protocol stack, filtering or
546   redirecting HTTP traffic without the knowledge or permission of message
547   senders. Network intermediaries often introduce security flaws or
548   interoperability problems by violating HTTP semantics.  For example, an
549   "<x:dfn>interception proxy</x:dfn>" <xref target="RFC3040"/> (also commonly
550   known as a "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/> or
551   "<x:dfn>captive portal</x:dfn>")
552   differs from an HTTP proxy because it is not selected by the client.
553   Instead, an interception proxy filters or redirects outgoing TCP port 80
554   packets (and occasionally other common port traffic).
555   Interception proxies are commonly found on public network access points,
556   as a means of enforcing account subscription prior to allowing use of
557   non-local Internet services, and within corporate firewalls to enforce
558   network usage policies.
559   They are indistinguishable from a man-in-the-middle attack.
560</t>
561<t>
562   HTTP is defined as a stateless protocol, meaning that each request message
563   can be understood in isolation.  Many implementations depend on HTTP's
564   stateless design in order to reuse proxied connections or dynamically
565   load balance requests across multiple servers.  Hence, servers &MUST-NOT;
566   assume that two requests on the same connection are from the same user
567   agent unless the connection is secured and specific to that agent.
568   Some non-standard HTTP extensions (e.g., <xref target="RFC4559"/>) have
569   been known to violate this requirement, resulting in security and
570   interoperability problems.
571</t>
572</section>
573
574<section title="Caches" anchor="caches">
575<iref primary="true" item="cache"/>
576<t>
577   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
578   subsystem that controls its message storage, retrieval, and deletion.
579   A cache stores cacheable responses in order to reduce the response
580   time and network bandwidth consumption on future, equivalent
581   requests. Any client or server &MAY; employ a cache, though a cache
582   cannot be used by a server while it is acting as a tunnel.
583</t>
584<t>
585   The effect of a cache is that the request/response chain is shortened
586   if one of the participants along the chain has a cached response
587   applicable to that request. The following illustrates the resulting
588   chain if B has a cached copy of an earlier response from O (via C)
589   for a request which has not been cached by UA or A.
590</t>
591<figure><artwork type="drawing">
592            &gt;             &gt;
593       <x:highlight>UA</x:highlight> =========== <x:highlight>A</x:highlight> =========== <x:highlight>B</x:highlight> - - - - - - <x:highlight>C</x:highlight> - - - - - - <x:highlight>O</x:highlight>
594                  &lt;             &lt;
595</artwork></figure>
596<t><iref primary="true" item="cacheable"/>
597   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
598   the response message for use in answering subsequent requests.
599   Even when a response is cacheable, there might be additional
600   constraints placed by the client or by the origin server on when
601   that cached response can be used for a particular request. HTTP
602   requirements for cache behavior and cacheable responses are
603   defined in &caching-overview;
604</t>
605<t>
606   There are a wide variety of architectures and configurations
607   of caches and proxies deployed across the World Wide Web and
608   inside large organizations. These systems include national hierarchies
609   of proxy caches to save transoceanic bandwidth, systems that
610   broadcast or multicast cache entries, organizations that distribute
611   subsets of cached data via optical media, and so on.
612</t>
613</section>
614
615<section title="Conformance and Error Handling" anchor="conformance">
616<t>
617   This specification targets conformance criteria according to the role of
618   a participant in HTTP communication.  Hence, HTTP requirements are placed
619   on senders, recipients, clients, servers, user agents, intermediaries,
620   origin servers, proxies, gateways, or caches, depending on what behavior
621   is being constrained by the requirement. Additional (social) requirements
622   are placed on implementations, resource owners, and protocol element
623   registrations when they apply beyond the scope of a single communication.
624</t>
625<t>
626   The verb "generate" is used instead of "send" where a requirement
627   differentiates between creating a protocol element and merely forwarding a
628   received element downstream.
629</t>
630<t>
631   An implementation is considered conformant if it complies with all of the
632   requirements associated with the roles it partakes in HTTP. Note that
633   SHOULD-level requirements are relevant here, unless one of the documented
634   exceptions is applicable.
635</t>
636<t>
637   Conformance applies to both the syntax and semantics of HTTP protocol
638   elements. A sender &MUST-NOT; generate protocol elements that convey a
639   meaning that is known by that sender to be false. A sender &MUST-NOT;
640   generate protocol elements that do not match the grammar defined by the
641   ABNF rules for those protocol elements that are applicable to the sender's
642   role. If a received protocol element is processed, the recipient &MUST; be
643   able to parse any value that would match the ABNF rules for that protocol
644   element, excluding only those rules not applicable to the recipient's role.
645</t>
646<t>
647   Unless noted otherwise, a recipient &MAY; attempt to recover a usable
648   protocol element from an invalid construct.  HTTP does not define
649   specific error handling mechanisms except when they have a direct impact
650   on security, since different applications of the protocol require
651   different error handling strategies.  For example, a Web browser might
652   wish to transparently recover from a response where the
653   <x:ref>Location</x:ref> header field doesn't parse according to the ABNF,
654   whereas a systems control client might consider any form of error recovery
655   to be dangerous.
656</t>
657</section>
658
659<section title="Protocol Versioning" anchor="http.version">
660  <x:anchor-alias value="HTTP-version"/>
661  <x:anchor-alias value="HTTP-name"/>
662<t>
663   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
664   versions of the protocol. This specification defines version "1.1".
665   The protocol version as a whole indicates the sender's conformance
666   with the set of requirements laid out in that version's corresponding
667   specification of HTTP.
668</t>
669<t>
670   The version of an HTTP message is indicated by an HTTP-version field
671   in the first line of the message. HTTP-version is case-sensitive.
672</t>
673<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-version"/><iref primary="true" item="Grammar" subitem="HTTP-name"/>
674  <x:ref>HTTP-version</x:ref>  = <x:ref>HTTP-name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
675  <x:ref>HTTP-name</x:ref>     = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
676</artwork></figure>
677<t>
678   The HTTP version number consists of two decimal digits separated by a "."
679   (period or decimal point).  The first digit ("major version") indicates the
680   HTTP messaging syntax, whereas the second digit ("minor version") indicates
681   the highest minor version to which the sender is
682   conformant and able to understand for future communication.  The minor
683   version advertises the sender's communication capabilities even when the
684   sender is only using a backwards-compatible subset of the protocol,
685   thereby letting the recipient know that more advanced features can
686   be used in response (by servers) or in future requests (by clients).
687</t>
688<t>
689   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
690   <xref target="RFC1945"/> or a recipient whose version is unknown,
691   the HTTP/1.1 message is constructed such that it can be interpreted
692   as a valid HTTP/1.0 message if all of the newer features are ignored.
693   This specification places recipient-version requirements on some
694   new features so that a conformant sender will only use compatible
695   features until it has determined, through configuration or the
696   receipt of a message, that the recipient supports HTTP/1.1.
697</t>
698<t>
699   The interpretation of a header field does not change between minor
700   versions of the same major HTTP version, though the default
701   behavior of a recipient in the absence of such a field can change.
702   Unless specified otherwise, header fields defined in HTTP/1.1 are
703   defined for all versions of HTTP/1.x.  In particular, the <x:ref>Host</x:ref>
704   and <x:ref>Connection</x:ref> header fields ought to be implemented by all
705   HTTP/1.x implementations whether or not they advertise conformance with
706   HTTP/1.1.
707</t>
708<t>
709   New header fields can be defined such that, when they are
710   understood by a recipient, they might override or enhance the
711   interpretation of previously defined header fields.  When an
712   implementation receives an unrecognized header field, the recipient
713   &MUST; ignore that header field for local processing regardless of
714   the message's HTTP version.  An unrecognized header field received
715   by a proxy &MUST; be forwarded downstream unless the header field's
716   field-name is listed in the message's <x:ref>Connection</x:ref> header field
717   (see <xref target="header.connection"/>).
718   These requirements allow HTTP's functionality to be enhanced without
719   requiring prior update of deployed intermediaries.
720</t>
721<t>
722   Intermediaries that process HTTP messages (i.e., all intermediaries
723   other than those acting as tunnels) &MUST; send their own HTTP-version
724   in forwarded messages.  In other words, they &MUST-NOT; blindly
725   forward the first line of an HTTP message without ensuring that the
726   protocol version in that message matches a version to which that
727   intermediary is conformant for both the receiving and
728   sending of messages.  Forwarding an HTTP message without rewriting
729   the HTTP-version might result in communication errors when downstream
730   recipients use the message sender's version to determine what features
731   are safe to use for later communication with that sender.
732</t>
733<t>
734   An HTTP client &SHOULD; send a request version equal to the highest
735   version to which the client is conformant and
736   whose major version is no higher than the highest version supported
737   by the server, if this is known.  An HTTP client &MUST-NOT; send a
738   version to which it is not conformant.
739</t>
740<t>
741   An HTTP client &MAY; send a lower request version if it is known that
742   the server incorrectly implements the HTTP specification, but only
743   after the client has attempted at least one normal request and determined
744   from the response status or header fields (e.g., <x:ref>Server</x:ref>) that
745   the server improperly handles higher request versions.
746</t>
747<t>
748   An HTTP server &SHOULD; send a response version equal to the highest
749   version to which the server is conformant and
750   whose major version is less than or equal to the one received in the
751   request.  An HTTP server &MUST-NOT; send a version to which it is not
752   conformant.  A server &MAY; send a <x:ref>505 (HTTP Version Not
753   Supported)</x:ref> response if it cannot send a response using the
754   major version used in the client's request.
755</t>
756<t>
757   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
758   if it is known or suspected that the client incorrectly implements the
759   HTTP specification and is incapable of correctly processing later
760   version responses, such as when a client fails to parse the version
761   number correctly or when an intermediary is known to blindly forward
762   the HTTP-version even when it doesn't conform to the given minor
763   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
764   performed unless triggered by specific client attributes, such as when
765   one or more of the request header fields (e.g., <x:ref>User-Agent</x:ref>)
766   uniquely match the values sent by a client known to be in error.
767</t>
768<t>
769   The intention of HTTP's versioning design is that the major number
770   will only be incremented if an incompatible message syntax is
771   introduced, and that the minor number will only be incremented when
772   changes made to the protocol have the effect of adding to the message
773   semantics or implying additional capabilities of the sender.  However,
774   the minor version was not incremented for the changes introduced between
775   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
776   is specifically avoiding any such changes to the protocol.
777</t>
778</section>
779
780<section title="Uniform Resource Identifiers" anchor="uri">
781<iref primary="true" item="resource"/>
782<t>
783   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
784   throughout HTTP as the means for identifying resources (&resource;).
785   URI references are used to target requests, indicate redirects, and define
786   relationships.
787</t>
788  <x:anchor-alias value="URI-reference"/>
789  <x:anchor-alias value="absolute-URI"/>
790  <x:anchor-alias value="relative-part"/>
791  <x:anchor-alias value="authority"/>
792  <x:anchor-alias value="path-abempty"/>
793  <x:anchor-alias value="path-absolute"/>
794  <x:anchor-alias value="port"/>
795  <x:anchor-alias value="query"/>
796  <x:anchor-alias value="uri-host"/>
797  <x:anchor-alias value="partial-URI"/>
798<t>
799   This specification adopts the definitions of "URI-reference",
800   "absolute-URI", "relative-part", "port", "host",
801   "path-abempty", "path-absolute", "query", and "authority" from the
802   URI generic syntax.
803   In addition, we define a partial-URI rule for protocol elements
804   that allow a relative URI but not a fragment.
805</t>
806<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="URI-reference"><!--exported production--></iref><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"/><iref primary="true" item="Grammar" subitem="partial-URI"><!--exported production--></iref>
807  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
808  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
809  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
810  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
811  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
812  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
813  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
814  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
815  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
816 
817  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
818</artwork></figure>
819<t>
820   Each protocol element in HTTP that allows a URI reference will indicate
821   in its ABNF production whether the element allows any form of reference
822   (URI-reference), only a URI in absolute form (absolute-URI), only the
823   path and optional query components, or some combination of the above.
824   Unless otherwise indicated, URI references are parsed
825   relative to the effective request URI
826   (<xref target="effective.request.uri"/>).
827</t>
828
829<section title="http URI scheme" anchor="http.uri">
830  <x:anchor-alias value="http-URI"/>
831  <iref item="http URI scheme" primary="true"/>
832  <iref item="URI scheme" subitem="http" primary="true"/>
833<t>
834   The "http" URI scheme is hereby defined for the purpose of minting
835   identifiers according to their association with the hierarchical
836   namespace governed by a potential HTTP origin server listening for
837   TCP connections on a given port.
838</t>
839<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"><!--terminal production--></iref>
840  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
841</artwork></figure>
842<t>
843   The HTTP origin server is identified by the generic syntax's
844   <x:ref>authority</x:ref> component, which includes a host identifier
845   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
846   The remainder of the URI, consisting of both the hierarchical path
847   component and optional query component, serves as an identifier for
848   a potential resource within that origin server's name space.
849</t>
850<t>
851   If the host identifier is provided as an IP literal or IPv4 address,
852   then the origin server is any listener on the indicated TCP port at
853   that IP address. If host is a registered name, then that name is
854   considered an indirect identifier and the recipient might use a name
855   resolution service, such as DNS, to find the address of a listener
856   for that host.
857   The host &MUST-NOT; be empty; if an "http" URI is received with an
858   empty host, then it &MUST; be rejected as invalid.
859   If the port subcomponent is empty or not given, then TCP port 80 is
860   assumed (the default reserved port for WWW services).
861</t>
862<t>
863   Regardless of the form of host identifier, access to that host is not
864   implied by the mere presence of its name or address. The host might or might
865   not exist and, even when it does exist, might or might not be running an
866   HTTP server or listening to the indicated port. The "http" URI scheme
867   makes use of the delegated nature of Internet names and addresses to
868   establish a naming authority (whatever entity has the ability to place
869   an HTTP server at that Internet name or address) and allows that
870   authority to determine which names are valid and how they might be used.
871</t>
872<t>
873   When an "http" URI is used within a context that calls for access to the
874   indicated resource, a client &MAY; attempt access by resolving
875   the host to an IP address, establishing a TCP connection to that address
876   on the indicated port, and sending an HTTP request message
877   (<xref target="http.message"/>) containing the URI's identifying data
878   (<xref target="message.routing"/>) to the server.
879   If the server responds to that request with a non-interim HTTP response
880   message, as described in &status-codes;, then that response
881   is considered an authoritative answer to the client's request.
882</t>
883<t>
884   Although HTTP is independent of the transport protocol, the "http"
885   scheme is specific to TCP-based services because the name delegation
886   process depends on TCP for establishing authority.
887   An HTTP service based on some other underlying connection protocol
888   would presumably be identified using a different URI scheme, just as
889   the "https" scheme (below) is used for resources that require an
890   end-to-end secured connection. Other protocols might also be used to
891   provide access to "http" identified resources &mdash; it is only the
892   authoritative interface used for mapping the namespace that is
893   specific to TCP.
894</t>
895<t>
896   The URI generic syntax for authority also includes a deprecated
897   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
898   for including user authentication information in the URI.  Some
899   implementations make use of the userinfo component for internal
900   configuration of authentication information, such as within command
901   invocation options, configuration files, or bookmark lists, even
902   though such usage might expose a user identifier or password.
903   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
904   delimiter) when transmitting an "http" URI in a message.  Recipients
905   of HTTP messages that contain a URI reference &SHOULD; parse for the
906   existence of userinfo and treat its presence as an error, likely
907   indicating that the deprecated subcomponent is being used to obscure
908   the authority for the sake of phishing attacks.
909</t>
910</section>
911
912<section title="https URI scheme" anchor="https.uri">
913   <x:anchor-alias value="https-URI"/>
914   <iref item="https URI scheme"/>
915   <iref item="URI scheme" subitem="https"/>
916<t>
917   The "https" URI scheme is hereby defined for the purpose of minting
918   identifiers according to their association with the hierarchical
919   namespace governed by a potential HTTP origin server listening to a
920   given TCP port for TLS-secured connections <xref target="RFC5246"/>.
921</t>
922<t>
923   All of the requirements listed above for the "http" scheme are also
924   requirements for the "https" scheme, except that a default TCP port
925   of 443 is assumed if the port subcomponent is empty or not given,
926   and the TCP connection &MUST; be secured, end-to-end, through the
927   use of strong encryption prior to sending the first HTTP request.
928</t>
929<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"><!--terminal production--></iref>
930  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
931</artwork></figure>
932<t>
933   Unlike the "http" scheme, responses to "https" identified requests
934   are never "public" and thus &MUST-NOT; be reused for shared caching.
935   They can, however, be reused in a private cache if the message is
936   cacheable by default in HTTP or specifically indicated as such by
937   the Cache-Control header field (&header-cache-control;).
938</t>
939<t>
940   Resources made available via the "https" scheme have no shared
941   identity with the "http" scheme even if their resource identifiers
942   indicate the same authority (the same host listening to the same
943   TCP port).  They are distinct name spaces and are considered to be
944   distinct origin servers.  However, an extension to HTTP that is
945   defined to apply to entire host domains, such as the Cookie protocol
946   <xref target="RFC6265"/>, can allow information
947   set by one service to impact communication with other services
948   within a matching group of host domains.
949</t>
950<t>
951   The process for authoritative access to an "https" identified
952   resource is defined in <xref target="RFC2818"/>.
953</t>
954</section>
955
956<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
957<t>
958   Since the "http" and "https" schemes conform to the URI generic syntax,
959   such URIs are normalized and compared according to the algorithm defined
960   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
961   described above for each scheme.
962</t>
963<t>
964   If the port is equal to the default port for a scheme, the normal
965   form is to elide the port subcomponent. Likewise, an empty path
966   component is equivalent to an absolute path of "/", so the normal
967   form is to provide a path of "/" instead. The scheme and host
968   are case-insensitive and normally provided in lowercase; all
969   other components are compared in a case-sensitive manner.
970   Characters other than those in the "reserved" set are equivalent
971   to their percent-encoded octets (see <xref target="RFC3986"
972   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
973</t>
974<t>
975   For example, the following three URIs are equivalent:
976</t>
977<figure><artwork type="example">
978   http://example.com:80/~smith/home.html
979   http://EXAMPLE.com/%7Esmith/home.html
980   http://EXAMPLE.com:/%7esmith/home.html
981</artwork></figure>
982</section>
983</section>
984</section>
985
986<section title="Message Format" anchor="http.message">
987<x:anchor-alias value="generic-message"/>
988<x:anchor-alias value="message.types"/>
989<x:anchor-alias value="HTTP-message"/>
990<x:anchor-alias value="start-line"/>
991<iref item="header section"/>
992<iref item="headers"/>
993<iref item="header field"/>
994<t>
995   All HTTP/1.1 messages consist of a start-line followed by a sequence of
996   octets in a format similar to the Internet Message Format
997   <xref target="RFC5322"/>: zero or more header fields (collectively
998   referred to as the "headers" or the "header section"), an empty line
999   indicating the end of the header section, and an optional message body.
1000</t>
1001<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"><!--terminal production--></iref>
1002  <x:ref>HTTP-message</x:ref>   = <x:ref>start-line</x:ref>
1003                   *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1004                   <x:ref>CRLF</x:ref>
1005                   [ <x:ref>message-body</x:ref> ]
1006</artwork></figure>
1007<t>
1008   The normal procedure for parsing an HTTP message is to read the
1009   start-line into a structure, read each header field into a hash
1010   table by field name until the empty line, and then use the parsed
1011   data to determine if a message body is expected.  If a message body
1012   has been indicated, then it is read as a stream until an amount
1013   of octets equal to the message body length is read or the connection
1014   is closed.
1015</t>
1016<t>
1017   Recipients &MUST; parse an HTTP message as a sequence of octets in an
1018   encoding that is a superset of US-ASCII <xref target="USASCII"/>.
1019   Parsing an HTTP message as a stream of Unicode characters, without regard
1020   for the specific encoding, creates security vulnerabilities due to the
1021   varying ways that string processing libraries handle invalid multibyte
1022   character sequences that contain the octet LF (%x0A).  String-based
1023   parsers can only be safely used within protocol elements after the element
1024   has been extracted from the message, such as within a header field-value
1025   after message parsing has delineated the individual fields.
1026</t>
1027<t>
1028   An HTTP message can be parsed as a stream for incremental processing or
1029   forwarding downstream.  However, recipients cannot rely on incremental
1030   delivery of partial messages, since some implementations will buffer or
1031   delay message forwarding for the sake of network efficiency, security
1032   checks, or payload transformations.
1033</t>
1034
1035<section title="Start Line" anchor="start.line">
1036  <x:anchor-alias value="Start-Line"/>
1037<t>
1038   An HTTP message can either be a request from client to server or a
1039   response from server to client.  Syntactically, the two types of message
1040   differ only in the start-line, which is either a request-line (for requests)
1041   or a status-line (for responses), and in the algorithm for determining
1042   the length of the message body (<xref target="message.body"/>).
1043   In theory, a client could receive requests and a server could receive
1044   responses, distinguishing them by their different start-line formats,
1045   but in practice servers are implemented to only expect a request
1046   (a response is interpreted as an unknown or invalid request method)
1047   and clients are implemented to only expect a response.
1048</t>
1049<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="start-line"/>
1050  <x:ref>start-line</x:ref>     = <x:ref>request-line</x:ref> / <x:ref>status-line</x:ref>
1051</artwork></figure>
1052<t>
1053   A sender &MUST-NOT; send whitespace between the start-line and
1054   the first header field. The presence of such whitespace in a request
1055   might be an attempt to trick a server into ignoring that field or
1056   processing the line after it as a new request, either of which might
1057   result in a security vulnerability if other implementations within
1058   the request chain interpret the same message differently.
1059   Likewise, the presence of such whitespace in a response might be
1060   ignored by some clients or cause others to cease parsing.
1061</t>
1062
1063<section title="Request Line" anchor="request.line">
1064  <x:anchor-alias value="Request"/>
1065  <x:anchor-alias value="request-line"/>
1066<t>
1067   A request-line begins with a method token, followed by a single
1068   space (SP), the request-target, another single space (SP), the
1069   protocol version, and ending with CRLF.
1070</t>
1071<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-line"/>
1072  <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>
1073</artwork></figure>
1074<t>
1075   A server &MUST; be able to parse any received message that begins
1076   with a request-line and matches the ABNF rule for HTTP-message.
1077</t>
1078<iref primary="true" item="method"/>
1079<t anchor="method">
1080   The method token indicates the request method to be performed on the
1081   target resource. The request method is case-sensitive.
1082</t>
1083<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="method"/>
1084  <x:ref>method</x:ref>         = <x:ref>token</x:ref>
1085</artwork></figure>
1086<t>
1087   The methods defined by this specification can be found in
1088   &methods;, along with information regarding the HTTP method registry
1089   and considerations for defining new methods.
1090</t>
1091<iref item="request-target"/>
1092<t>
1093   The request-target identifies the target resource upon which to apply
1094   the request, as defined in <xref target="request-target"/>.
1095</t>
1096<t>
1097   No whitespace is allowed inside the method, request-target, and
1098   protocol version.  Hence, recipients typically parse the request-line
1099   into its component parts by splitting on the SP characters.
1100</t>
1101<t>
1102   Unfortunately, some user agents fail to properly encode hypertext
1103   references that have embedded whitespace, sending the characters
1104   directly instead of properly percent-encoding the disallowed characters.
1105   Recipients of an invalid request-line &SHOULD; respond with either a
1106   <x:ref>400 (Bad Request)</x:ref> error or a <x:ref>301 (Moved Permanently)</x:ref>
1107   redirect with the request-target properly encoded.  Recipients &SHOULD-NOT;
1108   attempt to autocorrect and then process the request without a redirect,
1109   since the invalid request-line might be deliberately crafted to bypass
1110   security filters along the request chain.
1111</t>
1112<t>
1113   HTTP does not place a pre-defined limit on the length of a request-line.
1114   A server that receives a method longer than any that it implements
1115   &SHOULD; respond with either a <x:ref>405 (Method Not Allowed)</x:ref>, if it is an origin
1116   server, or a <x:ref>501 (Not Implemented)</x:ref> status code.
1117   A server &MUST; be prepared to receive URIs of unbounded length and
1118   respond with the <x:ref>414 (URI Too Long)</x:ref> status code if the received
1119   request-target would be longer than the server wishes to handle
1120   (see &status-414;).
1121</t>
1122<t>
1123   Various ad-hoc limitations on request-line length are found in practice.
1124   It is &RECOMMENDED; that all HTTP senders and recipients support, at a
1125   minimum, request-line lengths of up to 8000 octets.
1126</t>
1127</section>
1128
1129<section title="Status Line" anchor="status.line">
1130  <x:anchor-alias value="response"/>
1131  <x:anchor-alias value="status-line"/>
1132  <x:anchor-alias value="status-code"/>
1133  <x:anchor-alias value="reason-phrase"/>
1134<t>
1135   The first line of a response message is the status-line, consisting
1136   of the protocol version, a space (SP), the status code, another space,
1137   a possibly-empty textual phrase describing the status code, and
1138   ending with CRLF.
1139</t>
1140<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-line"/>
1141  <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>
1142</artwork></figure>
1143<t>
1144   A client &MUST; be able to parse any received message that begins
1145   with a status-line and matches the ABNF rule for HTTP-message.
1146</t>
1147<t>
1148   The status-code element is a 3-digit integer code describing the
1149   result of the server's attempt to understand and satisfy the client's
1150   corresponding request. The rest of the response message is to be
1151   interpreted in light of the semantics defined for that status code.
1152   See &status-codes; for information about the semantics of status codes,
1153   including the classes of status code (indicated by the first digit),
1154   the status codes defined by this specification, considerations for the
1155   definition of new status codes, and the IANA registry.
1156</t>
1157<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-code"/>
1158  <x:ref>status-code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1159</artwork></figure>
1160<t>   
1161   The reason-phrase element exists for the sole purpose of providing a
1162   textual description associated with the numeric status code, mostly
1163   out of deference to earlier Internet application protocols that were more
1164   frequently used with interactive text clients. A client &SHOULD; ignore
1165   the reason-phrase content.
1166</t>
1167<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="reason-phrase"/>
1168  <x:ref>reason-phrase</x:ref>  = *( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1169</artwork></figure>
1170</section>
1171</section>
1172
1173<section title="Header Fields" anchor="header.fields">
1174  <x:anchor-alias value="header-field"/>
1175  <x:anchor-alias value="field-content"/>
1176  <x:anchor-alias value="field-name"/>
1177  <x:anchor-alias value="field-value"/>
1178  <x:anchor-alias value="obs-fold"/>
1179<t>
1180   Each HTTP header field consists of a case-insensitive field name
1181   followed by a colon (":"), optional whitespace, and the field value.
1182</t>
1183<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"/><iref primary="true" item="Grammar" subitem="obs-fold"/>
1184  <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>BWS</x:ref>
1185  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1186  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>obs-fold</x:ref> )
1187  <x:ref>field-content</x:ref>  = *( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1188  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref> ( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1189                 ; obsolete line folding
1190                 ; see <xref target="field.parsing"/>
1191</artwork></figure>
1192<t>
1193   The field-name token labels the corresponding field-value as having the
1194   semantics defined by that header field.  For example, the <x:ref>Date</x:ref>
1195   header field is defined in &header-date; as containing the origination
1196   timestamp for the message in which it appears.
1197</t>
1198<t>
1199   HTTP header fields are fully extensible: there is no limit on the
1200   introduction of new field names, each presumably defining new semantics,
1201   or on the number of header fields used in a given message.  Existing
1202   fields are defined in each part of this specification and in many other
1203   specifications outside the standards process.
1204   New header fields can be introduced without changing the protocol version
1205   if their defined semantics allow them to be safely ignored by recipients
1206   that do not recognize them.
1207</t>
1208<t>
1209   New HTTP header fields &SHOULD; be registered with IANA in the
1210   Message Header Field Registry, as described in &iana-header-registry;.
1211   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1212   field-name is listed in the <x:ref>Connection</x:ref> header field
1213   (<xref target="header.connection"/>) or the proxy is specifically
1214   configured to block or otherwise transform such fields.
1215   Unrecognized header fields &SHOULD; be ignored by other recipients.
1216</t>
1217<t>
1218   The order in which header fields with differing field names are
1219   received is not significant. However, it is "good practice" to send
1220   header fields that contain control data first, such as <x:ref>Host</x:ref>
1221   on requests and <x:ref>Date</x:ref> on responses, so that implementations
1222   can decide when not to handle a message as early as possible.  A server
1223   &MUST; wait until the entire header section is received before interpreting
1224   a request message, since later header fields might include conditionals,
1225   authentication credentials, or deliberately misleading duplicate
1226   header fields that would impact request processing.
1227</t>
1228<t>
1229   Multiple header fields with the same field name &MUST-NOT; be
1230   sent in a message unless the entire field value for that
1231   header field is defined as a comma-separated list [i.e., #(values)].
1232   Multiple header fields with the same field name can be combined into
1233   one "field-name: field-value" pair, without changing the semantics of the
1234   message, by appending each subsequent field value to the combined
1235   field value in order, separated by a comma. The order in which
1236   header fields with the same field name are received is therefore
1237   significant to the interpretation of the combined field value;
1238   a proxy &MUST-NOT; change the order of these field values when
1239   forwarding a message.
1240</t>
1241<x:note>
1242  <t>
1243   &Note; The "Set-Cookie" header field as implemented in
1244   practice can occur multiple times, but does not use the list syntax, and
1245   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1246   for details.) Also note that the Set-Cookie2 header field specified in
1247   <xref target="RFC2965"/> does not share this problem.
1248  </t>
1249</x:note>
1250
1251<section title="Whitespace" anchor="whitespace">
1252<t anchor="rule.LWS">
1253   This specification uses three rules to denote the use of linear
1254   whitespace: OWS (optional whitespace), RWS (required whitespace), and
1255   BWS ("bad" whitespace).
1256</t>
1257<t anchor="rule.OWS">
1258   The OWS rule is used where zero or more linear whitespace octets might
1259   appear. OWS &SHOULD; either not be produced or be produced as a single
1260   SP. Multiple OWS octets that occur within field-content &SHOULD; either
1261   be replaced with a single SP or transformed to all SP octets (each
1262   octet other than SP replaced with SP) before interpreting the field value
1263   or forwarding the message downstream.
1264</t>
1265<t anchor="rule.RWS">
1266   RWS is used when at least one linear whitespace octet is required to
1267   separate field tokens. RWS &SHOULD; be produced as a single SP.
1268   Multiple RWS octets that occur within field-content &SHOULD; either
1269   be replaced with a single SP or transformed to all SP octets before
1270   interpreting the field value or forwarding the message downstream.
1271</t>
1272<t anchor="rule.BWS">
1273   BWS is used where the grammar allows optional whitespace, for historical
1274   reasons, but senders &SHOULD-NOT; produce it in messages;
1275   recipients &MUST; accept such bad optional whitespace and remove it before
1276   interpreting the field value or forwarding the message downstream.
1277</t>
1278<t anchor="rule.whitespace">
1279  <x:anchor-alias value="BWS"/>
1280  <x:anchor-alias value="OWS"/>
1281  <x:anchor-alias value="RWS"/>
1282</t>
1283<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"/>
1284  <x:ref>OWS</x:ref>            = *( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1285                 ; "optional" whitespace
1286  <x:ref>RWS</x:ref>            = 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1287                 ; "required" whitespace
1288  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
1289                 ; "bad" whitespace
1290</artwork></figure>
1291</section>
1292
1293<section title="Field Parsing" anchor="field.parsing">
1294<t>
1295   No whitespace is allowed between the header field-name and colon.
1296   In the past, differences in the handling of such whitespace have led to
1297   security vulnerabilities in request routing and response handling.
1298   Any received request message that contains whitespace between a header
1299   field-name and colon &MUST; be rejected with a response code of 400
1300   (Bad Request).  A proxy &MUST; remove any such whitespace from a response
1301   message before forwarding the message downstream.
1302</t>
1303<t>
1304   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1305   preferred. The field value does not include any leading or trailing white
1306   space: OWS occurring before the first non-whitespace octet of the
1307   field value or after the last non-whitespace octet of the field value
1308   is ignored and &SHOULD; be removed before further processing (as this does
1309   not change the meaning of the header field).
1310</t>
1311<t>
1312   Historically, HTTP header field values could be extended over multiple
1313   lines by preceding each extra line with at least one space or horizontal
1314   tab (obs-fold). This specification deprecates such line
1315   folding except within the message/http media type
1316   (<xref target="internet.media.type.message.http"/>).
1317   HTTP senders &MUST-NOT; produce messages that include line folding
1318   (i.e., that contain any field-value that matches the obs-fold rule) unless
1319   the message is intended for packaging within the message/http media type.
1320   HTTP recipients &SHOULD; accept line folding and replace any embedded
1321   obs-fold whitespace with either a single SP or a matching number of SP
1322   octets (to avoid buffer copying) prior to interpreting the field value or
1323   forwarding the message downstream.
1324</t>
1325<t>
1326   Historically, HTTP has allowed field content with text in the ISO-8859-1
1327   <xref target="ISO-8859-1"/> character encoding and supported other
1328   character sets only through use of <xref target="RFC2047"/> encoding.
1329   In practice, most HTTP header field values use only a subset of the
1330   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1331   header fields &SHOULD; limit their field values to US-ASCII octets.
1332   Recipients &SHOULD; treat other (obs-text) octets in field content as
1333   opaque data.
1334</t>
1335</section>
1336
1337<section title="Field Length" anchor="field.length">
1338<t>
1339   HTTP does not place a pre-defined limit on the length of header fields,
1340   either in isolation or as a set. A server &MUST; be prepared to receive
1341   request header fields of unbounded length and respond with a <x:ref>4xx
1342   (Client Error)</x:ref> status code if the received header field(s) would be
1343   longer than the server wishes to handle.
1344</t>
1345<t>
1346   A client that receives response header fields that are longer than it wishes
1347   to handle can only treat it as a server error.
1348</t>
1349<t>
1350   Various ad-hoc limitations on header field length are found in practice. It
1351   is &RECOMMENDED; that all HTTP senders and recipients support messages whose
1352   combined header fields have 4000 or more octets.
1353</t>
1354</section>
1355
1356<section title="Field value components" anchor="field.components">
1357<t anchor="rule.token.separators">
1358  <x:anchor-alias value="tchar"/>
1359  <x:anchor-alias value="token"/>
1360  <x:anchor-alias value="special"/>
1361  <x:anchor-alias value="word"/>
1362   Many HTTP header field values consist of words (token or quoted-string)
1363   separated by whitespace or special characters. These special characters
1364   &MUST; be in a quoted string to be used within a parameter value (as defined
1365   in <xref target="transfer.codings"/>).
1366</t>
1367<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="word"/><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/><iref primary="true" item="Grammar" subitem="special"><!--unused production--></iref>
1368  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1369
1370  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
1371<!--
1372  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
1373 -->
1374  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
1375                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1376                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
1377                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
1378
1379  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
1380                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1381                 / "]" / "?" / "=" / "{" / "}"
1382</artwork></figure>
1383<t anchor="rule.quoted-string">
1384  <x:anchor-alias value="quoted-string"/>
1385  <x:anchor-alias value="qdtext"/>
1386  <x:anchor-alias value="obs-text"/>
1387   A string of text is parsed as a single word if it is quoted using
1388   double-quote marks.
1389</t>
1390<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"/>
1391  <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>
1392  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1393  <x:ref>obs-text</x:ref>       = %x80-FF
1394</artwork></figure>
1395<t anchor="rule.quoted-pair">
1396  <x:anchor-alias value="quoted-pair"/>
1397   The backslash octet ("\") can be used as a single-octet
1398   quoting mechanism within quoted-string constructs:
1399</t>
1400<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
1401  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1402</artwork></figure>
1403<t>
1404   Recipients that process the value of the quoted-string &MUST; handle a
1405   quoted-pair as if it were replaced by the octet following the backslash.
1406</t>
1407<t>
1408   Senders &SHOULD-NOT; escape octets in quoted-strings that do not require
1409   escaping (i.e., other than DQUOTE and the backslash octet).
1410</t>
1411<t anchor="rule.comment">
1412  <x:anchor-alias value="comment"/>
1413  <x:anchor-alias value="ctext"/>
1414   Comments can be included in some HTTP header fields by surrounding
1415   the comment text with parentheses. Comments are only allowed in
1416   fields containing "comment" as part of their field value definition.
1417</t>
1418<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1419  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1420  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1421</artwork></figure>
1422<t anchor="rule.quoted-cpair">
1423  <x:anchor-alias value="quoted-cpair"/>
1424   The backslash octet ("\") can be used as a single-octet
1425   quoting mechanism within comment constructs:
1426</t>
1427<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1428  <x:ref>quoted-cpair</x:ref>   = "\" ( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1429</artwork></figure>
1430<t>
1431   Senders &SHOULD-NOT; escape octets in comments that do not require escaping
1432   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
1433</t>
1434</section>
1435
1436</section>
1437
1438<section title="Message Body" anchor="message.body">
1439  <x:anchor-alias value="message-body"/>
1440<t>
1441   The message body (if any) of an HTTP message is used to carry the
1442   payload body of that request or response.  The message body is
1443   identical to the payload body unless a transfer coding has been
1444   applied, as described in <xref target="header.transfer-encoding"/>.
1445</t>
1446<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1447  <x:ref>message-body</x:ref> = *OCTET
1448</artwork></figure>
1449<t>
1450   The rules for when a message body is allowed in a message differ for
1451   requests and responses.
1452</t>
1453<t>
1454   The presence of a message body in a request is signaled by a
1455   a <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1456   field. Request message framing is independent of method semantics,
1457   even if the method does not define any use for a message body.
1458</t>
1459<t>
1460   The presence of a message body in a response depends on both
1461   the request method to which it is responding and the response
1462   status code (<xref target="status.line"/>).
1463   Responses to the HEAD request method never include a message body
1464   because the associated response header fields (e.g.,
1465   <x:ref>Transfer-Encoding</x:ref>, <x:ref>Content-Length</x:ref>, etc.),
1466   if present, indicate only what their values would have been if the request
1467   method had been GET (&HEAD;).
1468   <x:ref>2xx (Successful)</x:ref> responses to CONNECT switch to tunnel
1469   mode instead of having a message body (&CONNECT;).
1470   All <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, and
1471   <x:ref>304 (Not Modified)</x:ref> responses &MUST-NOT; include a message body.
1472   All other responses do include a message body, although the body
1473   &MAY; be of zero length.
1474</t>
1475
1476<section title="Transfer-Encoding" anchor="header.transfer-encoding">
1477  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
1478  <x:anchor-alias value="Transfer-Encoding"/>
1479<t>
1480   When one or more transfer codings are applied to a payload body in order
1481   to form the message body, a Transfer-Encoding header field &MUST; be sent
1482   in the message and &MUST; contain the list of corresponding
1483   transfer-coding names in the same order that they were applied.
1484   Transfer codings are defined in <xref target="transfer.codings"/>.
1485</t>
1486<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
1487  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
1488</artwork></figure>
1489<t>
1490   Transfer-Encoding is analogous to the Content-Transfer-Encoding field of
1491   MIME, which was designed to enable safe transport of binary data over a
1492   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1493   However, safe transport has a different focus for an 8bit-clean transfer
1494   protocol. In HTTP's case, Transfer-Encoding is primarily intended to
1495   accurately delimit a dynamically generated payload and to distinguish
1496   payload encodings that are only applied for transport efficiency or
1497   security from those that are characteristics of the target resource.
1498</t>
1499<t>
1500   The "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1501   &MUST; be implemented by all HTTP/1.1 recipients because it plays a
1502   crucial role in delimiting messages when the payload body size is not
1503   known in advance.
1504   When the "chunked" transfer-coding is used, it &MUST; be the last
1505   transfer-coding applied to form the message body and &MUST-NOT;
1506   be applied more than once in a message body.
1507   If any transfer-coding is applied to a request payload body,
1508   the final transfer-coding applied &MUST; be "chunked".
1509   If any transfer-coding is applied to a response payload body, then either
1510   the final transfer-coding applied &MUST; be "chunked" or
1511   the message &MUST; be terminated by closing the connection.
1512</t>
1513<figure><preamble>
1514   For example,
1515</preamble><artwork type="example">
1516  Transfer-Encoding: gzip, chunked
1517</artwork><postamble>
1518   indicates that the payload body has been compressed using the gzip
1519   coding and then chunked using the chunked coding while forming the
1520   message body.
1521</postamble></figure>
1522<t>
1523   If more than one Transfer-Encoding header field is present in a message,
1524   the multiple field-values &MUST; be combined into one field-value,
1525   according to the algorithm defined in <xref target="header.fields"/>,
1526   before determining the message body length.
1527</t>
1528<t>
1529   Unlike <x:ref>Content-Encoding</x:ref> (&content-codings;),
1530   Transfer-Encoding is a property of the message, not of the payload, and thus
1531   &MAY; be added or removed by any implementation along the request/response
1532   chain. Additional information about the encoding parameters &MAY; be
1533   provided by other header fields not defined by this specification.
1534</t>
1535<t>
1536   Transfer-Encoding &MAY; be sent in a response to a HEAD request or in a
1537   <x:ref>304 (Not Modified)</x:ref> response (&status-304;) to a GET request,
1538   neither of which includes a message body,
1539   to indicate that the origin server would have applied a transfer coding
1540   to the message body if the request had been an unconditional GET.
1541   This indication is not required, however, because any recipient on
1542   the response chain (including the origin server) can remove transfer
1543   codings when they are not needed.
1544</t>
1545<t>
1546   Transfer-Encoding was added in HTTP/1.1.  It is generally assumed that
1547   implementations advertising only HTTP/1.0 support will not understand
1548   how to process a transfer-encoded payload.
1549   A client &MUST-NOT; send a request containing Transfer-Encoding unless it
1550   knows the server will handle HTTP/1.1 (or later) requests; such knowledge
1551   might be in the form of specific user configuration or by remembering the
1552   version of a prior received response.
1553   A server &MUST-NOT; send a response containing Transfer-Encoding unless
1554   the corresponding request indicates HTTP/1.1 (or later).
1555</t>
1556<t>
1557   A server that receives a request message with a transfer-coding it does
1558   not understand &SHOULD; respond with <x:ref>501 (Not Implemented)</x:ref> and then
1559   close the connection.
1560</t>
1561</section>
1562
1563<section title="Content-Length" anchor="header.content-length">
1564  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
1565  <x:anchor-alias value="Content-Length"/>
1566<t>
1567   When a message is allowed to contain a message body, does not have a
1568   <x:ref>Transfer-Encoding</x:ref> header field, and has a payload body
1569   length that is known to the sender before the message header section has
1570   been sent, the sender &SHOULD; send a Content-Length header field to
1571   indicate the length of the payload body as a decimal number of octets.
1572</t>
1573<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
1574  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
1575</artwork></figure>
1576<t>
1577   An example is
1578</t>
1579<figure><artwork type="example">
1580  Content-Length: 3495
1581</artwork></figure>
1582<t>
1583   A sender &MUST-NOT; send a Content-Length header field in any message that
1584   contains a <x:ref>Transfer-Encoding</x:ref> header field.
1585</t>
1586<t>
1587   A server &MAY; send a Content-Length header field in a response to a HEAD
1588   request (&HEAD;) in order to indicate the size of the payload body,
1589   excluding any potential transfer-coding, that would have been sent had the
1590   same request been a GET.
1591</t>
1592<t>
1593   A server &MAY; send a Content-Length header field in a
1594   <x:ref>304 (Not Modified)</x:ref> response to a conditional GET request
1595   (&status-304;) in order to indicate the size of the payload body,
1596   excluding any potential transfer-coding, that would have been sent in a
1597   <x:ref>200 (OK)</x:ref> response.
1598</t>
1599<t>
1600   A server &MUST-NOT; send a Content-Length header field in any response
1601   with a status code of
1602   <x:ref>1xx (Informational)</x:ref> or <x:ref>204 (No Content)</x:ref>.
1603   A server &SHOULD-NOT; send a Content-Length header field in any
1604   <x:ref>2xx (Successful)</x:ref> response to a CONNECT request (&CONNECT;).
1605</t>
1606<t>
1607   Any Content-Length field value greater than or equal to zero is valid.
1608   Since there is no predefined limit to the length of an HTTP payload,
1609   recipients &SHOULD; anticipate potentially large decimal numerals and
1610   prevent parsing errors due to integer conversion overflows
1611   (<xref target="attack.protocol.element.size.overflows"/>).
1612</t>
1613<t>
1614   If a message is received that has multiple Content-Length header fields
1615   with field-values consisting of the same decimal value, or a single
1616   Content-Length header field with a field value containing a list of
1617   identical decimal values (e.g., "Content-Length: 42, 42"), indicating that
1618   duplicate Content-Length header fields have been generated or combined by an
1619   upstream message processor, then the recipient &MUST; either reject the
1620   message as invalid or replace the duplicated field-values with a single
1621   valid Content-Length field containing that decimal value prior to
1622   determining the message body length.
1623</t>
1624<x:note>
1625  <t>
1626   &Note; HTTP's use of Content-Length for message framing differs
1627   significantly from the same field's use in MIME, where it is an optional
1628   field used only within the "message/external-body" media-type.
1629  </t>
1630</x:note>
1631</section>
1632
1633<section title="Message Body Length" anchor="message.body.length">
1634<t>
1635   The length of a message body is determined by one of the following
1636   (in order of precedence):
1637</t>
1638<t>
1639  <list style="numbers">
1640    <x:lt><t>
1641     Any response to a HEAD request and any response with a
1642     <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, or
1643     <x:ref>304 (Not Modified)</x:ref> status code is always
1644     terminated by the first empty line after the header fields, regardless of
1645     the header fields present in the message, and thus cannot contain a
1646     message body.
1647    </t></x:lt>
1648    <x:lt><t>
1649     Any <x:ref>2xx (Successful)</x:ref> response to a CONNECT request implies that the
1650     connection will become a tunnel immediately after the empty line that
1651     concludes the header fields.  A client &MUST; ignore any
1652     <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1653     fields received in such a message.
1654    </t></x:lt>
1655    <x:lt><t>
1656     If a <x:ref>Transfer-Encoding</x:ref> header field is present
1657     and the "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1658     is the final encoding, the message body length is determined by reading
1659     and decoding the chunked data until the transfer-coding indicates the
1660     data is complete.
1661    </t>
1662    <t>
1663     If a <x:ref>Transfer-Encoding</x:ref> header field is present in a
1664     response and the "chunked" transfer-coding is not the final encoding, the
1665     message body length is determined by reading the connection until it is
1666     closed by the server.
1667     If a Transfer-Encoding header field is present in a request and the
1668     "chunked" transfer-coding is not the final encoding, the message body
1669     length cannot be determined reliably; the server &MUST; respond with
1670     the <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1671    </t>
1672    <t>
1673     If a message is received with both a <x:ref>Transfer-Encoding</x:ref>
1674     and a <x:ref>Content-Length</x:ref> header field, the
1675     Transfer-Encoding overrides the Content-Length.
1676     Such a message might indicate an attempt to perform request or response
1677     smuggling (bypass of security-related checks on message routing or content)
1678     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1679     be removed, prior to forwarding the message downstream, or replaced with
1680     the real message body length after the transfer-coding is decoded.
1681    </t></x:lt>
1682    <x:lt><t>
1683     If a message is received without <x:ref>Transfer-Encoding</x:ref> and with
1684     either multiple <x:ref>Content-Length</x:ref> header fields having
1685     differing field-values or a single Content-Length header field having an
1686     invalid value, then the message framing is invalid and &MUST; be treated
1687     as an error to prevent request or response smuggling.
1688     If this is a request message, the server &MUST; respond with
1689     a <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1690     If this is a response message received by a proxy, the proxy
1691     &MUST; discard the received response, send a <x:ref>502 (Bad Gateway)</x:ref>
1692     status code as its downstream response, and then close the connection.
1693     If this is a response message received by a user-agent, it &MUST; be
1694     treated as an error by discarding the message and closing the connection.
1695    </t></x:lt>
1696    <x:lt><t>
1697     If a valid <x:ref>Content-Length</x:ref> header field is present without
1698     <x:ref>Transfer-Encoding</x:ref>, its decimal value defines the
1699     message body length in octets.  If the actual number of octets sent in
1700     the message is less than the indicated Content-Length, the recipient
1701     &MUST; consider the message to be incomplete and treat the connection
1702     as no longer usable.
1703     If the actual number of octets sent in the message is more than the indicated
1704     Content-Length, the recipient &MUST; only process the message body up to the
1705     field value's number of octets; the remainder of the message &MUST; either
1706     be discarded or treated as the next message in a pipeline.  For the sake of
1707     robustness, a user-agent &MAY; attempt to detect and correct such an error
1708     in message framing if it is parsing the response to the last request on
1709     a connection and the connection has been closed by the server.
1710    </t></x:lt>
1711    <x:lt><t>
1712     If this is a request message and none of the above are true, then the
1713     message body length is zero (no message body is present).
1714    </t></x:lt>
1715    <x:lt><t>
1716     Otherwise, this is a response message without a declared message body
1717     length, so the message body length is determined by the number of octets
1718     received prior to the server closing the connection.
1719    </t></x:lt>
1720  </list>
1721</t>
1722<t>
1723   Since there is no way to distinguish a successfully completed,
1724   close-delimited message from a partially-received message interrupted
1725   by network failure, a server &SHOULD; use encoding or
1726   length-delimited messages whenever possible.  The close-delimiting
1727   feature exists primarily for backwards compatibility with HTTP/1.0.
1728</t>
1729<t>
1730   A server &MAY; reject a request that contains a message body but
1731   not a <x:ref>Content-Length</x:ref> by responding with
1732   <x:ref>411 (Length Required)</x:ref>.
1733</t>
1734<t>
1735   Unless a transfer-coding other than "chunked" has been applied,
1736   a client that sends a request containing a message body &SHOULD;
1737   use a valid <x:ref>Content-Length</x:ref> header field if the message body
1738   length is known in advance, rather than the "chunked" encoding, since some
1739   existing services respond to "chunked" with a <x:ref>411 (Length Required)</x:ref>
1740   status code even though they understand the chunked encoding.  This
1741   is typically because such services are implemented via a gateway that
1742   requires a content-length in advance of being called and the server
1743   is unable or unwilling to buffer the entire request before processing.
1744</t>
1745<t>
1746   A client that sends a request containing a message body &MUST; include a
1747   valid <x:ref>Content-Length</x:ref> header field if it does not know the
1748   server will handle HTTP/1.1 (or later) requests; such knowledge can be in
1749   the form of specific user configuration or by remembering the version of a
1750   prior received response.
1751</t>
1752</section>
1753</section>
1754
1755<section anchor="incomplete.messages" title="Handling Incomplete Messages">
1756<t>
1757   Request messages that are prematurely terminated, possibly due to a
1758   canceled connection or a server-imposed time-out exception, &MUST;
1759   result in closure of the connection; sending an error response
1760   prior to closing the connection is &OPTIONAL;.
1761</t>
1762<t>
1763   Response messages that are prematurely terminated, usually by closure
1764   of the connection prior to receiving the expected number of octets or by
1765   failure to decode a transfer-encoded message body, &MUST; be recorded
1766   as incomplete.  A response that terminates in the middle of the header
1767   block (before the empty line is received) cannot be assumed to convey the
1768   full semantics of the response and &MUST; be treated as an error.
1769</t>
1770<t>
1771   A message body that uses the chunked transfer encoding is
1772   incomplete if the zero-sized chunk that terminates the encoding has not
1773   been received.  A message that uses a valid <x:ref>Content-Length</x:ref> is
1774   incomplete if the size of the message body received (in octets) is less than
1775   the value given by Content-Length.  A response that has neither chunked
1776   transfer encoding nor Content-Length is terminated by closure of the
1777   connection, and thus is considered complete regardless of the number of
1778   message body octets received, provided that the header block was received
1779   intact.
1780</t>
1781<t>
1782   A user agent &MUST-NOT; render an incomplete response message body as if
1783   it were complete (i.e., some indication needs to be given to the user that an
1784   error occurred).  Cache requirements for incomplete responses are defined
1785   in &cache-incomplete;.
1786</t>
1787<t>
1788   A server &MUST; read the entire request message body or close
1789   the connection after sending its response, since otherwise the
1790   remaining data on a persistent connection would be misinterpreted
1791   as the next request.  Likewise,
1792   a client &MUST; read the entire response message body if it intends
1793   to reuse the same connection for a subsequent request.  Pipelining
1794   multiple requests on a connection is described in <xref target="pipelining"/>.
1795</t>
1796</section>
1797
1798<section title="Message Parsing Robustness" anchor="message.robustness">
1799<t>
1800   Older HTTP/1.0 client implementations might send an extra CRLF
1801   after a POST request as a lame workaround for some early server
1802   applications that failed to read message body content that was
1803   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1804   preface or follow a request with an extra CRLF.  If terminating
1805   the request message body with a line-ending is desired, then the
1806   client &MUST; include the terminating CRLF octets as part of the
1807   message body length.
1808</t>
1809<t>
1810   In the interest of robustness, servers &SHOULD; ignore at least one
1811   empty line received where a request-line is expected. In other words, if
1812   the server is reading the protocol stream at the beginning of a
1813   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1814   Likewise, although the line terminator for the start-line and header
1815   fields is the sequence CRLF, we recommend that recipients recognize a
1816   single LF as a line terminator and ignore any CR.
1817</t>
1818<t>
1819   When a server listening only for HTTP request messages, or processing
1820   what appears from the start-line to be an HTTP request message,
1821   receives a sequence of octets that does not match the HTTP-message
1822   grammar aside from the robustness exceptions listed above, the
1823   server &MUST; respond with an HTTP/1.1 <x:ref>400 (Bad Request)</x:ref> response. 
1824</t>
1825</section>
1826</section>
1827
1828<section title="Transfer Codings" anchor="transfer.codings">
1829  <x:anchor-alias value="transfer-coding"/>
1830  <x:anchor-alias value="transfer-extension"/>
1831<t>
1832   Transfer-coding values are used to indicate an encoding
1833   transformation that has been, can be, or might need to be applied to a
1834   payload body in order to ensure "safe transport" through the network.
1835   This differs from a content coding in that the transfer-coding is a
1836   property of the message rather than a property of the representation
1837   that is being transferred.
1838</t>
1839<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1840  <x:ref>transfer-coding</x:ref>    = "chunked" ; <xref target="chunked.encoding"/>
1841                     / "compress" ; <xref target="compress.coding"/>
1842                     / "deflate" ; <xref target="deflate.coding"/>
1843                     / "gzip" ; <xref target="gzip.coding"/>
1844                     / <x:ref>transfer-extension</x:ref>
1845  <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> )
1846</artwork></figure>
1847<t anchor="rule.parameter">
1848  <x:anchor-alias value="attribute"/>
1849  <x:anchor-alias value="transfer-parameter"/>
1850  <x:anchor-alias value="value"/>
1851   Parameters are in the form of attribute/value pairs.
1852</t>
1853<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"/>
1854  <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>
1855  <x:ref>attribute</x:ref>          = <x:ref>token</x:ref>
1856  <x:ref>value</x:ref>              = <x:ref>word</x:ref>
1857</artwork></figure>
1858<t>
1859   All transfer-coding values are case-insensitive and &SHOULD; be registered
1860   within the HTTP Transfer Coding registry, as defined in
1861   <xref target="transfer.coding.registry"/>.
1862   They are used in the <x:ref>TE</x:ref> (<xref target="header.te"/>) and
1863   <x:ref>Transfer-Encoding</x:ref> (<xref target="header.transfer-encoding"/>)
1864   header fields.
1865</t>
1866
1867<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1868  <iref item="chunked (Coding Format)"/>
1869  <x:anchor-alias value="chunk"/>
1870  <x:anchor-alias value="chunked-body"/>
1871  <x:anchor-alias value="chunk-data"/>
1872  <x:anchor-alias value="chunk-ext"/>
1873  <x:anchor-alias value="chunk-ext-name"/>
1874  <x:anchor-alias value="chunk-ext-val"/>
1875  <x:anchor-alias value="chunk-size"/>
1876  <x:anchor-alias value="last-chunk"/>
1877  <x:anchor-alias value="trailer-part"/>
1878  <x:anchor-alias value="quoted-str-nf"/>
1879  <x:anchor-alias value="qdtext-nf"/>
1880<t>
1881   The chunked encoding modifies the body of a message in order to
1882   transfer it as a series of chunks, each with its own size indicator,
1883   followed by an &OPTIONAL; trailer containing header fields. This
1884   allows dynamically produced content to be transferred along with the
1885   information necessary for the recipient to verify that it has
1886   received the full message.
1887</t>
1888<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="chunked-body"><!--terminal production--></iref><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"/>
1889  <x:ref>chunked-body</x:ref>   = *<x:ref>chunk</x:ref>
1890                   <x:ref>last-chunk</x:ref>
1891                   <x:ref>trailer-part</x:ref>
1892                   <x:ref>CRLF</x:ref>
1893 
1894  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1895                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1896  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1897  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1898 
1899  <x:ref>chunk-ext</x:ref>      = *( ";" <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] )
1900  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1901  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
1902  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1903  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1904 
1905  <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>
1906                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
1907  <x:ref>qdtext-nf</x:ref>      = <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1908</artwork></figure>
1909<t>
1910   Chunk extensions within the chucked encoding are deprecated.
1911   Senders &SHOULD-NOT; send chunk-ext.
1912   Definition of new chunk extensions is discouraged.
1913</t>
1914<t>
1915   The chunk-size field is a string of hex digits indicating the size of
1916   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1917   zero, followed by the trailer, which is terminated by an empty line.
1918</t>
1919
1920<section title="Trailer" anchor="header.trailer">
1921  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
1922  <x:anchor-alias value="Trailer"/>
1923<t>
1924   A trailer allows the sender to include additional fields at the end of a
1925   chunked message in order to supply metadata that might be dynamically
1926   generated while the message body is sent, such as a message integrity
1927   check, digital signature, or post-processing status.
1928   The trailer &MUST-NOT; contain fields that need to be known before a
1929   recipient processes the body, such as <x:ref>Transfer-Encoding</x:ref>,
1930   <x:ref>Content-Length</x:ref>, and <x:ref>Trailer</x:ref>.
1931</t>
1932<t>
1933   When a message includes a message body encoded with the chunked
1934   transfer-coding and the sender desires to send metadata in the form of
1935   trailer fields at the end of the message, the sender &SHOULD; send a
1936   <x:ref>Trailer</x:ref> header field before the message body to indicate
1937   which fields will be present in the trailers. This allows the recipient
1938   to prepare for receipt of that metadata before it starts processing the body,
1939   which is useful if the message is being streamed and the recipient wishes
1940   to confirm an integrity check on the fly.
1941</t>
1942<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
1943  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
1944</artwork></figure>
1945<t>
1946   If no <x:ref>Trailer</x:ref> header field is present, the sender of a
1947   chunked message body &SHOULD; send an empty trailer.
1948</t>
1949<t>
1950   A server &MUST; send an empty trailer with the chunked transfer-coding
1951   unless at least one of the following is true:
1952  <list style="numbers">
1953    <t>the request included a <x:ref>TE</x:ref> header field that indicates
1954    "trailers" is acceptable in the transfer-coding of the response, as
1955    described in <xref target="header.te"/>; or,</t>
1956     
1957    <t>the trailer fields consist entirely of optional metadata and the
1958    recipient could use the message (in a manner acceptable to the server where
1959    the field originated) without receiving that metadata. In other words,
1960    the server that generated the header field is willing to accept the
1961    possibility that the trailer fields might be silently discarded along
1962    the path to the client.</t>
1963  </list>
1964</t>
1965<t>
1966   The above requirement prevents the need for an infinite buffer when a
1967   message is being received by an HTTP/1.1 (or later) proxy and forwarded to
1968   an HTTP/1.0 recipient.
1969</t>
1970</section>
1971
1972<section title="Decoding chunked" anchor="decoding.chunked">
1973<t>
1974   A process for decoding the "chunked" transfer-coding
1975   can be represented in pseudo-code as:
1976</t>
1977<figure><artwork type="code">
1978  length := 0
1979  read chunk-size, chunk-ext (if any) and CRLF
1980  while (chunk-size &gt; 0) {
1981     read chunk-data and CRLF
1982     append chunk-data to decoded-body
1983     length := length + chunk-size
1984     read chunk-size and CRLF
1985  }
1986  read header-field
1987  while (header-field not empty) {
1988     append header-field to existing header fields
1989     read header-field
1990  }
1991  Content-Length := length
1992  Remove "chunked" from Transfer-Encoding
1993  Remove Trailer from existing header fields
1994</artwork></figure>
1995<t>
1996   All recipients &MUST; be able to receive and decode the
1997   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
1998   they do not understand.
1999</t>
2000</section>
2001</section>
2002
2003<section title="Compression Codings" anchor="compression.codings">
2004<t>
2005   The codings defined below can be used to compress the payload of a
2006   message.
2007</t>
2008
2009<section title="Compress Coding" anchor="compress.coding">
2010<iref item="compress (Coding Format)"/>
2011<t>
2012   The "compress" format is produced by the common UNIX file compression
2013   program "compress". This format is an adaptive Lempel-Ziv-Welch
2014   coding (LZW). Recipients &SHOULD; consider "x-compress" to be
2015   equivalent to "compress".
2016</t>
2017</section>
2018
2019<section title="Deflate Coding" anchor="deflate.coding">
2020<iref item="deflate (Coding Format)"/>
2021<t>
2022   The "deflate" format is defined as the "deflate" compression mechanism
2023   (described in <xref target="RFC1951"/>) used inside the "zlib"
2024   data format (<xref target="RFC1950"/>).
2025</t>
2026<x:note>
2027  <t>
2028    &Note; Some incorrect implementations send the "deflate"
2029    compressed data without the zlib wrapper.
2030   </t>
2031</x:note>
2032</section>
2033
2034<section title="Gzip Coding" anchor="gzip.coding">
2035<iref item="gzip (Coding Format)"/>
2036<t>
2037   The "gzip" format is produced by the file compression program
2038   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2039   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2040   Recipients &SHOULD; consider "x-gzip" to be equivalent to "gzip".
2041</t>
2042</section>
2043
2044</section>
2045
2046<section title="TE" anchor="header.te">
2047  <iref primary="true" item="TE header field" x:for-anchor=""/>
2048  <x:anchor-alias value="TE"/>
2049  <x:anchor-alias value="t-codings"/>
2050  <x:anchor-alias value="t-ranking"/>
2051  <x:anchor-alias value="rank"/>
2052<t>
2053   The "TE" header field in a request indicates what transfer-codings,
2054   besides "chunked", the client is willing to accept in response, and
2055   whether or not the client is willing to accept trailer fields in a
2056   chunked transfer-coding.
2057</t>
2058<t>
2059   The TE field-value consists of a comma-separated list of transfer-coding
2060   names, each allowing for optional parameters (as described in
2061   <xref target="transfer.codings"/>), and/or the keyword "trailers".
2062   Clients &MUST-NOT; send the chunked transfer-coding name in TE;
2063   chunked is always acceptable for HTTP/1.1 recipients.
2064</t>
2065<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="t-codings"/><iref primary="true" item="Grammar" subitem="t-ranking"/><iref primary="true" item="Grammar" subitem="rank"/>
2066  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
2067  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-coding</x:ref> [ <x:ref>t-ranking</x:ref> ] )
2068  <x:ref>t-ranking</x:ref> = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>rank</x:ref>
2069  <x:ref>rank</x:ref>      = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2070             / ( "1" [ "." 0*3("0") ] )
2071</artwork></figure>
2072<t>
2073   Three examples of TE use are below.
2074</t>
2075<figure><artwork type="example">
2076  TE: deflate
2077  TE:
2078  TE: trailers, deflate;q=0.5
2079</artwork></figure>
2080<t>
2081   The presence of the keyword "trailers" indicates that the client is
2082   willing to accept trailer fields in a chunked transfer-coding,
2083   as defined in <xref target="chunked.encoding"/>, on behalf of itself and
2084   any downstream clients. For chained requests, this implies that either:
2085   (a) all downstream clients are willing to accept trailer fields in the
2086   forwarded response; or,
2087   (b) the client will attempt to buffer the response on behalf of downstream
2088   recipients.
2089   Note that HTTP/1.1 does not define any means to limit the size of a
2090   chunked response such that a client can be assured of buffering the
2091   entire response.
2092</t>
2093<t>
2094   When multiple transfer-codings are acceptable, the client &MAY; rank the
2095   codings by preference using a case-insensitive "q" parameter (similar to
2096   the qvalues used in content negotiation fields, &qvalue;). The rank value
2097   is a real number in the range 0 through 1, where 0.001 is the least
2098   preferred and 1 is the most preferred; a value of 0 means "not acceptable".
2099</t>
2100<t>
2101   If the TE field-value is empty or if no TE field is present, the only
2102   acceptable transfer-coding is "chunked". A message with no transfer-coding
2103   is always acceptable.
2104</t>
2105<t>
2106   Since the TE header field only applies to the immediate connection,
2107   a sender of TE &MUST; also send a "TE" connection option within the
2108   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>)
2109   in order to prevent the TE field from being forwarded by intermediaries
2110   that do not support its semantics.
2111</t>
2112</section>
2113</section>
2114
2115<section title="Message Routing" anchor="message.routing">
2116<t>
2117   HTTP request message routing is determined by each client based on the
2118   target resource, the client's proxy configuration, and
2119   establishment or reuse of an inbound connection.  The corresponding
2120   response routing follows the same connection chain back to the client.
2121</t>
2122
2123<section title="Identifying a Target Resource" anchor="target-resource">
2124  <iref primary="true" item="target resource"/>
2125  <iref primary="true" item="target URI"/>
2126  <x:anchor-alias value="target resource"/>
2127  <x:anchor-alias value="target URI"/>
2128<t>
2129   HTTP is used in a wide variety of applications, ranging from
2130   general-purpose computers to home appliances.  In some cases,
2131   communication options are hard-coded in a client's configuration.
2132   However, most HTTP clients rely on the same resource identification
2133   mechanism and configuration techniques as general-purpose Web browsers.
2134</t>
2135<t>
2136   HTTP communication is initiated by a user agent for some purpose.
2137   The purpose is a combination of request semantics, which are defined in
2138   <xref target="Part2"/>, and a target resource upon which to apply those
2139   semantics.  A URI reference (<xref target="uri"/>) is typically used as
2140   an identifier for the "<x:dfn>target resource</x:dfn>", which a user agent
2141   would resolve to its absolute form in order to obtain the
2142   "<x:dfn>target URI</x:dfn>".  The target URI
2143   excludes the reference's fragment identifier component, if any,
2144   since fragment identifiers are reserved for client-side processing
2145   (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>).
2146</t>
2147</section>
2148
2149<section title="Connecting Inbound" anchor="connecting.inbound">
2150<t>
2151   Once the target URI is determined, a client needs to decide whether
2152   a network request is necessary to accomplish the desired semantics and,
2153   if so, where that request is to be directed.
2154</t>
2155<t>
2156   If the client has a response cache and the request semantics can be
2157   satisfied by a cache (<xref target="Part6"/>), then the request is
2158   usually directed to the cache first.
2159</t>
2160<t>
2161   If the request is not satisfied by a cache, then a typical client will
2162   check its configuration to determine whether a proxy is to be used to
2163   satisfy the request.  Proxy configuration is implementation-dependent,
2164   but is often based on URI prefix matching, selective authority matching,
2165   or both, and the proxy itself is usually identified by an "http" or
2166   "https" URI.  If a proxy is applicable, the client connects inbound by
2167   establishing (or reusing) a connection to that proxy.
2168</t>
2169<t>
2170   If no proxy is applicable, a typical client will invoke a handler routine,
2171   usually specific to the target URI's scheme, to connect directly
2172   to an authority for the target resource.  How that is accomplished is
2173   dependent on the target URI scheme and defined by its associated
2174   specification, similar to how this specification defines origin server
2175   access for resolution of the "http" (<xref target="http.uri"/>) and
2176   "https" (<xref target="https.uri"/>) schemes.
2177</t>
2178<t>
2179   HTTP requirements regarding connection management are defined in
2180   <xref target="connection.management"/>.
2181</t>
2182</section>
2183
2184<section title="Request Target" anchor="request-target">
2185<t>
2186   Once an inbound connection is obtained,
2187   the client sends an HTTP request message (<xref target="http.message"/>)
2188   with a request-target derived from the target URI.
2189   There are four distinct formats for the request-target, depending on both
2190   the method being requested and whether the request is to a proxy.
2191</t>   
2192<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/><iref primary="true" item="Grammar" subitem="origin-form"/><iref primary="true" item="Grammar" subitem="absolute-form"/><iref primary="true" item="Grammar" subitem="authority-form"/><iref primary="true" item="Grammar" subitem="asterisk-form"/>
2193  <x:ref>request-target</x:ref> = <x:ref>origin-form</x:ref>
2194                 / <x:ref>absolute-form</x:ref>
2195                 / <x:ref>authority-form</x:ref>
2196                 / <x:ref>asterisk-form</x:ref>
2197
2198  <x:ref>origin-form</x:ref>    = <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ]
2199  <x:ref>absolute-form</x:ref>  = <x:ref>absolute-URI</x:ref>
2200  <x:ref>authority-form</x:ref> = <x:ref>authority</x:ref>
2201  <x:ref>asterisk-form</x:ref>  = "*"
2202</artwork></figure>
2203<t anchor="origin-form"><iref item="origin-form (of request-target)"/>
2204   The most common form of request-target is the origin-form.
2205   When making a request directly to an origin server, other than a CONNECT
2206   or server-wide OPTIONS request (as detailed below),
2207   a client &MUST; send only the absolute path and query components of
2208   the target URI as the request-target.
2209   If the target URI's path component is empty, then the client &MUST; send
2210   "/" as the path within the origin-form of request-target.
2211   A <x:ref>Host</x:ref> header field is also sent, as defined in
2212   <xref target="header.host"/>, containing the target URI's
2213   authority component (excluding any userinfo).
2214</t>
2215<t>
2216   For example, a client wishing to retrieve a representation of the resource
2217   identified as
2218</t>
2219<figure><artwork x:indent-with="  " type="example">
2220http://www.example.org/where?q=now
2221</artwork></figure>
2222<t>
2223   directly from the origin server would open (or reuse) a TCP connection
2224   to port 80 of the host "www.example.org" and send the lines:
2225</t>
2226<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2227GET /where?q=now HTTP/1.1
2228Host: www.example.org
2229</artwork></figure>
2230<t>
2231   followed by the remainder of the request message.
2232</t>
2233<t anchor="absolute-form"><iref item="absolute-form (of request-target)"/>
2234   When making a request to a proxy, other than a CONNECT or server-wide
2235   OPTIONS request (as detailed below), a client &MUST; send the target URI
2236   in absolute-form as the request-target.
2237   The proxy is requested to either service that request from a valid cache,
2238   if possible, or make the same request on the client's behalf to either
2239   the next inbound proxy server or directly to the origin server indicated
2240   by the request-target.  Requirements on such "forwarding" of messages are
2241   defined in <xref target="message.forwarding"/>.
2242</t>
2243<t>
2244   An example absolute-form of request-line would be:
2245</t>
2246<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2247GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
2248</artwork></figure>
2249<t>
2250   To allow for transition to the absolute-form for all requests in some
2251   future version of HTTP, HTTP/1.1 servers &MUST; accept the absolute-form
2252   in requests, even though HTTP/1.1 clients will only send them in requests
2253   to proxies.
2254</t>
2255<t anchor="authority-form"><iref item="authority-form (of request-target)"/>
2256   The authority-form of request-target is only used for CONNECT requests
2257   (&CONNECT;).  When making a CONNECT request to establish a tunnel through
2258   one or more proxies, a client &MUST; send only the target URI's
2259   authority component (excluding any userinfo) as the request-target.
2260   For example,
2261</t>
2262<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2263CONNECT www.example.com:80 HTTP/1.1
2264</artwork></figure>
2265<t anchor="asterisk-form"><iref item="asterisk-form (of request-target)"/>
2266   The asterisk-form of request-target is only used for a server-wide
2267   OPTIONS request (&OPTIONS;).  When a client wishes to request OPTIONS
2268   for the server as a whole, as opposed to a specific named resource of
2269   that server, the client &MUST; send only "*" (%x2A) as the request-target.
2270   For example,
2271</t>
2272<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2273OPTIONS * HTTP/1.1
2274</artwork></figure>
2275<t>
2276   If a proxy receives an OPTIONS request with an absolute-form of
2277   request-target in which the URI has an empty path and no query component,
2278   then the last proxy on the request chain &MUST; send a request-target
2279   of "*" when it forwards the request to the indicated origin server.
2280</t>
2281<figure><preamble>   
2282   For example, the request
2283</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2284OPTIONS http://www.example.org:8001 HTTP/1.1
2285</artwork></figure>
2286<figure><preamble>   
2287  would be forwarded by the final proxy as
2288</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2289OPTIONS * HTTP/1.1
2290Host: www.example.org:8001
2291</artwork>
2292<postamble>
2293   after connecting to port 8001 of host "www.example.org".
2294</postamble>
2295</figure>
2296</section>
2297
2298<section title="Host" anchor="header.host">
2299  <iref primary="true" item="Host header field" x:for-anchor=""/>
2300  <x:anchor-alias value="Host"/>
2301<t>
2302   The "Host" header field in a request provides the host and port
2303   information from the target URI, enabling the origin
2304   server to distinguish among resources while servicing requests
2305   for multiple host names on a single IP address.  Since the Host
2306   field-value is critical information for handling a request, it
2307   &SHOULD; be sent as the first header field following the request-line.
2308</t>
2309<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2310  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2311</artwork></figure>
2312<t>
2313   A client &MUST; send a Host header field in all HTTP/1.1 request
2314   messages.  If the target URI includes an authority component, then
2315   the Host field-value &MUST; be identical to that authority component
2316   after excluding any userinfo (<xref target="http.uri"/>).
2317   If the authority component is missing or undefined for the target URI,
2318   then the Host header field &MUST; be sent with an empty field-value.
2319</t>
2320<t>
2321   For example, a GET request to the origin server for
2322   &lt;http://www.example.org/pub/WWW/&gt; would begin with:
2323</t>
2324<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2325GET /pub/WWW/ HTTP/1.1
2326Host: www.example.org
2327</artwork></figure>
2328<t>
2329   The Host header field &MUST; be sent in an HTTP/1.1 request even
2330   if the request-target is in the absolute-form, since this
2331   allows the Host information to be forwarded through ancient HTTP/1.0
2332   proxies that might not have implemented Host.
2333</t>
2334<t>
2335   When a proxy receives a request with an absolute-form of
2336   request-target, the proxy &MUST; ignore the received
2337   Host header field (if any) and instead replace it with the host
2338   information of the request-target.  If the proxy forwards the request,
2339   it &MUST; generate a new Host field-value based on the received
2340   request-target rather than forward the received Host field-value.
2341</t>
2342<t>
2343   Since the Host header field acts as an application-level routing
2344   mechanism, it is a frequent target for malware seeking to poison
2345   a shared cache or redirect a request to an unintended server.
2346   An interception proxy is particularly vulnerable if it relies on
2347   the Host field-value for redirecting requests to internal
2348   servers, or for use as a cache key in a shared cache, without
2349   first verifying that the intercepted connection is targeting a
2350   valid IP address for that host.
2351</t>
2352<t>
2353   A server &MUST; respond with a <x:ref>400 (Bad Request)</x:ref> status code
2354   to any HTTP/1.1 request message that lacks a Host header field and
2355   to any request message that contains more than one Host header field
2356   or a Host header field with an invalid field-value.
2357</t>
2358</section>
2359
2360<section title="Effective Request URI" anchor="effective.request.uri">
2361  <iref primary="true" item="effective request URI"/>
2362<t>
2363   A server that receives an HTTP request message &MUST; reconstruct
2364   the user agent's original target URI, based on the pieces of information
2365   learned from the request-target, <x:ref>Host</x:ref> header field, and
2366   connection context, in order to identify the intended target resource and
2367   properly service the request. The URI derived from this reconstruction
2368   process is referred to as the "<x:dfn>effective request URI</x:dfn>".
2369</t>
2370<t>
2371   For a user agent, the effective request URI is the target URI.
2372</t>
2373<t>
2374   If the request-target is in absolute-form, then the effective request URI
2375   is the same as the request-target.  Otherwise, the effective request URI
2376   is constructed as follows.
2377</t>
2378<t>
2379   If the request is received over a TLS-secured TCP connection,
2380   then the effective request URI's scheme is "https"; otherwise, the
2381   scheme is "http".
2382</t>
2383<t>
2384   If the request-target is in authority-form, then the effective
2385   request URI's authority component is the same as the request-target.
2386   Otherwise, if a <x:ref>Host</x:ref> header field is supplied with a
2387   non-empty field-value, then the authority component is the same as the
2388   Host field-value. Otherwise, the authority component is the concatenation of
2389   the default host name configured for the server, a colon (":"), and the
2390   connection's incoming TCP port number in decimal form.
2391</t>
2392<t>
2393   If the request-target is in authority-form or asterisk-form, then the
2394   effective request URI's combined path and query component is empty.
2395   Otherwise, the combined path and query component is the same as the
2396   request-target.
2397</t>
2398<t>
2399   The components of the effective request URI, once determined as above,
2400   can be combined into absolute-URI form by concatenating the scheme,
2401   "://", authority, and combined path and query component.
2402</t>
2403<figure>
2404<preamble>
2405   Example 1: the following message received over an insecure TCP connection
2406</preamble> 
2407<artwork type="example" x:indent-with="  ">
2408GET /pub/WWW/TheProject.html HTTP/1.1
2409Host: www.example.org:8080
2410</artwork>
2411</figure>
2412<figure>
2413<preamble>
2414  has an effective request URI of
2415</preamble>
2416<artwork type="example" x:indent-with="  ">
2417http://www.example.org:8080/pub/WWW/TheProject.html
2418</artwork>
2419</figure>
2420<figure>
2421<preamble>
2422   Example 2: the following message received over a TLS-secured TCP connection
2423</preamble> 
2424<artwork type="example" x:indent-with="  ">
2425OPTIONS * HTTP/1.1
2426Host: www.example.org
2427</artwork>
2428</figure>
2429<figure>
2430<preamble>
2431  has an effective request URI of
2432</preamble>
2433<artwork type="example" x:indent-with="  ">
2434https://www.example.org
2435</artwork>
2436</figure>
2437<t>
2438   An origin server that does not allow resources to differ by requested
2439   host &MAY; ignore the <x:ref>Host</x:ref> field-value and instead replace it
2440   with a configured server name when constructing the effective request URI.
2441</t>
2442<t>
2443   Recipients of an HTTP/1.0 request that lacks a <x:ref>Host</x:ref> header
2444   field &MAY; attempt to use heuristics (e.g., examination of the URI path for
2445   something unique to a particular host) in order to guess the
2446   effective request URI's authority component.
2447</t>
2448</section>
2449
2450<section title="Message Forwarding" anchor="message.forwarding">
2451<t>
2452   As described in <xref target="intermediaries"/>, intermediaries can serve
2453   a variety of roles in the processing of HTTP requests and responses.
2454   Some intermediaries are used to improve performance or availability.
2455   Others are used for access control or to filter content.
2456   Since an HTTP stream has characteristics similar to a pipe-and-filter
2457   architecture, there are no inherent limits to the extent an intermediary
2458   can enhance (or interfere) with either direction of the stream.
2459</t>
2460<t>
2461   Intermediaries that forward a message &MUST; implement the
2462   <x:ref>Connection</x:ref> header field, as specified in
2463   <xref target="header.connection"/>, to exclude fields that are only
2464   intended for the incoming connection.
2465</t>
2466<t>
2467   In order to avoid request loops, a proxy that forwards requests to other
2468   proxies &MUST; be able to recognize and exclude all of its own server
2469   names, including any aliases, local variations, or literal IP addresses.
2470</t>
2471</section>
2472
2473<section title="Via" anchor="header.via">
2474  <iref primary="true" item="Via header field" x:for-anchor=""/>
2475  <x:anchor-alias value="pseudonym"/>
2476  <x:anchor-alias value="received-by"/>
2477  <x:anchor-alias value="received-protocol"/>
2478  <x:anchor-alias value="Via"/>
2479<t>
2480   The "Via" header field &MUST; be sent by a proxy or gateway
2481   in forwarded messages to
2482   indicate the intermediate protocols and recipients between the user
2483   agent and the server on requests, and between the origin server and
2484   the client on responses. It is analogous to the "Received" field
2485   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>).
2486   Via is used in HTTP for tracking message forwards,
2487   avoiding request loops, and identifying the protocol capabilities of
2488   all senders along the request/response chain.
2489</t>
2490<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Via"/><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"/>
2491  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2492                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2493  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2494  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2495  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2496</artwork></figure>
2497<t>
2498   The received-protocol indicates the protocol version of the message
2499   received by the server or client along each segment of the
2500   request/response chain. The received-protocol version is appended to
2501   the Via field value when the message is forwarded so that information
2502   about the protocol capabilities of upstream applications remains
2503   visible to all recipients.
2504</t>
2505<t>
2506   The protocol-name is excluded if and only if it would be "HTTP". The
2507   received-by field is normally the host and optional port number of a
2508   recipient server or client that subsequently forwarded the message.
2509   However, if the real host is considered to be sensitive information,
2510   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2511   be assumed to be the default port of the received-protocol.
2512</t>
2513<t>
2514   Multiple Via field values represent each proxy or gateway that has
2515   forwarded the message. Each recipient &MUST; append its information
2516   such that the end result is ordered according to the sequence of
2517   forwarding applications.
2518</t>
2519<t>
2520   Comments &MAY; be used in the Via header field to identify the software
2521   of each recipient, analogous to the <x:ref>User-Agent</x:ref> and
2522   <x:ref>Server</x:ref> header fields. However, all comments in the Via field
2523   are optional and &MAY; be removed by any recipient prior to forwarding the
2524   message.
2525</t>
2526<t>
2527   For example, a request message could be sent from an HTTP/1.0 user
2528   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2529   forward the request to a public proxy at p.example.net, which completes
2530   the request by forwarding it to the origin server at www.example.com.
2531   The request received by www.example.com would then have the following
2532   Via header field:
2533</t>
2534<figure><artwork type="example">
2535  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2536</artwork></figure>
2537<t>
2538   A proxy or gateway used as a portal through a network firewall
2539   &SHOULD-NOT; forward the names and ports of hosts within the firewall
2540   region unless it is explicitly enabled to do so. If not enabled, the
2541   received-by host of any host behind the firewall &SHOULD; be replaced
2542   by an appropriate pseudonym for that host.
2543</t>
2544<t>
2545   A proxy or gateway &MAY; combine an ordered subsequence of Via header
2546   field entries into a single such entry if the entries have identical
2547   received-protocol values. For example,
2548</t>
2549<figure><artwork type="example">
2550  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2551</artwork></figure>
2552<t>
2553  could be collapsed to
2554</t>
2555<figure><artwork type="example">
2556  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2557</artwork></figure>
2558<t>
2559   Senders &SHOULD-NOT; combine multiple entries unless they are all
2560   under the same organizational control and the hosts have already been
2561   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
2562   have different received-protocol values.
2563</t>
2564</section>
2565
2566<section title="Message Transforming" anchor="message.transforming">
2567<t>
2568   If a proxy receives a request-target with a host name that is not a
2569   fully qualified domain name, it &MAY; add its own domain to the host name
2570   it received when forwarding the request.  A proxy &MUST-NOT; change the
2571   host name if it is a fully qualified domain name.
2572</t>
2573<t>
2574   A non-transforming proxy &MUST-NOT; modify the "path-absolute" and "query"
2575   parts of the received request-target when forwarding it to the next inbound
2576   server, except as noted above to replace an empty path with "/" or "*".
2577</t>
2578<t>
2579   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2580   though it &MAY; change the message body through application or removal
2581   of a transfer-coding (<xref target="transfer.codings"/>).
2582</t>
2583<t>
2584   A non-transforming proxy &SHOULD-NOT; modify header fields that provide
2585   information about the end points of the communication chain, the resource
2586   state, or the selected representation.
2587</t>
2588<t>
2589   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2590   request or response, and it &MUST-NOT; add any of these fields if not
2591   already present:
2592  <list style="symbols">
2593    <t><x:ref>Allow</x:ref> (&header-allow;)</t>
2594    <t><x:ref>Content-Location</x:ref> (&header-content-location;)</t>
2595    <t>Content-MD5 (<xref target="RFC2616" x:fmt="of" x:sec="14.15"/>)</t>
2596    <t><x:ref>ETag</x:ref> (&header-etag;)</t>
2597    <t><x:ref>Last-Modified</x:ref> (&header-last-modified;)</t>
2598    <t><x:ref>Server</x:ref> (&header-server;)</t>
2599  </list>
2600</t>
2601<t>
2602   A non-transforming proxy &MUST-NOT; modify an <x:ref>Expires</x:ref>
2603   header field (&header-expires;) if already present in a response, but
2604   it &MAY; add an <x:ref>Expires</x:ref> header field with a field-value
2605   identical to that of the <x:ref>Date</x:ref> header field.
2606</t>
2607<t>
2608   A proxy &MUST-NOT; modify or add any of the following fields in a
2609   message that contains the no-transform cache-control directive:
2610  <list style="symbols">
2611    <t><x:ref>Content-Encoding</x:ref> (&header-content-encoding;)</t>
2612    <t><x:ref>Content-Range</x:ref> (&header-content-range;)</t>
2613    <t><x:ref>Content-Type</x:ref> (&header-content-type;)</t>
2614  </list>
2615</t>
2616<t>
2617   A transforming proxy &MAY; modify or add these fields to a message
2618   that does not include no-transform, but if it does so, it &MUST; add a
2619   Warning 214 (Transformation applied) if one does not already appear
2620   in the message (see &header-warning;).
2621</t>
2622<x:note>
2623  <t>
2624    <x:h>Warning:</x:h> Unnecessary modification of header fields might
2625    cause authentication failures if stronger authentication
2626    mechanisms are introduced in later versions of HTTP. Such
2627    authentication mechanisms &MAY; rely on the values of header fields
2628    not listed here.
2629  </t>
2630</x:note>
2631</section>
2632
2633<section title="Associating a Response to a Request" anchor="associating.response.to.request">
2634<t>
2635   HTTP does not include a request identifier for associating a given
2636   request message with its corresponding one or more response messages.
2637   Hence, it relies on the order of response arrival to correspond exactly
2638   to the order in which requests are made on the same connection.
2639   More than one response message per request only occurs when one or more
2640   informational responses (<x:ref>1xx</x:ref>, see &status-1xx;) precede a final response
2641   to the same request.
2642</t>
2643<t>
2644   A client that uses persistent connections and sends more than one request
2645   per connection &MUST; maintain a list of outstanding requests in the
2646   order sent on that connection and &MUST; associate each received response
2647   message to the highest ordered request that has not yet received a final
2648   (non-<x:ref>1xx</x:ref>) response.
2649</t>
2650</section>
2651</section>
2652
2653<section title="Connection Management" anchor="connection.management">
2654<t>
2655   HTTP messaging is independent of the underlying transport or
2656   session-layer connection protocol(s).  HTTP only presumes a reliable
2657   transport with in-order delivery of requests and the corresponding
2658   in-order delivery of responses.  The mapping of HTTP request and
2659   response structures onto the data units of an underlying transport
2660   protocol is outside the scope of this specification.
2661</t>
2662<t>
2663   As described in <xref target="connecting.inbound"/>, the specific
2664   connection protocols to be used for an HTTP interaction are determined by
2665   client configuration and the <x:ref>target URI</x:ref>.
2666   For example, the "http" URI scheme
2667   (<xref target="http.uri"/>) indicates a default connection of TCP
2668   over IP, with a default TCP port of 80, but the client might be
2669   configured to use a proxy via some other connection, port, or protocol.
2670</t>
2671<t>
2672   HTTP implementations are expected to engage in connection management,
2673   which includes maintaining the state of current connections,
2674   establishing a new connection or reusing an existing connection,
2675   processing messages received on a connection, detecting connection
2676   failures, and closing each connection.
2677   Most clients maintain multiple connections in parallel, including
2678   more than one connection per server endpoint.
2679   Most servers are designed to maintain thousands of concurrent connections,
2680   while controlling request queues to enable fair use and detect
2681   denial of service attacks.
2682</t>
2683
2684<section title="Connection" anchor="header.connection">
2685  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2686  <iref primary="true" item="close" x:for-anchor=""/>
2687  <x:anchor-alias value="Connection"/>
2688  <x:anchor-alias value="connection-option"/>
2689  <x:anchor-alias value="close"/>
2690<t>
2691   The "Connection" header field allows the sender to indicate desired
2692   control options for the current connection.  In order to avoid confusing
2693   downstream recipients, a proxy or gateway &MUST; remove or replace any
2694   received connection options before forwarding the message.
2695</t>
2696<t>
2697   When a header field is used to supply control information for or about
2698   the current connection, the sender &SHOULD; list the corresponding
2699   field-name within the "Connection" header field.
2700   A proxy or gateway &MUST; parse a received Connection
2701   header field before a message is forwarded and, for each
2702   connection-option in this field, remove any header field(s) from
2703   the message with the same name as the connection-option, and then
2704   remove the Connection header field itself (or replace it with the
2705   intermediary's own connection options for the forwarded message).
2706</t>
2707<t>
2708   Hence, the Connection header field provides a declarative way of
2709   distinguishing header fields that are only intended for the
2710   immediate recipient ("hop-by-hop") from those fields that are
2711   intended for all recipients on the chain ("end-to-end"), enabling the
2712   message to be self-descriptive and allowing future connection-specific
2713   extensions to be deployed without fear that they will be blindly
2714   forwarded by older intermediaries.
2715</t>
2716<t>
2717   The Connection header field's value has the following grammar:
2718</t>
2719<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-option"/>
2720  <x:ref>Connection</x:ref>        = 1#<x:ref>connection-option</x:ref>
2721  <x:ref>connection-option</x:ref> = <x:ref>token</x:ref>
2722</artwork></figure>
2723<t>
2724   Connection options are case-insensitive.
2725</t>
2726<t>
2727   A sender &MUST-NOT; include field-names in the Connection header
2728   field-value for fields that are defined as expressing constraints
2729   for all recipients in the request or response chain, such as the
2730   Cache-Control header field (&header-cache-control;).
2731</t>
2732<t>
2733   The connection options do not have to correspond to a header field
2734   present in the message, since a connection-specific header field
2735   might not be needed if there are no parameters associated with that
2736   connection option.  Recipients that trigger certain connection
2737   behavior based on the presence of connection options &MUST; do so
2738   based on the presence of the connection-option rather than only the
2739   presence of the optional header field.  In other words, if the
2740   connection option is received as a header field but not indicated
2741   within the Connection field-value, then the recipient &MUST; ignore
2742   the connection-specific header field because it has likely been
2743   forwarded by an intermediary that is only partially conformant.
2744</t>
2745<t>
2746   When defining new connection options, specifications ought to
2747   carefully consider existing deployed header fields and ensure
2748   that the new connection option does not share the same name as
2749   an unrelated header field that might already be deployed.
2750   Defining a new connection option essentially reserves that potential
2751   field-name for carrying additional information related to the
2752   connection option, since it would be unwise for senders to use
2753   that field-name for anything else.
2754</t>
2755<t>
2756   The "<x:dfn>close</x:dfn>" connection option is defined for a
2757   sender to signal that this connection will be closed after completion of
2758   the response. For example,
2759</t>
2760<figure><artwork type="example">
2761  Connection: close
2762</artwork></figure>
2763<t>
2764   in either the request or the response header fields indicates that
2765   the connection &SHOULD; be closed after the current request/response
2766   is complete (<xref target="persistent.tear-down"/>).
2767</t>
2768<t>
2769   A client that does not support persistent connections &MUST;
2770   send the "close" connection option in every request message.
2771</t>
2772<t>
2773   A server that does not support persistent connections &MUST;
2774   send the "close" connection option in every response message that
2775   does not have a <x:ref>1xx (Informational)</x:ref> status code.
2776</t>
2777</section>
2778
2779<section title="Persistent Connections" anchor="persistent.connections">
2780  <x:anchor-alias value="persistent connections"/>
2781<t>
2782   HTTP was originally designed to use a separate connection for each
2783   request/response pair. As the Web evolved and embedded requests became
2784   common for inline images, the connection establishment overhead was
2785   a significant drain on performance and a concern for Internet congestion.
2786   Message framing (via <x:ref>Content-Length</x:ref>) and optional
2787   long-lived connections (via Keep-Alive) were added to HTTP/1.0 in order
2788   to improve performance for some requests. However, these extensions were
2789   insufficient for dynamically generated responses and difficult to use
2790   with intermediaries.
2791</t>
2792<t>
2793   HTTP/1.1 defaults to the use of "<x:ref>persistent connections</x:ref>",
2794   which allow multiple requests and responses to be carried over a single
2795   connection. The "<x:ref>close</x:ref>" connection-option is used to
2796   signal that a connection will close after the current request/response.
2797   Persistent connections have a number of advantages:
2798  <list style="symbols">
2799      <t>
2800        By opening and closing fewer connections, CPU time is saved
2801        in routers and hosts (clients, servers, proxies, gateways,
2802        tunnels, or caches), and memory used for protocol control
2803        blocks can be saved in hosts.
2804      </t>
2805      <t>
2806        Most requests and responses can be pipelined on a connection.
2807        Pipelining allows a client to make multiple requests without
2808        waiting for each response, allowing a single connection to
2809        be used much more efficiently and with less overall latency.
2810      </t>
2811      <t>
2812        For TCP connections, network congestion is reduced by eliminating the
2813        packets associated with the three way handshake and graceful close
2814        procedures, and by allowing sufficient time to determine the
2815        congestion state of the network.
2816      </t>
2817      <t>
2818        Latency on subsequent requests is reduced since there is no time
2819        spent in the connection opening handshake.
2820      </t>
2821      <t>
2822        HTTP can evolve more gracefully, since most errors can be reported
2823        without the penalty of closing the connection. Clients using
2824        future versions of HTTP might optimistically try a new feature,
2825        but if communicating with an older server, retry with old
2826        semantics after an error is reported.
2827      </t>
2828    </list>
2829</t>
2830<t>
2831   HTTP implementations &SHOULD; implement persistent connections.
2832</t>
2833   
2834<section title="Establishment" anchor="persistent.establishment">
2835<t>
2836   It is beyond the scope of this specification to describe how connections
2837   are established via various transport or session-layer protocols.
2838   Each connection applies to only one transport link.
2839</t>
2840<t>
2841   A recipient determines whether a connection is persistent or not based on
2842   the most recently received message's protocol version and
2843   <x:ref>Connection</x:ref> header field (if any):
2844   <list style="symbols">
2845     <t>If the <x:ref>close</x:ref> connection option is present, the
2846        connection will not persist after the current response; else,</t>
2847     <t>If the received protocol is HTTP/1.1 (or later), the connection will
2848        persist after the current response; else,</t>
2849     <t>If the received protocol is HTTP/1.0, the "keep-alive"
2850        connection option is present, the recipient is not a proxy, and
2851        the recipient wishes to honor the HTTP/1.0 "keep-alive" mechanism,
2852        the connection will persist after the current response; otherwise,</t>
2853     <t>The connection will close after the current response.</t>
2854   </list>
2855</t>
2856<t>
2857   A proxy server &MUST-NOT; maintain a persistent connection with an
2858   HTTP/1.0 client (see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/> for
2859   information and discussion of the problems with the Keep-Alive header field
2860   implemented by many HTTP/1.0 clients).
2861</t>
2862</section>
2863
2864<section title="Reuse" anchor="persistent.reuse">
2865<t>
2866   In order to remain persistent, all messages on a connection &MUST;
2867   have a self-defined message length (i.e., one not defined by closure
2868   of the connection), as described in <xref target="message.body"/>.
2869</t>
2870<t>
2871   A server &MAY; assume that an HTTP/1.1 client intends to maintain a
2872   persistent connection until a <x:ref>close</x:ref> connection option
2873   is received in a request.
2874</t>
2875<t>
2876   A client &MAY; reuse a persistent connection until it sends or receives
2877   a <x:ref>close</x:ref> connection option or receives an HTTP/1.0 response
2878   without a "keep-alive" connection option.
2879</t>
2880<t>
2881   Clients and servers &SHOULD-NOT; assume that a persistent connection is
2882   maintained for HTTP versions less than 1.1 unless it is explicitly
2883   signaled.
2884   See <xref target="compatibility.with.http.1.0.persistent.connections"/>
2885   for more information on backward compatibility with HTTP/1.0 clients.
2886</t>
2887
2888<section title="Pipelining" anchor="pipelining">
2889<t>
2890   A client that supports persistent connections &MAY; "pipeline" its
2891   requests (i.e., send multiple requests without waiting for each
2892   response). A server &MUST; send its responses to those requests in the
2893   same order that the requests were received.
2894</t>
2895<t>
2896   Clients which assume persistent connections and pipeline immediately
2897   after connection establishment &SHOULD; be prepared to retry their
2898   connection if the first pipelined attempt fails. If a client does
2899   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2900   persistent. Clients &MUST; also be prepared to resend their requests if
2901   the server closes the connection before sending all of the
2902   corresponding responses.
2903</t>
2904<t>
2905   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods
2906   or non-idempotent sequences of request methods (see &idempotent-methods;).
2907   Otherwise, a premature termination of the transport connection could lead
2908   to indeterminate results. A client wishing to send a non-idempotent
2909   request &SHOULD; wait to send that request until it has received the
2910   response status line for the previous request.
2911</t>
2912</section>
2913
2914<section title="Retrying Requests" anchor="persistent.retrying.requests">
2915<t>
2916   Senders can close the transport connection at any time. Therefore,
2917   clients, servers, and proxies &MUST; be able to recover
2918   from asynchronous close events. Client software &MAY; reopen the
2919   transport connection and retransmit the aborted sequence of requests
2920   without user interaction so long as the request sequence is
2921   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2922   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2923   human operator the choice of retrying the request(s). Confirmation by
2924   user-agent software with semantic understanding of the application
2925   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2926   be repeated if the second sequence of requests fails.
2927</t>
2928</section>
2929</section>
2930   
2931<section title="Concurrency" anchor="persistent.concurrency">
2932<t>
2933   Clients &SHOULD; limit the number of simultaneous
2934   connections that they maintain to a given server.
2935</t>
2936<t>
2937   Previous revisions of HTTP gave a specific number of connections as a
2938   ceiling, but this was found to be impractical for many applications. As a
2939   result, this specification does not mandate a particular maximum number of
2940   connections, but instead encourages clients to be conservative when opening
2941   multiple connections.
2942</t>
2943<t>
2944   Multiple connections are typically used to avoid the "head-of-line
2945   blocking" problem, wherein a request that takes significant server-side
2946   processing and/or has a large payload blocks subsequent requests on the
2947   same connection. However, each connection consumes server resources.
2948   Furthermore, using multiple connections can cause undesirable side effects
2949   in congested networks.
2950</t>
2951<t>
2952   Note that servers might reject traffic that they deem abusive, including an
2953   excessive number of connections from a client.
2954</t>
2955</section>
2956
2957<section title="Failures and Time-outs" anchor="persistent.failures">
2958<t>
2959   Servers will usually have some time-out value beyond which they will
2960   no longer maintain an inactive connection. Proxy servers might make
2961   this a higher value since it is likely that the client will be making
2962   more connections through the same server. The use of persistent
2963   connections places no requirements on the length (or existence) of
2964   this time-out for either the client or the server.
2965</t>
2966<t>
2967   When a client or server wishes to time-out it &SHOULD; issue a graceful
2968   close on the transport connection. Clients and servers &SHOULD; both
2969   constantly watch for the other side of the transport close, and
2970   respond to it as appropriate. If a client or server does not detect
2971   the other side's close promptly it could cause unnecessary resource
2972   drain on the network.
2973</t>
2974<t>
2975   A client, server, or proxy &MAY; close the transport connection at any
2976   time. For example, a client might have started to send a new request
2977   at the same time that the server has decided to close the "idle"
2978   connection. From the server's point of view, the connection is being
2979   closed while it was idle, but from the client's point of view, a
2980   request is in progress.
2981</t>
2982<t>
2983   Servers &SHOULD; maintain persistent connections and allow the underlying
2984   transport's flow control mechanisms to resolve temporary overloads, rather
2985   than terminate connections with the expectation that clients will retry.
2986   The latter technique can exacerbate network congestion.
2987</t>
2988<t>
2989   A client sending a message body &SHOULD; monitor
2990   the network connection for an error status code while it is transmitting
2991   the request. If the client sees an error status code, it &SHOULD;
2992   immediately cease transmitting the body and close the connection.
2993</t>
2994</section>
2995   
2996<section title="Tear-down" anchor="persistent.tear-down">
2997  <iref primary="false" item="Connection header field" x:for-anchor=""/>
2998  <iref primary="false" item="close" x:for-anchor=""/>
2999<t>
3000   The <x:ref>Connection</x:ref> header field
3001   (<xref target="header.connection"/>) provides a "<x:ref>close</x:ref>"
3002   connection option that a sender &SHOULD; send when it wishes to close
3003   the connection after the current request/response pair.
3004</t>
3005<t>
3006   A client that sends a <x:ref>close</x:ref> connection option &MUST-NOT;
3007   send further requests on that connection (after the one containing
3008   <x:ref>close</x:ref>) and &MUST; close the connection after reading the
3009   final response message corresponding to this request.
3010</t>
3011<t>
3012   A server that receives a <x:ref>close</x:ref> connection option &MUST;
3013   initiate a lingering close of the connection after it sends the final
3014   response to the request that contained <x:ref>close</x:ref>.
3015   The server &SHOULD; include a <x:ref>close</x:ref> connection option
3016   in its final response on that connection. The server &MUST-NOT; process
3017   any further requests received on that connection.
3018</t>
3019<t>
3020   A server that sends a <x:ref>close</x:ref> connection option &MUST;
3021   initiate a lingering close of the connection after it sends the
3022   response containing <x:ref>close</x:ref>. The server &MUST-NOT; process
3023   any further requests received on that connection.
3024</t>
3025<t>
3026   A client that receives a <x:ref>close</x:ref> connection option &MUST;
3027   cease sending requests on that connection and close the connection
3028   after reading the response message containing the close; if additional
3029   pipelined requests had been sent on the connection, the client &SHOULD;
3030   assume that they will not be processed by the server.
3031</t>
3032<t>
3033   If a server performs an immediate close of a TCP connection, there is a
3034   significant risk that the client will not be able to read the last HTTP
3035   response.  If the server receives additional data from the client on a
3036   fully-closed connection, such as another request that was sent by the
3037   client before receiving the server's response, the server's TCP stack will
3038   send a reset packet to the client; unfortunately, the reset packet might
3039   erase the client's unacknowledged input buffers before they can be read
3040   and interpreted by the client's HTTP parser.
3041</t>
3042<t>
3043   To avoid the TCP reset problem, a server can perform a lingering close on a
3044   connection by closing only the write side of the read/write connection
3045   (a half-close) and continuing to read from the connection until the
3046   connection is closed by the client or the server is reasonably certain
3047   that its own TCP stack has received the client's acknowledgement of the
3048   packet(s) containing the server's last response. It is then safe for the
3049   server to fully close the connection.
3050</t>
3051<t>
3052   It is unknown whether the reset problem is exclusive to TCP or might also
3053   be found in other transport connection protocols.
3054</t>
3055</section>
3056</section>
3057
3058<section title="Upgrade" anchor="header.upgrade">
3059  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3060  <x:anchor-alias value="Upgrade"/>
3061  <x:anchor-alias value="protocol"/>
3062  <x:anchor-alias value="protocol-name"/>
3063  <x:anchor-alias value="protocol-version"/>
3064<t>
3065   The "Upgrade" header field is intended to provide a simple mechanism
3066   for transitioning from HTTP/1.1 to some other protocol on the same
3067   connection.  A client &MAY; send a list of protocols in the Upgrade
3068   header field of a request to invite the server to switch to one or
3069   more of those protocols before sending the final response.
3070   A server &MUST; send an Upgrade header field in <x:ref>101 (Switching
3071   Protocols)</x:ref> responses to indicate which protocol(s) are being
3072   switched to, and &MUST; send it in <x:ref>426 (Upgrade Required)</x:ref>
3073   responses to indicate acceptable protocols.
3074   A server &MAY; send an Upgrade header field in any other response to
3075   indicate that they might be willing to upgrade to one of the
3076   specified protocols for a future request.
3077</t>
3078<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3079  <x:ref>Upgrade</x:ref>          = 1#<x:ref>protocol</x:ref>
3080
3081  <x:ref>protocol</x:ref>         = <x:ref>protocol-name</x:ref> ["/" <x:ref>protocol-version</x:ref>]
3082  <x:ref>protocol-name</x:ref>    = <x:ref>token</x:ref>
3083  <x:ref>protocol-version</x:ref> = <x:ref>token</x:ref>
3084</artwork></figure>
3085<t>
3086   For example,
3087</t>
3088<figure><artwork type="example">
3089  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3090</artwork></figure>
3091<t>
3092   Upgrade eases the difficult transition between incompatible protocols by
3093   allowing the client to initiate a request in the more commonly
3094   supported protocol while indicating to the server that it would like
3095   to use a "better" protocol if available (where "better" is determined
3096   by the server, possibly according to the nature of the request method
3097   or target resource).
3098</t>
3099<t>
3100   Upgrade cannot be used to insist on a protocol change; its acceptance and
3101   use by the server is optional. The capabilities and nature of the
3102   application-level communication after the protocol change is entirely
3103   dependent upon the new protocol chosen, although the first action
3104   after changing the protocol &MUST; be a response to the initial HTTP
3105   request that contained the Upgrade header field.
3106</t>
3107<t>
3108   For example, if the Upgrade header field is received in a GET request
3109   and the server decides to switch protocols, then it &MUST; first respond
3110   with a <x:ref>101 (Switching Protocols)</x:ref> message in HTTP/1.1 and
3111   then immediately follow that with the new protocol's equivalent of a
3112   response to a GET on the target resource.  This allows a connection to be
3113   upgraded to protocols with the same semantics as HTTP without the
3114   latency cost of an additional round-trip.  A server &MUST-NOT; switch
3115   protocols unless the received message semantics can be honored by the new
3116   protocol; an OPTIONS request can be honored by any protocol.
3117</t>
3118<t>
3119   When Upgrade is sent, a sender &MUST; also send a
3120   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>)
3121   that contains the "upgrade" connection option, in order to prevent Upgrade
3122   from being accidentally forwarded by intermediaries that might not implement
3123   the listed protocols.  A server &MUST; ignore an Upgrade header field that
3124   is received in an HTTP/1.0 request.
3125</t>
3126<t>
3127   The Upgrade header field only applies to switching application-level
3128   protocols on the existing connection; it cannot be used
3129   to switch to a protocol on a different connection. For that purpose, it is
3130   more appropriate to use a <x:ref>3xx (Redirection)</x:ref> response
3131   (&status-3xx;).
3132</t>
3133<t>
3134   This specification only defines the protocol name "HTTP" for use by
3135   the family of Hypertext Transfer Protocols, as defined by the HTTP
3136   version rules of <xref target="http.version"/> and future updates to this
3137   specification. Additional tokens can be registered with IANA using the
3138   registration procedure defined in <xref target="upgrade.token.registry"/>.
3139</t>
3140</section>
3141</section>
3142
3143<section title="IANA Considerations" anchor="IANA.considerations">
3144
3145<section title="Header Field Registration" anchor="header.field.registration">
3146<t>
3147   HTTP header fields are registered within the Message Header Field Registry
3148   <xref target="RFC3864"/> maintained by IANA at
3149   <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/>.
3150</t>
3151<t>
3152   This document defines the following HTTP header fields, so their
3153   associated registry entries shall be updated according to the permanent
3154   registrations below:
3155</t>
3156<?BEGININC p1-messaging.iana-headers ?>
3157<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3158<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3159   <ttcol>Header Field Name</ttcol>
3160   <ttcol>Protocol</ttcol>
3161   <ttcol>Status</ttcol>
3162   <ttcol>Reference</ttcol>
3163
3164   <c>Connection</c>
3165   <c>http</c>
3166   <c>standard</c>
3167   <c>
3168      <xref target="header.connection"/>
3169   </c>
3170   <c>Content-Length</c>
3171   <c>http</c>
3172   <c>standard</c>
3173   <c>
3174      <xref target="header.content-length"/>
3175   </c>
3176   <c>Host</c>
3177   <c>http</c>
3178   <c>standard</c>
3179   <c>
3180      <xref target="header.host"/>
3181   </c>
3182   <c>TE</c>
3183   <c>http</c>
3184   <c>standard</c>
3185   <c>
3186      <xref target="header.te"/>
3187   </c>
3188   <c>Trailer</c>
3189   <c>http</c>
3190   <c>standard</c>
3191   <c>
3192      <xref target="header.trailer"/>
3193   </c>
3194   <c>Transfer-Encoding</c>
3195   <c>http</c>
3196   <c>standard</c>
3197   <c>
3198      <xref target="header.transfer-encoding"/>
3199   </c>
3200   <c>Upgrade</c>
3201   <c>http</c>
3202   <c>standard</c>
3203   <c>
3204      <xref target="header.upgrade"/>
3205   </c>
3206   <c>Via</c>
3207   <c>http</c>
3208   <c>standard</c>
3209   <c>
3210      <xref target="header.via"/>
3211   </c>
3212</texttable>
3213<!--(END)-->
3214<?ENDINC p1-messaging.iana-headers ?>
3215<t>
3216   Furthermore, the header field-name "Close" shall be registered as
3217   "reserved", since using that name as an HTTP header field might
3218   conflict with the "close" connection option of the "<x:ref>Connection</x:ref>"
3219   header field (<xref target="header.connection"/>).
3220</t>
3221<texttable align="left" suppress-title="true">
3222   <ttcol>Header Field Name</ttcol>
3223   <ttcol>Protocol</ttcol>
3224   <ttcol>Status</ttcol>
3225   <ttcol>Reference</ttcol>
3226
3227   <c>Close</c>
3228   <c>http</c>
3229   <c>reserved</c>
3230   <c>
3231      <xref target="header.field.registration"/>
3232   </c>
3233</texttable>
3234<t>
3235   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3236</t>
3237</section>
3238
3239<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3240<t>
3241   IANA maintains the registry of URI Schemes <xref target="RFC4395"/> at
3242   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>.
3243</t>
3244<t>
3245   This document defines the following URI schemes, so their
3246   associated registry entries shall be updated according to the permanent
3247   registrations below:
3248</t>
3249<texttable align="left" suppress-title="true">
3250   <ttcol>URI Scheme</ttcol>
3251   <ttcol>Description</ttcol>
3252   <ttcol>Reference</ttcol>
3253
3254   <c>http</c>
3255   <c>Hypertext Transfer Protocol</c>
3256   <c><xref target="http.uri"/></c>
3257
3258   <c>https</c>
3259   <c>Hypertext Transfer Protocol Secure</c>
3260   <c><xref target="https.uri"/></c>
3261</texttable>
3262</section>
3263
3264<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3265<t>
3266   This document serves as the specification for the Internet media types
3267   "message/http" and "application/http". The following is to be registered with
3268   IANA (see <xref target="RFC4288"/>).
3269</t>
3270<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3271<iref item="Media Type" subitem="message/http" primary="true"/>
3272<iref item="message/http Media Type" primary="true"/>
3273<t>
3274   The message/http type can be used to enclose a single HTTP request or
3275   response message, provided that it obeys the MIME restrictions for all
3276   "message" types regarding line length and encodings.
3277</t>
3278<t>
3279  <list style="hanging" x:indent="12em">
3280    <t hangText="Type name:">
3281      message
3282    </t>
3283    <t hangText="Subtype name:">
3284      http
3285    </t>
3286    <t hangText="Required parameters:">
3287      none
3288    </t>
3289    <t hangText="Optional parameters:">
3290      version, msgtype
3291      <list style="hanging">
3292        <t hangText="version:">
3293          The HTTP-version number of the enclosed message
3294          (e.g., "1.1"). If not present, the version can be
3295          determined from the first line of the body.
3296        </t>
3297        <t hangText="msgtype:">
3298          The message type &mdash; "request" or "response". If not
3299          present, the type can be determined from the first
3300          line of the body.
3301        </t>
3302      </list>
3303    </t>
3304    <t hangText="Encoding considerations:">
3305      only "7bit", "8bit", or "binary" are permitted
3306    </t>
3307    <t hangText="Security considerations:">
3308      none
3309    </t>
3310    <t hangText="Interoperability considerations:">
3311      none
3312    </t>
3313    <t hangText="Published specification:">
3314      This specification (see <xref target="internet.media.type.message.http"/>).
3315    </t>
3316    <t hangText="Applications that use this media type:">
3317    </t>
3318    <t hangText="Additional information:">
3319      <list style="hanging">
3320        <t hangText="Magic number(s):">none</t>
3321        <t hangText="File extension(s):">none</t>
3322        <t hangText="Macintosh file type code(s):">none</t>
3323      </list>
3324    </t>
3325    <t hangText="Person and email address to contact for further information:">
3326      See Authors Section.
3327    </t>
3328    <t hangText="Intended usage:">
3329      COMMON
3330    </t>
3331    <t hangText="Restrictions on usage:">
3332      none
3333    </t>
3334    <t hangText="Author/Change controller:">
3335      IESG
3336    </t>
3337  </list>
3338</t>
3339</section>
3340<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3341<iref item="Media Type" subitem="application/http" primary="true"/>
3342<iref item="application/http Media Type" primary="true"/>
3343<t>
3344   The application/http type can be used to enclose a pipeline of one or more
3345   HTTP request or response messages (not intermixed).
3346</t>
3347<t>
3348  <list style="hanging" x:indent="12em">
3349    <t hangText="Type name:">
3350      application
3351    </t>
3352    <t hangText="Subtype name:">
3353      http
3354    </t>
3355    <t hangText="Required parameters:">
3356      none
3357    </t>
3358    <t hangText="Optional parameters:">
3359      version, msgtype
3360      <list style="hanging">
3361        <t hangText="version:">
3362          The HTTP-version number of the enclosed messages
3363          (e.g., "1.1"). If not present, the version can be
3364          determined from the first line of the body.
3365        </t>
3366        <t hangText="msgtype:">
3367          The message type &mdash; "request" or "response". If not
3368          present, the type can be determined from the first
3369          line of the body.
3370        </t>
3371      </list>
3372    </t>
3373    <t hangText="Encoding considerations:">
3374      HTTP messages enclosed by this type
3375      are in "binary" format; use of an appropriate
3376      Content-Transfer-Encoding is required when
3377      transmitted via E-mail.
3378    </t>
3379    <t hangText="Security considerations:">
3380      none
3381    </t>
3382    <t hangText="Interoperability considerations:">
3383      none
3384    </t>
3385    <t hangText="Published specification:">
3386      This specification (see <xref target="internet.media.type.application.http"/>).
3387    </t>
3388    <t hangText="Applications that use this media type:">
3389    </t>
3390    <t hangText="Additional information:">
3391      <list style="hanging">
3392        <t hangText="Magic number(s):">none</t>
3393        <t hangText="File extension(s):">none</t>
3394        <t hangText="Macintosh file type code(s):">none</t>
3395      </list>
3396    </t>
3397    <t hangText="Person and email address to contact for further information:">
3398      See Authors Section.
3399    </t>
3400    <t hangText="Intended usage:">
3401      COMMON
3402    </t>
3403    <t hangText="Restrictions on usage:">
3404      none
3405    </t>
3406    <t hangText="Author/Change controller:">
3407      IESG
3408    </t>
3409  </list>
3410</t>
3411</section>
3412</section>
3413
3414<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
3415<t>
3416   The HTTP Transfer Coding Registry defines the name space for transfer
3417   coding names.
3418</t>
3419<t>
3420   Registrations &MUST; include the following fields:
3421   <list style="symbols">
3422     <t>Name</t>
3423     <t>Description</t>
3424     <t>Pointer to specification text</t>
3425   </list>
3426</t>
3427<t>
3428   Names of transfer codings &MUST-NOT; overlap with names of content codings
3429   (&content-codings;) unless the encoding transformation is identical, as
3430   is the case for the compression codings defined in
3431   <xref target="compression.codings"/>.
3432</t>
3433<t>
3434   Values to be added to this name space require IETF Review (see
3435   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
3436   conform to the purpose of transfer coding defined in this section.
3437   Use of program names for the identification of encoding formats
3438   is not desirable and is discouraged for future encodings.
3439</t>
3440<t>
3441   The registry itself is maintained at
3442   <eref target="http://www.iana.org/assignments/http-parameters"/>.
3443</t>
3444</section>
3445
3446<section title="Transfer Coding Registrations" anchor="transfer.coding.registration">
3447<t>
3448   The HTTP Transfer Coding Registry shall be updated with the registrations
3449   below:
3450</t>
3451<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3452   <ttcol>Name</ttcol>
3453   <ttcol>Description</ttcol>
3454   <ttcol>Reference</ttcol>
3455   <c>chunked</c>
3456   <c>Transfer in a series of chunks</c>
3457   <c>
3458      <xref target="chunked.encoding"/>
3459   </c>
3460   <c>compress</c>
3461   <c>UNIX "compress" program method</c>
3462   <c>
3463      <xref target="compress.coding"/>
3464   </c>
3465   <c>deflate</c>
3466   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3467   the "zlib" data format (<xref target="RFC1950"/>)
3468   </c>
3469   <c>
3470      <xref target="deflate.coding"/>
3471   </c>
3472   <c>gzip</c>
3473   <c>Same as GNU zip <xref target="RFC1952"/></c>
3474   <c>
3475      <xref target="gzip.coding"/>
3476   </c>
3477</texttable>
3478</section>
3479
3480<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3481<t>
3482   The HTTP Upgrade Token Registry defines the name space for protocol-name
3483   tokens used to identify protocols in the <x:ref>Upgrade</x:ref> header
3484   field. Each registered protocol name is associated with contact information
3485   and an optional set of specifications that details how the connection
3486   will be processed after it has been upgraded.
3487</t>
3488<t>
3489   Registrations happen on a "First Come First Served" basis (see
3490   <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>) and are subject to the
3491   following rules:
3492  <list style="numbers">
3493    <t>A protocol-name token, once registered, stays registered forever.</t>
3494    <t>The registration &MUST; name a responsible party for the
3495       registration.</t>
3496    <t>The registration &MUST; name a point of contact.</t>
3497    <t>The registration &MAY; name a set of specifications associated with
3498       that token. Such specifications need not be publicly available.</t>
3499    <t>The registration &SHOULD; name a set of expected "protocol-version"
3500       tokens associated with that token at the time of registration.</t>
3501    <t>The responsible party &MAY; change the registration at any time.
3502       The IANA will keep a record of all such changes, and make them
3503       available upon request.</t>
3504    <t>The IESG &MAY; reassign responsibility for a protocol token.
3505       This will normally only be used in the case when a
3506       responsible party cannot be contacted.</t>
3507  </list>
3508</t>
3509<t>
3510   This registration procedure for HTTP Upgrade Tokens replaces that
3511   previously defined in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
3512</t>
3513</section>
3514
3515<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3516<t>
3517   The HTTP Upgrade Token Registry shall be updated with the registration
3518   below:
3519</t>
3520<texttable align="left" suppress-title="true">
3521   <ttcol>Value</ttcol>
3522   <ttcol>Description</ttcol>
3523   <ttcol>Expected Version Tokens</ttcol>
3524   <ttcol>Reference</ttcol>
3525
3526   <c>HTTP</c>
3527   <c>Hypertext Transfer Protocol</c>
3528   <c>any DIGIT.DIGIT (e.g, "2.0")</c>
3529   <c><xref target="http.version"/></c>
3530</texttable>
3531<t>
3532   The responsible party is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3533</t>
3534</section>
3535
3536</section>
3537
3538<section title="Security Considerations" anchor="security.considerations">
3539<t>
3540   This section is meant to inform application developers, information
3541   providers, and users of the security limitations in HTTP/1.1 as
3542   described by this document. The discussion does not include
3543   definitive solutions to the problems revealed, though it does make
3544   some suggestions for reducing security risks.
3545</t>
3546
3547<section title="Personal Information" anchor="personal.information">
3548<t>
3549   HTTP clients are often privy to large amounts of personal information,
3550   including both information provided by the user to interact with resources
3551   (e.g., the user's name, location, mail address, passwords, encryption
3552   keys, etc.) and information about the user's browsing activity over
3553   time (e.g., history, bookmarks, etc.). HTTP implementations need to
3554   prevent unintentional leakage of this information.
3555</t>
3556</section>
3557
3558<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3559<t>
3560   A server is in the position to save personal data about a user's
3561   requests which might identify their reading patterns or subjects of
3562   interest.  In particular, log information gathered at an intermediary
3563   often contains a history of user agent interaction, across a multitude
3564   of sites, that can be traced to individual users.
3565</t>
3566<t>
3567   HTTP log information is confidential in nature; its handling is often
3568   constrained by laws and regulations.  Log information needs to be securely
3569   stored and appropriate guidelines followed for its analysis.
3570   Anonymization of personal information within individual entries helps,
3571   but is generally not sufficient to prevent real log traces from being
3572   re-identified based on correlation with other access characteristics.
3573   As such, access traces that are keyed to a specific client should not
3574   be published even if the key is pseudonymous.
3575</t>
3576<t>
3577   To minimize the risk of theft or accidental publication, log information
3578   should be purged of personally identifiable information, including
3579   user identifiers, IP addresses, and user-provided query parameters,
3580   as soon as that information is no longer necessary to support operational
3581   needs for security, auditing, or fraud control.
3582</t>
3583</section>
3584
3585<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3586<t>
3587   Origin servers &SHOULD; be careful to restrict
3588   the documents returned by HTTP requests to be only those that were
3589   intended by the server administrators. If an HTTP server translates
3590   HTTP URIs directly into file system calls, the server &MUST; take
3591   special care not to serve files that were not intended to be
3592   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3593   other operating systems use ".." as a path component to indicate a
3594   directory level above the current one. On such a system, an HTTP
3595   server &MUST; disallow any such construct in the request-target if it
3596   would otherwise allow access to a resource outside those intended to
3597   be accessible via the HTTP server. Similarly, files intended for
3598   reference only internally to the server (such as access control
3599   files, configuration files, and script code) &MUST; be protected from
3600   inappropriate retrieval, since they might contain sensitive
3601   information.
3602</t>
3603</section>
3604
3605<section title="DNS-related Attacks" anchor="dns.related.attacks">
3606<t>
3607   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
3608   generally prone to security attacks based on the deliberate misassociation
3609   of IP addresses and DNS names not protected by DNSSec. Clients need to be
3610   cautious in assuming the validity of an IP number/DNS name association unless
3611   the response is protected by DNSSec (<xref target="RFC4033"/>).
3612</t>
3613</section>
3614
3615<section title="Intermediaries and Caching" anchor="attack.intermediaries">
3616<t>
3617   By their very nature, HTTP intermediaries are men-in-the-middle, and
3618   represent an opportunity for man-in-the-middle attacks. Compromise of
3619   the systems on which the intermediaries run can result in serious security
3620   and privacy problems. Intermediaries have access to security-related
3621   information, personal information about individual users and
3622   organizations, and proprietary information belonging to users and
3623   content providers. A compromised intermediary, or an intermediary
3624   implemented or configured without regard to security and privacy
3625   considerations, might be used in the commission of a wide range of
3626   potential attacks.
3627</t>
3628<t>
3629   Intermediaries that contain a shared cache are especially vulnerable
3630   to cache poisoning attacks.
3631</t>
3632<t>
3633   Implementers need to consider the privacy and security
3634   implications of their design and coding decisions, and of the
3635   configuration options they provide to operators (especially the
3636   default configuration).
3637</t>
3638<t>
3639   Users need to be aware that intermediaries are no more trustworthy than
3640   the people who run them; HTTP itself cannot solve this problem.
3641</t>
3642</section>
3643
3644<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
3645<t>
3646   Because HTTP uses mostly textual, character-delimited fields, attackers can
3647   overflow buffers in implementations, and/or perform a Denial of Service
3648   against implementations that accept fields with unlimited lengths.
3649</t>
3650<t>
3651   To promote interoperability, this specification makes specific
3652   recommendations for minimum size limits on request-line
3653   (<xref target="request.line"/>)
3654   and blocks of header fields (<xref target="header.fields"/>). These are
3655   minimum recommendations, chosen to be supportable even by implementations
3656   with limited resources; it is expected that most implementations will
3657   choose substantially higher limits.
3658</t>
3659<t>
3660   This specification also provides a way for servers to reject messages that
3661   have request-targets that are too long (&status-414;) or request entities
3662   that are too large (&status-4xx;).
3663</t>
3664<t>
3665   Recipients &SHOULD; carefully limit the extent to which they read other
3666   fields, including (but not limited to) request methods, response status
3667   phrases, header field-names, and body chunks, so as to avoid denial of
3668   service attacks without impeding interoperability.
3669</t>
3670</section>
3671</section>
3672
3673<section title="Acknowledgments" anchor="acks">
3674<t>
3675   This edition of HTTP builds on the many contributions that went into
3676   <xref target="RFC1945" format="none">RFC 1945</xref>,
3677   <xref target="RFC2068" format="none">RFC 2068</xref>,
3678   <xref target="RFC2145" format="none">RFC 2145</xref>, and
3679   <xref target="RFC2616" format="none">RFC 2616</xref>, including
3680   substantial contributions made by the previous authors, editors, and
3681   working group chairs: Tim Berners-Lee, Ari Luotonen, Roy T. Fielding,
3682   Henrik Frystyk Nielsen, Jim Gettys, Jeffrey C. Mogul, Larry Masinter,
3683   Paul J. Leach, and Mark Nottingham.
3684   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for additional
3685   acknowledgements from prior revisions.
3686</t>
3687<t>
3688   Since 1999, the following contributors have helped improve the HTTP
3689   specification by reporting bugs, asking smart questions, drafting or
3690   reviewing text, and evaluating open issues:
3691</t>
3692<?BEGININC acks ?>
3693<t>Adam Barth,
3694Adam Roach,
3695Addison Phillips,
3696Adrian Chadd,
3697Adrien W. de Croy,
3698Alan Ford,
3699Alan Ruttenberg,
3700Albert Lunde,
3701Alek Storm,
3702Alex Rousskov,
3703Alexandre Morgaut,
3704Alexey Melnikov,
3705Alisha Smith,
3706Amichai Rothman,
3707Amit Klein,
3708Amos Jeffries,
3709Andreas Maier,
3710Andreas Petersson,
3711Anil Sharma,
3712Anne van Kesteren,
3713Anthony Bryan,
3714Asbjorn Ulsberg,
3715Balachander Krishnamurthy,
3716Barry Leiba,
3717Ben Laurie,
3718Benjamin Niven-Jenkins,
3719Bil Corry,
3720Bill Burke,
3721Bjoern Hoehrmann,
3722Bob Scheifler,
3723Boris Zbarsky,
3724Brett Slatkin,
3725Brian Kell,
3726Brian McBarron,
3727Brian Pane,
3728Brian Smith,
3729Bryce Nesbitt,
3730Cameron Heavon-Jones,
3731Carl Kugler,
3732Carsten Bormann,
3733Charles Fry,
3734Chris Newman,
3735Cyrus Daboo,
3736Dale Robert Anderson,
3737Dan Wing,
3738Dan Winship,
3739Daniel Stenberg,
3740Dave Cridland,
3741Dave Crocker,
3742Dave Kristol,
3743David Booth,
3744David Singer,
3745David W. Morris,
3746Diwakar Shetty,
3747Dmitry Kurochkin,
3748Drummond Reed,
3749Duane Wessels,
3750Edward Lee,
3751Eliot Lear,
3752Eran Hammer-Lahav,
3753Eric D. Williams,
3754Eric J. Bowman,
3755Eric Lawrence,
3756Eric Rescorla,
3757Erik Aronesty,
3758Evan Prodromou,
3759Florian Weimer,
3760Frank Ellermann,
3761Fred Bohle,
3762Gabriel Montenegro,
3763Geoffrey Sneddon,
3764Gervase Markham,
3765Grahame Grieve,
3766Greg Wilkins,
3767Harald Tveit Alvestrand,
3768Harry Halpin,
3769Helge Hess,
3770Henrik Nordstrom,
3771Henry S. Thompson,
3772Henry Story,
3773Herbert van de Sompel,
3774Howard Melman,
3775Hugo Haas,
3776Ian Fette,
3777Ian Hickson,
3778Ido Safruti,
3779Ingo Struck,
3780J. Ross Nicoll,
3781James H. Manger,
3782James Lacey,
3783James M. Snell,
3784Jamie Lokier,
3785Jan Algermissen,
3786Jeff Hodges (who came up with the term 'effective Request-URI'),
3787Jeff Walden,
3788Jim Luther,
3789Joe D. Williams,
3790Joe Gregorio,
3791Joe Orton,
3792John C. Klensin,
3793John C. Mallery,
3794John Cowan,
3795John Kemp,
3796John Panzer,
3797John Schneider,
3798John Stracke,
3799John Sullivan,
3800Jonas Sicking,
3801Jonathan Billington,
3802Jonathan Moore,
3803Jonathan Rees,
3804Jonathan Silvera,
3805Jordi Ros,
3806Joris Dobbelsteen,
3807Josh Cohen,
3808Julien Pierre,
3809Jungshik Shin,
3810Justin Chapweske,
3811Justin Erenkrantz,
3812Justin James,
3813Kalvinder Singh,
3814Karl Dubost,
3815Keith Hoffman,
3816Keith Moore,
3817Koen Holtman,
3818Konstantin Voronkov,
3819Kris Zyp,
3820Lisa Dusseault,
3821Maciej Stachowiak,
3822Marc Schneider,
3823Marc Slemko,
3824Mark Baker,
3825Mark Pauley,
3826Mark Watson,
3827Markus Isomaki,
3828Markus Lanthaler,
3829Martin J. Duerst,
3830Martin Musatov,
3831Martin Nilsson,
3832Martin Thomson,
3833Matt Lynch,
3834Matthew Cox,
3835Max Clark,
3836Michael Burrows,
3837Michael Hausenblas,
3838Mike Amundsen,
3839Mike Belshe,
3840Mike Kelly,
3841Mike Schinkel,
3842Miles Sabin,
3843Murray S. Kucherawy,
3844Mykyta Yevstifeyev,
3845Nathan Rixham,
3846Nicholas Shanks,
3847Nico Williams,
3848Nicolas Alvarez,
3849Nicolas Mailhot,
3850Noah Slater,
3851Pablo Castro,
3852Pat Hayes,
3853Patrick R. McManus,
3854Paul E. Jones,
3855Paul Hoffman,
3856Paul Marquess,
3857Peter Lepeska,
3858Peter Saint-Andre,
3859Peter Watkins,
3860Phil Archer,
3861Philippe Mougin,
3862Phillip Hallam-Baker,
3863Poul-Henning Kamp,
3864Preethi Natarajan,
3865Rajeev Bector,
3866Ray Polk,
3867Reto Bachmann-Gmuer,
3868Richard Cyganiak,
3869Robert Brewer,
3870Robert Collins,
3871Robert O'Callahan,
3872Robert Olofsson,
3873Robert Sayre,
3874Robert Siemer,
3875Robert de Wilde,
3876Roberto Javier Godoy,
3877Roberto Peon,
3878Ronny Widjaja,
3879S. Mike Dierken,
3880Salvatore Loreto,
3881Sam Johnston,
3882Sam Ruby,
3883Scott Lawrence (who maintained the original issues list),
3884Sean B. Palmer,
3885Shane McCarron,
3886Stefan Eissing,
3887Stefan Tilkov,
3888Stefanos Harhalakis,
3889Stephane Bortzmeyer,
3890Stephen Farrell,
3891Stephen Ludin,
3892Stuart Williams,
3893Subbu Allamaraju,
3894Sylvain Hellegouarch,
3895Tapan Divekar,
3896Tatsuya Hayashi,
3897Ted Hardie,
3898Thomas Broyer,
3899Thomas Nordin,
3900Thomas Roessler,
3901Tim Bray,
3902Tim Morgan,
3903Tim Olsen,
3904Tom Zhou,
3905Travis Snoozy,
3906Tyler Close,
3907Vincent Murphy,
3908Wenbo Zhu,
3909Werner Baumann,
3910Wilbur Streett,
3911Wilfredo Sanchez Vega,
3912William A. Rowe Jr.,
3913William Chan,
3914Willy Tarreau,
3915Xiaoshu Wang,
3916Yaron Goland,
3917Yngve Nysaeter Pettersen,
3918Yoav Nir,
3919Yogesh Bang,
3920Yutaka Oiwa,
3921Zed A. Shaw, and
3922Zhong Yu.
3923</t>
3924<?ENDINC acks ?>
3925</section>
3926
3927</middle>
3928<back>
3929
3930<references title="Normative References">
3931
3932<reference anchor="Part2">
3933  <front>
3934    <title>Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content</title>
3935    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3936      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3937      <address><email>fielding@gbiv.com</email></address>
3938    </author>
3939    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3940      <organization abbrev="W3C">World Wide Web Consortium</organization>
3941      <address><email>ylafon@w3.org</email></address>
3942    </author>
3943    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3944      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3945      <address><email>julian.reschke@greenbytes.de</email></address>
3946    </author>
3947    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3948  </front>
3949  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3950  <x:source href="p2-semantics.xml" basename="p2-semantics">
3951    <x:defines>1xx (Informational)</x:defines>
3952    <x:defines>1xx</x:defines>
3953    <x:defines>100 (Continue)</x:defines>
3954    <x:defines>101 (Switching Protocols)</x:defines>
3955    <x:defines>2xx (Successful)</x:defines>
3956    <x:defines>2xx</x:defines>
3957    <x:defines>200 (OK)</x:defines>
3958    <x:defines>204 (No Content)</x:defines>
3959    <x:defines>3xx (Redirection)</x:defines>
3960    <x:defines>3xx</x:defines>
3961    <x:defines>301 (Moved Permanently)</x:defines>
3962    <x:defines>4xx (Client Error)</x:defines>
3963    <x:defines>4xx</x:defines>
3964    <x:defines>400 (Bad Request)</x:defines>
3965    <x:defines>405 (Method Not Allowed)</x:defines>
3966    <x:defines>411 (Length Required)</x:defines>
3967    <x:defines>414 (URI Too Long)</x:defines>
3968    <x:defines>417 (Expectation Failed)</x:defines>
3969    <x:defines>426 (Upgrade Required)</x:defines>
3970    <x:defines>501 (Not Implemented)</x:defines>
3971    <x:defines>502 (Bad Gateway)</x:defines>
3972    <x:defines>505 (HTTP Version Not Supported)</x:defines>
3973    <x:defines>Allow</x:defines>
3974    <x:defines>Content-Encoding</x:defines>
3975    <x:defines>Content-Location</x:defines>
3976    <x:defines>Content-Type</x:defines>
3977    <x:defines>Date</x:defines>
3978    <x:defines>Expect</x:defines>
3979    <x:defines>Location</x:defines>
3980    <x:defines>Server</x:defines>
3981    <x:defines>User-Agent</x:defines>
3982  </x:source>
3983</reference>
3984
3985<reference anchor="Part4">
3986  <front>
3987    <title>Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests</title>
3988    <author fullname="Roy T. Fielding" initials="R." role="editor" surname="Fielding">
3989      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3990      <address><email>fielding@gbiv.com</email></address>
3991    </author>
3992    <author fullname="Yves Lafon" initials="Y." role="editor" surname="Lafon">
3993      <organization abbrev="W3C">World Wide Web Consortium</organization>
3994      <address><email>ylafon@w3.org</email></address>
3995    </author>
3996    <author fullname="Julian F. Reschke" initials="J. F." role="editor" surname="Reschke">
3997      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3998      <address><email>julian.reschke@greenbytes.de</email></address>
3999    </author>
4000    <date month="&ID-MONTH;" year="&ID-YEAR;" />
4001  </front>
4002  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;" />
4003  <x:source basename="p4-conditional" href="p4-conditional.xml">
4004    <x:defines>304 (Not Modified)</x:defines>
4005    <x:defines>ETag</x:defines>
4006    <x:defines>Last-Modified</x:defines>
4007  </x:source>
4008</reference>
4009
4010<reference anchor="Part5">
4011  <front>
4012    <title>Hypertext Transfer Protocol (HTTP/1.1): Range Requests</title>
4013    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4014      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4015      <address><email>fielding@gbiv.com</email></address>
4016    </author>
4017    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4018      <organization abbrev="W3C">World Wide Web Consortium</organization>
4019      <address><email>ylafon@w3.org</email></address>
4020    </author>
4021    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4022      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4023      <address><email>julian.reschke@greenbytes.de</email></address>
4024    </author>
4025    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4026  </front>
4027  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
4028  <x:source href="p5-range.xml" basename="p5-range">
4029    <x:defines>Content-Range</x:defines>
4030  </x:source>
4031</reference>
4032
4033<reference anchor="Part6">
4034  <front>
4035    <title>Hypertext Transfer Protocol (HTTP/1.1): Caching</title>
4036    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4037      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4038      <address><email>fielding@gbiv.com</email></address>
4039    </author>
4040    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4041      <organization abbrev="W3C">World Wide Web Consortium</organization>
4042      <address><email>ylafon@w3.org</email></address>
4043    </author>
4044    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4045      <address><email>mnot@mnot.net</email></address>
4046    </author>
4047    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4048      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4049      <address><email>julian.reschke@greenbytes.de</email></address>
4050    </author>
4051    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4052  </front>
4053  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4054  <x:source href="p6-cache.xml" basename="p6-cache">
4055    <x:defines>Expires</x:defines>
4056  </x:source>
4057</reference>
4058
4059<reference anchor="Part7">
4060  <front>
4061    <title>Hypertext Transfer Protocol (HTTP/1.1): Authentication</title>
4062    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4063      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4064      <address><email>fielding@gbiv.com</email></address>
4065    </author>
4066    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4067      <organization abbrev="W3C">World Wide Web Consortium</organization>
4068      <address><email>ylafon@w3.org</email></address>
4069    </author>
4070    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4071      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4072      <address><email>julian.reschke@greenbytes.de</email></address>
4073    </author>
4074    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4075  </front>
4076  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
4077  <x:source href="p7-auth.xml" basename="p7-auth">
4078    <x:defines>Proxy-Authenticate</x:defines>
4079    <x:defines>Proxy-Authorization</x:defines>
4080  </x:source>
4081</reference>
4082
4083<reference anchor="RFC5234">
4084  <front>
4085    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4086    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4087      <organization>Brandenburg InternetWorking</organization>
4088      <address>
4089        <email>dcrocker@bbiw.net</email>
4090      </address> 
4091    </author>
4092    <author initials="P." surname="Overell" fullname="Paul Overell">
4093      <organization>THUS plc.</organization>
4094      <address>
4095        <email>paul.overell@thus.net</email>
4096      </address>
4097    </author>
4098    <date month="January" year="2008"/>
4099  </front>
4100  <seriesInfo name="STD" value="68"/>
4101  <seriesInfo name="RFC" value="5234"/>
4102</reference>
4103
4104<reference anchor="RFC2119">
4105  <front>
4106    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4107    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4108      <organization>Harvard University</organization>
4109      <address><email>sob@harvard.edu</email></address>
4110    </author>
4111    <date month="March" year="1997"/>
4112  </front>
4113  <seriesInfo name="BCP" value="14"/>
4114  <seriesInfo name="RFC" value="2119"/>
4115</reference>
4116
4117<reference anchor="RFC3986">
4118 <front>
4119  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4120  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4121    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4122    <address>
4123       <email>timbl@w3.org</email>
4124       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4125    </address>
4126  </author>
4127  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4128    <organization abbrev="Day Software">Day Software</organization>
4129    <address>
4130      <email>fielding@gbiv.com</email>
4131      <uri>http://roy.gbiv.com/</uri>
4132    </address>
4133  </author>
4134  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4135    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4136    <address>
4137      <email>LMM@acm.org</email>
4138      <uri>http://larry.masinter.net/</uri>
4139    </address>
4140  </author>
4141  <date month='January' year='2005'></date>
4142 </front>
4143 <seriesInfo name="STD" value="66"/>
4144 <seriesInfo name="RFC" value="3986"/>
4145</reference>
4146
4147<reference anchor="USASCII">
4148  <front>
4149    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4150    <author>
4151      <organization>American National Standards Institute</organization>
4152    </author>
4153    <date year="1986"/>
4154  </front>
4155  <seriesInfo name="ANSI" value="X3.4"/>
4156</reference>
4157
4158<reference anchor="RFC1950">
4159  <front>
4160    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4161    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4162      <organization>Aladdin Enterprises</organization>
4163      <address><email>ghost@aladdin.com</email></address>
4164    </author>
4165    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4166    <date month="May" year="1996"/>
4167  </front>
4168  <seriesInfo name="RFC" value="1950"/>
4169  <!--<annotation>
4170    RFC 1950 is an Informational RFC, thus it might be less stable than
4171    this specification. On the other hand, this downward reference was
4172    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4173    therefore it is unlikely to cause problems in practice. See also
4174    <xref target="BCP97"/>.
4175  </annotation>-->
4176</reference>
4177
4178<reference anchor="RFC1951">
4179  <front>
4180    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4181    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4182      <organization>Aladdin Enterprises</organization>
4183      <address><email>ghost@aladdin.com</email></address>
4184    </author>
4185    <date month="May" year="1996"/>
4186  </front>
4187  <seriesInfo name="RFC" value="1951"/>
4188  <!--<annotation>
4189    RFC 1951 is an Informational RFC, thus it might be less stable than
4190    this specification. On the other hand, this downward reference was
4191    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4192    therefore it is unlikely to cause problems in practice. See also
4193    <xref target="BCP97"/>.
4194  </annotation>-->
4195</reference>
4196
4197<reference anchor="RFC1952">
4198  <front>
4199    <title>GZIP file format specification version 4.3</title>
4200    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4201      <organization>Aladdin Enterprises</organization>
4202      <address><email>ghost@aladdin.com</email></address>
4203    </author>
4204    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4205      <address><email>gzip@prep.ai.mit.edu</email></address>
4206    </author>
4207    <author initials="M." surname="Adler" fullname="Mark Adler">
4208      <address><email>madler@alumni.caltech.edu</email></address>
4209    </author>
4210    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4211      <address><email>ghost@aladdin.com</email></address>
4212    </author>
4213    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4214      <address><email>randeg@alumni.rpi.edu</email></address>
4215    </author>
4216    <date month="May" year="1996"/>
4217  </front>
4218  <seriesInfo name="RFC" value="1952"/>
4219  <!--<annotation>
4220    RFC 1952 is an Informational RFC, thus it might be less stable than
4221    this specification. On the other hand, this downward reference was
4222    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4223    therefore it is unlikely to cause problems in practice. See also
4224    <xref target="BCP97"/>.
4225  </annotation>-->
4226</reference>
4227
4228</references>
4229
4230<references title="Informative References">
4231
4232<reference anchor="ISO-8859-1">
4233  <front>
4234    <title>
4235     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4236    </title>
4237    <author>
4238      <organization>International Organization for Standardization</organization>
4239    </author>
4240    <date year="1998"/>
4241  </front>
4242  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4243</reference>
4244
4245<reference anchor='RFC1919'>
4246  <front>
4247    <title>Classical versus Transparent IP Proxies</title>
4248    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4249      <address><email>mchatel@pax.eunet.ch</email></address>
4250    </author>
4251    <date year='1996' month='March' />
4252  </front>
4253  <seriesInfo name='RFC' value='1919' />
4254</reference>
4255
4256<reference anchor="RFC1945">
4257  <front>
4258    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4259    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4260      <organization>MIT, Laboratory for Computer Science</organization>
4261      <address><email>timbl@w3.org</email></address>
4262    </author>
4263    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4264      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4265      <address><email>fielding@ics.uci.edu</email></address>
4266    </author>
4267    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4268      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4269      <address><email>frystyk@w3.org</email></address>
4270    </author>
4271    <date month="May" year="1996"/>
4272  </front>
4273  <seriesInfo name="RFC" value="1945"/>
4274</reference>
4275
4276<reference anchor="RFC2045">
4277  <front>
4278    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4279    <author initials="N." surname="Freed" fullname="Ned Freed">
4280      <organization>Innosoft International, Inc.</organization>
4281      <address><email>ned@innosoft.com</email></address>
4282    </author>
4283    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4284      <organization>First Virtual Holdings</organization>
4285      <address><email>nsb@nsb.fv.com</email></address>
4286    </author>
4287    <date month="November" year="1996"/>
4288  </front>
4289  <seriesInfo name="RFC" value="2045"/>
4290</reference>
4291
4292<reference anchor="RFC2047">
4293  <front>
4294    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4295    <author initials="K." surname="Moore" fullname="Keith Moore">
4296      <organization>University of Tennessee</organization>
4297      <address><email>moore@cs.utk.edu</email></address>
4298    </author>
4299    <date month="November" year="1996"/>
4300  </front>
4301  <seriesInfo name="RFC" value="2047"/>
4302</reference>
4303
4304<reference anchor="RFC2068">
4305  <front>
4306    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4307    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4308      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4309      <address><email>fielding@ics.uci.edu</email></address>
4310    </author>
4311    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4312      <organization>MIT Laboratory for Computer Science</organization>
4313      <address><email>jg@w3.org</email></address>
4314    </author>
4315    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4316      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4317      <address><email>mogul@wrl.dec.com</email></address>
4318    </author>
4319    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4320      <organization>MIT Laboratory for Computer Science</organization>
4321      <address><email>frystyk@w3.org</email></address>
4322    </author>
4323    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4324      <organization>MIT Laboratory for Computer Science</organization>
4325      <address><email>timbl@w3.org</email></address>
4326    </author>
4327    <date month="January" year="1997"/>
4328  </front>
4329  <seriesInfo name="RFC" value="2068"/>
4330</reference>
4331
4332<reference anchor="RFC2145">
4333  <front>
4334    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4335    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4336      <organization>Western Research Laboratory</organization>
4337      <address><email>mogul@wrl.dec.com</email></address>
4338    </author>
4339    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4340      <organization>Department of Information and Computer Science</organization>
4341      <address><email>fielding@ics.uci.edu</email></address>
4342    </author>
4343    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4344      <organization>MIT Laboratory for Computer Science</organization>
4345      <address><email>jg@w3.org</email></address>
4346    </author>
4347    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4348      <organization>W3 Consortium</organization>
4349      <address><email>frystyk@w3.org</email></address>
4350    </author>
4351    <date month="May" year="1997"/>
4352  </front>
4353  <seriesInfo name="RFC" value="2145"/>
4354</reference>
4355
4356<reference anchor="RFC2616">
4357  <front>
4358    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4359    <author initials="R." surname="Fielding" fullname="R. Fielding">
4360      <organization>University of California, Irvine</organization>
4361      <address><email>fielding@ics.uci.edu</email></address>
4362    </author>
4363    <author initials="J." surname="Gettys" fullname="J. Gettys">
4364      <organization>W3C</organization>
4365      <address><email>jg@w3.org</email></address>
4366    </author>
4367    <author initials="J." surname="Mogul" fullname="J. Mogul">
4368      <organization>Compaq Computer Corporation</organization>
4369      <address><email>mogul@wrl.dec.com</email></address>
4370    </author>
4371    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4372      <organization>MIT Laboratory for Computer Science</organization>
4373      <address><email>frystyk@w3.org</email></address>
4374    </author>
4375    <author initials="L." surname="Masinter" fullname="L. Masinter">
4376      <organization>Xerox Corporation</organization>
4377      <address><email>masinter@parc.xerox.com</email></address>
4378    </author>
4379    <author initials="P." surname="Leach" fullname="P. Leach">
4380      <organization>Microsoft Corporation</organization>
4381      <address><email>paulle@microsoft.com</email></address>
4382    </author>
4383    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4384      <organization>W3C</organization>
4385      <address><email>timbl@w3.org</email></address>
4386    </author>
4387    <date month="June" year="1999"/>
4388  </front>
4389  <seriesInfo name="RFC" value="2616"/>
4390</reference>
4391
4392<reference anchor='RFC2817'>
4393  <front>
4394    <title>Upgrading to TLS Within HTTP/1.1</title>
4395    <author initials='R.' surname='Khare' fullname='R. Khare'>
4396      <organization>4K Associates / UC Irvine</organization>
4397      <address><email>rohit@4K-associates.com</email></address>
4398    </author>
4399    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4400      <organization>Agranat Systems, Inc.</organization>
4401      <address><email>lawrence@agranat.com</email></address>
4402    </author>
4403    <date year='2000' month='May' />
4404  </front>
4405  <seriesInfo name='RFC' value='2817' />
4406</reference>
4407
4408<reference anchor='RFC2818'>
4409  <front>
4410    <title>HTTP Over TLS</title>
4411    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4412      <organization>RTFM, Inc.</organization>
4413      <address><email>ekr@rtfm.com</email></address>
4414    </author>
4415    <date year='2000' month='May' />
4416  </front>
4417  <seriesInfo name='RFC' value='2818' />
4418</reference>
4419
4420<reference anchor='RFC2965'>
4421  <front>
4422    <title>HTTP State Management Mechanism</title>
4423    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4424      <organization>Bell Laboratories, Lucent Technologies</organization>
4425      <address><email>dmk@bell-labs.com</email></address>
4426    </author>
4427    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4428      <organization>Epinions.com, Inc.</organization>
4429      <address><email>lou@montulli.org</email></address>
4430    </author>
4431    <date year='2000' month='October' />
4432  </front>
4433  <seriesInfo name='RFC' value='2965' />
4434</reference>
4435
4436<reference anchor='RFC3040'>
4437  <front>
4438    <title>Internet Web Replication and Caching Taxonomy</title>
4439    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4440      <organization>Equinix, Inc.</organization>
4441    </author>
4442    <author initials='I.' surname='Melve' fullname='I. Melve'>
4443      <organization>UNINETT</organization>
4444    </author>
4445    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4446      <organization>CacheFlow Inc.</organization>
4447    </author>
4448    <date year='2001' month='January' />
4449  </front>
4450  <seriesInfo name='RFC' value='3040' />
4451</reference>
4452
4453<reference anchor='RFC3864'>
4454  <front>
4455    <title>Registration Procedures for Message Header Fields</title>
4456    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4457      <organization>Nine by Nine</organization>
4458      <address><email>GK-IETF@ninebynine.org</email></address>
4459    </author>
4460    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4461      <organization>BEA Systems</organization>
4462      <address><email>mnot@pobox.com</email></address>
4463    </author>
4464    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4465      <organization>HP Labs</organization>
4466      <address><email>JeffMogul@acm.org</email></address>
4467    </author>
4468    <date year='2004' month='September' />
4469  </front>
4470  <seriesInfo name='BCP' value='90' />
4471  <seriesInfo name='RFC' value='3864' />
4472</reference>
4473
4474<reference anchor='RFC4033'>
4475  <front>
4476    <title>DNS Security Introduction and Requirements</title>
4477    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4478    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4479    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4480    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4481    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4482    <date year='2005' month='March' />
4483  </front>
4484  <seriesInfo name='RFC' value='4033' />
4485</reference>
4486
4487<reference anchor="RFC4288">
4488  <front>
4489    <title>Media Type Specifications and Registration Procedures</title>
4490    <author initials="N." surname="Freed" fullname="N. Freed">
4491      <organization>Sun Microsystems</organization>
4492      <address>
4493        <email>ned.freed@mrochek.com</email>
4494      </address>
4495    </author>
4496    <author initials="J." surname="Klensin" fullname="J. Klensin">
4497      <address>
4498        <email>klensin+ietf@jck.com</email>
4499      </address>
4500    </author>
4501    <date year="2005" month="December"/>
4502  </front>
4503  <seriesInfo name="BCP" value="13"/>
4504  <seriesInfo name="RFC" value="4288"/>
4505</reference>
4506
4507<reference anchor='RFC4395'>
4508  <front>
4509    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4510    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4511      <organization>AT&amp;T Laboratories</organization>
4512      <address>
4513        <email>tony+urireg@maillennium.att.com</email>
4514      </address>
4515    </author>
4516    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4517      <organization>Qualcomm, Inc.</organization>
4518      <address>
4519        <email>hardie@qualcomm.com</email>
4520      </address>
4521    </author>
4522    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4523      <organization>Adobe Systems</organization>
4524      <address>
4525        <email>LMM@acm.org</email>
4526      </address>
4527    </author>
4528    <date year='2006' month='February' />
4529  </front>
4530  <seriesInfo name='BCP' value='115' />
4531  <seriesInfo name='RFC' value='4395' />
4532</reference>
4533
4534<reference anchor='RFC4559'>
4535  <front>
4536    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4537    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4538    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4539    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4540    <date year='2006' month='June' />
4541  </front>
4542  <seriesInfo name='RFC' value='4559' />
4543</reference>
4544
4545<reference anchor='RFC5226'>
4546  <front>
4547    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4548    <author initials='T.' surname='Narten' fullname='T. Narten'>
4549      <organization>IBM</organization>
4550      <address><email>narten@us.ibm.com</email></address>
4551    </author>
4552    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4553      <organization>Google</organization>
4554      <address><email>Harald@Alvestrand.no</email></address>
4555    </author>
4556    <date year='2008' month='May' />
4557  </front>
4558  <seriesInfo name='BCP' value='26' />
4559  <seriesInfo name='RFC' value='5226' />
4560</reference>
4561
4562<reference anchor='RFC5246'>
4563   <front>
4564      <title>The Transport Layer Security (TLS) Protocol Version 1.2</title>
4565      <author initials='T.' surname='Dierks' fullname='T. Dierks'>
4566         <organization />
4567      </author>
4568      <author initials='E.' surname='Rescorla' fullname='E. Rescorla'>
4569         <organization>RTFM, Inc.</organization>
4570      </author>
4571      <date year='2008' month='August' />
4572   </front>
4573   <seriesInfo name='RFC' value='5246' />
4574</reference>
4575
4576<reference anchor="RFC5322">
4577  <front>
4578    <title>Internet Message Format</title>
4579    <author initials="P." surname="Resnick" fullname="P. Resnick">
4580      <organization>Qualcomm Incorporated</organization>
4581    </author>
4582    <date year="2008" month="October"/>
4583  </front> 
4584  <seriesInfo name="RFC" value="5322"/>
4585</reference>
4586
4587<reference anchor="RFC6265">
4588  <front>
4589    <title>HTTP State Management Mechanism</title>
4590    <author initials="A." surname="Barth" fullname="Adam Barth">
4591      <organization abbrev="U.C. Berkeley">
4592        University of California, Berkeley
4593      </organization>
4594      <address><email>abarth@eecs.berkeley.edu</email></address>
4595    </author>
4596    <date year="2011" month="April" />
4597  </front>
4598  <seriesInfo name="RFC" value="6265"/>
4599</reference>
4600
4601<!--<reference anchor='BCP97'>
4602  <front>
4603    <title>Handling Normative References to Standards-Track Documents</title>
4604    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4605      <address>
4606        <email>klensin+ietf@jck.com</email>
4607      </address>
4608    </author>
4609    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4610      <organization>MIT</organization>
4611      <address>
4612        <email>hartmans-ietf@mit.edu</email>
4613      </address>
4614    </author>
4615    <date year='2007' month='June' />
4616  </front>
4617  <seriesInfo name='BCP' value='97' />
4618  <seriesInfo name='RFC' value='4897' />
4619</reference>-->
4620
4621<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4622  <front>
4623    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4624    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4625    <date year="2001" month="November"/>
4626  </front>
4627  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4628</reference>
4629
4630</references>
4631
4632
4633<section title="HTTP Version History" anchor="compatibility">
4634<t>
4635   HTTP has been in use by the World-Wide Web global information initiative
4636   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4637   was a simple protocol for hypertext data transfer across the Internet
4638   with only a single request method (GET) and no metadata.
4639   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4640   methods and MIME-like messaging that could include metadata about the data
4641   transferred and modifiers on the request/response semantics. However,
4642   HTTP/1.0 did not sufficiently take into consideration the effects of
4643   hierarchical proxies, caching, the need for persistent connections, or
4644   name-based virtual hosts. The proliferation of incompletely-implemented
4645   applications calling themselves "HTTP/1.0" further necessitated a
4646   protocol version change in order for two communicating applications
4647   to determine each other's true capabilities.
4648</t>
4649<t>
4650   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4651   requirements that enable reliable implementations, adding only
4652   those new features that will either be safely ignored by an HTTP/1.0
4653   recipient or only sent when communicating with a party advertising
4654   conformance with HTTP/1.1.
4655</t>
4656<t>
4657   It is beyond the scope of a protocol specification to mandate
4658   conformance with previous versions. HTTP/1.1 was deliberately
4659   designed, however, to make supporting previous versions easy.
4660   We would expect a general-purpose HTTP/1.1 server to understand
4661   any valid request in the format of HTTP/1.0 and respond appropriately
4662   with an HTTP/1.1 message that only uses features understood (or
4663   safely ignored) by HTTP/1.0 clients.  Likewise, we would expect
4664   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4665</t>
4666<t>
4667   Since HTTP/0.9 did not support header fields in a request,
4668   there is no mechanism for it to support name-based virtual
4669   hosts (selection of resource by inspection of the <x:ref>Host</x:ref> header
4670   field).  Any server that implements name-based virtual hosts
4671   ought to disable support for HTTP/0.9.  Most requests that
4672   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4673   requests wherein a buggy client failed to properly encode
4674   linear whitespace found in a URI reference and placed in
4675   the request-target.
4676</t>
4677
4678<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4679<t>
4680   This section summarizes major differences between versions HTTP/1.0
4681   and HTTP/1.1.
4682</t>
4683
4684<section title="Multi-homed Web Servers" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
4685<t>
4686   The requirements that clients and servers support the <x:ref>Host</x:ref>
4687   header field (<xref target="header.host"/>), report an error if it is
4688   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4689   are among the most important changes defined by HTTP/1.1.
4690</t>
4691<t>
4692   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4693   addresses and servers; there was no other established mechanism for
4694   distinguishing the intended server of a request than the IP address
4695   to which that request was directed. The <x:ref>Host</x:ref> header field was
4696   introduced during the development of HTTP/1.1 and, though it was
4697   quickly implemented by most HTTP/1.0 browsers, additional requirements
4698   were placed on all HTTP/1.1 requests in order to ensure complete
4699   adoption.  At the time of this writing, most HTTP-based services
4700   are dependent upon the Host header field for targeting requests.
4701</t>
4702</section>
4703
4704<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4705<t>
4706   In HTTP/1.0, each connection is established by the client prior to the
4707   request and closed by the server after sending the response. However, some
4708   implementations implement the explicitly negotiated ("Keep-Alive") version
4709   of persistent connections described in <xref x:sec="19.7.1" x:fmt="of"
4710   target="RFC2068"/>.
4711</t>
4712<t>
4713   Some clients and servers might wish to be compatible with these previous
4714   approaches to persistent connections, by explicitly negotiating for them
4715   with a "Connection: keep-alive" request header field. However, some
4716   experimental implementations of HTTP/1.0 persistent connections are faulty;
4717   for example, if a HTTP/1.0 proxy server doesn't understand
4718   <x:ref>Connection</x:ref>, it will erroneously forward that header field
4719   to the next inbound server, which would result in a hung connection.
4720</t>
4721<t>
4722   One attempted solution was the introduction of a Proxy-Connection header
4723   field, targeted specifically at proxies. In practice, this was also
4724   unworkable, because proxies are often deployed in multiple layers, bringing
4725   about the same problem discussed above.
4726</t>
4727<t>
4728   As a result, clients are encouraged not to send the Proxy-Connection header
4729   field in any requests.
4730</t>
4731<t>
4732   Clients are also encouraged to consider the use of Connection: keep-alive
4733   in requests carefully; while they can enable persistent connections with
4734   HTTP/1.0 servers, clients using them need will need to monitor the
4735   connection for "hung" requests (which indicate that the client ought stop
4736   sending the header field), and this mechanism ought not be used by clients
4737   at all when a proxy is being used.
4738</t>
4739</section>
4740
4741<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
4742<t>
4743   HTTP/1.1 introduces the <x:ref>Transfer-Encoding</x:ref> header field
4744   (<xref target="header.transfer-encoding"/>). Proxies/gateways &MUST; remove
4745   any transfer-coding prior to forwarding a message via a MIME-compliant
4746   protocol.
4747</t>
4748</section>
4749
4750</section>
4751
4752<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4753<t>
4754  Clarify that the string "HTTP" in the HTTP-version ABNF production is case
4755  sensitive. Restrict the version numbers to be single digits due to the fact
4756  that implementations are known to handle multi-digit version numbers
4757  incorrectly.
4758  (<xref target="http.version"/>)
4759</t>
4760<t>
4761  Require that invalid whitespace around field-names be rejected.
4762  Change ABNF productions for header fields to only define the field value.
4763  (<xref target="header.fields"/>)
4764</t>
4765<t>
4766  Rules about implicit linear whitespace between certain grammar productions
4767  have been removed; now whitespace is only allowed where specifically
4768  defined in the ABNF.
4769  (<xref target="whitespace"/>)
4770</t>
4771<t> 
4772  The NUL octet is no longer allowed in comment and quoted-string
4773  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4774  Non-ASCII content in header fields and reason phrase has been obsoleted and
4775  made opaque (the TEXT rule was removed).
4776  (<xref target="field.components"/>)
4777</t>
4778<t>
4779  Require recipients to handle bogus "<x:ref>Content-Length</x:ref>" header
4780  fields as errors.
4781  (<xref target="message.body"/>)
4782</t>
4783<t>
4784  Remove reference to non-existent identity transfer-coding value tokens.
4785  (Sections <xref format="counter" target="message.body"/> and
4786  <xref format="counter" target="transfer.codings"/>)
4787</t>
4788<t>
4789  Clarification that the chunk length does not include the count of the octets
4790  in the chunk header and trailer. Furthermore disallowed line folding
4791  in chunk extensions, and deprecate their use.
4792  (<xref target="chunked.encoding"/>)
4793</t>
4794<t>
4795  Update use of abs_path production from RFC 1808 to the path-absolute + query
4796  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4797  request method only.
4798  (<xref target="request-target"/>)
4799</t>
4800<t>
4801  Clarify exactly when "close" connection options have to be sent; drop
4802  notion of header fields being "hop-by-hop" without being listed in the
4803  Connection header field.
4804  (<xref target="header.connection"/>)
4805</t>
4806<t>
4807  Remove hard limit of two connections per server.
4808  Remove requirement to retry a sequence of requests as long it was idempotent.
4809  Remove requirements about when servers are allowed to close connections
4810  prematurely.
4811  (<xref target="persistent.connections"/>)
4812</t>
4813<t>
4814  Remove requirement to retry requests under certain circumstances when the
4815  server prematurely closes the connection.
4816  (<xref target="persistent.reuse"/>)
4817</t>
4818<t>
4819  Define the semantics of the <x:ref>Upgrade</x:ref> header field in responses
4820  other than 101 (this was incorporated from <xref target="RFC2817"/>).
4821  (<xref target="header.upgrade"/>)
4822</t>
4823<t>
4824  Registration of Transfer Codings now requires IETF Review
4825  (<xref target="transfer.coding.registry"/>)
4826</t>
4827<t>
4828  Take over the Upgrade Token Registry, previously defined in
4829  <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
4830  (<xref target="upgrade.token.registry"/>)
4831</t>
4832<t>
4833  Empty list elements in list productions have been deprecated.
4834  (<xref target="abnf.extension"/>)
4835</t>
4836</section>
4837</section>
4838
4839<section title="ABNF list extension: #rule" anchor="abnf.extension">
4840<t>
4841  A #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
4842  improve readability in the definitions of some header field values.
4843</t>
4844<t>
4845  A construct "#" is defined, similar to "*", for defining comma-delimited
4846  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
4847  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
4848  comma (",") and optional whitespace (OWS).   
4849</t>
4850<figure><preamble>
4851  Thus,
4852</preamble><artwork type="example">
4853  1#element =&gt; element *( OWS "," OWS element )
4854</artwork></figure>
4855<figure><preamble>
4856  and:
4857</preamble><artwork type="example">
4858  #element =&gt; [ 1#element ]
4859</artwork></figure>
4860<figure><preamble>
4861  and for n &gt;= 1 and m &gt; 1:
4862</preamble><artwork type="example">
4863  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
4864</artwork></figure>
4865<t>
4866  For compatibility with legacy list rules, recipients &SHOULD; accept empty
4867  list elements. In other words, consumers would follow the list productions:
4868</t>
4869<figure><artwork type="example">
4870  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
4871 
4872  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
4873</artwork></figure>
4874<t>
4875  Note that empty elements do not contribute to the count of elements present,
4876  though.
4877</t>
4878<t>
4879  For example, given these ABNF productions:
4880</t>
4881<figure><artwork type="example">
4882  example-list      = 1#example-list-elmt
4883  example-list-elmt = token ; see <xref target="field.components"/> 
4884</artwork></figure>
4885<t>
4886  Then these are valid values for example-list (not including the double
4887  quotes, which are present for delimitation only):
4888</t>
4889<figure><artwork type="example">
4890  "foo,bar"
4891  "foo ,bar,"
4892  "foo , ,bar,charlie   "
4893</artwork></figure>
4894<t>
4895  But these values would be invalid, as at least one non-empty element is
4896  required:
4897</t>
4898<figure><artwork type="example">
4899  ""
4900  ","
4901  ",   ,"
4902</artwork></figure>
4903<t>
4904  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
4905  expanded as explained above.
4906</t>
4907</section>
4908
4909<?BEGININC p1-messaging.abnf-appendix ?>
4910<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4911<figure>
4912<artwork type="abnf" name="p1-messaging.parsed-abnf">
4913<x:ref>BWS</x:ref> = OWS
4914
4915<x:ref>Connection</x:ref> = *( "," OWS ) connection-option *( OWS "," [ OWS
4916 connection-option ] )
4917<x:ref>Content-Length</x:ref> = 1*DIGIT
4918
4919<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
4920 ]
4921<x:ref>HTTP-name</x:ref> = %x48.54.54.50 ; HTTP
4922<x:ref>HTTP-version</x:ref> = HTTP-name "/" DIGIT "." DIGIT
4923<x:ref>Host</x:ref> = uri-host [ ":" port ]
4924
4925<x:ref>OWS</x:ref> = *( SP / HTAB )
4926
4927<x:ref>RWS</x:ref> = 1*( SP / HTAB )
4928
4929<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4930<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4931<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4932 transfer-coding ] )
4933
4934<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4935<x:ref>Upgrade</x:ref> = *( "," OWS ) protocol *( OWS "," [ OWS protocol ] )
4936
4937<x:ref>Via</x:ref> = *( "," OWS ) ( received-protocol RWS received-by [ RWS comment
4938 ] ) *( OWS "," [ OWS ( received-protocol RWS received-by [ RWS
4939 comment ] ) ] )
4940
4941<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4942<x:ref>absolute-form</x:ref> = absolute-URI
4943<x:ref>asterisk-form</x:ref> = "*"
4944<x:ref>attribute</x:ref> = token
4945<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4946<x:ref>authority-form</x:ref> = authority
4947
4948<x:ref>chunk</x:ref> = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
4949<x:ref>chunk-data</x:ref> = 1*OCTET
4950<x:ref>chunk-ext</x:ref> = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
4951<x:ref>chunk-ext-name</x:ref> = token
4952<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
4953<x:ref>chunk-size</x:ref> = 1*HEXDIG
4954<x:ref>chunked-body</x:ref> = *chunk last-chunk trailer-part CRLF
4955<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
4956<x:ref>connection-option</x:ref> = token
4957<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4958 / %x2A-5B ; '*'-'['
4959 / %x5D-7E ; ']'-'~'
4960 / obs-text
4961
4962<x:ref>field-content</x:ref> = *( HTAB / SP / VCHAR / obs-text )
4963<x:ref>field-name</x:ref> = token
4964<x:ref>field-value</x:ref> = *( field-content / obs-fold )
4965
4966<x:ref>header-field</x:ref> = field-name ":" OWS field-value BWS
4967<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4968<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
4969
4970<x:ref>last-chunk</x:ref> = 1*"0" [ chunk-ext ] CRLF
4971
4972<x:ref>message-body</x:ref> = *OCTET
4973<x:ref>method</x:ref> = token
4974
4975<x:ref>obs-fold</x:ref> = CRLF ( SP / HTAB )
4976<x:ref>obs-text</x:ref> = %x80-FF
4977<x:ref>origin-form</x:ref> = path-absolute [ "?" query ]
4978
4979<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4980<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4981<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4982<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4983<x:ref>protocol</x:ref> = protocol-name [ "/" protocol-version ]
4984<x:ref>protocol-name</x:ref> = token
4985<x:ref>protocol-version</x:ref> = token
4986<x:ref>pseudonym</x:ref> = token
4987
4988<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
4989 / %x5D-7E ; ']'-'~'
4990 / obs-text
4991<x:ref>qdtext-nf</x:ref> = HTAB / SP / "!" / %x23-5B ; '#'-'['
4992 / %x5D-7E ; ']'-'~'
4993 / obs-text
4994<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
4995<x:ref>quoted-cpair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
4996<x:ref>quoted-pair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
4997<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
4998<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
4999
5000<x:ref>rank</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5001<x:ref>reason-phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5002<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5003<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5004<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5005<x:ref>request-line</x:ref> = method SP request-target SP HTTP-version CRLF
5006<x:ref>request-target</x:ref> = origin-form / absolute-form / authority-form /
5007 asterisk-form
5008
5009<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5010 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5011<x:ref>start-line</x:ref> = request-line / status-line
5012<x:ref>status-code</x:ref> = 3DIGIT
5013<x:ref>status-line</x:ref> = HTTP-version SP status-code SP reason-phrase CRLF
5014
5015<x:ref>t-codings</x:ref> = "trailers" / ( transfer-coding [ t-ranking ] )
5016<x:ref>t-ranking</x:ref> = OWS ";" OWS "q=" rank
5017<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5018 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5019<x:ref>token</x:ref> = 1*tchar
5020<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5021<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5022 transfer-extension
5023<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5024<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5025
5026<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5027
5028<x:ref>value</x:ref> = word
5029
5030<x:ref>word</x:ref> = token / quoted-string
5031</artwork>
5032</figure>
5033</section>
5034<?ENDINC p1-messaging.abnf-appendix ?>
5035
5036<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5037
5038<section title="Since RFC 2616">
5039<t>
5040  Extracted relevant partitions from <xref target="RFC2616"/>.
5041</t>
5042</section>
5043
5044<section title="Since draft-ietf-httpbis-p1-messaging-00">
5045<t>
5046  Closed issues:
5047  <list style="symbols"> 
5048    <t>
5049      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5050      "HTTP Version should be case sensitive"
5051      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5052    </t>
5053    <t>
5054      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5055      "'unsafe' characters"
5056      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5057    </t>
5058    <t>
5059      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5060      "Chunk Size Definition"
5061      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5062    </t>
5063    <t>
5064      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5065      "Message Length"
5066      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5067    </t>
5068    <t>
5069      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5070      "Media Type Registrations"
5071      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5072    </t>
5073    <t>
5074      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5075      "URI includes query"
5076      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5077    </t>
5078    <t>
5079      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5080      "No close on 1xx responses"
5081      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5082    </t>
5083    <t>
5084      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5085      "Remove 'identity' token references"
5086      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5087    </t>
5088    <t>
5089      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5090      "Import query BNF"
5091    </t>
5092    <t>
5093      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5094      "qdtext BNF"
5095    </t>
5096    <t>
5097      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5098      "Normative and Informative references"
5099    </t>
5100    <t>
5101      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5102      "RFC2606 Compliance"
5103    </t>
5104    <t>
5105      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5106      "RFC977 reference"
5107    </t>
5108    <t>
5109      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5110      "RFC1700 references"
5111    </t>
5112    <t>
5113      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5114      "inconsistency in date format explanation"
5115    </t>
5116    <t>
5117      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5118      "Date reference typo"
5119    </t>
5120    <t>
5121      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5122      "Informative references"
5123    </t>
5124    <t>
5125      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5126      "ISO-8859-1 Reference"
5127    </t>
5128    <t>
5129      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5130      "Normative up-to-date references"
5131    </t>
5132  </list>
5133</t>
5134<t>
5135  Other changes:
5136  <list style="symbols"> 
5137    <t>
5138      Update media type registrations to use RFC4288 template.
5139    </t>
5140    <t>
5141      Use names of RFC4234 core rules DQUOTE and HTAB,
5142      fix broken ABNF for chunk-data
5143      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5144    </t>
5145  </list>
5146</t>
5147</section>
5148
5149<section title="Since draft-ietf-httpbis-p1-messaging-01">
5150<t>
5151  Closed issues:
5152  <list style="symbols"> 
5153    <t>
5154      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5155      "Bodies on GET (and other) requests"
5156    </t>
5157    <t>
5158      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5159      "Updating to RFC4288"
5160    </t>
5161    <t>
5162      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5163      "Status Code and Reason Phrase"
5164    </t>
5165    <t>
5166      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5167      "rel_path not used"
5168    </t>
5169  </list>
5170</t>
5171<t>
5172  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5173  <list style="symbols"> 
5174    <t>
5175      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5176      "trailer-part").
5177    </t>
5178    <t>
5179      Avoid underscore character in rule names ("http_URL" ->
5180      "http-URL", "abs_path" -> "path-absolute").
5181    </t>
5182    <t>
5183      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5184      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5185      have to be updated when switching over to RFC3986.
5186    </t>
5187    <t>
5188      Synchronize core rules with RFC5234.
5189    </t>
5190    <t>
5191      Get rid of prose rules that span multiple lines.
5192    </t>
5193    <t>
5194      Get rid of unused rules LOALPHA and UPALPHA.
5195    </t>
5196    <t>
5197      Move "Product Tokens" section (back) into Part 1, as "token" is used
5198      in the definition of the Upgrade header field.
5199    </t>
5200    <t>
5201      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5202    </t>
5203    <t>
5204      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5205    </t>
5206  </list>
5207</t>
5208</section>
5209
5210<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5211<t>
5212  Closed issues:
5213  <list style="symbols"> 
5214    <t>
5215      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5216      "HTTP-date vs. rfc1123-date"
5217    </t>
5218    <t>
5219      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5220      "WS in quoted-pair"
5221    </t>
5222  </list>
5223</t>
5224<t>
5225  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5226  <list style="symbols"> 
5227    <t>
5228      Reference RFC 3984, and update header field registrations for header
5229      fields defined in this document.
5230    </t>
5231  </list>
5232</t>
5233<t>
5234  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5235  <list style="symbols"> 
5236    <t>
5237      Replace string literals when the string really is case-sensitive (HTTP-version).
5238    </t>
5239  </list>
5240</t>
5241</section>
5242
5243<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5244<t>
5245  Closed issues:
5246  <list style="symbols"> 
5247    <t>
5248      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5249      "Connection closing"
5250    </t>
5251    <t>
5252      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5253      "Move registrations and registry information to IANA Considerations"
5254    </t>
5255    <t>
5256      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5257      "need new URL for PAD1995 reference"
5258    </t>
5259    <t>
5260      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5261      "IANA Considerations: update HTTP URI scheme registration"
5262    </t>
5263    <t>
5264      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5265      "Cite HTTPS URI scheme definition"
5266    </t>
5267    <t>
5268      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5269      "List-type header fields vs Set-Cookie"
5270    </t>
5271  </list>
5272</t>
5273<t>
5274  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5275  <list style="symbols"> 
5276    <t>
5277      Replace string literals when the string really is case-sensitive (HTTP-Date).
5278    </t>
5279    <t>
5280      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5281    </t>
5282  </list>
5283</t>
5284</section>
5285
5286<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5287<t>
5288  Closed issues:
5289  <list style="symbols"> 
5290    <t>
5291      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5292      "Out-of-date reference for URIs"
5293    </t>
5294    <t>
5295      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5296      "RFC 2822 is updated by RFC 5322"
5297    </t>
5298  </list>
5299</t>
5300<t>
5301  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5302  <list style="symbols"> 
5303    <t>
5304      Use "/" instead of "|" for alternatives.
5305    </t>
5306    <t>
5307      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5308    </t>
5309    <t>
5310      Only reference RFC 5234's core rules.
5311    </t>
5312    <t>
5313      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5314      whitespace ("OWS") and required whitespace ("RWS").
5315    </t>
5316    <t>
5317      Rewrite ABNFs to spell out whitespace rules, factor out
5318      header field value format definitions.
5319    </t>
5320  </list>
5321</t>
5322</section>
5323
5324<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5325<t>
5326  Closed issues:
5327  <list style="symbols"> 
5328    <t>
5329      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5330      "Header LWS"
5331    </t>
5332    <t>
5333      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5334      "Sort 1.3 Terminology"
5335    </t>
5336    <t>
5337      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5338      "RFC2047 encoded words"
5339    </t>
5340    <t>
5341      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5342      "Character Encodings in TEXT"
5343    </t>
5344    <t>
5345      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5346      "Line Folding"
5347    </t>
5348    <t>
5349      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5350      "OPTIONS * and proxies"
5351    </t>
5352    <t>
5353      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5354      "reason-phrase BNF"
5355    </t>
5356    <t>
5357      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5358      "Use of TEXT"
5359    </t>
5360    <t>
5361      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5362      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5363    </t>
5364    <t>
5365      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5366      "RFC822 reference left in discussion of date formats"
5367    </t>
5368  </list>
5369</t>
5370<t>
5371  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5372  <list style="symbols"> 
5373    <t>
5374      Rewrite definition of list rules, deprecate empty list elements.
5375    </t>
5376    <t>
5377      Add appendix containing collected and expanded ABNF.
5378    </t>
5379  </list>
5380</t>
5381<t>
5382  Other changes:
5383  <list style="symbols"> 
5384    <t>
5385      Rewrite introduction; add mostly new Architecture Section.
5386    </t>
5387    <t>
5388      Move definition of quality values from Part 3 into Part 1;
5389      make TE request header field grammar independent of accept-params (defined in Part 3).
5390    </t>
5391  </list>
5392</t>
5393</section>
5394
5395<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5396<t>
5397  Closed issues:
5398  <list style="symbols"> 
5399    <t>
5400      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5401      "base for numeric protocol elements"
5402    </t>
5403    <t>
5404      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5405      "comment ABNF"
5406    </t>
5407  </list>
5408</t>
5409<t>
5410  Partly resolved issues:
5411  <list style="symbols"> 
5412    <t>
5413      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5414      "205 Bodies" (took out language that implied that there might be
5415      methods for which a payload body MUST NOT be included)
5416    </t>
5417    <t>
5418      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5419      "editorial improvements around HTTP-date"
5420    </t>
5421  </list>
5422</t>
5423</section>
5424
5425<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5426<t>
5427  Closed issues:
5428  <list style="symbols"> 
5429    <t>
5430      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5431      "Repeating single-value header fields"
5432    </t>
5433    <t>
5434      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5435      "increase connection limit"
5436    </t>
5437    <t>
5438      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5439      "IP addresses in URLs"
5440    </t>
5441    <t>
5442      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5443      "take over HTTP Upgrade Token Registry"
5444    </t>
5445    <t>
5446      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5447      "CR and LF in chunk extension values"
5448    </t>
5449    <t>
5450      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5451      "HTTP/0.9 support"
5452    </t>
5453    <t>
5454      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5455      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5456    </t>
5457    <t>
5458      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5459      "move definitions of gzip/deflate/compress to part 1"
5460    </t>
5461    <t>
5462      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5463      "disallow control characters in quoted-pair"
5464    </t>
5465  </list>
5466</t>
5467<t>
5468  Partly resolved issues:
5469  <list style="symbols"> 
5470    <t>
5471      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5472      "update IANA requirements wrt Transfer-Coding values" (add the
5473      IANA Considerations subsection)
5474    </t>
5475  </list>
5476</t>
5477</section>
5478
5479<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5480<t>
5481  Closed issues:
5482  <list style="symbols"> 
5483    <t>
5484      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5485      "header parsing, treatment of leading and trailing OWS"
5486    </t>
5487  </list>
5488</t>
5489<t>
5490  Partly resolved issues:
5491  <list style="symbols"> 
5492    <t>
5493      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5494      "Placement of 13.5.1 and 13.5.2"
5495    </t>
5496    <t>
5497      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5498      "use of term "word" when talking about header field structure"
5499    </t>
5500  </list>
5501</t>
5502</section>
5503
5504<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5505<t>
5506  Closed issues:
5507  <list style="symbols"> 
5508    <t>
5509      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5510      "Clarification of the term 'deflate'"
5511    </t>
5512    <t>
5513      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5514      "OPTIONS * and proxies"
5515    </t>
5516    <t>
5517      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5518      "MIME-Version not listed in P1, general header fields"
5519    </t>
5520    <t>
5521      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5522      "IANA registry for content/transfer encodings"
5523    </t>
5524    <t>
5525      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5526      "Case-sensitivity of HTTP-date"
5527    </t>
5528    <t>
5529      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5530      "use of term "word" when talking about header field structure"
5531    </t>
5532  </list>
5533</t>
5534<t>
5535  Partly resolved issues:
5536  <list style="symbols"> 
5537    <t>
5538      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5539      "Term for the requested resource's URI"
5540    </t>
5541  </list>
5542</t>
5543</section>
5544
5545<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5546<t>
5547  Closed issues:
5548  <list style="symbols">
5549    <t>
5550      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5551      "Connection Closing"
5552    </t>
5553    <t>
5554      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5555      "Delimiting messages with multipart/byteranges"
5556    </t>
5557    <t>
5558      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5559      "Handling multiple Content-Length header fields"
5560    </t>
5561    <t>
5562      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
5563      "Clarify entity / representation / variant terminology"
5564    </t>
5565    <t>
5566      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5567      "consider removing the 'changes from 2068' sections"
5568    </t>
5569  </list>
5570</t>
5571<t>
5572  Partly resolved issues:
5573  <list style="symbols"> 
5574    <t>
5575      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5576      "HTTP(s) URI scheme definitions"
5577    </t>
5578  </list>
5579</t>
5580</section>
5581
5582<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5583<t>
5584  Closed issues:
5585  <list style="symbols">
5586    <t>
5587      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
5588      "Trailer requirements"
5589    </t>
5590    <t>
5591      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
5592      "Text about clock requirement for caches belongs in p6"
5593    </t>
5594    <t>
5595      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
5596      "effective request URI: handling of missing host in HTTP/1.0"
5597    </t>
5598    <t>
5599      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
5600      "confusing Date requirements for clients"
5601    </t>
5602  </list>
5603</t>
5604<t>
5605  Partly resolved issues:
5606  <list style="symbols"> 
5607    <t>
5608      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5609      "Handling multiple Content-Length header fields"
5610    </t>
5611  </list>
5612</t>
5613</section>
5614
5615<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5616<t>
5617  Closed issues:
5618  <list style="symbols">
5619    <t>
5620      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/75"/>:
5621      "RFC2145 Normative"
5622    </t>
5623    <t>
5624      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5625      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5626    </t>
5627    <t>
5628      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/210"/>:
5629      "define 'transparent' proxy"
5630    </t>
5631    <t>
5632      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
5633      "Header Field Classification"
5634    </t>
5635    <t>
5636      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/233"/>:
5637      "Is * usable as a request-uri for new methods?"
5638    </t>
5639    <t>
5640      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
5641      "Migrate Upgrade details from RFC2817"
5642    </t>
5643    <t>
5644      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5645      "untangle ABNFs for header fields"
5646    </t>
5647    <t>
5648      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/279"/>:
5649      "update RFC 2109 reference"
5650    </t>
5651  </list>
5652</t>
5653</section>
5654
5655<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5656<t>
5657  Closed issues:
5658  <list style="symbols">
5659    <t>
5660      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/53"/>:
5661      "Allow is not in 13.5.2"
5662    </t>
5663    <t>
5664      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5665      "Handling multiple Content-Length header fields"
5666    </t>
5667    <t>
5668      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5669      "untangle ABNFs for header fields"
5670    </t>
5671    <t>
5672      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/286"/>:
5673      "Content-Length ABNF broken"
5674    </t>
5675  </list>
5676</t>
5677</section>
5678
5679<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5680<t>
5681  Closed issues:
5682  <list style="symbols">
5683    <t>
5684      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/273"/>:
5685      "HTTP-version should be redefined as fixed length pair of DIGIT . DIGIT"
5686    </t>
5687    <t>
5688      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/282"/>:
5689      "Recommend minimum sizes for protocol elements"
5690    </t>
5691    <t>
5692      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/283"/>:
5693      "Set expectations around buffering"
5694    </t>
5695    <t>
5696      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/288"/>:
5697      "Considering messages in isolation"
5698    </t>
5699  </list>
5700</t>
5701</section>
5702
5703<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5704<t>
5705  Closed issues:
5706  <list style="symbols">
5707    <t>
5708      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/100"/>:
5709      "DNS Spoofing / DNS Binding advice"
5710    </t>
5711    <t>
5712      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/254"/>:
5713      "move RFCs 2145, 2616, 2817 to Historic status"
5714    </t>
5715    <t>
5716      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/270"/>:
5717      "\-escaping in quoted strings"
5718    </t>
5719    <t>
5720      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/305"/>:
5721      "'Close' should be reserved in the HTTP header field registry"
5722    </t>
5723  </list>
5724</t>
5725</section>
5726
5727<section title="Since draft-ietf-httpbis-p1-messaging-16" anchor="changes.since.16">
5728<t>
5729  Closed issues:
5730  <list style="symbols">
5731    <t>
5732      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
5733      "Document HTTP's error-handling philosophy"
5734    </t>
5735    <t>
5736      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/215"/>:
5737      "Explain header field registration"
5738    </t>
5739    <t>
5740      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/219"/>:
5741      "Revise Acknowledgements Sections"
5742    </t>
5743    <t>
5744      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/297"/>:
5745      "Retrying Requests"
5746    </t>
5747    <t>
5748      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/318"/>:
5749      "Closing the connection on server error"
5750    </t>
5751  </list>
5752</t>
5753</section>
5754
5755<section title="Since draft-ietf-httpbis-p1-messaging-17" anchor="changes.since.17">
5756<t>
5757  Closed issues:
5758  <list style="symbols">
5759    <t>
5760      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/158"/>:
5761      "Proxy-Connection and Keep-Alive"
5762    </t>
5763    <t>
5764      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/166"/>:
5765      "Clarify 'User Agent'"
5766    </t>
5767    <t>
5768      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/300"/>:
5769      "Define non-final responses"
5770    </t>
5771    <t>
5772      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/323"/>:
5773      "intended maturity level vs normative references"
5774    </t>
5775    <t>
5776      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/324"/>:
5777      "Intermediary rewriting of queries"
5778    </t>
5779  </list>
5780</t>
5781</section>
5782
5783<section title="Since draft-ietf-httpbis-p1-messaging-18" anchor="changes.since.18">
5784<t>
5785  Closed issues:
5786  <list style="symbols">
5787    <t>
5788      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/250"/>:
5789      "message-body in CONNECT response"
5790    </t>
5791    <t>
5792      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/302"/>:
5793      "Misplaced text on connection handling in p2"
5794    </t>
5795    <t>
5796      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/335"/>:
5797      "wording of line folding rule"
5798    </t>
5799    <t>
5800      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/343"/>:
5801      "chunk-extensions"
5802    </t>
5803    <t>
5804      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/346"/>:
5805      "make IANA policy definitions consistent"
5806    </t>
5807  </list>
5808</t>
5809</section>
5810
5811<section title="Since draft-ietf-httpbis-p1-messaging-19" anchor="changes.since.19">
5812<t>
5813  Closed issues:
5814  <list style="symbols">
5815    <t>
5816      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/346"/>:
5817      "make IANA policy definitions consistent"
5818    </t>
5819    <t>
5820      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/359"/>:
5821      "clarify connection header field values are case-insensitive"
5822    </t>
5823    <t>
5824      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/361"/>:
5825      "ABNF requirements for recipients"
5826    </t>
5827    <t>
5828      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/368"/>:
5829      "note introduction of new IANA registries as normative changes"
5830    </t>
5831    <t>
5832      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/374"/>:
5833      "Reference to ISO-8859-1 is informative"
5834    </t>
5835  </list>
5836</t>
5837</section>
5838
5839<section title="Since draft-ietf-httpbis-p1-messaging-20" anchor="changes.since.20">
5840<t>
5841  Closed issues:
5842  <list style="symbols"> 
5843    <t>
5844      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/378"/>:
5845      "is 'q=' case-sensitive?"
5846    </t>
5847    <t>
5848      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/383"/>:
5849      "Semantics of HTTPS"
5850    </t>
5851  </list>
5852</t>
5853<t>
5854  Other changes:
5855  <list style="symbols">
5856    <t>
5857      Drop notion of header fields being "hop-by-hop" without being listed in
5858      the Connection header field.     
5859    </t>
5860    <t>
5861      Section about connection management rewritten; dropping some historic
5862      information.
5863    </t>
5864    <t>
5865      Move description of "100-continue" into Part 2.
5866    </t>
5867    <t>
5868      Rewrite the persistent connection and Upgrade requirements to be
5869      actionable by role and consistent with the rest of HTTP.
5870    </t>
5871  </list>
5872</t>
5873</section>
5874
5875</section>
5876
5877</back>
5878</rfc>
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