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<h1>The WebSocket API</h1>

<h2 class="no-num no-toc" id="cr-20-sep-2012">W3C Candidate Recommendation 20 September 2012</h2>

<h2 class="no-num no-toc" id="editor-s-draft-4-june-2014">Editor's Draft 4 June 2014</h2>

<dl>

<dl><dt>Latest Published Version:</dt>

<dt>This Version:</dt>

<dd><a href="http://www.w3.org/TR/2012/CR-websockets-20120920/">http://www.w3.org/TR/2012/CR-websockets-20120920/</a>

<dt>Latest Published Version:</dt>

<dd><a href="http://www.w3.org/TR/websockets/">http://www.w3.org/TR/websockets/</a></dd>

<dt>Latest Editor's Draft:</dt>

<dd><a class="latest-link" href="http://dev.w3.org/html5/websockets/">http://dev.w3.org/html5/websockets/</a></dd>

<dd><a href="http://dev.w3.org/html5/websockets/" class="latest-link">http://dev.w3.org/html5/websockets/</a></dd>

<dt>Previous Versions:</dt>

<dd><a href="http://www.w3.org/TR/2012/WD-websockets-20120809/">http://www.w3.org/TR/2012/WD-websockets-20120809/</a>

<dd><a href="http://www.w3.org/TR/2012/WD-websockets-20120524/">http://www.w3.org/TR/2012/WD-websockets-20120524/</a>

<dd><a href="http://www.w3.org/TR/2011/CR-websockets-20111208/">http://www.w3.org/TR/2011/CR-websockets-20111208/</a>

<dd><a href="http://www.w3.org/TR/2011/WD-websockets-20110929/">http://www.w3.org/TR/2011/WD-websockets-20110929/</a>

<dd><a href="http://www.w3.org/TR/2011/WD-websockets-20110419/">http://www.w3.org/TR/2011/WD-websockets-20110419/</a>

<dd><a href="http://www.w3.org/TR/2009/WD-websockets-20090423/">http://www.w3.org/TR/2009/WD-websockets-20090423/</a>

<dd><a href="http://www.w3.org/TR/2009/WD-websockets-20091029/">http://www.w3.org/TR/2009/WD-websockets-20091029/</a></dd>

<dt>Editor:</dt>

<dd><a href="mailto:ian@hixie.ch">Ian Hickson</a>, Google, Inc.</dd>

</dl><a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a>

Web Consortium">W3C</abbr></a>® (<a href="http://www.csail.mit.edu/"><abbr title="Massachusetts

Institute of Technology">MIT</abbr></a>, <a href="http://www.ercim.eu/"><abbr title="European Research

<a href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,

<a href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a>

and <a href="http://www.w3.org/Consortium/Legal/copyright-documents">document

use</a> rules apply.

The bulk of the text of this specification is also

available in the WHATWG <a href="http://www.whatwg.org/specs/web-apps/current-work/complete.html#network">Web Applications 1.0</a> specification, under a license that permits

reuse of the specification text.

</div>

<hr class="top"><h2 class="no-num no-toc" id="abstract">Abstract</h2>

This specification defines an API that enables Web pages to use

the WebSocket protocol (defined by the IETF) for two-way

communication with a remote host.

<h2 class="no-num no-toc" id="status-of-this-document">Status of This document</h2>

This section describes the status of this document at the

time of its publication. Other documents may supersede this

document. A list of current W3C publications and the

latest

most recently formally published

revision of this technical report can be found in the <a href="http://www.w3.org/TR/">W3C technical reports index</a> at

http://www.w3.org/TR/.

If you wish to make comments regarding this document in a manner

If you wish to make comments regarding this document, you can

that is tracked by the W3C, please submit them via using <a href="https://www.w3.org/Bugs/Public/describecomponents.cgi?product=WebAppsWG">our

public bug database</a>. If you do not have an account then you can

enter feedback using this form:

<fieldset><legend>Feedback Comments</legend>

<input name="id" type="hidden" value="top"><input name="component" type="hidden" value="WebSocket API (editor: Ian Hickson)"><input name="response" type="hidden" value="html"><label for="feedbackBox">Please enter your feedback, carefully

<input value="top" name="id" type="hidden"><input value="WebSocket API (editor: Ian Hickson)" name="component" type="hidden"><input value="html" name="response" type="hidden"><label for="feedbackBox">Please enter your feedback, carefully

indicating the title of the section for which you are submitting

feedback, quoting the text that's wrong today if appropriate. If

you're suggesting a new feature, it's really important to say

what the problem you're trying to solve is. That's more

important than the solution, in fact.</label>

Please don't use section numbers as these tend to

change rapidly and make your feedback harder to understand.

function checkFeedbackForm(form) {

if (form.elements.text.value.match(/^ *</)) {

alert('Please don\'t start your feedback with an angle bracket, instead explain what topic your feedback is about first.');

return true;

} else if (form.elements.text.value.match(/ [^ ]+ [^ ]+ [^ ]+ [^ ]+ /)) {

if (form.elements.text.value.match(/^Please enter your feedback, carefully/)) {

alert('Please enter your feedback, explaining what is wrong, and without repeating the instructions. Thanks!');

return true;

} else if (form.elements.text.value.match(/ [^ ]+ [^ ]+ [^ ]+ [^ ]+ /)) {

form.action = "http://www.whatwg.org/specs/web-apps/current-work/file-bug.cgi";

return true;

} else {

alert('Please include significantly more detail about exactly what problem you are trying to solve.');

return false;

}

</script>

<input onclick="return checkFeedbackForm(form)" type="submit" value="Submit feedback">(Note: Your IP address and user agent will be publicly recorded for spam prevention purposes.)

<input value="Submit feedback" onclick="return checkFeedbackForm(form)" type="submit">(Note: Your IP address and user agent will be publicly recorded for spam prevention purposes.)

</fieldset></form>

You can also e-mail feedback to <a href="mailto:public-webapps@w3.org">public-webapps@w3.org</a> (<a href="mailto:public-webapps-request@w3.org?subject=subscribe">subscribe</a>,

<a href="http://lists.w3.org/Archives/Public/public-webapps/">archives</a>),

or <a href="mailto:whatwg@whatwg.org">whatwg@whatwg.org</a> (<a href="http://lists.whatwg.org/listinfo.cgi/whatwg-whatwg.org">subscribe</a>,

<a href="http://lists.whatwg.org/pipermail/whatwg-whatwg.org/">archives</a>).

All feedback is welcome.

Implementors should be aware that this specification is not

stable. Implementors who are not taking part in the

discussions are likely to find the specification changing out from

under them in incompatible ways. Vendors interested in

implementing this specification before it eventually reaches the

Candidate Recommendation stage should join the aforementioned

mailing lists and take part in the discussions.

</div>

The latest

stable version of the editor's draft of this specification is always

available on <a href="http://dev.w3.org/html5/websockets/">the W3C CVS server</a>

and in the <a href="http://svn.whatwg.org/webapps/">WHATWG

Subversion repository</a>. The <a href="http://www.whatwg.org/specs/web-apps/current-work/complete.html">latest

editor's working copy</a> (which may contain unfinished text in the

process of being prepared) contains the latest draft text of this

specification (amongst others). For more details, please see the <a href="http://wiki.whatwg.org/wiki/FAQ#What_are_the_various_versions_of_the_spec.3F">WHATWG

FAQ</a>.

Notifications of changes to this specification are sent along

with notifications of changes to related specifications using the

following mechanisms:

<dl><dt>E-mail notifications of changes</dt>

<dd>Commit-Watchers mailing list (complete source diffs): <a href="http://lists.whatwg.org/listinfo.cgi/commit-watchers-whatwg.org">http://lists.whatwg.org/listinfo.cgi/commit-watchers-whatwg.org</a></dd>

<dt>Browsable version-control record of all changes:</dt>

<dd>CVSWeb interface with side-by-side diffs: <a href="http://dev.w3.org/cvsweb/html5/">http://dev.w3.org/cvsweb/html5/</a></dd>

<dd>Annotated summary with unified diffs: <a href="http://html5.org/tools/web-apps-tracker">http://html5.org/tools/web-apps-tracker</a></dd>

<dd>Raw Subversion interface: <code>svn checkout http://svn.whatwg.org/webapps/</code></dd>

</dl>

</dl>The W3C <a href="http://www.w3.org/2008/webapps/">Web Applications

The W3C <a href="http://www.w3.org/2008/webapps/">Web Applications

Working Group</a> is the W3C working group responsible for this

specification's progress along the W3C Recommendation track.

This specification is the 20 September 2012 Candidate Recommendation.

This specification is the 4 June 2014 Editor's Draft.

Comments and bugs submitted against the

<a href="http://www.w3.org/TR/2012/WD-websockets-20120809/">09 August 2012 Last Call Working Draft</a>

are tracked in a

<a href="http://www.w3.org/2008/webapps/wiki/Websockets-Comments-LC-09Aug2012">comment tracking document</a>.

Publication as a Candidate Recommendation does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

This specification is being developed in conjunction with an

RFC for a wire protocol, the WebSocket Protocol,

available from the following location:

<ul><li>RFC 6455: The WebSocket Protocol: <a href="http://tools.ietf.org/html/rfc6455">http://tools.ietf.org/html/rfc6455</a></li>

</ul>

</ul>This document was produced by a group operating under the <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/">5

February 2004 W3C Patent Policy</a>. W3C maintains a <a rel="disclosure" href="http://www.w3.org/2004/01/pp-impl/42538/status">public list of

any patent disclosures</a> made in connection with the deliverables

of the group; that page also includes instructions for disclosing a

patent. An individual who has actual knowledge of a patent which the

individual believes contains <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">Essential

Claim(s)</a> must disclose the information in accordance with <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">section

6 of the W3C Patent Policy</a>.

This document was produced by a group operating under the <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/">5

February 2004 W3C Patent Policy</a>. W3C maintains a <a href="http://www.w3.org/2004/01/pp-impl/42538/status" rel="disclosure">public list of

February 2004 W3C Patent Policy</a>. W3C maintains a <a rel="disclosure" href="http://www.w3.org/2004/01/pp-impl/42538/status">public list of

any patent disclosures</a> made in connection with the deliverables

of the group; that page also includes instructions for disclosing a

patent. An individual who has actual knowledge of a patent which the

individual believes contains <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">Essential

Claim(s)</a> must disclose the information in accordance with <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">section

6 of the W3C Patent Policy</a>.

<h3 class="no-num no-toc" id="crec">Candidate Recommendation Exit Criteria</h3>

To exit the Candidate Recommendation (CR) stage, the following criteria

must have been met:

<ol>

<li>There will be at least two interoperable implementations passing all

approved test cases in the

<a href="http://w3c-test.org/webapps/WebSockets/tests/">test suite</a>

for this specification. An implementation is to be available (i.e. for

download), shipping (i.e. not private), and not experimental (i.e. intended

for a wide audience). The working group will decide when the test suite is

of sufficient quality to test interoperability and will produce an

implementation report (hosted together with the test suite).

<li>A minimum of one month of the CR stage will have elapsed (i.e. not

until after 18 October 2012). This is to ensure that enough time is given

for any remaining major errors to be caught. The CR period will be extended

if implementations are slow to appear.

</ol>

<h2 class="no-num no-toc" id="contents">Table of Contents</h2>

<li><a href="#network-intro">1 Introduction</a></li>

<li><a href="#conformance-requirements">2 Conformance requirements</a>

<ol>

<li><a href="#dependencies">2.1 Dependencies</a></ol></li>

<li><a href="#terminology">3 Terminology</a></li>

<li><a href="#the-websocket-interface">4 The <code>WebSocket</code> interface</a></li>

<li><a href="#feedback-from-the-protocol">5 Feedback from the protocol</a></li>

<li><a href="#ping-and-pong-frames">6 Ping and Pong frames</a></li>

<li><a href="#parsing-websocket-urls">7 Parsing WebSocket URLs</a></li>

<li><a href="#event-definitions">8 Event definitions</a></li>

<li><a href="#the-closeevent-interfaces">8 The <code>CloseEvent</code> interfaces</a></li>

<li><a href="#garbage-collection">9 Garbage collection</a></li>

<li><a class="no-num" href="#references">References</a></li>

<li><a href="#references" class="no-num">References</a></li>

<li><a class="no-num" href="#acknowledgements">Acknowledgements</a></ol>

<li><a href="#acknowledgements" class="no-num">Acknowledgements</a></ol>

<hr><h2 id="network-intro">1 Introduction</h2>

This section is non-normative.

To enable Web applications to maintain bidirectional

To enable Web applications to maintain bidirectional communications with server-side processes,

communications with server-side processes, this specification

this specification introduces the <code><a href="#websocket">WebSocket</a></code> interface.

introduces the <code><a href="#websocket">WebSocket</a></code> interface.

This interface does not allow for raw access to the

This interface does not allow for raw access to the underlying network. For

underlying network. For example, this interface could not be used to

example, this interface could not be used to implement an IRC client without proxying messages

implement an IRC client without proxying messages through a custom

through a custom server.

server.

<h2 id="conformance-requirements">2 Conformance requirements</h2>

All diagrams, examples, and notes in this specification are

non-normative, as are all sections explicitly marked non-normative.

Everything else in this specification is normative.

The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and

"OPTIONAL" in the normative parts of this document are to be

interpreted as described in RFC2119. For readability, these words do

not appear in all uppercase letters in this specification. <a href="#refsRFC2119">[RFC2119]</a>

Requirements phrased in the imperative as part of algorithms

(such as "strip any leading space characters" or "return false and

abor

abort these steps") are to be interpreted with the meaning of the

key word ("must", "should", "may", etc) used in introducing the

algorithm.

Some conformance requirements are phrased as requirements on

attributes, methods or objects. Such requirements are to be

interpreted as requirements on user agents.

Conformance requirements phrased as algorithms or specific steps

may be implemented in any manner, so long as the end result is

equivalent. (In particular, the algorithms defined in this

specification are intended to be easy to follow, and not intended

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<h1>The WebSocket API</h1>
 
 <h2 class="no-num no-toc" id="cr-20-sep-2012">W3C Candidate Recommendation 20 September 2012</h2>
 <dl>
 <dt>This Version:</dt>
 <dd><a href="http://www.w3.org/TR/2012/CR-websockets-20120920/">http://www.w3.org/TR/2012/CR-websockets-20120920/</a>
 <dt>Latest Published Version:</dt>
 <dd><a href="http://www.w3.org/TR/websockets/">http://www.w3.org/TR/websockets/</a></dd>
 <dt>Latest Editor's Draft:</dt>
 <dd><a class="latest-link" href="http://dev.w3.org/html5/websockets/">http://dev.w3.org/html5/websockets/</a></dd>

<dt>Previous Versions:</dt>
 <dd><a href="http://www.w3.org/TR/2012/WD-websockets-20120809/">http://www.w3.org/TR/2012/WD-websockets-20120809/</a>
 <dd><a href="http://www.w3.org/TR/2012/WD-websockets-20120524/">http://www.w3.org/TR/2012/WD-websockets-20120524/</a>
 <dd><a href="http://www.w3.org/TR/2011/CR-websockets-20111208/">http://www.w3.org/TR/2011/CR-websockets-20111208/</a>
 <dd><a href="http://www.w3.org/TR/2011/WD-websockets-20110929/">http://www.w3.org/TR/2011/WD-websockets-20110929/</a>
 <dd><a href="http://www.w3.org/TR/2011/WD-websockets-20110419/">http://www.w3.org/TR/2011/WD-websockets-20110419/</a>
 <dd><a href="http://www.w3.org/TR/2009/WD-websockets-20090423/">http://www.w3.org/TR/2009/WD-websockets-20090423/</a>
 <dd><a href="http://www.w3.org/TR/2009/WD-websockets-20091029/">http://www.w3.org/TR/2009/WD-websockets-20091029/</a></dd>

 <dt>Editor:</dt>
 <dd><a href="mailto:ian@hixie.ch">Ian Hickson</a>, Google, Inc.</dd>
 </dl><a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a>
 &copy; 2012 <a href="http://www.w3.org/"><abbr title="World Wide
 Web Consortium">W3C</abbr></a>&reg; (<a href="http://www.csail.mit.edu/"><abbr title="Massachusetts
 Institute of Technology">MIT</abbr></a>, <a href="http://www.ercim.eu/"><abbr title="European Research
 Consortium for Informatics and Mathematics">ERCIM</abbr></a>, <a href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. W3C
 <a href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
 <a href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a>
 and <a href="http://www.w3.org/Consortium/Legal/copyright-documents">document
 use</a> rules apply.

The bulk of the text of this specification is also
 available in the WHATWG <a href="http://www.whatwg.org/specs/web-apps/current-work/complete.html#network">Web Applications 1.0</a> specification, under a license that permits
 reuse of the specification text.

</div>

<hr class="top"><h2 class="no-num no-toc" id="abstract">Abstract</h2>

This specification defines an API that enables Web pages to use
 the WebSocket protocol (defined by the IETF) for two-way
 communication with a remote host.

<h2 class="no-num no-toc" id="status-of-this-document">Status of This document</h2>

This section describes the status of this document at the
 time of its publication. Other documents may supersede this
 document. A list of current W3C publications and the

latest

revision of this technical report can be found in the <a href="http://www.w3.org/TR/">W3C technical reports index</a> at
 http://www.w3.org/TR/.

If you wish to make comments regarding this document in a manner
 that is tracked by the W3C, please submit them via using <a href="https://www.w3.org/Bugs/Public/describecomponents.cgi?product=WebAppsWG">our
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<form action="http://www.whatwg.org/specs/web-apps/current-work/file-spam.cgi" method="post">
 <fieldset><legend>Feedback Comments</legend>
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 indicating the title of the section for which you are submitting
 feedback, quoting the text that's wrong today if appropriate. If
 you're suggesting a new feature, it's really important to say
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 Please don't use section numbers as these tend to
 change rapidly and make your feedback harder to understand.
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 <a href="http://lists.whatwg.org/pipermail/whatwg-whatwg.org/">archives</a>).
 All feedback is welcome.

Notifications of changes to this specification are sent along
 with notifications of changes to related specifications using the
 following mechanisms:
 <dl><dt>E-mail notifications of changes</dt>
 <dd>Commit-Watchers mailing list (complete source diffs): <a href="http://lists.whatwg.org/listinfo.cgi/commit-watchers-whatwg.org">http://lists.whatwg.org/listinfo.cgi/commit-watchers-whatwg.org</a></dd>
 <dt>Browsable version-control record of all changes:</dt>
 <dd>CVSWeb interface with side-by-side diffs: <a href="http://dev.w3.org/cvsweb/html5/">http://dev.w3.org/cvsweb/html5/</a></dd>
 <dd>Annotated summary with unified diffs: <a href="http://html5.org/tools/web-apps-tracker">http://html5.org/tools/web-apps-tracker</a></dd>
 <dd>Raw Subversion interface: <code>svn checkout http://svn.whatwg.org/webapps/</code></dd>
 </dl>

The W3C <a href="http://www.w3.org/2008/webapps/">Web Applications
 Working Group</a> is the W3C working group responsible for this
 specification's progress along the W3C Recommendation track.
 This specification is the 20 September 2012 Candidate Recommendation.
 Comments and bugs submitted against the 
 <a href="http://www.w3.org/TR/2012/WD-websockets-20120809/">09 August 2012 Last Call Working Draft</a> 
 are tracked in a 
 <a href="http://www.w3.org/2008/webapps/wiki/Websockets-Comments-LC-09Aug2012">comment tracking document</a>.

This specification is being developed in conjunction with an
 RFC for a wire protocol, the WebSocket Protocol,
 available from the following location:

<ul><li>RFC 6455: The WebSocket Protocol: <a href="http://tools.ietf.org/html/rfc6455">http://tools.ietf.org/html/rfc6455</a></li>
 </ul>

This document was produced by a group operating under the <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/">5
 February 2004 W3C Patent Policy</a>. W3C maintains a <a href="http://www.w3.org/2004/01/pp-impl/42538/status" rel="disclosure">public list of
 any patent disclosures</a> made in connection with the deliverables
 of the group; that page also includes instructions for disclosing a
 patent. An individual who has actual knowledge of a patent which the
 individual believes contains <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">Essential
 Claim(s)</a> must disclose the information in accordance with <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">section
 6 of the W3C Patent Policy</a>.

<h3 class="no-num no-toc" id="crec">Candidate Recommendation Exit Criteria</h3>

To exit the Candidate Recommendation (CR) stage, the following criteria
must have been met:

<ol>
 <li>There will be at least two interoperable implementations passing all
 approved test cases in the
 <a href="http://w3c-test.org/webapps/WebSockets/tests/">test suite</a>
 for this specification. An implementation is to be available (i.e. for
 download), shipping (i.e. not private), and not experimental (i.e. intended
 for a wide audience). The working group will decide when the test suite is
 of sufficient quality to test interoperability and will produce an
 implementation report (hosted together with the test suite).

<li>A minimum of one month of the CR stage will have elapsed (i.e. not
 until after 18 October 2012). This is to ensure that enough time is given
 for any remaining major errors to be caught. The CR period will be extended
 if implementations are slow to appear.
</ol>

<h2 class="no-num no-toc" id="contents">Table of Contents</h2>

<ol class="toc">
 <li><a href="#network-intro">1 Introduction</a></li>
 <li><a href="#conformance-requirements">2 Conformance requirements</a>
 <ol>
 <li><a href="#dependencies">2.1 Dependencies</a></ol></li>
 <li><a href="#terminology">3 Terminology</a></li>
 <li><a href="#the-websocket-interface">4 The <code>WebSocket</code> interface</a></li>
 <li><a href="#feedback-from-the-protocol">5 Feedback from the protocol</a></li>
 <li><a href="#ping-and-pong-frames">6 Ping and Pong frames</a></li>
 <li><a href="#parsing-websocket-urls">7 Parsing WebSocket URLs</a></li>
 <li><a href="#event-definitions">8 Event definitions</a></li>
 <li><a href="#garbage-collection">9 Garbage collection</a></li>
 <li><a class="no-num" href="#references">References</a></li>
 <li><a class="no-num" href="#acknowledgements">Acknowledgements</a></ol>

<hr><h2 id="network-intro">1 Introduction</h2>

This section is non-normative.

To enable Web applications to maintain bidirectional
 communications with server-side processes, this specification
 introduces the <code><a href="#websocket">WebSocket</a></code> interface.

This interface does not allow for raw access to the
 underlying network. For example, this interface could not be used to
 implement an IRC client without proxying messages through a custom
 server.

<h2 id="conformance-requirements">2 Conformance requirements</h2>

All diagrams, examples, and notes in this specification are
 non-normative, as are all sections explicitly marked non-normative.
 Everything else in this specification is normative.

The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
 "OPTIONAL" in the normative parts of this document are to be
 interpreted as described in RFC2119. For readability, these words do
 not appear in all uppercase letters in this specification. <a href="#refsRFC2119">[RFC2119]</a>

Requirements phrased in the imperative as part of algorithms
 (such as "strip any leading space characters" or "return false and
 abort these steps") are to be interpreted with the meaning of the
 key word ("must", "should", "may", etc) used in introducing the
 algorithm.

Some conformance requirements are phrased as requirements on
 attributes, methods or objects. Such requirements are to be
 interpreted as requirements on user agents.

Conformance requirements phrased as algorithms or specific steps
 may be implemented in any manner, so long as the end result is
 equivalent. (In particular, the algorithms defined in this
 specification are intended to be easy to follow, and not intended to
 be performant.)

The only conformance class defined by this specification is user
 agents.

User agents may impose implementation-specific limits on
 otherwise unconstrained inputs, e.g. to prevent denial of service
 attacks, to guard against running out of memory, or to work around
 platform-specific limitations.

When support for a feature is disabled (e.g. as an emergency
 measure to mitigate a security problem, or to aid in development, or
 for performance reasons), user agents must act as if they had no
 support for the feature whatsoever, and as if the feature was not
 mentioned in this specification. For example, if a particular
 feature is accessed via an attribute in a Web IDL interface, the
 attribute itself would be omitted from the objects that implement
 that interface &mdash; leaving the attribute on the object but
 making it return null or throw an exception is insufficient.

<h3 id="dependencies">2.1 Dependencies</h3>

This specification relies on several other underlying
 specifications.

<dd>

Many fundamental concepts from HTML are used by this
 specification. <a href="#refsHTML">[HTML]</a>

</dd>

<dt>WebIDL</dt>

<dd>

The IDL blocks in this specification use the semantics of the
 WebIDL specification. <a href="#refsWEBIDL">[WEBIDL]</a>

</dd>

</dl><h2 id="terminology">3 Terminology</h2>

The construction "a <code title="">Foo</code> object", where
 <code title="">Foo</code> is actually an interface, is sometimes
 used instead of the more accurate "an object implementing the
 interface <code title="">Foo</code>".

The term DOM is used to refer to the API set made available to
 scripts in Web applications, and does not necessarily imply the
 existence of an actual <code>Document</code> object or of any other
 <code>Node</code> objects as defined in the DOM Core
 specifications. <a href="#refsDOMCORE">[DOMCORE]</a>

An IDL attribute is said to be getting when its value is
 being retrieved (e.g. by author script), and is said to be
 setting when a new value is assigned to it.

<h2 id="the-websocket-interface">4 The <code><a href="#websocket">WebSocket</a></code> interface</h2>

<pre class="idl">[<a href="#dom-websocket" title="dom-WebSocket">Constructor</a>(DOMString url, optional (DOMString or DOMString[]) protocols)]
interface <dfn id="websocket">WebSocket</dfn> : <a href="http://dev.w3.org/html5/spec/infrastructure.html#eventtarget">EventTarget</a> {
 readonly attribute DOMString <a href="#dom-websocket-url" title="dom-WebSocket-url">url</a>;

// ready state
 const unsigned short <a href="#dom-websocket-connecting" title="dom-WebSocket-CONNECTING">CONNECTING</a> = 0;
 const unsigned short <a href="#dom-websocket-open" title="dom-WebSocket-OPEN">OPEN</a> = 1;
 const unsigned short <a href="#dom-websocket-closing" title="dom-WebSocket-CLOSING">CLOSING</a> = 2;
 const unsigned short <a href="#dom-websocket-closed" title="dom-WebSocket-CLOSED">CLOSED</a> = 3;
 readonly attribute unsigned short <a href="#dom-websocket-readystate" title="dom-WebSocket-readyState">readyState</a>;
 readonly attribute unsigned long <a href="#dom-websocket-bufferedamount" title="dom-WebSocket-bufferedAmount">bufferedAmount</a>;

// networking
 attribute <a href="http://dev.w3.org/html5/spec/webappapis.html#eventhandler">EventHandler</a> <a href="#handler-websocket-onopen" title="handler-WebSocket-onopen">onopen</a>;
 attribute <a href="http://dev.w3.org/html5/spec/webappapis.html#eventhandler">EventHandler</a> <a href="#handler-websocket-onerror" title="handler-WebSocket-onerror">onerror</a>;
 attribute <a href="http://dev.w3.org/html5/spec/webappapis.html#eventhandler">EventHandler</a> <a href="#handler-websocket-onclose" title="handler-WebSocket-onclose">onclose</a>;
 readonly attribute DOMString <a href="#dom-websocket-extensions" title="dom-WebSocket-extensions">extensions</a>;
 readonly attribute DOMString <a href="#dom-websocket-protocol" title="dom-WebSocket-protocol">protocol</a>;
 void <a href="#dom-websocket-close" title="dom-WebSocket-close">close</a>([Clamp] optional unsigned short code, optional DOMString reason);

// messaging
 attribute <a href="http://dev.w3.org/html5/spec/webappapis.html#eventhandler">EventHandler</a> <a href="#handler-websocket-onmessage" title="handler-WebSocket-onmessage">onmessage</a>;
 attribute DOMString <a href="#dom-websocket-binarytype" title="dom-WebSocket-binaryType">binaryType</a>;
 void <a href="#dom-websocket-send" title="dom-WebSocket-send">send</a>(DOMString data);
 void <a href="#dom-websocket-send" title="dom-WebSocket-send">send</a>(<a href="http://dev.w3.org/html5/spec/infrastructure.html#blob">Blob</a> data);
 void <a href="#dom-websocket-send" title="dom-WebSocket-send">send</a>(ArrayBuffer data);
 void <a href="#dom-websocket-send" title="dom-WebSocket-send">send</a>(ArrayBufferView data);
};</pre>

The <dfn id="dom-websocket" title="dom-WebSocket"><code>WebSocket(<var title="">url</var>, <var title="">protocols</var>)</code></dfn>
 constructor takes one or two arguments. The first argument, <var title="">url</var>, specifies the <a href="http://dev.w3.org/html5/spec/urls.html#url">URL</a> to which to
 connect. The second, <var title="">protocols</var>, if present, is
 either a string or an array of strings. If it is a string, it is
 equivalent to an array consisting of just that string; if it is
 omitted, it is equivalent to the empty array. Each string in the
 array is a subprotocol name. The connection will only be established
 if the server reports that it has selected one of these
 subprotocols. The subprotocol names must all be strings that match
 the requirements for elements that comprise the value of <code title="http-sec-websocket-protocol">Sec-WebSocket-Protocol</code>
 header fields as defined by the WebSocket protocol specification. <a href="#refsWSP">[WSP]</a>

When the <code>WebSocket()</code> constructor is invoked, the UA
 must run these steps:

<ol><li><a href="#parse-a-websocket-url-s-components">Parse a WebSocket URL's components</a> from the <var title="">url</var> argument, to obtain <var title="">host</var>,
 <var title="">port</var>, <var title="">resource name</var>, and
 <var title="">secure</var>. If this fails, throw a
 <code>SyntaxError</code> exception and abort these steps. <a href="#refsWSP">[WSP]</a></li>

<li>If <var title="">secure</var> is false but the
 <a href="http://dev.w3.org/html5/spec/browsers.html#origin">origin</a> of the <a href="http://dev.w3.org/html5/spec/browsers.html#entry-script">entry script</a> has a scheme
 component that is itself a secure protocol, e.g. HTTPS, then throw
 a <code>SecurityError</code> exception.</li>

<li>

If <var title="">port</var> is a port to which the user agent
 is configured to block access, then throw a
 <code>SecurityError</code> exception. (User agents typically block
 access to well-known ports like SMTP.)

Access to ports 80 and 443 should not be blocked, including the
 unlikely cases when <var title="">secure</var> is false but <var title="">port</var> is 443 or <var title="">secure</var> is true
 but <var title="">port</var> is 80.

</li>

<li>

If <var title="">protocols</var> is absent, let <var title="">protocols</var> be an empty array.

Otherwise, if <var title="">protocols</var> is present and a
 string, let <var title="">protocols</var> instead be an array
 consisting of just that string.

</li>

<li>If any of the values in <var title="">protocols</var> occur
 more than once or otherwise fail to match the requirements for
 elements that comprise the value of <code title="http-sec-websocket-protocol">Sec-WebSocket-Protocol</code>
 header fields as defined by the WebSocket protocol specification,
 then throw a <code>SyntaxError</code> exception and abort these
 steps. <a href="#refsWSP">[WSP]</a></li>

<li>Let <var title="">origin</var> be the ASCII serialization of the
 <a href="http://dev.w3.org/html5/spec/browsers.html#origin">origin</a> of the <a href="http://dev.w3.org/html5/spec/browsers.html#entry-script">entry script</a>,
 <a href="http://dev.w3.org/html5/spec/infrastructure.html#converted-to-ascii-lowercase">converted to ASCII lowercase</a>.</li>

<li>Return a new <code><a href="#websocket">WebSocket</a></code> object, and continue
 these steps in the background (without blocking scripts).</li>

<li>

Establish a WebSocket connection given the set (<var title="">host</var>, <var title="">port</var>, <var title="">resource name</var>, <var title="">secure</var>), along
 with the <var title="">protocols</var> list, an empty list for the
 extensions, and <var title="">origin</var>. The headers to send
 appropriate cookies must be a <code title="http-Cookie">Cookie</code> header whose value is the
 cookie-string computed from the user's cookie store and the
 URL <var title="">url</var>; for these purposes this is
 not a "non-HTTP" API. <a href="#refsWSP">[WSP]</a> <a href="#refsCOOKIES">[COOKIES]</a>

When the user agent validates the server's response during the
 "establish a WebSocket connection" algorithm, if the status
 code received from the server is not 101 (e.g. it is a redirect),
 the user agent must fail the WebSocket connection.

Following HTTP procedures here could introduce
 serious security problems in a Web browser context. For example,
 consider a host with a WebSocket server at one path and an open
 HTTP redirector at another. Suddenly, any script that can be given
 a particular WebSocket URL can be tricked into communicating to
 (and potentially sharing secrets with) any host on the Internet,
 even if the script checks that the URL has the right hostname.

If the establish a WebSocket connection
 algorithm fails, it triggers the fail the WebSocket
 connection algorithm, which then invokes the close the
 WebSocket connection algorithm, which then establishes that
 the WebSocket connection is closed, which fires the <code title="event-socket-close">close</code> event <a href="#closeWebSocket">as described below</a>.

</li>

</ol>This constructor must be visible when the <a href="http://dev.w3.org/html5/spec/webappapis.html#script's-global-object">script's global
 object</a> is either a <code>Window</code> object or an object
 implementing the <code>WorkerUtils</code> interface.

<hr>The <dfn id="dom-websocket-url" title="dom-WebSocket-url"><code>url</code></dfn>
 attribute must return the result of resolving the <a href="http://dev.w3.org/html5/spec/urls.html#url">URL</a> that was passed to the
 constructor. (It doesn't matter what it is resolved relative to,
 since we already know it is an <a href="http://dev.w3.org/html5/spec/urls.html#absolute-url">absolute URL</a>.)

The <dfn id="dom-websocket-readystate" title="dom-WebSocket-readyState"><code>readyState</code></dfn>
 attribute represents the state of the connection. It can have the
 following values:

<dl><dt><dfn id="dom-websocket-connecting" title="dom-WebSocket-CONNECTING"><code>CONNECTING</code></dfn> (numeric value 0)</dt>

<dd>The connection has not yet been established.</dd>

<dt><dfn id="dom-websocket-open" title="dom-WebSocket-OPEN"><code>OPEN</code></dfn> (numeric value 1)</dt>

<dd>The WebSocket connection is established and communication is possible.</dd>

<dt><dfn id="dom-websocket-closing" title="dom-WebSocket-CLOSING"><code>CLOSING</code></dfn> (numeric value 2)</dt>

<dd>The connection is going through the closing handshake, or the <code title="dom-WebSocket-close"><a href="#dom-websocket-close">close()</a></code> method has been invoked.</dd>

<dt><dfn id="dom-websocket-closed" title="dom-WebSocket-CLOSED"><code>CLOSED</code></dfn> (numeric value 3)</dt>

<dd>The connection has been closed or could not be opened.</dd>

</dl>When the object is created its <code title="dom-WebSocket-readyState"><a href="#dom-websocket-readystate">readyState</a></code> must be set to
 <code title="dom-WebSocket-CONNECTING"><a href="#dom-websocket-connecting">CONNECTING</a></code> (0).

The <dfn id="dom-websocket-extensions" title="dom-WebSocket-extensions"><code>extensions</code></dfn>
 attribute must initially return the empty string. After the
 WebSocket connection is established, its value might change, as
 defined below.

The <code title="dom-WebSocket-extensions"><a href="#dom-websocket-extensions">extensions</a></code> attribute returns
 the extensions selected by the server, if any. (Currently this will
 only ever be the empty string.)

The <dfn id="dom-websocket-protocol" title="dom-WebSocket-protocol"><code>protocol</code></dfn> attribute
 must initially return the empty string. After the WebSocket
 connection is established, its value might change, as defined
 below.

The <code title="dom-WebSocket-protocol"><a href="#dom-websocket-protocol">protocol</a></code> attribute returns the
 subprotocol selected by the server, if any. It can be used in
 conjunction with the array form of the constructor's second argument
 to perform subprotocol negotiation.

The <dfn id="dom-websocket-close" title="dom-WebSocket-close"><code>close()</code></dfn>
 method must run the following steps:

<ol><li>If the method's first argument is present but is not an
 integer equal to 1000 or in the range 3000 to 4999, throw an
 <code>InvalidAccessError</code> exception and abort these
 steps.</li>

<li>

If the method's second argument is present, then run these
 substeps:

<ol><li>Let <var title="">raw reason</var> be the method's second
 argument.</li>

<li>Let <var title="">Unicode reason</var> be the result of
 converting <var title="">raw reason</var> to a
 sequence of Unicode characters.</li>

<li>Let <var title="">reason</var> be the result of encoding
 <var title="">Unicode reason</var> as UTF-8.</li>

<li>If <var title="">reason</var> is longer than 123 bytes,
 then throw a <code>SyntaxError</code> exception and abort these
 steps. <a href="#refsRFC3629">[RFC3629]</a></li>

</ol></li>

<li>Run the first matching steps from the following list:

<dl class="switch"><dt>If the <code title="dom-WebSocket-readyState"><a href="#dom-websocket-readystate">readyState</a></code>
 attribute is in the <code title="dom-WebSocket-CLOSING"><a href="#dom-websocket-closing">CLOSING</a></code> (2) or <code title="dom-WebSocket-CLOSED"><a href="#dom-websocket-closed">CLOSED</a></code> (3) state</dt>

<dd>

Do nothing.

The connection is already closing or is already
 closed. If it has not already, a <code title="event-socket-close">close</code> event will eventually fire <a href="#closeWebSocket">as described below</a>.

</dd>

<dt>If the WebSocket connection is not yet established <a href="#refsWSP">[WSP]</a></dt>

<dd>

Fail the WebSocket connection and set the <code title="dom-WebSocket-readyState"><a href="#dom-websocket-readystate">readyState</a></code> attribute's
 value to <code title="dom-WebSocket-CLOSING"><a href="#dom-websocket-closing">CLOSING</a></code> (2).
 <a href="#refsWSP">[WSP]</a>

The fail the WebSocket connection
 algorithm invokes the close the WebSocket
 connection algorithm, which then establishes that 
 the WebSocket connection is closed, which fires the
 <code title="event-socket-close">close</code> event <a href="#closeWebSocket">as described below</a>.

</dd>

<dt>If the WebSocket closing handshake has not yet been started <a href="#refsWSP">[WSP]</a></dt>

<dd>

Start the WebSocket closing handshake and set the
 <code title="dom-WebSocket-readyState"><a href="#dom-websocket-readystate">readyState</a></code>
 attribute's value to <code title="dom-WebSocket-CLOSING"><a href="#dom-websocket-closing">CLOSING</a></code> (2). <a href="#refsWSP">[WSP]</a>

If the first argument is present, then the status
 code to use in the WebSocket Close message must
 be the integer given by the first argument. <a href="#refsWSP">[WSP]</a>

If the second argument is also present, then <var title="">reason</var> must be provided in the Close message
 after the status code. <a href="#refsRFC3629">[RFC3629]</a> <a href="#refsWSP">[WSP]</a>

The start the WebSocket closing handshake
 algorithm eventually invokes the close the WebSocket
 connection algorithm, which then establishes that the
 WebSocket connection is closed, which fires the <code title="event-socket-close">close</code> event <a href="#closeWebSocket">as described below</a>.

</dd>

<dt>Otherwise</dt>

<dd>

Set the <code title="dom-WebSocket-readyState"><a href="#dom-websocket-readystate">readyState</a></code> attribute's
 value to <code title="dom-WebSocket-CLOSING"><a href="#dom-websocket-closing">CLOSING</a></code>
 (2).

The WebSocket closing handshake is
 started, and will eventually invoke the close the
 WebSocket connection algorithm, which will establish that
 the WebSocket connection is closed, and thus the <code title="event-socket-close">close</code> event will fire, <a href="#closeWebSocket">as described below</a>.

</dd>

</dl></li>

</ol><hr>The <dfn id="dom-websocket-bufferedamount" title="dom-WebSocket-bufferedAmount"><code>bufferedAmount</code></dfn>
 attribute must return the number of bytes of application data (UTF-8
 text and binary data) that have been queued using <code title="dom-WebSocket-send"><a href="#dom-websocket-send">send()</a></code> but that, as of the last
 time the <a href="http://dev.w3.org/html5/spec/webappapis.html#event-loop">event loop</a> started executing a task, had not yet been transmitted to
 the network. (This thus includes any text sent during the execution
 of the current task, regardless of whether the user agent is able to
 transmit text asynchronously with script execution.) This does not
 include framing overhead incurred by the protocol, or buffering done
 by the operating system or network hardware. If the connection is
 closed, this attribute's value will only increase with each call to
 the <code title="dom-WebSocket-send"><a href="#dom-websocket-send">send()</a></code> method (the
 number does not reset to zero once the connection closes).

In this simple example, the <code title="dom-WebSocket-bufferedAmount"><a href="#dom-websocket-bufferedamount">bufferedAmount</a></code>
 attribute is used to ensure that updates are sent either at the
 rate of one update every 50ms, if the network can handle that rate,
 or at whatever rate the network can handle, if that is too
 fast.

<pre>var socket = new WebSocket('ws://game.example.com:12010/updates');
socket.onopen = function () {
 setInterval(function() {
 if (socket.bufferedAmount == 0)
 socket.send(getUpdateData());
 }, 50);
};</pre>

The <code title="dom-WebSocket-bufferedAmount"><a href="#dom-websocket-bufferedamount">bufferedAmount</a></code>
 attribute can also be used to saturate the network without sending
 the data at a higher rate than the network can handle, though this
 requires more careful monitoring of the value of the attribute over
 time.

</div>

<hr>When a <code><a href="#websocket">WebSocket</a></code> object is created, its <dfn id="dom-websocket-binarytype" title="dom-WebSocket-binaryType"><code>binaryType</code></dfn> IDL
 attribute must be set to the string "<code title="">blob</code>". On
 getting, it must return the last value it was set to. On setting, if
 the new value is either the string "<code title="">blob</code>" or
 the string "<code title="">arraybuffer</code>", then set the IDL
 attribute to this new value. Otherwise, throw a
 <code>SyntaxError</code> exception.

This attribute allows authors to control how binary
 data is exposed to scripts. By setting the attribute to "<code title="">blob</code>", binary data is returned in <code>Blob</code>
 form; by setting it to "<code title="">arraybuffer</code>", it is
 returned in <code>ArrayBuffer</code> form. User agents can use this
 as a hint for how to handle incoming binary data: if the attribute
 is set to "<code title="">blob</code>", it is safe to spool it to
 disk, and if it is set to "<code title="">arraybuffer</code>", it is
 likely more efficient to keep the data in memory. Naturally, user
 agents are encouraged to use more subtle heuristics to decide
 whether to keep incoming data in memory or not, e.g. based on how
 big the data is or how common it is for a script to change the
 attribute at the last minute. This latter aspect is important in
 particular because it is quite possible for the attribute to be
 changed after the user agent has received the data but before the
 user agent has fired the event for it.

The <dfn id="dom-websocket-send" title="dom-WebSocket-send"><code>send(<var title="">data</var>)</code></dfn> method transmits data using the
 connection. If the <code title="dom-WebSocket-readyState"><a href="#dom-websocket-readystate">readyState</a></code> attribute is
 <code title="dom-WebSocket-CONNECTING"><a href="#dom-websocket-connecting">CONNECTING</a></code>, it must
 throw an <code>InvalidStateError</code> exception. Otherwise, the
 user agent must run the appropriate set of steps from the following
 list:

<dl><dt>If the argument is a string</dt>

<dd>

Let <var title="">data</var> be the result of converting the <var title="">data</var> argument to a
 sequence of Unicode characters. If the WebSocket
 connection is established and the WebSocket closing handshake has not yet
 started, then the user agent must send a WebSocket
 Message comprised of <var title="">data</var> using a text
 frame opcode; if the data cannot be sent, e.g. because it would
 need to be buffered but the buffer is full, the user agent must
 close the WebSocket connection <a href="#concept-websocket-close-fail" title="concept-websocket-close-fail">with prejudice</a>. Any
 invocation of this method with a string argument that does not
 throw an exception must increase the <code title="dom-WebSocket-bufferedAmount"><a href="#dom-websocket-bufferedamount">bufferedAmount</a></code>
 attribute by the number of bytes needed to express the argument as
 UTF-8. <a href="#refsUNICODE">[UNICODE]</a> <a href="#refsRFC3629">[RFC3629]</a> <a href="#refsWSP">[WSP]</a>

</dd>

<dt>If the argument is a <code>Blob</code> object</dt>

<dd>

If the WebSocket connection is established, and the WebSocket
 closing handshake has not yet started, then the user agent
 must send a WebSocket Message comprised of <var title="">data</var> using a binary frame opcode; if the data
 cannot be sent, e.g. because it would need to be buffered but the
 buffer is full, the user agent must close the WebSocket
 connection <a href="#concept-websocket-close-fail" title="concept-websocket-close-fail">with
 prejudice</a>. The data to be sent is the raw data represented
 by the <code>Blob</code> object. Any
 invocation of this method with a <code>Blob</code> argument that
 does not throw an exception must increase the <code title="dom-WebSocket-bufferedAmount"><a href="#dom-websocket-bufferedamount">bufferedAmount</a></code>
 attribute by the size of the <code>Blob</code> object's raw data,
 in bytes. <a href="#refsWSP">[WSP]</a> <a href="#refsFILEAPI">[FILEAPI]</a>

</dd>

<dt>If the argument is an <code>ArrayBuffer</code> object</dt>

<dd>

If the WebSocket connection is established, and the WebSocket
 closing handshake has not yet started, then the user agent
 must send a WebSocket Message comprised of <var title="">data</var> using a binary frame opcode; if the data
 cannot be sent, e.g. because it would need to be buffered but the
 buffer is full, the user agent must close the WebSocket
 connection <a href="#concept-websocket-close-fail" title="concept-websocket-close-fail">with
 prejudice</a>. The data to be sent is the data stored in the
 buffer described by the <code>ArrayBuffer</code> object. Any invocation of
 this method with an <code>ArrayBuffer</code> argument that does
 not throw an exception must increase the <code title="dom-WebSocket-bufferedAmount"><a href="#dom-websocket-bufferedamount">bufferedAmount</a></code>
 attribute by the length of the <code>ArrayBuffer</code> in bytes.
 <a href="#refsWSP">[WSP]</a> <a href="#refsTYPEDARRAY">[TYPEDARRAY]</a>

</dd>

<dt>If the argument is an <code>ArrayBufferView</code> object</dt>

<dd>

If the WebSocket connection is established, and the WebSocket
 closing handshake has not yet started, then the user agent
 must send a WebSocket Message comprised of <var title="">data</var> using a binary frame opcode; if the data
 cannot be sent, e.g. because it would need to be buffered but the
 buffer is full, the user agent must close the WebSocket
 connection <a href="#concept-websocket-close-fail" title="concept-websocket-close-fail">with
 prejudice</a>. The data to be sent is the data stored in the
 section of the buffer described by the <code>ArrayBuffer</code>
 object that the <code>ArrayBufferView</code> object references.
 Any invocation
 of this method with an <code>ArrayBufferView</code> argument that
 does not throw an exception must increase the <code title="dom-WebSocket-bufferedAmount"><a href="#dom-websocket-bufferedamount">bufferedAmount</a></code>
 attribute by the length of the <code>ArrayBufferView</code> in
 bytes. <a href="#refsWSP">[WSP]</a> <a href="#refsTYPEDARRAY">[TYPEDARRAY]</a>

</dd>

</dl><hr>The following are the <a href="http://dev.w3.org/html5/spec/webappapis.html#event-handlers">event handlers</a> (and their
 corresponding <a title="event handler event type" href="http://dev.w3.org/html5/spec/webappapis.html#event-handler-event-type">event handler
 event types</a>) that must be supported, as IDL attributes, by
 all objects implementing the <code><a href="#websocket">WebSocket</a></code> interface:

<table><thead><tr><th>Event handler <th><a href="http://dev.w3.org/html5/spec/webappapis.html#event-handler-event-type">Event handler event type</a>
 <tbody><tr><td><dfn id="handler-websocket-onopen" title="handler-WebSocket-onopen"><code>onopen</code></dfn> <td> <code title="event-open">open</code>
 <tr><td><dfn id="handler-websocket-onmessage" title="handler-WebSocket-onmessage"><code>onmessage</code></dfn> <td> <code title="event-message">message</code>
 <tr><td><dfn id="handler-websocket-onerror" title="handler-WebSocket-onerror"><code>onerror</code></dfn> <td> <code title="event-error">error</code>
 <tr><td><dfn id="handler-websocket-onclose" title="handler-WebSocket-onclose"><code>onclose</code></dfn> <td> <code title="event-socket-close">close</code>
 </table><h2 id="feedback-from-the-protocol">5 Feedback from the protocol</h2>

When the WebSocket connection is established, the user
 agent must <a href="http://dev.w3.org/html5/spec/webappapis.html#queue-a-task">queue a task</a> to run these steps:

<ol><li>Change the <code title="dom-WebSocket-readyState"><a href="#dom-websocket-readystate">readyState</a></code> attribute's
 value to <code title="dom-WebSocket-OPEN"><a href="#dom-websocket-open">OPEN</a></code> (1).</li>

<li>Change the <code title="dom-WebSocket-extensions"><a href="#dom-websocket-extensions">extensions</a></code> attribute's
 value to the extensions in use, if is not the null value. <a href="#refsWSP">[WSP]</a></li>

<li>Change the <code title="dom-WebSocket-protocol"><a href="#dom-websocket-protocol">protocol</a></code> attribute's value to
 the subprotocol in use, if is not the null value. <a href="#refsWSP">[WSP]</a></li>

<li>Act as if the user agent had received a set-cookie-string consisting
 of the cookies set during the server's opening handshake,
 for the URL <var title="">url</var> given to the <code title="dom-WebSocket"><a href="#dom-websocket">WebSocket()</a></code> constructor. <a href="#refsCOOKIES">[COOKIES]</a> <a href="#refsRFC3629">[RFC3629]</a> <a href="#refsWSP">[WSP]</a></li>

<li><a href="http://dev.w3.org/html5/spec/webappapis.html#fire-a-simple-event">Fire a simple event</a> named <code title="event-open">open</code> at the <code><a href="#websocket">WebSocket</a></code>
 object.

</ol><hr>When a WebSocket message has been received with type <var title="">type</var> and data <var title="">data</var>, the user
 agent must <a href="http://dev.w3.org/html5/spec/webappapis.html#queue-a-task">queue a task</a> to follow these steps: <a href="#refsWSP">[WSP]</a>

If the <code title="dom-WebSocket-readyState"><a href="#dom-websocket-readystate">readyState</a></code>
 attribute's value is not <code title="dom-WebSocket-OPEN"><a href="#dom-websocket-open">OPEN</a></code> (1), then abort these
 steps.

</li>

<li>

Let <var title="">event</var> be an event that uses the
 <code>MessageEvent</code> interface, with the event type <code title="event-message">message</code>, which does not bubble, is
 not cancelable, and has no default action.
 
 <a href="#refsHTML">[HTML]</a>

</li>

<li>Initialize <var title="">event</var>'s <code title="dom-MessageEvent-origin">origin</code> attribute to the
 Unicode
 serialization of the <a href="http://dev.w3.org/html5/spec/browsers.html#origin">origin</a> of the
 <a href="http://dev.w3.org/html5/spec/urls.html#url">URL</a> that was passed to the <code><a href="#websocket">WebSocket</a></code>
 object's constructor.</li>

<li>

If <var title="">type</var> indicates that the data is Text,
 then initialize <var title="">event</var>'s <code title="dom-MessageEvent-data">data</code> attribute to <var title="">data</var>.

If <var title="">type</var> indicates that the data is Binary,
 and <code title="dom-WebSocket-binaryType"><a href="#dom-websocket-binarytype">binaryType</a></code> is
 set to "<code title="">blob</code>", then initialize <var title="">event</var>'s <code title="dom-MessageEvent-data">data</code> attribute to a new
 <code>Blob</code> object that represents <var title="">data</var>
 as its raw data. <a href="#refsFILEAPI">[FILEAPI]</a>

If <var title="">type</var> indicates that the data is Binary,
 and <code title="dom-WebSocket-binaryType"><a href="#dom-websocket-binarytype">binaryType</a></code> is
 set to "<code title="">arraybuffer</code>", then initialize <var title="">event</var>'s <code title="dom-MessageEvent-data">data</code> attribute to a new
 read-only <code>ArrayBuffer</code> object whose contents are <var title="">data</var>. <a href="#refsTYPEDARRAY">[TYPEDARRAY]</a>

</li>

<li>

Dispatch <var title="">event</var> at the
 <code><a href="#websocket">WebSocket</a></code> object.

</li>

</ol>User agents are encouraged to check if they can
 perform the above steps efficiently before they run the task,
 picking tasks from other task queues
 while they prepare the buffers if not. For example, if the <code title="dom-WebSocket-binaryType"><a href="#dom-websocket-binarytype">binaryType</a></code> attribute was set
 to "<code title="">blob</code>" when the data arrived, and the user
 agent spooled all the data to disk, but just before running the
 above task for this particular
 message the script switched <code title="dom-WebSocket-binaryType"><a href="#dom-websocket-binarytype">binaryType</a></code> to "<code title="">arraybuffer</code>", the user agent would want to page the
 data back to RAM before running this task so as to avoid stalling the main
 thread while it created the <code>ArrayBuffer</code> object.

Here is an example of how to define a handler for the <code title="event-message">message</code> event in the case of text
 frames:

<pre>mysocket.onmessage = function (event) {
 if (event.data == 'on') {
 turnLampOn();
 } else if (event.data == 'off') {
 turnLampOff();
 }
};</pre>

The protocol here is a trivial one, with the server just sending
 "on" or "off" messages.

</div>

<hr>When the WebSocket closing handshake is started, the user
 agent must <a href="http://dev.w3.org/html5/spec/webappapis.html#queue-a-task">queue a task</a> to change the <code title="dom-WebSocket-readyState"><a href="#dom-websocket-readystate">readyState</a></code> attribute's value
 to <code title="dom-WebSocket-CLOSING"><a href="#dom-websocket-closing">CLOSING</a></code> (2). (If the
 <code title="dom-WebSocket-close"><a href="#dom-websocket-close">close()</a></code> method was called,
 the <code title="dom-WebSocket-readyState"><a href="#dom-websocket-readystate">readyState</a></code>
 attribute's value will already be set to <code title="dom-WebSocket-CLOSING"><a href="#dom-websocket-closing">CLOSING</a></code> (2) when this task
 runs.) <a href="#refsWSP">[WSP]</a>

<hr>When the WebSocket connection is
 closed, possibly cleanly, the user agent must
 <a href="http://dev.w3.org/html5/spec/webappapis.html#queue-a-task">queue a task</a> to run the following substeps:

<ol><li>Change the <code title="dom-WebSocket-readyState"><a href="#dom-websocket-readystate">readyState</a></code> attribute's
 value to <code title="dom-WebSocket-CLOSED"><a href="#dom-websocket-closed">CLOSED</a></code>
 (3).</li>

<li>If the user agent was required to fail the WebSocket
 connection or the WebSocket connection is closed <dfn id="concept-websocket-close-fail" title="concept-websocket-close-fail">with prejudice</dfn>,
 <a href="http://dev.w3.org/html5/spec/webappapis.html#fire-a-simple-event">fire a simple event</a> named <code title="">error</code>
 at the <code><a href="#websocket">WebSocket</a></code> object. <a href="#refsWSP">[WSP]</a></li>

<li>Create an event that uses the <code><a href="#closeevent">CloseEvent</a></code>
 interface, with the event type <code title="event-socket-close">close</code>, which does not bubble, is not
 cancelable, has no default action, whose <code title="dom-CloseEvent-wasClean"><a href="#dom-closeevent-wasclean">wasClean</a></code> attribute is initialized to
 true if the connection closed cleanly and false
 otherwise, whose <code title="dom-CloseEvent-code"><a href="#dom-closeevent-code">code</a></code>
 attribute is initialized to the WebSocket connection close code, and
 whose <code title="dom-CloseEvent-reason"><a href="#dom-closeevent-reason">reason</a></code> attribute
 is initialized to the WebSocket connection close reason
 <a href="http://dev.w3.org/html5/spec/single-page.html#decoded-as-utf-8,-with-error-handling">decoded as UTF-8, with error handling</a>, and dispatch
 the event at the <code><a href="#websocket">WebSocket</a></code> object. <a href="#refsWSP">[WSP]</a></li>

</ol><div class="warning">

User agents must not convey any failure information to scripts
 in a way that would allow a script to distinguish the following
 situations:

<ul><li>A server whose host name could not be resolved.

<li>A server to which packets could not successfully be routed.

<li>A server that refused the connection on the specified port.

<li>A server that failed to correctly perform a TLS handshake
 (e.g., the server certificate can't be verified).

<li>A server that did not complete the opening handshake (e.g.
 because it was not a WebSocket server).

<li>A WebSocket server that sent a correct opening handshake, but
 that specified options that caused the client to drop the
 connection (e.g. the server specified a subprotocol that the
 client did not offer).

<li>A WebSocket server that abruptly closed the connection after
 successfully completing the opening handshake.

</ul>In all of these cases, the the WebSocket connection close
 code would be 1006, as required by the WebSocket Protocol
 specification. <a href="#refsWSP">[WSP]</a>

Allowing a script to distinguish these cases would allow a
 script to probe the user's local network in preparation for an
 attack.

In particular, this means the code 1015 is not used
 by the user agent (unless the server erroneously uses it in its
 close frame, of course).

</div>

<hr>The <a href="http://dev.w3.org/html5/spec/webappapis.html#task-source">task source</a> for all tasks queued in this section is the <dfn id="websocket-task-source">WebSocket task
 source</dfn>.

<h2 id="ping-and-pong-frames">6 Ping and Pong frames</h2>

The WebSocket protocol specification defines Ping and Pong frames
 that can be used for keep-alive, heart-beats, network status
 probing, latency instrumentation, and so forth. These are not
 currently exposed in the API.

User agents may send ping and unsolicited pong frames as desired,
 for example in an attempt to maintain local network NAT mappings, to
 detect failed connections, or to display latency metrics to the
 user. User agents must not use pings or unsolicited pongs to aid the
 server; it is assumed that servers will solicit pongs whenever
 appropriate for the server's needs.

<h2 id="parsing-websocket-urls">7 Parsing WebSocket URLs</h2>

The steps to <dfn id="parse-a-websocket-url-s-components">parse a WebSocket URL's components</dfn> from
 a string <var title="">url</var> are as follows. These steps return
 either a <var title="">host</var>, a <var title="">port</var>, a
 <var title="">resource name</var>, and a <var title="">secure</var>
 flag, or they fail.

<ol><li>If the <var title="">url</var> string is not an
 <a href="http://dev.w3.org/html5/spec/urls.html#absolute-url">absolute URL</a>, then fail this algorithm.</li>

<li>

Resolve the <var title="">url</var> string, with the URL character encoding set to
 UTF-8. <a href="#refsRFC3629">[RFC3629]</a>

It doesn't matter what it is resolved relative to,
 since we already know it is an <a href="http://dev.w3.org/html5/spec/urls.html#absolute-url">absolute URL</a> at this
 point.

</li>

<li>If <var title="">url</var> does not have a &lt;scheme&gt; component whose value,
 when <a href="http://dev.w3.org/html5/spec/infrastructure.html#converted-to-ascii-lowercase">converted to ASCII lowercase</a>, is either "<code title="">ws</code>" or "<code title="">wss</code>", then fail this
 algorithm.</li>

<li>If <var title="">url</var> has a &lt;fragment&gt; component, then fail
 this algorithm.</li>

<li>If the &lt;scheme&gt;
 component of <var title="">url</var> is "<code title="">ws</code>",
 set <var title="">secure</var> to false; otherwise, the &lt;scheme&gt; component is "<code title="">wss</code>", set <var title="">secure</var> to
 true.</li>

<li>Let <var title="">host</var> be the value of the &lt;host&gt; component of <var title="">url</var>, <a href="http://dev.w3.org/html5/spec/infrastructure.html#converted-to-ascii-lowercase">converted to ASCII
 lowercase</a>.</li>

<li>If <var title="">url</var> has a &lt;port&gt; component, then let <var title="">port</var> be that component's value; otherwise, there is
 no explicit <var title="">port</var>.</li>

<li>If there is no explicit <var title="">port</var>, then: if
 <var title="">secure</var> is false, let <var title="">port</var>
 be 80, otherwise let <var title="">port</var> be 443.</li>

<li>Let <var title="">resource name</var> be the value of the
 &lt;path&gt; component (which might
 be empty) of <var title="">url</var>.</li>

<li>If <var title="">resource name</var> is the empty string,
 set it to a single character U+002F SOLIDUS (/).</li>

<li>If <var title="">url</var> has a &lt;query&gt; component, then append a
 single U+003F QUESTION MARK character (?) to <var title="">resource
 name</var>, followed by the value of the &lt;query&gt; component.</li>

<li>Return <var title="">host</var>, <var title="">port</var>,
 <var title="">resource name</var>, and <var title="">secure</var>.</li>

</ol><h2 id="event-definitions">8 Event definitions</h2>

<pre class="idl">[Constructor(DOMString type, optional <a href="#closeeventinit">CloseEventInit</a> eventInitDict)]
interface <dfn id="closeevent">CloseEvent</dfn> : <a href="http://dev.w3.org/html5/spec/infrastructure.html#event">Event</a> {
 readonly attribute boolean <a href="#dom-closeevent-wasclean" title="dom-CloseEvent-wasClean">wasClean</a>;
 readonly attribute unsigned short <a href="#dom-closeevent-code" title="dom-CloseEvent-code">code</a>;
 readonly attribute DOMString <a href="#dom-closeevent-reason" title="dom-CloseEvent-reason">reason</a>;
};

dictionary <dfn id="closeeventinit">CloseEventInit</dfn> : <a href="http://dev.w3.org/html5/spec/infrastructure.html#eventinit">EventInit</a> {
 boolean wasClean;
 unsigned short code;
 DOMString reason;
};</pre>

The <dfn id="dom-closeevent-wasclean" title="dom-CloseEvent-wasClean"><code>wasClean</code></dfn>
 attribute must return the value it was initialized to. When the
 object is created, this attribute must be initialized to false. It
 represents whether the connection closed cleanly or not.

The <dfn id="dom-closeevent-code" title="dom-CloseEvent-code"><code>code</code></dfn>
 attribute must return the value it was initialized to. When the
 object is created, this attribute must be initialized to zero. It
 represents the WebSocket connection close code provided by the
 server.

The <dfn id="dom-closeevent-reason" title="dom-CloseEvent-reason"><code>reason</code></dfn>
 attribute must return the value it was initialized to. When the
 object is created, this attribute must be initialized to empty
 string. It represents the WebSocket connection close reason provided
 by the server.

<h2 id="garbage-collection">9 Garbage collection</h2>

A <code><a href="#websocket">WebSocket</a></code> object whose <code title="dom-WebSocket-readyState"><a href="#dom-websocket-readystate">readyState</a></code> attribute's value
 was set to <code title="dom-WebSocket-CONNECTING"><a href="#dom-websocket-connecting">CONNECTING</a></code>
 (0) as of the last time the <a href="http://dev.w3.org/html5/spec/webappapis.html#event-loop">event loop</a> started
 executing a task must not be
 garbage collected if there are any event listeners registered for
 <code title="event-open">open</code> events, <code title="event-message">message</code> events, <code title="event-error">error</code> events, or <code title="event-socket-close">close</code> events.

A <code><a href="#websocket">WebSocket</a></code> object whose <code title="dom-WebSocket-readyState"><a href="#dom-websocket-readystate">readyState</a></code> attribute's value
 was set to <code title="dom-WebSocket-OPEN"><a href="#dom-websocket-open">OPEN</a></code> (1) as of
 the last time the <a href="http://dev.w3.org/html5/spec/webappapis.html#event-loop">event loop</a> started executing a task must not be garbage collected if
 there are any event listeners registered for <code title="event-message">message</code> events, <code title="event-error">error</code>, or <code title="event-socket-close">close</code> events.

A <code><a href="#websocket">WebSocket</a></code> object whose <code title="dom-WebSocket-readyState"><a href="#dom-websocket-readystate">readyState</a></code> attribute's value
 was set to <code title="dom-WebSocket-CLOSING"><a href="#dom-websocket-closing">CLOSING</a></code> (2) as
 of the last time the <a href="http://dev.w3.org/html5/spec/webappapis.html#event-loop">event loop</a> started executing a
 task must not be garbage collected
 if there are any event listeners registered for <code title="event-error">error</code> or <code title="event-socket-close">close</code> events.

A <code><a href="#websocket">WebSocket</a></code> object with an established connection that has
 data queued to be transmitted to the network must not be garbage
 collected. <a href="#refsWSP">[WSP]</a>

If a <code><a href="#websocket">WebSocket</a></code> object is garbage collected while its
 connection is still open, the user agent must start the
 WebSocket closing handshake, with no status code for the Close message. <a href="#refsWSP">[WSP]</a>

<hr>If a user agent is to <dfn id="make-disappear">make disappear</dfn> a
 <code><a href="#websocket">WebSocket</a></code> object (this happens when a
 <code>Document</code> object goes away), the user agent must follow
 the first appropriate set of steps from the following list:

<dl class="switch"><dt>If the WebSocket connection is not yet established <a href="#refsWSP">[WSP]</a></dt>

<dd>

Fail the WebSocket connection. <a href="#refsWSP">[WSP]</a>

</dd>

<dt>If the WebSocket closing handshake has not yet been started
 <a href="#refsWSP">[WSP]</a></dt>

<dd>

Start the WebSocket closing handshake, with the
 status code to use in the WebSocket Close message
 being 1001. <a href="#refsWSP">[WSP]</a>

</dd>

<dt>Otherwise</dt>

<dd>

Do nothing.

</dd>

</dl><h2 class="no-num" id="references">References</h2>

All references are normative unless marked "Non-normative".

<dl><dt id="refsCOOKIES">[COOKIES]</dt>
 
 <dd><cite><a href="http://tools.ietf.org/html/rfc6265">HTTP State Management Mechanism</a></cite>, A. Barth. IETF.</dd>

<dt id="refsDOMCORE">[DOMCORE]</dt>
 <dd><cite><a href="http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html">DOM4</a></cite>, A. van Kesteren. W3C.</dd>

<dt id="refsFILEAPI">[FILEAPI]</dt>
 <dd><cite><a href="http://dev.w3.org/2006/webapi/FileUpload/publish/FileAPI.html">File
 API</a></cite>, A. Ranganathan. W3C.</dd>

<dt id="refsHTML">[HTML]</dt>
 <dd><cite><a href="http://dev.w3.org/html5/spec/">HTML5</a></cite>,
 I. Hickson. W3C.</dd>

<dt id="refsRFC2119">[RFC2119]</dt>
 <dd><cite><a href="http://tools.ietf.org/html/rfc2119">Key words for use in
 RFCs to Indicate Requirement Levels</a></cite>, S. Bradner. IETF.</dd>

<dt id="refsRFC3629">[RFC3629]</dt>
 <dd><cite><a href="http://tools.ietf.org/html/rfc3629">UTF-8, a
 transformation format of ISO 10646</a></cite>, F. Yergeau. IETF.</dd>

<dt id="refsTYPEDARRAY">[TYPEDARRAY]</dt>
 <dd><cite><a href="http://www.khronos.org/registry/typedarray/specs/latest/">Typed Array Specification</a></cite>, D. Herman, K. Russell. Khronos.</dd>

<dt id="refsUNICODE">[UNICODE]</dt>
 <dd><cite><a href="http://www.unicode.org/versions/">The Unicode Standard</a></cite>. Unicode Consortium.</dd>

<dt id="refsWEBIDL">[WEBIDL]</dt>
 
 <dd><cite><a href="http://dev.w3.org/2006/webapi/WebIDL/">Web
 IDL</a></cite>, C. McCormack. W3C.</dd>

<dt id="refsWSP">[WSP]</dt>
 <dd><cite><a href="http://tools.ietf.org/html/rfc6455">The WebSocket protocol</a></cite>, I. Fette, A. Melnikov. IETF.</dd>

</dl><h2 class="no-num" id="acknowledgements">Acknowledgements</h2>

For a full list of acknowledgements, please see the HTML
 specification. <a href="#refsHTML">[HTML]</a>

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<h1>The WebSocket API</h1>
 
 <h2 class="no-num no-toc" id="editor-s-draft-4-june-2014">Editor's Draft 4 June 2014</h2>
 <dl><dt>Latest Published Version:</dt>
 <dd><a href="http://www.w3.org/TR/websockets/">http://www.w3.org/TR/websockets/</a></dd>
 <dt>Latest Editor's Draft:</dt>
 <dd><a href="http://dev.w3.org/html5/websockets/" class="latest-link">http://dev.w3.org/html5/websockets/</a></dd>

<dt>Previous Versions:</dt>
 <dd><a href="http://www.w3.org/TR/2009/WD-websockets-20090423/">http://www.w3.org/TR/2009/WD-websockets-20090423/</a>
 <dd><a href="http://www.w3.org/TR/2009/WD-websockets-20091029/">http://www.w3.org/TR/2009/WD-websockets-20091029/</a></dd>

 <dt>Editor:</dt>
 <dd><a href="mailto:ian@hixie.ch">Ian Hickson</a>, Google, Inc.</dd>
 </dl><a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a>
 &copy; 2012 <a href="http://www.w3.org/"><abbr title="World Wide
 Web Consortium">W3C</abbr></a>&reg; (<a href="http://www.csail.mit.edu/"><abbr title="Massachusetts
 Institute of Technology">MIT</abbr></a>, <a href="http://www.ercim.eu/"><abbr title="European Research
 Consortium for Informatics and Mathematics">ERCIM</abbr></a>, <a href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. W3C
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 use</a> rules apply.

</div>

<hr class="top"><h2 class="no-num no-toc" id="abstract">Abstract</h2>

This specification defines an API that enables Web pages to use
 the WebSocket protocol (defined by the IETF) for two-way
 communication with a remote host.

<h2 class="no-num no-toc" id="status-of-this-document">Status of This document</h2>

This section describes the status of this document at the
 time of its publication. Other documents may supersede this
 document. A list of current W3C publications and the

most recently formally published

revision of this technical report can be found in the <a href="http://www.w3.org/TR/">W3C technical reports index</a> at
 http://www.w3.org/TR/.

If you wish to make comments regarding this document, you can
 enter feedback using this form:

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Implementors should be aware that this specification is not
 stable. Implementors who are not taking part in the
 discussions are likely to find the specification changing out from
 under them in incompatible ways. Vendors interested in
 implementing this specification before it eventually reaches the
 Candidate Recommendation stage should join the aforementioned
 mailing lists and take part in the discussions.

The latest
 stable version of the editor's draft of this specification is always
 available on <a href="http://dev.w3.org/html5/websockets/">the W3C CVS server</a>
 and in the <a href="http://svn.whatwg.org/webapps/">WHATWG
 Subversion repository</a>. The <a href="http://www.whatwg.org/specs/web-apps/current-work/complete.html">latest
 editor's working copy</a> (which may contain unfinished text in the
 process of being prepared) contains the latest draft text of this
 specification (amongst others). For more details, please see the <a href="http://wiki.whatwg.org/wiki/FAQ#What_are_the_various_versions_of_the_spec.3F">WHATWG
 FAQ</a>.

This specification is being developed in conjunction with an
 RFC for a wire protocol, the WebSocket Protocol,
 available from the following location:

<ul><li>RFC 6455: The WebSocket Protocol: <a href="http://tools.ietf.org/html/rfc6455">http://tools.ietf.org/html/rfc6455</a></li>
 </ul>This document was produced by a group operating under the <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/">5
 February 2004 W3C Patent Policy</a>. W3C maintains a <a rel="disclosure" href="http://www.w3.org/2004/01/pp-impl/42538/status">public list of
 any patent disclosures</a> made in connection with the deliverables
 of the group; that page also includes instructions for disclosing a
 patent. An individual who has actual knowledge of a patent which the
 individual believes contains <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">Essential
 Claim(s)</a> must disclose the information in accordance with <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">section
 6 of the W3C Patent Policy</a>.

This document was produced by a group operating under the <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/">5
 February 2004 W3C Patent Policy</a>. W3C maintains a <a rel="disclosure" href="http://www.w3.org/2004/01/pp-impl/42538/status">public list of
 any patent disclosures</a> made in connection with the deliverables
 of the group; that page also includes instructions for disclosing a
 patent. An individual who has actual knowledge of a patent which the
 individual believes contains <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">Essential
 Claim(s)</a> must disclose the information in accordance with <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">section
 6 of the W3C Patent Policy</a>.

<h2 class="no-num no-toc" id="contents">Table of Contents</h2>

<ol class="toc">
 <li><a href="#network-intro">1 Introduction</a></li>
 <li><a href="#conformance-requirements">2 Conformance requirements</a>
 <ol>
 <li><a href="#dependencies">2.1 Dependencies</a></ol></li>
 <li><a href="#terminology">3 Terminology</a></li>
 <li><a href="#the-websocket-interface">4 The <code>WebSocket</code> interface</a></li>
 <li><a href="#feedback-from-the-protocol">5 Feedback from the protocol</a></li>
 <li><a href="#ping-and-pong-frames">6 Ping and Pong frames</a></li>
 <li><a href="#parsing-websocket-urls">7 Parsing WebSocket URLs</a></li>
 <li><a href="#the-closeevent-interfaces">8 The <code>CloseEvent</code> interfaces</a></li>
 <li><a href="#garbage-collection">9 Garbage collection</a></li>
 <li><a href="#references" class="no-num">References</a></li>
 <li><a href="#acknowledgements" class="no-num">Acknowledgements</a></ol>

<hr><h2 id="network-intro">1 Introduction</h2>

This section is non-normative.

To enable Web applications to maintain bidirectional communications with server-side processes,
 this specification introduces the <code><a href="#websocket">WebSocket</a></code> interface.

This interface does not allow for raw access to the underlying network. For
 example, this interface could not be used to implement an IRC client without proxying messages
 through a custom server.

<h2 id="conformance-requirements">2 Conformance requirements</h2>

All diagrams, examples, and notes in this specification are
 non-normative, as are all sections explicitly marked non-normative.
 Everything else in this specification is normative.

Some conformance requirements are phrased as requirements on
 attributes, methods or objects. Such requirements are to be
 interpreted as requirements on user agents.

The only conformance class defined by this specification is user
 agents.

<h3 id="dependencies">2.1 Dependencies</h3>

This specification relies on several other underlying
 specifications.

<dd>

Many fundamental concepts from HTML are used by this
 specification. <a href="#refsHTML">[HTML]</a>

</dd>

<dt>WebIDL</dt>

<dd>

The IDL blocks in this specification use the semantics of the
 WebIDL specification. <a href="#refsWEBIDL">[WEBIDL]</a>

</dd>

</dl><h2 id="terminology">3 Terminology</h2>

An IDL attribute is said to be getting when its value is
 being retrieved (e.g. by author script), and is said to be
 setting when a new value is assigned to it.

<h2 id="the-websocket-interface">4 The <code><a href="#websocket">WebSocket</a></code> interface</h2>

<pre class="idl">enum <dfn id="binarytype">BinaryType</dfn> { "blob", "arraybuffer" };
[<a href="#dom-websocket" title="dom-WebSocket">Constructor</a>(DOMString url, optional (DOMString or DOMString[]) protocols), Exposed=Window,Worker]
interface <dfn id="websocket">WebSocket</dfn> : EventTarget {
 readonly attribute DOMString <a href="#dom-websocket-url" title="dom-WebSocket-url">url</a>;

// networking
 attribute EventHandler <a href="#handler-websocket-onopen" title="handler-WebSocket-onopen">onopen</a>;
 attribute EventHandler <a href="#handler-websocket-onerror" title="handler-WebSocket-onerror">onerror</a>;
 attribute EventHandler <a href="#handler-websocket-onclose" title="handler-WebSocket-onclose">onclose</a>;
 readonly attribute DOMString <a href="#dom-websocket-extensions" title="dom-WebSocket-extensions">extensions</a>;
 readonly attribute DOMString <a href="#dom-websocket-protocol" title="dom-WebSocket-protocol">protocol</a>;
 void <a href="#dom-websocket-close" title="dom-WebSocket-close">close</a>([Clamp] optional unsigned short code, optional DOMString reason);

// messaging
 attribute EventHandler <a href="#handler-websocket-onmessage" title="handler-WebSocket-onmessage">onmessage</a>;
 attribute <a href="#binarytype">BinaryType</a> <a href="#dom-websocket-binarytype" title="dom-WebSocket-binaryType">binaryType</a>;
 void <a href="#dom-websocket-send" title="dom-WebSocket-send">send</a>(DOMString data);
 void <a href="#dom-websocket-send" title="dom-WebSocket-send">send</a>(Blob data);
 void <a href="#dom-websocket-send" title="dom-WebSocket-send">send</a>(ArrayBuffer data);
 void <a href="#dom-websocket-send" title="dom-WebSocket-send">send</a>(ArrayBufferView data);
};</pre>

The <dfn id="dom-websocket" title="dom-WebSocket"><code>WebSocket(<var title="">url</var>, <var title="">protocols</var>)</code></dfn> constructor takes one or two arguments. The first argument,
 <var title="">url</var>, specifies the URL to which to connect. The second, <var title="">protocols</var>, if present, is either a string or an array of strings. If it is a
 string, it is equivalent to an array consisting of just that string; if it is omitted, it is
 equivalent to the empty array. Each string in the array is a subprotocol name. The connection will
 only be established if the server reports that it has selected one of these subprotocols. The
 subprotocol names must all be strings that match the requirements for elements that comprise the
 value of <code title="http-sec-websocket-protocol">Sec-WebSocket-Protocol</code> fields as
 defined by the WebSocket protocol specification. <a href="#refsWSP">[WSP]</a>

When the <code>WebSocket()</code> constructor is invoked, the UA must run these steps:

<ol><li><a href="#parse-a-websocket-url-s-components">Parse a WebSocket URL's components</a> from the <var title="">url</var> argument, to
 obtain <var title="">host</var>, <var title="">port</var>, <var title="">resource name</var>, and
 <var title="">secure</var>. If this fails, throw a <code>SyntaxError</code> exception and abort
 these steps. <a href="#refsWSP">[WSP]</a></li>

<li>If <var title="">secure</var> is false but the origin specified by the
 entry settings object has a scheme component that is itself a secure protocol, e.g.
 HTTPS, then throw a <code>SecurityError</code> exception and abort these steps.</li>

<li>

If <var title="">port</var> is a port to which the user agent is configured to block access,
 then throw a <code>SecurityError</code> exception and abort these steps. (User agents typically
 block access to well-known ports like SMTP.)

Access to ports 80 and 443 should not be blocked, including the unlikely cases when <var title="">secure</var> is false but <var title="">port</var> is 443 or <var title="">secure</var> is true but <var title="">port</var> is 80.

</li>

<li>

If <var title="">protocols</var> is absent, let <var title="">protocols</var> be an empty
 array.

Otherwise, if <var title="">protocols</var> is present and a string, let <var title="">protocols</var> instead be an array consisting of just that string.

</li>

<li>If any of the values in <var title="">protocols</var> occur more than once or otherwise
 fail to match the requirements for elements that comprise the value of <code title="http-sec-websocket-protocol">Sec-WebSocket-Protocol</code> fields as defined by the
 WebSocket protocol specification, then throw a <code>SyntaxError</code> exception and abort these
 steps. <a href="#refsWSP">[WSP]</a></li>

<li>Let <var title="">origin</var> be the ASCII serialization of the origin specified by the entry
 settings object, converted to ASCII lowercase.</li>

<li>Return a new <code><a href="#websocket">WebSocket</a></code> object, but continue these steps
 asynchronously.</li>

<li>Let the new object's <dfn id="client-specified-protocols">client-specified protocols</dfn> be the values (if any) given in
 <var title="">protocols</var>.</li>

<li>

Establish a WebSocket connection given the set (<var title="">host</var>, <var title="">port</var>, <var title="">resource name</var>, <var title="">secure</var>), along with
 the <var title="">protocols</var> list, an empty list for the extensions, and <var title="">origin</var>. The headers to send appropriate cookies must be a <code title="http-Cookie">Cookie</code> header whose value is the cookie-string computed from
 the user's cookie store and the URL <var title="">url</var>; for these purposes this is
 not a "non-HTTP" API. <a href="#refsWSP">[WSP]</a> <a href="#refsCOOKIES">[COOKIES]</a>

When the user agent validates the server's
 response during the "establish a WebSocket connection" algorithm, if the status code
 received from the server is not 101 (e.g. it is a redirect), the user agent must fail the
 WebSocket connection.

Following HTTP procedures here could introduce serious security problems in a
 Web browser context. For example, consider a host with a WebSocket server at one path and an
 open HTTP redirector at another. Suddenly, any script that can be given a particular WebSocket
 URL can be tricked into communicating to (and potentially sharing secrets with) any host on the
 Internet, even if the script checks that the URL has the right hostname.

If the establish a WebSocket connection algorithm fails, it triggers the
 fail the WebSocket connection algorithm, which then invokes the close the WebSocket
 connection algorithm, which then establishes that the WebSocket connection is closed,
 which fires the <code title="event-close">close</code> event <a href="#closeWebSocket">as
 described below</a>.

</li>

</ol><hr>The <dfn id="dom-websocket-url" title="dom-WebSocket-url"><code>url</code></dfn> attribute must return the result of
 resolving the URL that was passed to the
 constructor, with the URL character encoding set to UTF-8. (It doesn't matter what it is resolved
 relative to, since we already know it is an absolute URL.)

The <dfn id="dom-websocket-readystate" title="dom-WebSocket-readyState"><code>readyState</code></dfn> attribute represents
 the state of the connection. It can have the following values:

<dl><dt><dfn id="dom-websocket-connecting" title="dom-WebSocket-CONNECTING"><code>CONNECTING</code></dfn> (numeric value 0)</dt>

<dd>The connection has not yet been established.</dd>

<dt><dfn id="dom-websocket-open" title="dom-WebSocket-OPEN"><code>OPEN</code></dfn> (numeric value 1)</dt>

<dd>The WebSocket connection is established and communication is possible.</dd>

<dt><dfn id="dom-websocket-closing" title="dom-WebSocket-CLOSING"><code>CLOSING</code></dfn> (numeric value 2)</dt>

<dd>The connection is going through the closing handshake, or the <code title="dom-WebSocket-close"><a href="#dom-websocket-close">close()</a></code> method has been invoked.</dd>

<dt><dfn id="dom-websocket-closed" title="dom-WebSocket-CLOSED"><code>CLOSED</code></dfn> (numeric value 3)</dt>

<dd>The connection has been closed or could not be opened.</dd>

</dl>When the object is created its <code title="dom-WebSocket-readyState"><a href="#dom-websocket-readystate">readyState</a></code> must be
 set to <code title="dom-WebSocket-CONNECTING"><a href="#dom-websocket-connecting">CONNECTING</a></code> (0).

The <dfn id="dom-websocket-extensions" title="dom-WebSocket-extensions"><code>extensions</code></dfn> attribute must
 initially return the empty string. After the WebSocket connection is established, its value
 might change, as defined below.

The <code title="dom-WebSocket-extensions"><a href="#dom-websocket-extensions">extensions</a></code> attribute returns the
 extensions selected by the server, if any. (Currently this will only ever be the empty
 string.)

The <dfn id="dom-websocket-protocol" title="dom-WebSocket-protocol"><code>protocol</code></dfn> attribute must initially
 return the empty string. After the WebSocket connection is established, its value might
 change, as defined below.

The <code title="dom-WebSocket-protocol"><a href="#dom-websocket-protocol">protocol</a></code> attribute returns the
 subprotocol selected by the server, if any. It can be used in conjunction with the array form of
 the constructor's second argument to perform subprotocol negotiation.

The <dfn id="dom-websocket-close" title="dom-WebSocket-close"><code>close()</code></dfn> method must run the following
 steps:

<ol><li>If the method's first argument is present but is neither an integer equal to 1000 nor an
 integer in the range 3000 to 4999, throw an <code>InvalidAccessError</code> exception and abort
 these steps.</li>

<li>

If the method's second argument is present, then run these substeps:

<ol><li>Let <var title="">raw reason</var> be the method's second argument.</li>

<li>Let <var title="">Unicode reason</var> be the result of converting <var title="">raw reason</var> to a sequence of
 Unicode characters.</li>

<li>Let <var title="">reason</var> be the result of encoding <var title="">Unicode
 reason</var> as UTF-8.</li>

<li>If <var title="">reason</var> is longer than 123 bytes, then throw a
 <code>SyntaxError</code> exception and abort these steps. <a href="#refsENCODING">[ENCODING]</a></li>

</ol></li>

<li>Run the first matching steps from the following list:

<dl class="switch"><dt>If the <code title="dom-WebSocket-readyState"><a href="#dom-websocket-readystate">readyState</a></code> attribute is in the <code title="dom-WebSocket-CLOSING"><a href="#dom-websocket-closing">CLOSING</a></code> (2) or <code title="dom-WebSocket-CLOSED"><a href="#dom-websocket-closed">CLOSED</a></code> (3) state</dt>

<dd>

Do nothing.

The connection is already closing or is already closed. If it has not already,
 a <code title="event-close">close</code> event will eventually fire <a href="#closeWebSocket">as described below</a>.

</dd>

<dt>If the WebSocket connection is not yet established <a href="#refsWSP">[WSP]</a></dt>

<dd>

Fail the WebSocket connection and set the <code title="dom-WebSocket-readyState"><a href="#dom-websocket-readystate">readyState</a></code> attribute's value to <code title="dom-WebSocket-CLOSING"><a href="#dom-websocket-closing">CLOSING</a></code> (2). <a href="#refsWSP">[WSP]</a>

The fail the WebSocket connection algorithm invokes the close the
 WebSocket connection algorithm, which then establishes that the WebSocket connection is
 closed, which fires the <code title="event-close">close</code> event <a href="#closeWebSocket">as described below</a>.

</dd>

<dt>If the WebSocket closing handshake has not yet been started <a href="#refsWSP">[WSP]</a></dt>

<dd>

Start the WebSocket closing handshake and set the <code title="dom-WebSocket-readyState"><a href="#dom-websocket-readystate">readyState</a></code> attribute's value to <code title="dom-WebSocket-CLOSING"><a href="#dom-websocket-closing">CLOSING</a></code> (2). <a href="#refsWSP">[WSP]</a>

If the first argument is present, then the status code to use in the
 WebSocket Close message must be the integer given by the first argument. <a href="#refsWSP">[WSP]</a>

If the second argument is also present, then <var title="">reason</var> must be provided in
 the Close message after the status code. <a href="#refsENCODING">[ENCODING]</a>
 <a href="#refsWSP">[WSP]</a>

The start the WebSocket closing handshake algorithm eventually invokes
 the close the WebSocket connection algorithm, which then establishes that the
 WebSocket connection is closed, which fires the <code title="event-close">close</code> event <a href="#closeWebSocket">as described
 below</a>.

</dd>

<dt>Otherwise</dt>

<dd>

Set the <code title="dom-WebSocket-readyState"><a href="#dom-websocket-readystate">readyState</a></code> attribute's value to <code title="dom-WebSocket-CLOSING"><a href="#dom-websocket-closing">CLOSING</a></code> (2).

The WebSocket closing handshake is started, and will eventually invoke
 the close the WebSocket connection algorithm, which will establish that the
 WebSocket connection is closed, and thus the <code title="event-close">close</code>
 event will fire, <a href="#closeWebSocket">as described below</a>.

</dd>

</dl></li>

</ol>The <code title="dom-WebSocket-close"><a href="#dom-websocket-close">close()</a></code> method does not discard
 previously sent messages before starting the WebSocket closing handshake &mdash; even if, in
 practice, the user agent is still busy sending those messages, the handshake will only start after
 the messages are sent.

<hr>The <dfn id="dom-websocket-bufferedamount" title="dom-WebSocket-bufferedAmount"><code>bufferedAmount</code></dfn> attribute must
 return the number of bytes of application data (UTF-8 text and binary data) that have been queued
 using <code title="dom-WebSocket-send"><a href="#dom-websocket-send">send()</a></code> but that, as of the last time the
 event loop reached step 1, had not yet been transmitted to the network. (This thus
 includes any text sent during the execution of the current task, regardless of whether the user
 agent is able to transmit text asynchronously with script execution.) This does not include
 framing overhead incurred by the protocol, or buffering done by the operating system or network
 hardware. If the connection is closed, this attribute's value will only increase with each call to
 the <code title="dom-WebSocket-send"><a href="#dom-websocket-send">send()</a></code> method (the number does not reset to zero once
 the connection closes).

In this simple example, the <code title="dom-WebSocket-bufferedAmount"><a href="#dom-websocket-bufferedamount">bufferedAmount</a></code>
 attribute is used to ensure that updates are sent either at the rate of one update every 50ms, if
 the network can handle that rate, or at whatever rate the network can handle, if that is
 too fast.

The <code title="dom-WebSocket-bufferedAmount"><a href="#dom-websocket-bufferedamount">bufferedAmount</a></code> attribute can also be
 used to saturate the network without sending the data at a higher rate than the network can
 handle, though this requires more careful monitoring of the value of the attribute over time.

</div>

This attribute allows authors to control how binary data is exposed to scripts. By
 setting the attribute to "<code title="">blob</code>", binary data is returned in
 <code>Blob</code> form; by setting it to "<code title="">arraybuffer</code>", it is returned in
 <code>ArrayBuffer</code> form. User agents can use this as a hint for how to handle incoming
 binary data: if the attribute is set to "<code title="">blob</code>", it is safe to spool it to
 disk, and if it is set to "<code title="">arraybuffer</code>", it is likely more efficient to
 keep the data in memory. Naturally, user agents are encouraged to use more subtle heuristics to
 decide whether to keep incoming data in memory or not, e.g. based on how big the data is or how
 common it is for a script to change the attribute at the last minute. This latter aspect is
 important in particular because it is quite possible for the attribute to be changed after the
 user agent has received the data but before the user agent has fired the event for it.

The <dfn id="dom-websocket-send" title="dom-WebSocket-send"><code>send(<var title="">data</var>)</code></dfn> method
 transmits data using the connection. If the <code title="dom-WebSocket-readyState"><a href="#dom-websocket-readystate">readyState</a></code> attribute is <code title="dom-WebSocket-CONNECTING"><a href="#dom-websocket-connecting">CONNECTING</a></code>, it must throw an
 <code>InvalidStateError</code> exception. Otherwise, the user agent must run the appropriate set
 of steps from the following list:

<dl><dt>If the argument is a string</dt>

<dd>

Let <var title="">data</var> be the result of converting the <var title="">data</var> argument to a sequence
 of Unicode characters. If the WebSocket connection is established and the WebSocket closing handshake has not yet
 started, then the user agent must send a WebSocket Message comprised of <var title="">data</var> using a text frame opcode; if the data cannot be sent, e.g. because it
 would need to be buffered but the buffer is full, the user agent must <a href="#concept-websocket-close-fail" title="concept-websocket-close-fail">flag the WebSocket as full</a> and then close the
 WebSocket connection. Any invocation of this method with a string argument that does not
 throw an exception must increase the <code title="dom-WebSocket-bufferedAmount"><a href="#dom-websocket-bufferedamount">bufferedAmount</a></code> attribute by the number of bytes
 needed to express the argument as UTF-8. <a href="#refsUNICODE">[UNICODE]</a> <a href="#refsENCODING">[ENCODING]</a> <a href="#refsWSP">[WSP]</a>

</dd>

<dt>If the argument is a <code>Blob</code> object</dt>

<dd>

If the WebSocket connection is established, and the WebSocket closing handshake has not yet started, then the user
 agent must send a WebSocket Message comprised of <var title="">data</var> using a binary
 frame opcode; if the data cannot be sent, e.g. because it would need to be buffered but the
 buffer is full, the user agent must <a href="#concept-websocket-close-fail" title="concept-websocket-close-fail">flag the
 WebSocket as full</a> and then close the WebSocket connection. The data to be sent is
 the raw data represented by the <code>Blob</code> object. Any invocation of this method with a
 <code>Blob</code> argument that does not throw an exception must increase the <code title="dom-WebSocket-bufferedAmount"><a href="#dom-websocket-bufferedamount">bufferedAmount</a></code> attribute by the size of the
 <code>Blob</code> object's raw data, in bytes. <a href="#refsWSP">[WSP]</a> <a href="#refsFILEAPI">[FILEAPI]</a>

</dd>

<dt>If the argument is an <code>ArrayBuffer</code> object</dt>

<dd>

If the WebSocket connection is established, and the WebSocket closing handshake has not yet started, then the user
 agent must send a WebSocket Message comprised of <var title="">data</var> using a binary
 frame opcode; if the data cannot be sent, e.g. because it would need to be buffered but the
 buffer is full, the user agent must <a href="#concept-websocket-close-fail" title="concept-websocket-close-fail">flag the
 WebSocket as full</a> and then close the WebSocket connection. The data to be sent is
 the data stored in the buffer described by the <code>ArrayBuffer</code> object. Any invocation
 of this method with an <code>ArrayBuffer</code> argument that does not throw an exception must
 increase the <code title="dom-WebSocket-bufferedAmount"><a href="#dom-websocket-bufferedamount">bufferedAmount</a></code> attribute by the
 length of the <code>ArrayBuffer</code> in bytes. <a href="#refsWSP">[WSP]</a> <a href="#refsECMA262">[ECMA262]</a>

</dd>

<dt>If the argument is an object that matches the <code>ArrayBufferView</code> type definition</dt>

<dd>

If the WebSocket connection is established, and the WebSocket closing handshake has not yet started, then the user
 agent must send a WebSocket Message comprised of <var title="">data</var> using a binary
 frame opcode; if the data cannot be sent, e.g. because it would need to be buffered but the
 buffer is full, the user agent must <a href="#concept-websocket-close-fail" title="concept-websocket-close-fail">flag the
 WebSocket as full</a> and then close the WebSocket connection. The data to be sent is
 the data stored in the section of the buffer described by the <code>ArrayBuffer</code> object
 that <var title="">data</var> references. Any invocation of this method with this kind of
 argument that does not throw an exception must increase the <code title="dom-WebSocket-bufferedAmount"><a href="#dom-websocket-bufferedamount">bufferedAmount</a></code> attribute by the length of <var title="">data</var>'s buffer in bytes. <a href="#refsWSP">[WSP]</a> <a href="#refsECMA262">[ECMA262]</a>

</dd>

</dl><hr>The following are the event handlers (and their corresponding event handler event types) that must be supported, as event
 handler IDL attributes, by all objects implementing the <code><a href="#websocket">WebSocket</a></code>
 interface:

<table><thead><tr><th>Event handler <th>Event handler event type
 <tbody><tr><td><dfn id="handler-websocket-onopen" title="handler-WebSocket-onopen"><code>onopen</code></dfn> <td> <code title="event-open">open</code>
 <tr><td><dfn id="handler-websocket-onmessage" title="handler-WebSocket-onmessage"><code>onmessage</code></dfn> <td> <code title="event-message">message</code>
 <tr><td><dfn id="handler-websocket-onerror" title="handler-WebSocket-onerror"><code>onerror</code></dfn> <td> <code title="event-error">error</code>
 <tr><td><dfn id="handler-websocket-onclose" title="handler-WebSocket-onclose"><code>onclose</code></dfn> <td> <code title="event-close">close</code>
 </table><h2 id="feedback-from-the-protocol">5 Feedback from the protocol</h2>

When the WebSocket connection is established, the user agent must queue a
 task to run these steps:

<ol><li>If the <code><a href="#websocket">WebSocket</a></code> object's <a href="#client-specified-protocols">client-specified protocols</a> was not an
 empty list, but the subprotocol in use is the null value, then fail the WebSocket
 connection, set the <code title="dom-WebSocket-readyState"><a href="#dom-websocket-readystate">readyState</a></code> attribute's
 value to <code title="dom-WebSocket-CLOSING"><a href="#dom-websocket-closing">CLOSING</a></code> (2), and abort these steps. <a href="#refsWSP">[WSP]</a></li>

<li>Change the <code title="dom-WebSocket-readyState"><a href="#dom-websocket-readystate">readyState</a></code> attribute's value to
 <code title="dom-WebSocket-OPEN"><a href="#dom-websocket-open">OPEN</a></code> (1).</li>

<li>Change the <code title="dom-WebSocket-extensions"><a href="#dom-websocket-extensions">extensions</a></code> attribute's value to
 the extensions in use, if is not the null value. <a href="#refsWSP">[WSP]</a></li>

<li>Change the <code title="dom-WebSocket-protocol"><a href="#dom-websocket-protocol">protocol</a></code> attribute's value to the
 subprotocol in use, if is not the null value. <a href="#refsWSP">[WSP]</a></li>

<li>Act as if the user agent had received a
 set-cookie-string consisting of the cookies set during the server's opening
 handshake, for the URL <var title="">url</var> given to the <code title="dom-WebSocket"><a href="#dom-websocket">WebSocket()</a></code> constructor. <a href="#refsCOOKIES">[COOKIES]</a> <a href="#refsENCODING">[ENCODING]</a> <a href="#refsWSP">[WSP]</a></li>

<li>Fire a simple event named <code title="event-open">open</code> at the
 <code><a href="#websocket">WebSocket</a></code> object.

</ol><hr>When a WebSocket message has been received with type <var title="">type</var> and data
 <var title="">data</var>, the user agent must queue a task to follow these steps: <a href="#refsWSP">[WSP]</a>

If the <code title="dom-WebSocket-readyState"><a href="#dom-websocket-readystate">readyState</a></code> attribute's value is not
 <code title="dom-WebSocket-OPEN"><a href="#dom-websocket-open">OPEN</a></code> (1), then abort these steps.

</li>

<li>

Let <var title="">event</var> be a newly created trusted event that uses the <code>MessageEvent</code>
 interface, with the event type <code title="event-message">message</code>, which does not
 bubble, is not cancelable, and has no default action.
 
 <a href="#refsHTML">[HTML]</a>

</li>

<li>Initialise <var title="">event</var>'s <code title="dom-MessageEvent-origin">origin</code>
 attribute to the Unicode serialization of
 the origin of the URL that was passed to the <code><a href="#websocket">WebSocket</a></code>
 object's constructor.</li>

<li>

If <var title="">type</var> indicates that the data is Text, then initialise <var title="">event</var>'s <code title="dom-MessageEvent-data">data</code> attribute to <var title="">data</var>.

If <var title="">type</var> indicates that the data is Binary, and <code title="dom-WebSocket-binaryType"><a href="#dom-websocket-binarytype">binaryType</a></code> is set to "<code title="">blob</code>", then
 initialise <var title="">event</var>'s <code title="dom-MessageEvent-data">data</code> attribute
 to a new <code>Blob</code> object that represents <var title="">data</var> as its raw data. <a href="#refsFILEAPI">[FILEAPI]</a>

If <var title="">type</var> indicates that the data is Binary, and <code title="dom-WebSocket-binaryType"><a href="#dom-websocket-binarytype">binaryType</a></code> is set to "<code title="">arraybuffer</code>", then initialise <var title="">event</var>'s <code title="dom-MessageEvent-data">data</code> attribute to a new <code>ArrayBuffer</code>
 object whose contents are <var title="">data</var>. <a href="#refsECMA262">[ECMA262]</a>

</li>

<li>

Dispatch <var title="">event</var> at the
 <code><a href="#websocket">WebSocket</a></code> object.

</li>

</ol>User agents are encouraged to check if they can perform the above steps
 efficiently before they run the task, picking tasks from other task
 queues while they prepare the buffers if not. For example, if the <code title="dom-WebSocket-binaryType"><a href="#dom-websocket-binarytype">binaryType</a></code> attribute was set to "<code title="">blob</code>" when the data arrived, and the user agent spooled all the data to disk, but
 just before running the above task for this particular message
 the script switched <code title="dom-WebSocket-binaryType"><a href="#dom-websocket-binarytype">binaryType</a></code> to "<code title="">arraybuffer</code>", the user agent would want to page the data back to RAM before
 running this task so as to avoid stalling the main thread while
 it created the <code>ArrayBuffer</code> object.

Here is an example of how to define a handler for the <code title="event-message">message</code> event in the case of text frames:

<pre>mysocket.onmessage = function (event) {
 if (event.data == 'on') {
 turnLampOn();
 } else if (event.data == 'off') {
 turnLampOff();
 }
};</pre>

The protocol here is a trivial one, with the server just sending "on" or "off" messages.

</div>

<hr>When the WebSocket closing handshake is started, the user agent must queue a
 task to change the <code title="dom-WebSocket-readyState"><a href="#dom-websocket-readystate">readyState</a></code> attribute's
 value to <code title="dom-WebSocket-CLOSING"><a href="#dom-websocket-closing">CLOSING</a></code> (2). (If the <code title="dom-WebSocket-close"><a href="#dom-websocket-close">close()</a></code> method was called, the <code title="dom-WebSocket-readyState"><a href="#dom-websocket-readystate">readyState</a></code> attribute's value will already be set to <code title="dom-WebSocket-CLOSING"><a href="#dom-websocket-closing">CLOSING</a></code> (2) when this task runs.) <a href="#refsWSP">[WSP]</a>

<hr>When the WebSocket connection is closed, possibly cleanly, the user agent must queue a task to run the following
 substeps:

<ol><li>Change the <code title="dom-WebSocket-readyState"><a href="#dom-websocket-readystate">readyState</a></code> attribute's value to
 <code title="dom-WebSocket-CLOSED"><a href="#dom-websocket-closed">CLOSED</a></code> (3).</li>

<li>If the user agent was required to fail the WebSocket connection, or if the the WebSocket connection was closed after being
 <dfn id="concept-websocket-close-fail" title="concept-websocket-close-fail">flagged as full</dfn>, fire a simple
 event named <code title="">error</code> at the <code><a href="#websocket">WebSocket</a></code> object. <a href="#refsWSP">[WSP]</a></li>

<li>Create a trusted event that uses the
 <code><a href="#closeevent">CloseEvent</a></code> interface, with the event type <code title="event-close">close</code>,
 which does not bubble, is not cancelable, has no default action, whose <code title="dom-CloseEvent-wasClean"><a href="#dom-closeevent-wasclean">wasClean</a></code> attribute is initialised to true if the
 connection closed cleanly and false otherwise, whose <code title="dom-CloseEvent-code"><a href="#dom-closeevent-code">code</a></code> attribute is initialised to the WebSocket connection
 close code, and whose <code title="dom-CloseEvent-reason"><a href="#dom-closeevent-reason">reason</a></code> attribute is
 initialised to the result of applying the UTF-8 decoder to the WebSocket
 connection close reason, and dispatch the event
 at the <code><a href="#websocket">WebSocket</a></code> object. <a href="#refsWSP">[WSP]</a></li>

</ol><div class="warning">

User agents must not convey any failure information to scripts in a way that would allow a
 script to distinguish the following situations:

<ul><li>A server whose host name could not be resolved.

<li>A server to which packets could not successfully be routed.

<li>A server that refused the connection on the specified port.

<li>A server that failed to correctly perform a TLS handshake (e.g., the server certificate
 can't be verified).

<li>A server that did not complete the opening handshake (e.g. because it was not a WebSocket
 server).

<li>A WebSocket server that sent a correct opening handshake, but that specified options that
 caused the client to drop the connection (e.g. the server specified a subprotocol that the
 client did not offer).

<li>A WebSocket server that abruptly closed the connection after successfully completing the
 opening handshake.

</ul>In all of these cases, the the WebSocket connection close code would be 1006, as
 required by the WebSocket Protocol specification. <a href="#refsWSP">[WSP]</a>

Allowing a script to distinguish these cases would allow a script to probe the user's local
 network in preparation for an attack.

In particular, this means the code 1015 is not used by the user agent (unless the
 server erroneously uses it in its close frame, of course).

</div>

<hr>The task source for all tasks queued in this section is the <dfn id="websocket-task-source">WebSocket task source</dfn>.

<h2 id="ping-and-pong-frames">6 Ping and Pong frames</h2>

The WebSocket protocol specification defines Ping and Pong frames that can be used for
 keep-alive, heart-beats, network status probing, latency instrumentation, and so forth. These are
 not currently exposed in the API.

User agents may send ping and unsolicited pong frames as desired, for example in an attempt to
 maintain local network NAT mappings, to detect failed connections, or to display latency metrics
 to the user. User agents must not use pings or unsolicited pongs to aid the server; it is assumed
 that servers will solicit pongs whenever appropriate for the server's needs.

<h2 id="parsing-websocket-urls">7 Parsing WebSocket URLs</h2>

The steps to <dfn id="parse-a-websocket-url-s-components">parse a WebSocket URL's components</dfn> from a string <var title="">url</var> are as follows. These steps return either a <var title="">host</var>, a <var title="">port</var>, a <var title="">resource name</var>, and a <var title="">secure</var> flag,
 or they fail.

<ol><li>If the <var title="">url</var> string is not an absolute URL, then fail this
 algorithm.</li>

<li>

Resolve the <var title="">url</var> string, with the URL
 character encoding set to UTF-8. <a href="#refsENCODING">[ENCODING]</a>

It doesn't matter what it is resolved relative to, since we already know it is
 an absolute URL at this point.

</li>

<li>If the resulting parsed URL does not have a scheme component whose value is either "<code title="">ws</code>" or "<code title="">wss</code>", then fail this algorithm.</li>

<li>If the resulting parsed URL has a non-null fragment component, then fail this algorithm.</li>

<li>If the scheme component of the resulting
 parsed URL is "<code title="">ws</code>", set <var title="">secure</var> to false;
 otherwise, the scheme component is "<code title="">wss</code>", set <var title="">secure</var> to true.</li>

<li>Let <var title="">host</var> be the value of the resulting parsed URL's host component.</li>

<li>If the resulting parsed URL has a port
 component that is not the empty string, then let <var title="">port</var> be that component's
 value; otherwise, there is no explicit <var title="">port</var>.</li>

<li>If there is no explicit <var title="">port</var>, then: if <var title="">secure</var> is
 false, let <var title="">port</var> be 80, otherwise let <var title="">port</var> be
 443.</li>

<li>Let <var title="">resource name</var> be the value of the resulting parsed
 URL's path component (which might be
 empty).</li>

<li>If <var title="">resource name</var> is the empty string, set it to a single character
 U+002F SOLIDUS (/).</li>

<li>If the resulting parsed URL has a non-null query component, then append a single U+003F QUESTION MARK
 character (?) to <var title="">resource name</var>, followed by the value of the query component.</li>

<li>Return <var title="">host</var>, <var title="">port</var>, <var title="">resource
 name</var>, and <var title="">secure</var>.</li>

</ol><h2 id="the-closeevent-interfaces">8 The <code><a href="#closeevent">CloseEvent</a></code> interfaces</h2>

<pre class="idl">[Constructor(DOMString type, optional <a href="#closeeventinit">CloseEventInit</a> eventInitDict), Exposed=Window,Worker]
interface <dfn id="closeevent">CloseEvent</dfn> : Event {
 readonly attribute boolean <a href="#dom-closeevent-wasclean" title="dom-CloseEvent-wasClean">wasClean</a>;
 readonly attribute unsigned short <a href="#dom-closeevent-code" title="dom-CloseEvent-code">code</a>;
 readonly attribute DOMString <a href="#dom-closeevent-reason" title="dom-CloseEvent-reason">reason</a>;
};

dictionary <dfn id="closeeventinit">CloseEventInit</dfn> : EventInit {
 boolean wasClean;
 unsigned short code;
 DOMString reason;
};</pre>

The <dfn id="dom-closeevent-wasclean" title="dom-CloseEvent-wasClean"><code>wasClean</code></dfn> attribute must return the
 value it was initialised to. When the object is created, this attribute must be initialised to
 false. It represents whether the connection closed cleanly or not.

The <dfn id="dom-closeevent-code" title="dom-CloseEvent-code"><code>code</code></dfn> attribute must return the value it
 was initialised to. When the object is created, this attribute must be initialised to zero. It
 represents the WebSocket connection close code provided by the server.

The <dfn id="dom-closeevent-reason" title="dom-CloseEvent-reason"><code>reason</code></dfn> attribute must return the
 value it was initialised to. When the object is created, this attribute must be initialised to
 empty string. It represents the WebSocket connection close reason provided by the server.

<h2 id="garbage-collection">9 Garbage collection</h2>

A <code><a href="#websocket">WebSocket</a></code> object whose <code title="dom-WebSocket-readyState"><a href="#dom-websocket-readystate">readyState</a></code>
 attribute's value was set to <code title="dom-WebSocket-CONNECTING"><a href="#dom-websocket-connecting">CONNECTING</a></code> (0) as of
 the last time the event loop reached step 1 must not be garbage collected if
 there are any event listeners registered for <code title="event-open">open</code> events, <code title="event-message">message</code> events, <code title="event-error">error</code> events, or
 <code title="event-close">close</code> events.

A <code><a href="#websocket">WebSocket</a></code> object whose <code title="dom-WebSocket-readyState"><a href="#dom-websocket-readystate">readyState</a></code>
 attribute's value was set to <code title="dom-WebSocket-OPEN"><a href="#dom-websocket-open">OPEN</a></code> (1) as of the last time
 the event loop reached step 1 must not be garbage collected if there are any event
 listeners registered for <code title="event-message">message</code> events, <code title="event-error">error</code>, or <code title="event-close">close</code> events.

A <code><a href="#websocket">WebSocket</a></code> object with an
 established connection that has data queued to be transmitted to the network must not be
 garbage collected. <a href="#refsWSP">[WSP]</a>

If a <code><a href="#websocket">WebSocket</a></code> object is garbage collected while its connection is still open, the
 user agent must start the WebSocket closing handshake, with no status code
 for the Close message. <a href="#refsWSP">[WSP]</a>

<hr>If a user agent is to <dfn id="make-disappear">make disappear</dfn> a <code><a href="#websocket">WebSocket</a></code> object (this happens
 when a <code>Document</code> object goes away), the user agent must follow the first appropriate
 set of steps from the following list:

<dl class="switch"><dt>If the WebSocket connection is not yet established <a href="#refsWSP">[WSP]</a></dt>

<dd>

Fail the WebSocket connection. <a href="#refsWSP">[WSP]</a>

</dd>

<dt>If the WebSocket closing handshake has not yet been started <a href="#refsWSP">[WSP]</a></dt>

<dd>

Start the WebSocket closing handshake, with the status code to use in
 the WebSocket Close message being 1001. <a href="#refsWSP">[WSP]</a>

</dd>

<dt>Otherwise</dt>

<dd>

Do nothing.

</dd>

</dl><h2 class="no-num" id="references">References</h2>

All references are normative unless marked "Non-normative".

<dl><dt id="refsCOOKIES">[COOKIES]</dt>
 <dd><cite><a href="http://tools.ietf.org/html/rfc6265">HTTP State Management Mechanism</a></cite>, A. Barth. IETF.</dd>

<dt id="refsDOM">[DOM]</dt>
 <dd><cite><a href="http://dom.spec.whatwg.org/">DOM</a></cite>, A. van Kesteren, A. Gregor, Ms2ger. WHATWG.</dd>

<dt id="refsECMA262">[ECMA262]</dt>
 <dd><cite><a href="http://people.mozilla.org/~jorendorff/es6-draft.html">ECMAScript Language Specification</a></cite>. ECMA.</dd>

<dt id="refsENCODING">[ENCODING]</dt>
 <dd><cite><a href="http://encoding.spec.whatwg.org/">Encoding</a></cite>, A. van Kesteren, J. Bell. WHATWG.</dd>

<dt id="refsFILEAPI">[FILEAPI]</dt>
 <dd><cite><a href="http://dev.w3.org/2006/webapi/FileUpload/publish/FileAPI.html">File API</a></cite>, A. Ranganathan. W3C.</dd>

<dt id="refsHTML">[HTML]</dt>
 <dd><cite><a href="//www.whatwg.org/specs/web-apps/current-work/">HTML</a></cite>, I. Hickson. WHATWG.</dd>

<dt id="refsRFC2119">[RFC2119]</dt>
 <dd><cite><a href="http://tools.ietf.org/html/rfc2119">Key words for use in RFCs to Indicate Requirement Levels</a></cite>, S. Bradner. IETF.</dd>

<dt id="refsUNICODE">[UNICODE]</dt>
 <dd><cite><a href="http://www.unicode.org/versions/">The Unicode Standard</a></cite>. Unicode Consortium.</dd>

<dt id="refsWEBIDL">[WEBIDL]</dt>
 <dd><cite><a href="http://dev.w3.org/2006/webapi/WebIDL/">Web IDL</a></cite>, C. McCormack. W3C.</dd>

<dt id="refsWSP">[WSP]</dt>
 <dd><cite><a href="http://tools.ietf.org/html/rfc6455">The WebSocket protocol</a></cite>, I. Fette, A. Melnikov. IETF.</dd>

</dl><h2 class="no-num" id="acknowledgements">Acknowledgements</h2>

For a full list of acknowledgements, please see the <a href="http://whatwg.org/html">WHATWG HTML standard</a>.