source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1884

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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "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 status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
49  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
50  <!ENTITY status-203             "<xref target='Part2' x:rel='#status.203' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
51  <!ENTITY status-3xx             "<xref target='Part2' x:rel='#status.3xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
52  <!ENTITY status-304             "<xref target='Part4' x:rel='#status.304' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
53  <!ENTITY status-4xx             "<xref target='Part2' x:rel='#status.4xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
54  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
55  <!ENTITY iana-header-registry   "<xref target='Part2' x:rel='#header.field.registry' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
56]>
57<?rfc toc="yes" ?>
58<?rfc symrefs="yes" ?>
59<?rfc sortrefs="yes" ?>
60<?rfc compact="yes"?>
61<?rfc subcompact="no" ?>
62<?rfc linkmailto="no" ?>
63<?rfc editing="no" ?>
64<?rfc comments="yes"?>
65<?rfc inline="yes"?>
66<?rfc rfcedstyle="yes"?>
67<?rfc-ext allow-markup-in-artwork="yes" ?>
68<?rfc-ext include-references-in-index="yes" ?>
69<rfc obsoletes="2145,2616" updates="2817" category="std" x:maturity-level="proposed"
70     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
71     xmlns:x='http://purl.org/net/xml2rfc/ext'>
72<x:link rel="next" basename="p2-semantics"/>
73<x:feedback template="mailto:ietf-http-wg@w3.org?subject={docname},%20%22{section}%22&amp;body=&lt;{ref}&gt;:"/>
74<front>
75
76  <title abbrev="HTTP/1.1 Message Syntax and Routing">Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing</title>
77
78  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
79    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
80    <address>
81      <postal>
82        <street>345 Park Ave</street>
83        <city>San Jose</city>
84        <region>CA</region>
85        <code>95110</code>
86        <country>USA</country>
87      </postal>
88      <email>fielding@gbiv.com</email>
89      <uri>http://roy.gbiv.com/</uri>
90    </address>
91  </author>
92
93  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
94    <organization abbrev="W3C">World Wide Web Consortium</organization>
95    <address>
96      <postal>
97        <street>W3C / ERCIM</street>
98        <street>2004, rte des Lucioles</street>
99        <city>Sophia-Antipolis</city>
100        <region>AM</region>
101        <code>06902</code>
102        <country>France</country>
103      </postal>
104      <email>ylafon@w3.org</email>
105      <uri>http://www.raubacapeu.net/people/yves/</uri>
106    </address>
107  </author>
108
109  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
110    <organization abbrev="greenbytes">greenbytes GmbH</organization>
111    <address>
112      <postal>
113        <street>Hafenweg 16</street>
114        <city>Muenster</city><region>NW</region><code>48155</code>
115        <country>Germany</country>
116      </postal>
117      <email>julian.reschke@greenbytes.de</email>
118      <uri>http://greenbytes.de/tech/webdav/</uri>
119    </address>
120  </author>
121
122  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
123  <workgroup>HTTPbis Working Group</workgroup>
124
125<abstract>
126<t>
127   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
128   distributed, collaborative, hypertext information systems. HTTP has been in
129   use by the World Wide Web global information initiative since 1990.
130   This document provides an overview of HTTP architecture and its associated
131   terminology, defines the "http" and "https" Uniform Resource Identifier
132   (URI) schemes, defines the HTTP/1.1 message syntax and parsing requirements,
133   and describes general security concerns for implementations.
134</t>   
135</abstract>
136
137<note title="Editorial Note (To be removed by RFC Editor)">
138  <t>
139    Discussion of this draft takes place on the HTTPBIS working group
140    mailing list (ietf-http-wg@w3.org), which is archived at
141    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
142  </t>
143  <t>
144    The current issues list is at
145    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
146    documents (including fancy diffs) can be found at
147    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
148  </t>
149  <t>
150    The changes in this draft are summarized in <xref target="changes.since.20"/>.
151  </t>
152</note>
153</front>
154<middle>
155<section title="Introduction" anchor="introduction">
156<t>
157   The Hypertext Transfer Protocol (HTTP) is an application-level
158   request/response protocol that uses extensible semantics and MIME-like
159   message payloads for flexible interaction with network-based hypertext
160   information systems. This document is the first in a series of documents
161   that collectively form the HTTP/1.1 specification:
162   <list style="empty">
163    <t>RFC xxx1: Message Syntax and Routing</t>
164    <t><xref target="Part2" x:fmt="none">RFC xxx2</xref>: Semantics and Content</t>
165    <t><xref target="Part4" x:fmt="none">RFC xxx3</xref>: Conditional Requests</t>
166    <t><xref target="Part5" x:fmt="none">RFC xxx4</xref>: Range Requests</t>
167    <t><xref target="Part6" x:fmt="none">RFC xxx5</xref>: Caching</t>
168    <t><xref target="Part7" x:fmt="none">RFC xxx6</xref>: Authentication</t>
169   </list>
170</t>
171<t>
172   This HTTP/1.1 specification obsoletes and moves to historic status
173   <xref target="RFC2616" x:fmt="none">RFC 2616</xref>, its predecessor
174   <xref target="RFC2068" x:fmt="none">RFC 2068</xref>,
175   <xref target="RFC2145" x:fmt="none">RFC 2145</xref> (on HTTP versioning),
176   and <xref target="RFC2817" x:fmt="none">RFC 2817</xref> (on using CONNECT
177   for TLS upgrades).
178</t>
179<t>
180   HTTP is a generic interface protocol for information systems. It is
181   designed to hide the details of how a service is implemented by presenting
182   a uniform interface to clients that is independent of the types of
183   resources provided. Likewise, servers do not need to be aware of each
184   client's purpose: an HTTP request can be considered in isolation rather
185   than being associated with a specific type of client or a predetermined
186   sequence of application steps. The result is a protocol that can be used
187   effectively in many different contexts and for which implementations can
188   evolve independently over time.
189</t>
190<t>
191   HTTP is also designed for use as an intermediation protocol for translating
192   communication to and from non-HTTP information systems.
193   HTTP proxies and gateways can provide access to alternative information
194   services by translating their diverse protocols into a hypertext
195   format that can be viewed and manipulated by clients in the same way
196   as HTTP services.
197</t>
198<t>
199   One consequence of HTTP flexibility is that the protocol cannot be
200   defined in terms of what occurs behind the interface. Instead, we
201   are limited to defining the syntax of communication, the intent
202   of received communication, and the expected behavior of recipients.
203   If the communication is considered in isolation, then successful
204   actions ought to be reflected in corresponding changes to the
205   observable interface provided by servers. However, since multiple
206   clients might act in parallel and perhaps at cross-purposes, we
207   cannot require that such changes be observable beyond the scope
208   of a single response.
209</t>
210<t>
211   This document describes the architectural elements that are used or
212   referred to in HTTP, defines the "http" and "https" URI schemes,
213   describes overall network operation and connection management,
214   and defines HTTP message framing and forwarding requirements.
215   Our goal is to define all of the mechanisms necessary for HTTP message
216   handling that are independent of message semantics, thereby defining the
217   complete set of requirements for message parsers and
218   message-forwarding intermediaries.
219</t>
220
221
222<section title="Requirement Notation" anchor="intro.requirements">
223<t>
224   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
225   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
226   document are to be interpreted as described in <xref target="RFC2119"/>.
227</t>
228<t>
229   Conformance criteria and considerations regarding error handling
230   are defined in <xref target="conformance"/>.
231</t>
232</section>
233
234<section title="Syntax Notation" anchor="notation">
235<iref primary="true" item="Grammar" subitem="ALPHA"/>
236<iref primary="true" item="Grammar" subitem="CR"/>
237<iref primary="true" item="Grammar" subitem="CRLF"/>
238<iref primary="true" item="Grammar" subitem="CTL"/>
239<iref primary="true" item="Grammar" subitem="DIGIT"/>
240<iref primary="true" item="Grammar" subitem="DQUOTE"/>
241<iref primary="true" item="Grammar" subitem="HEXDIG"/>
242<iref primary="true" item="Grammar" subitem="HTAB"/>
243<iref primary="true" item="Grammar" subitem="LF"/>
244<iref primary="true" item="Grammar" subitem="OCTET"/>
245<iref primary="true" item="Grammar" subitem="SP"/>
246<iref primary="true" item="Grammar" subitem="VCHAR"/>
247<t>
248   This specification uses the Augmented Backus-Naur Form (ABNF) notation
249   of <xref target="RFC5234"/> with the list rule extension defined in
250   <xref target="abnf.extension"/><xref target="collected.abnf"/> shows
251   the collected ABNF with the list rule expanded.
252</t>
253<t anchor="core.rules">
254  <x:anchor-alias value="ALPHA"/>
255  <x:anchor-alias value="CTL"/>
256  <x:anchor-alias value="CR"/>
257  <x:anchor-alias value="CRLF"/>
258  <x:anchor-alias value="DIGIT"/>
259  <x:anchor-alias value="DQUOTE"/>
260  <x:anchor-alias value="HEXDIG"/>
261  <x:anchor-alias value="HTAB"/>
262  <x:anchor-alias value="LF"/>
263  <x:anchor-alias value="OCTET"/>
264  <x:anchor-alias value="SP"/>
265  <x:anchor-alias value="VCHAR"/>
266   The following core rules are included by
267   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
268   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
269   DIGIT (decimal 0-9), DQUOTE (double quote),
270   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
271   OCTET (any 8-bit sequence of data), SP (space), and
272   VCHAR (any visible <xref target="USASCII"/> character).
273</t>
274<t>
275   As a convention, ABNF rule names prefixed with "obs-" denote
276   "obsolete" grammar rules that appear for historical reasons.
277</t>
278</section>
279</section>
280
281<section title="Architecture" anchor="architecture">
282<t>
283   HTTP was created for the World Wide Web architecture
284   and has evolved over time to support the scalability needs of a worldwide
285   hypertext system. Much of that architecture is reflected in the terminology
286   and syntax productions used to define HTTP.
287</t>
288
289<section title="Client/Server Messaging" anchor="operation">
290<iref primary="true" item="client"/>
291<iref primary="true" item="server"/>
292<iref primary="true" item="connection"/>
293<t>
294   HTTP is a stateless request/response protocol that operates by exchanging
295   <x:dfn>messages</x:dfn> (<xref target="http.message"/>) across a reliable
296   transport or session-layer
297   "<x:dfn>connection</x:dfn>" (<xref target="connection.management"/>).
298   An HTTP "<x:dfn>client</x:dfn>" is a program that establishes a connection
299   to a server for the purpose of sending one or more HTTP requests.
300   An HTTP "<x:dfn>server</x:dfn>" is a program that accepts connections
301   in order to service HTTP requests by sending HTTP responses.
302</t>
303<iref primary="true" item="user agent"/>
304<iref primary="true" item="origin server"/>
305<iref primary="true" item="browser"/>
306<iref primary="true" item="spider"/>
307<iref primary="true" item="sender"/>
308<iref primary="true" item="recipient"/>
309<t>
310   The terms client and server refer only to the roles that
311   these programs perform for a particular connection.  The same program
312   might act as a client on some connections and a server on others.  We use
313   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
314   such as a WWW browser, editor, or spider (web-traversing robot), and
315   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
316   authoritative responses to a request.  For general requirements, we use
317   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
318   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
319   message.
320</t>
321<t>
322   HTTP relies upon the Uniform Resource Identifier (URI)
323   standard <xref target="RFC3986"/> to indicate the target resource
324   (<xref target="target-resource"/>) and relationships between resources.
325   Messages are passed in a format similar to that used by Internet mail
326   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
327   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
328   between HTTP and MIME messages).
329</t>
330<t>
331   Most HTTP communication consists of a retrieval request (GET) for
332   a representation of some resource identified by a URI.  In the
333   simplest case, this might be accomplished via a single bidirectional
334   connection (===) between the user agent (UA) and the origin server (O).
335</t>
336<figure><artwork type="drawing">
337         request   &gt;
338    <x:highlight>UA</x:highlight> ======================================= <x:highlight>O</x:highlight>
339                                &lt;   response
340</artwork></figure>
341<iref primary="true" item="message"/>
342<iref primary="true" item="request"/>
343<iref primary="true" item="response"/>
344<t>
345   A client sends an HTTP request to a server in the form of a <x:dfn>request</x:dfn>
346   message, beginning with a request-line that includes a method, URI, and
347   protocol version (<xref target="request.line"/>),
348   followed by header fields containing
349   request modifiers, client information, and representation metadata
350   (<xref target="header.fields"/>),
351   an empty line to indicate the end of the header section, and finally
352   a message body containing the payload body (if any,
353   <xref target="message.body"/>).
354</t>
355<t>
356   A server responds to a client's request by sending one or more HTTP
357   <x:dfn>response</x:dfn>
358   messages, each beginning with a status line that
359   includes the protocol version, a success or error code, and textual
360   reason phrase (<xref target="status.line"/>),
361   possibly followed by header fields containing server
362   information, resource metadata, and representation metadata
363   (<xref target="header.fields"/>),
364   an empty line to indicate the end of the header section, and finally
365   a message body containing the payload body (if any,
366   <xref target="message.body"/>).
367</t>
368<t>
369   A connection might be used for multiple request/response exchanges,
370   as defined in <xref target="persistent.connections"/>.
371</t>
372<t>
373   The following example illustrates a typical message exchange for a
374   GET request on the URI "http://www.example.com/hello.txt":
375</t>
376<figure><preamble>
377client request:
378</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
379GET /hello.txt HTTP/1.1
380User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
381Host: www.example.com
382Accept-Language: en, mi
383
384</artwork></figure>
385<figure><preamble>
386server response:
387</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
388HTTP/1.1 200 OK
389Date: Mon, 27 Jul 2009 12:28:53 GMT
390Server: Apache
391Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
392ETag: "34aa387-d-1568eb00"
393Accept-Ranges: bytes
394Content-Length: <x:length-of target="exbody"/>
395Vary: Accept-Encoding
396Content-Type: text/plain
397
398<x:span anchor="exbody">Hello World!
399</x:span></artwork></figure>
400</section>
401
402<section title="Implementation Diversity" anchor="implementation-diversity">
403<t>
404   When considering the design of HTTP, it is easy to fall into a trap of
405   thinking that all user agents are general-purpose browsers and all origin
406   servers are large public websites. That is not the case in practice.
407   Common HTTP user agents include household appliances, stereos, scales,
408   firmware update scripts, command-line programs, mobile apps,
409   and communication devices in a multitude of shapes and sizes.  Likewise,
410   common HTTP origin servers include home automation units, configurable
411   networking components, office machines, autonomous robots, news feeds,
412   traffic cameras, ad selectors, and video delivery platforms.
413</t>
414<t>
415   The term "user agent" does not imply that there is a human user directly
416   interacting with the software agent at the time of a request. In many
417   cases, a user agent is installed or configured to run in the background
418   and save its results for later inspection (or save only a subset of those
419   results that might be interesting or erroneous). Spiders, for example, are
420   typically given a start URI and configured to follow certain behavior while
421   crawling the Web as a hypertext graph.
422</t>
423<t>
424   The implementation diversity of HTTP means that we cannot assume the
425   user agent can make interactive suggestions to a user or provide adequate
426   warning for security or privacy options.  In the few cases where this
427   specification requires reporting of errors to the user, it is acceptable
428   for such reporting to only be observable in an error console or log file.
429   Likewise, requirements that an automated action be confirmed by the user
430   before proceeding can me met via advance configuration choices,
431   run-time options, or simply not proceeding with the unsafe action.
432</t>
433</section>
434
435<section title="Intermediaries" anchor="intermediaries">
436<iref primary="true" item="intermediary"/>
437<t>
438   HTTP enables the use of intermediaries to satisfy requests through
439   a chain of connections.  There are three common forms of HTTP
440   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
441   a single intermediary might act as an origin server, proxy, gateway,
442   or tunnel, switching behavior based on the nature of each request.
443</t>
444<figure><artwork type="drawing">
445         &gt;             &gt;             &gt;             &gt;
446    <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>
447               &lt;             &lt;             &lt;             &lt;
448</artwork></figure>
449<t>
450   The figure above shows three intermediaries (A, B, and C) between the
451   user agent and origin server. A request or response message that
452   travels the whole chain will pass through four separate connections.
453   Some HTTP communication options
454   might apply only to the connection with the nearest, non-tunnel
455   neighbor, only to the end-points of the chain, or to all connections
456   along the chain. Although the diagram is linear, each participant might
457   be engaged in multiple, simultaneous communications. For example, B
458   might be receiving requests from many clients other than A, and/or
459   forwarding requests to servers other than C, at the same time that it
460   is handling A's request.
461</t>
462<t>
463<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
464<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
465   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
466   to describe various requirements in relation to the directional flow of a
467   message: all messages flow from upstream to downstream.
468   Likewise, we use the terms inbound and outbound to refer to
469   directions in relation to the request path:
470   "<x:dfn>inbound</x:dfn>" means toward the origin server and
471   "<x:dfn>outbound</x:dfn>" means toward the user agent.
472</t>
473<t><iref primary="true" item="proxy"/>
474   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
475   client, usually via local configuration rules, to receive requests
476   for some type(s) of absolute URI and attempt to satisfy those
477   requests via translation through the HTTP interface.  Some translations
478   are minimal, such as for proxy requests for "http" URIs, whereas
479   other requests might require translation to and from entirely different
480   application-level protocols. Proxies are often used to group an
481   organization's HTTP requests through a common intermediary for the
482   sake of security, annotation services, or shared caching.
483</t>
484<t>
485<iref primary="true" item="transforming proxy"/>
486<iref primary="true" item="non-transforming proxy"/>
487   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
488   or configured to modify request or response messages in a semantically
489   meaningful way (i.e., modifications, beyond those required by normal
490   HTTP processing, that change the message in a way that would be
491   significant to the original sender or potentially significant to
492   downstream recipients).  For example, a transforming proxy might be
493   acting as a shared annotation server (modifying responses to include
494   references to a local annotation database), a malware filter, a
495   format transcoder, or an intranet-to-Internet privacy filter.  Such
496   transformations are presumed to be desired by the client (or client
497   organization) that selected the proxy and are beyond the scope of
498   this specification.  However, when a proxy is not intended to transform
499   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
500   requirements that preserve HTTP message semantics. See &status-203; and
501   &header-warning; for status and warning codes related to transformations.
502</t>
503<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
504<iref primary="true" item="accelerator"/>
505   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
506   is a receiving agent that acts
507   as a layer above some other server(s) and translates the received
508   requests to the underlying server's protocol.  Gateways are often
509   used to encapsulate legacy or untrusted information services, to
510   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
511   enable partitioning or load-balancing of HTTP services across
512   multiple machines.
513</t>
514<t>
515   A gateway behaves as an origin server on its outbound connection and
516   as a user agent on its inbound connection.
517   All HTTP requirements applicable to an origin server
518   also apply to the outbound communication of a gateway.
519   A gateway communicates with inbound servers using any protocol that
520   it desires, including private extensions to HTTP that are outside
521   the scope of this specification.  However, an HTTP-to-HTTP gateway
522   that wishes to interoperate with third-party HTTP servers &MUST;
523   conform to HTTP user agent requirements on the gateway's inbound
524   connection and &MUST; implement the <x:ref>Connection</x:ref>
525   (<xref target="header.connection"/>) and <x:ref>Via</x:ref>
526   (<xref target="header.via"/>) header fields for both connections.
527</t>
528<t><iref primary="true" item="tunnel"/>
529   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
530   without changing the messages. Once active, a tunnel is not
531   considered a party to the HTTP communication, though the tunnel might
532   have been initiated by an HTTP request. A tunnel ceases to exist when
533   both ends of the relayed connection are closed. Tunnels are used to
534   extend a virtual connection through an intermediary, such as when
535   Transport Layer Security (TLS, <xref target="RFC5246"/>) is used to
536   establish confidential communication through a shared firewall proxy.
537</t>
538<t><iref primary="true" item="interception proxy"/>
539<iref primary="true" item="transparent proxy"/>
540<iref primary="true" item="captive portal"/>
541   The above categories for intermediary only consider those acting as
542   participants in the HTTP communication.  There are also intermediaries
543   that can act on lower layers of the network protocol stack, filtering or
544   redirecting HTTP traffic without the knowledge or permission of message
545   senders. Network intermediaries often introduce security flaws or
546   interoperability problems by violating HTTP semantics.  For example, an
547   "<x:dfn>interception proxy</x:dfn>" <xref target="RFC3040"/> (also commonly
548   known as a "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/> or
549   "<x:dfn>captive portal</x:dfn>")
550   differs from an HTTP proxy because it is not selected by the client.
551   Instead, an interception proxy filters or redirects outgoing TCP port 80
552   packets (and occasionally other common port traffic).
553   Interception proxies are commonly found on public network access points,
554   as a means of enforcing account subscription prior to allowing use of
555   non-local Internet services, and within corporate firewalls to enforce
556   network usage policies.
557   They are indistinguishable from a man-in-the-middle attack.
558</t>
559<t>
560   HTTP is defined as a stateless protocol, meaning that each request message
561   can be understood in isolation.  Many implementations depend on HTTP's
562   stateless design in order to reuse proxied connections or dynamically
563   load balance requests across multiple servers.  Hence, servers &MUST-NOT;
564   assume that two requests on the same connection are from the same user
565   agent unless the connection is secured and specific to that agent.
566   Some non-standard HTTP extensions (e.g., <xref target="RFC4559"/>) have
567   been known to violate this requirement, resulting in security and
568   interoperability problems.
569</t>
570</section>
571
572<section title="Caches" anchor="caches">
573<iref primary="true" item="cache"/>
574<t>
575   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
576   subsystem that controls its message storage, retrieval, and deletion.
577   A cache stores cacheable responses in order to reduce the response
578   time and network bandwidth consumption on future, equivalent
579   requests. Any client or server &MAY; employ a cache, though a cache
580   cannot be used by a server while it is acting as a tunnel.
581</t>
582<t>
583   The effect of a cache is that the request/response chain is shortened
584   if one of the participants along the chain has a cached response
585   applicable to that request. The following illustrates the resulting
586   chain if B has a cached copy of an earlier response from O (via C)
587   for a request which has not been cached by UA or A.
588</t>
589<figure><artwork type="drawing">
590            &gt;             &gt;
591       <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>
592                  &lt;             &lt;
593</artwork></figure>
594<t><iref primary="true" item="cacheable"/>
595   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
596   the response message for use in answering subsequent requests.
597   Even when a response is cacheable, there might be additional
598   constraints placed by the client or by the origin server on when
599   that cached response can be used for a particular request. HTTP
600   requirements for cache behavior and cacheable responses are
601   defined in &caching-overview;
602</t>
603<t>
604   There are a wide variety of architectures and configurations
605   of caches and proxies deployed across the World Wide Web and
606   inside large organizations. These systems include national hierarchies
607   of proxy caches to save transoceanic bandwidth, systems that
608   broadcast or multicast cache entries, organizations that distribute
609   subsets of cached data via optical media, and so on.
610</t>
611</section>
612
613<section title="Conformance and Error Handling" anchor="conformance">
614<t>
615   This specification targets conformance criteria according to the role of
616   a participant in HTTP communication.  Hence, HTTP requirements are placed
617   on senders, recipients, clients, servers, user agents, intermediaries,
618   origin servers, proxies, gateways, or caches, depending on what behavior
619   is being constrained by the requirement. Additional (social) requirements
620   are placed on implementations, resource owners, and protocol element
621   registrations when they apply beyond the scope of a single communication.
622</t>
623<t>
624   The verb "generate" is used instead of "send" where a requirement
625   differentiates between creating a protocol element and merely forwarding a
626   received element downstream.
627</t>
628<t>
629   An implementation is considered conformant if it complies with all of the
630   requirements associated with the roles it partakes in HTTP. Note that
631   SHOULD-level requirements are relevant here, unless one of the documented
632   exceptions is applicable.
633</t>
634<t>
635   Conformance applies to both the syntax and semantics of HTTP protocol
636   elements. A sender &MUST-NOT; generate protocol elements that convey a
637   meaning that is known by that sender to be false. A sender &MUST-NOT;
638   generate protocol elements that do not match the grammar defined by the
639   ABNF rules for those protocol elements that are applicable to the sender's
640   role. If a received protocol element is processed, the recipient &MUST; be
641   able to parse any value that would match the ABNF rules for that protocol
642   element, excluding only those rules not applicable to the recipient's role.
643</t>
644<t>
645   Unless noted otherwise, a recipient &MAY; attempt to recover a usable
646   protocol element from an invalid construct.  HTTP does not define
647   specific error handling mechanisms except when they have a direct impact
648   on security, since different applications of the protocol require
649   different error handling strategies.  For example, a Web browser might
650   wish to transparently recover from a response where the
651   <x:ref>Location</x:ref> header field doesn't parse according to the ABNF,
652   whereas a systems control client might consider any form of error recovery
653   to be dangerous.
654</t>
655</section>
656
657<section title="Protocol Versioning" anchor="http.version">
658  <x:anchor-alias value="HTTP-version"/>
659  <x:anchor-alias value="HTTP-name"/>
660<t>
661   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
662   versions of the protocol. This specification defines version "1.1".
663   The protocol version as a whole indicates the sender's conformance
664   with the set of requirements laid out in that version's corresponding
665   specification of HTTP.
666</t>
667<t>
668   The version of an HTTP message is indicated by an HTTP-version field
669   in the first line of the message. HTTP-version is case-sensitive.
670</t>
671<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-version"/><iref primary="true" item="Grammar" subitem="HTTP-name"/>
672  <x:ref>HTTP-version</x:ref>  = <x:ref>HTTP-name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
673  <x:ref>HTTP-name</x:ref>     = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
674</artwork></figure>
675<t>
676   The HTTP version number consists of two decimal digits separated by a "."
677   (period or decimal point).  The first digit ("major version") indicates the
678   HTTP messaging syntax, whereas the second digit ("minor version") indicates
679   the highest minor version to which the sender is
680   conformant and able to understand for future communication.  The minor
681   version advertises the sender's communication capabilities even when the
682   sender is only using a backwards-compatible subset of the protocol,
683   thereby letting the recipient know that more advanced features can
684   be used in response (by servers) or in future requests (by clients).
685</t>
686<t>
687   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
688   <xref target="RFC1945"/> or a recipient whose version is unknown,
689   the HTTP/1.1 message is constructed such that it can be interpreted
690   as a valid HTTP/1.0 message if all of the newer features are ignored.
691   This specification places recipient-version requirements on some
692   new features so that a conformant sender will only use compatible
693   features until it has determined, through configuration or the
694   receipt of a message, that the recipient supports HTTP/1.1.
695</t>
696<t>
697   The interpretation of a header field does not change between minor
698   versions of the same major HTTP version, though the default
699   behavior of a recipient in the absence of such a field can change.
700   Unless specified otherwise, header fields defined in HTTP/1.1 are
701   defined for all versions of HTTP/1.x.  In particular, the <x:ref>Host</x:ref>
702   and <x:ref>Connection</x:ref> header fields ought to be implemented by all
703   HTTP/1.x implementations whether or not they advertise conformance with
704   HTTP/1.1.
705</t>
706<t>
707   New header fields can be defined such that, when they are
708   understood by a recipient, they might override or enhance the
709   interpretation of previously defined header fields.  When an
710   implementation receives an unrecognized header field, the recipient
711   &MUST; ignore that header field for local processing regardless of
712   the message's HTTP version.  An unrecognized header field received
713   by a proxy &MUST; be forwarded downstream unless the header field's
714   field-name is listed in the message's <x:ref>Connection</x:ref> header field
715   (see <xref target="header.connection"/>).
716   These requirements allow HTTP's functionality to be enhanced without
717   requiring prior update of deployed intermediaries.
718</t>
719<t>
720   Intermediaries that process HTTP messages (i.e., all intermediaries
721   other than those acting as tunnels) &MUST; send their own HTTP-version
722   in forwarded messages.  In other words, they &MUST-NOT; blindly
723   forward the first line of an HTTP message without ensuring that the
724   protocol version in that message matches a version to which that
725   intermediary is conformant for both the receiving and
726   sending of messages.  Forwarding an HTTP message without rewriting
727   the HTTP-version might result in communication errors when downstream
728   recipients use the message sender's version to determine what features
729   are safe to use for later communication with that sender.
730</t>
731<t>
732   An HTTP client &SHOULD; send a request version equal to the highest
733   version to which the client is conformant and
734   whose major version is no higher than the highest version supported
735   by the server, if this is known.  An HTTP client &MUST-NOT; send a
736   version to which it is not conformant.
737</t>
738<t>
739   An HTTP client &MAY; send a lower request version if it is known that
740   the server incorrectly implements the HTTP specification, but only
741   after the client has attempted at least one normal request and determined
742   from the response status or header fields (e.g., <x:ref>Server</x:ref>) that
743   the server improperly handles higher request versions.
744</t>
745<t>
746   An HTTP server &SHOULD; send a response version equal to the highest
747   version to which the server is conformant and
748   whose major version is less than or equal to the one received in the
749   request.  An HTTP server &MUST-NOT; send a version to which it is not
750   conformant.  A server &MAY; send a <x:ref>505 (HTTP Version Not
751   Supported)</x:ref> response if it cannot send a response using the
752   major version used in the client's request.
753</t>
754<t>
755   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
756   if it is known or suspected that the client incorrectly implements the
757   HTTP specification and is incapable of correctly processing later
758   version responses, such as when a client fails to parse the version
759   number correctly or when an intermediary is known to blindly forward
760   the HTTP-version even when it doesn't conform to the given minor
761   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
762   performed unless triggered by specific client attributes, such as when
763   one or more of the request header fields (e.g., <x:ref>User-Agent</x:ref>)
764   uniquely match the values sent by a client known to be in error.
765</t>
766<t>
767   The intention of HTTP's versioning design is that the major number
768   will only be incremented if an incompatible message syntax is
769   introduced, and that the minor number will only be incremented when
770   changes made to the protocol have the effect of adding to the message
771   semantics or implying additional capabilities of the sender.  However,
772   the minor version was not incremented for the changes introduced between
773   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
774   is specifically avoiding any such changes to the protocol.
775</t>
776</section>
777
778<section title="Uniform Resource Identifiers" anchor="uri">
779<iref primary="true" item="resource"/>
780<t>
781   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
782   throughout HTTP as the means for identifying resources. URI references
783   are used to target requests, indicate redirects, and define relationships.
784   HTTP does not limit what a resource might be; it merely defines an interface
785   that can be used to interact with a resource via HTTP. More information on
786   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
787</t>
788  <x:anchor-alias value="URI-reference"/>
789  <x:anchor-alias value="absolute-URI"/>
790  <x:anchor-alias value="relative-part"/>
791  <x:anchor-alias value="authority"/>
792  <x:anchor-alias value="path-abempty"/>
793  <x:anchor-alias value="path-absolute"/>
794  <x:anchor-alias value="port"/>
795  <x:anchor-alias value="query"/>
796  <x:anchor-alias value="uri-host"/>
797  <x:anchor-alias value="partial-URI"/>
798<t>
799   This specification adopts the definitions of "URI-reference",
800   "absolute-URI", "relative-part", "port", "host",
801   "path-abempty", "path-absolute", "query", and "authority" from the
802   URI generic syntax <xref target="RFC3986"/>.
803   In addition, we define a partial-URI rule for protocol elements
804   that allow a relative URI but not a fragment.
805</t>
806<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="URI-reference"><!--exported production--></iref><iref primary="true" item="Grammar" subitem="absolute-URI"/><iref primary="true" item="Grammar" subitem="authority"/><iref primary="true" item="Grammar" subitem="path-absolute"/><iref primary="true" item="Grammar" subitem="port"/><iref primary="true" item="Grammar" subitem="query"/><iref primary="true" item="Grammar" subitem="uri-host"/><iref primary="true" item="Grammar" subitem="partial-URI"><!--exported production--></iref>
807  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
808  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
809  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
810  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
811  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
812  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
813  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
814  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
815  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
816 
817  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
818</artwork></figure>
819<t>
820   Each protocol element in HTTP that allows a URI reference will indicate
821   in its ABNF production whether the element allows any form of reference
822   (URI-reference), only a URI in absolute form (absolute-URI), only the
823   path and optional query components, or some combination of the above.
824   Unless otherwise indicated, URI references are parsed
825   relative to the effective request URI
826   (<xref target="effective.request.uri"/>).
827</t>
828
829<section title="http URI scheme" anchor="http.uri">
830  <x:anchor-alias value="http-URI"/>
831  <iref item="http URI scheme" primary="true"/>
832  <iref item="URI scheme" subitem="http" primary="true"/>
833<t>
834   The "http" URI scheme is hereby defined for the purpose of minting
835   identifiers according to their association with the hierarchical
836   namespace governed by a potential HTTP origin server listening for
837   TCP connections on a given port.
838</t>
839<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"><!--terminal production--></iref>
840  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
841</artwork></figure>
842<t>
843   The HTTP origin server is identified by the generic syntax's
844   <x:ref>authority</x:ref> component, which includes a host identifier
845   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
846   The remainder of the URI, consisting of both the hierarchical path
847   component and optional query component, serves as an identifier for
848   a potential resource within that origin server's name space.
849</t>
850<t>
851   If the host identifier is provided as an IP literal or IPv4 address,
852   then the origin server is any listener on the indicated TCP port at
853   that IP address. If host is a registered name, then that name is
854   considered an indirect identifier and the recipient might use a name
855   resolution service, such as DNS, to find the address of a listener
856   for that host.
857   The host &MUST-NOT; be empty; if an "http" URI is received with an
858   empty host, then it &MUST; be rejected as invalid.
859   If the port subcomponent is empty or not given, then TCP port 80 is
860   assumed (the default reserved port for WWW services).
861</t>
862<t>
863   Regardless of the form of host identifier, access to that host is not
864   implied by the mere presence of its name or address. The host might or might
865   not exist and, even when it does exist, might or might not be running an
866   HTTP server or listening to the indicated port. The "http" URI scheme
867   makes use of the delegated nature of Internet names and addresses to
868   establish a naming authority (whatever entity has the ability to place
869   an HTTP server at that Internet name or address) and allows that
870   authority to determine which names are valid and how they might be used.
871</t>
872<t>
873   When an "http" URI is used within a context that calls for access to the
874   indicated resource, a client &MAY; attempt access by resolving
875   the host to an IP address, establishing a TCP connection to that address
876   on the indicated port, and sending an HTTP request message
877   (<xref target="http.message"/>) containing the URI's identifying data
878   (<xref target="message.routing"/>) to the server.
879   If the server responds to that request with a non-interim HTTP response
880   message, as described in &status-codes;, then that response
881   is considered an authoritative answer to the client's request.
882</t>
883<t>
884   Although HTTP is independent of the transport protocol, the "http"
885   scheme is specific to TCP-based services because the name delegation
886   process depends on TCP for establishing authority.
887   An HTTP service based on some other underlying connection protocol
888   would presumably be identified using a different URI scheme, just as
889   the "https" scheme (below) is used for servers that require an SSL/TLS
890   transport layer on a connection. Other protocols might also be used to
891   provide access to "http" identified resources &mdash; it is only the
892   authoritative interface used for mapping the namespace that is
893   specific to TCP.
894</t>
895<t>
896   The URI generic syntax for authority also includes a deprecated
897   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
898   for including user authentication information in the URI.  Some
899   implementations make use of the userinfo component for internal
900   configuration of authentication information, such as within command
901   invocation options, configuration files, or bookmark lists, even
902   though such usage might expose a user identifier or password.
903   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
904   delimiter) when transmitting an "http" URI in a message.  Recipients
905   of HTTP messages that contain a URI reference &SHOULD; parse for the
906   existence of userinfo and treat its presence as an error, likely
907   indicating that the deprecated subcomponent is being used to obscure
908   the authority for the sake of phishing attacks.
909</t>
910</section>
911
912<section title="https URI scheme" anchor="https.uri">
913   <x:anchor-alias value="https-URI"/>
914   <iref item="https URI scheme"/>
915   <iref item="URI scheme" subitem="https"/>
916<t>
917   The "https" URI scheme is hereby defined for the purpose of minting
918   identifiers according to their association with the hierarchical
919   namespace governed by a potential HTTP origin server listening for
920   SSL/TLS-secured connections on a given TCP port.
921</t>
922<t>
923   All of the requirements listed above for the "http" scheme are also
924   requirements for the "https" scheme, except that a default TCP port
925   of 443 is assumed if the port subcomponent is empty or not given,
926   and the TCP connection &MUST; be secured through the
927   use of strong encryption prior to sending the first HTTP request.
928</t>
929<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"><!--terminal production--></iref>
930  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
931</artwork></figure>
932<t>
933   Unlike the "http" scheme, responses to "https" identified requests
934   are never "public" and thus &MUST-NOT; be reused for shared caching.
935   They can, however, be reused in a private cache if the message is
936   cacheable by default in HTTP or specifically indicated as such by
937   the Cache-Control header field (&header-cache-control;).
938</t>
939<t>
940   Resources made available via the "https" scheme have no shared
941   identity with the "http" scheme even if their resource identifiers
942   indicate the same authority (the same host listening to the same
943   TCP port).  They are distinct name spaces and are considered to be
944   distinct origin servers.  However, an extension to HTTP that is
945   defined to apply to entire host domains, such as the Cookie protocol
946   <xref target="RFC6265"/>, can allow information
947   set by one service to impact communication with other services
948   within a matching group of host domains.
949</t>
950<t>
951   The process for authoritative access to an "https" identified
952   resource is defined in <xref target="RFC2818"/>.
953</t>
954</section>
955
956<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
957<t>
958   Since the "http" and "https" schemes conform to the URI generic syntax,
959   such URIs are normalized and compared according to the algorithm defined
960   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
961   described above for each scheme.
962</t>
963<t>
964   If the port is equal to the default port for a scheme, the normal
965   form is to elide the port subcomponent. Likewise, an empty path
966   component is equivalent to an absolute path of "/", so the normal
967   form is to provide a path of "/" instead. The scheme and host
968   are case-insensitive and normally provided in lowercase; all
969   other components are compared in a case-sensitive manner.
970   Characters other than those in the "reserved" set are equivalent
971   to their percent-encoded octets (see <xref target="RFC3986"
972   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
973</t>
974<t>
975   For example, the following three URIs are equivalent:
976</t>
977<figure><artwork type="example">
978   http://example.com:80/~smith/home.html
979   http://EXAMPLE.com/%7Esmith/home.html
980   http://EXAMPLE.com:/%7esmith/home.html
981</artwork></figure>
982</section>
983</section>
984</section>
985
986<section title="Message Format" anchor="http.message">
987<x:anchor-alias value="generic-message"/>
988<x:anchor-alias value="message.types"/>
989<x:anchor-alias value="HTTP-message"/>
990<x:anchor-alias value="start-line"/>
991<iref item="header section"/>
992<iref item="headers"/>
993<iref item="header field"/>
994<t>
995   All HTTP/1.1 messages consist of a start-line followed by a sequence of
996   octets in a format similar to the Internet Message Format
997   <xref target="RFC5322"/>: zero or more header fields (collectively
998   referred to as the "headers" or the "header section"), an empty line
999   indicating the end of the header section, and an optional message body.
1000</t>
1001<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"><!--terminal production--></iref>
1002  <x:ref>HTTP-message</x:ref>   = <x:ref>start-line</x:ref>
1003                   *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1004                   <x:ref>CRLF</x:ref>
1005                   [ <x:ref>message-body</x:ref> ]
1006</artwork></figure>
1007<t>
1008   The normal procedure for parsing an HTTP message is to read the
1009   start-line into a structure, read each header field into a hash
1010   table by field name until the empty line, and then use the parsed
1011   data to determine if a message body is expected.  If a message body
1012   has been indicated, then it is read as a stream until an amount
1013   of octets equal to the message body length is read or the connection
1014   is closed.
1015</t>
1016<t>
1017   Recipients &MUST; parse an HTTP message as a sequence of octets in an
1018   encoding that is a superset of US-ASCII <xref target="USASCII"/>.
1019   Parsing an HTTP message as a stream of Unicode characters, without regard
1020   for the specific encoding, creates security vulnerabilities due to the
1021   varying ways that string processing libraries handle invalid multibyte
1022   character sequences that contain the octet LF (%x0A).  String-based
1023   parsers can only be safely used within protocol elements after the element
1024   has been extracted from the message, such as within a header field-value
1025   after message parsing has delineated the individual fields.
1026</t>
1027<t>
1028   An HTTP message can be parsed as a stream for incremental processing or
1029   forwarding downstream.  However, recipients cannot rely on incremental
1030   delivery of partial messages, since some implementations will buffer or
1031   delay message forwarding for the sake of network efficiency, security
1032   checks, or payload transformations.
1033</t>
1034
1035<section title="Start Line" anchor="start.line">
1036  <x:anchor-alias value="Start-Line"/>
1037<t>
1038   An HTTP message can either be a request from client to server or a
1039   response from server to client.  Syntactically, the two types of message
1040   differ only in the start-line, which is either a request-line (for requests)
1041   or a status-line (for responses), and in the algorithm for determining
1042   the length of the message body (<xref target="message.body"/>).
1043   In theory, a client could receive requests and a server could receive
1044   responses, distinguishing them by their different start-line formats,
1045   but in practice servers are implemented to only expect a request
1046   (a response is interpreted as an unknown or invalid request method)
1047   and clients are implemented to only expect a response.
1048</t>
1049<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="start-line"/>
1050  <x:ref>start-line</x:ref>     = <x:ref>request-line</x:ref> / <x:ref>status-line</x:ref>
1051</artwork></figure>
1052<t>
1053   A sender &MUST-NOT; send whitespace between the start-line and
1054   the first header field. The presence of such whitespace in a request
1055   might be an attempt to trick a server into ignoring that field or
1056   processing the line after it as a new request, either of which might
1057   result in a security vulnerability if other implementations within
1058   the request chain interpret the same message differently.
1059   Likewise, the presence of such whitespace in a response might be
1060   ignored by some clients or cause others to cease parsing.
1061</t>
1062
1063<section title="Request Line" anchor="request.line">
1064  <x:anchor-alias value="Request"/>
1065  <x:anchor-alias value="request-line"/>
1066<t>
1067   A request-line begins with a method token, followed by a single
1068   space (SP), the request-target, another single space (SP), the
1069   protocol version, and ending with CRLF.
1070</t>
1071<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-line"/>
1072  <x:ref>request-line</x:ref>   = <x:ref>method</x:ref> <x:ref>SP</x:ref> <x:ref>request-target</x:ref> <x:ref>SP</x:ref> <x:ref>HTTP-version</x:ref> <x:ref>CRLF</x:ref>
1073</artwork></figure>
1074<t>
1075   A server &MUST; be able to parse any received message that begins
1076   with a request-line and matches the ABNF rule for HTTP-message.
1077</t>
1078<iref primary="true" item="method"/>
1079<t anchor="method">
1080   The method token indicates the request method to be performed on the
1081   target resource. The request method is case-sensitive.
1082</t>
1083<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="method"/>
1084  <x:ref>method</x:ref>         = <x:ref>token</x:ref>
1085</artwork></figure>
1086<t>
1087   The methods defined by this specification can be found in
1088   &methods;, along with information regarding the HTTP method registry
1089   and considerations for defining new methods.
1090</t>
1091<iref item="request-target"/>
1092<t>
1093   The request-target identifies the target resource upon which to apply
1094   the request, as defined in <xref target="request-target"/>.
1095</t>
1096<t>
1097   No whitespace is allowed inside the method, request-target, and
1098   protocol version.  Hence, recipients typically parse the request-line
1099   into its component parts by splitting on the SP characters.
1100</t>
1101<t>
1102   Unfortunately, some user agents fail to properly encode hypertext
1103   references that have embedded whitespace, sending the characters
1104   directly instead of properly percent-encoding the disallowed characters.
1105   Recipients of an invalid request-line &SHOULD; respond with either a
1106   <x:ref>400 (Bad Request)</x:ref> error or a <x:ref>301 (Moved Permanently)</x:ref>
1107   redirect with the request-target properly encoded.  Recipients &SHOULD-NOT;
1108   attempt to autocorrect and then process the request without a redirect,
1109   since the invalid request-line might be deliberately crafted to bypass
1110   security filters along the request chain.
1111</t>
1112<t>
1113   HTTP does not place a pre-defined limit on the length of a request-line.
1114   A server that receives a method longer than any that it implements
1115   &SHOULD; respond with either a <x:ref>405 (Method Not Allowed)</x:ref>, if it is an origin
1116   server, or a <x:ref>501 (Not Implemented)</x:ref> status code.
1117   A server &MUST; be prepared to receive URIs of unbounded length and
1118   respond with the <x:ref>414 (URI Too Long)</x:ref> status code if the received
1119   request-target would be longer than the server wishes to handle
1120   (see &status-414;).
1121</t>
1122<t>
1123   Various ad-hoc limitations on request-line length are found in practice.
1124   It is &RECOMMENDED; that all HTTP senders and recipients support, at a
1125   minimum, request-line lengths of up to 8000 octets.
1126</t>
1127</section>
1128
1129<section title="Status Line" anchor="status.line">
1130  <x:anchor-alias value="response"/>
1131  <x:anchor-alias value="status-line"/>
1132  <x:anchor-alias value="status-code"/>
1133  <x:anchor-alias value="reason-phrase"/>
1134<t>
1135   The first line of a response message is the status-line, consisting
1136   of the protocol version, a space (SP), the status code, another space,
1137   a possibly-empty textual phrase describing the status code, and
1138   ending with CRLF.
1139</t>
1140<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-line"/>
1141  <x:ref>status-line</x:ref> = <x:ref>HTTP-version</x:ref> <x:ref>SP</x:ref> <x:ref>status-code</x:ref> <x:ref>SP</x:ref> <x:ref>reason-phrase</x:ref> <x:ref>CRLF</x:ref>
1142</artwork></figure>
1143<t>
1144   A client &MUST; be able to parse any received message that begins
1145   with a status-line and matches the ABNF rule for HTTP-message.
1146</t>
1147<t>
1148   The status-code element is a 3-digit integer code describing the
1149   result of the server's attempt to understand and satisfy the client's
1150   corresponding request. The rest of the response message is to be
1151   interpreted in light of the semantics defined for that status code.
1152   See &status-codes; for information about the semantics of status codes,
1153   including the classes of status code (indicated by the first digit),
1154   the status codes defined by this specification, considerations for the
1155   definition of new status codes, and the IANA registry.
1156</t>
1157<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-code"/>
1158  <x:ref>status-code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1159</artwork></figure>
1160<t>   
1161   The reason-phrase element exists for the sole purpose of providing a
1162   textual description associated with the numeric status code, mostly
1163   out of deference to earlier Internet application protocols that were more
1164   frequently used with interactive text clients. A client &SHOULD; ignore
1165   the reason-phrase content.
1166</t>
1167<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="reason-phrase"/>
1168  <x:ref>reason-phrase</x:ref>  = *( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1169</artwork></figure>
1170</section>
1171</section>
1172
1173<section title="Header Fields" anchor="header.fields">
1174  <x:anchor-alias value="header-field"/>
1175  <x:anchor-alias value="field-content"/>
1176  <x:anchor-alias value="field-name"/>
1177  <x:anchor-alias value="field-value"/>
1178  <x:anchor-alias value="obs-fold"/>
1179<t>
1180   Each HTTP header field consists of a case-insensitive field name
1181   followed by a colon (":"), optional whitespace, and the field value.
1182</t>
1183<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="header-field"/><iref primary="true" item="Grammar" subitem="field-name"/><iref primary="true" item="Grammar" subitem="field-value"/><iref primary="true" item="Grammar" subitem="field-content"/><iref primary="true" item="Grammar" subitem="obs-fold"/>
1184  <x:ref>header-field</x:ref>   = <x:ref>field-name</x:ref> ":" <x:ref>OWS</x:ref> <x:ref>field-value</x:ref> <x:ref>BWS</x:ref>
1185  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1186  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>obs-fold</x:ref> )
1187  <x:ref>field-content</x:ref>  = *( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1188  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref> ( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1189                 ; obsolete line folding
1190                 ; see <xref target="field.parsing"/>
1191</artwork></figure>
1192<t>
1193   The field-name token labels the corresponding field-value as having the
1194   semantics defined by that header field.  For example, the <x:ref>Date</x:ref>
1195   header field is defined in &header-date; as containing the origination
1196   timestamp for the message in which it appears.
1197</t>
1198<t>
1199   HTTP header fields are fully extensible: there is no limit on the
1200   introduction of new field names, each presumably defining new semantics,
1201   or on the number of header fields used in a given message.  Existing
1202   fields are defined in each part of this specification and in many other
1203   specifications outside the standards process.
1204   New header fields can be introduced without changing the protocol version
1205   if their defined semantics allow them to be safely ignored by recipients
1206   that do not recognize them.
1207</t>
1208<t>
1209   New HTTP header fields &SHOULD; be registered with IANA in the
1210   Message Header Field Registry, as described in &iana-header-registry;.
1211   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1212   field-name is listed in the <x:ref>Connection</x:ref> header field
1213   (<xref target="header.connection"/>) or the proxy is specifically
1214   configured to block or otherwise transform such fields.
1215   Unrecognized header fields &SHOULD; be ignored by other recipients.
1216</t>
1217<t>
1218   The order in which header fields with differing field names are
1219   received is not significant. However, it is "good practice" to send
1220   header fields that contain control data first, such as <x:ref>Host</x:ref>
1221   on requests and <x:ref>Date</x:ref> on responses, so that implementations
1222   can decide when not to handle a message as early as possible.  A server
1223   &MUST; wait until the entire header section is received before interpreting
1224   a request message, since later header fields might include conditionals,
1225   authentication credentials, or deliberately misleading duplicate
1226   header fields that would impact request processing.
1227</t>
1228<t>
1229   Multiple header fields with the same field name &MUST-NOT; be
1230   sent in a message unless the entire field value for that
1231   header field is defined as a comma-separated list [i.e., #(values)].
1232   Multiple header fields with the same field name can be combined into
1233   one "field-name: field-value" pair, without changing the semantics of the
1234   message, by appending each subsequent field value to the combined
1235   field value in order, separated by a comma. The order in which
1236   header fields with the same field name are received is therefore
1237   significant to the interpretation of the combined field value;
1238   a proxy &MUST-NOT; change the order of these field values when
1239   forwarding a message.
1240</t>
1241<x:note>
1242  <t>
1243   &Note; The "Set-Cookie" header field as implemented in
1244   practice can occur multiple times, but does not use the list syntax, and
1245   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1246   for details.) Also note that the Set-Cookie2 header field specified in
1247   <xref target="RFC2965"/> does not share this problem.
1248  </t>
1249</x:note>
1250
1251<section title="Whitespace" anchor="whitespace">
1252<t anchor="rule.LWS">
1253   This specification uses three rules to denote the use of linear
1254   whitespace: OWS (optional whitespace), RWS (required whitespace), and
1255   BWS ("bad" whitespace).
1256</t>
1257<t anchor="rule.OWS">
1258   The OWS rule is used where zero or more linear whitespace octets might
1259   appear. OWS &SHOULD; either not be produced or be produced as a single
1260   SP. Multiple OWS octets that occur within field-content &SHOULD; either
1261   be replaced with a single SP or transformed to all SP octets (each
1262   octet other than SP replaced with SP) before interpreting the field value
1263   or forwarding the message downstream.
1264</t>
1265<t anchor="rule.RWS">
1266   RWS is used when at least one linear whitespace octet is required to
1267   separate field tokens. RWS &SHOULD; be produced as a single SP.
1268   Multiple RWS octets that occur within field-content &SHOULD; either
1269   be replaced with a single SP or transformed to all SP octets before
1270   interpreting the field value or forwarding the message downstream.
1271</t>
1272<t anchor="rule.BWS">
1273   BWS is used where the grammar allows optional whitespace, for historical
1274   reasons, but senders &SHOULD-NOT; produce it in messages;
1275   recipients &MUST; accept such bad optional whitespace and remove it before
1276   interpreting the field value or forwarding the message downstream.
1277</t>
1278<t anchor="rule.whitespace">
1279  <x:anchor-alias value="BWS"/>
1280  <x:anchor-alias value="OWS"/>
1281  <x:anchor-alias value="RWS"/>
1282</t>
1283<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="OWS"/><iref primary="true" item="Grammar" subitem="RWS"/><iref primary="true" item="Grammar" subitem="BWS"/>
1284  <x:ref>OWS</x:ref>            = *( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1285                 ; "optional" whitespace
1286  <x:ref>RWS</x:ref>            = 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1287                 ; "required" whitespace
1288  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
1289                 ; "bad" whitespace
1290</artwork></figure>
1291</section>
1292
1293<section title="Field Parsing" anchor="field.parsing">
1294<t>
1295   No whitespace is allowed between the header field-name and colon.
1296   In the past, differences in the handling of such whitespace have led to
1297   security vulnerabilities in request routing and response handling.
1298   Any received request message that contains whitespace between a header
1299   field-name and colon &MUST; be rejected with a response code of 400
1300   (Bad Request).  A proxy &MUST; remove any such whitespace from a response
1301   message before forwarding the message downstream.
1302</t>
1303<t>
1304   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1305   preferred. The field value does not include any leading or trailing white
1306   space: OWS occurring before the first non-whitespace octet of the
1307   field value or after the last non-whitespace octet of the field value
1308   is ignored and &SHOULD; be removed before further processing (as this does
1309   not change the meaning of the header field).
1310</t>
1311<t>
1312   Historically, HTTP header field values could be extended over multiple
1313   lines by preceding each extra line with at least one space or horizontal
1314   tab (obs-fold). This specification deprecates such line
1315   folding except within the message/http media type
1316   (<xref target="internet.media.type.message.http"/>).
1317   HTTP senders &MUST-NOT; produce messages that include line folding
1318   (i.e., that contain any field-value that matches the obs-fold rule) unless
1319   the message is intended for packaging within the message/http media type.
1320   HTTP recipients &SHOULD; accept line folding and replace any embedded
1321   obs-fold whitespace with either a single SP or a matching number of SP
1322   octets (to avoid buffer copying) prior to interpreting the field value or
1323   forwarding the message downstream.
1324</t>
1325<t>
1326   Historically, HTTP has allowed field content with text in the ISO-8859-1
1327   <xref target="ISO-8859-1"/> character encoding and supported other
1328   character sets only through use of <xref target="RFC2047"/> encoding.
1329   In practice, most HTTP header field values use only a subset of the
1330   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1331   header fields &SHOULD; limit their field values to US-ASCII octets.
1332   Recipients &SHOULD; treat other (obs-text) octets in field content as
1333   opaque data.
1334</t>
1335</section>
1336
1337<section title="Field Length" anchor="field.length">
1338<t>
1339   HTTP does not place a pre-defined limit on the length of header fields,
1340   either in isolation or as a set. A server &MUST; be prepared to receive
1341   request header fields of unbounded length and respond with a <x:ref>4xx
1342   (Client Error)</x:ref> status code if the received header field(s) would be
1343   longer than the server wishes to handle.
1344</t>
1345<t>
1346   A client that receives response header fields that are longer than it wishes
1347   to handle can only treat it as a server error.
1348</t>
1349<t>
1350   Various ad-hoc limitations on header field length are found in practice. It
1351   is &RECOMMENDED; that all HTTP senders and recipients support messages whose
1352   combined header fields have 4000 or more octets.
1353</t>
1354</section>
1355
1356<section title="Field value components" anchor="field.components">
1357<t anchor="rule.token.separators">
1358  <x:anchor-alias value="tchar"/>
1359  <x:anchor-alias value="token"/>
1360  <x:anchor-alias value="special"/>
1361  <x:anchor-alias value="word"/>
1362   Many HTTP header field values consist of words (token or quoted-string)
1363   separated by whitespace or special characters. These special characters
1364   &MUST; be in a quoted string to be used within a parameter value (as defined
1365   in <xref target="transfer.codings"/>).
1366</t>
1367<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="word"/><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/><iref primary="true" item="Grammar" subitem="special"><!--unused production--></iref>
1368  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1369
1370  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
1371<!--
1372  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
1373 -->
1374  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
1375                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1376                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
1377                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
1378
1379  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
1380                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1381                 / "]" / "?" / "=" / "{" / "}"
1382</artwork></figure>
1383<t anchor="rule.quoted-string">
1384  <x:anchor-alias value="quoted-string"/>
1385  <x:anchor-alias value="qdtext"/>
1386  <x:anchor-alias value="obs-text"/>
1387   A string of text is parsed as a single word if it is quoted using
1388   double-quote marks.
1389</t>
1390<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/><iref primary="true" item="Grammar" subitem="obs-text"/>
1391  <x:ref>quoted-string</x:ref>  = <x:ref>DQUOTE</x:ref> *( <x:ref>qdtext</x:ref> / <x:ref>quoted-pair</x:ref> ) <x:ref>DQUOTE</x:ref>
1392  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1393  <x:ref>obs-text</x:ref>       = %x80-FF
1394</artwork></figure>
1395<t anchor="rule.quoted-pair">
1396  <x:anchor-alias value="quoted-pair"/>
1397   The backslash octet ("\") can be used as a single-octet
1398   quoting mechanism within quoted-string constructs:
1399</t>
1400<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
1401  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1402</artwork></figure>
1403<t>
1404   Recipients that process the value of the quoted-string &MUST; handle a
1405   quoted-pair as if it were replaced by the octet following the backslash.
1406</t>
1407<t>
1408   Senders &SHOULD-NOT; escape octets in quoted-strings that do not require
1409   escaping (i.e., other than DQUOTE and the backslash octet).
1410</t>
1411<t anchor="rule.comment">
1412  <x:anchor-alias value="comment"/>
1413  <x:anchor-alias value="ctext"/>
1414   Comments can be included in some HTTP header fields by surrounding
1415   the comment text with parentheses. Comments are only allowed in
1416   fields containing "comment" as part of their field value definition.
1417</t>
1418<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1419  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1420  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1421</artwork></figure>
1422<t anchor="rule.quoted-cpair">
1423  <x:anchor-alias value="quoted-cpair"/>
1424   The backslash octet ("\") can be used as a single-octet
1425   quoting mechanism within comment constructs:
1426</t>
1427<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1428  <x:ref>quoted-cpair</x:ref>   = "\" ( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1429</artwork></figure>
1430<t>
1431   Senders &SHOULD-NOT; escape octets in comments that do not require escaping
1432   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
1433</t>
1434</section>
1435
1436</section>
1437
1438<section title="Message Body" anchor="message.body">
1439  <x:anchor-alias value="message-body"/>
1440<t>
1441   The message body (if any) of an HTTP message is used to carry the
1442   payload body of that request or response.  The message body is
1443   identical to the payload body unless a transfer coding has been
1444   applied, as described in <xref target="header.transfer-encoding"/>.
1445</t>
1446<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1447  <x:ref>message-body</x:ref> = *OCTET
1448</artwork></figure>
1449<t>
1450   The rules for when a message body is allowed in a message differ for
1451   requests and responses.
1452</t>
1453<t>
1454   The presence of a message body in a request is signaled by a
1455   a <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1456   field. Request message framing is independent of method semantics,
1457   even if the method does not define any use for a message body.
1458</t>
1459<t>
1460   The presence of a message body in a response depends on both
1461   the request method to which it is responding and the response
1462   status code (<xref target="status.line"/>).
1463   Responses to the HEAD request method never include a message body
1464   because the associated response header fields (e.g.,
1465   <x:ref>Transfer-Encoding</x:ref>, <x:ref>Content-Length</x:ref>, etc.) only
1466   indicate what their values would have been if the request method had been
1467   GET. <x:ref>2xx (Successful)</x:ref> responses to CONNECT switch to tunnel
1468   mode instead of having a message body.
1469   All <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, and
1470   <x:ref>304 (Not Modified)</x:ref> responses &MUST-NOT; include a message body.
1471   All other responses do include a message body, although the body
1472   &MAY; be of zero length.
1473</t>
1474
1475<section title="Transfer-Encoding" anchor="header.transfer-encoding">
1476  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
1477  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
1478  <x:anchor-alias value="Transfer-Encoding"/>
1479<t>
1480   When one or more transfer codings are applied to a payload body in order
1481   to form the message body, a Transfer-Encoding header field &MUST; be sent
1482   in the message and &MUST; contain the list of corresponding
1483   transfer-coding names in the same order that they were applied.
1484   Transfer codings are defined in <xref target="transfer.codings"/>.
1485</t>
1486<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
1487  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
1488</artwork></figure>
1489<t>
1490   Transfer-Encoding is analogous to the Content-Transfer-Encoding field of
1491   MIME, which was designed to enable safe transport of binary data over a
1492   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1493   However, safe transport has a different focus for an 8bit-clean transfer
1494   protocol. In HTTP's case, Transfer-Encoding is primarily intended to
1495   accurately delimit a dynamically generated payload and to distinguish
1496   payload encodings that are only applied for transport efficiency or
1497   security from those that are characteristics of the target resource.
1498</t>
1499<t>
1500   The "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1501   &MUST; be implemented by all HTTP/1.1 recipients because it plays a
1502   crucial role in delimiting messages when the payload body size is not
1503   known in advance.
1504   When the "chunked" transfer-coding is used, it &MUST; be the last
1505   transfer-coding applied to form the message body and &MUST-NOT;
1506   be applied more than once in a message body.
1507   If any transfer-coding is applied to a request payload body,
1508   the final transfer-coding applied &MUST; be "chunked".
1509   If any transfer-coding is applied to a response payload body, then either
1510   the final transfer-coding applied &MUST; be "chunked" or
1511   the message &MUST; be terminated by closing the connection.
1512</t>
1513<figure><preamble>
1514   For example,
1515</preamble><artwork type="example">
1516  Transfer-Encoding: gzip, chunked
1517</artwork><postamble>
1518   indicates that the payload body has been compressed using the gzip
1519   coding and then chunked using the chunked coding while forming the
1520   message body.
1521</postamble></figure>
1522<t>
1523   If more than one Transfer-Encoding header field is present in a message,
1524   the multiple field-values &MUST; be combined into one field-value,
1525   according to the algorithm defined in <xref target="header.fields"/>,
1526   before determining the message body length.
1527</t>
1528<t>
1529   Unlike <x:ref>Content-Encoding</x:ref> (&content-codings;),
1530   Transfer-Encoding is a property of the message, not of the payload, and thus
1531   &MAY; be added or removed by any implementation along the request/response
1532   chain. Additional information about the encoding parameters &MAY; be
1533   provided by other header fields not defined by this specification.
1534</t>
1535<t>
1536   Transfer-Encoding &MAY; be sent in a response to a HEAD request or in a
1537   <x:ref>304 (Not Modified)</x:ref> response (&status-304;) to a GET request,
1538   neither of which includes a message body,
1539   to indicate that the origin server would have applied a transfer coding
1540   to the message body if the request had been an unconditional GET.
1541   This indication is not required, however, because any recipient on
1542   the response chain (including the origin server) can remove transfer
1543   codings when they are not needed.
1544</t>
1545<t>
1546   Transfer-Encoding was added in HTTP/1.1.  It is generally assumed that
1547   implementations advertising only HTTP/1.0 support will not understand
1548   how to process a transfer-encoded payload.
1549   A client &MUST-NOT; send a request containing Transfer-Encoding unless it
1550   knows the server will handle HTTP/1.1 (or later) requests; such knowledge
1551   might be in the form of specific user configuration or by remembering the
1552   version of a prior received response.
1553   A server &MUST-NOT; send a response containing Transfer-Encoding unless
1554   the corresponding request indicates HTTP/1.1 (or later).
1555</t>
1556<t>
1557   A server that receives a request message with a transfer-coding it does
1558   not understand &SHOULD; respond with <x:ref>501 (Not Implemented)</x:ref> and then
1559   close the connection.
1560</t>
1561</section>
1562
1563<section title="Content-Length" anchor="header.content-length">
1564  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
1565  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
1566  <x:anchor-alias value="Content-Length"/>
1567<t>
1568   When a message does not have a <x:ref>Transfer-Encoding</x:ref> header field
1569   and the payload body length can be determined prior to being transferred, a
1570   Content-Length header field &SHOULD; be sent to indicate the length of the
1571   payload body that is either present as the message body, for requests
1572   and non-HEAD responses other than <x:ref>304 (Not Modified)</x:ref>, or
1573   would have been present had the request been an unconditional GET.  The
1574   length is expressed as a decimal number of octets.
1575</t>
1576<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
1577  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
1578</artwork></figure>
1579<t>
1580   An example is
1581</t>
1582<figure><artwork type="example">
1583  Content-Length: 3495
1584</artwork></figure>
1585<t>
1586   In the case of a response to a HEAD request, Content-Length indicates
1587   the size of the payload body (without any potential transfer-coding)
1588   that would have been sent had the request been a GET.
1589   In the case of a <x:ref>304 (Not Modified)</x:ref> response (&status-304;)
1590   to a GET request, Content-Length indicates the size of the payload body (without
1591   any potential transfer-coding) that would have been sent in a <x:ref>200 (OK)</x:ref>
1592   response.
1593</t>
1594<t>
1595   Any Content-Length field value greater than or equal to zero is valid.
1596   Since there is no predefined limit to the length of an HTTP payload,
1597   recipients &SHOULD; anticipate potentially large decimal numerals and
1598   prevent parsing errors due to integer conversion overflows
1599   (<xref target="attack.protocol.element.size.overflows"/>).
1600</t>
1601<t>
1602   If a message is received that has multiple Content-Length header fields
1603   with field-values consisting of the same decimal value, or a single
1604   Content-Length header field with a field value containing a list of
1605   identical decimal values (e.g., "Content-Length: 42, 42"), indicating that
1606   duplicate Content-Length header fields have been generated or combined by an
1607   upstream message processor, then the recipient &MUST; either reject the
1608   message as invalid or replace the duplicated field-values with a single
1609   valid Content-Length field containing that decimal value prior to
1610   determining the message body length.
1611</t>
1612<x:note>
1613  <t>
1614   &Note; HTTP's use of Content-Length for message framing differs
1615   significantly from the same field's use in MIME, where it is an optional
1616   field used only within the "message/external-body" media-type.
1617  </t>
1618</x:note>
1619</section>
1620
1621<section title="Message Body Length" anchor="message.body.length">
1622<t>
1623   The length of a message body is determined by one of the following
1624   (in order of precedence):
1625</t>
1626<t>
1627  <list style="numbers">
1628    <x:lt><t>
1629     Any response to a HEAD request and any response with a
1630     <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, or
1631     <x:ref>304 (Not Modified)</x:ref> status code is always
1632     terminated by the first empty line after the header fields, regardless of
1633     the header fields present in the message, and thus cannot contain a
1634     message body.
1635    </t></x:lt>
1636    <x:lt><t>
1637     Any <x:ref>2xx (Successful)</x:ref> response to a CONNECT request implies that the
1638     connection will become a tunnel immediately after the empty line that
1639     concludes the header fields.  A client &MUST; ignore any
1640     <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1641     fields received in such a message.
1642    </t></x:lt>
1643    <x:lt><t>
1644     If a <x:ref>Transfer-Encoding</x:ref> header field is present
1645     and the "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1646     is the final encoding, the message body length is determined by reading
1647     and decoding the chunked data until the transfer-coding indicates the
1648     data is complete.
1649    </t>
1650    <t>
1651     If a <x:ref>Transfer-Encoding</x:ref> header field is present in a
1652     response and the "chunked" transfer-coding is not the final encoding, the
1653     message body length is determined by reading the connection until it is
1654     closed by the server.
1655     If a Transfer-Encoding header field is present in a request and the
1656     "chunked" transfer-coding is not the final encoding, the message body
1657     length cannot be determined reliably; the server &MUST; respond with
1658     the <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1659    </t>
1660    <t>
1661     If a message is received with both a <x:ref>Transfer-Encoding</x:ref>
1662     and a <x:ref>Content-Length</x:ref> header field, the
1663     Transfer-Encoding overrides the Content-Length.
1664     Such a message might indicate an attempt to perform request or response
1665     smuggling (bypass of security-related checks on message routing or content)
1666     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1667     be removed, prior to forwarding the message downstream, or replaced with
1668     the real message body length after the transfer-coding is decoded.
1669    </t></x:lt>
1670    <x:lt><t>
1671     If a message is received without <x:ref>Transfer-Encoding</x:ref> and with
1672     either multiple <x:ref>Content-Length</x:ref> header fields having
1673     differing field-values or a single Content-Length header field having an
1674     invalid value, then the message framing is invalid and &MUST; be treated
1675     as an error to prevent request or response smuggling.
1676     If this is a request message, the server &MUST; respond with
1677     a <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1678     If this is a response message received by a proxy, the proxy
1679     &MUST; discard the received response, send a <x:ref>502 (Bad Gateway)</x:ref>
1680     status code as its downstream response, and then close the connection.
1681     If this is a response message received by a user-agent, it &MUST; be
1682     treated as an error by discarding the message and closing the connection.
1683    </t></x:lt>
1684    <x:lt><t>
1685     If a valid <x:ref>Content-Length</x:ref> header field is present without
1686     <x:ref>Transfer-Encoding</x:ref>, its decimal value defines the
1687     message body length in octets.  If the actual number of octets sent in
1688     the message is less than the indicated Content-Length, the recipient
1689     &MUST; consider the message to be incomplete and treat the connection
1690     as no longer usable.
1691     If the actual number of octets sent in the message is more than the indicated
1692     Content-Length, the recipient &MUST; only process the message body up to the
1693     field value's number of octets; the remainder of the message &MUST; either
1694     be discarded or treated as the next message in a pipeline.  For the sake of
1695     robustness, a user-agent &MAY; attempt to detect and correct such an error
1696     in message framing if it is parsing the response to the last request on
1697     a connection and the connection has been closed by the server.
1698    </t></x:lt>
1699    <x:lt><t>
1700     If this is a request message and none of the above are true, then the
1701     message body length is zero (no message body is present).
1702    </t></x:lt>
1703    <x:lt><t>
1704     Otherwise, this is a response message without a declared message body
1705     length, so the message body length is determined by the number of octets
1706     received prior to the server closing the connection.
1707    </t></x:lt>
1708  </list>
1709</t>
1710<t>
1711   Since there is no way to distinguish a successfully completed,
1712   close-delimited message from a partially-received message interrupted
1713   by network failure, a server &SHOULD; use encoding or
1714   length-delimited messages whenever possible.  The close-delimiting
1715   feature exists primarily for backwards compatibility with HTTP/1.0.
1716</t>
1717<t>
1718   A server &MAY; reject a request that contains a message body but
1719   not a <x:ref>Content-Length</x:ref> by responding with
1720   <x:ref>411 (Length Required)</x:ref>.
1721</t>
1722<t>
1723   Unless a transfer-coding other than "chunked" has been applied,
1724   a client that sends a request containing a message body &SHOULD;
1725   use a valid <x:ref>Content-Length</x:ref> header field if the message body
1726   length is known in advance, rather than the "chunked" encoding, since some
1727   existing services respond to "chunked" with a <x:ref>411 (Length Required)</x:ref>
1728   status code even though they understand the chunked encoding.  This
1729   is typically because such services are implemented via a gateway that
1730   requires a content-length in advance of being called and the server
1731   is unable or unwilling to buffer the entire request before processing.
1732</t>
1733<t>
1734   A client that sends a request containing a message body &MUST; include a
1735   valid <x:ref>Content-Length</x:ref> header field if it does not know the
1736   server will handle HTTP/1.1 (or later) requests; such knowledge can be in
1737   the form of specific user configuration or by remembering the version of a
1738   prior received response.
1739</t>
1740</section>
1741</section>
1742
1743<section anchor="incomplete.messages" title="Handling Incomplete Messages">
1744<t>
1745   Request messages that are prematurely terminated, possibly due to a
1746   canceled connection or a server-imposed time-out exception, &MUST;
1747   result in closure of the connection; sending an error response
1748   prior to closing the connection is &OPTIONAL;.
1749</t>
1750<t>
1751   Response messages that are prematurely terminated, usually by closure
1752   of the connection prior to receiving the expected number of octets or by
1753   failure to decode a transfer-encoded message body, &MUST; be recorded
1754   as incomplete.  A response that terminates in the middle of the header
1755   block (before the empty line is received) cannot be assumed to convey the
1756   full semantics of the response and &MUST; be treated as an error.
1757</t>
1758<t>
1759   A message body that uses the chunked transfer encoding is
1760   incomplete if the zero-sized chunk that terminates the encoding has not
1761   been received.  A message that uses a valid <x:ref>Content-Length</x:ref> is
1762   incomplete if the size of the message body received (in octets) is less than
1763   the value given by Content-Length.  A response that has neither chunked
1764   transfer encoding nor Content-Length is terminated by closure of the
1765   connection, and thus is considered complete regardless of the number of
1766   message body octets received, provided that the header block was received
1767   intact.
1768</t>
1769<t>
1770   A user agent &MUST-NOT; render an incomplete response message body as if
1771   it were complete (i.e., some indication needs to be given to the user that an
1772   error occurred).  Cache requirements for incomplete responses are defined
1773   in &cache-incomplete;.
1774</t>
1775<t>
1776   A server &MUST; read the entire request message body or close
1777   the connection after sending its response, since otherwise the
1778   remaining data on a persistent connection would be misinterpreted
1779   as the next request.  Likewise,
1780   a client &MUST; read the entire response message body if it intends
1781   to reuse the same connection for a subsequent request.  Pipelining
1782   multiple requests on a connection is described in <xref target="pipelining"/>.
1783</t>
1784</section>
1785
1786<section title="Message Parsing Robustness" anchor="message.robustness">
1787<t>
1788   Older HTTP/1.0 client implementations might send an extra CRLF
1789   after a POST request as a lame workaround for some early server
1790   applications that failed to read message body content that was
1791   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1792   preface or follow a request with an extra CRLF.  If terminating
1793   the request message body with a line-ending is desired, then the
1794   client &MUST; include the terminating CRLF octets as part of the
1795   message body length.
1796</t>
1797<t>
1798   In the interest of robustness, servers &SHOULD; ignore at least one
1799   empty line received where a request-line is expected. In other words, if
1800   the server is reading the protocol stream at the beginning of a
1801   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1802   Likewise, although the line terminator for the start-line and header
1803   fields is the sequence CRLF, we recommend that recipients recognize a
1804   single LF as a line terminator and ignore any CR.
1805</t>
1806<t>
1807   When a server listening only for HTTP request messages, or processing
1808   what appears from the start-line to be an HTTP request message,
1809   receives a sequence of octets that does not match the HTTP-message
1810   grammar aside from the robustness exceptions listed above, the
1811   server &MUST; respond with an HTTP/1.1 <x:ref>400 (Bad Request)</x:ref> response. 
1812</t>
1813</section>
1814</section>
1815
1816<section title="Transfer Codings" anchor="transfer.codings">
1817  <x:anchor-alias value="transfer-coding"/>
1818  <x:anchor-alias value="transfer-extension"/>
1819<t>
1820   Transfer-coding values are used to indicate an encoding
1821   transformation that has been, can be, or might need to be applied to a
1822   payload body in order to ensure "safe transport" through the network.
1823   This differs from a content coding in that the transfer-coding is a
1824   property of the message rather than a property of the representation
1825   that is being transferred.
1826</t>
1827<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1828  <x:ref>transfer-coding</x:ref>    = "chunked" ; <xref target="chunked.encoding"/>
1829                     / "compress" ; <xref target="compress.coding"/>
1830                     / "deflate" ; <xref target="deflate.coding"/>
1831                     / "gzip" ; <xref target="gzip.coding"/>
1832                     / <x:ref>transfer-extension</x:ref>
1833  <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> )
1834</artwork></figure>
1835<t anchor="rule.parameter">
1836  <x:anchor-alias value="attribute"/>
1837  <x:anchor-alias value="transfer-parameter"/>
1838  <x:anchor-alias value="value"/>
1839   Parameters are in the form of attribute/value pairs.
1840</t>
1841<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"/>
1842  <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>
1843  <x:ref>attribute</x:ref>          = <x:ref>token</x:ref>
1844  <x:ref>value</x:ref>              = <x:ref>word</x:ref>
1845</artwork></figure>
1846<t>
1847   All transfer-coding values are case-insensitive and &SHOULD; be registered
1848   within the HTTP Transfer Coding registry, as defined in
1849   <xref target="transfer.coding.registry"/>.
1850   They are used in the <x:ref>TE</x:ref> (<xref target="header.te"/>) and
1851   <x:ref>Transfer-Encoding</x:ref> (<xref target="header.transfer-encoding"/>)
1852   header fields.
1853</t>
1854
1855<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1856  <iref item="chunked (Coding Format)"/>
1857  <iref item="Coding Format" subitem="chunked"/>
1858  <x:anchor-alias value="chunk"/>
1859  <x:anchor-alias value="chunked-body"/>
1860  <x:anchor-alias value="chunk-data"/>
1861  <x:anchor-alias value="chunk-ext"/>
1862  <x:anchor-alias value="chunk-ext-name"/>
1863  <x:anchor-alias value="chunk-ext-val"/>
1864  <x:anchor-alias value="chunk-size"/>
1865  <x:anchor-alias value="last-chunk"/>
1866  <x:anchor-alias value="trailer-part"/>
1867  <x:anchor-alias value="quoted-str-nf"/>
1868  <x:anchor-alias value="qdtext-nf"/>
1869<t>
1870   The chunked encoding modifies the body of a message in order to
1871   transfer it as a series of chunks, each with its own size indicator,
1872   followed by an &OPTIONAL; trailer containing header fields. This
1873   allows dynamically produced content to be transferred along with the
1874   information necessary for the recipient to verify that it has
1875   received the full message.
1876</t>
1877<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"/>
1878  <x:ref>chunked-body</x:ref>   = *<x:ref>chunk</x:ref>
1879                   <x:ref>last-chunk</x:ref>
1880                   <x:ref>trailer-part</x:ref>
1881                   <x:ref>CRLF</x:ref>
1882 
1883  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1884                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1885  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1886  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1887 
1888  <x:ref>chunk-ext</x:ref>      = *( ";" <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] )
1889  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1890  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
1891  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1892  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1893 
1894  <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>
1895                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
1896  <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>
1897</artwork></figure>
1898<t>
1899   Chunk extensions within the chucked encoding are deprecated.
1900   Senders &SHOULD-NOT; send chunk-ext.
1901   Definition of new chunk extensions is discouraged.
1902</t>
1903<t>
1904   The chunk-size field is a string of hex digits indicating the size of
1905   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1906   zero, followed by the trailer, which is terminated by an empty line.
1907</t>
1908
1909<section title="Trailer" anchor="header.trailer">
1910  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
1911  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
1912  <x:anchor-alias value="Trailer"/>
1913<t>
1914   A trailer allows the sender to include additional fields at the end of a
1915   chunked message in order to supply metadata that might be dynamically
1916   generated while the message body is sent, such as a message integrity
1917   check, digital signature, or post-processing status.
1918   The trailer &MUST-NOT; contain fields that need to be known before a
1919   recipient processes the body, such as <x:ref>Transfer-Encoding</x:ref>,
1920   <x:ref>Content-Length</x:ref>, and <x:ref>Trailer</x:ref>.
1921</t>
1922<t>
1923   When a message includes a message body encoded with the chunked
1924   transfer-coding and the sender desires to send metadata in the form of
1925   trailer fields at the end of the message, the sender &SHOULD; send a
1926   <x:ref>Trailer</x:ref> header field before the message body to indicate
1927   which fields will be present in the trailers. This allows the recipient
1928   to prepare for receipt of that metadata before it starts processing the body,
1929   which is useful if the message is being streamed and the recipient wishes
1930   to confirm an integrity check on the fly.
1931</t>
1932<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
1933  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
1934</artwork></figure>
1935<t>
1936   If no <x:ref>Trailer</x:ref> header field is present, the sender of a
1937   chunked message body &SHOULD; send an empty trailer.
1938</t>
1939<t>
1940   A server &MUST; send an empty trailer with the chunked transfer-coding
1941   unless at least one of the following is true:
1942  <list style="numbers">
1943    <t>the request included a <x:ref>TE</x:ref> header field that indicates
1944    "trailers" is acceptable in the transfer-coding of the response, as
1945    described in <xref target="header.te"/>; or,</t>
1946     
1947    <t>the trailer fields consist entirely of optional metadata and the
1948    recipient could use the message (in a manner acceptable to the server where
1949    the field originated) without receiving that metadata. In other words,
1950    the server that generated the header field is willing to accept the
1951    possibility that the trailer fields might be silently discarded along
1952    the path to the client.</t>
1953  </list>
1954</t>
1955<t>
1956   The above requirement prevents the need for an infinite buffer when a
1957   message is being received by an HTTP/1.1 (or later) proxy and forwarded to
1958   an HTTP/1.0 recipient.
1959</t>
1960</section>
1961
1962<section title="Decoding chunked" anchor="decoding.chunked">
1963<t>
1964   A process for decoding the "chunked" transfer-coding
1965   can be represented in pseudo-code as:
1966</t>
1967<figure><artwork type="code">
1968  length := 0
1969  read chunk-size, chunk-ext (if any) and CRLF
1970  while (chunk-size &gt; 0) {
1971     read chunk-data and CRLF
1972     append chunk-data to decoded-body
1973     length := length + chunk-size
1974     read chunk-size and CRLF
1975  }
1976  read header-field
1977  while (header-field not empty) {
1978     append header-field to existing header fields
1979     read header-field
1980  }
1981  Content-Length := length
1982  Remove "chunked" from Transfer-Encoding
1983  Remove Trailer from existing header fields
1984</artwork></figure>
1985<t>
1986   All recipients &MUST; be able to receive and decode the
1987   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
1988   they do not understand.
1989</t>
1990</section>
1991</section>
1992
1993<section title="Compression Codings" anchor="compression.codings">
1994<t>
1995   The codings defined below can be used to compress the payload of a
1996   message.
1997</t>
1998
1999<section title="Compress Coding" anchor="compress.coding">
2000<iref item="compress (Coding Format)"/>
2001<iref item="Coding Format" subitem="compress"/>
2002<t>
2003   The "compress" format is produced by the common UNIX file compression
2004   program "compress". This format is an adaptive Lempel-Ziv-Welch
2005   coding (LZW). Recipients &SHOULD; consider "x-compress" to be
2006   equivalent to "compress".
2007</t>
2008</section>
2009
2010<section title="Deflate Coding" anchor="deflate.coding">
2011<iref item="deflate (Coding Format)"/>
2012<iref item="Coding Format" subitem="deflate"/>
2013<t>
2014   The "deflate" format is defined as the "deflate" compression mechanism
2015   (described in <xref target="RFC1951"/>) used inside the "zlib"
2016   data format (<xref target="RFC1950"/>).
2017</t>
2018<x:note>
2019  <t>
2020    &Note; Some incorrect implementations send the "deflate"
2021    compressed data without the zlib wrapper.
2022   </t>
2023</x:note>
2024</section>
2025
2026<section title="Gzip Coding" anchor="gzip.coding">
2027<iref item="gzip (Coding Format)"/>
2028<iref item="Coding Format" subitem="gzip"/>
2029<t>
2030   The "gzip" format is produced by the file compression program
2031   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2032   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2033   Recipients &SHOULD; consider "x-gzip" to be equivalent to "gzip".
2034</t>
2035</section>
2036
2037</section>
2038
2039<section title="TE" anchor="header.te">
2040  <iref primary="true" item="TE header field" x:for-anchor=""/>
2041  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
2042  <x:anchor-alias value="TE"/>
2043  <x:anchor-alias value="t-codings"/>
2044  <x:anchor-alias value="t-ranking"/>
2045  <x:anchor-alias value="rank"/>
2046<t>
2047   The "TE" header field in a request indicates what transfer-codings,
2048   besides "chunked", the client is willing to accept in response, and
2049   whether or not the client is willing to accept trailer fields in a
2050   chunked transfer-coding.
2051</t>
2052<t>
2053   The TE field-value consists of a comma-separated list of transfer-coding
2054   names, each allowing for optional parameters (as described in
2055   <xref target="transfer.codings"/>), and/or the keyword "trailers".
2056   Clients &MUST-NOT; send the chunked transfer-coding name in TE;
2057   chunked is always acceptable for HTTP/1.1 recipients.
2058</t>
2059<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"/>
2060  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
2061  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-coding</x:ref> [ <x:ref>t-ranking</x:ref> ] )
2062  <x:ref>t-ranking</x:ref> = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>rank</x:ref>
2063  <x:ref>rank</x:ref>      = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2064             / ( "1" [ "." 0*3("0") ] )
2065</artwork></figure>
2066<t>
2067   Three examples of TE use are below.
2068</t>
2069<figure><artwork type="example">
2070  TE: deflate
2071  TE:
2072  TE: trailers, deflate;q=0.5
2073</artwork></figure>
2074<t>
2075   The presence of the keyword "trailers" indicates that the client is
2076   willing to accept trailer fields in a chunked transfer-coding,
2077   as defined in <xref target="chunked.encoding"/>, on behalf of itself and
2078   any downstream clients. For chained requests, this implies that either:
2079   (a) all downstream clients are willing to accept trailer fields in the
2080   forwarded response; or,
2081   (b) the client will attempt to buffer the response on behalf of downstream
2082   recipients.
2083   Note that HTTP/1.1 does not define any means to limit the size of a
2084   chunked response such that a client can be assured of buffering the
2085   entire response.
2086</t>
2087<t>
2088   When multiple transfer-codings are acceptable, the client &MAY; rank the
2089   codings by preference using a case-insensitive "q" parameter (similar to
2090   the qvalues used in content negotiation fields, &qvalue;). The rank value
2091   is a real number in the range 0 through 1, where 0.001 is the least
2092   preferred and 1 is the most preferred; a value of 0 means "not acceptable".
2093</t>
2094<t>
2095   If the TE field-value is empty or if no TE field is present, the only
2096   acceptable transfer-coding is "chunked". A message with no transfer-coding
2097   is always acceptable.
2098</t>
2099<t>
2100   Since the TE header field only applies to the immediate connection,
2101   a sender of TE &MUST; also send a "TE" connection option within the
2102   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>)
2103   in order to prevent the TE field from being forwarded by intermediaries
2104   that do not support its semantics.
2105</t>
2106</section>
2107</section>
2108
2109<section title="Message Routing" anchor="message.routing">
2110<t>
2111   HTTP request message routing is determined by each client based on the
2112   target resource, the client's proxy configuration, and
2113   establishment or reuse of an inbound connection.  The corresponding
2114   response routing follows the same connection chain back to the client.
2115</t>
2116
2117<section title="Identifying a Target Resource" anchor="target-resource">
2118  <iref primary="true" item="target resource"/>
2119  <iref primary="true" item="target URI"/>
2120  <x:anchor-alias value="target resource"/>
2121  <x:anchor-alias value="target URI"/>
2122<t>
2123   HTTP is used in a wide variety of applications, ranging from
2124   general-purpose computers to home appliances.  In some cases,
2125   communication options are hard-coded in a client's configuration.
2126   However, most HTTP clients rely on the same resource identification
2127   mechanism and configuration techniques as general-purpose Web browsers.
2128</t>
2129<t>
2130   HTTP communication is initiated by a user agent for some purpose.
2131   The purpose is a combination of request semantics, which are defined in
2132   <xref target="Part2"/>, and a target resource upon which to apply those
2133   semantics.  A URI reference (<xref target="uri"/>) is typically used as
2134   an identifier for the "<x:dfn>target resource</x:dfn>", which a user agent
2135   would resolve to its absolute form in order to obtain the
2136   "<x:dfn>target URI</x:dfn>".  The target URI
2137   excludes the reference's fragment identifier component, if any,
2138   since fragment identifiers are reserved for client-side processing
2139   (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>).
2140</t>
2141</section>
2142
2143<section title="Connecting Inbound" anchor="connecting.inbound">
2144<t>
2145   Once the target URI is determined, a client needs to decide whether
2146   a network request is necessary to accomplish the desired semantics and,
2147   if so, where that request is to be directed.
2148</t>
2149<t>
2150   If the client has a response cache and the request semantics can be
2151   satisfied by a cache (<xref target="Part6"/>), then the request is
2152   usually directed to the cache first.
2153</t>
2154<t>
2155   If the request is not satisfied by a cache, then a typical client will
2156   check its configuration to determine whether a proxy is to be used to
2157   satisfy the request.  Proxy configuration is implementation-dependent,
2158   but is often based on URI prefix matching, selective authority matching,
2159   or both, and the proxy itself is usually identified by an "http" or
2160   "https" URI.  If a proxy is applicable, the client connects inbound by
2161   establishing (or reusing) a connection to that proxy.
2162</t>
2163<t>
2164   If no proxy is applicable, a typical client will invoke a handler routine,
2165   usually specific to the target URI's scheme, to connect directly
2166   to an authority for the target resource.  How that is accomplished is
2167   dependent on the target URI scheme and defined by its associated
2168   specification, similar to how this specification defines origin server
2169   access for resolution of the "http" (<xref target="http.uri"/>) and
2170   "https" (<xref target="https.uri"/>) schemes.
2171</t>
2172<t>
2173   HTTP requirements regarding connection management are defined in
2174   <xref target="connection.management"/>.
2175</t>
2176</section>
2177
2178<section title="Request Target" anchor="request-target">
2179<t>
2180   Once an inbound connection is obtained,
2181   the client sends an HTTP request message (<xref target="http.message"/>)
2182   with a request-target derived from the target URI.
2183   There are four distinct formats for the request-target, depending on both
2184   the method being requested and whether the request is to a proxy.
2185</t>   
2186<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"/>
2187  <x:ref>request-target</x:ref> = <x:ref>origin-form</x:ref>
2188                 / <x:ref>absolute-form</x:ref>
2189                 / <x:ref>authority-form</x:ref>
2190                 / <x:ref>asterisk-form</x:ref>
2191
2192  <x:ref>origin-form</x:ref>    = <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ]
2193  <x:ref>absolute-form</x:ref>  = <x:ref>absolute-URI</x:ref>
2194  <x:ref>authority-form</x:ref> = <x:ref>authority</x:ref>
2195  <x:ref>asterisk-form</x:ref>  = "*"
2196</artwork></figure>
2197<t anchor="origin-form"><iref item="origin-form (of request-target)"/>
2198   The most common form of request-target is the origin-form.
2199   When making a request directly to an origin server, other than a CONNECT
2200   or server-wide OPTIONS request (as detailed below),
2201   a client &MUST; send only the absolute path and query components of
2202   the target URI as the request-target.
2203   If the target URI's path component is empty, then the client &MUST; send
2204   "/" as the path within the origin-form of request-target.
2205   A <x:ref>Host</x:ref> header field is also sent, as defined in
2206   <xref target="header.host"/>, containing the target URI's
2207   authority component (excluding any userinfo).
2208</t>
2209<t>
2210   For example, a client wishing to retrieve a representation of the resource
2211   identified as
2212</t>
2213<figure><artwork x:indent-with="  " type="example">
2214http://www.example.org/where?q=now
2215</artwork></figure>
2216<t>
2217   directly from the origin server would open (or reuse) a TCP connection
2218   to port 80 of the host "www.example.org" and send the lines:
2219</t>
2220<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2221GET /where?q=now HTTP/1.1
2222Host: www.example.org
2223</artwork></figure>
2224<t>
2225   followed by the remainder of the request message.
2226</t>
2227<t anchor="absolute-form"><iref item="absolute-form (of request-target)"/>
2228   When making a request to a proxy, other than a CONNECT or server-wide
2229   OPTIONS request (as detailed below), a client &MUST; send the target URI
2230   in absolute-form as the request-target.
2231   The proxy is requested to either service that request from a valid cache,
2232   if possible, or make the same request on the client's behalf to either
2233   the next inbound proxy server or directly to the origin server indicated
2234   by the request-target.  Requirements on such "forwarding" of messages are
2235   defined in <xref target="message.forwarding"/>.
2236</t>
2237<t>
2238   An example absolute-form of request-line would be:
2239</t>
2240<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2241GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
2242</artwork></figure>
2243<t>
2244   To allow for transition to the absolute-form for all requests in some
2245   future version of HTTP, HTTP/1.1 servers &MUST; accept the absolute-form
2246   in requests, even though HTTP/1.1 clients will only send them in requests
2247   to proxies.
2248</t>
2249<t anchor="authority-form"><iref item="authority-form (of request-target)"/>
2250   The authority-form of request-target is only used for CONNECT requests
2251   (&CONNECT;).  When making a CONNECT request to establish a tunnel through
2252   one or more proxies, a client &MUST; send only the target URI's
2253   authority component (excluding any userinfo) as the request-target.
2254   For example,
2255</t>
2256<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2257CONNECT www.example.com:80 HTTP/1.1
2258</artwork></figure>
2259<t anchor="asterisk-form"><iref item="asterisk-form (of request-target)"/>
2260   The asterisk-form of request-target is only used for a server-wide
2261   OPTIONS request (&OPTIONS;).  When a client wishes to request OPTIONS
2262   for the server as a whole, as opposed to a specific named resource of
2263   that server, the client &MUST; send only "*" (%x2A) as the request-target.
2264   For example,
2265</t>
2266<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2267OPTIONS * HTTP/1.1
2268</artwork></figure>
2269<t>
2270   If a proxy receives an OPTIONS request with an absolute-form of
2271   request-target in which the URI has an empty path and no query component,
2272   then the last proxy on the request chain &MUST; send a request-target
2273   of "*" when it forwards the request to the indicated origin server.
2274</t>
2275<figure><preamble>   
2276   For example, the request
2277</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2278OPTIONS http://www.example.org:8001 HTTP/1.1
2279</artwork></figure>
2280<figure><preamble>   
2281  would be forwarded by the final proxy as
2282</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2283OPTIONS * HTTP/1.1
2284Host: www.example.org:8001
2285</artwork>
2286<postamble>
2287   after connecting to port 8001 of host "www.example.org".
2288</postamble>
2289</figure>
2290</section>
2291
2292<section title="Host" anchor="header.host">
2293  <iref primary="true" item="Host header field" x:for-anchor=""/>
2294  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
2295  <x:anchor-alias value="Host"/>
2296<t>
2297   The "Host" header field in a request provides the host and port
2298   information from the target URI, enabling the origin
2299   server to distinguish among resources while servicing requests
2300   for multiple host names on a single IP address.  Since the Host
2301   field-value is critical information for handling a request, it
2302   &SHOULD; be sent as the first header field following the request-line.
2303</t>
2304<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2305  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2306</artwork></figure>
2307<t>
2308   A client &MUST; send a Host header field in all HTTP/1.1 request
2309   messages.  If the target URI includes an authority component, then
2310   the Host field-value &MUST; be identical to that authority component
2311   after excluding any userinfo (<xref target="http.uri"/>).
2312   If the authority component is missing or undefined for the target URI,
2313   then the Host header field &MUST; be sent with an empty field-value.
2314</t>
2315<t>
2316   For example, a GET request to the origin server for
2317   &lt;http://www.example.org/pub/WWW/&gt; would begin with:
2318</t>
2319<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2320GET /pub/WWW/ HTTP/1.1
2321Host: www.example.org
2322</artwork></figure>
2323<t>
2324   The Host header field &MUST; be sent in an HTTP/1.1 request even
2325   if the request-target is in the absolute-form, since this
2326   allows the Host information to be forwarded through ancient HTTP/1.0
2327   proxies that might not have implemented Host.
2328</t>
2329<t>
2330   When a proxy receives a request with an absolute-form of
2331   request-target, the proxy &MUST; ignore the received
2332   Host header field (if any) and instead replace it with the host
2333   information of the request-target.  If the proxy forwards the request,
2334   it &MUST; generate a new Host field-value based on the received
2335   request-target rather than forward the received Host field-value.
2336</t>
2337<t>
2338   Since the Host header field acts as an application-level routing
2339   mechanism, it is a frequent target for malware seeking to poison
2340   a shared cache or redirect a request to an unintended server.
2341   An interception proxy is particularly vulnerable if it relies on
2342   the Host field-value for redirecting requests to internal
2343   servers, or for use as a cache key in a shared cache, without
2344   first verifying that the intercepted connection is targeting a
2345   valid IP address for that host.
2346</t>
2347<t>
2348   A server &MUST; respond with a <x:ref>400 (Bad Request)</x:ref> status code
2349   to any HTTP/1.1 request message that lacks a Host header field and
2350   to any request message that contains more than one Host header field
2351   or a Host header field with an invalid field-value.
2352</t>
2353</section>
2354
2355<section title="Effective Request URI" anchor="effective.request.uri">
2356  <iref primary="true" item="effective request URI"/>
2357<t>
2358   A server that receives an HTTP request message &MUST; reconstruct
2359   the user agent's original target URI, based on the pieces of information
2360   learned from the request-target, <x:ref>Host</x:ref> header field, and
2361   connection context, in order to identify the intended target resource and
2362   properly service the request. The URI derived from this reconstruction
2363   process is referred to as the "<x:dfn>effective request URI</x:dfn>".
2364</t>
2365<t>
2366   For a user agent, the effective request URI is the target URI.
2367</t>
2368<t>
2369   If the request-target is in absolute-form, then the effective request URI
2370   is the same as the request-target.  Otherwise, the effective request URI
2371   is constructed as follows.
2372</t>
2373<t>
2374   If the request is received over an SSL/TLS-secured TCP connection,
2375   then the effective request URI's scheme is "https"; otherwise, the
2376   scheme is "http".
2377</t>
2378<t>
2379   If the request-target is in authority-form, then the effective
2380   request URI's authority component is the same as the request-target.
2381   Otherwise, if a <x:ref>Host</x:ref> header field is supplied with a
2382   non-empty field-value, then the authority component is the same as the
2383   Host field-value. Otherwise, the authority component is the concatenation of
2384   the default host name configured for the server, a colon (":"), and the
2385   connection's incoming TCP port number in decimal form.
2386</t>
2387<t>
2388   If the request-target is in authority-form or asterisk-form, then the
2389   effective request URI's combined path and query component is empty.
2390   Otherwise, the combined path and query component is the same as the
2391   request-target.
2392</t>
2393<t>
2394   The components of the effective request URI, once determined as above,
2395   can be combined into absolute-URI form by concatenating the scheme,
2396   "://", authority, and combined path and query component.
2397</t>
2398<figure>
2399<preamble>
2400   Example 1: the following message received over an insecure TCP connection
2401</preamble> 
2402<artwork type="example" x:indent-with="  ">
2403GET /pub/WWW/TheProject.html HTTP/1.1
2404Host: www.example.org:8080
2405</artwork>
2406</figure>
2407<figure>
2408<preamble>
2409  has an effective request URI of
2410</preamble>
2411<artwork type="example" x:indent-with="  ">
2412http://www.example.org:8080/pub/WWW/TheProject.html
2413</artwork>
2414</figure>
2415<figure>
2416<preamble>
2417   Example 2: the following message received over an SSL/TLS-secured TCP
2418   connection
2419</preamble> 
2420<artwork type="example" x:indent-with="  ">
2421OPTIONS * HTTP/1.1
2422Host: www.example.org
2423</artwork>
2424</figure>
2425<figure>
2426<preamble>
2427  has an effective request URI of
2428</preamble>
2429<artwork type="example" x:indent-with="  ">
2430https://www.example.org
2431</artwork>
2432</figure>
2433<t>
2434   An origin server that does not allow resources to differ by requested
2435   host &MAY; ignore the <x:ref>Host</x:ref> field-value and instead replace it
2436   with a configured server name when constructing the effective request URI.
2437</t>
2438<t>
2439   Recipients of an HTTP/1.0 request that lacks a <x:ref>Host</x:ref> header
2440   field &MAY; attempt to use heuristics (e.g., examination of the URI path for
2441   something unique to a particular host) in order to guess the
2442   effective request URI's authority component.
2443</t>
2444</section>
2445
2446<section title="Message Forwarding" anchor="message.forwarding">
2447<t>
2448   As described in <xref target="intermediaries"/>, intermediaries can serve
2449   a variety of roles in the processing of HTTP requests and responses.
2450   Some intermediaries are used to improve performance or availability.
2451   Others are used for access control or to filter content.
2452   Since an HTTP stream has characteristics similar to a pipe-and-filter
2453   architecture, there are no inherent limits to the extent an intermediary
2454   can enhance (or interfere) with either direction of the stream.
2455</t>
2456<t>
2457   Intermediaries that forward a message &MUST; implement the
2458   <x:ref>Connection</x:ref> header field, as specified in
2459   <xref target="header.connection"/>, to exclude fields that are only
2460   intended for the incoming connection.
2461</t>
2462<t>
2463   In order to avoid request loops, a proxy that forwards requests to other
2464   proxies &MUST; be able to recognize and exclude all of its own server
2465   names, including any aliases, local variations, or literal IP addresses.
2466</t>
2467</section>
2468
2469<section title="Via" anchor="header.via">
2470  <iref primary="true" item="Via header field" x:for-anchor=""/>
2471  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
2472  <x:anchor-alias value="pseudonym"/>
2473  <x:anchor-alias value="received-by"/>
2474  <x:anchor-alias value="received-protocol"/>
2475  <x:anchor-alias value="Via"/>
2476<t>
2477   The "Via" header field &MUST; be sent by a proxy or gateway
2478   in forwarded messages to
2479   indicate the intermediate protocols and recipients between the user
2480   agent and the server on requests, and between the origin server and
2481   the client on responses. It is analogous to the "Received" field
2482   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>).
2483   Via is used in HTTP for tracking message forwards,
2484   avoiding request loops, and identifying the protocol capabilities of
2485   all senders along the request/response chain.
2486</t>
2487<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"/>
2488  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2489                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2490  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2491  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2492  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2493</artwork></figure>
2494<t>
2495   The received-protocol indicates the protocol version of the message
2496   received by the server or client along each segment of the
2497   request/response chain. The received-protocol version is appended to
2498   the Via field value when the message is forwarded so that information
2499   about the protocol capabilities of upstream applications remains
2500   visible to all recipients.
2501</t>
2502<t>
2503   The protocol-name is excluded if and only if it would be "HTTP". The
2504   received-by field is normally the host and optional port number of a
2505   recipient server or client that subsequently forwarded the message.
2506   However, if the real host is considered to be sensitive information,
2507   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2508   be assumed to be the default port of the received-protocol.
2509</t>
2510<t>
2511   Multiple Via field values represent each proxy or gateway that has
2512   forwarded the message. Each recipient &MUST; append its information
2513   such that the end result is ordered according to the sequence of
2514   forwarding applications.
2515</t>
2516<t>
2517   Comments &MAY; be used in the Via header field to identify the software
2518   of each recipient, analogous to the <x:ref>User-Agent</x:ref> and
2519   <x:ref>Server</x:ref> header fields. However, all comments in the Via field
2520   are optional and &MAY; be removed by any recipient prior to forwarding the
2521   message.
2522</t>
2523<t>
2524   For example, a request message could be sent from an HTTP/1.0 user
2525   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2526   forward the request to a public proxy at p.example.net, which completes
2527   the request by forwarding it to the origin server at www.example.com.
2528   The request received by www.example.com would then have the following
2529   Via header field:
2530</t>
2531<figure><artwork type="example">
2532  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2533</artwork></figure>
2534<t>
2535   A proxy or gateway used as a portal through a network firewall
2536   &SHOULD-NOT; forward the names and ports of hosts within the firewall
2537   region unless it is explicitly enabled to do so. If not enabled, the
2538   received-by host of any host behind the firewall &SHOULD; be replaced
2539   by an appropriate pseudonym for that host.
2540</t>
2541<t>
2542   A proxy or gateway &MAY; combine an ordered subsequence of Via header
2543   field entries into a single such entry if the entries have identical
2544   received-protocol values. For example,
2545</t>
2546<figure><artwork type="example">
2547  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2548</artwork></figure>
2549<t>
2550  could be collapsed to
2551</t>
2552<figure><artwork type="example">
2553  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2554</artwork></figure>
2555<t>
2556   Senders &SHOULD-NOT; combine multiple entries unless they are all
2557   under the same organizational control and the hosts have already been
2558   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
2559   have different received-protocol values.
2560</t>
2561</section>
2562
2563<section title="Message Transforming" anchor="message.transforming">
2564<t>
2565   If a proxy receives a request-target with a host name that is not a
2566   fully qualified domain name, it &MAY; add its own domain to the host name
2567   it received when forwarding the request.  A proxy &MUST-NOT; change the
2568   host name if it is a fully qualified domain name.
2569</t>
2570<t>
2571   A non-transforming proxy &MUST-NOT; modify the "path-absolute" and "query"
2572   parts of the received request-target when forwarding it to the next inbound
2573   server, except as noted above to replace an empty path with "/" or "*".
2574</t>
2575<t>
2576   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2577   though it &MAY; change the message body through application or removal
2578   of a transfer-coding (<xref target="transfer.codings"/>).
2579</t>
2580<t>
2581   A non-transforming proxy &SHOULD-NOT; modify header fields that provide
2582   information about the end points of the communication chain, the resource
2583   state, or the selected representation.
2584</t>
2585<t>
2586   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2587   request or response, and it &MUST-NOT; add any of these fields if not
2588   already present:
2589  <list style="symbols">
2590    <t><x:ref>Allow</x:ref> (&header-allow;)</t>
2591    <t><x:ref>Content-Location</x:ref> (&header-content-location;)</t>
2592    <t>Content-MD5 (<xref target="RFC2616" x:fmt="of" x:sec="14.15"/>)</t>
2593    <t><x:ref>ETag</x:ref> (&header-etag;)</t>
2594    <t><x:ref>Last-Modified</x:ref> (&header-last-modified;)</t>
2595    <t><x:ref>Server</x:ref> (&header-server;)</t>
2596  </list>
2597</t>
2598<t>
2599   A non-transforming proxy &MUST-NOT; modify an <x:ref>Expires</x:ref>
2600   header field (&header-expires;) if already present in a response, but
2601   it &MAY; add an <x:ref>Expires</x:ref> header field with a field-value
2602   identical to that of the <x:ref>Date</x:ref> header field.
2603</t>
2604<t>
2605   A proxy &MUST-NOT; modify or add any of the following fields in a
2606   message that contains the no-transform cache-control directive:
2607  <list style="symbols">
2608    <t><x:ref>Content-Encoding</x:ref> (&header-content-encoding;)</t>
2609    <t><x:ref>Content-Range</x:ref> (&header-content-range;)</t>
2610    <t><x:ref>Content-Type</x:ref> (&header-content-type;)</t>
2611  </list>
2612</t>
2613<t>
2614   A transforming proxy &MAY; modify or add these fields to a message
2615   that does not include no-transform, but if it does so, it &MUST; add a
2616   Warning 214 (Transformation applied) if one does not already appear
2617   in the message (see &header-warning;).
2618</t>
2619<x:note>
2620  <t>
2621    <x:h>Warning:</x:h> Unnecessary modification of header fields might
2622    cause authentication failures if stronger authentication
2623    mechanisms are introduced in later versions of HTTP. Such
2624    authentication mechanisms &MAY; rely on the values of header fields
2625    not listed here.
2626  </t>
2627</x:note>
2628</section>
2629
2630<section title="Associating a Response to a Request" anchor="associating.response.to.request">
2631<t>
2632   HTTP does not include a request identifier for associating a given
2633   request message with its corresponding one or more response messages.
2634   Hence, it relies on the order of response arrival to correspond exactly
2635   to the order in which requests are made on the same connection.
2636   More than one response message per request only occurs when one or more
2637   informational responses (<x:ref>1xx</x:ref>, see &status-1xx;) precede a final response
2638   to the same request.
2639</t>
2640<t>
2641   A client that uses persistent connections and sends more than one request
2642   per connection &MUST; maintain a list of outstanding requests in the
2643   order sent on that connection and &MUST; associate each received response
2644   message to the highest ordered request that has not yet received a final
2645   (non-<x:ref>1xx</x:ref>) response.
2646</t>
2647</section>
2648</section>
2649
2650<section title="Connection Management" anchor="connection.management">
2651<t>
2652   HTTP messaging is independent of the underlying transport or
2653   session-layer connection protocol(s).  HTTP only presumes a reliable
2654   transport with in-order delivery of requests and the corresponding
2655   in-order delivery of responses.  The mapping of HTTP request and
2656   response structures onto the data units of an underlying transport
2657   protocol is outside the scope of this specification.
2658</t>
2659<t>
2660   As described in <xref target="connecting.inbound"/>, the specific
2661   connection protocols to be used for an HTTP interaction are determined by
2662   client configuration and the <x:ref>target URI</x:ref>.
2663   For example, the "http" URI scheme
2664   (<xref target="http.uri"/>) indicates a default connection of TCP
2665   over IP, with a default TCP port of 80, but the client might be
2666   configured to use a proxy via some other connection, port, or protocol.
2667</t>
2668<t>
2669   HTTP implementations are expected to engage in connection management,
2670   which includes maintaining the state of current connections,
2671   establishing a new connection or reusing an existing connection,
2672   processing messages received on a connection, detecting connection
2673   failures, and closing each connection.
2674   Most clients maintain multiple connections in parallel, including
2675   more than one connection per server endpoint.
2676   Most servers are designed to maintain thousands of concurrent connections,
2677   while controlling request queues to enable fair use and detect
2678   denial of service attacks.
2679</t>
2680
2681<section title="Connection" anchor="header.connection">
2682  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2683  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
2684  <iref primary="true" item="close" x:for-anchor=""/>
2685  <x:anchor-alias value="Connection"/>
2686  <x:anchor-alias value="connection-option"/>
2687  <x:anchor-alias value="close"/>
2688<t>
2689   The "Connection" header field allows the sender to indicate desired
2690   control options for the current connection.  In order to avoid confusing
2691   downstream recipients, a proxy or gateway &MUST; remove or replace any
2692   received connection options before forwarding the message.
2693</t>
2694<t>
2695   When a header field is used to supply control information for or about
2696   the current connection, the sender &SHOULD; list the corresponding
2697   field-name within the "Connection" header field.
2698   A proxy or gateway &MUST; parse a received Connection
2699   header field before a message is forwarded and, for each
2700   connection-option in this field, remove any header field(s) from
2701   the message with the same name as the connection-option, and then
2702   remove the Connection header field itself (or replace it with the
2703   intermediary's own connection options for the forwarded message).
2704</t>
2705<t>
2706   Hence, the Connection header field provides a declarative way of
2707   distinguishing header fields that are only intended for the
2708   immediate recipient ("hop-by-hop") from those fields that are
2709   intended for all recipients on the chain ("end-to-end"), enabling the
2710   message to be self-descriptive and allowing future connection-specific
2711   extensions to be deployed without fear that they will be blindly
2712   forwarded by older intermediaries.
2713</t>
2714<t>
2715   The Connection header field's value has the following grammar:
2716</t>
2717<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-option"/>
2718  <x:ref>Connection</x:ref>        = 1#<x:ref>connection-option</x:ref>
2719  <x:ref>connection-option</x:ref> = <x:ref>token</x:ref>
2720</artwork></figure>
2721<t>
2722   Connection options are case-insensitive.
2723</t>
2724<t>
2725   A sender &MUST-NOT; include field-names in the Connection header
2726   field-value for fields that are defined as expressing constraints
2727   for all recipients in the request or response chain, such as the
2728   Cache-Control header field (&header-cache-control;).
2729</t>
2730<t>
2731   The connection options do not have to correspond to a header field
2732   present in the message, since a connection-specific header field
2733   might not be needed if there are no parameters associated with that
2734   connection option.  Recipients that trigger certain connection
2735   behavior based on the presence of connection options &MUST; do so
2736   based on the presence of the connection-option rather than only the
2737   presence of the optional header field.  In other words, if the
2738   connection option is received as a header field but not indicated
2739   within the Connection field-value, then the recipient &MUST; ignore
2740   the connection-specific header field because it has likely been
2741   forwarded by an intermediary that is only partially conformant.
2742</t>
2743<t>
2744   When defining new connection options, specifications ought to
2745   carefully consider existing deployed header fields and ensure
2746   that the new connection option does not share the same name as
2747   an unrelated header field that might already be deployed.
2748   Defining a new connection option essentially reserves that potential
2749   field-name for carrying additional information related to the
2750   connection option, since it would be unwise for senders to use
2751   that field-name for anything else.
2752</t>
2753<t>
2754   The "<x:dfn>close</x:dfn>" connection option is defined for a
2755   sender to signal that this connection will be closed after completion of
2756   the response. For example,
2757</t>
2758<figure><artwork type="example">
2759  Connection: close
2760</artwork></figure>
2761<t>
2762   in either the request or the response header fields indicates that
2763   the connection &SHOULD; be closed after the current request/response
2764   is complete (<xref target="persistent.tear-down"/>).
2765</t>
2766<t>
2767   A client that does not support persistent connections &MUST;
2768   send the "close" connection option in every request message.
2769</t>
2770<t>
2771   A server that does not support persistent connections &MUST;
2772   send the "close" connection option in every response message that
2773   does not have a <x:ref>1xx (Informational)</x:ref> status code.
2774</t>
2775</section>
2776
2777<section title="Persistent Connections" anchor="persistent.connections">
2778  <x:anchor-alias value="persistent connections"/>
2779<t>
2780   HTTP was originally designed to use a separate connection for each
2781   request/response pair. As the Web evolved and embedded requests became
2782   common for inline images, the connection establishment overhead was
2783   a significant drain on performance and a concern for Internet congestion.
2784   Message framing (via <x:ref>Content-Length</x:ref>) and optional
2785   long-lived connections (via Keep-Alive) were added to HTTP/1.0 in order
2786   to improve performance for some requests. However, these extensions were
2787   insufficient for dynamically generated responses and difficult to use
2788   with intermediaries.
2789</t>
2790<t>
2791   HTTP/1.1 defaults to the use of "<x:ref>persistent connections</x:ref>",
2792   which allow multiple requests and responses to be carried over a single
2793   connection. The "<x:ref>close</x:ref>" connection-option is used to
2794   signal that a connection will close after the current request/response.
2795   Persistent connections have a number of advantages:
2796  <list style="symbols">
2797      <t>
2798        By opening and closing fewer connections, CPU time is saved
2799        in routers and hosts (clients, servers, proxies, gateways,
2800        tunnels, or caches), and memory used for protocol control
2801        blocks can be saved in hosts.
2802      </t>
2803      <t>
2804        Most requests and responses can be pipelined on a connection.
2805        Pipelining allows a client to make multiple requests without
2806        waiting for each response, allowing a single connection to
2807        be used much more efficiently and with less overall latency.
2808      </t>
2809      <t>
2810        For TCP connections, network congestion is reduced by eliminating the
2811        packets associated with the three way handshake and graceful close
2812        procedures, and by allowing sufficient time to determine the
2813        congestion state of the network.
2814      </t>
2815      <t>
2816        Latency on subsequent requests is reduced since there is no time
2817        spent in the connection opening handshake.
2818      </t>
2819      <t>
2820        HTTP can evolve more gracefully, since most errors can be reported
2821        without the penalty of closing the connection. Clients using
2822        future versions of HTTP might optimistically try a new feature,
2823        but if communicating with an older server, retry with old
2824        semantics after an error is reported.
2825      </t>
2826    </list>
2827</t>
2828<t>
2829   HTTP implementations &SHOULD; implement persistent connections.
2830</t>
2831   
2832<section title="Establishment" anchor="persistent.establishment">
2833<t>
2834   It is beyond the scope of this specification to describe how connections
2835   are established via various transport or session-layer protocols.
2836   Each connection applies to only one transport link.
2837</t>
2838<t>
2839   A recipient determines whether a connection is persistent or not based on
2840   the most recently received message's protocol version and
2841   <x:ref>Connection</x:ref> header field (if any):
2842   <list style="symbols">
2843     <t>If the <x:ref>close</x:ref> connection option is present, the
2844        connection will not persist after the current response; else,</t>
2845     <t>If the received protocol is HTTP/1.1 (or later), the connection will
2846        persist after the current response; else,</t>
2847     <t>If the received protocol is HTTP/1.0, the "keep-alive"
2848        connection option is present, the recipient is not a proxy, and
2849        the recipient wishes to honor the HTTP/1.0 "keep-alive" mechanism,
2850        the connection will persist after the current response; otherwise,</t>
2851     <t>The connection will close after the current response.</t>
2852   </list>
2853</t>
2854<t>
2855   A proxy server &MUST-NOT; maintain a persistent connection with an
2856   HTTP/1.0 client (see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/> for
2857   information and discussion of the problems with the Keep-Alive header field
2858   implemented by many HTTP/1.0 clients).
2859</t>
2860</section>
2861
2862<section title="Reuse" anchor="persistent.reuse">
2863<t>
2864   In order to remain persistent, all messages on a connection &MUST;
2865   have a self-defined message length (i.e., one not defined by closure
2866   of the connection), as described in <xref target="message.body"/>.
2867</t>
2868<t>
2869   A server &MAY; assume that an HTTP/1.1 client intends to maintain a
2870   persistent connection until a <x:ref>close</x:ref> connection option
2871   is received in a request.
2872</t>
2873<t>
2874   A client &MAY; reuse a persistent connection until it sends or receives
2875   a <x:ref>close</x:ref> connection option or receives an HTTP/1.0 response
2876   without a "keep-alive" connection option.
2877</t>
2878<t>
2879   Clients and servers &SHOULD-NOT; assume that a persistent connection is
2880   maintained for HTTP versions less than 1.1 unless it is explicitly
2881   signaled.
2882   See <xref target="compatibility.with.http.1.0.persistent.connections"/>
2883   for more information on backward compatibility with HTTP/1.0 clients.
2884</t>
2885
2886<section title="Pipelining" anchor="pipelining">
2887<t>
2888   A client that supports persistent connections &MAY; "pipeline" its
2889   requests (i.e., send multiple requests without waiting for each
2890   response). A server &MUST; send its responses to those requests in the
2891   same order that the requests were received.
2892</t>
2893<t>
2894   Clients which assume persistent connections and pipeline immediately
2895   after connection establishment &SHOULD; be prepared to retry their
2896   connection if the first pipelined attempt fails. If a client does
2897   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2898   persistent. Clients &MUST; also be prepared to resend their requests if
2899   the server closes the connection before sending all of the
2900   corresponding responses.
2901</t>
2902<t>
2903   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods
2904   or non-idempotent sequences of request methods (see &idempotent-methods;).
2905   Otherwise, a premature termination of the transport connection could lead
2906   to indeterminate results. A client wishing to send a non-idempotent
2907   request &SHOULD; wait to send that request until it has received the
2908   response status line for the previous request.
2909</t>
2910</section>
2911
2912<section title="Retrying Requests" anchor="persistent.retrying.requests">
2913<t>
2914   Senders can close the transport connection at any time. Therefore,
2915   clients, servers, and proxies &MUST; be able to recover
2916   from asynchronous close events. Client software &MAY; reopen the
2917   transport connection and retransmit the aborted sequence of requests
2918   without user interaction so long as the request sequence is
2919   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2920   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2921   human operator the choice of retrying the request(s). Confirmation by
2922   user-agent software with semantic understanding of the application
2923   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2924   be repeated if the second sequence of requests fails.
2925</t>
2926</section>
2927</section>
2928   
2929<section title="Concurrency" anchor="persistent.concurrency">
2930<t>
2931   Clients &SHOULD; limit the number of simultaneous
2932   connections that they maintain to a given server.
2933</t>
2934<t>
2935   Previous revisions of HTTP gave a specific number of connections as a
2936   ceiling, but this was found to be impractical for many applications. As a
2937   result, this specification does not mandate a particular maximum number of
2938   connections, but instead encourages clients to be conservative when opening
2939   multiple connections.
2940</t>
2941<t>
2942   Multiple connections are typically used to avoid the "head-of-line
2943   blocking" problem, wherein a request that takes significant server-side
2944   processing and/or has a large payload blocks subsequent requests on the
2945   same connection. However, each connection consumes server resources.
2946   Furthermore, using multiple connections can cause undesirable side effects
2947   in congested networks.
2948</t>
2949<t>
2950   Note that servers might reject traffic that they deem abusive, including an
2951   excessive number of connections from a client.
2952</t>
2953</section>
2954
2955<section title="Failures and Time-outs" anchor="persistent.failures">
2956<t>
2957   Servers will usually have some time-out value beyond which they will
2958   no longer maintain an inactive connection. Proxy servers might make
2959   this a higher value since it is likely that the client will be making
2960   more connections through the same server. The use of persistent
2961   connections places no requirements on the length (or existence) of
2962   this time-out for either the client or the server.
2963</t>
2964<t>
2965   When a client or server wishes to time-out it &SHOULD; issue a graceful
2966   close on the transport connection. Clients and servers &SHOULD; both
2967   constantly watch for the other side of the transport close, and
2968   respond to it as appropriate. If a client or server does not detect
2969   the other side's close promptly it could cause unnecessary resource
2970   drain on the network.
2971</t>
2972<t>
2973   A client, server, or proxy &MAY; close the transport connection at any
2974   time. For example, a client might have started to send a new request
2975   at the same time that the server has decided to close the "idle"
2976   connection. From the server's point of view, the connection is being
2977   closed while it was idle, but from the client's point of view, a
2978   request is in progress.
2979</t>
2980<t>
2981   Servers &SHOULD; maintain persistent connections and allow the underlying
2982   transport's flow control mechanisms to resolve temporary overloads, rather
2983   than terminate connections with the expectation that clients will retry.
2984   The latter technique can exacerbate network congestion.
2985</t>
2986<t>
2987   A client sending a message body &SHOULD; monitor
2988   the network connection for an error status code while it is transmitting
2989   the request. If the client sees an error status code, it &SHOULD;
2990   immediately cease transmitting the body and close the connection.
2991</t>
2992</section>
2993   
2994<section title="Tear-down" anchor="persistent.tear-down">
2995  <iref primary="false" item="Connection header field" x:for-anchor=""/>
2996  <iref primary="false" item="close" x:for-anchor=""/>
2997<t>
2998   The <x:ref>Connection</x:ref> header field
2999   (<xref target="header.connection"/>) provides a "<x:ref>close</x:ref>"
3000   connection option that a sender &SHOULD; send when it wishes to close
3001   the connection after the current request/response pair.
3002</t>
3003<t>
3004   A client that sends a <x:ref>close</x:ref> connection option &MUST-NOT;
3005   send further requests on that connection (after the one containing
3006   <x:ref>close</x:ref>) and &MUST; close the connection after reading the
3007   final response message corresponding to this request.
3008</t>
3009<t>
3010   A server that receives a <x:ref>close</x:ref> connection option &MUST;
3011   initiate a lingering close of the connection after it sends the final
3012   response to the request that contained <x:ref>close</x:ref>.
3013   The server &SHOULD; include a <x:ref>close</x:ref> connection option
3014   in its final response on that connection. The server &MUST-NOT; process
3015   any further requests received on that connection.
3016</t>
3017<t>
3018   A server that sends a <x:ref>close</x:ref> connection option &MUST;
3019   initiate a lingering close of the connection after it sends the
3020   response containing <x:ref>close</x:ref>. The server &MUST-NOT; process
3021   any further requests received on that connection.
3022</t>
3023<t>
3024   A client that receives a <x:ref>close</x:ref> connection option &MUST;
3025   cease sending requests on that connection and close the connection
3026   after reading the response message containing the close; if additional
3027   pipelined requests had been sent on the connection, the client &SHOULD;
3028   assume that they will not be processed by the server.
3029</t>
3030<t>
3031   If a server performs an immediate close of a TCP connection, there is a
3032   significant risk that the client will not be able to read the last HTTP
3033   response.  If the server receives additional data from the client on a
3034   fully-closed connection, such as another request that was sent by the
3035   client before receiving the server's response, the server's TCP stack will
3036   send a reset packet to the client; unfortunately, the reset packet might
3037   erase the client's unacknowledged input buffers before they can be read
3038   and interpreted by the client's HTTP parser.
3039</t>
3040<t>
3041   To avoid the TCP reset problem, a server can perform a lingering close on a
3042   connection by closing only the write side of the read/write connection
3043   (a half-close) and continuing to read from the connection until the
3044   connection is closed by the client or the server is reasonably certain
3045   that its own TCP stack has received the client's acknowledgement of the
3046   packet(s) containing the server's last response. It is then safe for the
3047   server to fully close the connection.
3048</t>
3049<t>
3050   It is unknown whether the reset problem is exclusive to TCP or might also
3051   be found in other transport connection protocols.
3052</t>
3053</section>
3054</section>
3055
3056<section title="Upgrade" anchor="header.upgrade">
3057  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3058  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3059  <x:anchor-alias value="Upgrade"/>
3060  <x:anchor-alias value="protocol"/>
3061  <x:anchor-alias value="protocol-name"/>
3062  <x:anchor-alias value="protocol-version"/>
3063<t>
3064   The "Upgrade" header field is intended to provide a simple mechanism
3065   for transitioning from HTTP/1.1 to some other protocol on the same
3066   connection.  A client &MAY; send a list of protocols in the Upgrade
3067   header field of a request to invite the server to switch to one or
3068   more of those protocols before sending the final response.
3069   A server &MUST; send an Upgrade header field in <x:ref>101 (Switching
3070   Protocols)</x:ref> responses to indicate which protocol(s) are being
3071   switched to, and &MUST; send it in <x:ref>426 (Upgrade Required)</x:ref>
3072   responses to indicate acceptable protocols.
3073   A server &MAY; send an Upgrade header field in any other response to
3074   indicate that they might be willing to upgrade to one of the
3075   specified protocols for a future request.
3076</t>
3077<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3078  <x:ref>Upgrade</x:ref>          = 1#<x:ref>protocol</x:ref>
3079
3080  <x:ref>protocol</x:ref>         = <x:ref>protocol-name</x:ref> ["/" <x:ref>protocol-version</x:ref>]
3081  <x:ref>protocol-name</x:ref>    = <x:ref>token</x:ref>
3082  <x:ref>protocol-version</x:ref> = <x:ref>token</x:ref>
3083</artwork></figure>
3084<t>
3085   For example,
3086</t>
3087<figure><artwork type="example">
3088  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3089</artwork></figure>
3090<t>
3091   Upgrade eases the difficult transition between incompatible protocols by
3092   allowing the client to initiate a request in the more commonly
3093   supported protocol while indicating to the server that it would like
3094   to use a "better" protocol if available (where "better" is determined
3095   by the server, possibly according to the nature of the request method
3096   or target resource).
3097</t>
3098<t>
3099   Upgrade cannot be used to insist on a protocol change; its acceptance and
3100   use by the server is optional. The capabilities and nature of the
3101   application-level communication after the protocol change is entirely
3102   dependent upon the new protocol chosen, although the first action
3103   after changing the protocol &MUST; be a response to the initial HTTP
3104   request that contained the Upgrade header field.
3105</t>
3106<t>
3107   For example, if the Upgrade header field is received in a GET request
3108   and the server decides to switch protocols, then it &MUST; first respond
3109   with a <x:ref>101 (Switching Protocols)</x:ref> message in HTTP/1.1 and
3110   then immediately follow that with the new protocol's equivalent of a
3111   response to a GET on the target resource.  This allows a connection to be
3112   upgraded to protocols with the same semantics as HTTP without the
3113   latency cost of an additional round-trip.  A server &MUST-NOT; switch
3114   protocols unless the received message semantics can be honored by the new
3115   protocol; an OPTIONS request can be honored by any protocol.
3116</t>
3117<t>
3118   When Upgrade is sent, a sender &MUST; also send a
3119   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>)
3120   that contains the "upgrade" connection option, in order to prevent Upgrade
3121   from being accidentally forwarded by intermediaries that might not implement
3122   the listed protocols.  A server &MUST; ignore an Upgrade header field that
3123   is received in an HTTP/1.0 request.
3124</t>
3125<t>
3126   The Upgrade header field only applies to switching application-level
3127   protocols on the existing connection; it cannot be used
3128   to switch to a protocol on a different connection. For that purpose, it is
3129   more appropriate to use a <x:ref>3xx (Redirection)</x:ref> response
3130   (&status-3xx;).
3131</t>
3132<t>
3133   This specification only defines the protocol name "HTTP" for use by
3134   the family of Hypertext Transfer Protocols, as defined by the HTTP
3135   version rules of <xref target="http.version"/> and future updates to this
3136   specification. Additional tokens can be registered with IANA using the
3137   registration procedure defined in <xref target="upgrade.token.registry"/>.
3138</t>
3139</section>
3140</section>
3141
3142<section title="IANA Considerations" anchor="IANA.considerations">
3143
3144<section title="Header Field Registration" anchor="header.field.registration">
3145<t>
3146   HTTP header fields are registered within the Message Header Field Registry
3147   <xref target="RFC3864"/> maintained by IANA at
3148   <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/>.
3149</t>
3150<t>
3151   This document defines the following HTTP header fields, so their
3152   associated registry entries shall be updated according to the permanent
3153   registrations below:
3154</t>
3155<?BEGININC p1-messaging.iana-headers ?>
3156<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3157<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3158   <ttcol>Header Field Name</ttcol>
3159   <ttcol>Protocol</ttcol>
3160   <ttcol>Status</ttcol>
3161   <ttcol>Reference</ttcol>
3162
3163   <c>Connection</c>
3164   <c>http</c>
3165   <c>standard</c>
3166   <c>
3167      <xref target="header.connection"/>
3168   </c>
3169   <c>Content-Length</c>
3170   <c>http</c>
3171   <c>standard</c>
3172   <c>
3173      <xref target="header.content-length"/>
3174   </c>
3175   <c>Host</c>
3176   <c>http</c>
3177   <c>standard</c>
3178   <c>
3179      <xref target="header.host"/>
3180   </c>
3181   <c>TE</c>
3182   <c>http</c>
3183   <c>standard</c>
3184   <c>
3185      <xref target="header.te"/>
3186   </c>
3187   <c>Trailer</c>
3188   <c>http</c>
3189   <c>standard</c>
3190   <c>
3191      <xref target="header.trailer"/>
3192   </c>
3193   <c>Transfer-Encoding</c>
3194   <c>http</c>
3195   <c>standard</c>
3196   <c>
3197      <xref target="header.transfer-encoding"/>
3198   </c>
3199   <c>Upgrade</c>
3200   <c>http</c>
3201   <c>standard</c>
3202   <c>
3203      <xref target="header.upgrade"/>
3204   </c>
3205   <c>Via</c>
3206   <c>http</c>
3207   <c>standard</c>
3208   <c>
3209      <xref target="header.via"/>
3210   </c>
3211</texttable>
3212<!--(END)-->
3213<?ENDINC p1-messaging.iana-headers ?>
3214<t>
3215   Furthermore, the header field-name "Close" shall be registered as
3216   "reserved", since using that name as an HTTP header field might
3217   conflict with the "close" connection option of the "<x:ref>Connection</x:ref>"
3218   header field (<xref target="header.connection"/>).
3219</t>
3220<texttable align="left" suppress-title="true">
3221   <ttcol>Header Field Name</ttcol>
3222   <ttcol>Protocol</ttcol>
3223   <ttcol>Status</ttcol>
3224   <ttcol>Reference</ttcol>
3225
3226   <c>Close</c>
3227   <c>http</c>
3228   <c>reserved</c>
3229   <c>
3230      <xref target="header.field.registration"/>
3231   </c>
3232</texttable>
3233<t>
3234   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3235</t>
3236</section>
3237
3238<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3239<t>
3240   IANA maintains the registry of URI Schemes <xref target="RFC4395"/> at
3241   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>.
3242</t>
3243<t>
3244   This document defines the following URI schemes, so their
3245   associated registry entries shall be updated according to the permanent
3246   registrations below:
3247</t>
3248<texttable align="left" suppress-title="true">
3249   <ttcol>URI Scheme</ttcol>
3250   <ttcol>Description</ttcol>
3251   <ttcol>Reference</ttcol>
3252
3253   <c>http</c>
3254   <c>Hypertext Transfer Protocol</c>
3255   <c><xref target="http.uri"/></c>
3256
3257   <c>https</c>
3258   <c>Hypertext Transfer Protocol Secure</c>
3259   <c><xref target="https.uri"/></c>
3260</texttable>
3261</section>
3262
3263<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3264<t>
3265   This document serves as the specification for the Internet media types
3266   "message/http" and "application/http". The following is to be registered with
3267   IANA (see <xref target="RFC4288"/>).
3268</t>
3269<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3270<iref item="Media Type" subitem="message/http" primary="true"/>
3271<iref item="message/http Media Type" primary="true"/>
3272<t>
3273   The message/http type can be used to enclose a single HTTP request or
3274   response message, provided that it obeys the MIME restrictions for all
3275   "message" types regarding line length and encodings.
3276</t>
3277<t>
3278  <list style="hanging" x:indent="12em">
3279    <t hangText="Type name:">
3280      message
3281    </t>
3282    <t hangText="Subtype name:">
3283      http
3284    </t>
3285    <t hangText="Required parameters:">
3286      none
3287    </t>
3288    <t hangText="Optional parameters:">
3289      version, msgtype
3290      <list style="hanging">
3291        <t hangText="version:">
3292          The HTTP-version number of the enclosed message
3293          (e.g., "1.1"). If not present, the version can be
3294          determined from the first line of the body.
3295        </t>
3296        <t hangText="msgtype:">
3297          The message type &mdash; "request" or "response". If not
3298          present, the type can be determined from the first
3299          line of the body.
3300        </t>
3301      </list>
3302    </t>
3303    <t hangText="Encoding considerations:">
3304      only "7bit", "8bit", or "binary" are permitted
3305    </t>
3306    <t hangText="Security considerations:">
3307      none
3308    </t>
3309    <t hangText="Interoperability considerations:">
3310      none
3311    </t>
3312    <t hangText="Published specification:">
3313      This specification (see <xref target="internet.media.type.message.http"/>).
3314    </t>
3315    <t hangText="Applications that use this media type:">
3316    </t>
3317    <t hangText="Additional information:">
3318      <list style="hanging">
3319        <t hangText="Magic number(s):">none</t>
3320        <t hangText="File extension(s):">none</t>
3321        <t hangText="Macintosh file type code(s):">none</t>
3322      </list>
3323    </t>
3324    <t hangText="Person and email address to contact for further information:">
3325      See Authors Section.
3326    </t>
3327    <t hangText="Intended usage:">
3328      COMMON
3329    </t>
3330    <t hangText="Restrictions on usage:">
3331      none
3332    </t>
3333    <t hangText="Author/Change controller:">
3334      IESG
3335    </t>
3336  </list>
3337</t>
3338</section>
3339<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3340<iref item="Media Type" subitem="application/http" primary="true"/>
3341<iref item="application/http Media Type" primary="true"/>
3342<t>
3343   The application/http type can be used to enclose a pipeline of one or more
3344   HTTP request or response messages (not intermixed).
3345</t>
3346<t>
3347  <list style="hanging" x:indent="12em">
3348    <t hangText="Type name:">
3349      application
3350    </t>
3351    <t hangText="Subtype name:">
3352      http
3353    </t>
3354    <t hangText="Required parameters:">
3355      none
3356    </t>
3357    <t hangText="Optional parameters:">
3358      version, msgtype
3359      <list style="hanging">
3360        <t hangText="version:">
3361          The HTTP-version number of the enclosed messages
3362          (e.g., "1.1"). If not present, the version can be
3363          determined from the first line of the body.
3364        </t>
3365        <t hangText="msgtype:">
3366          The message type &mdash; "request" or "response". If not
3367          present, the type can be determined from the first
3368          line of the body.
3369        </t>
3370      </list>
3371    </t>
3372    <t hangText="Encoding considerations:">
3373      HTTP messages enclosed by this type
3374      are in "binary" format; use of an appropriate
3375      Content-Transfer-Encoding is required when
3376      transmitted via E-mail.
3377    </t>
3378    <t hangText="Security considerations:">
3379      none
3380    </t>
3381    <t hangText="Interoperability considerations:">
3382      none
3383    </t>
3384    <t hangText="Published specification:">
3385      This specification (see <xref target="internet.media.type.application.http"/>).
3386    </t>
3387    <t hangText="Applications that use this media type:">
3388    </t>
3389    <t hangText="Additional information:">
3390      <list style="hanging">
3391        <t hangText="Magic number(s):">none</t>
3392        <t hangText="File extension(s):">none</t>
3393        <t hangText="Macintosh file type code(s):">none</t>
3394      </list>
3395    </t>
3396    <t hangText="Person and email address to contact for further information:">
3397      See Authors Section.
3398    </t>
3399    <t hangText="Intended usage:">
3400      COMMON
3401    </t>
3402    <t hangText="Restrictions on usage:">
3403      none
3404    </t>
3405    <t hangText="Author/Change controller:">
3406      IESG
3407    </t>
3408  </list>
3409</t>
3410</section>
3411</section>
3412
3413<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
3414<t>
3415   The HTTP Transfer Coding Registry defines the name space for transfer
3416   coding names.
3417</t>
3418<t>
3419   Registrations &MUST; include the following fields:
3420   <list style="symbols">
3421     <t>Name</t>
3422     <t>Description</t>
3423     <t>Pointer to specification text</t>
3424   </list>
3425</t>
3426<t>
3427   Names of transfer codings &MUST-NOT; overlap with names of content codings
3428   (&content-codings;) unless the encoding transformation is identical, as
3429   is the case for the compression codings defined in
3430   <xref target="compression.codings"/>.
3431</t>
3432<t>
3433   Values to be added to this name space require IETF Review (see
3434   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
3435   conform to the purpose of transfer coding defined in this section.
3436   Use of program names for the identification of encoding formats
3437   is not desirable and is discouraged for future encodings.
3438</t>
3439<t>
3440   The registry itself is maintained at
3441   <eref target="http://www.iana.org/assignments/http-parameters"/>.
3442</t>
3443</section>
3444
3445<section title="Transfer Coding Registrations" anchor="transfer.coding.registration">
3446<t>
3447   The HTTP Transfer Coding Registry shall be updated with the registrations
3448   below:
3449</t>
3450<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3451   <ttcol>Name</ttcol>
3452   <ttcol>Description</ttcol>
3453   <ttcol>Reference</ttcol>
3454   <c>chunked</c>
3455   <c>Transfer in a series of chunks</c>
3456   <c>
3457      <xref target="chunked.encoding"/>
3458   </c>
3459   <c>compress</c>
3460   <c>UNIX "compress" program method</c>
3461   <c>
3462      <xref target="compress.coding"/>
3463   </c>
3464   <c>deflate</c>
3465   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3466   the "zlib" data format (<xref target="RFC1950"/>)
3467   </c>
3468   <c>
3469      <xref target="deflate.coding"/>
3470   </c>
3471   <c>gzip</c>
3472   <c>Same as GNU zip <xref target="RFC1952"/></c>
3473   <c>
3474      <xref target="gzip.coding"/>
3475   </c>
3476</texttable>
3477</section>
3478
3479<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3480<t>
3481   The HTTP Upgrade Token Registry defines the name space for protocol-name
3482   tokens used to identify protocols in the <x:ref>Upgrade</x:ref> header
3483   field. Each registered protocol name is associated with contact information
3484   and an optional set of specifications that details how the connection
3485   will be processed after it has been upgraded.
3486</t>
3487<t>
3488   Registrations happen on a "First Come First Served" basis (see
3489   <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>) and are subject to the
3490   following rules:
3491  <list style="numbers">
3492    <t>A protocol-name token, once registered, stays registered forever.</t>
3493    <t>The registration &MUST; name a responsible party for the
3494       registration.</t>
3495    <t>The registration &MUST; name a point of contact.</t>
3496    <t>The registration &MAY; name a set of specifications associated with
3497       that token. Such specifications need not be publicly available.</t>
3498    <t>The registration &SHOULD; name a set of expected "protocol-version"
3499       tokens associated with that token at the time of registration.</t>
3500    <t>The responsible party &MAY; change the registration at any time.
3501       The IANA will keep a record of all such changes, and make them
3502       available upon request.</t>
3503    <t>The IESG &MAY; reassign responsibility for a protocol token.
3504       This will normally only be used in the case when a
3505       responsible party cannot be contacted.</t>
3506  </list>
3507</t>
3508<t>
3509   This registration procedure for HTTP Upgrade Tokens replaces that
3510   previously defined in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
3511</t>
3512</section>
3513
3514<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3515<t>
3516   The HTTP Upgrade Token Registry shall be updated with the registration
3517   below:
3518</t>
3519<texttable align="left" suppress-title="true">
3520   <ttcol>Value</ttcol>
3521   <ttcol>Description</ttcol>
3522   <ttcol>Expected Version Tokens</ttcol>
3523   <ttcol>Reference</ttcol>
3524
3525   <c>HTTP</c>
3526   <c>Hypertext Transfer Protocol</c>
3527   <c>any DIGIT.DIGIT (e.g, "2.0")</c>
3528   <c><xref target="http.version"/></c>
3529</texttable>
3530<t>
3531   The responsible party is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3532</t>
3533</section>
3534
3535</section>
3536
3537<section title="Security Considerations" anchor="security.considerations">
3538<t>
3539   This section is meant to inform application developers, information
3540   providers, and users of the security limitations in HTTP/1.1 as
3541   described by this document. The discussion does not include
3542   definitive solutions to the problems revealed, though it does make
3543   some suggestions for reducing security risks.
3544</t>
3545
3546<section title="Personal Information" anchor="personal.information">
3547<t>
3548   HTTP clients are often privy to large amounts of personal information,
3549   including both information provided by the user to interact with resources
3550   (e.g., the user's name, location, mail address, passwords, encryption
3551   keys, etc.) and information about the user's browsing activity over
3552   time (e.g., history, bookmarks, etc.). HTTP implementations need to
3553   prevent unintentional leakage of this information.
3554</t>
3555</section>
3556
3557<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3558<t>
3559   A server is in the position to save personal data about a user's
3560   requests which might identify their reading patterns or subjects of
3561   interest.  In particular, log information gathered at an intermediary
3562   often contains a history of user agent interaction, across a multitude
3563   of sites, that can be traced to individual users.
3564</t>
3565<t>
3566   HTTP log information is confidential in nature; its handling is often
3567   constrained by laws and regulations.  Log information needs to be securely
3568   stored and appropriate guidelines followed for its analysis.
3569   Anonymization of personal information within individual entries helps,
3570   but is generally not sufficient to prevent real log traces from being
3571   re-identified based on correlation with other access characteristics.
3572   As such, access traces that are keyed to a specific client should not
3573   be published even if the key is pseudonymous.
3574</t>
3575<t>
3576   To minimize the risk of theft or accidental publication, log information
3577   should be purged of personally identifiable information, including
3578   user identifiers, IP addresses, and user-provided query parameters,
3579   as soon as that information is no longer necessary to support operational
3580   needs for security, auditing, or fraud control.
3581</t>
3582</section>
3583
3584<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3585<t>
3586   Origin servers &SHOULD; be careful to restrict
3587   the documents returned by HTTP requests to be only those that were
3588   intended by the server administrators. If an HTTP server translates
3589   HTTP URIs directly into file system calls, the server &MUST; take
3590   special care not to serve files that were not intended to be
3591   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3592   other operating systems use ".." as a path component to indicate a
3593   directory level above the current one. On such a system, an HTTP
3594   server &MUST; disallow any such construct in the request-target if it
3595   would otherwise allow access to a resource outside those intended to
3596   be accessible via the HTTP server. Similarly, files intended for
3597   reference only internally to the server (such as access control
3598   files, configuration files, and script code) &MUST; be protected from
3599   inappropriate retrieval, since they might contain sensitive
3600   information.
3601</t>
3602</section>
3603
3604<section title="DNS-related Attacks" anchor="dns.related.attacks">
3605<t>
3606   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
3607   generally prone to security attacks based on the deliberate misassociation
3608   of IP addresses and DNS names not protected by DNSSec. Clients need to be
3609   cautious in assuming the validity of an IP number/DNS name association unless
3610   the response is protected by DNSSec (<xref target="RFC4033"/>).
3611</t>
3612</section>
3613
3614<section title="Intermediaries and Caching" anchor="attack.intermediaries">
3615<t>
3616   By their very nature, HTTP intermediaries are men-in-the-middle, and
3617   represent an opportunity for man-in-the-middle attacks. Compromise of
3618   the systems on which the intermediaries run can result in serious security
3619   and privacy problems. Intermediaries have access to security-related
3620   information, personal information about individual users and
3621   organizations, and proprietary information belonging to users and
3622   content providers. A compromised intermediary, or an intermediary
3623   implemented or configured without regard to security and privacy
3624   considerations, might be used in the commission of a wide range of
3625   potential attacks.
3626</t>
3627<t>
3628   Intermediaries that contain a shared cache are especially vulnerable
3629   to cache poisoning attacks.
3630</t>
3631<t>
3632   Implementers need to consider the privacy and security
3633   implications of their design and coding decisions, and of the
3634   configuration options they provide to operators (especially the
3635   default configuration).
3636</t>
3637<t>
3638   Users need to be aware that intermediaries are no more trustworthy than
3639   the people who run them; HTTP itself cannot solve this problem.
3640</t>
3641</section>
3642
3643<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
3644<t>
3645   Because HTTP uses mostly textual, character-delimited fields, attackers can
3646   overflow buffers in implementations, and/or perform a Denial of Service
3647   against implementations that accept fields with unlimited lengths.
3648</t>
3649<t>
3650   To promote interoperability, this specification makes specific
3651   recommendations for minimum size limits on request-line
3652   (<xref target="request.line"/>)
3653   and blocks of header fields (<xref target="header.fields"/>). These are
3654   minimum recommendations, chosen to be supportable even by implementations
3655   with limited resources; it is expected that most implementations will
3656   choose substantially higher limits.
3657</t>
3658<t>
3659   This specification also provides a way for servers to reject messages that
3660   have request-targets that are too long (&status-414;) or request entities
3661   that are too large (&status-4xx;).
3662</t>
3663<t>
3664   Recipients &SHOULD; carefully limit the extent to which they read other
3665   fields, including (but not limited to) request methods, response status
3666   phrases, header field-names, and body chunks, so as to avoid denial of
3667   service attacks without impeding interoperability.
3668</t>
3669</section>
3670</section>
3671
3672<section title="Acknowledgments" anchor="acks">
3673<t>
3674   This edition of HTTP builds on the many contributions that went into
3675   <xref target="RFC1945" format="none">RFC 1945</xref>,
3676   <xref target="RFC2068" format="none">RFC 2068</xref>,
3677   <xref target="RFC2145" format="none">RFC 2145</xref>, and
3678   <xref target="RFC2616" format="none">RFC 2616</xref>, including
3679   substantial contributions made by the previous authors, editors, and
3680   working group chairs: Tim Berners-Lee, Ari Luotonen, Roy T. Fielding,
3681   Henrik Frystyk Nielsen, Jim Gettys, Jeffrey C. Mogul, Larry Masinter,
3682   Paul J. Leach, and Mark Nottingham.
3683   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for additional
3684   acknowledgements from prior revisions.
3685</t>
3686<t>
3687   Since 1999, the following contributors have helped improve the HTTP
3688   specification by reporting bugs, asking smart questions, drafting or
3689   reviewing text, and evaluating open issues:
3690</t>
3691<?BEGININC acks ?>
3692<t>Adam Barth,
3693Adam Roach,
3694Addison Phillips,
3695Adrian Chadd,
3696Adrien W. de Croy,
3697Alan Ford,
3698Alan Ruttenberg,
3699Albert Lunde,
3700Alek Storm,
3701Alex Rousskov,
3702Alexandre Morgaut,
3703Alexey Melnikov,
3704Alisha Smith,
3705Amichai Rothman,
3706Amit Klein,
3707Amos Jeffries,
3708Andreas Maier,
3709Andreas Petersson,
3710Anil Sharma,
3711Anne van Kesteren,
3712Anthony Bryan,
3713Asbjorn Ulsberg,
3714Balachander Krishnamurthy,
3715Barry Leiba,
3716Ben Laurie,
3717Benjamin Niven-Jenkins,
3718Bil Corry,
3719Bill Burke,
3720Bjoern Hoehrmann,
3721Bob Scheifler,
3722Boris Zbarsky,
3723Brett Slatkin,
3724Brian Kell,
3725Brian McBarron,
3726Brian Pane,
3727Brian Smith,
3728Bryce Nesbitt,
3729Cameron Heavon-Jones,
3730Carl Kugler,
3731Carsten Bormann,
3732Charles Fry,
3733Chris Newman,
3734Cyrus Daboo,
3735Dale Robert Anderson,
3736Dan Wing,
3737Dan Winship,
3738Daniel Stenberg,
3739Dave Cridland,
3740Dave Crocker,
3741Dave Kristol,
3742David Booth,
3743David Singer,
3744David W. Morris,
3745Diwakar Shetty,
3746Dmitry Kurochkin,
3747Drummond Reed,
3748Duane Wessels,
3749Edward Lee,
3750Eliot Lear,
3751Eran Hammer-Lahav,
3752Eric D. Williams,
3753Eric J. Bowman,
3754Eric Lawrence,
3755Eric Rescorla,
3756Erik Aronesty,
3757Evan Prodromou,
3758Florian Weimer,
3759Frank Ellermann,
3760Fred Bohle,
3761Gabriel Montenegro,
3762Geoffrey Sneddon,
3763Gervase Markham,
3764Grahame Grieve,
3765Greg Wilkins,
3766Harald Tveit Alvestrand,
3767Harry Halpin,
3768Helge Hess,
3769Henrik Nordstrom,
3770Henry S. Thompson,
3771Henry Story,
3772Herbert van de Sompel,
3773Howard Melman,
3774Hugo Haas,
3775Ian Fette,
3776Ian Hickson,
3777Ido Safruti,
3778Ingo Struck,
3779J. Ross Nicoll,
3780James H. Manger,
3781James Lacey,
3782James M. Snell,
3783Jamie Lokier,
3784Jan Algermissen,
3785Jeff Hodges (who came up with the term 'effective Request-URI'),
3786Jeff Walden,
3787Jim Luther,
3788Joe D. Williams,
3789Joe Gregorio,
3790Joe Orton,
3791John C. Klensin,
3792John C. Mallery,
3793John Cowan,
3794John Kemp,
3795John Panzer,
3796John Schneider,
3797John Stracke,
3798John Sullivan,
3799Jonas Sicking,
3800Jonathan Billington,
3801Jonathan Moore,
3802Jonathan Rees,
3803Jonathan Silvera,
3804Jordi Ros,
3805Joris Dobbelsteen,
3806Josh Cohen,
3807Julien Pierre,
3808Jungshik Shin,
3809Justin Chapweske,
3810Justin Erenkrantz,
3811Justin James,
3812Kalvinder Singh,
3813Karl Dubost,
3814Keith Hoffman,
3815Keith Moore,
3816Koen Holtman,
3817Konstantin Voronkov,
3818Kris Zyp,
3819Lisa Dusseault,
3820Maciej Stachowiak,
3821Marc Schneider,
3822Marc Slemko,
3823Mark Baker,
3824Mark Pauley,
3825Mark Watson,
3826Markus Isomaki,
3827Markus Lanthaler,
3828Martin J. Duerst,
3829Martin Musatov,
3830Martin Nilsson,
3831Martin Thomson,
3832Matt Lynch,
3833Matthew Cox,
3834Max Clark,
3835Michael Burrows,
3836Michael Hausenblas,
3837Mike Amundsen,
3838Mike Belshe,
3839Mike Kelly,
3840Mike Schinkel,
3841Miles Sabin,
3842Murray S. Kucherawy,
3843Mykyta Yevstifeyev,
3844Nathan Rixham,
3845Nicholas Shanks,
3846Nico Williams,
3847Nicolas Alvarez,
3848Nicolas Mailhot,
3849Noah Slater,
3850Pablo Castro,
3851Pat Hayes,
3852Patrick R. McManus,
3853Paul E. Jones,
3854Paul Hoffman,
3855Paul Marquess,
3856Peter Lepeska,
3857Peter Saint-Andre,
3858Peter Watkins,
3859Phil Archer,
3860Philippe Mougin,
3861Phillip Hallam-Baker,
3862Poul-Henning Kamp,
3863Preethi Natarajan,
3864Rajeev Bector,
3865Ray Polk,
3866Reto Bachmann-Gmuer,
3867Richard Cyganiak,
3868Robert Brewer,
3869Robert Collins,
3870Robert O'Callahan,
3871Robert Olofsson,
3872Robert Sayre,
3873Robert Siemer,
3874Robert de Wilde,
3875Roberto Javier Godoy,
3876Roberto Peon,
3877Ronny Widjaja,
3878S. Mike Dierken,
3879Salvatore Loreto,
3880Sam Johnston,
3881Sam Ruby,
3882Scott Lawrence (who maintained the original issues list),
3883Sean B. Palmer,
3884Shane McCarron,
3885Stefan Eissing,
3886Stefan Tilkov,
3887Stefanos Harhalakis,
3888Stephane Bortzmeyer,
3889Stephen Farrell,
3890Stephen Ludin,
3891Stuart Williams,
3892Subbu Allamaraju,
3893Sylvain Hellegouarch,
3894Tapan Divekar,
3895Tatsuya Hayashi,
3896Ted Hardie,
3897Thomas Broyer,
3898Thomas Nordin,
3899Thomas Roessler,
3900Tim Bray,
3901Tim Morgan,
3902Tim Olsen,
3903Tom Zhou,
3904Travis Snoozy,
3905Tyler Close,
3906Vincent Murphy,
3907Wenbo Zhu,
3908Werner Baumann,
3909Wilbur Streett,
3910Wilfredo Sanchez Vega,
3911William A. Rowe Jr.,
3912William Chan,
3913Willy Tarreau,
3914Xiaoshu Wang,
3915Yaron Goland,
3916Yngve Nysaeter Pettersen,
3917Yoav Nir,
3918Yogesh Bang,
3919Yutaka Oiwa,
3920Zed A. Shaw, and
3921Zhong Yu.
3922</t>
3923<?ENDINC acks ?>
3924</section>
3925
3926</middle>
3927<back>
3928
3929<references title="Normative References">
3930
3931<reference anchor="Part2">
3932  <front>
3933    <title>Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content</title>
3934    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3935      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3936      <address><email>fielding@gbiv.com</email></address>
3937    </author>
3938    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3939      <organization abbrev="W3C">World Wide Web Consortium</organization>
3940      <address><email>ylafon@w3.org</email></address>
3941    </author>
3942    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3943      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3944      <address><email>julian.reschke@greenbytes.de</email></address>
3945    </author>
3946    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3947  </front>
3948  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3949  <x:source href="p2-semantics.xml" basename="p2-semantics">
3950    <x:defines>1xx (Informational)</x:defines>
3951    <x:defines>1xx</x:defines>
3952    <x:defines>100 (Continue)</x:defines>
3953    <x:defines>101 (Switching Protocols)</x:defines>
3954    <x:defines>2xx (Successful)</x:defines>
3955    <x:defines>2xx</x:defines>
3956    <x:defines>200 (OK)</x:defines>
3957    <x:defines>204 (No Content)</x:defines>
3958    <x:defines>3xx (Redirection)</x:defines>
3959    <x:defines>3xx</x:defines>
3960    <x:defines>301 (Moved Permanently)</x:defines>
3961    <x:defines>4xx (Client Error)</x:defines>
3962    <x:defines>4xx</x:defines>
3963    <x:defines>400 (Bad Request)</x:defines>
3964    <x:defines>405 (Method Not Allowed)</x:defines>
3965    <x:defines>411 (Length Required)</x:defines>
3966    <x:defines>414 (URI Too Long)</x:defines>
3967    <x:defines>417 (Expectation Failed)</x:defines>
3968    <x:defines>426 (Upgrade Required)</x:defines>
3969    <x:defines>501 (Not Implemented)</x:defines>
3970    <x:defines>502 (Bad Gateway)</x:defines>
3971    <x:defines>505 (HTTP Version Not Supported)</x:defines>
3972    <x:defines>Allow</x:defines>
3973    <x:defines>Content-Encoding</x:defines>
3974    <x:defines>Content-Location</x:defines>
3975    <x:defines>Content-Type</x:defines>
3976    <x:defines>Date</x:defines>
3977    <x:defines>Expect</x:defines>
3978    <x:defines>Location</x:defines>
3979    <x:defines>Server</x:defines>
3980    <x:defines>User-Agent</x:defines>
3981  </x:source>
3982</reference>
3983
3984<reference anchor="Part4">
3985  <front>
3986    <title>Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests</title>
3987    <author fullname="Roy T. Fielding" initials="R." role="editor" surname="Fielding">
3988      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3989      <address><email>fielding@gbiv.com</email></address>
3990    </author>
3991    <author fullname="Yves Lafon" initials="Y." role="editor" surname="Lafon">
3992      <organization abbrev="W3C">World Wide Web Consortium</organization>
3993      <address><email>ylafon@w3.org</email></address>
3994    </author>
3995    <author fullname="Julian F. Reschke" initials="J. F." role="editor" surname="Reschke">
3996      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3997      <address><email>julian.reschke@greenbytes.de</email></address>
3998    </author>
3999    <date month="&ID-MONTH;" year="&ID-YEAR;" />
4000  </front>
4001  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;" />
4002  <x:source basename="p4-conditional" href="p4-conditional.xml">
4003    <x:defines>304 (Not Modified)</x:defines>
4004    <x:defines>ETag</x:defines>
4005    <x:defines>Last-Modified</x:defines>
4006  </x:source>
4007</reference>
4008
4009<reference anchor="Part5">
4010  <front>
4011    <title>Hypertext Transfer Protocol (HTTP/1.1): Range Requests</title>
4012    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4013      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4014      <address><email>fielding@gbiv.com</email></address>
4015    </author>
4016    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4017      <organization abbrev="W3C">World Wide Web Consortium</organization>
4018      <address><email>ylafon@w3.org</email></address>
4019    </author>
4020    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4021      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4022      <address><email>julian.reschke@greenbytes.de</email></address>
4023    </author>
4024    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4025  </front>
4026  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
4027  <x:source href="p5-range.xml" basename="p5-range">
4028    <x:defines>Content-Range</x:defines>
4029  </x:source>
4030</reference>
4031
4032<reference anchor="Part6">
4033  <front>
4034    <title>Hypertext Transfer Protocol (HTTP/1.1): Caching</title>
4035    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4036      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4037      <address><email>fielding@gbiv.com</email></address>
4038    </author>
4039    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4040      <organization abbrev="W3C">World Wide Web Consortium</organization>
4041      <address><email>ylafon@w3.org</email></address>
4042    </author>
4043    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4044      <address><email>mnot@mnot.net</email></address>
4045    </author>
4046    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4047      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4048      <address><email>julian.reschke@greenbytes.de</email></address>
4049    </author>
4050    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4051  </front>
4052  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4053  <x:source href="p6-cache.xml" basename="p6-cache">
4054    <x:defines>Expires</x:defines>
4055  </x:source>
4056</reference>
4057
4058<reference anchor="Part7">
4059  <front>
4060    <title>Hypertext Transfer Protocol (HTTP/1.1): Authentication</title>
4061    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4062      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4063      <address><email>fielding@gbiv.com</email></address>
4064    </author>
4065    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4066      <organization abbrev="W3C">World Wide Web Consortium</organization>
4067      <address><email>ylafon@w3.org</email></address>
4068    </author>
4069    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4070      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4071      <address><email>julian.reschke@greenbytes.de</email></address>
4072    </author>
4073    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4074  </front>
4075  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
4076  <x:source href="p7-auth.xml" basename="p7-auth">
4077    <x:defines>Proxy-Authenticate</x:defines>
4078    <x:defines>Proxy-Authorization</x:defines>
4079  </x:source>
4080</reference>
4081
4082<reference anchor="RFC5234">
4083  <front>
4084    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4085    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4086      <organization>Brandenburg InternetWorking</organization>
4087      <address>
4088        <email>dcrocker@bbiw.net</email>
4089      </address> 
4090    </author>
4091    <author initials="P." surname="Overell" fullname="Paul Overell">
4092      <organization>THUS plc.</organization>
4093      <address>
4094        <email>paul.overell@thus.net</email>
4095      </address>
4096    </author>
4097    <date month="January" year="2008"/>
4098  </front>
4099  <seriesInfo name="STD" value="68"/>
4100  <seriesInfo name="RFC" value="5234"/>
4101</reference>
4102
4103<reference anchor="RFC2119">
4104  <front>
4105    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4106    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4107      <organization>Harvard University</organization>
4108      <address><email>sob@harvard.edu</email></address>
4109    </author>
4110    <date month="March" year="1997"/>
4111  </front>
4112  <seriesInfo name="BCP" value="14"/>
4113  <seriesInfo name="RFC" value="2119"/>
4114</reference>
4115
4116<reference anchor="RFC3986">
4117 <front>
4118  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4119  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4120    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4121    <address>
4122       <email>timbl@w3.org</email>
4123       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4124    </address>
4125  </author>
4126  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4127    <organization abbrev="Day Software">Day Software</organization>
4128    <address>
4129      <email>fielding@gbiv.com</email>
4130      <uri>http://roy.gbiv.com/</uri>
4131    </address>
4132  </author>
4133  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4134    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4135    <address>
4136      <email>LMM@acm.org</email>
4137      <uri>http://larry.masinter.net/</uri>
4138    </address>
4139  </author>
4140  <date month='January' year='2005'></date>
4141 </front>
4142 <seriesInfo name="STD" value="66"/>
4143 <seriesInfo name="RFC" value="3986"/>
4144</reference>
4145
4146<reference anchor="USASCII">
4147  <front>
4148    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4149    <author>
4150      <organization>American National Standards Institute</organization>
4151    </author>
4152    <date year="1986"/>
4153  </front>
4154  <seriesInfo name="ANSI" value="X3.4"/>
4155</reference>
4156
4157<reference anchor="RFC1950">
4158  <front>
4159    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4160    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4161      <organization>Aladdin Enterprises</organization>
4162      <address><email>ghost@aladdin.com</email></address>
4163    </author>
4164    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4165    <date month="May" year="1996"/>
4166  </front>
4167  <seriesInfo name="RFC" value="1950"/>
4168  <!--<annotation>
4169    RFC 1950 is an Informational RFC, thus it might be less stable than
4170    this specification. On the other hand, this downward reference was
4171    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4172    therefore it is unlikely to cause problems in practice. See also
4173    <xref target="BCP97"/>.
4174  </annotation>-->
4175</reference>
4176
4177<reference anchor="RFC1951">
4178  <front>
4179    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4180    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4181      <organization>Aladdin Enterprises</organization>
4182      <address><email>ghost@aladdin.com</email></address>
4183    </author>
4184    <date month="May" year="1996"/>
4185  </front>
4186  <seriesInfo name="RFC" value="1951"/>
4187  <!--<annotation>
4188    RFC 1951 is an Informational RFC, thus it might be less stable than
4189    this specification. On the other hand, this downward reference was
4190    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4191    therefore it is unlikely to cause problems in practice. See also
4192    <xref target="BCP97"/>.
4193  </annotation>-->
4194</reference>
4195
4196<reference anchor="RFC1952">
4197  <front>
4198    <title>GZIP file format specification version 4.3</title>
4199    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4200      <organization>Aladdin Enterprises</organization>
4201      <address><email>ghost@aladdin.com</email></address>
4202    </author>
4203    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4204      <address><email>gzip@prep.ai.mit.edu</email></address>
4205    </author>
4206    <author initials="M." surname="Adler" fullname="Mark Adler">
4207      <address><email>madler@alumni.caltech.edu</email></address>
4208    </author>
4209    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4210      <address><email>ghost@aladdin.com</email></address>
4211    </author>
4212    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4213      <address><email>randeg@alumni.rpi.edu</email></address>
4214    </author>
4215    <date month="May" year="1996"/>
4216  </front>
4217  <seriesInfo name="RFC" value="1952"/>
4218  <!--<annotation>
4219    RFC 1952 is an Informational RFC, thus it might be less stable than
4220    this specification. On the other hand, this downward reference was
4221    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4222    therefore it is unlikely to cause problems in practice. See also
4223    <xref target="BCP97"/>.
4224  </annotation>-->
4225</reference>
4226
4227</references>
4228
4229<references title="Informative References">
4230
4231<reference anchor="ISO-8859-1">
4232  <front>
4233    <title>
4234     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4235    </title>
4236    <author>
4237      <organization>International Organization for Standardization</organization>
4238    </author>
4239    <date year="1998"/>
4240  </front>
4241  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4242</reference>
4243
4244<reference anchor='RFC1919'>
4245  <front>
4246    <title>Classical versus Transparent IP Proxies</title>
4247    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4248      <address><email>mchatel@pax.eunet.ch</email></address>
4249    </author>
4250    <date year='1996' month='March' />
4251  </front>
4252  <seriesInfo name='RFC' value='1919' />
4253</reference>
4254
4255<reference anchor="RFC1945">
4256  <front>
4257    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4258    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4259      <organization>MIT, Laboratory for Computer Science</organization>
4260      <address><email>timbl@w3.org</email></address>
4261    </author>
4262    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4263      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4264      <address><email>fielding@ics.uci.edu</email></address>
4265    </author>
4266    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4267      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4268      <address><email>frystyk@w3.org</email></address>
4269    </author>
4270    <date month="May" year="1996"/>
4271  </front>
4272  <seriesInfo name="RFC" value="1945"/>
4273</reference>
4274
4275<reference anchor="RFC2045">
4276  <front>
4277    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4278    <author initials="N." surname="Freed" fullname="Ned Freed">
4279      <organization>Innosoft International, Inc.</organization>
4280      <address><email>ned@innosoft.com</email></address>
4281    </author>
4282    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4283      <organization>First Virtual Holdings</organization>
4284      <address><email>nsb@nsb.fv.com</email></address>
4285    </author>
4286    <date month="November" year="1996"/>
4287  </front>
4288  <seriesInfo name="RFC" value="2045"/>
4289</reference>
4290
4291<reference anchor="RFC2047">
4292  <front>
4293    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4294    <author initials="K." surname="Moore" fullname="Keith Moore">
4295      <organization>University of Tennessee</organization>
4296      <address><email>moore@cs.utk.edu</email></address>
4297    </author>
4298    <date month="November" year="1996"/>
4299  </front>
4300  <seriesInfo name="RFC" value="2047"/>
4301</reference>
4302
4303<reference anchor="RFC2068">
4304  <front>
4305    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4306    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4307      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4308      <address><email>fielding@ics.uci.edu</email></address>
4309    </author>
4310    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4311      <organization>MIT Laboratory for Computer Science</organization>
4312      <address><email>jg@w3.org</email></address>
4313    </author>
4314    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4315      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4316      <address><email>mogul@wrl.dec.com</email></address>
4317    </author>
4318    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4319      <organization>MIT Laboratory for Computer Science</organization>
4320      <address><email>frystyk@w3.org</email></address>
4321    </author>
4322    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4323      <organization>MIT Laboratory for Computer Science</organization>
4324      <address><email>timbl@w3.org</email></address>
4325    </author>
4326    <date month="January" year="1997"/>
4327  </front>
4328  <seriesInfo name="RFC" value="2068"/>
4329</reference>
4330
4331<reference anchor="RFC2145">
4332  <front>
4333    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4334    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4335      <organization>Western Research Laboratory</organization>
4336      <address><email>mogul@wrl.dec.com</email></address>
4337    </author>
4338    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4339      <organization>Department of Information and Computer Science</organization>
4340      <address><email>fielding@ics.uci.edu</email></address>
4341    </author>
4342    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4343      <organization>MIT Laboratory for Computer Science</organization>
4344      <address><email>jg@w3.org</email></address>
4345    </author>
4346    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4347      <organization>W3 Consortium</organization>
4348      <address><email>frystyk@w3.org</email></address>
4349    </author>
4350    <date month="May" year="1997"/>
4351  </front>
4352  <seriesInfo name="RFC" value="2145"/>
4353</reference>
4354
4355<reference anchor="RFC2616">
4356  <front>
4357    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4358    <author initials="R." surname="Fielding" fullname="R. Fielding">
4359      <organization>University of California, Irvine</organization>
4360      <address><email>fielding@ics.uci.edu</email></address>
4361    </author>
4362    <author initials="J." surname="Gettys" fullname="J. Gettys">
4363      <organization>W3C</organization>
4364      <address><email>jg@w3.org</email></address>
4365    </author>
4366    <author initials="J." surname="Mogul" fullname="J. Mogul">
4367      <organization>Compaq Computer Corporation</organization>
4368      <address><email>mogul@wrl.dec.com</email></address>
4369    </author>
4370    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4371      <organization>MIT Laboratory for Computer Science</organization>
4372      <address><email>frystyk@w3.org</email></address>
4373    </author>
4374    <author initials="L." surname="Masinter" fullname="L. Masinter">
4375      <organization>Xerox Corporation</organization>
4376      <address><email>masinter@parc.xerox.com</email></address>
4377    </author>
4378    <author initials="P." surname="Leach" fullname="P. Leach">
4379      <organization>Microsoft Corporation</organization>
4380      <address><email>paulle@microsoft.com</email></address>
4381    </author>
4382    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4383      <organization>W3C</organization>
4384      <address><email>timbl@w3.org</email></address>
4385    </author>
4386    <date month="June" year="1999"/>
4387  </front>
4388  <seriesInfo name="RFC" value="2616"/>
4389</reference>
4390
4391<reference anchor='RFC2817'>
4392  <front>
4393    <title>Upgrading to TLS Within HTTP/1.1</title>
4394    <author initials='R.' surname='Khare' fullname='R. Khare'>
4395      <organization>4K Associates / UC Irvine</organization>
4396      <address><email>rohit@4K-associates.com</email></address>
4397    </author>
4398    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4399      <organization>Agranat Systems, Inc.</organization>
4400      <address><email>lawrence@agranat.com</email></address>
4401    </author>
4402    <date year='2000' month='May' />
4403  </front>
4404  <seriesInfo name='RFC' value='2817' />
4405</reference>
4406
4407<reference anchor='RFC2818'>
4408  <front>
4409    <title>HTTP Over TLS</title>
4410    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4411      <organization>RTFM, Inc.</organization>
4412      <address><email>ekr@rtfm.com</email></address>
4413    </author>
4414    <date year='2000' month='May' />
4415  </front>
4416  <seriesInfo name='RFC' value='2818' />
4417</reference>
4418
4419<reference anchor='RFC2965'>
4420  <front>
4421    <title>HTTP State Management Mechanism</title>
4422    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4423      <organization>Bell Laboratories, Lucent Technologies</organization>
4424      <address><email>dmk@bell-labs.com</email></address>
4425    </author>
4426    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4427      <organization>Epinions.com, Inc.</organization>
4428      <address><email>lou@montulli.org</email></address>
4429    </author>
4430    <date year='2000' month='October' />
4431  </front>
4432  <seriesInfo name='RFC' value='2965' />
4433</reference>
4434
4435<reference anchor='RFC3040'>
4436  <front>
4437    <title>Internet Web Replication and Caching Taxonomy</title>
4438    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4439      <organization>Equinix, Inc.</organization>
4440    </author>
4441    <author initials='I.' surname='Melve' fullname='I. Melve'>
4442      <organization>UNINETT</organization>
4443    </author>
4444    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4445      <organization>CacheFlow Inc.</organization>
4446    </author>
4447    <date year='2001' month='January' />
4448  </front>
4449  <seriesInfo name='RFC' value='3040' />
4450</reference>
4451
4452<reference anchor='RFC3864'>
4453  <front>
4454    <title>Registration Procedures for Message Header Fields</title>
4455    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4456      <organization>Nine by Nine</organization>
4457      <address><email>GK-IETF@ninebynine.org</email></address>
4458    </author>
4459    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4460      <organization>BEA Systems</organization>
4461      <address><email>mnot@pobox.com</email></address>
4462    </author>
4463    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4464      <organization>HP Labs</organization>
4465      <address><email>JeffMogul@acm.org</email></address>
4466    </author>
4467    <date year='2004' month='September' />
4468  </front>
4469  <seriesInfo name='BCP' value='90' />
4470  <seriesInfo name='RFC' value='3864' />
4471</reference>
4472
4473<reference anchor='RFC4033'>
4474  <front>
4475    <title>DNS Security Introduction and Requirements</title>
4476    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4477    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4478    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4479    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4480    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4481    <date year='2005' month='March' />
4482  </front>
4483  <seriesInfo name='RFC' value='4033' />
4484</reference>
4485
4486<reference anchor="RFC4288">
4487  <front>
4488    <title>Media Type Specifications and Registration Procedures</title>
4489    <author initials="N." surname="Freed" fullname="N. Freed">
4490      <organization>Sun Microsystems</organization>
4491      <address>
4492        <email>ned.freed@mrochek.com</email>
4493      </address>
4494    </author>
4495    <author initials="J." surname="Klensin" fullname="J. Klensin">
4496      <address>
4497        <email>klensin+ietf@jck.com</email>
4498      </address>
4499    </author>
4500    <date year="2005" month="December"/>
4501  </front>
4502  <seriesInfo name="BCP" value="13"/>
4503  <seriesInfo name="RFC" value="4288"/>
4504</reference>
4505
4506<reference anchor='RFC4395'>
4507  <front>
4508    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4509    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4510      <organization>AT&amp;T Laboratories</organization>
4511      <address>
4512        <email>tony+urireg@maillennium.att.com</email>
4513      </address>
4514    </author>
4515    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4516      <organization>Qualcomm, Inc.</organization>
4517      <address>
4518        <email>hardie@qualcomm.com</email>
4519      </address>
4520    </author>
4521    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4522      <organization>Adobe Systems</organization>
4523      <address>
4524        <email>LMM@acm.org</email>
4525      </address>
4526    </author>
4527    <date year='2006' month='February' />
4528  </front>
4529  <seriesInfo name='BCP' value='115' />
4530  <seriesInfo name='RFC' value='4395' />
4531</reference>
4532
4533<reference anchor='RFC4559'>
4534  <front>
4535    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4536    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4537    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4538    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4539    <date year='2006' month='June' />
4540  </front>
4541  <seriesInfo name='RFC' value='4559' />
4542</reference>
4543
4544<reference anchor='RFC5226'>
4545  <front>
4546    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4547    <author initials='T.' surname='Narten' fullname='T. Narten'>
4548      <organization>IBM</organization>
4549      <address><email>narten@us.ibm.com</email></address>
4550    </author>
4551    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4552      <organization>Google</organization>
4553      <address><email>Harald@Alvestrand.no</email></address>
4554    </author>
4555    <date year='2008' month='May' />
4556  </front>
4557  <seriesInfo name='BCP' value='26' />
4558  <seriesInfo name='RFC' value='5226' />
4559</reference>
4560
4561<reference anchor='RFC5246'>
4562   <front>
4563      <title>The Transport Layer Security (TLS) Protocol Version 1.2</title>
4564      <author initials='T.' surname='Dierks' fullname='T. Dierks'>
4565         <organization />
4566      </author>
4567      <author initials='E.' surname='Rescorla' fullname='E. Rescorla'>
4568         <organization>RTFM, Inc.</organization>
4569      </author>
4570      <date year='2008' month='August' />
4571   </front>
4572   <seriesInfo name='RFC' value='5246' />
4573</reference>
4574
4575<reference anchor="RFC5322">
4576  <front>
4577    <title>Internet Message Format</title>
4578    <author initials="P." surname="Resnick" fullname="P. Resnick">
4579      <organization>Qualcomm Incorporated</organization>
4580    </author>
4581    <date year="2008" month="October"/>
4582  </front> 
4583  <seriesInfo name="RFC" value="5322"/>
4584</reference>
4585
4586<reference anchor="RFC6265">
4587  <front>
4588    <title>HTTP State Management Mechanism</title>
4589    <author initials="A." surname="Barth" fullname="Adam Barth">
4590      <organization abbrev="U.C. Berkeley">
4591        University of California, Berkeley
4592      </organization>
4593      <address><email>abarth@eecs.berkeley.edu</email></address>
4594    </author>
4595    <date year="2011" month="April" />
4596  </front>
4597  <seriesInfo name="RFC" value="6265"/>
4598</reference>
4599
4600<!--<reference anchor='BCP97'>
4601  <front>
4602    <title>Handling Normative References to Standards-Track Documents</title>
4603    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4604      <address>
4605        <email>klensin+ietf@jck.com</email>
4606      </address>
4607    </author>
4608    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4609      <organization>MIT</organization>
4610      <address>
4611        <email>hartmans-ietf@mit.edu</email>
4612      </address>
4613    </author>
4614    <date year='2007' month='June' />
4615  </front>
4616  <seriesInfo name='BCP' value='97' />
4617  <seriesInfo name='RFC' value='4897' />
4618</reference>-->
4619
4620<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4621  <front>
4622    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4623    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4624    <date year="2001" month="November"/>
4625  </front>
4626  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4627</reference>
4628
4629</references>
4630
4631
4632<section title="HTTP Version History" anchor="compatibility">
4633<t>
4634   HTTP has been in use by the World-Wide Web global information initiative
4635   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4636   was a simple protocol for hypertext data transfer across the Internet
4637   with only a single request method (GET) and no metadata.
4638   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4639   methods and MIME-like messaging that could include metadata about the data
4640   transferred and modifiers on the request/response semantics. However,
4641   HTTP/1.0 did not sufficiently take into consideration the effects of
4642   hierarchical proxies, caching, the need for persistent connections, or
4643   name-based virtual hosts. The proliferation of incompletely-implemented
4644   applications calling themselves "HTTP/1.0" further necessitated a
4645   protocol version change in order for two communicating applications
4646   to determine each other's true capabilities.
4647</t>
4648<t>
4649   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4650   requirements that enable reliable implementations, adding only
4651   those new features that will either be safely ignored by an HTTP/1.0
4652   recipient or only sent when communicating with a party advertising
4653   conformance with HTTP/1.1.
4654</t>
4655<t>
4656   It is beyond the scope of a protocol specification to mandate
4657   conformance with previous versions. HTTP/1.1 was deliberately
4658   designed, however, to make supporting previous versions easy.
4659   We would expect a general-purpose HTTP/1.1 server to understand
4660   any valid request in the format of HTTP/1.0 and respond appropriately
4661   with an HTTP/1.1 message that only uses features understood (or
4662   safely ignored) by HTTP/1.0 clients.  Likewise, we would expect
4663   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4664</t>
4665<t>
4666   Since HTTP/0.9 did not support header fields in a request,
4667   there is no mechanism for it to support name-based virtual
4668   hosts (selection of resource by inspection of the <x:ref>Host</x:ref> header
4669   field).  Any server that implements name-based virtual hosts
4670   ought to disable support for HTTP/0.9.  Most requests that
4671   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4672   requests wherein a buggy client failed to properly encode
4673   linear whitespace found in a URI reference and placed in
4674   the request-target.
4675</t>
4676
4677<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4678<t>
4679   This section summarizes major differences between versions HTTP/1.0
4680   and HTTP/1.1.
4681</t>
4682
4683<section title="Multi-homed Web Servers" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
4684<t>
4685   The requirements that clients and servers support the <x:ref>Host</x:ref>
4686   header field (<xref target="header.host"/>), report an error if it is
4687   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4688   are among the most important changes defined by HTTP/1.1.
4689</t>
4690<t>
4691   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4692   addresses and servers; there was no other established mechanism for
4693   distinguishing the intended server of a request than the IP address
4694   to which that request was directed. The <x:ref>Host</x:ref> header field was
4695   introduced during the development of HTTP/1.1 and, though it was
4696   quickly implemented by most HTTP/1.0 browsers, additional requirements
4697   were placed on all HTTP/1.1 requests in order to ensure complete
4698   adoption.  At the time of this writing, most HTTP-based services
4699   are dependent upon the Host header field for targeting requests.
4700</t>
4701</section>
4702
4703<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4704<t>
4705   In HTTP/1.0, each connection is established by the client prior to the
4706   request and closed by the server after sending the response. However, some
4707   implementations implement the explicitly negotiated ("Keep-Alive") version
4708   of persistent connections described in <xref x:sec="19.7.1" x:fmt="of"
4709   target="RFC2068"/>.
4710</t>
4711<t>
4712   Some clients and servers might wish to be compatible with these previous
4713   approaches to persistent connections, by explicitly negotiating for them
4714   with a "Connection: keep-alive" request header field. However, some
4715   experimental implementations of HTTP/1.0 persistent connections are faulty;
4716   for example, if a HTTP/1.0 proxy server doesn't understand
4717   <x:ref>Connection</x:ref>, it will erroneously forward that header field
4718   to the next inbound server, which would result in a hung connection.
4719</t>
4720<t>
4721   One attempted solution was the introduction of a Proxy-Connection header
4722   field, targeted specifically at proxies. In practice, this was also
4723   unworkable, because proxies are often deployed in multiple layers, bringing
4724   about the same problem discussed above.
4725</t>
4726<t>
4727   As a result, clients are encouraged not to send the Proxy-Connection header
4728   field in any requests.
4729</t>
4730<t>
4731   Clients are also encouraged to consider the use of Connection: keep-alive
4732   in requests carefully; while they can enable persistent connections with
4733   HTTP/1.0 servers, clients using them need will need to monitor the
4734   connection for "hung" requests (which indicate that the client ought stop
4735   sending the header field), and this mechanism ought not be used by clients
4736   at all when a proxy is being used.
4737</t>
4738</section>
4739
4740<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
4741<t>
4742   HTTP/1.1 introduces the <x:ref>Transfer-Encoding</x:ref> header field
4743   (<xref target="header.transfer-encoding"/>). Proxies/gateways &MUST; remove
4744   any transfer-coding prior to forwarding a message via a MIME-compliant
4745   protocol.
4746</t>
4747</section>
4748
4749</section>
4750
4751<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4752<t>
4753  Clarify that the string "HTTP" in the HTTP-version ABNF production is case
4754  sensitive. Restrict the version numbers to be single digits due to the fact
4755  that implementations are known to handle multi-digit version numbers
4756  incorrectly.
4757  (<xref target="http.version"/>)
4758</t>
4759<t>
4760  Update use of abs_path production from RFC 1808 to the path-absolute + query
4761  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4762  request method only.
4763  (<xref target="request-target"/>)
4764</t>
4765<t>
4766  Require that invalid whitespace around field-names be rejected.
4767  (<xref target="header.fields"/>)
4768</t>
4769<t>
4770  Rules about implicit linear whitespace between certain grammar productions
4771  have been removed; now whitespace is only allowed where specifically
4772  defined in the ABNF.
4773  (<xref target="whitespace"/>)
4774</t>
4775<t> 
4776  The NUL octet is no longer allowed in comment and quoted-string
4777  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4778  Non-ASCII content in header fields and reason phrase has been obsoleted and
4779  made opaque (the TEXT rule was removed).
4780  (<xref target="field.components"/>)
4781</t>
4782<t>
4783  Empty list elements in list productions have been deprecated.
4784  (<xref target="abnf.extension"/>)
4785</t>
4786<t>
4787  Require recipients to handle bogus <x:ref>Content-Length</x:ref> header
4788  fields as errors.
4789  (<xref target="message.body"/>)
4790</t>
4791<t>
4792  Remove reference to non-existent identity transfer-coding value tokens.
4793  (Sections <xref format="counter" target="message.body"/> and
4794  <xref format="counter" target="transfer.codings"/>)
4795</t>
4796<t>
4797  Clarification that the chunk length does not include the count of the octets
4798  in the chunk header and trailer. Furthermore disallowed line folding
4799  in chunk extensions, and deprecate their use.
4800  (<xref target="chunked.encoding"/>)
4801</t>
4802<t>
4803  Registration of Transfer Codings now requires IETF Review
4804  (<xref target="transfer.coding.registry"/>)
4805</t>
4806<t>
4807  Remove hard limit of two connections per server.
4808  Remove requirement to retry a sequence of requests as long it was idempotent.
4809  Remove requirements about when servers are allowed to close connections
4810  prematurely.
4811  (<xref target="persistent.connections"/>)
4812</t>
4813<t>
4814  Remove requirement to retry requests under certain circumstances when the
4815  server prematurely closes the connection.
4816  (<xref target="persistent.reuse"/>)
4817</t>
4818<t>
4819  Change ABNF productions for header fields to only define the field value.
4820</t>
4821<t>
4822  Clarify exactly when "close" connection options have to be sent; drop
4823  notion of header fields being "hop-by-hop" without being listed in the
4824  Connection header field.
4825  (<xref target="header.connection"/>)
4826</t>
4827<t>
4828  Define the semantics of the <x:ref>Upgrade</x:ref> header field in responses
4829  other than 101 (this was incorporated from <xref target="RFC2817"/>).
4830  (<xref target="header.upgrade"/>)
4831</t>
4832<t>
4833  Take over the Upgrade Token Registry, previously defined in
4834  <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
4835  (<xref target="upgrade.token.registry"/>)
4836</t>
4837</section>
4838</section>
4839
4840<section title="ABNF list extension: #rule" anchor="abnf.extension">
4841<t>
4842  A #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
4843  improve readability in the definitions of some header field values.
4844</t>
4845<t>
4846  A construct "#" is defined, similar to "*", for defining comma-delimited
4847  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
4848  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
4849  comma (",") and optional whitespace (OWS).   
4850</t>
4851<figure><preamble>
4852  Thus,
4853</preamble><artwork type="example">
4854  1#element =&gt; element *( OWS "," OWS element )
4855</artwork></figure>
4856<figure><preamble>
4857  and:
4858</preamble><artwork type="example">
4859  #element =&gt; [ 1#element ]
4860</artwork></figure>
4861<figure><preamble>
4862  and for n &gt;= 1 and m &gt; 1:
4863</preamble><artwork type="example">
4864  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
4865</artwork></figure>
4866<t>
4867  For compatibility with legacy list rules, recipients &SHOULD; accept empty
4868  list elements. In other words, consumers would follow the list productions:
4869</t>
4870<figure><artwork type="example">
4871  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
4872 
4873  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
4874</artwork></figure>
4875<t>
4876  Note that empty elements do not contribute to the count of elements present,
4877  though.
4878</t>
4879<t>
4880  For example, given these ABNF productions:
4881</t>
4882<figure><artwork type="example">
4883  example-list      = 1#example-list-elmt
4884  example-list-elmt = token ; see <xref target="field.components"/> 
4885</artwork></figure>
4886<t>
4887  Then these are valid values for example-list (not including the double
4888  quotes, which are present for delimitation only):
4889</t>
4890<figure><artwork type="example">
4891  "foo,bar"
4892  "foo ,bar,"
4893  "foo , ,bar,charlie   "
4894</artwork></figure>
4895<t>
4896  But these values would be invalid, as at least one non-empty element is
4897  required:
4898</t>
4899<figure><artwork type="example">
4900  ""
4901  ","
4902  ",   ,"
4903</artwork></figure>
4904<t>
4905  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
4906  expanded as explained above.
4907</t>
4908</section>
4909
4910<?BEGININC p1-messaging.abnf-appendix ?>
4911<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4912<figure>
4913<artwork type="abnf" name="p1-messaging.parsed-abnf">
4914<x:ref>BWS</x:ref> = OWS
4915
4916<x:ref>Connection</x:ref> = *( "," OWS ) connection-option *( OWS "," [ OWS
4917 connection-option ] )
4918<x:ref>Content-Length</x:ref> = 1*DIGIT
4919
4920<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
4921 ]
4922<x:ref>HTTP-name</x:ref> = %x48.54.54.50 ; HTTP
4923<x:ref>HTTP-version</x:ref> = HTTP-name "/" DIGIT "." DIGIT
4924<x:ref>Host</x:ref> = uri-host [ ":" port ]
4925
4926<x:ref>OWS</x:ref> = *( SP / HTAB )
4927
4928<x:ref>RWS</x:ref> = 1*( SP / HTAB )
4929
4930<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4931<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4932<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4933 transfer-coding ] )
4934
4935<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4936<x:ref>Upgrade</x:ref> = *( "," OWS ) protocol *( OWS "," [ OWS protocol ] )
4937
4938<x:ref>Via</x:ref> = *( "," OWS ) ( received-protocol RWS received-by [ RWS comment
4939 ] ) *( OWS "," [ OWS ( received-protocol RWS received-by [ RWS
4940 comment ] ) ] )
4941
4942<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4943<x:ref>absolute-form</x:ref> = absolute-URI
4944<x:ref>asterisk-form</x:ref> = "*"
4945<x:ref>attribute</x:ref> = token
4946<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4947<x:ref>authority-form</x:ref> = authority
4948
4949<x:ref>chunk</x:ref> = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
4950<x:ref>chunk-data</x:ref> = 1*OCTET
4951<x:ref>chunk-ext</x:ref> = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
4952<x:ref>chunk-ext-name</x:ref> = token
4953<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
4954<x:ref>chunk-size</x:ref> = 1*HEXDIG
4955<x:ref>chunked-body</x:ref> = *chunk last-chunk trailer-part CRLF
4956<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
4957<x:ref>connection-option</x:ref> = token
4958<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4959 / %x2A-5B ; '*'-'['
4960 / %x5D-7E ; ']'-'~'
4961 / obs-text
4962
4963<x:ref>field-content</x:ref> = *( HTAB / SP / VCHAR / obs-text )
4964<x:ref>field-name</x:ref> = token
4965<x:ref>field-value</x:ref> = *( field-content / obs-fold )
4966
4967<x:ref>header-field</x:ref> = field-name ":" OWS field-value BWS
4968<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4969<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
4970
4971<x:ref>last-chunk</x:ref> = 1*"0" [ chunk-ext ] CRLF
4972
4973<x:ref>message-body</x:ref> = *OCTET
4974<x:ref>method</x:ref> = token
4975
4976<x:ref>obs-fold</x:ref> = CRLF ( SP / HTAB )
4977<x:ref>obs-text</x:ref> = %x80-FF
4978<x:ref>origin-form</x:ref> = path-absolute [ "?" query ]
4979
4980<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4981<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4982<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4983<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4984<x:ref>protocol</x:ref> = protocol-name [ "/" protocol-version ]
4985<x:ref>protocol-name</x:ref> = token
4986<x:ref>protocol-version</x:ref> = token
4987<x:ref>pseudonym</x:ref> = token
4988
4989<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
4990 / %x5D-7E ; ']'-'~'
4991 / obs-text
4992<x:ref>qdtext-nf</x:ref> = HTAB / SP / "!" / %x23-5B ; '#'-'['
4993 / %x5D-7E ; ']'-'~'
4994 / obs-text
4995<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
4996<x:ref>quoted-cpair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
4997<x:ref>quoted-pair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
4998<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
4999<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5000
5001<x:ref>rank</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5002<x:ref>reason-phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5003<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5004<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5005<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5006<x:ref>request-line</x:ref> = method SP request-target SP HTTP-version CRLF
5007<x:ref>request-target</x:ref> = origin-form / absolute-form / authority-form /
5008 asterisk-form
5009
5010<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5011 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5012<x:ref>start-line</x:ref> = request-line / status-line
5013<x:ref>status-code</x:ref> = 3DIGIT
5014<x:ref>status-line</x:ref> = HTTP-version SP status-code SP reason-phrase CRLF
5015
5016<x:ref>t-codings</x:ref> = "trailers" / ( transfer-coding [ t-ranking ] )
5017<x:ref>t-ranking</x:ref> = OWS ";" OWS "q=" rank
5018<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5019 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5020<x:ref>token</x:ref> = 1*tchar
5021<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5022<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5023 transfer-extension
5024<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5025<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5026
5027<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5028
5029<x:ref>value</x:ref> = word
5030
5031<x:ref>word</x:ref> = token / quoted-string
5032</artwork>
5033</figure>
5034</section>
5035<?ENDINC p1-messaging.abnf-appendix ?>
5036
5037<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5038
5039<section title="Since RFC 2616">
5040<t>
5041  Extracted relevant partitions from <xref target="RFC2616"/>.
5042</t>
5043</section>
5044
5045<section title="Since draft-ietf-httpbis-p1-messaging-00">
5046<t>
5047  Closed issues:
5048  <list style="symbols"> 
5049    <t>
5050      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5051      "HTTP Version should be case sensitive"
5052      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5053    </t>
5054    <t>
5055      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5056      "'unsafe' characters"
5057      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5058    </t>
5059    <t>
5060      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5061      "Chunk Size Definition"
5062      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5063    </t>
5064    <t>
5065      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5066      "Message Length"
5067      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5068    </t>
5069    <t>
5070      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5071      "Media Type Registrations"
5072      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5073    </t>
5074    <t>
5075      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5076      "URI includes query"
5077      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5078    </t>
5079    <t>
5080      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5081      "No close on 1xx responses"
5082      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5083    </t>
5084    <t>
5085      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5086      "Remove 'identity' token references"
5087      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5088    </t>
5089    <t>
5090      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5091      "Import query BNF"
5092    </t>
5093    <t>
5094      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5095      "qdtext BNF"
5096    </t>
5097    <t>
5098      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5099      "Normative and Informative references"
5100    </t>
5101    <t>
5102      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5103      "RFC2606 Compliance"
5104    </t>
5105    <t>
5106      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5107      "RFC977 reference"
5108    </t>
5109    <t>
5110      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5111      "RFC1700 references"
5112    </t>
5113    <t>
5114      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5115      "inconsistency in date format explanation"
5116    </t>
5117    <t>
5118      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5119      "Date reference typo"
5120    </t>
5121    <t>
5122      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5123      "Informative references"
5124    </t>
5125    <t>
5126      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5127      "ISO-8859-1 Reference"
5128    </t>
5129    <t>
5130      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5131      "Normative up-to-date references"
5132    </t>
5133  </list>
5134</t>
5135<t>
5136  Other changes:
5137  <list style="symbols"> 
5138    <t>
5139      Update media type registrations to use RFC4288 template.
5140    </t>
5141    <t>
5142      Use names of RFC4234 core rules DQUOTE and HTAB,
5143      fix broken ABNF for chunk-data
5144      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5145    </t>
5146  </list>
5147</t>
5148</section>
5149
5150<section title="Since draft-ietf-httpbis-p1-messaging-01">
5151<t>
5152  Closed issues:
5153  <list style="symbols"> 
5154    <t>
5155      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5156      "Bodies on GET (and other) requests"
5157    </t>
5158    <t>
5159      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5160      "Updating to RFC4288"
5161    </t>
5162    <t>
5163      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5164      "Status Code and Reason Phrase"
5165    </t>
5166    <t>
5167      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5168      "rel_path not used"
5169    </t>
5170  </list>
5171</t>
5172<t>
5173  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5174  <list style="symbols"> 
5175    <t>
5176      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5177      "trailer-part").
5178    </t>
5179    <t>
5180      Avoid underscore character in rule names ("http_URL" ->
5181      "http-URL", "abs_path" -> "path-absolute").
5182    </t>
5183    <t>
5184      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5185      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5186      have to be updated when switching over to RFC3986.
5187    </t>
5188    <t>
5189      Synchronize core rules with RFC5234.
5190    </t>
5191    <t>
5192      Get rid of prose rules that span multiple lines.
5193    </t>
5194    <t>
5195      Get rid of unused rules LOALPHA and UPALPHA.
5196    </t>
5197    <t>
5198      Move "Product Tokens" section (back) into Part 1, as "token" is used
5199      in the definition of the Upgrade header field.
5200    </t>
5201    <t>
5202      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5203    </t>
5204    <t>
5205      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5206    </t>
5207  </list>
5208</t>
5209</section>
5210
5211<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5212<t>
5213  Closed issues:
5214  <list style="symbols"> 
5215    <t>
5216      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5217      "HTTP-date vs. rfc1123-date"
5218    </t>
5219    <t>
5220      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5221      "WS in quoted-pair"
5222    </t>
5223  </list>
5224</t>
5225<t>
5226  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5227  <list style="symbols"> 
5228    <t>
5229      Reference RFC 3984, and update header field registrations for header
5230      fields defined in this document.
5231    </t>
5232  </list>
5233</t>
5234<t>
5235  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5236  <list style="symbols"> 
5237    <t>
5238      Replace string literals when the string really is case-sensitive (HTTP-version).
5239    </t>
5240  </list>
5241</t>
5242</section>
5243
5244<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5245<t>
5246  Closed issues:
5247  <list style="symbols"> 
5248    <t>
5249      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5250      "Connection closing"
5251    </t>
5252    <t>
5253      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5254      "Move registrations and registry information to IANA Considerations"
5255    </t>
5256    <t>
5257      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5258      "need new URL for PAD1995 reference"
5259    </t>
5260    <t>
5261      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5262      "IANA Considerations: update HTTP URI scheme registration"
5263    </t>
5264    <t>
5265      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5266      "Cite HTTPS URI scheme definition"
5267    </t>
5268    <t>
5269      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5270      "List-type header fields vs Set-Cookie"
5271    </t>
5272  </list>
5273</t>
5274<t>
5275  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5276  <list style="symbols"> 
5277    <t>
5278      Replace string literals when the string really is case-sensitive (HTTP-Date).
5279    </t>
5280    <t>
5281      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5282    </t>
5283  </list>
5284</t>
5285</section>
5286
5287<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5288<t>
5289  Closed issues:
5290  <list style="symbols"> 
5291    <t>
5292      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5293      "Out-of-date reference for URIs"
5294    </t>
5295    <t>
5296      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5297      "RFC 2822 is updated by RFC 5322"
5298    </t>
5299  </list>
5300</t>
5301<t>
5302  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5303  <list style="symbols"> 
5304    <t>
5305      Use "/" instead of "|" for alternatives.
5306    </t>
5307    <t>
5308      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5309    </t>
5310    <t>
5311      Only reference RFC 5234's core rules.
5312    </t>
5313    <t>
5314      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5315      whitespace ("OWS") and required whitespace ("RWS").
5316    </t>
5317    <t>
5318      Rewrite ABNFs to spell out whitespace rules, factor out
5319      header field value format definitions.
5320    </t>
5321  </list>
5322</t>
5323</section>
5324
5325<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5326<t>
5327  Closed issues:
5328  <list style="symbols"> 
5329    <t>
5330      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5331      "Header LWS"
5332    </t>
5333    <t>
5334      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5335      "Sort 1.3 Terminology"
5336    </t>
5337    <t>
5338      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5339      "RFC2047 encoded words"
5340    </t>
5341    <t>
5342      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5343      "Character Encodings in TEXT"
5344    </t>
5345    <t>
5346      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5347      "Line Folding"
5348    </t>
5349    <t>
5350      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5351      "OPTIONS * and proxies"
5352    </t>
5353    <t>
5354      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5355      "reason-phrase BNF"
5356    </t>
5357    <t>
5358      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5359      "Use of TEXT"
5360    </t>
5361    <t>
5362      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5363      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5364    </t>
5365    <t>
5366      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5367      "RFC822 reference left in discussion of date formats"
5368    </t>
5369  </list>
5370</t>
5371<t>
5372  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5373  <list style="symbols"> 
5374    <t>
5375      Rewrite definition of list rules, deprecate empty list elements.
5376    </t>
5377    <t>
5378      Add appendix containing collected and expanded ABNF.
5379    </t>
5380  </list>
5381</t>
5382<t>
5383  Other changes:
5384  <list style="symbols"> 
5385    <t>
5386      Rewrite introduction; add mostly new Architecture Section.
5387    </t>
5388    <t>
5389      Move definition of quality values from Part 3 into Part 1;
5390      make TE request header field grammar independent of accept-params (defined in Part 3).
5391    </t>
5392  </list>
5393</t>
5394</section>
5395
5396<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5397<t>
5398  Closed issues:
5399  <list style="symbols"> 
5400    <t>
5401      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5402      "base for numeric protocol elements"
5403    </t>
5404    <t>
5405      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5406      "comment ABNF"
5407    </t>
5408  </list>
5409</t>
5410<t>
5411  Partly resolved issues:
5412  <list style="symbols"> 
5413    <t>
5414      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5415      "205 Bodies" (took out language that implied that there might be
5416      methods for which a request body MUST NOT be included)
5417    </t>
5418    <t>
5419      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5420      "editorial improvements around HTTP-date"
5421    </t>
5422  </list>
5423</t>
5424</section>
5425
5426<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5427<t>
5428  Closed issues:
5429  <list style="symbols"> 
5430    <t>
5431      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5432      "Repeating single-value header fields"
5433    </t>
5434    <t>
5435      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5436      "increase connection limit"
5437    </t>
5438    <t>
5439      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5440      "IP addresses in URLs"
5441    </t>
5442    <t>
5443      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5444      "take over HTTP Upgrade Token Registry"
5445    </t>
5446    <t>
5447      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5448      "CR and LF in chunk extension values"
5449    </t>
5450    <t>
5451      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5452      "HTTP/0.9 support"
5453    </t>
5454    <t>
5455      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5456      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5457    </t>
5458    <t>
5459      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5460      "move definitions of gzip/deflate/compress to part 1"
5461    </t>
5462    <t>
5463      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5464      "disallow control characters in quoted-pair"
5465    </t>
5466  </list>
5467</t>
5468<t>
5469  Partly resolved issues:
5470  <list style="symbols"> 
5471    <t>
5472      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5473      "update IANA requirements wrt Transfer-Coding values" (add the
5474      IANA Considerations subsection)
5475    </t>
5476  </list>
5477</t>
5478</section>
5479
5480<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5481<t>
5482  Closed issues:
5483  <list style="symbols"> 
5484    <t>
5485      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5486      "header parsing, treatment of leading and trailing OWS"
5487    </t>
5488  </list>
5489</t>
5490<t>
5491  Partly resolved issues:
5492  <list style="symbols"> 
5493    <t>
5494      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5495      "Placement of 13.5.1 and 13.5.2"
5496    </t>
5497    <t>
5498      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5499      "use of term "word" when talking about header field structure"
5500    </t>
5501  </list>
5502</t>
5503</section>
5504
5505<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5506<t>
5507  Closed issues:
5508  <list style="symbols"> 
5509    <t>
5510      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5511      "Clarification of the term 'deflate'"
5512    </t>
5513    <t>
5514      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5515      "OPTIONS * and proxies"
5516    </t>
5517    <t>
5518      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5519      "MIME-Version not listed in P1, general header fields"
5520    </t>
5521    <t>
5522      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5523      "IANA registry for content/transfer encodings"
5524    </t>
5525    <t>
5526      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5527      "Case-sensitivity of HTTP-date"
5528    </t>
5529    <t>
5530      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5531      "use of term "word" when talking about header field structure"
5532    </t>
5533  </list>
5534</t>
5535<t>
5536  Partly resolved issues:
5537  <list style="symbols"> 
5538    <t>
5539      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5540      "Term for the requested resource's URI"
5541    </t>
5542  </list>
5543</t>
5544</section>
5545
5546<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5547<t>
5548  Closed issues:
5549  <list style="symbols">
5550    <t>
5551      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5552      "Connection Closing"
5553    </t>
5554    <t>
5555      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5556      "Delimiting messages with multipart/byteranges"
5557    </t>
5558    <t>
5559      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5560      "Handling multiple Content-Length header fields"
5561    </t>
5562    <t>
5563      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
5564      "Clarify entity / representation / variant terminology"
5565    </t>
5566    <t>
5567      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5568      "consider removing the 'changes from 2068' sections"
5569    </t>
5570  </list>
5571</t>
5572<t>
5573  Partly resolved issues:
5574  <list style="symbols"> 
5575    <t>
5576      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5577      "HTTP(s) URI scheme definitions"
5578    </t>
5579  </list>
5580</t>
5581</section>
5582
5583<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5584<t>
5585  Closed issues:
5586  <list style="symbols">
5587    <t>
5588      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
5589      "Trailer requirements"
5590    </t>
5591    <t>
5592      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
5593      "Text about clock requirement for caches belongs in p6"
5594    </t>
5595    <t>
5596      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
5597      "effective request URI: handling of missing host in HTTP/1.0"
5598    </t>
5599    <t>
5600      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
5601      "confusing Date requirements for clients"
5602    </t>
5603  </list>
5604</t>
5605<t>
5606  Partly resolved issues:
5607  <list style="symbols"> 
5608    <t>
5609      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5610      "Handling multiple Content-Length header fields"
5611    </t>
5612  </list>
5613</t>
5614</section>
5615
5616<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5617<t>
5618  Closed issues:
5619  <list style="symbols">
5620    <t>
5621      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/75"/>:
5622      "RFC2145 Normative"
5623    </t>
5624    <t>
5625      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5626      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5627    </t>
5628    <t>
5629      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/210"/>:
5630      "define 'transparent' proxy"
5631    </t>
5632    <t>
5633      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
5634      "Header Field Classification"
5635    </t>
5636    <t>
5637      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/233"/>:
5638      "Is * usable as a request-uri for new methods?"
5639    </t>
5640    <t>
5641      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
5642      "Migrate Upgrade details from RFC2817"
5643    </t>
5644    <t>
5645      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5646      "untangle ABNFs for header fields"
5647    </t>
5648    <t>
5649      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/279"/>:
5650      "update RFC 2109 reference"
5651    </t>
5652  </list>
5653</t>
5654</section>
5655
5656<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5657<t>
5658  Closed issues:
5659  <list style="symbols">
5660    <t>
5661      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/53"/>:
5662      "Allow is not in 13.5.2"
5663    </t>
5664    <t>
5665      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5666      "Handling multiple Content-Length header fields"
5667    </t>
5668    <t>
5669      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5670      "untangle ABNFs for header fields"
5671    </t>
5672    <t>
5673      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/286"/>:
5674      "Content-Length ABNF broken"
5675    </t>
5676  </list>
5677</t>
5678</section>
5679
5680<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5681<t>
5682  Closed issues:
5683  <list style="symbols">
5684    <t>
5685      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/273"/>:
5686      "HTTP-version should be redefined as fixed length pair of DIGIT . DIGIT"
5687    </t>
5688    <t>
5689      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/282"/>:
5690      "Recommend minimum sizes for protocol elements"
5691    </t>
5692    <t>
5693      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/283"/>:
5694      "Set expectations around buffering"
5695    </t>
5696    <t>
5697      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/288"/>:
5698      "Considering messages in isolation"
5699    </t>
5700  </list>
5701</t>
5702</section>
5703
5704<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5705<t>
5706  Closed issues:
5707  <list style="symbols">
5708    <t>
5709      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/100"/>:
5710      "DNS Spoofing / DNS Binding advice"
5711    </t>
5712    <t>
5713      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/254"/>:
5714      "move RFCs 2145, 2616, 2817 to Historic status"
5715    </t>
5716    <t>
5717      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/270"/>:
5718      "\-escaping in quoted strings"
5719    </t>
5720    <t>
5721      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/305"/>:
5722      "'Close' should be reserved in the HTTP header field registry"
5723    </t>
5724  </list>
5725</t>
5726</section>
5727
5728<section title="Since draft-ietf-httpbis-p1-messaging-16" anchor="changes.since.16">
5729<t>
5730  Closed issues:
5731  <list style="symbols">
5732    <t>
5733      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
5734      "Document HTTP's error-handling philosophy"
5735    </t>
5736    <t>
5737      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/215"/>:
5738      "Explain header field registration"
5739    </t>
5740    <t>
5741      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/219"/>:
5742      "Revise Acknowledgements Sections"
5743    </t>
5744    <t>
5745      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/297"/>:
5746      "Retrying Requests"
5747    </t>
5748    <t>
5749      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/318"/>:
5750      "Closing the connection on server error"
5751    </t>
5752  </list>
5753</t>
5754</section>
5755
5756<section title="Since draft-ietf-httpbis-p1-messaging-17" anchor="changes.since.17">
5757<t>
5758  Closed issues:
5759  <list style="symbols">
5760    <t>
5761      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/158"/>:
5762      "Proxy-Connection and Keep-Alive"
5763    </t>
5764    <t>
5765      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/166"/>:
5766      "Clarify 'User Agent'"
5767    </t>
5768    <t>
5769      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/300"/>:
5770      "Define non-final responses"
5771    </t>
5772    <t>
5773      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/323"/>:
5774      "intended maturity level vs normative references"
5775    </t>
5776    <t>
5777      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/324"/>:
5778      "Intermediary rewriting of queries"
5779    </t>
5780  </list>
5781</t>
5782</section>
5783
5784<section title="Since draft-ietf-httpbis-p1-messaging-18" anchor="changes.since.18">
5785<t>
5786  Closed issues:
5787  <list style="symbols">
5788    <t>
5789      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/250"/>:
5790      "message-body in CONNECT response"
5791    </t>
5792    <t>
5793      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/302"/>:
5794      "Misplaced text on connection handling in p2"
5795    </t>
5796    <t>
5797      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/335"/>:
5798      "wording of line folding rule"
5799    </t>
5800    <t>
5801      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/343"/>:
5802      "chunk-extensions"
5803    </t>
5804    <t>
5805      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/346"/>:
5806      "make IANA policy definitions consistent"
5807    </t>
5808  </list>
5809</t>
5810</section>
5811
5812<section title="Since draft-ietf-httpbis-p1-messaging-19" anchor="changes.since.19">
5813<t>
5814  Closed issues:
5815  <list style="symbols">
5816    <t>
5817      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/346"/>:
5818      "make IANA policy definitions consistent"
5819    </t>
5820    <t>
5821      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/359"/>:
5822      "clarify connection header field values are case-insensitive"
5823    </t>
5824    <t>
5825      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/361"/>:
5826      "ABNF requirements for recipients"
5827    </t>
5828    <t>
5829      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/368"/>:
5830      "note introduction of new IANA registries as normative changes"
5831    </t>
5832    <t>
5833      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/374"/>:
5834      "Reference to ISO-8859-1 is informative"
5835    </t>
5836  </list>
5837</t>
5838</section>
5839
5840<section title="Since draft-ietf-httpbis-p1-messaging-20" anchor="changes.since.20">
5841<t>
5842  <list style="symbols">
5843    <t>
5844      Drop notion of header fields being "hop-by-hop" without being listed in
5845      the Connection header field.     
5846    </t>
5847    <t>
5848      Section about connection management rewritten; dropping some historic
5849      information.
5850    </t>
5851    <t>
5852      Move description of "100-continue" into Part 2.
5853    </t>
5854  </list>
5855</t>
5856</section>
5857
5858</section>
5859
5860</back>
5861</rfc>
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