source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1899

Last change on this file since 1899 was 1899, checked in by fielding@…, 7 years ago

(editorial) description of resource is now in p2, remove redundant xrefs to 3986

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
File size: 242.8 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' 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 header-allow           "<xref target='Part2' x:rel='#header.allow' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-content-encoding    "<xref target='Part2' x:rel='#header.content-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-content-location    "<xref target='Part2' x:rel='#header.content-location' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY header-content-range   "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY header-content-type    "<xref target='Part2' x:rel='#header.content-type' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY header-date            "<xref target='Part2' x:rel='#header.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY header-etag            "<xref target='Part4' x:rel='#header.etag' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY header-expires         "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY header-last-modified   "<xref target='Part4' x:rel='#header.last-modified' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY header-mime-version    "<xref target='Part2' x:rel='#mime-version' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY header-proxy-authenticate  "<xref target='Part7' x:rel='#header.proxy-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41  <!ENTITY header-proxy-authorization "<xref target='Part7' x:rel='#header.proxy-authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
42  <!ENTITY header-server          "<xref target='Part2' x:rel='#header.server' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
43  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
44  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
45  <!ENTITY methods                "<xref target='Part2' x:rel='#methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
46  <!ENTITY OPTIONS                "<xref target='Part2' x:rel='#OPTIONS' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
47  <!ENTITY qvalue                 "<xref target='Part2' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
48  <!ENTITY resource               "<xref target='Part2' x:rel='#resource' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
49  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
50  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
51  <!ENTITY status-203             "<xref target='Part2' x:rel='#status.203' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
52  <!ENTITY status-3xx             "<xref target='Part2' x:rel='#status.3xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
53  <!ENTITY status-304             "<xref target='Part4' x:rel='#status.304' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
54  <!ENTITY status-4xx             "<xref target='Part2' x:rel='#status.4xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
55  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
56  <!ENTITY iana-header-registry   "<xref target='Part2' x:rel='#header.field.registry' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
57]>
58<?rfc toc="yes" ?>
59<?rfc symrefs="yes" ?>
60<?rfc sortrefs="yes" ?>
61<?rfc compact="yes"?>
62<?rfc subcompact="no" ?>
63<?rfc linkmailto="no" ?>
64<?rfc editing="no" ?>
65<?rfc comments="yes"?>
66<?rfc inline="yes"?>
67<?rfc rfcedstyle="yes"?>
68<?rfc-ext allow-markup-in-artwork="yes" ?>
69<?rfc-ext include-references-in-index="yes" ?>
70<rfc obsoletes="2145,2616" updates="2817" category="std" x:maturity-level="proposed"
71     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
72     xmlns:x='http://purl.org/net/xml2rfc/ext'>
73<x:link rel="next" basename="p2-semantics"/>
74<x:feedback template="mailto:ietf-http-wg@w3.org?subject={docname},%20%22{section}%22&amp;body=&lt;{ref}&gt;:"/>
75<front>
76
77  <title abbrev="HTTP/1.1 Message Syntax and Routing">Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing</title>
78
79  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
80    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
81    <address>
82      <postal>
83        <street>345 Park Ave</street>
84        <city>San Jose</city>
85        <region>CA</region>
86        <code>95110</code>
87        <country>USA</country>
88      </postal>
89      <email>fielding@gbiv.com</email>
90      <uri>http://roy.gbiv.com/</uri>
91    </address>
92  </author>
93
94  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
95    <organization abbrev="W3C">World Wide Web Consortium</organization>
96    <address>
97      <postal>
98        <street>W3C / ERCIM</street>
99        <street>2004, rte des Lucioles</street>
100        <city>Sophia-Antipolis</city>
101        <region>AM</region>
102        <code>06902</code>
103        <country>France</country>
104      </postal>
105      <email>ylafon@w3.org</email>
106      <uri>http://www.raubacapeu.net/people/yves/</uri>
107    </address>
108  </author>
109
110  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
111    <organization abbrev="greenbytes">greenbytes GmbH</organization>
112    <address>
113      <postal>
114        <street>Hafenweg 16</street>
115        <city>Muenster</city><region>NW</region><code>48155</code>
116        <country>Germany</country>
117      </postal>
118      <email>julian.reschke@greenbytes.de</email>
119      <uri>http://greenbytes.de/tech/webdav/</uri>
120    </address>
121  </author>
122
123  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
124  <workgroup>HTTPbis Working Group</workgroup>
125
126<abstract>
127<t>
128   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
129   distributed, collaborative, hypertext information systems. HTTP has been in
130   use by the World Wide Web global information initiative since 1990.
131   This document provides an overview of HTTP architecture and its associated
132   terminology, defines the "http" and "https" Uniform Resource Identifier
133   (URI) schemes, defines the HTTP/1.1 message syntax and parsing requirements,
134   and describes general security concerns for implementations.
135</t>   
136</abstract>
137
138<note title="Editorial Note (To be removed by RFC Editor)">
139  <t>
140    Discussion of this draft takes place on the HTTPBIS working group
141    mailing list (ietf-http-wg@w3.org), which is archived at
142    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
143  </t>
144  <t>
145    The current issues list is at
146    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
147    documents (including fancy diffs) can be found at
148    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
149  </t>
150  <t>
151    The changes in this draft are summarized in <xref target="changes.since.20"/>.
152  </t>
153</note>
154</front>
155<middle>
156<section title="Introduction" anchor="introduction">
157<t>
158   The Hypertext Transfer Protocol (HTTP) is an application-level
159   request/response protocol that uses extensible semantics and MIME-like
160   message payloads for flexible interaction with network-based hypertext
161   information systems. This document is the first in a series of documents
162   that collectively form the HTTP/1.1 specification:
163   <list style="empty">
164    <t>RFC xxx1: Message Syntax and Routing</t>
165    <t><xref target="Part2" x:fmt="none">RFC xxx2</xref>: Semantics and Content</t>
166    <t><xref target="Part4" x:fmt="none">RFC xxx3</xref>: Conditional Requests</t>
167    <t><xref target="Part5" x:fmt="none">RFC xxx4</xref>: Range Requests</t>
168    <t><xref target="Part6" x:fmt="none">RFC xxx5</xref>: Caching</t>
169    <t><xref target="Part7" x:fmt="none">RFC xxx6</xref>: Authentication</t>
170   </list>
171</t>
172<t>
173   This HTTP/1.1 specification obsoletes and moves to historic status
174   <xref target="RFC2616" x:fmt="none">RFC 2616</xref>, its predecessor
175   <xref target="RFC2068" x:fmt="none">RFC 2068</xref>,
176   <xref target="RFC2145" x:fmt="none">RFC 2145</xref> (on HTTP versioning),
177   and <xref target="RFC2817" x:fmt="none">RFC 2817</xref> (on using CONNECT
178   for TLS upgrades).
179</t>
180<t>
181   HTTP is a generic interface protocol for information systems. It is
182   designed to hide the details of how a service is implemented by presenting
183   a uniform interface to clients that is independent of the types of
184   resources provided. Likewise, servers do not need to be aware of each
185   client's purpose: an HTTP request can be considered in isolation rather
186   than being associated with a specific type of client or a predetermined
187   sequence of application steps. The result is a protocol that can be used
188   effectively in many different contexts and for which implementations can
189   evolve independently over time.
190</t>
191<t>
192   HTTP is also designed for use as an intermediation protocol for translating
193   communication to and from non-HTTP information systems.
194   HTTP proxies and gateways can provide access to alternative information
195   services by translating their diverse protocols into a hypertext
196   format that can be viewed and manipulated by clients in the same way
197   as HTTP services.
198</t>
199<t>
200   One consequence of HTTP flexibility is that the protocol cannot be
201   defined in terms of what occurs behind the interface. Instead, we
202   are limited to defining the syntax of communication, the intent
203   of received communication, and the expected behavior of recipients.
204   If the communication is considered in isolation, then successful
205   actions ought to be reflected in corresponding changes to the
206   observable interface provided by servers. However, since multiple
207   clients might act in parallel and perhaps at cross-purposes, we
208   cannot require that such changes be observable beyond the scope
209   of a single response.
210</t>
211<t>
212   This document describes the architectural elements that are used or
213   referred to in HTTP, defines the "http" and "https" URI schemes,
214   describes overall network operation and connection management,
215   and defines HTTP message framing and forwarding requirements.
216   Our goal is to define all of the mechanisms necessary for HTTP message
217   handling that are independent of message semantics, thereby defining the
218   complete set of requirements for message parsers and
219   message-forwarding intermediaries.
220</t>
221
222
223<section title="Requirement Notation" anchor="intro.requirements">
224<t>
225   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
226   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
227   document are to be interpreted as described in <xref target="RFC2119"/>.
228</t>
229<t>
230   Conformance criteria and considerations regarding error handling
231   are defined in <xref target="conformance"/>.
232</t>
233</section>
234
235<section title="Syntax Notation" anchor="notation">
236<iref primary="true" item="Grammar" subitem="ALPHA"/>
237<iref primary="true" item="Grammar" subitem="CR"/>
238<iref primary="true" item="Grammar" subitem="CRLF"/>
239<iref primary="true" item="Grammar" subitem="CTL"/>
240<iref primary="true" item="Grammar" subitem="DIGIT"/>
241<iref primary="true" item="Grammar" subitem="DQUOTE"/>
242<iref primary="true" item="Grammar" subitem="HEXDIG"/>
243<iref primary="true" item="Grammar" subitem="HTAB"/>
244<iref primary="true" item="Grammar" subitem="LF"/>
245<iref primary="true" item="Grammar" subitem="OCTET"/>
246<iref primary="true" item="Grammar" subitem="SP"/>
247<iref primary="true" item="Grammar" subitem="VCHAR"/>
248<t>
249   This specification uses the Augmented Backus-Naur Form (ABNF) notation
250   of <xref target="RFC5234"/> with the list rule extension defined in
251   <xref target="abnf.extension"/><xref target="collected.abnf"/> shows
252   the collected ABNF with the list rule expanded.
253</t>
254<t anchor="core.rules">
255  <x:anchor-alias value="ALPHA"/>
256  <x:anchor-alias value="CTL"/>
257  <x:anchor-alias value="CR"/>
258  <x:anchor-alias value="CRLF"/>
259  <x:anchor-alias value="DIGIT"/>
260  <x:anchor-alias value="DQUOTE"/>
261  <x:anchor-alias value="HEXDIG"/>
262  <x:anchor-alias value="HTAB"/>
263  <x:anchor-alias value="LF"/>
264  <x:anchor-alias value="OCTET"/>
265  <x:anchor-alias value="SP"/>
266  <x:anchor-alias value="VCHAR"/>
267   The following core rules are included by
268   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
269   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
270   DIGIT (decimal 0-9), DQUOTE (double quote),
271   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
272   OCTET (any 8-bit sequence of data), SP (space), and
273   VCHAR (any visible <xref target="USASCII"/> character).
274</t>
275<t>
276   As a convention, ABNF rule names prefixed with "obs-" denote
277   "obsolete" grammar rules that appear for historical reasons.
278</t>
279</section>
280</section>
281
282<section title="Architecture" anchor="architecture">
283<t>
284   HTTP was created for the World Wide Web architecture
285   and has evolved over time to support the scalability needs of a worldwide
286   hypertext system. Much of that architecture is reflected in the terminology
287   and syntax productions used to define HTTP.
288</t>
289
290<section title="Client/Server Messaging" anchor="operation">
291<iref primary="true" item="client"/>
292<iref primary="true" item="server"/>
293<iref primary="true" item="connection"/>
294<t>
295   HTTP is a stateless request/response protocol that operates by exchanging
296   <x:dfn>messages</x:dfn> (<xref target="http.message"/>) across a reliable
297   transport or session-layer
298   "<x:dfn>connection</x:dfn>" (<xref target="connection.management"/>).
299   An HTTP "<x:dfn>client</x:dfn>" is a program that establishes a connection
300   to a server for the purpose of sending one or more HTTP requests.
301   An HTTP "<x:dfn>server</x:dfn>" is a program that accepts connections
302   in order to service HTTP requests by sending HTTP responses.
303</t>
304<iref primary="true" item="user agent"/>
305<iref primary="true" item="origin server"/>
306<iref primary="true" item="browser"/>
307<iref primary="true" item="spider"/>
308<iref primary="true" item="sender"/>
309<iref primary="true" item="recipient"/>
310<t>
311   The terms client and server refer only to the roles that
312   these programs perform for a particular connection.  The same program
313   might act as a client on some connections and a server on others.  We use
314   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
315   such as a WWW browser, editor, or spider (web-traversing robot), and
316   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
317   authoritative responses to a request.  For general requirements, we use
318   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
319   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
320   message.
321</t>
322<t>
323   HTTP relies upon the Uniform Resource Identifier (URI)
324   standard <xref target="RFC3986"/> to indicate the target resource
325   (<xref target="target-resource"/>) and relationships between resources.
326   Messages are passed in a format similar to that used by Internet mail
327   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
328   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
329   between HTTP and MIME messages).
330</t>
331<t>
332   Most HTTP communication consists of a retrieval request (GET) for
333   a representation of some resource identified by a URI.  In the
334   simplest case, this might be accomplished via a single bidirectional
335   connection (===) between the user agent (UA) and the origin server (O).
336</t>
337<figure><artwork type="drawing">
338         request   &gt;
339    <x:highlight>UA</x:highlight> ======================================= <x:highlight>O</x:highlight>
340                                &lt;   response
341</artwork></figure>
342<iref primary="true" item="message"/>
343<iref primary="true" item="request"/>
344<iref primary="true" item="response"/>
345<t>
346   A client sends an HTTP request to a server in the form of a <x:dfn>request</x:dfn>
347   message, beginning with a request-line that includes a method, URI, and
348   protocol version (<xref target="request.line"/>),
349   followed by header fields containing
350   request modifiers, client information, and representation metadata
351   (<xref target="header.fields"/>),
352   an empty line to indicate the end of the header section, and finally
353   a message body containing the payload body (if any,
354   <xref target="message.body"/>).
355</t>
356<t>
357   A server responds to a client's request by sending one or more HTTP
358   <x:dfn>response</x:dfn>
359   messages, each beginning with a status line that
360   includes the protocol version, a success or error code, and textual
361   reason phrase (<xref target="status.line"/>),
362   possibly followed by header fields containing server
363   information, resource metadata, and representation metadata
364   (<xref target="header.fields"/>),
365   an empty line to indicate the end of the header section, and finally
366   a message body containing the payload body (if any,
367   <xref target="message.body"/>).
368</t>
369<t>
370   A connection might be used for multiple request/response exchanges,
371   as defined in <xref target="persistent.connections"/>.
372</t>
373<t>
374   The following example illustrates a typical message exchange for a
375   GET request on the URI "http://www.example.com/hello.txt":
376</t>
377<figure><preamble>
378client request:
379</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
380GET /hello.txt HTTP/1.1
381User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
382Host: www.example.com
383Accept-Language: en, mi
384
385</artwork></figure>
386<figure><preamble>
387server response:
388</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
389HTTP/1.1 200 OK
390Date: Mon, 27 Jul 2009 12:28:53 GMT
391Server: Apache
392Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
393ETag: "34aa387-d-1568eb00"
394Accept-Ranges: bytes
395Content-Length: <x:length-of target="exbody"/>
396Vary: Accept-Encoding
397Content-Type: text/plain
398
399<x:span anchor="exbody">Hello World!
400</x:span></artwork></figure>
401</section>
402
403<section title="Implementation Diversity" anchor="implementation-diversity">
404<t>
405   When considering the design of HTTP, it is easy to fall into a trap of
406   thinking that all user agents are general-purpose browsers and all origin
407   servers are large public websites. That is not the case in practice.
408   Common HTTP user agents include household appliances, stereos, scales,
409   firmware update scripts, command-line programs, mobile apps,
410   and communication devices in a multitude of shapes and sizes.  Likewise,
411   common HTTP origin servers include home automation units, configurable
412   networking components, office machines, autonomous robots, news feeds,
413   traffic cameras, ad selectors, and video delivery platforms.
414</t>
415<t>
416   The term "user agent" does not imply that there is a human user directly
417   interacting with the software agent at the time of a request. In many
418   cases, a user agent is installed or configured to run in the background
419   and save its results for later inspection (or save only a subset of those
420   results that might be interesting or erroneous). Spiders, for example, are
421   typically given a start URI and configured to follow certain behavior while
422   crawling the Web as a hypertext graph.
423</t>
424<t>
425   The implementation diversity of HTTP means that we cannot assume the
426   user agent can make interactive suggestions to a user or provide adequate
427   warning for security or privacy options.  In the few cases where this
428   specification requires reporting of errors to the user, it is acceptable
429   for such reporting to only be observable in an error console or log file.
430   Likewise, requirements that an automated action be confirmed by the user
431   before proceeding can me met via advance configuration choices,
432   run-time options, or simply not proceeding with the unsafe action.
433</t>
434</section>
435
436<section title="Intermediaries" anchor="intermediaries">
437<iref primary="true" item="intermediary"/>
438<t>
439   HTTP enables the use of intermediaries to satisfy requests through
440   a chain of connections.  There are three common forms of HTTP
441   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
442   a single intermediary might act as an origin server, proxy, gateway,
443   or tunnel, switching behavior based on the nature of each request.
444</t>
445<figure><artwork type="drawing">
446         &gt;             &gt;             &gt;             &gt;
447    <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>
448               &lt;             &lt;             &lt;             &lt;
449</artwork></figure>
450<t>
451   The figure above shows three intermediaries (A, B, and C) between the
452   user agent and origin server. A request or response message that
453   travels the whole chain will pass through four separate connections.
454   Some HTTP communication options
455   might apply only to the connection with the nearest, non-tunnel
456   neighbor, only to the end-points of the chain, or to all connections
457   along the chain. Although the diagram is linear, each participant might
458   be engaged in multiple, simultaneous communications. For example, B
459   might be receiving requests from many clients other than A, and/or
460   forwarding requests to servers other than C, at the same time that it
461   is handling A's request.
462</t>
463<t>
464<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
465<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
466   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
467   to describe various requirements in relation to the directional flow of a
468   message: all messages flow from upstream to downstream.
469   Likewise, we use the terms inbound and outbound to refer to
470   directions in relation to the request path:
471   "<x:dfn>inbound</x:dfn>" means toward the origin server and
472   "<x:dfn>outbound</x:dfn>" means toward the user agent.
473</t>
474<t><iref primary="true" item="proxy"/>
475   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
476   client, usually via local configuration rules, to receive requests
477   for some type(s) of absolute URI and attempt to satisfy those
478   requests via translation through the HTTP interface.  Some translations
479   are minimal, such as for proxy requests for "http" URIs, whereas
480   other requests might require translation to and from entirely different
481   application-level protocols. Proxies are often used to group an
482   organization's HTTP requests through a common intermediary for the
483   sake of security, annotation services, or shared caching.
484</t>
485<t>
486<iref primary="true" item="transforming proxy"/>
487<iref primary="true" item="non-transforming proxy"/>
488   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
489   or configured to modify request or response messages in a semantically
490   meaningful way (i.e., modifications, beyond those required by normal
491   HTTP processing, that change the message in a way that would be
492   significant to the original sender or potentially significant to
493   downstream recipients).  For example, a transforming proxy might be
494   acting as a shared annotation server (modifying responses to include
495   references to a local annotation database), a malware filter, a
496   format transcoder, or an intranet-to-Internet privacy filter.  Such
497   transformations are presumed to be desired by the client (or client
498   organization) that selected the proxy and are beyond the scope of
499   this specification.  However, when a proxy is not intended to transform
500   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
501   requirements that preserve HTTP message semantics. See &status-203; and
502   &header-warning; for status and warning codes related to transformations.
503</t>
504<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
505<iref primary="true" item="accelerator"/>
506   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
507   is a receiving agent that acts
508   as a layer above some other server(s) and translates the received
509   requests to the underlying server's protocol.  Gateways are often
510   used to encapsulate legacy or untrusted information services, to
511   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
512   enable partitioning or load-balancing of HTTP services across
513   multiple machines.
514</t>
515<t>
516   A gateway behaves as an origin server on its outbound connection and
517   as a user agent on its inbound connection.
518   All HTTP requirements applicable to an origin server
519   also apply to the outbound communication of a gateway.
520   A gateway communicates with inbound servers using any protocol that
521   it desires, including private extensions to HTTP that are outside
522   the scope of this specification.  However, an HTTP-to-HTTP gateway
523   that wishes to interoperate with third-party HTTP servers &MUST;
524   conform to HTTP user agent requirements on the gateway's inbound
525   connection and &MUST; implement the <x:ref>Connection</x:ref>
526   (<xref target="header.connection"/>) and <x:ref>Via</x:ref>
527   (<xref target="header.via"/>) header fields for both connections.
528</t>
529<t><iref primary="true" item="tunnel"/>
530   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
531   without changing the messages. Once active, a tunnel is not
532   considered a party to the HTTP communication, though the tunnel might
533   have been initiated by an HTTP request. A tunnel ceases to exist when
534   both ends of the relayed connection are closed. Tunnels are used to
535   extend a virtual connection through an intermediary, such as when
536   Transport Layer Security (TLS, <xref target="RFC5246"/>) is used to
537   establish confidential communication through a shared firewall proxy.
538</t>
539<t><iref primary="true" item="interception proxy"/>
540<iref primary="true" item="transparent proxy"/>
541<iref primary="true" item="captive portal"/>
542   The above categories for intermediary only consider those acting as
543   participants in the HTTP communication.  There are also intermediaries
544   that can act on lower layers of the network protocol stack, filtering or
545   redirecting HTTP traffic without the knowledge or permission of message
546   senders. Network intermediaries often introduce security flaws or
547   interoperability problems by violating HTTP semantics.  For example, an
548   "<x:dfn>interception proxy</x:dfn>" <xref target="RFC3040"/> (also commonly
549   known as a "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/> or
550   "<x:dfn>captive portal</x:dfn>")
551   differs from an HTTP proxy because it is not selected by the client.
552   Instead, an interception proxy filters or redirects outgoing TCP port 80
553   packets (and occasionally other common port traffic).
554   Interception proxies are commonly found on public network access points,
555   as a means of enforcing account subscription prior to allowing use of
556   non-local Internet services, and within corporate firewalls to enforce
557   network usage policies.
558   They are indistinguishable from a man-in-the-middle attack.
559</t>
560<t>
561   HTTP is defined as a stateless protocol, meaning that each request message
562   can be understood in isolation.  Many implementations depend on HTTP's
563   stateless design in order to reuse proxied connections or dynamically
564   load balance requests across multiple servers.  Hence, servers &MUST-NOT;
565   assume that two requests on the same connection are from the same user
566   agent unless the connection is secured and specific to that agent.
567   Some non-standard HTTP extensions (e.g., <xref target="RFC4559"/>) have
568   been known to violate this requirement, resulting in security and
569   interoperability problems.
570</t>
571</section>
572
573<section title="Caches" anchor="caches">
574<iref primary="true" item="cache"/>
575<t>
576   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
577   subsystem that controls its message storage, retrieval, and deletion.
578   A cache stores cacheable responses in order to reduce the response
579   time and network bandwidth consumption on future, equivalent
580   requests. Any client or server &MAY; employ a cache, though a cache
581   cannot be used by a server while it is acting as a tunnel.
582</t>
583<t>
584   The effect of a cache is that the request/response chain is shortened
585   if one of the participants along the chain has a cached response
586   applicable to that request. The following illustrates the resulting
587   chain if B has a cached copy of an earlier response from O (via C)
588   for a request which has not been cached by UA or A.
589</t>
590<figure><artwork type="drawing">
591            &gt;             &gt;
592       <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>
593                  &lt;             &lt;
594</artwork></figure>
595<t><iref primary="true" item="cacheable"/>
596   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
597   the response message for use in answering subsequent requests.
598   Even when a response is cacheable, there might be additional
599   constraints placed by the client or by the origin server on when
600   that cached response can be used for a particular request. HTTP
601   requirements for cache behavior and cacheable responses are
602   defined in &caching-overview;
603</t>
604<t>
605   There are a wide variety of architectures and configurations
606   of caches and proxies deployed across the World Wide Web and
607   inside large organizations. These systems include national hierarchies
608   of proxy caches to save transoceanic bandwidth, systems that
609   broadcast or multicast cache entries, organizations that distribute
610   subsets of cached data via optical media, and so on.
611</t>
612</section>
613
614<section title="Conformance and Error Handling" anchor="conformance">
615<t>
616   This specification targets conformance criteria according to the role of
617   a participant in HTTP communication.  Hence, HTTP requirements are placed
618   on senders, recipients, clients, servers, user agents, intermediaries,
619   origin servers, proxies, gateways, or caches, depending on what behavior
620   is being constrained by the requirement. Additional (social) requirements
621   are placed on implementations, resource owners, and protocol element
622   registrations when they apply beyond the scope of a single communication.
623</t>
624<t>
625   The verb "generate" is used instead of "send" where a requirement
626   differentiates between creating a protocol element and merely forwarding a
627   received element downstream.
628</t>
629<t>
630   An implementation is considered conformant if it complies with all of the
631   requirements associated with the roles it partakes in HTTP. Note that
632   SHOULD-level requirements are relevant here, unless one of the documented
633   exceptions is applicable.
634</t>
635<t>
636   Conformance applies to both the syntax and semantics of HTTP protocol
637   elements. A sender &MUST-NOT; generate protocol elements that convey a
638   meaning that is known by that sender to be false. A sender &MUST-NOT;
639   generate protocol elements that do not match the grammar defined by the
640   ABNF rules for those protocol elements that are applicable to the sender's
641   role. If a received protocol element is processed, the recipient &MUST; be
642   able to parse any value that would match the ABNF rules for that protocol
643   element, excluding only those rules not applicable to the recipient's role.
644</t>
645<t>
646   Unless noted otherwise, a recipient &MAY; attempt to recover a usable
647   protocol element from an invalid construct.  HTTP does not define
648   specific error handling mechanisms except when they have a direct impact
649   on security, since different applications of the protocol require
650   different error handling strategies.  For example, a Web browser might
651   wish to transparently recover from a response where the
652   <x:ref>Location</x:ref> header field doesn't parse according to the ABNF,
653   whereas a systems control client might consider any form of error recovery
654   to be dangerous.
655</t>
656</section>
657
658<section title="Protocol Versioning" anchor="http.version">
659  <x:anchor-alias value="HTTP-version"/>
660  <x:anchor-alias value="HTTP-name"/>
661<t>
662   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
663   versions of the protocol. This specification defines version "1.1".
664   The protocol version as a whole indicates the sender's conformance
665   with the set of requirements laid out in that version's corresponding
666   specification of HTTP.
667</t>
668<t>
669   The version of an HTTP message is indicated by an HTTP-version field
670   in the first line of the message. HTTP-version is case-sensitive.
671</t>
672<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-version"/><iref primary="true" item="Grammar" subitem="HTTP-name"/>
673  <x:ref>HTTP-version</x:ref>  = <x:ref>HTTP-name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
674  <x:ref>HTTP-name</x:ref>     = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
675</artwork></figure>
676<t>
677   The HTTP version number consists of two decimal digits separated by a "."
678   (period or decimal point).  The first digit ("major version") indicates the
679   HTTP messaging syntax, whereas the second digit ("minor version") indicates
680   the highest minor version to which the sender is
681   conformant and able to understand for future communication.  The minor
682   version advertises the sender's communication capabilities even when the
683   sender is only using a backwards-compatible subset of the protocol,
684   thereby letting the recipient know that more advanced features can
685   be used in response (by servers) or in future requests (by clients).
686</t>
687<t>
688   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
689   <xref target="RFC1945"/> or a recipient whose version is unknown,
690   the HTTP/1.1 message is constructed such that it can be interpreted
691   as a valid HTTP/1.0 message if all of the newer features are ignored.
692   This specification places recipient-version requirements on some
693   new features so that a conformant sender will only use compatible
694   features until it has determined, through configuration or the
695   receipt of a message, that the recipient supports HTTP/1.1.
696</t>
697<t>
698   The interpretation of a header field does not change between minor
699   versions of the same major HTTP version, though the default
700   behavior of a recipient in the absence of such a field can change.
701   Unless specified otherwise, header fields defined in HTTP/1.1 are
702   defined for all versions of HTTP/1.x.  In particular, the <x:ref>Host</x:ref>
703   and <x:ref>Connection</x:ref> header fields ought to be implemented by all
704   HTTP/1.x implementations whether or not they advertise conformance with
705   HTTP/1.1.
706</t>
707<t>
708   New header fields can be defined such that, when they are
709   understood by a recipient, they might override or enhance the
710   interpretation of previously defined header fields.  When an
711   implementation receives an unrecognized header field, the recipient
712   &MUST; ignore that header field for local processing regardless of
713   the message's HTTP version.  An unrecognized header field received
714   by a proxy &MUST; be forwarded downstream unless the header field's
715   field-name is listed in the message's <x:ref>Connection</x:ref> header field
716   (see <xref target="header.connection"/>).
717   These requirements allow HTTP's functionality to be enhanced without
718   requiring prior update of deployed intermediaries.
719</t>
720<t>
721   Intermediaries that process HTTP messages (i.e., all intermediaries
722   other than those acting as tunnels) &MUST; send their own HTTP-version
723   in forwarded messages.  In other words, they &MUST-NOT; blindly
724   forward the first line of an HTTP message without ensuring that the
725   protocol version in that message matches a version to which that
726   intermediary is conformant for both the receiving and
727   sending of messages.  Forwarding an HTTP message without rewriting
728   the HTTP-version might result in communication errors when downstream
729   recipients use the message sender's version to determine what features
730   are safe to use for later communication with that sender.
731</t>
732<t>
733   An HTTP client &SHOULD; send a request version equal to the highest
734   version to which the client is conformant and
735   whose major version is no higher than the highest version supported
736   by the server, if this is known.  An HTTP client &MUST-NOT; send a
737   version to which it is not conformant.
738</t>
739<t>
740   An HTTP client &MAY; send a lower request version if it is known that
741   the server incorrectly implements the HTTP specification, but only
742   after the client has attempted at least one normal request and determined
743   from the response status or header fields (e.g., <x:ref>Server</x:ref>) that
744   the server improperly handles higher request versions.
745</t>
746<t>
747   An HTTP server &SHOULD; send a response version equal to the highest
748   version to which the server is conformant and
749   whose major version is less than or equal to the one received in the
750   request.  An HTTP server &MUST-NOT; send a version to which it is not
751   conformant.  A server &MAY; send a <x:ref>505 (HTTP Version Not
752   Supported)</x:ref> response if it cannot send a response using the
753   major version used in the client's request.
754</t>
755<t>
756   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
757   if it is known or suspected that the client incorrectly implements the
758   HTTP specification and is incapable of correctly processing later
759   version responses, such as when a client fails to parse the version
760   number correctly or when an intermediary is known to blindly forward
761   the HTTP-version even when it doesn't conform to the given minor
762   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
763   performed unless triggered by specific client attributes, such as when
764   one or more of the request header fields (e.g., <x:ref>User-Agent</x:ref>)
765   uniquely match the values sent by a client known to be in error.
766</t>
767<t>
768   The intention of HTTP's versioning design is that the major number
769   will only be incremented if an incompatible message syntax is
770   introduced, and that the minor number will only be incremented when
771   changes made to the protocol have the effect of adding to the message
772   semantics or implying additional capabilities of the sender.  However,
773   the minor version was not incremented for the changes introduced between
774   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
775   is specifically avoiding any such changes to the protocol.
776</t>
777</section>
778
779<section title="Uniform Resource Identifiers" anchor="uri">
780<iref primary="true" item="resource"/>
781<t>
782   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
783   throughout HTTP as the means for identifying resources (&resource;).
784   URI references are used to target requests, indicate redirects, and define
785   relationships.
786</t>
787  <x:anchor-alias value="URI-reference"/>
788  <x:anchor-alias value="absolute-URI"/>
789  <x:anchor-alias value="relative-part"/>
790  <x:anchor-alias value="authority"/>
791  <x:anchor-alias value="path-abempty"/>
792  <x:anchor-alias value="path-absolute"/>
793  <x:anchor-alias value="port"/>
794  <x:anchor-alias value="query"/>
795  <x:anchor-alias value="uri-host"/>
796  <x:anchor-alias value="partial-URI"/>
797<t>
798   This specification adopts the definitions of "URI-reference",
799   "absolute-URI", "relative-part", "port", "host",
800   "path-abempty", "path-absolute", "query", and "authority" from the
801   URI generic syntax.
802   In addition, we define a partial-URI rule for protocol elements
803   that allow a relative URI but not a fragment.
804</t>
805<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>
806  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
807  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
808  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
809  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
810  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
811  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
812  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
813  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
814  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
815 
816  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
817</artwork></figure>
818<t>
819   Each protocol element in HTTP that allows a URI reference will indicate
820   in its ABNF production whether the element allows any form of reference
821   (URI-reference), only a URI in absolute form (absolute-URI), only the
822   path and optional query components, or some combination of the above.
823   Unless otherwise indicated, URI references are parsed
824   relative to the effective request URI
825   (<xref target="effective.request.uri"/>).
826</t>
827
828<section title="http URI scheme" anchor="http.uri">
829  <x:anchor-alias value="http-URI"/>
830  <iref item="http URI scheme" primary="true"/>
831  <iref item="URI scheme" subitem="http" primary="true"/>
832<t>
833   The "http" URI scheme is hereby defined for the purpose of minting
834   identifiers according to their association with the hierarchical
835   namespace governed by a potential HTTP origin server listening for
836   TCP connections on a given port.
837</t>
838<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"><!--terminal production--></iref>
839  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
840</artwork></figure>
841<t>
842   The HTTP origin server is identified by the generic syntax's
843   <x:ref>authority</x:ref> component, which includes a host identifier
844   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
845   The remainder of the URI, consisting of both the hierarchical path
846   component and optional query component, serves as an identifier for
847   a potential resource within that origin server's name space.
848</t>
849<t>
850   If the host identifier is provided as an IP literal or IPv4 address,
851   then the origin server is any listener on the indicated TCP port at
852   that IP address. If host is a registered name, then that name is
853   considered an indirect identifier and the recipient might use a name
854   resolution service, such as DNS, to find the address of a listener
855   for that host.
856   The host &MUST-NOT; be empty; if an "http" URI is received with an
857   empty host, then it &MUST; be rejected as invalid.
858   If the port subcomponent is empty or not given, then TCP port 80 is
859   assumed (the default reserved port for WWW services).
860</t>
861<t>
862   Regardless of the form of host identifier, access to that host is not
863   implied by the mere presence of its name or address. The host might or might
864   not exist and, even when it does exist, might or might not be running an
865   HTTP server or listening to the indicated port. The "http" URI scheme
866   makes use of the delegated nature of Internet names and addresses to
867   establish a naming authority (whatever entity has the ability to place
868   an HTTP server at that Internet name or address) and allows that
869   authority to determine which names are valid and how they might be used.
870</t>
871<t>
872   When an "http" URI is used within a context that calls for access to the
873   indicated resource, a client &MAY; attempt access by resolving
874   the host to an IP address, establishing a TCP connection to that address
875   on the indicated port, and sending an HTTP request message
876   (<xref target="http.message"/>) containing the URI's identifying data
877   (<xref target="message.routing"/>) to the server.
878   If the server responds to that request with a non-interim HTTP response
879   message, as described in &status-codes;, then that response
880   is considered an authoritative answer to the client's request.
881</t>
882<t>
883   Although HTTP is independent of the transport protocol, the "http"
884   scheme is specific to TCP-based services because the name delegation
885   process depends on TCP for establishing authority.
886   An HTTP service based on some other underlying connection protocol
887   would presumably be identified using a different URI scheme, just as
888   the "https" scheme (below) is used for servers that require an SSL/TLS
889   transport layer on a connection. Other protocols might also be used to
890   provide access to "http" identified resources &mdash; it is only the
891   authoritative interface used for mapping the namespace that is
892   specific to TCP.
893</t>
894<t>
895   The URI generic syntax for authority also includes a deprecated
896   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
897   for including user authentication information in the URI.  Some
898   implementations make use of the userinfo component for internal
899   configuration of authentication information, such as within command
900   invocation options, configuration files, or bookmark lists, even
901   though such usage might expose a user identifier or password.
902   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
903   delimiter) when transmitting an "http" URI in a message.  Recipients
904   of HTTP messages that contain a URI reference &SHOULD; parse for the
905   existence of userinfo and treat its presence as an error, likely
906   indicating that the deprecated subcomponent is being used to obscure
907   the authority for the sake of phishing attacks.
908</t>
909</section>
910
911<section title="https URI scheme" anchor="https.uri">
912   <x:anchor-alias value="https-URI"/>
913   <iref item="https URI scheme"/>
914   <iref item="URI scheme" subitem="https"/>
915<t>
916   The "https" URI scheme is hereby defined for the purpose of minting
917   identifiers according to their association with the hierarchical
918   namespace governed by a potential HTTP origin server listening for
919   SSL/TLS-secured connections on a given TCP port.
920</t>
921<t>
922   All of the requirements listed above for the "http" scheme are also
923   requirements for the "https" scheme, except that a default TCP port
924   of 443 is assumed if the port subcomponent is empty or not given,
925   and the TCP connection &MUST; be secured through the
926   use of strong encryption prior to sending the first HTTP request.
927</t>
928<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"><!--terminal production--></iref>
929  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
930</artwork></figure>
931<t>
932   Unlike the "http" scheme, responses to "https" identified requests
933   are never "public" and thus &MUST-NOT; be reused for shared caching.
934   They can, however, be reused in a private cache if the message is
935   cacheable by default in HTTP or specifically indicated as such by
936   the Cache-Control header field (&header-cache-control;).
937</t>
938<t>
939   Resources made available via the "https" scheme have no shared
940   identity with the "http" scheme even if their resource identifiers
941   indicate the same authority (the same host listening to the same
942   TCP port).  They are distinct name spaces and are considered to be
943   distinct origin servers.  However, an extension to HTTP that is
944   defined to apply to entire host domains, such as the Cookie protocol
945   <xref target="RFC6265"/>, can allow information
946   set by one service to impact communication with other services
947   within a matching group of host domains.
948</t>
949<t>
950   The process for authoritative access to an "https" identified
951   resource is defined in <xref target="RFC2818"/>.
952</t>
953</section>
954
955<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
956<t>
957   Since the "http" and "https" schemes conform to the URI generic syntax,
958   such URIs are normalized and compared according to the algorithm defined
959   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
960   described above for each scheme.
961</t>
962<t>
963   If the port is equal to the default port for a scheme, the normal
964   form is to elide the port subcomponent. Likewise, an empty path
965   component is equivalent to an absolute path of "/", so the normal
966   form is to provide a path of "/" instead. The scheme and host
967   are case-insensitive and normally provided in lowercase; all
968   other components are compared in a case-sensitive manner.
969   Characters other than those in the "reserved" set are equivalent
970   to their percent-encoded octets (see <xref target="RFC3986"
971   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
972</t>
973<t>
974   For example, the following three URIs are equivalent:
975</t>
976<figure><artwork type="example">
977   http://example.com:80/~smith/home.html
978   http://EXAMPLE.com/%7Esmith/home.html
979   http://EXAMPLE.com:/%7esmith/home.html
980</artwork></figure>
981</section>
982</section>
983</section>
984
985<section title="Message Format" anchor="http.message">
986<x:anchor-alias value="generic-message"/>
987<x:anchor-alias value="message.types"/>
988<x:anchor-alias value="HTTP-message"/>
989<x:anchor-alias value="start-line"/>
990<iref item="header section"/>
991<iref item="headers"/>
992<iref item="header field"/>
993<t>
994   All HTTP/1.1 messages consist of a start-line followed by a sequence of
995   octets in a format similar to the Internet Message Format
996   <xref target="RFC5322"/>: zero or more header fields (collectively
997   referred to as the "headers" or the "header section"), an empty line
998   indicating the end of the header section, and an optional message body.
999</t>
1000<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"><!--terminal production--></iref>
1001  <x:ref>HTTP-message</x:ref>   = <x:ref>start-line</x:ref>
1002                   *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1003                   <x:ref>CRLF</x:ref>
1004                   [ <x:ref>message-body</x:ref> ]
1005</artwork></figure>
1006<t>
1007   The normal procedure for parsing an HTTP message is to read the
1008   start-line into a structure, read each header field into a hash
1009   table by field name until the empty line, and then use the parsed
1010   data to determine if a message body is expected.  If a message body
1011   has been indicated, then it is read as a stream until an amount
1012   of octets equal to the message body length is read or the connection
1013   is closed.
1014</t>
1015<t>
1016   Recipients &MUST; parse an HTTP message as a sequence of octets in an
1017   encoding that is a superset of US-ASCII <xref target="USASCII"/>.
1018   Parsing an HTTP message as a stream of Unicode characters, without regard
1019   for the specific encoding, creates security vulnerabilities due to the
1020   varying ways that string processing libraries handle invalid multibyte
1021   character sequences that contain the octet LF (%x0A).  String-based
1022   parsers can only be safely used within protocol elements after the element
1023   has been extracted from the message, such as within a header field-value
1024   after message parsing has delineated the individual fields.
1025</t>
1026<t>
1027   An HTTP message can be parsed as a stream for incremental processing or
1028   forwarding downstream.  However, recipients cannot rely on incremental
1029   delivery of partial messages, since some implementations will buffer or
1030   delay message forwarding for the sake of network efficiency, security
1031   checks, or payload transformations.
1032</t>
1033
1034<section title="Start Line" anchor="start.line">
1035  <x:anchor-alias value="Start-Line"/>
1036<t>
1037   An HTTP message can either be a request from client to server or a
1038   response from server to client.  Syntactically, the two types of message
1039   differ only in the start-line, which is either a request-line (for requests)
1040   or a status-line (for responses), and in the algorithm for determining
1041   the length of the message body (<xref target="message.body"/>).
1042   In theory, a client could receive requests and a server could receive
1043   responses, distinguishing them by their different start-line formats,
1044   but in practice servers are implemented to only expect a request
1045   (a response is interpreted as an unknown or invalid request method)
1046   and clients are implemented to only expect a response.
1047</t>
1048<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="start-line"/>
1049  <x:ref>start-line</x:ref>     = <x:ref>request-line</x:ref> / <x:ref>status-line</x:ref>
1050</artwork></figure>
1051<t>
1052   A sender &MUST-NOT; send whitespace between the start-line and
1053   the first header field. The presence of such whitespace in a request
1054   might be an attempt to trick a server into ignoring that field or
1055   processing the line after it as a new request, either of which might
1056   result in a security vulnerability if other implementations within
1057   the request chain interpret the same message differently.
1058   Likewise, the presence of such whitespace in a response might be
1059   ignored by some clients or cause others to cease parsing.
1060</t>
1061
1062<section title="Request Line" anchor="request.line">
1063  <x:anchor-alias value="Request"/>
1064  <x:anchor-alias value="request-line"/>
1065<t>
1066   A request-line begins with a method token, followed by a single
1067   space (SP), the request-target, another single space (SP), the
1068   protocol version, and ending with CRLF.
1069</t>
1070<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-line"/>
1071  <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>
1072</artwork></figure>
1073<t>
1074   A server &MUST; be able to parse any received message that begins
1075   with a request-line and matches the ABNF rule for HTTP-message.
1076</t>
1077<iref primary="true" item="method"/>
1078<t anchor="method">
1079   The method token indicates the request method to be performed on the
1080   target resource. The request method is case-sensitive.
1081</t>
1082<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="method"/>
1083  <x:ref>method</x:ref>         = <x:ref>token</x:ref>
1084</artwork></figure>
1085<t>
1086   The methods defined by this specification can be found in
1087   &methods;, along with information regarding the HTTP method registry
1088   and considerations for defining new methods.
1089</t>
1090<iref item="request-target"/>
1091<t>
1092   The request-target identifies the target resource upon which to apply
1093   the request, as defined in <xref target="request-target"/>.
1094</t>
1095<t>
1096   No whitespace is allowed inside the method, request-target, and
1097   protocol version.  Hence, recipients typically parse the request-line
1098   into its component parts by splitting on the SP characters.
1099</t>
1100<t>
1101   Unfortunately, some user agents fail to properly encode hypertext
1102   references that have embedded whitespace, sending the characters
1103   directly instead of properly percent-encoding the disallowed characters.
1104   Recipients of an invalid request-line &SHOULD; respond with either a
1105   <x:ref>400 (Bad Request)</x:ref> error or a <x:ref>301 (Moved Permanently)</x:ref>
1106   redirect with the request-target properly encoded.  Recipients &SHOULD-NOT;
1107   attempt to autocorrect and then process the request without a redirect,
1108   since the invalid request-line might be deliberately crafted to bypass
1109   security filters along the request chain.
1110</t>
1111<t>
1112   HTTP does not place a pre-defined limit on the length of a request-line.
1113   A server that receives a method longer than any that it implements
1114   &SHOULD; respond with either a <x:ref>405 (Method Not Allowed)</x:ref>, if it is an origin
1115   server, or a <x:ref>501 (Not Implemented)</x:ref> status code.
1116   A server &MUST; be prepared to receive URIs of unbounded length and
1117   respond with the <x:ref>414 (URI Too Long)</x:ref> status code if the received
1118   request-target would be longer than the server wishes to handle
1119   (see &status-414;).
1120</t>
1121<t>
1122   Various ad-hoc limitations on request-line length are found in practice.
1123   It is &RECOMMENDED; that all HTTP senders and recipients support, at a
1124   minimum, request-line lengths of up to 8000 octets.
1125</t>
1126</section>
1127
1128<section title="Status Line" anchor="status.line">
1129  <x:anchor-alias value="response"/>
1130  <x:anchor-alias value="status-line"/>
1131  <x:anchor-alias value="status-code"/>
1132  <x:anchor-alias value="reason-phrase"/>
1133<t>
1134   The first line of a response message is the status-line, consisting
1135   of the protocol version, a space (SP), the status code, another space,
1136   a possibly-empty textual phrase describing the status code, and
1137   ending with CRLF.
1138</t>
1139<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-line"/>
1140  <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>
1141</artwork></figure>
1142<t>
1143   A client &MUST; be able to parse any received message that begins
1144   with a status-line and matches the ABNF rule for HTTP-message.
1145</t>
1146<t>
1147   The status-code element is a 3-digit integer code describing the
1148   result of the server's attempt to understand and satisfy the client's
1149   corresponding request. The rest of the response message is to be
1150   interpreted in light of the semantics defined for that status code.
1151   See &status-codes; for information about the semantics of status codes,
1152   including the classes of status code (indicated by the first digit),
1153   the status codes defined by this specification, considerations for the
1154   definition of new status codes, and the IANA registry.
1155</t>
1156<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-code"/>
1157  <x:ref>status-code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1158</artwork></figure>
1159<t>   
1160   The reason-phrase element exists for the sole purpose of providing a
1161   textual description associated with the numeric status code, mostly
1162   out of deference to earlier Internet application protocols that were more
1163   frequently used with interactive text clients. A client &SHOULD; ignore
1164   the reason-phrase content.
1165</t>
1166<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="reason-phrase"/>
1167  <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> )
1168</artwork></figure>
1169</section>
1170</section>
1171
1172<section title="Header Fields" anchor="header.fields">
1173  <x:anchor-alias value="header-field"/>
1174  <x:anchor-alias value="field-content"/>
1175  <x:anchor-alias value="field-name"/>
1176  <x:anchor-alias value="field-value"/>
1177  <x:anchor-alias value="obs-fold"/>
1178<t>
1179   Each HTTP header field consists of a case-insensitive field name
1180   followed by a colon (":"), optional whitespace, and the field value.
1181</t>
1182<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"/>
1183  <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>
1184  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1185  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>obs-fold</x:ref> )
1186  <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> )
1187  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref> ( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1188                 ; obsolete line folding
1189                 ; see <xref target="field.parsing"/>
1190</artwork></figure>
1191<t>
1192   The field-name token labels the corresponding field-value as having the
1193   semantics defined by that header field.  For example, the <x:ref>Date</x:ref>
1194   header field is defined in &header-date; as containing the origination
1195   timestamp for the message in which it appears.
1196</t>
1197<t>
1198   HTTP header fields are fully extensible: there is no limit on the
1199   introduction of new field names, each presumably defining new semantics,
1200   or on the number of header fields used in a given message.  Existing
1201   fields are defined in each part of this specification and in many other
1202   specifications outside the standards process.
1203   New header fields can be introduced without changing the protocol version
1204   if their defined semantics allow them to be safely ignored by recipients
1205   that do not recognize them.
1206</t>
1207<t>
1208   New HTTP header fields &SHOULD; be registered with IANA in the
1209   Message Header Field Registry, as described in &iana-header-registry;.
1210   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1211   field-name is listed in the <x:ref>Connection</x:ref> header field
1212   (<xref target="header.connection"/>) or the proxy is specifically
1213   configured to block or otherwise transform such fields.
1214   Unrecognized header fields &SHOULD; be ignored by other recipients.
1215</t>
1216<t>
1217   The order in which header fields with differing field names are
1218   received is not significant. However, it is "good practice" to send
1219   header fields that contain control data first, such as <x:ref>Host</x:ref>
1220   on requests and <x:ref>Date</x:ref> on responses, so that implementations
1221   can decide when not to handle a message as early as possible.  A server
1222   &MUST; wait until the entire header section is received before interpreting
1223   a request message, since later header fields might include conditionals,
1224   authentication credentials, or deliberately misleading duplicate
1225   header fields that would impact request processing.
1226</t>
1227<t>
1228   Multiple header fields with the same field name &MUST-NOT; be
1229   sent in a message unless the entire field value for that
1230   header field is defined as a comma-separated list [i.e., #(values)].
1231   Multiple header fields with the same field name can be combined into
1232   one "field-name: field-value" pair, without changing the semantics of the
1233   message, by appending each subsequent field value to the combined
1234   field value in order, separated by a comma. The order in which
1235   header fields with the same field name are received is therefore
1236   significant to the interpretation of the combined field value;
1237   a proxy &MUST-NOT; change the order of these field values when
1238   forwarding a message.
1239</t>
1240<x:note>
1241  <t>
1242   &Note; The "Set-Cookie" header field as implemented in
1243   practice can occur multiple times, but does not use the list syntax, and
1244   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1245   for details.) Also note that the Set-Cookie2 header field specified in
1246   <xref target="RFC2965"/> does not share this problem.
1247  </t>
1248</x:note>
1249
1250<section title="Whitespace" anchor="whitespace">
1251<t anchor="rule.LWS">
1252   This specification uses three rules to denote the use of linear
1253   whitespace: OWS (optional whitespace), RWS (required whitespace), and
1254   BWS ("bad" whitespace).
1255</t>
1256<t anchor="rule.OWS">
1257   The OWS rule is used where zero or more linear whitespace octets might
1258   appear. OWS &SHOULD; either not be produced or be produced as a single
1259   SP. Multiple OWS octets that occur within field-content &SHOULD; either
1260   be replaced with a single SP or transformed to all SP octets (each
1261   octet other than SP replaced with SP) before interpreting the field value
1262   or forwarding the message downstream.
1263</t>
1264<t anchor="rule.RWS">
1265   RWS is used when at least one linear whitespace octet is required to
1266   separate field tokens. RWS &SHOULD; be produced as a single SP.
1267   Multiple RWS octets that occur within field-content &SHOULD; either
1268   be replaced with a single SP or transformed to all SP octets before
1269   interpreting the field value or forwarding the message downstream.
1270</t>
1271<t anchor="rule.BWS">
1272   BWS is used where the grammar allows optional whitespace, for historical
1273   reasons, but senders &SHOULD-NOT; produce it in messages;
1274   recipients &MUST; accept such bad optional whitespace and remove it before
1275   interpreting the field value or forwarding the message downstream.
1276</t>
1277<t anchor="rule.whitespace">
1278  <x:anchor-alias value="BWS"/>
1279  <x:anchor-alias value="OWS"/>
1280  <x:anchor-alias value="RWS"/>
1281</t>
1282<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"/>
1283  <x:ref>OWS</x:ref>            = *( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1284                 ; "optional" whitespace
1285  <x:ref>RWS</x:ref>            = 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1286                 ; "required" whitespace
1287  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
1288                 ; "bad" whitespace
1289</artwork></figure>
1290</section>
1291
1292<section title="Field Parsing" anchor="field.parsing">
1293<t>
1294   No whitespace is allowed between the header field-name and colon.
1295   In the past, differences in the handling of such whitespace have led to
1296   security vulnerabilities in request routing and response handling.
1297   Any received request message that contains whitespace between a header
1298   field-name and colon &MUST; be rejected with a response code of 400
1299   (Bad Request).  A proxy &MUST; remove any such whitespace from a response
1300   message before forwarding the message downstream.
1301</t>
1302<t>
1303   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1304   preferred. The field value does not include any leading or trailing white
1305   space: OWS occurring before the first non-whitespace octet of the
1306   field value or after the last non-whitespace octet of the field value
1307   is ignored and &SHOULD; be removed before further processing (as this does
1308   not change the meaning of the header field).
1309</t>
1310<t>
1311   Historically, HTTP header field values could be extended over multiple
1312   lines by preceding each extra line with at least one space or horizontal
1313   tab (obs-fold). This specification deprecates such line
1314   folding except within the message/http media type
1315   (<xref target="internet.media.type.message.http"/>).
1316   HTTP senders &MUST-NOT; produce messages that include line folding
1317   (i.e., that contain any field-value that matches the obs-fold rule) unless
1318   the message is intended for packaging within the message/http media type.
1319   HTTP recipients &SHOULD; accept line folding and replace any embedded
1320   obs-fold whitespace with either a single SP or a matching number of SP
1321   octets (to avoid buffer copying) prior to interpreting the field value or
1322   forwarding the message downstream.
1323</t>
1324<t>
1325   Historically, HTTP has allowed field content with text in the ISO-8859-1
1326   <xref target="ISO-8859-1"/> character encoding and supported other
1327   character sets only through use of <xref target="RFC2047"/> encoding.
1328   In practice, most HTTP header field values use only a subset of the
1329   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1330   header fields &SHOULD; limit their field values to US-ASCII octets.
1331   Recipients &SHOULD; treat other (obs-text) octets in field content as
1332   opaque data.
1333</t>
1334</section>
1335
1336<section title="Field Length" anchor="field.length">
1337<t>
1338   HTTP does not place a pre-defined limit on the length of header fields,
1339   either in isolation or as a set. A server &MUST; be prepared to receive
1340   request header fields of unbounded length and respond with a <x:ref>4xx
1341   (Client Error)</x:ref> status code if the received header field(s) would be
1342   longer than the server wishes to handle.
1343</t>
1344<t>
1345   A client that receives response header fields that are longer than it wishes
1346   to handle can only treat it as a server error.
1347</t>
1348<t>
1349   Various ad-hoc limitations on header field length are found in practice. It
1350   is &RECOMMENDED; that all HTTP senders and recipients support messages whose
1351   combined header fields have 4000 or more octets.
1352</t>
1353</section>
1354
1355<section title="Field value components" anchor="field.components">
1356<t anchor="rule.token.separators">
1357  <x:anchor-alias value="tchar"/>
1358  <x:anchor-alias value="token"/>
1359  <x:anchor-alias value="special"/>
1360  <x:anchor-alias value="word"/>
1361   Many HTTP header field values consist of words (token or quoted-string)
1362   separated by whitespace or special characters. These special characters
1363   &MUST; be in a quoted string to be used within a parameter value (as defined
1364   in <xref target="transfer.codings"/>).
1365</t>
1366<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>
1367  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1368
1369  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
1370<!--
1371  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
1372 -->
1373  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
1374                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1375                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
1376                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
1377
1378  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
1379                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1380                 / "]" / "?" / "=" / "{" / "}"
1381</artwork></figure>
1382<t anchor="rule.quoted-string">
1383  <x:anchor-alias value="quoted-string"/>
1384  <x:anchor-alias value="qdtext"/>
1385  <x:anchor-alias value="obs-text"/>
1386   A string of text is parsed as a single word if it is quoted using
1387   double-quote marks.
1388</t>
1389<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"/>
1390  <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>
1391  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1392  <x:ref>obs-text</x:ref>       = %x80-FF
1393</artwork></figure>
1394<t anchor="rule.quoted-pair">
1395  <x:anchor-alias value="quoted-pair"/>
1396   The backslash octet ("\") can be used as a single-octet
1397   quoting mechanism within quoted-string constructs:
1398</t>
1399<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
1400  <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> )
1401</artwork></figure>
1402<t>
1403   Recipients that process the value of the quoted-string &MUST; handle a
1404   quoted-pair as if it were replaced by the octet following the backslash.
1405</t>
1406<t>
1407   Senders &SHOULD-NOT; escape octets in quoted-strings that do not require
1408   escaping (i.e., other than DQUOTE and the backslash octet).
1409</t>
1410<t anchor="rule.comment">
1411  <x:anchor-alias value="comment"/>
1412  <x:anchor-alias value="ctext"/>
1413   Comments can be included in some HTTP header fields by surrounding
1414   the comment text with parentheses. Comments are only allowed in
1415   fields containing "comment" as part of their field value definition.
1416</t>
1417<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1418  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1419  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1420</artwork></figure>
1421<t anchor="rule.quoted-cpair">
1422  <x:anchor-alias value="quoted-cpair"/>
1423   The backslash octet ("\") can be used as a single-octet
1424   quoting mechanism within comment constructs:
1425</t>
1426<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1427  <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> )
1428</artwork></figure>
1429<t>
1430   Senders &SHOULD-NOT; escape octets in comments that do not require escaping
1431   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
1432</t>
1433</section>
1434
1435</section>
1436
1437<section title="Message Body" anchor="message.body">
1438  <x:anchor-alias value="message-body"/>
1439<t>
1440   The message body (if any) of an HTTP message is used to carry the
1441   payload body of that request or response.  The message body is
1442   identical to the payload body unless a transfer coding has been
1443   applied, as described in <xref target="header.transfer-encoding"/>.
1444</t>
1445<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1446  <x:ref>message-body</x:ref> = *OCTET
1447</artwork></figure>
1448<t>
1449   The rules for when a message body is allowed in a message differ for
1450   requests and responses.
1451</t>
1452<t>
1453   The presence of a message body in a request is signaled by a
1454   a <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1455   field. Request message framing is independent of method semantics,
1456   even if the method does not define any use for a message body.
1457</t>
1458<t>
1459   The presence of a message body in a response depends on both
1460   the request method to which it is responding and the response
1461   status code (<xref target="status.line"/>).
1462   Responses to the HEAD request method never include a message body
1463   because the associated response header fields (e.g.,
1464   <x:ref>Transfer-Encoding</x:ref>, <x:ref>Content-Length</x:ref>, etc.) only
1465   indicate what their values would have been if the request method had been
1466   GET. <x:ref>2xx (Successful)</x:ref> responses to CONNECT switch to tunnel
1467   mode instead of having a message body.
1468   All <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, and
1469   <x:ref>304 (Not Modified)</x:ref> responses &MUST-NOT; include a message body.
1470   All other responses do include a message body, although the body
1471   &MAY; be of zero length.
1472</t>
1473
1474<section title="Transfer-Encoding" anchor="header.transfer-encoding">
1475  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
1476  <x:anchor-alias value="Transfer-Encoding"/>
1477<t>
1478   When one or more transfer codings are applied to a payload body in order
1479   to form the message body, a Transfer-Encoding header field &MUST; be sent
1480   in the message and &MUST; contain the list of corresponding
1481   transfer-coding names in the same order that they were applied.
1482   Transfer codings are defined in <xref target="transfer.codings"/>.
1483</t>
1484<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
1485  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
1486</artwork></figure>
1487<t>
1488   Transfer-Encoding is analogous to the Content-Transfer-Encoding field of
1489   MIME, which was designed to enable safe transport of binary data over a
1490   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1491   However, safe transport has a different focus for an 8bit-clean transfer
1492   protocol. In HTTP's case, Transfer-Encoding is primarily intended to
1493   accurately delimit a dynamically generated payload and to distinguish
1494   payload encodings that are only applied for transport efficiency or
1495   security from those that are characteristics of the target resource.
1496</t>
1497<t>
1498   The "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1499   &MUST; be implemented by all HTTP/1.1 recipients because it plays a
1500   crucial role in delimiting messages when the payload body size is not
1501   known in advance.
1502   When the "chunked" transfer-coding is used, it &MUST; be the last
1503   transfer-coding applied to form the message body and &MUST-NOT;
1504   be applied more than once in a message body.
1505   If any transfer-coding is applied to a request payload body,
1506   the final transfer-coding applied &MUST; be "chunked".
1507   If any transfer-coding is applied to a response payload body, then either
1508   the final transfer-coding applied &MUST; be "chunked" or
1509   the message &MUST; be terminated by closing the connection.
1510</t>
1511<figure><preamble>
1512   For example,
1513</preamble><artwork type="example">
1514  Transfer-Encoding: gzip, chunked
1515</artwork><postamble>
1516   indicates that the payload body has been compressed using the gzip
1517   coding and then chunked using the chunked coding while forming the
1518   message body.
1519</postamble></figure>
1520<t>
1521   If more than one Transfer-Encoding header field is present in a message,
1522   the multiple field-values &MUST; be combined into one field-value,
1523   according to the algorithm defined in <xref target="header.fields"/>,
1524   before determining the message body length.
1525</t>
1526<t>
1527   Unlike <x:ref>Content-Encoding</x:ref> (&content-codings;),
1528   Transfer-Encoding is a property of the message, not of the payload, and thus
1529   &MAY; be added or removed by any implementation along the request/response
1530   chain. Additional information about the encoding parameters &MAY; be
1531   provided by other header fields not defined by this specification.
1532</t>
1533<t>
1534   Transfer-Encoding &MAY; be sent in a response to a HEAD request or in a
1535   <x:ref>304 (Not Modified)</x:ref> response (&status-304;) to a GET request,
1536   neither of which includes a message body,
1537   to indicate that the origin server would have applied a transfer coding
1538   to the message body if the request had been an unconditional GET.
1539   This indication is not required, however, because any recipient on
1540   the response chain (including the origin server) can remove transfer
1541   codings when they are not needed.
1542</t>
1543<t>
1544   Transfer-Encoding was added in HTTP/1.1.  It is generally assumed that
1545   implementations advertising only HTTP/1.0 support will not understand
1546   how to process a transfer-encoded payload.
1547   A client &MUST-NOT; send a request containing Transfer-Encoding unless it
1548   knows the server will handle HTTP/1.1 (or later) requests; such knowledge
1549   might be in the form of specific user configuration or by remembering the
1550   version of a prior received response.
1551   A server &MUST-NOT; send a response containing Transfer-Encoding unless
1552   the corresponding request indicates HTTP/1.1 (or later).
1553</t>
1554<t>
1555   A server that receives a request message with a transfer-coding it does
1556   not understand &SHOULD; respond with <x:ref>501 (Not Implemented)</x:ref> and then
1557   close the connection.
1558</t>
1559</section>
1560
1561<section title="Content-Length" anchor="header.content-length">
1562  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
1563  <x:anchor-alias value="Content-Length"/>
1564<t>
1565   When a message does not have a <x:ref>Transfer-Encoding</x:ref> header field
1566   and the payload body length can be determined prior to being transferred, a
1567   Content-Length header field &SHOULD; be sent to indicate the length of the
1568   payload body that is either present as the message body, for requests
1569   and non-HEAD responses other than <x:ref>304 (Not Modified)</x:ref>, or
1570   would have been present had the request been an unconditional GET.  The
1571   length is expressed 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   In the case of a response to a HEAD request, Content-Length indicates
1584   the size of the payload body (without any potential transfer-coding)
1585   that would have been sent had the request been a GET.
1586   In the case of a <x:ref>304 (Not Modified)</x:ref> response (&status-304;)
1587   to a GET request, Content-Length indicates the size of the payload body (without
1588   any potential transfer-coding) that would have been sent in a <x:ref>200 (OK)</x:ref>
1589   response.
1590</t>
1591<t>
1592   Any Content-Length field value greater than or equal to zero is valid.
1593   Since there is no predefined limit to the length of an HTTP payload,
1594   recipients &SHOULD; anticipate potentially large decimal numerals and
1595   prevent parsing errors due to integer conversion overflows
1596   (<xref target="attack.protocol.element.size.overflows"/>).
1597</t>
1598<t>
1599   If a message is received that has multiple Content-Length header fields
1600   with field-values consisting of the same decimal value, or a single
1601   Content-Length header field with a field value containing a list of
1602   identical decimal values (e.g., "Content-Length: 42, 42"), indicating that
1603   duplicate Content-Length header fields have been generated or combined by an
1604   upstream message processor, then the recipient &MUST; either reject the
1605   message as invalid or replace the duplicated field-values with a single
1606   valid Content-Length field containing that decimal value prior to
1607   determining the message body length.
1608</t>
1609<x:note>
1610  <t>
1611   &Note; HTTP's use of Content-Length for message framing differs
1612   significantly from the same field's use in MIME, where it is an optional
1613   field used only within the "message/external-body" media-type.
1614  </t>
1615</x:note>
1616</section>
1617
1618<section title="Message Body Length" anchor="message.body.length">
1619<t>
1620   The length of a message body is determined by one of the following
1621   (in order of precedence):
1622</t>
1623<t>
1624  <list style="numbers">
1625    <x:lt><t>
1626     Any response to a HEAD request and any response with a
1627     <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, or
1628     <x:ref>304 (Not Modified)</x:ref> status code is always
1629     terminated by the first empty line after the header fields, regardless of
1630     the header fields present in the message, and thus cannot contain a
1631     message body.
1632    </t></x:lt>
1633    <x:lt><t>
1634     Any <x:ref>2xx (Successful)</x:ref> response to a CONNECT request implies that the
1635     connection will become a tunnel immediately after the empty line that
1636     concludes the header fields.  A client &MUST; ignore any
1637     <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1638     fields received in such a message.
1639    </t></x:lt>
1640    <x:lt><t>
1641     If a <x:ref>Transfer-Encoding</x:ref> header field is present
1642     and the "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1643     is the final encoding, the message body length is determined by reading
1644     and decoding the chunked data until the transfer-coding indicates the
1645     data is complete.
1646    </t>
1647    <t>
1648     If a <x:ref>Transfer-Encoding</x:ref> header field is present in a
1649     response and the "chunked" transfer-coding is not the final encoding, the
1650     message body length is determined by reading the connection until it is
1651     closed by the server.
1652     If a Transfer-Encoding header field is present in a request and the
1653     "chunked" transfer-coding is not the final encoding, the message body
1654     length cannot be determined reliably; the server &MUST; respond with
1655     the <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1656    </t>
1657    <t>
1658     If a message is received with both a <x:ref>Transfer-Encoding</x:ref>
1659     and a <x:ref>Content-Length</x:ref> header field, the
1660     Transfer-Encoding overrides the Content-Length.
1661     Such a message might indicate an attempt to perform request or response
1662     smuggling (bypass of security-related checks on message routing or content)
1663     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1664     be removed, prior to forwarding the message downstream, or replaced with
1665     the real message body length after the transfer-coding is decoded.
1666    </t></x:lt>
1667    <x:lt><t>
1668     If a message is received without <x:ref>Transfer-Encoding</x:ref> and with
1669     either multiple <x:ref>Content-Length</x:ref> header fields having
1670     differing field-values or a single Content-Length header field having an
1671     invalid value, then the message framing is invalid and &MUST; be treated
1672     as an error to prevent request or response smuggling.
1673     If this is a request message, the server &MUST; respond with
1674     a <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1675     If this is a response message received by a proxy, the proxy
1676     &MUST; discard the received response, send a <x:ref>502 (Bad Gateway)</x:ref>
1677     status code as its downstream response, and then close the connection.
1678     If this is a response message received by a user-agent, it &MUST; be
1679     treated as an error by discarding the message and closing the connection.
1680    </t></x:lt>
1681    <x:lt><t>
1682     If a valid <x:ref>Content-Length</x:ref> header field is present without
1683     <x:ref>Transfer-Encoding</x:ref>, its decimal value defines the
1684     message body length in octets.  If the actual number of octets sent in
1685     the message is less than the indicated Content-Length, the recipient
1686     &MUST; consider the message to be incomplete and treat the connection
1687     as no longer usable.
1688     If the actual number of octets sent in the message is more than the indicated
1689     Content-Length, the recipient &MUST; only process the message body up to the
1690     field value's number of octets; the remainder of the message &MUST; either
1691     be discarded or treated as the next message in a pipeline.  For the sake of
1692     robustness, a user-agent &MAY; attempt to detect and correct such an error
1693     in message framing if it is parsing the response to the last request on
1694     a connection and the connection has been closed by the server.
1695    </t></x:lt>
1696    <x:lt><t>
1697     If this is a request message and none of the above are true, then the
1698     message body length is zero (no message body is present).
1699    </t></x:lt>
1700    <x:lt><t>
1701     Otherwise, this is a response message without a declared message body
1702     length, so the message body length is determined by the number of octets
1703     received prior to the server closing the connection.
1704    </t></x:lt>
1705  </list>
1706</t>
1707<t>
1708   Since there is no way to distinguish a successfully completed,
1709   close-delimited message from a partially-received message interrupted
1710   by network failure, a server &SHOULD; use encoding or
1711   length-delimited messages whenever possible.  The close-delimiting
1712   feature exists primarily for backwards compatibility with HTTP/1.0.
1713</t>
1714<t>
1715   A server &MAY; reject a request that contains a message body but
1716   not a <x:ref>Content-Length</x:ref> by responding with
1717   <x:ref>411 (Length Required)</x:ref>.
1718</t>
1719<t>
1720   Unless a transfer-coding other than "chunked" has been applied,
1721   a client that sends a request containing a message body &SHOULD;
1722   use a valid <x:ref>Content-Length</x:ref> header field if the message body
1723   length is known in advance, rather than the "chunked" encoding, since some
1724   existing services respond to "chunked" with a <x:ref>411 (Length Required)</x:ref>
1725   status code even though they understand the chunked encoding.  This
1726   is typically because such services are implemented via a gateway that
1727   requires a content-length in advance of being called and the server
1728   is unable or unwilling to buffer the entire request before processing.
1729</t>
1730<t>
1731   A client that sends a request containing a message body &MUST; include a
1732   valid <x:ref>Content-Length</x:ref> header field if it does not know the
1733   server will handle HTTP/1.1 (or later) requests; such knowledge can be in
1734   the form of specific user configuration or by remembering the version of a
1735   prior received response.
1736</t>
1737</section>
1738</section>
1739
1740<section anchor="incomplete.messages" title="Handling Incomplete Messages">
1741<t>
1742   Request messages that are prematurely terminated, possibly due to a
1743   canceled connection or a server-imposed time-out exception, &MUST;
1744   result in closure of the connection; sending an error response
1745   prior to closing the connection is &OPTIONAL;.
1746</t>
1747<t>
1748   Response messages that are prematurely terminated, usually by closure
1749   of the connection prior to receiving the expected number of octets or by
1750   failure to decode a transfer-encoded message body, &MUST; be recorded
1751   as incomplete.  A response that terminates in the middle of the header
1752   block (before the empty line is received) cannot be assumed to convey the
1753   full semantics of the response and &MUST; be treated as an error.
1754</t>
1755<t>
1756   A message body that uses the chunked transfer encoding is
1757   incomplete if the zero-sized chunk that terminates the encoding has not
1758   been received.  A message that uses a valid <x:ref>Content-Length</x:ref> is
1759   incomplete if the size of the message body received (in octets) is less than
1760   the value given by Content-Length.  A response that has neither chunked
1761   transfer encoding nor Content-Length is terminated by closure of the
1762   connection, and thus is considered complete regardless of the number of
1763   message body octets received, provided that the header block was received
1764   intact.
1765</t>
1766<t>
1767   A user agent &MUST-NOT; render an incomplete response message body as if
1768   it were complete (i.e., some indication needs to be given to the user that an
1769   error occurred).  Cache requirements for incomplete responses are defined
1770   in &cache-incomplete;.
1771</t>
1772<t>
1773   A server &MUST; read the entire request message body or close
1774   the connection after sending its response, since otherwise the
1775   remaining data on a persistent connection would be misinterpreted
1776   as the next request.  Likewise,
1777   a client &MUST; read the entire response message body if it intends
1778   to reuse the same connection for a subsequent request.  Pipelining
1779   multiple requests on a connection is described in <xref target="pipelining"/>.
1780</t>
1781</section>
1782
1783<section title="Message Parsing Robustness" anchor="message.robustness">
1784<t>
1785   Older HTTP/1.0 client implementations might send an extra CRLF
1786   after a POST request as a lame workaround for some early server
1787   applications that failed to read message body content that was
1788   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1789   preface or follow a request with an extra CRLF.  If terminating
1790   the request message body with a line-ending is desired, then the
1791   client &MUST; include the terminating CRLF octets as part of the
1792   message body length.
1793</t>
1794<t>
1795   In the interest of robustness, servers &SHOULD; ignore at least one
1796   empty line received where a request-line is expected. In other words, if
1797   the server is reading the protocol stream at the beginning of a
1798   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1799   Likewise, although the line terminator for the start-line and header
1800   fields is the sequence CRLF, we recommend that recipients recognize a
1801   single LF as a line terminator and ignore any CR.
1802</t>
1803<t>
1804   When a server listening only for HTTP request messages, or processing
1805   what appears from the start-line to be an HTTP request message,
1806   receives a sequence of octets that does not match the HTTP-message
1807   grammar aside from the robustness exceptions listed above, the
1808   server &MUST; respond with an HTTP/1.1 <x:ref>400 (Bad Request)</x:ref> response. 
1809</t>
1810</section>
1811</section>
1812
1813<section title="Transfer Codings" anchor="transfer.codings">
1814  <x:anchor-alias value="transfer-coding"/>
1815  <x:anchor-alias value="transfer-extension"/>
1816<t>
1817   Transfer-coding values are used to indicate an encoding
1818   transformation that has been, can be, or might need to be applied to a
1819   payload body in order to ensure "safe transport" through the network.
1820   This differs from a content coding in that the transfer-coding is a
1821   property of the message rather than a property of the representation
1822   that is being transferred.
1823</t>
1824<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1825  <x:ref>transfer-coding</x:ref>    = "chunked" ; <xref target="chunked.encoding"/>
1826                     / "compress" ; <xref target="compress.coding"/>
1827                     / "deflate" ; <xref target="deflate.coding"/>
1828                     / "gzip" ; <xref target="gzip.coding"/>
1829                     / <x:ref>transfer-extension</x:ref>
1830  <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> )
1831</artwork></figure>
1832<t anchor="rule.parameter">
1833  <x:anchor-alias value="attribute"/>
1834  <x:anchor-alias value="transfer-parameter"/>
1835  <x:anchor-alias value="value"/>
1836   Parameters are in the form of attribute/value pairs.
1837</t>
1838<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"/>
1839  <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>
1840  <x:ref>attribute</x:ref>          = <x:ref>token</x:ref>
1841  <x:ref>value</x:ref>              = <x:ref>word</x:ref>
1842</artwork></figure>
1843<t>
1844   All transfer-coding values are case-insensitive and &SHOULD; be registered
1845   within the HTTP Transfer Coding registry, as defined in
1846   <xref target="transfer.coding.registry"/>.
1847   They are used in the <x:ref>TE</x:ref> (<xref target="header.te"/>) and
1848   <x:ref>Transfer-Encoding</x:ref> (<xref target="header.transfer-encoding"/>)
1849   header fields.
1850</t>
1851
1852<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1853  <iref item="chunked (Coding Format)"/>
1854  <iref item="Coding Format" subitem="chunked"/>
1855  <x:anchor-alias value="chunk"/>
1856  <x:anchor-alias value="chunked-body"/>
1857  <x:anchor-alias value="chunk-data"/>
1858  <x:anchor-alias value="chunk-ext"/>
1859  <x:anchor-alias value="chunk-ext-name"/>
1860  <x:anchor-alias value="chunk-ext-val"/>
1861  <x:anchor-alias value="chunk-size"/>
1862  <x:anchor-alias value="last-chunk"/>
1863  <x:anchor-alias value="trailer-part"/>
1864  <x:anchor-alias value="quoted-str-nf"/>
1865  <x:anchor-alias value="qdtext-nf"/>
1866<t>
1867   The chunked encoding modifies the body of a message in order to
1868   transfer it as a series of chunks, each with its own size indicator,
1869   followed by an &OPTIONAL; trailer containing header fields. This
1870   allows dynamically produced content to be transferred along with the
1871   information necessary for the recipient to verify that it has
1872   received the full message.
1873</t>
1874<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"/>
1875  <x:ref>chunked-body</x:ref>   = *<x:ref>chunk</x:ref>
1876                   <x:ref>last-chunk</x:ref>
1877                   <x:ref>trailer-part</x:ref>
1878                   <x:ref>CRLF</x:ref>
1879 
1880  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1881                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1882  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1883  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1884 
1885  <x:ref>chunk-ext</x:ref>      = *( ";" <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] )
1886  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1887  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
1888  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1889  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1890 
1891  <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>
1892                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
1893  <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>
1894</artwork></figure>
1895<t>
1896   Chunk extensions within the chucked encoding are deprecated.
1897   Senders &SHOULD-NOT; send chunk-ext.
1898   Definition of new chunk extensions is discouraged.
1899</t>
1900<t>
1901   The chunk-size field is a string of hex digits indicating the size of
1902   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1903   zero, followed by the trailer, which is terminated by an empty line.
1904</t>
1905
1906<section title="Trailer" anchor="header.trailer">
1907  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
1908  <x:anchor-alias value="Trailer"/>
1909<t>
1910   A trailer allows the sender to include additional fields at the end of a
1911   chunked message in order to supply metadata that might be dynamically
1912   generated while the message body is sent, such as a message integrity
1913   check, digital signature, or post-processing status.
1914   The trailer &MUST-NOT; contain fields that need to be known before a
1915   recipient processes the body, such as <x:ref>Transfer-Encoding</x:ref>,
1916   <x:ref>Content-Length</x:ref>, and <x:ref>Trailer</x:ref>.
1917</t>
1918<t>
1919   When a message includes a message body encoded with the chunked
1920   transfer-coding and the sender desires to send metadata in the form of
1921   trailer fields at the end of the message, the sender &SHOULD; send a
1922   <x:ref>Trailer</x:ref> header field before the message body to indicate
1923   which fields will be present in the trailers. This allows the recipient
1924   to prepare for receipt of that metadata before it starts processing the body,
1925   which is useful if the message is being streamed and the recipient wishes
1926   to confirm an integrity check on the fly.
1927</t>
1928<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
1929  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
1930</artwork></figure>
1931<t>
1932   If no <x:ref>Trailer</x:ref> header field is present, the sender of a
1933   chunked message body &SHOULD; send an empty trailer.
1934</t>
1935<t>
1936   A server &MUST; send an empty trailer with the chunked transfer-coding
1937   unless at least one of the following is true:
1938  <list style="numbers">
1939    <t>the request included a <x:ref>TE</x:ref> header field that indicates
1940    "trailers" is acceptable in the transfer-coding of the response, as
1941    described in <xref target="header.te"/>; or,</t>
1942     
1943    <t>the trailer fields consist entirely of optional metadata and the
1944    recipient could use the message (in a manner acceptable to the server where
1945    the field originated) without receiving that metadata. In other words,
1946    the server that generated the header field is willing to accept the
1947    possibility that the trailer fields might be silently discarded along
1948    the path to the client.</t>
1949  </list>
1950</t>
1951<t>
1952   The above requirement prevents the need for an infinite buffer when a
1953   message is being received by an HTTP/1.1 (or later) proxy and forwarded to
1954   an HTTP/1.0 recipient.
1955</t>
1956</section>
1957
1958<section title="Decoding chunked" anchor="decoding.chunked">
1959<t>
1960   A process for decoding the "chunked" transfer-coding
1961   can be represented in pseudo-code as:
1962</t>
1963<figure><artwork type="code">
1964  length := 0
1965  read chunk-size, chunk-ext (if any) and CRLF
1966  while (chunk-size &gt; 0) {
1967     read chunk-data and CRLF
1968     append chunk-data to decoded-body
1969     length := length + chunk-size
1970     read chunk-size and CRLF
1971  }
1972  read header-field
1973  while (header-field not empty) {
1974     append header-field to existing header fields
1975     read header-field
1976  }
1977  Content-Length := length
1978  Remove "chunked" from Transfer-Encoding
1979  Remove Trailer from existing header fields
1980</artwork></figure>
1981<t>
1982   All recipients &MUST; be able to receive and decode the
1983   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
1984   they do not understand.
1985</t>
1986</section>
1987</section>
1988
1989<section title="Compression Codings" anchor="compression.codings">
1990<t>
1991   The codings defined below can be used to compress the payload of a
1992   message.
1993</t>
1994
1995<section title="Compress Coding" anchor="compress.coding">
1996<iref item="compress (Coding Format)"/>
1997<iref item="Coding Format" subitem="compress"/>
1998<t>
1999   The "compress" format is produced by the common UNIX file compression
2000   program "compress". This format is an adaptive Lempel-Ziv-Welch
2001   coding (LZW). Recipients &SHOULD; consider "x-compress" to be
2002   equivalent to "compress".
2003</t>
2004</section>
2005
2006<section title="Deflate Coding" anchor="deflate.coding">
2007<iref item="deflate (Coding Format)"/>
2008<iref item="Coding Format" subitem="deflate"/>
2009<t>
2010   The "deflate" format is defined as the "deflate" compression mechanism
2011   (described in <xref target="RFC1951"/>) used inside the "zlib"
2012   data format (<xref target="RFC1950"/>).
2013</t>
2014<x:note>
2015  <t>
2016    &Note; Some incorrect implementations send the "deflate"
2017    compressed data without the zlib wrapper.
2018   </t>
2019</x:note>
2020</section>
2021
2022<section title="Gzip Coding" anchor="gzip.coding">
2023<iref item="gzip (Coding Format)"/>
2024<iref item="Coding Format" subitem="gzip"/>
2025<t>
2026   The "gzip" format is produced by the file compression program
2027   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2028   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2029   Recipients &SHOULD; consider "x-gzip" to be equivalent to "gzip".
2030</t>
2031</section>
2032
2033</section>
2034
2035<section title="TE" anchor="header.te">
2036  <iref primary="true" item="TE header field" x:for-anchor=""/>
2037  <x:anchor-alias value="TE"/>
2038  <x:anchor-alias value="t-codings"/>
2039  <x:anchor-alias value="t-ranking"/>
2040  <x:anchor-alias value="rank"/>
2041<t>
2042   The "TE" header field in a request indicates what transfer-codings,
2043   besides "chunked", the client is willing to accept in response, and
2044   whether or not the client is willing to accept trailer fields in a
2045   chunked transfer-coding.
2046</t>
2047<t>
2048   The TE field-value consists of a comma-separated list of transfer-coding
2049   names, each allowing for optional parameters (as described in
2050   <xref target="transfer.codings"/>), and/or the keyword "trailers".
2051   Clients &MUST-NOT; send the chunked transfer-coding name in TE;
2052   chunked is always acceptable for HTTP/1.1 recipients.
2053</t>
2054<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"/>
2055  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
2056  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-coding</x:ref> [ <x:ref>t-ranking</x:ref> ] )
2057  <x:ref>t-ranking</x:ref> = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>rank</x:ref>
2058  <x:ref>rank</x:ref>      = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2059             / ( "1" [ "." 0*3("0") ] )
2060</artwork></figure>
2061<t>
2062   Three examples of TE use are below.
2063</t>
2064<figure><artwork type="example">
2065  TE: deflate
2066  TE:
2067  TE: trailers, deflate;q=0.5
2068</artwork></figure>
2069<t>
2070   The presence of the keyword "trailers" indicates that the client is
2071   willing to accept trailer fields in a chunked transfer-coding,
2072   as defined in <xref target="chunked.encoding"/>, on behalf of itself and
2073   any downstream clients. For chained requests, this implies that either:
2074   (a) all downstream clients are willing to accept trailer fields in the
2075   forwarded response; or,
2076   (b) the client will attempt to buffer the response on behalf of downstream
2077   recipients.
2078   Note that HTTP/1.1 does not define any means to limit the size of a
2079   chunked response such that a client can be assured of buffering the
2080   entire response.
2081</t>
2082<t>
2083   When multiple transfer-codings are acceptable, the client &MAY; rank the
2084   codings by preference using a case-insensitive "q" parameter (similar to
2085   the qvalues used in content negotiation fields, &qvalue;). The rank value
2086   is a real number in the range 0 through 1, where 0.001 is the least
2087   preferred and 1 is the most preferred; a value of 0 means "not acceptable".
2088</t>
2089<t>
2090   If the TE field-value is empty or if no TE field is present, the only
2091   acceptable transfer-coding is "chunked". A message with no transfer-coding
2092   is always acceptable.
2093</t>
2094<t>
2095   Since the TE header field only applies to the immediate connection,
2096   a sender of TE &MUST; also send a "TE" connection option within the
2097   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>)
2098   in order to prevent the TE field from being forwarded by intermediaries
2099   that do not support its semantics.
2100</t>
2101</section>
2102</section>
2103
2104<section title="Message Routing" anchor="message.routing">
2105<t>
2106   HTTP request message routing is determined by each client based on the
2107   target resource, the client's proxy configuration, and
2108   establishment or reuse of an inbound connection.  The corresponding
2109   response routing follows the same connection chain back to the client.
2110</t>
2111
2112<section title="Identifying a Target Resource" anchor="target-resource">
2113  <iref primary="true" item="target resource"/>
2114  <iref primary="true" item="target URI"/>
2115  <x:anchor-alias value="target resource"/>
2116  <x:anchor-alias value="target URI"/>
2117<t>
2118   HTTP is used in a wide variety of applications, ranging from
2119   general-purpose computers to home appliances.  In some cases,
2120   communication options are hard-coded in a client's configuration.
2121   However, most HTTP clients rely on the same resource identification
2122   mechanism and configuration techniques as general-purpose Web browsers.
2123</t>
2124<t>
2125   HTTP communication is initiated by a user agent for some purpose.
2126   The purpose is a combination of request semantics, which are defined in
2127   <xref target="Part2"/>, and a target resource upon which to apply those
2128   semantics.  A URI reference (<xref target="uri"/>) is typically used as
2129   an identifier for the "<x:dfn>target resource</x:dfn>", which a user agent
2130   would resolve to its absolute form in order to obtain the
2131   "<x:dfn>target URI</x:dfn>".  The target URI
2132   excludes the reference's fragment identifier component, if any,
2133   since fragment identifiers are reserved for client-side processing
2134   (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>).
2135</t>
2136</section>
2137
2138<section title="Connecting Inbound" anchor="connecting.inbound">
2139<t>
2140   Once the target URI is determined, a client needs to decide whether
2141   a network request is necessary to accomplish the desired semantics and,
2142   if so, where that request is to be directed.
2143</t>
2144<t>
2145   If the client has a response cache and the request semantics can be
2146   satisfied by a cache (<xref target="Part6"/>), then the request is
2147   usually directed to the cache first.
2148</t>
2149<t>
2150   If the request is not satisfied by a cache, then a typical client will
2151   check its configuration to determine whether a proxy is to be used to
2152   satisfy the request.  Proxy configuration is implementation-dependent,
2153   but is often based on URI prefix matching, selective authority matching,
2154   or both, and the proxy itself is usually identified by an "http" or
2155   "https" URI.  If a proxy is applicable, the client connects inbound by
2156   establishing (or reusing) a connection to that proxy.
2157</t>
2158<t>
2159   If no proxy is applicable, a typical client will invoke a handler routine,
2160   usually specific to the target URI's scheme, to connect directly
2161   to an authority for the target resource.  How that is accomplished is
2162   dependent on the target URI scheme and defined by its associated
2163   specification, similar to how this specification defines origin server
2164   access for resolution of the "http" (<xref target="http.uri"/>) and
2165   "https" (<xref target="https.uri"/>) schemes.
2166</t>
2167<t>
2168   HTTP requirements regarding connection management are defined in
2169   <xref target="connection.management"/>.
2170</t>
2171</section>
2172
2173<section title="Request Target" anchor="request-target">
2174<t>
2175   Once an inbound connection is obtained,
2176   the client sends an HTTP request message (<xref target="http.message"/>)
2177   with a request-target derived from the target URI.
2178   There are four distinct formats for the request-target, depending on both
2179   the method being requested and whether the request is to a proxy.
2180</t>   
2181<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"/>
2182  <x:ref>request-target</x:ref> = <x:ref>origin-form</x:ref>
2183                 / <x:ref>absolute-form</x:ref>
2184                 / <x:ref>authority-form</x:ref>
2185                 / <x:ref>asterisk-form</x:ref>
2186
2187  <x:ref>origin-form</x:ref>    = <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ]
2188  <x:ref>absolute-form</x:ref>  = <x:ref>absolute-URI</x:ref>
2189  <x:ref>authority-form</x:ref> = <x:ref>authority</x:ref>
2190  <x:ref>asterisk-form</x:ref>  = "*"
2191</artwork></figure>
2192<t anchor="origin-form"><iref item="origin-form (of request-target)"/>
2193   The most common form of request-target is the origin-form.
2194   When making a request directly to an origin server, other than a CONNECT
2195   or server-wide OPTIONS request (as detailed below),
2196   a client &MUST; send only the absolute path and query components of
2197   the target URI as the request-target.
2198   If the target URI's path component is empty, then the client &MUST; send
2199   "/" as the path within the origin-form of request-target.
2200   A <x:ref>Host</x:ref> header field is also sent, as defined in
2201   <xref target="header.host"/>, containing the target URI's
2202   authority component (excluding any userinfo).
2203</t>
2204<t>
2205   For example, a client wishing to retrieve a representation of the resource
2206   identified as
2207</t>
2208<figure><artwork x:indent-with="  " type="example">
2209http://www.example.org/where?q=now
2210</artwork></figure>
2211<t>
2212   directly from the origin server would open (or reuse) a TCP connection
2213   to port 80 of the host "www.example.org" and send the lines:
2214</t>
2215<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2216GET /where?q=now HTTP/1.1
2217Host: www.example.org
2218</artwork></figure>
2219<t>
2220   followed by the remainder of the request message.
2221</t>
2222<t anchor="absolute-form"><iref item="absolute-form (of request-target)"/>
2223   When making a request to a proxy, other than a CONNECT or server-wide
2224   OPTIONS request (as detailed below), a client &MUST; send the target URI
2225   in absolute-form as the request-target.
2226   The proxy is requested to either service that request from a valid cache,
2227   if possible, or make the same request on the client's behalf to either
2228   the next inbound proxy server or directly to the origin server indicated
2229   by the request-target.  Requirements on such "forwarding" of messages are
2230   defined in <xref target="message.forwarding"/>.
2231</t>
2232<t>
2233   An example absolute-form of request-line would be:
2234</t>
2235<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2236GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
2237</artwork></figure>
2238<t>
2239   To allow for transition to the absolute-form for all requests in some
2240   future version of HTTP, HTTP/1.1 servers &MUST; accept the absolute-form
2241   in requests, even though HTTP/1.1 clients will only send them in requests
2242   to proxies.
2243</t>
2244<t anchor="authority-form"><iref item="authority-form (of request-target)"/>
2245   The authority-form of request-target is only used for CONNECT requests
2246   (&CONNECT;).  When making a CONNECT request to establish a tunnel through
2247   one or more proxies, a client &MUST; send only the target URI's
2248   authority component (excluding any userinfo) as the request-target.
2249   For example,
2250</t>
2251<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2252CONNECT www.example.com:80 HTTP/1.1
2253</artwork></figure>
2254<t anchor="asterisk-form"><iref item="asterisk-form (of request-target)"/>
2255   The asterisk-form of request-target is only used for a server-wide
2256   OPTIONS request (&OPTIONS;).  When a client wishes to request OPTIONS
2257   for the server as a whole, as opposed to a specific named resource of
2258   that server, the client &MUST; send only "*" (%x2A) as the request-target.
2259   For example,
2260</t>
2261<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2262OPTIONS * HTTP/1.1
2263</artwork></figure>
2264<t>
2265   If a proxy receives an OPTIONS request with an absolute-form of
2266   request-target in which the URI has an empty path and no query component,
2267   then the last proxy on the request chain &MUST; send a request-target
2268   of "*" when it forwards the request to the indicated origin server.
2269</t>
2270<figure><preamble>   
2271   For example, the request
2272</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2273OPTIONS http://www.example.org:8001 HTTP/1.1
2274</artwork></figure>
2275<figure><preamble>   
2276  would be forwarded by the final proxy as
2277</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2278OPTIONS * HTTP/1.1
2279Host: www.example.org:8001
2280</artwork>
2281<postamble>
2282   after connecting to port 8001 of host "www.example.org".
2283</postamble>
2284</figure>
2285</section>
2286
2287<section title="Host" anchor="header.host">
2288  <iref primary="true" item="Host header field" x:for-anchor=""/>
2289  <x:anchor-alias value="Host"/>
2290<t>
2291   The "Host" header field in a request provides the host and port
2292   information from the target URI, enabling the origin
2293   server to distinguish among resources while servicing requests
2294   for multiple host names on a single IP address.  Since the Host
2295   field-value is critical information for handling a request, it
2296   &SHOULD; be sent as the first header field following the request-line.
2297</t>
2298<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2299  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2300</artwork></figure>
2301<t>
2302   A client &MUST; send a Host header field in all HTTP/1.1 request
2303   messages.  If the target URI includes an authority component, then
2304   the Host field-value &MUST; be identical to that authority component
2305   after excluding any userinfo (<xref target="http.uri"/>).
2306   If the authority component is missing or undefined for the target URI,
2307   then the Host header field &MUST; be sent with an empty field-value.
2308</t>
2309<t>
2310   For example, a GET request to the origin server for
2311   &lt;http://www.example.org/pub/WWW/&gt; would begin with:
2312</t>
2313<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2314GET /pub/WWW/ HTTP/1.1
2315Host: www.example.org
2316</artwork></figure>
2317<t>
2318   The Host header field &MUST; be sent in an HTTP/1.1 request even
2319   if the request-target is in the absolute-form, since this
2320   allows the Host information to be forwarded through ancient HTTP/1.0
2321   proxies that might not have implemented Host.
2322</t>
2323<t>
2324   When a proxy receives a request with an absolute-form of
2325   request-target, the proxy &MUST; ignore the received
2326   Host header field (if any) and instead replace it with the host
2327   information of the request-target.  If the proxy forwards the request,
2328   it &MUST; generate a new Host field-value based on the received
2329   request-target rather than forward the received Host field-value.
2330</t>
2331<t>
2332   Since the Host header field acts as an application-level routing
2333   mechanism, it is a frequent target for malware seeking to poison
2334   a shared cache or redirect a request to an unintended server.
2335   An interception proxy is particularly vulnerable if it relies on
2336   the Host field-value for redirecting requests to internal
2337   servers, or for use as a cache key in a shared cache, without
2338   first verifying that the intercepted connection is targeting a
2339   valid IP address for that host.
2340</t>
2341<t>
2342   A server &MUST; respond with a <x:ref>400 (Bad Request)</x:ref> status code
2343   to any HTTP/1.1 request message that lacks a Host header field and
2344   to any request message that contains more than one Host header field
2345   or a Host header field with an invalid field-value.
2346</t>
2347</section>
2348
2349<section title="Effective Request URI" anchor="effective.request.uri">
2350  <iref primary="true" item="effective request URI"/>
2351<t>
2352   A server that receives an HTTP request message &MUST; reconstruct
2353   the user agent's original target URI, based on the pieces of information
2354   learned from the request-target, <x:ref>Host</x:ref> header field, and
2355   connection context, in order to identify the intended target resource and
2356   properly service the request. The URI derived from this reconstruction
2357   process is referred to as the "<x:dfn>effective request URI</x:dfn>".
2358</t>
2359<t>
2360   For a user agent, the effective request URI is the target URI.
2361</t>
2362<t>
2363   If the request-target is in absolute-form, then the effective request URI
2364   is the same as the request-target.  Otherwise, the effective request URI
2365   is constructed as follows.
2366</t>
2367<t>
2368   If the request is received over an SSL/TLS-secured TCP connection,
2369   then the effective request URI's scheme is "https"; otherwise, the
2370   scheme is "http".
2371</t>
2372<t>
2373   If the request-target is in authority-form, then the effective
2374   request URI's authority component is the same as the request-target.
2375   Otherwise, if a <x:ref>Host</x:ref> header field is supplied with a
2376   non-empty field-value, then the authority component is the same as the
2377   Host field-value. Otherwise, the authority component is the concatenation of
2378   the default host name configured for the server, a colon (":"), and the
2379   connection's incoming TCP port number in decimal form.
2380</t>
2381<t>
2382   If the request-target is in authority-form or asterisk-form, then the
2383   effective request URI's combined path and query component is empty.
2384   Otherwise, the combined path and query component is the same as the
2385   request-target.
2386</t>
2387<t>
2388   The components of the effective request URI, once determined as above,
2389   can be combined into absolute-URI form by concatenating the scheme,
2390   "://", authority, and combined path and query component.
2391</t>
2392<figure>
2393<preamble>
2394   Example 1: the following message received over an insecure TCP connection
2395</preamble> 
2396<artwork type="example" x:indent-with="  ">
2397GET /pub/WWW/TheProject.html HTTP/1.1
2398Host: www.example.org:8080
2399</artwork>
2400</figure>
2401<figure>
2402<preamble>
2403  has an effective request URI of
2404</preamble>
2405<artwork type="example" x:indent-with="  ">
2406http://www.example.org:8080/pub/WWW/TheProject.html
2407</artwork>
2408</figure>
2409<figure>
2410<preamble>
2411   Example 2: the following message received over an SSL/TLS-secured TCP
2412   connection
2413</preamble> 
2414<artwork type="example" x:indent-with="  ">
2415OPTIONS * HTTP/1.1
2416Host: www.example.org
2417</artwork>
2418</figure>
2419<figure>
2420<preamble>
2421  has an effective request URI of
2422</preamble>
2423<artwork type="example" x:indent-with="  ">
2424https://www.example.org
2425</artwork>
2426</figure>
2427<t>
2428   An origin server that does not allow resources to differ by requested
2429   host &MAY; ignore the <x:ref>Host</x:ref> field-value and instead replace it
2430   with a configured server name when constructing the effective request URI.
2431</t>
2432<t>
2433   Recipients of an HTTP/1.0 request that lacks a <x:ref>Host</x:ref> header
2434   field &MAY; attempt to use heuristics (e.g., examination of the URI path for
2435   something unique to a particular host) in order to guess the
2436   effective request URI's authority component.
2437</t>
2438</section>
2439
2440<section title="Message Forwarding" anchor="message.forwarding">
2441<t>
2442   As described in <xref target="intermediaries"/>, intermediaries can serve
2443   a variety of roles in the processing of HTTP requests and responses.
2444   Some intermediaries are used to improve performance or availability.
2445   Others are used for access control or to filter content.
2446   Since an HTTP stream has characteristics similar to a pipe-and-filter
2447   architecture, there are no inherent limits to the extent an intermediary
2448   can enhance (or interfere) with either direction of the stream.
2449</t>
2450<t>
2451   Intermediaries that forward a message &MUST; implement the
2452   <x:ref>Connection</x:ref> header field, as specified in
2453   <xref target="header.connection"/>, to exclude fields that are only
2454   intended for the incoming connection.
2455</t>
2456<t>
2457   In order to avoid request loops, a proxy that forwards requests to other
2458   proxies &MUST; be able to recognize and exclude all of its own server
2459   names, including any aliases, local variations, or literal IP addresses.
2460</t>
2461</section>
2462
2463<section title="Via" anchor="header.via">
2464  <iref primary="true" item="Via header field" x:for-anchor=""/>
2465  <x:anchor-alias value="pseudonym"/>
2466  <x:anchor-alias value="received-by"/>
2467  <x:anchor-alias value="received-protocol"/>
2468  <x:anchor-alias value="Via"/>
2469<t>
2470   The "Via" header field &MUST; be sent by a proxy or gateway
2471   in forwarded messages to
2472   indicate the intermediate protocols and recipients between the user
2473   agent and the server on requests, and between the origin server and
2474   the client on responses. It is analogous to the "Received" field
2475   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>).
2476   Via is used in HTTP for tracking message forwards,
2477   avoiding request loops, and identifying the protocol capabilities of
2478   all senders along the request/response chain.
2479</t>
2480<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"/>
2481  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2482                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2483  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2484  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2485  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2486</artwork></figure>
2487<t>
2488   The received-protocol indicates the protocol version of the message
2489   received by the server or client along each segment of the
2490   request/response chain. The received-protocol version is appended to
2491   the Via field value when the message is forwarded so that information
2492   about the protocol capabilities of upstream applications remains
2493   visible to all recipients.
2494</t>
2495<t>
2496   The protocol-name is excluded if and only if it would be "HTTP". The
2497   received-by field is normally the host and optional port number of a
2498   recipient server or client that subsequently forwarded the message.
2499   However, if the real host is considered to be sensitive information,
2500   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2501   be assumed to be the default port of the received-protocol.
2502</t>
2503<t>
2504   Multiple Via field values represent each proxy or gateway that has
2505   forwarded the message. Each recipient &MUST; append its information
2506   such that the end result is ordered according to the sequence of
2507   forwarding applications.
2508</t>
2509<t>
2510   Comments &MAY; be used in the Via header field to identify the software
2511   of each recipient, analogous to the <x:ref>User-Agent</x:ref> and
2512   <x:ref>Server</x:ref> header fields. However, all comments in the Via field
2513   are optional and &MAY; be removed by any recipient prior to forwarding the
2514   message.
2515</t>
2516<t>
2517   For example, a request message could be sent from an HTTP/1.0 user
2518   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2519   forward the request to a public proxy at p.example.net, which completes
2520   the request by forwarding it to the origin server at www.example.com.
2521   The request received by www.example.com would then have the following
2522   Via header field:
2523</t>
2524<figure><artwork type="example">
2525  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2526</artwork></figure>
2527<t>
2528   A proxy or gateway used as a portal through a network firewall
2529   &SHOULD-NOT; forward the names and ports of hosts within the firewall
2530   region unless it is explicitly enabled to do so. If not enabled, the
2531   received-by host of any host behind the firewall &SHOULD; be replaced
2532   by an appropriate pseudonym for that host.
2533</t>
2534<t>
2535   A proxy or gateway &MAY; combine an ordered subsequence of Via header
2536   field entries into a single such entry if the entries have identical
2537   received-protocol values. For example,
2538</t>
2539<figure><artwork type="example">
2540  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2541</artwork></figure>
2542<t>
2543  could be collapsed to
2544</t>
2545<figure><artwork type="example">
2546  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2547</artwork></figure>
2548<t>
2549   Senders &SHOULD-NOT; combine multiple entries unless they are all
2550   under the same organizational control and the hosts have already been
2551   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
2552   have different received-protocol values.
2553</t>
2554</section>
2555
2556<section title="Message Transforming" anchor="message.transforming">
2557<t>
2558   If a proxy receives a request-target with a host name that is not a
2559   fully qualified domain name, it &MAY; add its own domain to the host name
2560   it received when forwarding the request.  A proxy &MUST-NOT; change the
2561   host name if it is a fully qualified domain name.
2562</t>
2563<t>
2564   A non-transforming proxy &MUST-NOT; modify the "path-absolute" and "query"
2565   parts of the received request-target when forwarding it to the next inbound
2566   server, except as noted above to replace an empty path with "/" or "*".
2567</t>
2568<t>
2569   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2570   though it &MAY; change the message body through application or removal
2571   of a transfer-coding (<xref target="transfer.codings"/>).
2572</t>
2573<t>
2574   A non-transforming proxy &SHOULD-NOT; modify header fields that provide
2575   information about the end points of the communication chain, the resource
2576   state, or the selected representation.
2577</t>
2578<t>
2579   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2580   request or response, and it &MUST-NOT; add any of these fields if not
2581   already present:
2582  <list style="symbols">
2583    <t><x:ref>Allow</x:ref> (&header-allow;)</t>
2584    <t><x:ref>Content-Location</x:ref> (&header-content-location;)</t>
2585    <t>Content-MD5 (<xref target="RFC2616" x:fmt="of" x:sec="14.15"/>)</t>
2586    <t><x:ref>ETag</x:ref> (&header-etag;)</t>
2587    <t><x:ref>Last-Modified</x:ref> (&header-last-modified;)</t>
2588    <t><x:ref>Server</x:ref> (&header-server;)</t>
2589  </list>
2590</t>
2591<t>
2592   A non-transforming proxy &MUST-NOT; modify an <x:ref>Expires</x:ref>
2593   header field (&header-expires;) if already present in a response, but
2594   it &MAY; add an <x:ref>Expires</x:ref> header field with a field-value
2595   identical to that of the <x:ref>Date</x:ref> header field.
2596</t>
2597<t>
2598   A proxy &MUST-NOT; modify or add any of the following fields in a
2599   message that contains the no-transform cache-control directive:
2600  <list style="symbols">
2601    <t><x:ref>Content-Encoding</x:ref> (&header-content-encoding;)</t>
2602    <t><x:ref>Content-Range</x:ref> (&header-content-range;)</t>
2603    <t><x:ref>Content-Type</x:ref> (&header-content-type;)</t>
2604  </list>
2605</t>
2606<t>
2607   A transforming proxy &MAY; modify or add these fields to a message
2608   that does not include no-transform, but if it does so, it &MUST; add a
2609   Warning 214 (Transformation applied) if one does not already appear
2610   in the message (see &header-warning;).
2611</t>
2612<x:note>
2613  <t>
2614    <x:h>Warning:</x:h> Unnecessary modification of header fields might
2615    cause authentication failures if stronger authentication
2616    mechanisms are introduced in later versions of HTTP. Such
2617    authentication mechanisms &MAY; rely on the values of header fields
2618    not listed here.
2619  </t>
2620</x:note>
2621</section>
2622
2623<section title="Associating a Response to a Request" anchor="associating.response.to.request">
2624<t>
2625   HTTP does not include a request identifier for associating a given
2626   request message with its corresponding one or more response messages.
2627   Hence, it relies on the order of response arrival to correspond exactly
2628   to the order in which requests are made on the same connection.
2629   More than one response message per request only occurs when one or more
2630   informational responses (<x:ref>1xx</x:ref>, see &status-1xx;) precede a final response
2631   to the same request.
2632</t>
2633<t>
2634   A client that uses persistent connections and sends more than one request
2635   per connection &MUST; maintain a list of outstanding requests in the
2636   order sent on that connection and &MUST; associate each received response
2637   message to the highest ordered request that has not yet received a final
2638   (non-<x:ref>1xx</x:ref>) response.
2639</t>
2640</section>
2641</section>
2642
2643<section title="Connection Management" anchor="connection.management">
2644<t>
2645   HTTP messaging is independent of the underlying transport or
2646   session-layer connection protocol(s).  HTTP only presumes a reliable
2647   transport with in-order delivery of requests and the corresponding
2648   in-order delivery of responses.  The mapping of HTTP request and
2649   response structures onto the data units of an underlying transport
2650   protocol is outside the scope of this specification.
2651</t>
2652<t>
2653   As described in <xref target="connecting.inbound"/>, the specific
2654   connection protocols to be used for an HTTP interaction are determined by
2655   client configuration and the <x:ref>target URI</x:ref>.
2656   For example, the "http" URI scheme
2657   (<xref target="http.uri"/>) indicates a default connection of TCP
2658   over IP, with a default TCP port of 80, but the client might be
2659   configured to use a proxy via some other connection, port, or protocol.
2660</t>
2661<t>
2662   HTTP implementations are expected to engage in connection management,
2663   which includes maintaining the state of current connections,
2664   establishing a new connection or reusing an existing connection,
2665   processing messages received on a connection, detecting connection
2666   failures, and closing each connection.
2667   Most clients maintain multiple connections in parallel, including
2668   more than one connection per server endpoint.
2669   Most servers are designed to maintain thousands of concurrent connections,
2670   while controlling request queues to enable fair use and detect
2671   denial of service attacks.
2672</t>
2673
2674<section title="Connection" anchor="header.connection">
2675  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2676  <iref primary="true" item="close" x:for-anchor=""/>
2677  <x:anchor-alias value="Connection"/>
2678  <x:anchor-alias value="connection-option"/>
2679  <x:anchor-alias value="close"/>
2680<t>
2681   The "Connection" header field allows the sender to indicate desired
2682   control options for the current connection.  In order to avoid confusing
2683   downstream recipients, a proxy or gateway &MUST; remove or replace any
2684   received connection options before forwarding the message.
2685</t>
2686<t>
2687   When a header field is used to supply control information for or about
2688   the current connection, the sender &SHOULD; list the corresponding
2689   field-name within the "Connection" header field.
2690   A proxy or gateway &MUST; parse a received Connection
2691   header field before a message is forwarded and, for each
2692   connection-option in this field, remove any header field(s) from
2693   the message with the same name as the connection-option, and then
2694   remove the Connection header field itself (or replace it with the
2695   intermediary's own connection options for the forwarded message).
2696</t>
2697<t>
2698   Hence, the Connection header field provides a declarative way of
2699   distinguishing header fields that are only intended for the
2700   immediate recipient ("hop-by-hop") from those fields that are
2701   intended for all recipients on the chain ("end-to-end"), enabling the
2702   message to be self-descriptive and allowing future connection-specific
2703   extensions to be deployed without fear that they will be blindly
2704   forwarded by older intermediaries.
2705</t>
2706<t>
2707   The Connection header field's value has the following grammar:
2708</t>
2709<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-option"/>
2710  <x:ref>Connection</x:ref>        = 1#<x:ref>connection-option</x:ref>
2711  <x:ref>connection-option</x:ref> = <x:ref>token</x:ref>
2712</artwork></figure>
2713<t>
2714   Connection options are case-insensitive.
2715</t>
2716<t>
2717   A sender &MUST-NOT; include field-names in the Connection header
2718   field-value for fields that are defined as expressing constraints
2719   for all recipients in the request or response chain, such as the
2720   Cache-Control header field (&header-cache-control;).
2721</t>
2722<t>
2723   The connection options do not have to correspond to a header field
2724   present in the message, since a connection-specific header field
2725   might not be needed if there are no parameters associated with that
2726   connection option.  Recipients that trigger certain connection
2727   behavior based on the presence of connection options &MUST; do so
2728   based on the presence of the connection-option rather than only the
2729   presence of the optional header field.  In other words, if the
2730   connection option is received as a header field but not indicated
2731   within the Connection field-value, then the recipient &MUST; ignore
2732   the connection-specific header field because it has likely been
2733   forwarded by an intermediary that is only partially conformant.
2734</t>
2735<t>
2736   When defining new connection options, specifications ought to
2737   carefully consider existing deployed header fields and ensure
2738   that the new connection option does not share the same name as
2739   an unrelated header field that might already be deployed.
2740   Defining a new connection option essentially reserves that potential
2741   field-name for carrying additional information related to the
2742   connection option, since it would be unwise for senders to use
2743   that field-name for anything else.
2744</t>
2745<t>
2746   The "<x:dfn>close</x:dfn>" connection option is defined for a
2747   sender to signal that this connection will be closed after completion of
2748   the response. For example,
2749</t>
2750<figure><artwork type="example">
2751  Connection: close
2752</artwork></figure>
2753<t>
2754   in either the request or the response header fields indicates that
2755   the connection &SHOULD; be closed after the current request/response
2756   is complete (<xref target="persistent.tear-down"/>).
2757</t>
2758<t>
2759   A client that does not support persistent connections &MUST;
2760   send the "close" connection option in every request message.
2761</t>
2762<t>
2763   A server that does not support persistent connections &MUST;
2764   send the "close" connection option in every response message that
2765   does not have a <x:ref>1xx (Informational)</x:ref> status code.
2766</t>
2767</section>
2768
2769<section title="Persistent Connections" anchor="persistent.connections">
2770  <x:anchor-alias value="persistent connections"/>
2771<t>
2772   HTTP was originally designed to use a separate connection for each
2773   request/response pair. As the Web evolved and embedded requests became
2774   common for inline images, the connection establishment overhead was
2775   a significant drain on performance and a concern for Internet congestion.
2776   Message framing (via <x:ref>Content-Length</x:ref>) and optional
2777   long-lived connections (via Keep-Alive) were added to HTTP/1.0 in order
2778   to improve performance for some requests. However, these extensions were
2779   insufficient for dynamically generated responses and difficult to use
2780   with intermediaries.
2781</t>
2782<t>
2783   HTTP/1.1 defaults to the use of "<x:ref>persistent connections</x:ref>",
2784   which allow multiple requests and responses to be carried over a single
2785   connection. The "<x:ref>close</x:ref>" connection-option is used to
2786   signal that a connection will close after the current request/response.
2787   Persistent connections have a number of advantages:
2788  <list style="symbols">
2789      <t>
2790        By opening and closing fewer connections, CPU time is saved
2791        in routers and hosts (clients, servers, proxies, gateways,
2792        tunnels, or caches), and memory used for protocol control
2793        blocks can be saved in hosts.
2794      </t>
2795      <t>
2796        Most requests and responses can be pipelined on a connection.
2797        Pipelining allows a client to make multiple requests without
2798        waiting for each response, allowing a single connection to
2799        be used much more efficiently and with less overall latency.
2800      </t>
2801      <t>
2802        For TCP connections, network congestion is reduced by eliminating the
2803        packets associated with the three way handshake and graceful close
2804        procedures, and by allowing sufficient time to determine the
2805        congestion state of the network.
2806      </t>
2807      <t>
2808        Latency on subsequent requests is reduced since there is no time
2809        spent in the connection opening handshake.
2810      </t>
2811      <t>
2812        HTTP can evolve more gracefully, since most errors can be reported
2813        without the penalty of closing the connection. Clients using
2814        future versions of HTTP might optimistically try a new feature,
2815        but if communicating with an older server, retry with old
2816        semantics after an error is reported.
2817      </t>
2818    </list>
2819</t>
2820<t>
2821   HTTP implementations &SHOULD; implement persistent connections.
2822</t>
2823   
2824<section title="Establishment" anchor="persistent.establishment">
2825<t>
2826   It is beyond the scope of this specification to describe how connections
2827   are established via various transport or session-layer protocols.
2828   Each connection applies to only one transport link.
2829</t>
2830<t>
2831   A recipient determines whether a connection is persistent or not based on
2832   the most recently received message's protocol version and
2833   <x:ref>Connection</x:ref> header field (if any):
2834   <list style="symbols">
2835     <t>If the <x:ref>close</x:ref> connection option is present, the
2836        connection will not persist after the current response; else,</t>
2837     <t>If the received protocol is HTTP/1.1 (or later), the connection will
2838        persist after the current response; else,</t>
2839     <t>If the received protocol is HTTP/1.0, the "keep-alive"
2840        connection option is present, the recipient is not a proxy, and
2841        the recipient wishes to honor the HTTP/1.0 "keep-alive" mechanism,
2842        the connection will persist after the current response; otherwise,</t>
2843     <t>The connection will close after the current response.</t>
2844   </list>
2845</t>
2846<t>
2847   A proxy server &MUST-NOT; maintain a persistent connection with an
2848   HTTP/1.0 client (see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/> for
2849   information and discussion of the problems with the Keep-Alive header field
2850   implemented by many HTTP/1.0 clients).
2851</t>
2852</section>
2853
2854<section title="Reuse" anchor="persistent.reuse">
2855<t>
2856   In order to remain persistent, all messages on a connection &MUST;
2857   have a self-defined message length (i.e., one not defined by closure
2858   of the connection), as described in <xref target="message.body"/>.
2859</t>
2860<t>
2861   A server &MAY; assume that an HTTP/1.1 client intends to maintain a
2862   persistent connection until a <x:ref>close</x:ref> connection option
2863   is received in a request.
2864</t>
2865<t>
2866   A client &MAY; reuse a persistent connection until it sends or receives
2867   a <x:ref>close</x:ref> connection option or receives an HTTP/1.0 response
2868   without a "keep-alive" connection option.
2869</t>
2870<t>
2871   Clients and servers &SHOULD-NOT; assume that a persistent connection is
2872   maintained for HTTP versions less than 1.1 unless it is explicitly
2873   signaled.
2874   See <xref target="compatibility.with.http.1.0.persistent.connections"/>
2875   for more information on backward compatibility with HTTP/1.0 clients.
2876</t>
2877
2878<section title="Pipelining" anchor="pipelining">
2879<t>
2880   A client that supports persistent connections &MAY; "pipeline" its
2881   requests (i.e., send multiple requests without waiting for each
2882   response). A server &MUST; send its responses to those requests in the
2883   same order that the requests were received.
2884</t>
2885<t>
2886   Clients which assume persistent connections and pipeline immediately
2887   after connection establishment &SHOULD; be prepared to retry their
2888   connection if the first pipelined attempt fails. If a client does
2889   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2890   persistent. Clients &MUST; also be prepared to resend their requests if
2891   the server closes the connection before sending all of the
2892   corresponding responses.
2893</t>
2894<t>
2895   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods
2896   or non-idempotent sequences of request methods (see &idempotent-methods;).
2897   Otherwise, a premature termination of the transport connection could lead
2898   to indeterminate results. A client wishing to send a non-idempotent
2899   request &SHOULD; wait to send that request until it has received the
2900   response status line for the previous request.
2901</t>
2902</section>
2903
2904<section title="Retrying Requests" anchor="persistent.retrying.requests">
2905<t>
2906   Senders can close the transport connection at any time. Therefore,
2907   clients, servers, and proxies &MUST; be able to recover
2908   from asynchronous close events. Client software &MAY; reopen the
2909   transport connection and retransmit the aborted sequence of requests
2910   without user interaction so long as the request sequence is
2911   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2912   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2913   human operator the choice of retrying the request(s). Confirmation by
2914   user-agent software with semantic understanding of the application
2915   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2916   be repeated if the second sequence of requests fails.
2917</t>
2918</section>
2919</section>
2920   
2921<section title="Concurrency" anchor="persistent.concurrency">
2922<t>
2923   Clients &SHOULD; limit the number of simultaneous
2924   connections that they maintain to a given server.
2925</t>
2926<t>
2927   Previous revisions of HTTP gave a specific number of connections as a
2928   ceiling, but this was found to be impractical for many applications. As a
2929   result, this specification does not mandate a particular maximum number of
2930   connections, but instead encourages clients to be conservative when opening
2931   multiple connections.
2932</t>
2933<t>
2934   Multiple connections are typically used to avoid the "head-of-line
2935   blocking" problem, wherein a request that takes significant server-side
2936   processing and/or has a large payload blocks subsequent requests on the
2937   same connection. However, each connection consumes server resources.
2938   Furthermore, using multiple connections can cause undesirable side effects
2939   in congested networks.
2940</t>
2941<t>
2942   Note that servers might reject traffic that they deem abusive, including an
2943   excessive number of connections from a client.
2944</t>
2945</section>
2946
2947<section title="Failures and Time-outs" anchor="persistent.failures">
2948<t>
2949   Servers will usually have some time-out value beyond which they will
2950   no longer maintain an inactive connection. Proxy servers might make
2951   this a higher value since it is likely that the client will be making
2952   more connections through the same server. The use of persistent
2953   connections places no requirements on the length (or existence) of
2954   this time-out for either the client or the server.
2955</t>
2956<t>
2957   When a client or server wishes to time-out it &SHOULD; issue a graceful
2958   close on the transport connection. Clients and servers &SHOULD; both
2959   constantly watch for the other side of the transport close, and
2960   respond to it as appropriate. If a client or server does not detect
2961   the other side's close promptly it could cause unnecessary resource
2962   drain on the network.
2963</t>
2964<t>
2965   A client, server, or proxy &MAY; close the transport connection at any
2966   time. For example, a client might have started to send a new request
2967   at the same time that the server has decided to close the "idle"
2968   connection. From the server's point of view, the connection is being
2969   closed while it was idle, but from the client's point of view, a
2970   request is in progress.
2971</t>
2972<t>
2973   Servers &SHOULD; maintain persistent connections and allow the underlying
2974   transport's flow control mechanisms to resolve temporary overloads, rather
2975   than terminate connections with the expectation that clients will retry.
2976   The latter technique can exacerbate network congestion.
2977</t>
2978<t>
2979   A client sending a message body &SHOULD; monitor
2980   the network connection for an error status code while it is transmitting
2981   the request. If the client sees an error status code, it &SHOULD;
2982   immediately cease transmitting the body and close the connection.
2983</t>
2984</section>
2985   
2986<section title="Tear-down" anchor="persistent.tear-down">
2987  <iref primary="false" item="Connection header field" x:for-anchor=""/>
2988  <iref primary="false" item="close" x:for-anchor=""/>
2989<t>
2990   The <x:ref>Connection</x:ref> header field
2991   (<xref target="header.connection"/>) provides a "<x:ref>close</x:ref>"
2992   connection option that a sender &SHOULD; send when it wishes to close
2993   the connection after the current request/response pair.
2994</t>
2995<t>
2996   A client that sends a <x:ref>close</x:ref> connection option &MUST-NOT;
2997   send further requests on that connection (after the one containing
2998   <x:ref>close</x:ref>) and &MUST; close the connection after reading the
2999   final response message corresponding to this request.
3000</t>
3001<t>
3002   A server that receives a <x:ref>close</x:ref> connection option &MUST;
3003   initiate a lingering close of the connection after it sends the final
3004   response to the request that contained <x:ref>close</x:ref>.
3005   The server &SHOULD; include a <x:ref>close</x:ref> connection option
3006   in its final response on that connection. The server &MUST-NOT; process
3007   any further requests received on that connection.
3008</t>
3009<t>
3010   A server that sends a <x:ref>close</x:ref> connection option &MUST;
3011   initiate a lingering close of the connection after it sends the
3012   response containing <x:ref>close</x:ref>. The server &MUST-NOT; process
3013   any further requests received on that connection.
3014</t>
3015<t>
3016   A client that receives a <x:ref>close</x:ref> connection option &MUST;
3017   cease sending requests on that connection and close the connection
3018   after reading the response message containing the close; if additional
3019   pipelined requests had been sent on the connection, the client &SHOULD;
3020   assume that they will not be processed by the server.
3021</t>
3022<t>
3023   If a server performs an immediate close of a TCP connection, there is a
3024   significant risk that the client will not be able to read the last HTTP
3025   response.  If the server receives additional data from the client on a
3026   fully-closed connection, such as another request that was sent by the
3027   client before receiving the server's response, the server's TCP stack will
3028   send a reset packet to the client; unfortunately, the reset packet might
3029   erase the client's unacknowledged input buffers before they can be read
3030   and interpreted by the client's HTTP parser.
3031</t>
3032<t>
3033   To avoid the TCP reset problem, a server can perform a lingering close on a
3034   connection by closing only the write side of the read/write connection
3035   (a half-close) and continuing to read from the connection until the
3036   connection is closed by the client or the server is reasonably certain
3037   that its own TCP stack has received the client's acknowledgement of the
3038   packet(s) containing the server's last response. It is then safe for the
3039   server to fully close the connection.
3040</t>
3041<t>
3042   It is unknown whether the reset problem is exclusive to TCP or might also
3043   be found in other transport connection protocols.
3044</t>
3045</section>
3046</section>
3047
3048<section title="Upgrade" anchor="header.upgrade">
3049  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3050  <x:anchor-alias value="Upgrade"/>
3051  <x:anchor-alias value="protocol"/>
3052  <x:anchor-alias value="protocol-name"/>
3053  <x:anchor-alias value="protocol-version"/>
3054<t>
3055   The "Upgrade" header field is intended to provide a simple mechanism
3056   for transitioning from HTTP/1.1 to some other protocol on the same
3057   connection.  A client &MAY; send a list of protocols in the Upgrade
3058   header field of a request to invite the server to switch to one or
3059   more of those protocols before sending the final response.
3060   A server &MUST; send an Upgrade header field in <x:ref>101 (Switching
3061   Protocols)</x:ref> responses to indicate which protocol(s) are being
3062   switched to, and &MUST; send it in <x:ref>426 (Upgrade Required)</x:ref>
3063   responses to indicate acceptable protocols.
3064   A server &MAY; send an Upgrade header field in any other response to
3065   indicate that they might be willing to upgrade to one of the
3066   specified protocols for a future request.
3067</t>
3068<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3069  <x:ref>Upgrade</x:ref>          = 1#<x:ref>protocol</x:ref>
3070
3071  <x:ref>protocol</x:ref>         = <x:ref>protocol-name</x:ref> ["/" <x:ref>protocol-version</x:ref>]
3072  <x:ref>protocol-name</x:ref>    = <x:ref>token</x:ref>
3073  <x:ref>protocol-version</x:ref> = <x:ref>token</x:ref>
3074</artwork></figure>
3075<t>
3076   For example,
3077</t>
3078<figure><artwork type="example">
3079  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3080</artwork></figure>
3081<t>
3082   Upgrade eases the difficult transition between incompatible protocols by
3083   allowing the client to initiate a request in the more commonly
3084   supported protocol while indicating to the server that it would like
3085   to use a "better" protocol if available (where "better" is determined
3086   by the server, possibly according to the nature of the request method
3087   or target resource).
3088</t>
3089<t>
3090   Upgrade cannot be used to insist on a protocol change; its acceptance and
3091   use by the server is optional. The capabilities and nature of the
3092   application-level communication after the protocol change is entirely
3093   dependent upon the new protocol chosen, although the first action
3094   after changing the protocol &MUST; be a response to the initial HTTP
3095   request that contained the Upgrade header field.
3096</t>
3097<t>
3098   For example, if the Upgrade header field is received in a GET request
3099   and the server decides to switch protocols, then it &MUST; first respond
3100   with a <x:ref>101 (Switching Protocols)</x:ref> message in HTTP/1.1 and
3101   then immediately follow that with the new protocol's equivalent of a
3102   response to a GET on the target resource.  This allows a connection to be
3103   upgraded to protocols with the same semantics as HTTP without the
3104   latency cost of an additional round-trip.  A server &MUST-NOT; switch
3105   protocols unless the received message semantics can be honored by the new
3106   protocol; an OPTIONS request can be honored by any protocol.
3107</t>
3108<t>
3109   When Upgrade is sent, a sender &MUST; also send a
3110   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>)
3111   that contains the "upgrade" connection option, in order to prevent Upgrade
3112   from being accidentally forwarded by intermediaries that might not implement
3113   the listed protocols.  A server &MUST; ignore an Upgrade header field that
3114   is received in an HTTP/1.0 request.
3115</t>
3116<t>
3117   The Upgrade header field only applies to switching application-level
3118   protocols on the existing connection; it cannot be used
3119   to switch to a protocol on a different connection. For that purpose, it is
3120   more appropriate to use a <x:ref>3xx (Redirection)</x:ref> response
3121   (&status-3xx;).
3122</t>
3123<t>
3124   This specification only defines the protocol name "HTTP" for use by
3125   the family of Hypertext Transfer Protocols, as defined by the HTTP
3126   version rules of <xref target="http.version"/> and future updates to this
3127   specification. Additional tokens can be registered with IANA using the
3128   registration procedure defined in <xref target="upgrade.token.registry"/>.
3129</t>
3130</section>
3131</section>
3132
3133<section title="IANA Considerations" anchor="IANA.considerations">
3134
3135<section title="Header Field Registration" anchor="header.field.registration">
3136<t>
3137   HTTP header fields are registered within the Message Header Field Registry
3138   <xref target="RFC3864"/> maintained by IANA at
3139   <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/>.
3140</t>
3141<t>
3142   This document defines the following HTTP header fields, so their
3143   associated registry entries shall be updated according to the permanent
3144   registrations below:
3145</t>
3146<?BEGININC p1-messaging.iana-headers ?>
3147<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3148<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3149   <ttcol>Header Field Name</ttcol>
3150   <ttcol>Protocol</ttcol>
3151   <ttcol>Status</ttcol>
3152   <ttcol>Reference</ttcol>
3153
3154   <c>Connection</c>
3155   <c>http</c>
3156   <c>standard</c>
3157   <c>
3158      <xref target="header.connection"/>
3159   </c>
3160   <c>Content-Length</c>
3161   <c>http</c>
3162   <c>standard</c>
3163   <c>
3164      <xref target="header.content-length"/>
3165   </c>
3166   <c>Host</c>
3167   <c>http</c>
3168   <c>standard</c>
3169   <c>
3170      <xref target="header.host"/>
3171   </c>
3172   <c>TE</c>
3173   <c>http</c>
3174   <c>standard</c>
3175   <c>
3176      <xref target="header.te"/>
3177   </c>
3178   <c>Trailer</c>
3179   <c>http</c>
3180   <c>standard</c>
3181   <c>
3182      <xref target="header.trailer"/>
3183   </c>
3184   <c>Transfer-Encoding</c>
3185   <c>http</c>
3186   <c>standard</c>
3187   <c>
3188      <xref target="header.transfer-encoding"/>
3189   </c>
3190   <c>Upgrade</c>
3191   <c>http</c>
3192   <c>standard</c>
3193   <c>
3194      <xref target="header.upgrade"/>
3195   </c>
3196   <c>Via</c>
3197   <c>http</c>
3198   <c>standard</c>
3199   <c>
3200      <xref target="header.via"/>
3201   </c>
3202</texttable>
3203<!--(END)-->
3204<?ENDINC p1-messaging.iana-headers ?>
3205<t>
3206   Furthermore, the header field-name "Close" shall be registered as
3207   "reserved", since using that name as an HTTP header field might
3208   conflict with the "close" connection option of the "<x:ref>Connection</x:ref>"
3209   header field (<xref target="header.connection"/>).
3210</t>
3211<texttable align="left" suppress-title="true">
3212   <ttcol>Header Field Name</ttcol>
3213   <ttcol>Protocol</ttcol>
3214   <ttcol>Status</ttcol>
3215   <ttcol>Reference</ttcol>
3216
3217   <c>Close</c>
3218   <c>http</c>
3219   <c>reserved</c>
3220   <c>
3221      <xref target="header.field.registration"/>
3222   </c>
3223</texttable>
3224<t>
3225   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3226</t>
3227</section>
3228
3229<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3230<t>
3231   IANA maintains the registry of URI Schemes <xref target="RFC4395"/> at
3232   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>.
3233</t>
3234<t>
3235   This document defines the following URI schemes, so their
3236   associated registry entries shall be updated according to the permanent
3237   registrations below:
3238</t>
3239<texttable align="left" suppress-title="true">
3240   <ttcol>URI Scheme</ttcol>
3241   <ttcol>Description</ttcol>
3242   <ttcol>Reference</ttcol>
3243
3244   <c>http</c>
3245   <c>Hypertext Transfer Protocol</c>
3246   <c><xref target="http.uri"/></c>
3247
3248   <c>https</c>
3249   <c>Hypertext Transfer Protocol Secure</c>
3250   <c><xref target="https.uri"/></c>
3251</texttable>
3252</section>
3253
3254<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3255<t>
3256   This document serves as the specification for the Internet media types
3257   "message/http" and "application/http". The following is to be registered with
3258   IANA (see <xref target="RFC4288"/>).
3259</t>
3260<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3261<iref item="Media Type" subitem="message/http" primary="true"/>
3262<iref item="message/http Media Type" primary="true"/>
3263<t>
3264   The message/http type can be used to enclose a single HTTP request or
3265   response message, provided that it obeys the MIME restrictions for all
3266   "message" types regarding line length and encodings.
3267</t>
3268<t>
3269  <list style="hanging" x:indent="12em">
3270    <t hangText="Type name:">
3271      message
3272    </t>
3273    <t hangText="Subtype name:">
3274      http
3275    </t>
3276    <t hangText="Required parameters:">
3277      none
3278    </t>
3279    <t hangText="Optional parameters:">
3280      version, msgtype
3281      <list style="hanging">
3282        <t hangText="version:">
3283          The HTTP-version number of the enclosed message
3284          (e.g., "1.1"). If not present, the version can be
3285          determined from the first line of the body.
3286        </t>
3287        <t hangText="msgtype:">
3288          The message type &mdash; "request" or "response". If not
3289          present, the type can be determined from the first
3290          line of the body.
3291        </t>
3292      </list>
3293    </t>
3294    <t hangText="Encoding considerations:">
3295      only "7bit", "8bit", or "binary" are permitted
3296    </t>
3297    <t hangText="Security considerations:">
3298      none
3299    </t>
3300    <t hangText="Interoperability considerations:">
3301      none
3302    </t>
3303    <t hangText="Published specification:">
3304      This specification (see <xref target="internet.media.type.message.http"/>).
3305    </t>
3306    <t hangText="Applications that use this media type:">
3307    </t>
3308    <t hangText="Additional information:">
3309      <list style="hanging">
3310        <t hangText="Magic number(s):">none</t>
3311        <t hangText="File extension(s):">none</t>
3312        <t hangText="Macintosh file type code(s):">none</t>
3313      </list>
3314    </t>
3315    <t hangText="Person and email address to contact for further information:">
3316      See Authors Section.
3317    </t>
3318    <t hangText="Intended usage:">
3319      COMMON
3320    </t>
3321    <t hangText="Restrictions on usage:">
3322      none
3323    </t>
3324    <t hangText="Author/Change controller:">
3325      IESG
3326    </t>
3327  </list>
3328</t>
3329</section>
3330<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3331<iref item="Media Type" subitem="application/http" primary="true"/>
3332<iref item="application/http Media Type" primary="true"/>
3333<t>
3334   The application/http type can be used to enclose a pipeline of one or more
3335   HTTP request or response messages (not intermixed).
3336</t>
3337<t>
3338  <list style="hanging" x:indent="12em">
3339    <t hangText="Type name:">
3340      application
3341    </t>
3342    <t hangText="Subtype name:">
3343      http
3344    </t>
3345    <t hangText="Required parameters:">
3346      none
3347    </t>
3348    <t hangText="Optional parameters:">
3349      version, msgtype
3350      <list style="hanging">
3351        <t hangText="version:">
3352          The HTTP-version number of the enclosed messages
3353          (e.g., "1.1"). If not present, the version can be
3354          determined from the first line of the body.
3355        </t>
3356        <t hangText="msgtype:">
3357          The message type &mdash; "request" or "response". If not
3358          present, the type can be determined from the first
3359          line of the body.
3360        </t>
3361      </list>
3362    </t>
3363    <t hangText="Encoding considerations:">
3364      HTTP messages enclosed by this type
3365      are in "binary" format; use of an appropriate
3366      Content-Transfer-Encoding is required when
3367      transmitted via E-mail.
3368    </t>
3369    <t hangText="Security considerations:">
3370      none
3371    </t>
3372    <t hangText="Interoperability considerations:">
3373      none
3374    </t>
3375    <t hangText="Published specification:">
3376      This specification (see <xref target="internet.media.type.application.http"/>).
3377    </t>
3378    <t hangText="Applications that use this media type:">
3379    </t>
3380    <t hangText="Additional information:">
3381      <list style="hanging">
3382        <t hangText="Magic number(s):">none</t>
3383        <t hangText="File extension(s):">none</t>
3384        <t hangText="Macintosh file type code(s):">none</t>
3385      </list>
3386    </t>
3387    <t hangText="Person and email address to contact for further information:">
3388      See Authors Section.
3389    </t>
3390    <t hangText="Intended usage:">
3391      COMMON
3392    </t>
3393    <t hangText="Restrictions on usage:">
3394      none
3395    </t>
3396    <t hangText="Author/Change controller:">
3397      IESG
3398    </t>
3399  </list>
3400</t>
3401</section>
3402</section>
3403
3404<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
3405<t>
3406   The HTTP Transfer Coding Registry defines the name space for transfer
3407   coding names.
3408</t>
3409<t>
3410   Registrations &MUST; include the following fields:
3411   <list style="symbols">
3412     <t>Name</t>
3413     <t>Description</t>
3414     <t>Pointer to specification text</t>
3415   </list>
3416</t>
3417<t>
3418   Names of transfer codings &MUST-NOT; overlap with names of content codings
3419   (&content-codings;) unless the encoding transformation is identical, as
3420   is the case for the compression codings defined in
3421   <xref target="compression.codings"/>.
3422</t>
3423<t>
3424   Values to be added to this name space require IETF Review (see
3425   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
3426   conform to the purpose of transfer coding defined in this section.
3427   Use of program names for the identification of encoding formats
3428   is not desirable and is discouraged for future encodings.
3429</t>
3430<t>
3431   The registry itself is maintained at
3432   <eref target="http://www.iana.org/assignments/http-parameters"/>.
3433</t>
3434</section>
3435
3436<section title="Transfer Coding Registrations" anchor="transfer.coding.registration">
3437<t>
3438   The HTTP Transfer Coding Registry shall be updated with the registrations
3439   below:
3440</t>
3441<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3442   <ttcol>Name</ttcol>
3443   <ttcol>Description</ttcol>
3444   <ttcol>Reference</ttcol>
3445   <c>chunked</c>
3446   <c>Transfer in a series of chunks</c>
3447   <c>
3448      <xref target="chunked.encoding"/>
3449   </c>
3450   <c>compress</c>
3451   <c>UNIX "compress" program method</c>
3452   <c>
3453      <xref target="compress.coding"/>
3454   </c>
3455   <c>deflate</c>
3456   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3457   the "zlib" data format (<xref target="RFC1950"/>)
3458   </c>
3459   <c>
3460      <xref target="deflate.coding"/>
3461   </c>
3462   <c>gzip</c>
3463   <c>Same as GNU zip <xref target="RFC1952"/></c>
3464   <c>
3465      <xref target="gzip.coding"/>
3466   </c>
3467</texttable>
3468</section>
3469
3470<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3471<t>
3472   The HTTP Upgrade Token Registry defines the name space for protocol-name
3473   tokens used to identify protocols in the <x:ref>Upgrade</x:ref> header
3474   field. Each registered protocol name is associated with contact information
3475   and an optional set of specifications that details how the connection
3476   will be processed after it has been upgraded.
3477</t>
3478<t>
3479   Registrations happen on a "First Come First Served" basis (see
3480   <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>) and are subject to the
3481   following rules:
3482  <list style="numbers">
3483    <t>A protocol-name token, once registered, stays registered forever.</t>
3484    <t>The registration &MUST; name a responsible party for the
3485       registration.</t>
3486    <t>The registration &MUST; name a point of contact.</t>
3487    <t>The registration &MAY; name a set of specifications associated with
3488       that token. Such specifications need not be publicly available.</t>
3489    <t>The registration &SHOULD; name a set of expected "protocol-version"
3490       tokens associated with that token at the time of registration.</t>
3491    <t>The responsible party &MAY; change the registration at any time.
3492       The IANA will keep a record of all such changes, and make them
3493       available upon request.</t>
3494    <t>The IESG &MAY; reassign responsibility for a protocol token.
3495       This will normally only be used in the case when a
3496       responsible party cannot be contacted.</t>
3497  </list>
3498</t>
3499<t>
3500   This registration procedure for HTTP Upgrade Tokens replaces that
3501   previously defined in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
3502</t>
3503</section>
3504
3505<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3506<t>
3507   The HTTP Upgrade Token Registry shall be updated with the registration
3508   below:
3509</t>
3510<texttable align="left" suppress-title="true">
3511   <ttcol>Value</ttcol>
3512   <ttcol>Description</ttcol>
3513   <ttcol>Expected Version Tokens</ttcol>
3514   <ttcol>Reference</ttcol>
3515
3516   <c>HTTP</c>
3517   <c>Hypertext Transfer Protocol</c>
3518   <c>any DIGIT.DIGIT (e.g, "2.0")</c>
3519   <c><xref target="http.version"/></c>
3520</texttable>
3521<t>
3522   The responsible party is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3523</t>
3524</section>
3525
3526</section>
3527
3528<section title="Security Considerations" anchor="security.considerations">
3529<t>
3530   This section is meant to inform application developers, information
3531   providers, and users of the security limitations in HTTP/1.1 as
3532   described by this document. The discussion does not include
3533   definitive solutions to the problems revealed, though it does make
3534   some suggestions for reducing security risks.
3535</t>
3536
3537<section title="Personal Information" anchor="personal.information">
3538<t>
3539   HTTP clients are often privy to large amounts of personal information,
3540   including both information provided by the user to interact with resources
3541   (e.g., the user's name, location, mail address, passwords, encryption
3542   keys, etc.) and information about the user's browsing activity over
3543   time (e.g., history, bookmarks, etc.). HTTP implementations need to
3544   prevent unintentional leakage of this information.
3545</t>
3546</section>
3547
3548<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3549<t>
3550   A server is in the position to save personal data about a user's
3551   requests which might identify their reading patterns or subjects of
3552   interest.  In particular, log information gathered at an intermediary
3553   often contains a history of user agent interaction, across a multitude
3554   of sites, that can be traced to individual users.
3555</t>
3556<t>
3557   HTTP log information is confidential in nature; its handling is often
3558   constrained by laws and regulations.  Log information needs to be securely
3559   stored and appropriate guidelines followed for its analysis.
3560   Anonymization of personal information within individual entries helps,
3561   but is generally not sufficient to prevent real log traces from being
3562   re-identified based on correlation with other access characteristics.
3563   As such, access traces that are keyed to a specific client should not
3564   be published even if the key is pseudonymous.
3565</t>
3566<t>
3567   To minimize the risk of theft or accidental publication, log information
3568   should be purged of personally identifiable information, including
3569   user identifiers, IP addresses, and user-provided query parameters,
3570   as soon as that information is no longer necessary to support operational
3571   needs for security, auditing, or fraud control.
3572</t>
3573</section>
3574
3575<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3576<t>
3577   Origin servers &SHOULD; be careful to restrict
3578   the documents returned by HTTP requests to be only those that were
3579   intended by the server administrators. If an HTTP server translates
3580   HTTP URIs directly into file system calls, the server &MUST; take
3581   special care not to serve files that were not intended to be
3582   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3583   other operating systems use ".." as a path component to indicate a
3584   directory level above the current one. On such a system, an HTTP
3585   server &MUST; disallow any such construct in the request-target if it
3586   would otherwise allow access to a resource outside those intended to
3587   be accessible via the HTTP server. Similarly, files intended for
3588   reference only internally to the server (such as access control
3589   files, configuration files, and script code) &MUST; be protected from
3590   inappropriate retrieval, since they might contain sensitive
3591   information.
3592</t>
3593</section>
3594
3595<section title="DNS-related Attacks" anchor="dns.related.attacks">
3596<t>
3597   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
3598   generally prone to security attacks based on the deliberate misassociation
3599   of IP addresses and DNS names not protected by DNSSec. Clients need to be
3600   cautious in assuming the validity of an IP number/DNS name association unless
3601   the response is protected by DNSSec (<xref target="RFC4033"/>).
3602</t>
3603</section>
3604
3605<section title="Intermediaries and Caching" anchor="attack.intermediaries">
3606<t>
3607   By their very nature, HTTP intermediaries are men-in-the-middle, and
3608   represent an opportunity for man-in-the-middle attacks. Compromise of
3609   the systems on which the intermediaries run can result in serious security
3610   and privacy problems. Intermediaries have access to security-related
3611   information, personal information about individual users and
3612   organizations, and proprietary information belonging to users and
3613   content providers. A compromised intermediary, or an intermediary
3614   implemented or configured without regard to security and privacy
3615   considerations, might be used in the commission of a wide range of
3616   potential attacks.
3617</t>
3618<t>
3619   Intermediaries that contain a shared cache are especially vulnerable
3620   to cache poisoning attacks.
3621</t>
3622<t>
3623   Implementers need to consider the privacy and security
3624   implications of their design and coding decisions, and of the
3625   configuration options they provide to operators (especially the
3626   default configuration).
3627</t>
3628<t>
3629   Users need to be aware that intermediaries are no more trustworthy than
3630   the people who run them; HTTP itself cannot solve this problem.
3631</t>
3632</section>
3633
3634<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
3635<t>
3636   Because HTTP uses mostly textual, character-delimited fields, attackers can
3637   overflow buffers in implementations, and/or perform a Denial of Service
3638   against implementations that accept fields with unlimited lengths.
3639</t>
3640<t>
3641   To promote interoperability, this specification makes specific
3642   recommendations for minimum size limits on request-line
3643   (<xref target="request.line"/>)
3644   and blocks of header fields (<xref target="header.fields"/>). These are
3645   minimum recommendations, chosen to be supportable even by implementations
3646   with limited resources; it is expected that most implementations will
3647   choose substantially higher limits.
3648</t>
3649<t>
3650   This specification also provides a way for servers to reject messages that
3651   have request-targets that are too long (&status-414;) or request entities
3652   that are too large (&status-4xx;).
3653</t>
3654<t>
3655   Recipients &SHOULD; carefully limit the extent to which they read other
3656   fields, including (but not limited to) request methods, response status
3657   phrases, header field-names, and body chunks, so as to avoid denial of
3658   service attacks without impeding interoperability.
3659</t>
3660</section>
3661</section>
3662
3663<section title="Acknowledgments" anchor="acks">
3664<t>
3665   This edition of HTTP builds on the many contributions that went into
3666   <xref target="RFC1945" format="none">RFC 1945</xref>,
3667   <xref target="RFC2068" format="none">RFC 2068</xref>,
3668   <xref target="RFC2145" format="none">RFC 2145</xref>, and
3669   <xref target="RFC2616" format="none">RFC 2616</xref>, including
3670   substantial contributions made by the previous authors, editors, and
3671   working group chairs: Tim Berners-Lee, Ari Luotonen, Roy T. Fielding,
3672   Henrik Frystyk Nielsen, Jim Gettys, Jeffrey C. Mogul, Larry Masinter,
3673   Paul J. Leach, and Mark Nottingham.
3674   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for additional
3675   acknowledgements from prior revisions.
3676</t>
3677<t>
3678   Since 1999, the following contributors have helped improve the HTTP
3679   specification by reporting bugs, asking smart questions, drafting or
3680   reviewing text, and evaluating open issues:
3681</t>
3682<?BEGININC acks ?>
3683<t>Adam Barth,
3684Adam Roach,
3685Addison Phillips,
3686Adrian Chadd,
3687Adrien W. de Croy,
3688Alan Ford,
3689Alan Ruttenberg,
3690Albert Lunde,
3691Alek Storm,
3692Alex Rousskov,
3693Alexandre Morgaut,
3694Alexey Melnikov,
3695Alisha Smith,
3696Amichai Rothman,
3697Amit Klein,
3698Amos Jeffries,
3699Andreas Maier,
3700Andreas Petersson,
3701Anil Sharma,
3702Anne van Kesteren,
3703Anthony Bryan,
3704Asbjorn Ulsberg,
3705Balachander Krishnamurthy,
3706Barry Leiba,
3707Ben Laurie,
3708Benjamin Niven-Jenkins,
3709Bil Corry,
3710Bill Burke,
3711Bjoern Hoehrmann,
3712Bob Scheifler,
3713Boris Zbarsky,
3714Brett Slatkin,
3715Brian Kell,
3716Brian McBarron,
3717Brian Pane,
3718Brian Smith,
3719Bryce Nesbitt,
3720Cameron Heavon-Jones,
3721Carl Kugler,
3722Carsten Bormann,
3723Charles Fry,
3724Chris Newman,
3725Cyrus Daboo,
3726Dale Robert Anderson,
3727Dan Wing,
3728Dan Winship,
3729Daniel Stenberg,
3730Dave Cridland,
3731Dave Crocker,
3732Dave Kristol,
3733David Booth,
3734David Singer,
3735David W. Morris,
3736Diwakar Shetty,
3737Dmitry Kurochkin,
3738Drummond Reed,
3739Duane Wessels,
3740Edward Lee,
3741Eliot Lear,
3742Eran Hammer-Lahav,
3743Eric D. Williams,
3744Eric J. Bowman,
3745Eric Lawrence,
3746Eric Rescorla,
3747Erik Aronesty,
3748Evan Prodromou,
3749Florian Weimer,
3750Frank Ellermann,
3751Fred Bohle,
3752Gabriel Montenegro,
3753Geoffrey Sneddon,
3754Gervase Markham,
3755Grahame Grieve,
3756Greg Wilkins,
3757Harald Tveit Alvestrand,
3758Harry Halpin,
3759Helge Hess,
3760Henrik Nordstrom,
3761Henry S. Thompson,
3762Henry Story,
3763Herbert van de Sompel,
3764Howard Melman,
3765Hugo Haas,
3766Ian Fette,
3767Ian Hickson,
3768Ido Safruti,
3769Ingo Struck,
3770J. Ross Nicoll,
3771James H. Manger,
3772James Lacey,
3773James M. Snell,
3774Jamie Lokier,
3775Jan Algermissen,
3776Jeff Hodges (who came up with the term 'effective Request-URI'),
3777Jeff Walden,
3778Jim Luther,
3779Joe D. Williams,
3780Joe Gregorio,
3781Joe Orton,
3782John C. Klensin,
3783John C. Mallery,
3784John Cowan,
3785John Kemp,
3786John Panzer,
3787John Schneider,
3788John Stracke,
3789John Sullivan,
3790Jonas Sicking,
3791Jonathan Billington,
3792Jonathan Moore,
3793Jonathan Rees,
3794Jonathan Silvera,
3795Jordi Ros,
3796Joris Dobbelsteen,
3797Josh Cohen,
3798Julien Pierre,
3799Jungshik Shin,
3800Justin Chapweske,
3801Justin Erenkrantz,
3802Justin James,
3803Kalvinder Singh,
3804Karl Dubost,
3805Keith Hoffman,
3806Keith Moore,
3807Koen Holtman,
3808Konstantin Voronkov,
3809Kris Zyp,
3810Lisa Dusseault,
3811Maciej Stachowiak,
3812Marc Schneider,
3813Marc Slemko,
3814Mark Baker,
3815Mark Pauley,
3816Mark Watson,
3817Markus Isomaki,
3818Markus Lanthaler,
3819Martin J. Duerst,
3820Martin Musatov,
3821Martin Nilsson,
3822Martin Thomson,
3823Matt Lynch,
3824Matthew Cox,
3825Max Clark,
3826Michael Burrows,
3827Michael Hausenblas,
3828Mike Amundsen,
3829Mike Belshe,
3830Mike Kelly,
3831Mike Schinkel,
3832Miles Sabin,
3833Murray S. Kucherawy,
3834Mykyta Yevstifeyev,
3835Nathan Rixham,
3836Nicholas Shanks,
3837Nico Williams,
3838Nicolas Alvarez,
3839Nicolas Mailhot,
3840Noah Slater,
3841Pablo Castro,
3842Pat Hayes,
3843Patrick R. McManus,
3844Paul E. Jones,
3845Paul Hoffman,
3846Paul Marquess,
3847Peter Lepeska,
3848Peter Saint-Andre,
3849Peter Watkins,
3850Phil Archer,
3851Philippe Mougin,
3852Phillip Hallam-Baker,
3853Poul-Henning Kamp,
3854Preethi Natarajan,
3855Rajeev Bector,
3856Ray Polk,
3857Reto Bachmann-Gmuer,
3858Richard Cyganiak,
3859Robert Brewer,
3860Robert Collins,
3861Robert O'Callahan,
3862Robert Olofsson,
3863Robert Sayre,
3864Robert Siemer,
3865Robert de Wilde,
3866Roberto Javier Godoy,
3867Roberto Peon,
3868Ronny Widjaja,
3869S. Mike Dierken,
3870Salvatore Loreto,
3871Sam Johnston,
3872Sam Ruby,
3873Scott Lawrence (who maintained the original issues list),
3874Sean B. Palmer,
3875Shane McCarron,
3876Stefan Eissing,
3877Stefan Tilkov,
3878Stefanos Harhalakis,
3879Stephane Bortzmeyer,
3880Stephen Farrell,
3881Stephen Ludin,
3882Stuart Williams,
3883Subbu Allamaraju,
3884Sylvain Hellegouarch,
3885Tapan Divekar,
3886Tatsuya Hayashi,
3887Ted Hardie,
3888Thomas Broyer,
3889Thomas Nordin,
3890Thomas Roessler,
3891Tim Bray,
3892Tim Morgan,
3893Tim Olsen,
3894Tom Zhou,
3895Travis Snoozy,
3896Tyler Close,
3897Vincent Murphy,
3898Wenbo Zhu,
3899Werner Baumann,
3900Wilbur Streett,
3901Wilfredo Sanchez Vega,
3902William A. Rowe Jr.,
3903William Chan,
3904Willy Tarreau,
3905Xiaoshu Wang,
3906Yaron Goland,
3907Yngve Nysaeter Pettersen,
3908Yoav Nir,
3909Yogesh Bang,
3910Yutaka Oiwa,
3911Zed A. Shaw, and
3912Zhong Yu.
3913</t>
3914<?ENDINC acks ?>
3915</section>
3916
3917</middle>
3918<back>
3919
3920<references title="Normative References">
3921
3922<reference anchor="Part2">
3923  <front>
3924    <title>Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content</title>
3925    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3926      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3927      <address><email>fielding@gbiv.com</email></address>
3928    </author>
3929    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3930      <organization abbrev="W3C">World Wide Web Consortium</organization>
3931      <address><email>ylafon@w3.org</email></address>
3932    </author>
3933    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3934      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3935      <address><email>julian.reschke@greenbytes.de</email></address>
3936    </author>
3937    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3938  </front>
3939  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3940  <x:source href="p2-semantics.xml" basename="p2-semantics">
3941    <x:defines>1xx (Informational)</x:defines>
3942    <x:defines>1xx</x:defines>
3943    <x:defines>100 (Continue)</x:defines>
3944    <x:defines>101 (Switching Protocols)</x:defines>
3945    <x:defines>2xx (Successful)</x:defines>
3946    <x:defines>2xx</x:defines>
3947    <x:defines>200 (OK)</x:defines>
3948    <x:defines>204 (No Content)</x:defines>
3949    <x:defines>3xx (Redirection)</x:defines>
3950    <x:defines>3xx</x:defines>
3951    <x:defines>301 (Moved Permanently)</x:defines>
3952    <x:defines>4xx (Client Error)</x:defines>
3953    <x:defines>4xx</x:defines>
3954    <x:defines>400 (Bad Request)</x:defines>
3955    <x:defines>405 (Method Not Allowed)</x:defines>
3956    <x:defines>411 (Length Required)</x:defines>
3957    <x:defines>414 (URI Too Long)</x:defines>
3958    <x:defines>417 (Expectation Failed)</x:defines>
3959    <x:defines>426 (Upgrade Required)</x:defines>
3960    <x:defines>501 (Not Implemented)</x:defines>
3961    <x:defines>502 (Bad Gateway)</x:defines>
3962    <x:defines>505 (HTTP Version Not Supported)</x:defines>
3963    <x:defines>Allow</x:defines>
3964    <x:defines>Content-Encoding</x:defines>
3965    <x:defines>Content-Location</x:defines>
3966    <x:defines>Content-Type</x:defines>
3967    <x:defines>Date</x:defines>
3968    <x:defines>Expect</x:defines>
3969    <x:defines>Location</x:defines>
3970    <x:defines>Server</x:defines>
3971    <x:defines>User-Agent</x:defines>
3972  </x:source>
3973</reference>
3974
3975<reference anchor="Part4">
3976  <front>
3977    <title>Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests</title>
3978    <author fullname="Roy T. Fielding" initials="R." role="editor" surname="Fielding">
3979      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3980      <address><email>fielding@gbiv.com</email></address>
3981    </author>
3982    <author fullname="Yves Lafon" initials="Y." role="editor" surname="Lafon">
3983      <organization abbrev="W3C">World Wide Web Consortium</organization>
3984      <address><email>ylafon@w3.org</email></address>
3985    </author>
3986    <author fullname="Julian F. Reschke" initials="J. F." role="editor" surname="Reschke">
3987      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3988      <address><email>julian.reschke@greenbytes.de</email></address>
3989    </author>
3990    <date month="&ID-MONTH;" year="&ID-YEAR;" />
3991  </front>
3992  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;" />
3993  <x:source basename="p4-conditional" href="p4-conditional.xml">
3994    <x:defines>304 (Not Modified)</x:defines>
3995    <x:defines>ETag</x:defines>
3996    <x:defines>Last-Modified</x:defines>
3997  </x:source>
3998</reference>
3999
4000<reference anchor="Part5">
4001  <front>
4002    <title>Hypertext Transfer Protocol (HTTP/1.1): Range Requests</title>
4003    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4004      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4005      <address><email>fielding@gbiv.com</email></address>
4006    </author>
4007    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4008      <organization abbrev="W3C">World Wide Web Consortium</organization>
4009      <address><email>ylafon@w3.org</email></address>
4010    </author>
4011    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4012      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4013      <address><email>julian.reschke@greenbytes.de</email></address>
4014    </author>
4015    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4016  </front>
4017  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
4018  <x:source href="p5-range.xml" basename="p5-range">
4019    <x:defines>Content-Range</x:defines>
4020  </x:source>
4021</reference>
4022
4023<reference anchor="Part6">
4024  <front>
4025    <title>Hypertext Transfer Protocol (HTTP/1.1): Caching</title>
4026    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4027      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4028      <address><email>fielding@gbiv.com</email></address>
4029    </author>
4030    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4031      <organization abbrev="W3C">World Wide Web Consortium</organization>
4032      <address><email>ylafon@w3.org</email></address>
4033    </author>
4034    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4035      <address><email>mnot@mnot.net</email></address>
4036    </author>
4037    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4038      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4039      <address><email>julian.reschke@greenbytes.de</email></address>
4040    </author>
4041    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4042  </front>
4043  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4044  <x:source href="p6-cache.xml" basename="p6-cache">
4045    <x:defines>Expires</x:defines>
4046  </x:source>
4047</reference>
4048
4049<reference anchor="Part7">
4050  <front>
4051    <title>Hypertext Transfer Protocol (HTTP/1.1): Authentication</title>
4052    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4053      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4054      <address><email>fielding@gbiv.com</email></address>
4055    </author>
4056    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4057      <organization abbrev="W3C">World Wide Web Consortium</organization>
4058      <address><email>ylafon@w3.org</email></address>
4059    </author>
4060    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4061      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4062      <address><email>julian.reschke@greenbytes.de</email></address>
4063    </author>
4064    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4065  </front>
4066  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
4067  <x:source href="p7-auth.xml" basename="p7-auth">
4068    <x:defines>Proxy-Authenticate</x:defines>
4069    <x:defines>Proxy-Authorization</x:defines>
4070  </x:source>
4071</reference>
4072
4073<reference anchor="RFC5234">
4074  <front>
4075    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4076    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4077      <organization>Brandenburg InternetWorking</organization>
4078      <address>
4079        <email>dcrocker@bbiw.net</email>
4080      </address> 
4081    </author>
4082    <author initials="P." surname="Overell" fullname="Paul Overell">
4083      <organization>THUS plc.</organization>
4084      <address>
4085        <email>paul.overell@thus.net</email>
4086      </address>
4087    </author>
4088    <date month="January" year="2008"/>
4089  </front>
4090  <seriesInfo name="STD" value="68"/>
4091  <seriesInfo name="RFC" value="5234"/>
4092</reference>
4093
4094<reference anchor="RFC2119">
4095  <front>
4096    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4097    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4098      <organization>Harvard University</organization>
4099      <address><email>sob@harvard.edu</email></address>
4100    </author>
4101    <date month="March" year="1997"/>
4102  </front>
4103  <seriesInfo name="BCP" value="14"/>
4104  <seriesInfo name="RFC" value="2119"/>
4105</reference>
4106
4107<reference anchor="RFC3986">
4108 <front>
4109  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4110  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4111    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4112    <address>
4113       <email>timbl@w3.org</email>
4114       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4115    </address>
4116  </author>
4117  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4118    <organization abbrev="Day Software">Day Software</organization>
4119    <address>
4120      <email>fielding@gbiv.com</email>
4121      <uri>http://roy.gbiv.com/</uri>
4122    </address>
4123  </author>
4124  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4125    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4126    <address>
4127      <email>LMM@acm.org</email>
4128      <uri>http://larry.masinter.net/</uri>
4129    </address>
4130  </author>
4131  <date month='January' year='2005'></date>
4132 </front>
4133 <seriesInfo name="STD" value="66"/>
4134 <seriesInfo name="RFC" value="3986"/>
4135</reference>
4136
4137<reference anchor="USASCII">
4138  <front>
4139    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4140    <author>
4141      <organization>American National Standards Institute</organization>
4142    </author>
4143    <date year="1986"/>
4144  </front>
4145  <seriesInfo name="ANSI" value="X3.4"/>
4146</reference>
4147
4148<reference anchor="RFC1950">
4149  <front>
4150    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4151    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4152      <organization>Aladdin Enterprises</organization>
4153      <address><email>ghost@aladdin.com</email></address>
4154    </author>
4155    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4156    <date month="May" year="1996"/>
4157  </front>
4158  <seriesInfo name="RFC" value="1950"/>
4159  <!--<annotation>
4160    RFC 1950 is an Informational RFC, thus it might be less stable than
4161    this specification. On the other hand, this downward reference was
4162    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4163    therefore it is unlikely to cause problems in practice. See also
4164    <xref target="BCP97"/>.
4165  </annotation>-->
4166</reference>
4167
4168<reference anchor="RFC1951">
4169  <front>
4170    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4171    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4172      <organization>Aladdin Enterprises</organization>
4173      <address><email>ghost@aladdin.com</email></address>
4174    </author>
4175    <date month="May" year="1996"/>
4176  </front>
4177  <seriesInfo name="RFC" value="1951"/>
4178  <!--<annotation>
4179    RFC 1951 is an Informational RFC, thus it might be less stable than
4180    this specification. On the other hand, this downward reference was
4181    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4182    therefore it is unlikely to cause problems in practice. See also
4183    <xref target="BCP97"/>.
4184  </annotation>-->
4185</reference>
4186
4187<reference anchor="RFC1952">
4188  <front>
4189    <title>GZIP file format specification version 4.3</title>
4190    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4191      <organization>Aladdin Enterprises</organization>
4192      <address><email>ghost@aladdin.com</email></address>
4193    </author>
4194    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4195      <address><email>gzip@prep.ai.mit.edu</email></address>
4196    </author>
4197    <author initials="M." surname="Adler" fullname="Mark Adler">
4198      <address><email>madler@alumni.caltech.edu</email></address>
4199    </author>
4200    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4201      <address><email>ghost@aladdin.com</email></address>
4202    </author>
4203    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4204      <address><email>randeg@alumni.rpi.edu</email></address>
4205    </author>
4206    <date month="May" year="1996"/>
4207  </front>
4208  <seriesInfo name="RFC" value="1952"/>
4209  <!--<annotation>
4210    RFC 1952 is an Informational RFC, thus it might be less stable than
4211    this specification. On the other hand, this downward reference was
4212    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4213    therefore it is unlikely to cause problems in practice. See also
4214    <xref target="BCP97"/>.
4215  </annotation>-->
4216</reference>
4217
4218</references>
4219
4220<references title="Informative References">
4221
4222<reference anchor="ISO-8859-1">
4223  <front>
4224    <title>
4225     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4226    </title>
4227    <author>
4228      <organization>International Organization for Standardization</organization>
4229    </author>
4230    <date year="1998"/>
4231  </front>
4232  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4233</reference>
4234
4235<reference anchor='RFC1919'>
4236  <front>
4237    <title>Classical versus Transparent IP Proxies</title>
4238    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4239      <address><email>mchatel@pax.eunet.ch</email></address>
4240    </author>
4241    <date year='1996' month='March' />
4242  </front>
4243  <seriesInfo name='RFC' value='1919' />
4244</reference>
4245
4246<reference anchor="RFC1945">
4247  <front>
4248    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4249    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4250      <organization>MIT, Laboratory for Computer Science</organization>
4251      <address><email>timbl@w3.org</email></address>
4252    </author>
4253    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4254      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4255      <address><email>fielding@ics.uci.edu</email></address>
4256    </author>
4257    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4258      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4259      <address><email>frystyk@w3.org</email></address>
4260    </author>
4261    <date month="May" year="1996"/>
4262  </front>
4263  <seriesInfo name="RFC" value="1945"/>
4264</reference>
4265
4266<reference anchor="RFC2045">
4267  <front>
4268    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4269    <author initials="N." surname="Freed" fullname="Ned Freed">
4270      <organization>Innosoft International, Inc.</organization>
4271      <address><email>ned@innosoft.com</email></address>
4272    </author>
4273    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4274      <organization>First Virtual Holdings</organization>
4275      <address><email>nsb@nsb.fv.com</email></address>
4276    </author>
4277    <date month="November" year="1996"/>
4278  </front>
4279  <seriesInfo name="RFC" value="2045"/>
4280</reference>
4281
4282<reference anchor="RFC2047">
4283  <front>
4284    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4285    <author initials="K." surname="Moore" fullname="Keith Moore">
4286      <organization>University of Tennessee</organization>
4287      <address><email>moore@cs.utk.edu</email></address>
4288    </author>
4289    <date month="November" year="1996"/>
4290  </front>
4291  <seriesInfo name="RFC" value="2047"/>
4292</reference>
4293
4294<reference anchor="RFC2068">
4295  <front>
4296    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4297    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4298      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4299      <address><email>fielding@ics.uci.edu</email></address>
4300    </author>
4301    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4302      <organization>MIT Laboratory for Computer Science</organization>
4303      <address><email>jg@w3.org</email></address>
4304    </author>
4305    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4306      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4307      <address><email>mogul@wrl.dec.com</email></address>
4308    </author>
4309    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4310      <organization>MIT Laboratory for Computer Science</organization>
4311      <address><email>frystyk@w3.org</email></address>
4312    </author>
4313    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4314      <organization>MIT Laboratory for Computer Science</organization>
4315      <address><email>timbl@w3.org</email></address>
4316    </author>
4317    <date month="January" year="1997"/>
4318  </front>
4319  <seriesInfo name="RFC" value="2068"/>
4320</reference>
4321
4322<reference anchor="RFC2145">
4323  <front>
4324    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4325    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4326      <organization>Western Research Laboratory</organization>
4327      <address><email>mogul@wrl.dec.com</email></address>
4328    </author>
4329    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4330      <organization>Department of Information and Computer Science</organization>
4331      <address><email>fielding@ics.uci.edu</email></address>
4332    </author>
4333    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4334      <organization>MIT Laboratory for Computer Science</organization>
4335      <address><email>jg@w3.org</email></address>
4336    </author>
4337    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4338      <organization>W3 Consortium</organization>
4339      <address><email>frystyk@w3.org</email></address>
4340    </author>
4341    <date month="May" year="1997"/>
4342  </front>
4343  <seriesInfo name="RFC" value="2145"/>
4344</reference>
4345
4346<reference anchor="RFC2616">
4347  <front>
4348    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4349    <author initials="R." surname="Fielding" fullname="R. Fielding">
4350      <organization>University of California, Irvine</organization>
4351      <address><email>fielding@ics.uci.edu</email></address>
4352    </author>
4353    <author initials="J." surname="Gettys" fullname="J. Gettys">
4354      <organization>W3C</organization>
4355      <address><email>jg@w3.org</email></address>
4356    </author>
4357    <author initials="J." surname="Mogul" fullname="J. Mogul">
4358      <organization>Compaq Computer Corporation</organization>
4359      <address><email>mogul@wrl.dec.com</email></address>
4360    </author>
4361    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4362      <organization>MIT Laboratory for Computer Science</organization>
4363      <address><email>frystyk@w3.org</email></address>
4364    </author>
4365    <author initials="L." surname="Masinter" fullname="L. Masinter">
4366      <organization>Xerox Corporation</organization>
4367      <address><email>masinter@parc.xerox.com</email></address>
4368    </author>
4369    <author initials="P." surname="Leach" fullname="P. Leach">
4370      <organization>Microsoft Corporation</organization>
4371      <address><email>paulle@microsoft.com</email></address>
4372    </author>
4373    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4374      <organization>W3C</organization>
4375      <address><email>timbl@w3.org</email></address>
4376    </author>
4377    <date month="June" year="1999"/>
4378  </front>
4379  <seriesInfo name="RFC" value="2616"/>
4380</reference>
4381
4382<reference anchor='RFC2817'>
4383  <front>
4384    <title>Upgrading to TLS Within HTTP/1.1</title>
4385    <author initials='R.' surname='Khare' fullname='R. Khare'>
4386      <organization>4K Associates / UC Irvine</organization>
4387      <address><email>rohit@4K-associates.com</email></address>
4388    </author>
4389    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4390      <organization>Agranat Systems, Inc.</organization>
4391      <address><email>lawrence@agranat.com</email></address>
4392    </author>
4393    <date year='2000' month='May' />
4394  </front>
4395  <seriesInfo name='RFC' value='2817' />
4396</reference>
4397
4398<reference anchor='RFC2818'>
4399  <front>
4400    <title>HTTP Over TLS</title>
4401    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4402      <organization>RTFM, Inc.</organization>
4403      <address><email>ekr@rtfm.com</email></address>
4404    </author>
4405    <date year='2000' month='May' />
4406  </front>
4407  <seriesInfo name='RFC' value='2818' />
4408</reference>
4409
4410<reference anchor='RFC2965'>
4411  <front>
4412    <title>HTTP State Management Mechanism</title>
4413    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4414      <organization>Bell Laboratories, Lucent Technologies</organization>
4415      <address><email>dmk@bell-labs.com</email></address>
4416    </author>
4417    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4418      <organization>Epinions.com, Inc.</organization>
4419      <address><email>lou@montulli.org</email></address>
4420    </author>
4421    <date year='2000' month='October' />
4422  </front>
4423  <seriesInfo name='RFC' value='2965' />
4424</reference>
4425
4426<reference anchor='RFC3040'>
4427  <front>
4428    <title>Internet Web Replication and Caching Taxonomy</title>
4429    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4430      <organization>Equinix, Inc.</organization>
4431    </author>
4432    <author initials='I.' surname='Melve' fullname='I. Melve'>
4433      <organization>UNINETT</organization>
4434    </author>
4435    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4436      <organization>CacheFlow Inc.</organization>
4437    </author>
4438    <date year='2001' month='January' />
4439  </front>
4440  <seriesInfo name='RFC' value='3040' />
4441</reference>
4442
4443<reference anchor='RFC3864'>
4444  <front>
4445    <title>Registration Procedures for Message Header Fields</title>
4446    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4447      <organization>Nine by Nine</organization>
4448      <address><email>GK-IETF@ninebynine.org</email></address>
4449    </author>
4450    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4451      <organization>BEA Systems</organization>
4452      <address><email>mnot@pobox.com</email></address>
4453    </author>
4454    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4455      <organization>HP Labs</organization>
4456      <address><email>JeffMogul@acm.org</email></address>
4457    </author>
4458    <date year='2004' month='September' />
4459  </front>
4460  <seriesInfo name='BCP' value='90' />
4461  <seriesInfo name='RFC' value='3864' />
4462</reference>
4463
4464<reference anchor='RFC4033'>
4465  <front>
4466    <title>DNS Security Introduction and Requirements</title>
4467    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4468    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4469    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4470    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4471    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4472    <date year='2005' month='March' />
4473  </front>
4474  <seriesInfo name='RFC' value='4033' />
4475</reference>
4476
4477<reference anchor="RFC4288">
4478  <front>
4479    <title>Media Type Specifications and Registration Procedures</title>
4480    <author initials="N." surname="Freed" fullname="N. Freed">
4481      <organization>Sun Microsystems</organization>
4482      <address>
4483        <email>ned.freed@mrochek.com</email>
4484      </address>
4485    </author>
4486    <author initials="J." surname="Klensin" fullname="J. Klensin">
4487      <address>
4488        <email>klensin+ietf@jck.com</email>
4489      </address>
4490    </author>
4491    <date year="2005" month="December"/>
4492  </front>
4493  <seriesInfo name="BCP" value="13"/>
4494  <seriesInfo name="RFC" value="4288"/>
4495</reference>
4496
4497<reference anchor='RFC4395'>
4498  <front>
4499    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4500    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4501      <organization>AT&amp;T Laboratories</organization>
4502      <address>
4503        <email>tony+urireg@maillennium.att.com</email>
4504      </address>
4505    </author>
4506    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4507      <organization>Qualcomm, Inc.</organization>
4508      <address>
4509        <email>hardie@qualcomm.com</email>
4510      </address>
4511    </author>
4512    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4513      <organization>Adobe Systems</organization>
4514      <address>
4515        <email>LMM@acm.org</email>
4516      </address>
4517    </author>
4518    <date year='2006' month='February' />
4519  </front>
4520  <seriesInfo name='BCP' value='115' />
4521  <seriesInfo name='RFC' value='4395' />
4522</reference>
4523
4524<reference anchor='RFC4559'>
4525  <front>
4526    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4527    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4528    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4529    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4530    <date year='2006' month='June' />
4531  </front>
4532  <seriesInfo name='RFC' value='4559' />
4533</reference>
4534
4535<reference anchor='RFC5226'>
4536  <front>
4537    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4538    <author initials='T.' surname='Narten' fullname='T. Narten'>
4539      <organization>IBM</organization>
4540      <address><email>narten@us.ibm.com</email></address>
4541    </author>
4542    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4543      <organization>Google</organization>
4544      <address><email>Harald@Alvestrand.no</email></address>
4545    </author>
4546    <date year='2008' month='May' />
4547  </front>
4548  <seriesInfo name='BCP' value='26' />
4549  <seriesInfo name='RFC' value='5226' />
4550</reference>
4551
4552<reference anchor='RFC5246'>
4553   <front>
4554      <title>The Transport Layer Security (TLS) Protocol Version 1.2</title>
4555      <author initials='T.' surname='Dierks' fullname='T. Dierks'>
4556         <organization />
4557      </author>
4558      <author initials='E.' surname='Rescorla' fullname='E. Rescorla'>
4559         <organization>RTFM, Inc.</organization>
4560      </author>
4561      <date year='2008' month='August' />
4562   </front>
4563   <seriesInfo name='RFC' value='5246' />
4564</reference>
4565
4566<reference anchor="RFC5322">
4567  <front>
4568    <title>Internet Message Format</title>
4569    <author initials="P." surname="Resnick" fullname="P. Resnick">
4570      <organization>Qualcomm Incorporated</organization>
4571    </author>
4572    <date year="2008" month="October"/>
4573  </front> 
4574  <seriesInfo name="RFC" value="5322"/>
4575</reference>
4576
4577<reference anchor="RFC6265">
4578  <front>
4579    <title>HTTP State Management Mechanism</title>
4580    <author initials="A." surname="Barth" fullname="Adam Barth">
4581      <organization abbrev="U.C. Berkeley">
4582        University of California, Berkeley
4583      </organization>
4584      <address><email>abarth@eecs.berkeley.edu</email></address>
4585    </author>
4586    <date year="2011" month="April" />
4587  </front>
4588  <seriesInfo name="RFC" value="6265"/>
4589</reference>
4590
4591<!--<reference anchor='BCP97'>
4592  <front>
4593    <title>Handling Normative References to Standards-Track Documents</title>
4594    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4595      <address>
4596        <email>klensin+ietf@jck.com</email>
4597      </address>
4598    </author>
4599    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4600      <organization>MIT</organization>
4601      <address>
4602        <email>hartmans-ietf@mit.edu</email>
4603      </address>
4604    </author>
4605    <date year='2007' month='June' />
4606  </front>
4607  <seriesInfo name='BCP' value='97' />
4608  <seriesInfo name='RFC' value='4897' />
4609</reference>-->
4610
4611<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4612  <front>
4613    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4614    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4615    <date year="2001" month="November"/>
4616  </front>
4617  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4618</reference>
4619
4620</references>
4621
4622
4623<section title="HTTP Version History" anchor="compatibility">
4624<t>
4625   HTTP has been in use by the World-Wide Web global information initiative
4626   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4627   was a simple protocol for hypertext data transfer across the Internet
4628   with only a single request method (GET) and no metadata.
4629   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4630   methods and MIME-like messaging that could include metadata about the data
4631   transferred and modifiers on the request/response semantics. However,
4632   HTTP/1.0 did not sufficiently take into consideration the effects of
4633   hierarchical proxies, caching, the need for persistent connections, or
4634   name-based virtual hosts. The proliferation of incompletely-implemented
4635   applications calling themselves "HTTP/1.0" further necessitated a
4636   protocol version change in order for two communicating applications
4637   to determine each other's true capabilities.
4638</t>
4639<t>
4640   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4641   requirements that enable reliable implementations, adding only
4642   those new features that will either be safely ignored by an HTTP/1.0
4643   recipient or only sent when communicating with a party advertising
4644   conformance with HTTP/1.1.
4645</t>
4646<t>
4647   It is beyond the scope of a protocol specification to mandate
4648   conformance with previous versions. HTTP/1.1 was deliberately
4649   designed, however, to make supporting previous versions easy.
4650   We would expect a general-purpose HTTP/1.1 server to understand
4651   any valid request in the format of HTTP/1.0 and respond appropriately
4652   with an HTTP/1.1 message that only uses features understood (or
4653   safely ignored) by HTTP/1.0 clients.  Likewise, we would expect
4654   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4655</t>
4656<t>
4657   Since HTTP/0.9 did not support header fields in a request,
4658   there is no mechanism for it to support name-based virtual
4659   hosts (selection of resource by inspection of the <x:ref>Host</x:ref> header
4660   field).  Any server that implements name-based virtual hosts
4661   ought to disable support for HTTP/0.9.  Most requests that
4662   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4663   requests wherein a buggy client failed to properly encode
4664   linear whitespace found in a URI reference and placed in
4665   the request-target.
4666</t>
4667
4668<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4669<t>
4670   This section summarizes major differences between versions HTTP/1.0
4671   and HTTP/1.1.
4672</t>
4673
4674<section title="Multi-homed Web Servers" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
4675<t>
4676   The requirements that clients and servers support the <x:ref>Host</x:ref>
4677   header field (<xref target="header.host"/>), report an error if it is
4678   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4679   are among the most important changes defined by HTTP/1.1.
4680</t>
4681<t>
4682   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4683   addresses and servers; there was no other established mechanism for
4684   distinguishing the intended server of a request than the IP address
4685   to which that request was directed. The <x:ref>Host</x:ref> header field was
4686   introduced during the development of HTTP/1.1 and, though it was
4687   quickly implemented by most HTTP/1.0 browsers, additional requirements
4688   were placed on all HTTP/1.1 requests in order to ensure complete
4689   adoption.  At the time of this writing, most HTTP-based services
4690   are dependent upon the Host header field for targeting requests.
4691</t>
4692</section>
4693
4694<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4695<t>
4696   In HTTP/1.0, each connection is established by the client prior to the
4697   request and closed by the server after sending the response. However, some
4698   implementations implement the explicitly negotiated ("Keep-Alive") version
4699   of persistent connections described in <xref x:sec="19.7.1" x:fmt="of"
4700   target="RFC2068"/>.
4701</t>
4702<t>
4703   Some clients and servers might wish to be compatible with these previous
4704   approaches to persistent connections, by explicitly negotiating for them
4705   with a "Connection: keep-alive" request header field. However, some
4706   experimental implementations of HTTP/1.0 persistent connections are faulty;
4707   for example, if a HTTP/1.0 proxy server doesn't understand
4708   <x:ref>Connection</x:ref>, it will erroneously forward that header field
4709   to the next inbound server, which would result in a hung connection.
4710</t>
4711<t>
4712   One attempted solution was the introduction of a Proxy-Connection header
4713   field, targeted specifically at proxies. In practice, this was also
4714   unworkable, because proxies are often deployed in multiple layers, bringing
4715   about the same problem discussed above.
4716</t>
4717<t>
4718   As a result, clients are encouraged not to send the Proxy-Connection header
4719   field in any requests.
4720</t>
4721<t>
4722   Clients are also encouraged to consider the use of Connection: keep-alive
4723   in requests carefully; while they can enable persistent connections with
4724   HTTP/1.0 servers, clients using them need will need to monitor the
4725   connection for "hung" requests (which indicate that the client ought stop
4726   sending the header field), and this mechanism ought not be used by clients
4727   at all when a proxy is being used.
4728</t>
4729</section>
4730
4731<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
4732<t>
4733   HTTP/1.1 introduces the <x:ref>Transfer-Encoding</x:ref> header field
4734   (<xref target="header.transfer-encoding"/>). Proxies/gateways &MUST; remove
4735   any transfer-coding prior to forwarding a message via a MIME-compliant
4736   protocol.
4737</t>
4738</section>
4739
4740</section>
4741
4742<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4743<t>
4744  Clarify that the string "HTTP" in the HTTP-version ABNF production is case
4745  sensitive. Restrict the version numbers to be single digits due to the fact
4746  that implementations are known to handle multi-digit version numbers
4747  incorrectly.
4748  (<xref target="http.version"/>)
4749</t>
4750<t>
4751  Require that invalid whitespace around field-names be rejected.
4752  Change ABNF productions for header fields to only define the field value.
4753  (<xref target="header.fields"/>)
4754</t>
4755<t>
4756  Rules about implicit linear whitespace between certain grammar productions
4757  have been removed; now whitespace is only allowed where specifically
4758  defined in the ABNF.
4759  (<xref target="whitespace"/>)
4760</t>
4761<t> 
4762  The NUL octet is no longer allowed in comment and quoted-string
4763  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4764  Non-ASCII content in header fields and reason phrase has been obsoleted and
4765  made opaque (the TEXT rule was removed).
4766  (<xref target="field.components"/>)
4767</t>
4768<t>
4769  Require recipients to handle bogus "<x:ref>Content-Length</x:ref>" header
4770  fields as errors.
4771  (<xref target="message.body"/>)
4772</t>
4773<t>
4774  Remove reference to non-existent identity transfer-coding value tokens.
4775  (Sections <xref format="counter" target="message.body"/> and
4776  <xref format="counter" target="transfer.codings"/>)
4777</t>
4778<t>
4779  Clarification that the chunk length does not include the count of the octets
4780  in the chunk header and trailer. Furthermore disallowed line folding
4781  in chunk extensions, and deprecate their use.
4782  (<xref target="chunked.encoding"/>)
4783</t>
4784<t>
4785  Update use of abs_path production from RFC 1808 to the path-absolute + query
4786  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4787  request method only.
4788  (<xref target="request-target"/>)
4789</t>
4790<t>
4791  Clarify exactly when "close" connection options have to be sent; drop
4792  notion of header fields being "hop-by-hop" without being listed in the
4793  Connection header field.
4794  (<xref target="header.connection"/>)
4795</t>
4796<t>
4797  Remove hard limit of two connections per server.
4798  Remove requirement to retry a sequence of requests as long it was idempotent.
4799  Remove requirements about when servers are allowed to close connections
4800  prematurely.
4801  (<xref target="persistent.connections"/>)
4802</t>
4803<t>
4804  Remove requirement to retry requests under certain circumstances when the
4805  server prematurely closes the connection.
4806  (<xref target="persistent.reuse"/>)
4807</t>
4808<t>
4809  Define the semantics of the <x:ref>Upgrade</x:ref> header field in responses
4810  other than 101 (this was incorporated from <xref target="RFC2817"/>).
4811  (<xref target="header.upgrade"/>)
4812</t>
4813<t>
4814  Registration of Transfer Codings now requires IETF Review
4815  (<xref target="transfer.coding.registry"/>)
4816</t>
4817<t>
4818  Take over the Upgrade Token Registry, previously defined in
4819  <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
4820  (<xref target="upgrade.token.registry"/>)
4821</t>
4822<t>
4823  Empty list elements in list productions have been deprecated.
4824  (<xref target="abnf.extension"/>)
4825</t>
4826</section>
4827</section>
4828
4829<section title="ABNF list extension: #rule" anchor="abnf.extension">
4830<t>
4831  A #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
4832  improve readability in the definitions of some header field values.
4833</t>
4834<t>
4835  A construct "#" is defined, similar to "*", for defining comma-delimited
4836  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
4837  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
4838  comma (",") and optional whitespace (OWS).   
4839</t>
4840<figure><preamble>
4841  Thus,
4842</preamble><artwork type="example">
4843  1#element =&gt; element *( OWS "," OWS element )
4844</artwork></figure>
4845<figure><preamble>
4846  and:
4847</preamble><artwork type="example">
4848  #element =&gt; [ 1#element ]
4849</artwork></figure>
4850<figure><preamble>
4851  and for n &gt;= 1 and m &gt; 1:
4852</preamble><artwork type="example">
4853  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
4854</artwork></figure>
4855<t>
4856  For compatibility with legacy list rules, recipients &SHOULD; accept empty
4857  list elements. In other words, consumers would follow the list productions:
4858</t>
4859<figure><artwork type="example">
4860  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
4861 
4862  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
4863</artwork></figure>
4864<t>
4865  Note that empty elements do not contribute to the count of elements present,
4866  though.
4867</t>
4868<t>
4869  For example, given these ABNF productions:
4870</t>
4871<figure><artwork type="example">
4872  example-list      = 1#example-list-elmt
4873  example-list-elmt = token ; see <xref target="field.components"/> 
4874</artwork></figure>
4875<t>
4876  Then these are valid values for example-list (not including the double
4877  quotes, which are present for delimitation only):
4878</t>
4879<figure><artwork type="example">
4880  "foo,bar"
4881  "foo ,bar,"
4882  "foo , ,bar,charlie   "
4883</artwork></figure>
4884<t>
4885  But these values would be invalid, as at least one non-empty element is
4886  required:
4887</t>
4888<figure><artwork type="example">
4889  ""
4890  ","
4891  ",   ,"
4892</artwork></figure>
4893<t>
4894  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
4895  expanded as explained above.
4896</t>
4897</section>
4898
4899<?BEGININC p1-messaging.abnf-appendix ?>
4900<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4901<figure>
4902<artwork type="abnf" name="p1-messaging.parsed-abnf">
4903<x:ref>BWS</x:ref> = OWS
4904
4905<x:ref>Connection</x:ref> = *( "," OWS ) connection-option *( OWS "," [ OWS
4906 connection-option ] )
4907<x:ref>Content-Length</x:ref> = 1*DIGIT
4908
4909<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
4910 ]
4911<x:ref>HTTP-name</x:ref> = %x48.54.54.50 ; HTTP
4912<x:ref>HTTP-version</x:ref> = HTTP-name "/" DIGIT "." DIGIT
4913<x:ref>Host</x:ref> = uri-host [ ":" port ]
4914
4915<x:ref>OWS</x:ref> = *( SP / HTAB )
4916
4917<x:ref>RWS</x:ref> = 1*( SP / HTAB )
4918
4919<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4920<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4921<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4922 transfer-coding ] )
4923
4924<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4925<x:ref>Upgrade</x:ref> = *( "," OWS ) protocol *( OWS "," [ OWS protocol ] )
4926
4927<x:ref>Via</x:ref> = *( "," OWS ) ( received-protocol RWS received-by [ RWS comment
4928 ] ) *( OWS "," [ OWS ( received-protocol RWS received-by [ RWS
4929 comment ] ) ] )
4930
4931<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4932<x:ref>absolute-form</x:ref> = absolute-URI
4933<x:ref>asterisk-form</x:ref> = "*"
4934<x:ref>attribute</x:ref> = token
4935<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4936<x:ref>authority-form</x:ref> = authority
4937
4938<x:ref>chunk</x:ref> = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
4939<x:ref>chunk-data</x:ref> = 1*OCTET
4940<x:ref>chunk-ext</x:ref> = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
4941<x:ref>chunk-ext-name</x:ref> = token
4942<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
4943<x:ref>chunk-size</x:ref> = 1*HEXDIG
4944<x:ref>chunked-body</x:ref> = *chunk last-chunk trailer-part CRLF
4945<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
4946<x:ref>connection-option</x:ref> = token
4947<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4948 / %x2A-5B ; '*'-'['
4949 / %x5D-7E ; ']'-'~'
4950 / obs-text
4951
4952<x:ref>field-content</x:ref> = *( HTAB / SP / VCHAR / obs-text )
4953<x:ref>field-name</x:ref> = token
4954<x:ref>field-value</x:ref> = *( field-content / obs-fold )
4955
4956<x:ref>header-field</x:ref> = field-name ":" OWS field-value BWS
4957<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4958<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
4959
4960<x:ref>last-chunk</x:ref> = 1*"0" [ chunk-ext ] CRLF
4961
4962<x:ref>message-body</x:ref> = *OCTET
4963<x:ref>method</x:ref> = token
4964
4965<x:ref>obs-fold</x:ref> = CRLF ( SP / HTAB )
4966<x:ref>obs-text</x:ref> = %x80-FF
4967<x:ref>origin-form</x:ref> = path-absolute [ "?" query ]
4968
4969<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4970<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4971<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4972<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4973<x:ref>protocol</x:ref> = protocol-name [ "/" protocol-version ]
4974<x:ref>protocol-name</x:ref> = token
4975<x:ref>protocol-version</x:ref> = token
4976<x:ref>pseudonym</x:ref> = token
4977
4978<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
4979 / %x5D-7E ; ']'-'~'
4980 / obs-text
4981<x:ref>qdtext-nf</x:ref> = HTAB / SP / "!" / %x23-5B ; '#'-'['
4982 / %x5D-7E ; ']'-'~'
4983 / obs-text
4984<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
4985<x:ref>quoted-cpair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
4986<x:ref>quoted-pair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
4987<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
4988<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
4989
4990<x:ref>rank</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
4991<x:ref>reason-phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
4992<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
4993<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
4994<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
4995<x:ref>request-line</x:ref> = method SP request-target SP HTTP-version CRLF
4996<x:ref>request-target</x:ref> = origin-form / absolute-form / authority-form /
4997 asterisk-form
4998
4999<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5000 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5001<x:ref>start-line</x:ref> = request-line / status-line
5002<x:ref>status-code</x:ref> = 3DIGIT
5003<x:ref>status-line</x:ref> = HTTP-version SP status-code SP reason-phrase CRLF
5004
5005<x:ref>t-codings</x:ref> = "trailers" / ( transfer-coding [ t-ranking ] )
5006<x:ref>t-ranking</x:ref> = OWS ";" OWS "q=" rank
5007<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5008 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5009<x:ref>token</x:ref> = 1*tchar
5010<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5011<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5012 transfer-extension
5013<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5014<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5015
5016<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5017
5018<x:ref>value</x:ref> = word
5019
5020<x:ref>word</x:ref> = token / quoted-string
5021</artwork>
5022</figure>
5023</section>
5024<?ENDINC p1-messaging.abnf-appendix ?>
5025
5026<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5027
5028<section title="Since RFC 2616">
5029<t>
5030  Extracted relevant partitions from <xref target="RFC2616"/>.
5031</t>
5032</section>
5033
5034<section title="Since draft-ietf-httpbis-p1-messaging-00">
5035<t>
5036  Closed issues:
5037  <list style="symbols"> 
5038    <t>
5039      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5040      "HTTP Version should be case sensitive"
5041      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5042    </t>
5043    <t>
5044      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5045      "'unsafe' characters"
5046      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5047    </t>
5048    <t>
5049      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5050      "Chunk Size Definition"
5051      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5052    </t>
5053    <t>
5054      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5055      "Message Length"
5056      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5057    </t>
5058    <t>
5059      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5060      "Media Type Registrations"
5061      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5062    </t>
5063    <t>
5064      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5065      "URI includes query"
5066      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5067    </t>
5068    <t>
5069      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5070      "No close on 1xx responses"
5071      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5072    </t>
5073    <t>
5074      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5075      "Remove 'identity' token references"
5076      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5077    </t>
5078    <t>
5079      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5080      "Import query BNF"
5081    </t>
5082    <t>
5083      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5084      "qdtext BNF"
5085    </t>
5086    <t>
5087      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5088      "Normative and Informative references"
5089    </t>
5090    <t>
5091      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5092      "RFC2606 Compliance"
5093    </t>
5094    <t>
5095      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5096      "RFC977 reference"
5097    </t>
5098    <t>
5099      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5100      "RFC1700 references"
5101    </t>
5102    <t>
5103      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5104      "inconsistency in date format explanation"
5105    </t>
5106    <t>
5107      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5108      "Date reference typo"
5109    </t>
5110    <t>
5111      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5112      "Informative references"
5113    </t>
5114    <t>
5115      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5116      "ISO-8859-1 Reference"
5117    </t>
5118    <t>
5119      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5120      "Normative up-to-date references"
5121    </t>
5122  </list>
5123</t>
5124<t>
5125  Other changes:
5126  <list style="symbols"> 
5127    <t>
5128      Update media type registrations to use RFC4288 template.
5129    </t>
5130    <t>
5131      Use names of RFC4234 core rules DQUOTE and HTAB,
5132      fix broken ABNF for chunk-data
5133      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5134    </t>
5135  </list>
5136</t>
5137</section>
5138
5139<section title="Since draft-ietf-httpbis-p1-messaging-01">
5140<t>
5141  Closed issues:
5142  <list style="symbols"> 
5143    <t>
5144      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5145      "Bodies on GET (and other) requests"
5146    </t>
5147    <t>
5148      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5149      "Updating to RFC4288"
5150    </t>
5151    <t>
5152      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5153      "Status Code and Reason Phrase"
5154    </t>
5155    <t>
5156      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5157      "rel_path not used"
5158    </t>
5159  </list>
5160</t>
5161<t>
5162  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5163  <list style="symbols"> 
5164    <t>
5165      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5166      "trailer-part").
5167    </t>
5168    <t>
5169      Avoid underscore character in rule names ("http_URL" ->
5170      "http-URL", "abs_path" -> "path-absolute").
5171    </t>
5172    <t>
5173      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5174      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5175      have to be updated when switching over to RFC3986.
5176    </t>
5177    <t>
5178      Synchronize core rules with RFC5234.
5179    </t>
5180    <t>
5181      Get rid of prose rules that span multiple lines.
5182    </t>
5183    <t>
5184      Get rid of unused rules LOALPHA and UPALPHA.
5185    </t>
5186    <t>
5187      Move "Product Tokens" section (back) into Part 1, as "token" is used
5188      in the definition of the Upgrade header field.
5189    </t>
5190    <t>
5191      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5192    </t>
5193    <t>
5194      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5195    </t>
5196  </list>
5197</t>
5198</section>
5199
5200<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5201<t>
5202  Closed issues:
5203  <list style="symbols"> 
5204    <t>
5205      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5206      "HTTP-date vs. rfc1123-date"
5207    </t>
5208    <t>
5209      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5210      "WS in quoted-pair"
5211    </t>
5212  </list>
5213</t>
5214<t>
5215  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5216  <list style="symbols"> 
5217    <t>
5218      Reference RFC 3984, and update header field registrations for header
5219      fields defined in this document.
5220    </t>
5221  </list>
5222</t>
5223<t>
5224  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5225  <list style="symbols"> 
5226    <t>
5227      Replace string literals when the string really is case-sensitive (HTTP-version).
5228    </t>
5229  </list>
5230</t>
5231</section>
5232
5233<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5234<t>
5235  Closed issues:
5236  <list style="symbols"> 
5237    <t>
5238      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5239      "Connection closing"
5240    </t>
5241    <t>
5242      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5243      "Move registrations and registry information to IANA Considerations"
5244    </t>
5245    <t>
5246      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5247      "need new URL for PAD1995 reference"
5248    </t>
5249    <t>
5250      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5251      "IANA Considerations: update HTTP URI scheme registration"
5252    </t>
5253    <t>
5254      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5255      "Cite HTTPS URI scheme definition"
5256    </t>
5257    <t>
5258      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5259      "List-type header fields vs Set-Cookie"
5260    </t>
5261  </list>
5262</t>
5263<t>
5264  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5265  <list style="symbols"> 
5266    <t>
5267      Replace string literals when the string really is case-sensitive (HTTP-Date).
5268    </t>
5269    <t>
5270      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5271    </t>
5272  </list>
5273</t>
5274</section>
5275
5276<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5277<t>
5278  Closed issues:
5279  <list style="symbols"> 
5280    <t>
5281      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5282      "Out-of-date reference for URIs"
5283    </t>
5284    <t>
5285      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5286      "RFC 2822 is updated by RFC 5322"
5287    </t>
5288  </list>
5289</t>
5290<t>
5291  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5292  <list style="symbols"> 
5293    <t>
5294      Use "/" instead of "|" for alternatives.
5295    </t>
5296    <t>
5297      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5298    </t>
5299    <t>
5300      Only reference RFC 5234's core rules.
5301    </t>
5302    <t>
5303      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5304      whitespace ("OWS") and required whitespace ("RWS").
5305    </t>
5306    <t>
5307      Rewrite ABNFs to spell out whitespace rules, factor out
5308      header field value format definitions.
5309    </t>
5310  </list>
5311</t>
5312</section>
5313
5314<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5315<t>
5316  Closed issues:
5317  <list style="symbols"> 
5318    <t>
5319      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5320      "Header LWS"
5321    </t>
5322    <t>
5323      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5324      "Sort 1.3 Terminology"
5325    </t>
5326    <t>
5327      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5328      "RFC2047 encoded words"
5329    </t>
5330    <t>
5331      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5332      "Character Encodings in TEXT"
5333    </t>
5334    <t>
5335      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5336      "Line Folding"
5337    </t>
5338    <t>
5339      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5340      "OPTIONS * and proxies"
5341    </t>
5342    <t>
5343      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5344      "reason-phrase BNF"
5345    </t>
5346    <t>
5347      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5348      "Use of TEXT"
5349    </t>
5350    <t>
5351      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5352      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5353    </t>
5354    <t>
5355      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5356      "RFC822 reference left in discussion of date formats"
5357    </t>
5358  </list>
5359</t>
5360<t>
5361  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5362  <list style="symbols"> 
5363    <t>
5364      Rewrite definition of list rules, deprecate empty list elements.
5365    </t>
5366    <t>
5367      Add appendix containing collected and expanded ABNF.
5368    </t>
5369  </list>
5370</t>
5371<t>
5372  Other changes:
5373  <list style="symbols"> 
5374    <t>
5375      Rewrite introduction; add mostly new Architecture Section.
5376    </t>
5377    <t>
5378      Move definition of quality values from Part 3 into Part 1;
5379      make TE request header field grammar independent of accept-params (defined in Part 3).
5380    </t>
5381  </list>
5382</t>
5383</section>
5384
5385<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5386<t>
5387  Closed issues:
5388  <list style="symbols"> 
5389    <t>
5390      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5391      "base for numeric protocol elements"
5392    </t>
5393    <t>
5394      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5395      "comment ABNF"
5396    </t>
5397  </list>
5398</t>
5399<t>
5400  Partly resolved issues:
5401  <list style="symbols"> 
5402    <t>
5403      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5404      "205 Bodies" (took out language that implied that there might be
5405      methods for which a request body MUST NOT be included)
5406    </t>
5407    <t>
5408      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5409      "editorial improvements around HTTP-date"
5410    </t>
5411  </list>
5412</t>
5413</section>
5414
5415<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5416<t>
5417  Closed issues:
5418  <list style="symbols"> 
5419    <t>
5420      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5421      "Repeating single-value header fields"
5422    </t>
5423    <t>
5424      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5425      "increase connection limit"
5426    </t>
5427    <t>
5428      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5429      "IP addresses in URLs"
5430    </t>
5431    <t>
5432      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5433      "take over HTTP Upgrade Token Registry"
5434    </t>
5435    <t>
5436      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5437      "CR and LF in chunk extension values"
5438    </t>
5439    <t>
5440      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5441      "HTTP/0.9 support"
5442    </t>
5443    <t>
5444      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5445      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5446    </t>
5447    <t>
5448      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5449      "move definitions of gzip/deflate/compress to part 1"
5450    </t>
5451    <t>
5452      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5453      "disallow control characters in quoted-pair"
5454    </t>
5455  </list>
5456</t>
5457<t>
5458  Partly resolved issues:
5459  <list style="symbols"> 
5460    <t>
5461      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5462      "update IANA requirements wrt Transfer-Coding values" (add the
5463      IANA Considerations subsection)
5464    </t>
5465  </list>
5466</t>
5467</section>
5468
5469<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5470<t>
5471  Closed issues:
5472  <list style="symbols"> 
5473    <t>
5474      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5475      "header parsing, treatment of leading and trailing OWS"
5476    </t>
5477  </list>
5478</t>
5479<t>
5480  Partly resolved issues:
5481  <list style="symbols"> 
5482    <t>
5483      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5484      "Placement of 13.5.1 and 13.5.2"
5485    </t>
5486    <t>
5487      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5488      "use of term "word" when talking about header field structure"
5489    </t>
5490  </list>
5491</t>
5492</section>
5493
5494<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5495<t>
5496  Closed issues:
5497  <list style="symbols"> 
5498    <t>
5499      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5500      "Clarification of the term 'deflate'"
5501    </t>
5502    <t>
5503      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5504      "OPTIONS * and proxies"
5505    </t>
5506    <t>
5507      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5508      "MIME-Version not listed in P1, general header fields"
5509    </t>
5510    <t>
5511      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5512      "IANA registry for content/transfer encodings"
5513    </t>
5514    <t>
5515      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5516      "Case-sensitivity of HTTP-date"
5517    </t>
5518    <t>
5519      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5520      "use of term "word" when talking about header field structure"
5521    </t>
5522  </list>
5523</t>
5524<t>
5525  Partly resolved issues:
5526  <list style="symbols"> 
5527    <t>
5528      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5529      "Term for the requested resource's URI"
5530    </t>
5531  </list>
5532</t>
5533</section>
5534
5535<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5536<t>
5537  Closed issues:
5538  <list style="symbols">
5539    <t>
5540      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5541      "Connection Closing"
5542    </t>
5543    <t>
5544      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5545      "Delimiting messages with multipart/byteranges"
5546    </t>
5547    <t>
5548      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5549      "Handling multiple Content-Length header fields"
5550    </t>
5551    <t>
5552      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
5553      "Clarify entity / representation / variant terminology"
5554    </t>
5555    <t>
5556      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5557      "consider removing the 'changes from 2068' sections"
5558    </t>
5559  </list>
5560</t>
5561<t>
5562  Partly resolved issues:
5563  <list style="symbols"> 
5564    <t>
5565      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5566      "HTTP(s) URI scheme definitions"
5567    </t>
5568  </list>
5569</t>
5570</section>
5571
5572<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5573<t>
5574  Closed issues:
5575  <list style="symbols">
5576    <t>
5577      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
5578      "Trailer requirements"
5579    </t>
5580    <t>
5581      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
5582      "Text about clock requirement for caches belongs in p6"
5583    </t>
5584    <t>
5585      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
5586      "effective request URI: handling of missing host in HTTP/1.0"
5587    </t>
5588    <t>
5589      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
5590      "confusing Date requirements for clients"
5591    </t>
5592  </list>
5593</t>
5594<t>
5595  Partly resolved issues:
5596  <list style="symbols"> 
5597    <t>
5598      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5599      "Handling multiple Content-Length header fields"
5600    </t>
5601  </list>
5602</t>
5603</section>
5604
5605<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5606<t>
5607  Closed issues:
5608  <list style="symbols">
5609    <t>
5610      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/75"/>:
5611      "RFC2145 Normative"
5612    </t>
5613    <t>
5614      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5615      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5616    </t>
5617    <t>
5618      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/210"/>:
5619      "define 'transparent' proxy"
5620    </t>
5621    <t>
5622      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
5623      "Header Field Classification"
5624    </t>
5625    <t>
5626      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/233"/>:
5627      "Is * usable as a request-uri for new methods?"
5628    </t>
5629    <t>
5630      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
5631      "Migrate Upgrade details from RFC2817"
5632    </t>
5633    <t>
5634      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5635      "untangle ABNFs for header fields"
5636    </t>
5637    <t>
5638      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/279"/>:
5639      "update RFC 2109 reference"
5640    </t>
5641  </list>
5642</t>
5643</section>
5644
5645<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5646<t>
5647  Closed issues:
5648  <list style="symbols">
5649    <t>
5650      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/53"/>:
5651      "Allow is not in 13.5.2"
5652    </t>
5653    <t>
5654      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5655      "Handling multiple Content-Length header fields"
5656    </t>
5657    <t>
5658      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5659      "untangle ABNFs for header fields"
5660    </t>
5661    <t>
5662      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/286"/>:
5663      "Content-Length ABNF broken"
5664    </t>
5665  </list>
5666</t>
5667</section>
5668
5669<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5670<t>
5671  Closed issues:
5672  <list style="symbols">
5673    <t>
5674      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/273"/>:
5675      "HTTP-version should be redefined as fixed length pair of DIGIT . DIGIT"
5676    </t>
5677    <t>
5678      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/282"/>:
5679      "Recommend minimum sizes for protocol elements"
5680    </t>
5681    <t>
5682      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/283"/>:
5683      "Set expectations around buffering"
5684    </t>
5685    <t>
5686      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/288"/>:
5687      "Considering messages in isolation"
5688    </t>
5689  </list>
5690</t>
5691</section>
5692
5693<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5694<t>
5695  Closed issues:
5696  <list style="symbols">
5697    <t>
5698      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/100"/>:
5699      "DNS Spoofing / DNS Binding advice"
5700    </t>
5701    <t>
5702      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/254"/>:
5703      "move RFCs 2145, 2616, 2817 to Historic status"
5704    </t>
5705    <t>
5706      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/270"/>:
5707      "\-escaping in quoted strings"
5708    </t>
5709    <t>
5710      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/305"/>:
5711      "'Close' should be reserved in the HTTP header field registry"
5712    </t>
5713  </list>
5714</t>
5715</section>
5716
5717<section title="Since draft-ietf-httpbis-p1-messaging-16" anchor="changes.since.16">
5718<t>
5719  Closed issues:
5720  <list style="symbols">
5721    <t>
5722      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
5723      "Document HTTP's error-handling philosophy"
5724    </t>
5725    <t>
5726      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/215"/>:
5727      "Explain header field registration"
5728    </t>
5729    <t>
5730      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/219"/>:
5731      "Revise Acknowledgements Sections"
5732    </t>
5733    <t>
5734      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/297"/>:
5735      "Retrying Requests"
5736    </t>
5737    <t>
5738      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/318"/>:
5739      "Closing the connection on server error"
5740    </t>
5741  </list>
5742</t>
5743</section>
5744
5745<section title="Since draft-ietf-httpbis-p1-messaging-17" anchor="changes.since.17">
5746<t>
5747  Closed issues:
5748  <list style="symbols">
5749    <t>
5750      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/158"/>:
5751      "Proxy-Connection and Keep-Alive"
5752    </t>
5753    <t>
5754      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/166"/>:
5755      "Clarify 'User Agent'"
5756    </t>
5757    <t>
5758      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/300"/>:
5759      "Define non-final responses"
5760    </t>
5761    <t>
5762      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/323"/>:
5763      "intended maturity level vs normative references"
5764    </t>
5765    <t>
5766      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/324"/>:
5767      "Intermediary rewriting of queries"
5768    </t>
5769  </list>
5770</t>
5771</section>
5772
5773<section title="Since draft-ietf-httpbis-p1-messaging-18" anchor="changes.since.18">
5774<t>
5775  Closed issues:
5776  <list style="symbols">
5777    <t>
5778      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/250"/>:
5779      "message-body in CONNECT response"
5780    </t>
5781    <t>
5782      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/302"/>:
5783      "Misplaced text on connection handling in p2"
5784    </t>
5785    <t>
5786      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/335"/>:
5787      "wording of line folding rule"
5788    </t>
5789    <t>
5790      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/343"/>:
5791      "chunk-extensions"
5792    </t>
5793    <t>
5794      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/346"/>:
5795      "make IANA policy definitions consistent"
5796    </t>
5797  </list>
5798</t>
5799</section>
5800
5801<section title="Since draft-ietf-httpbis-p1-messaging-19" anchor="changes.since.19">
5802<t>
5803  Closed issues:
5804  <list style="symbols">
5805    <t>
5806      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/346"/>:
5807      "make IANA policy definitions consistent"
5808    </t>
5809    <t>
5810      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/359"/>:
5811      "clarify connection header field values are case-insensitive"
5812    </t>
5813    <t>
5814      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/361"/>:
5815      "ABNF requirements for recipients"
5816    </t>
5817    <t>
5818      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/368"/>:
5819      "note introduction of new IANA registries as normative changes"
5820    </t>
5821    <t>
5822      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/374"/>:
5823      "Reference to ISO-8859-1 is informative"
5824    </t>
5825  </list>
5826</t>
5827</section>
5828
5829<section title="Since draft-ietf-httpbis-p1-messaging-20" anchor="changes.since.20">
5830<t>
5831  Closed issues:
5832  <list style="symbols"> 
5833    <t>
5834      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/378"/>:
5835      "is 'q=' case-sensitive?"
5836    </t>
5837  </list>
5838</t>
5839<t>
5840  Other changes:
5841  <list style="symbols">
5842    <t>
5843      Drop notion of header fields being "hop-by-hop" without being listed in
5844      the Connection header field.     
5845    </t>
5846    <t>
5847      Section about connection management rewritten; dropping some historic
5848      information.
5849    </t>
5850    <t>
5851      Move description of "100-continue" into Part 2.
5852    </t>
5853    <t>
5854      Rewrite the persistent connection and Upgrade requirements to be
5855      actionable by role and consistent with the rest of HTTP.
5856    </t>
5857  </list>
5858</t>
5859</section>
5860
5861</section>
5862
5863</back>
5864</rfc>
Note: See TracBrowser for help on using the repository browser.