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

Web Consortium">W3C</abbr></a><sup>®</sup> (<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.</p>

<p class="alt">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.</p>

</div>

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

<p>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.</p>

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

<p><em>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/.</em></p>

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

<p>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:</p>

<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"><p><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"><p><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

<em>what</em> the problem you're trying to solve is. That's more

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

<p class="note">Please don't use section numbers as these tend to

change rapidly and make your feedback harder to understand.</p>

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><p>

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

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

</p>

</fieldset></form>

<p>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.</p>

<p>Implementors should be aware that this specification is not

stable. <strong>Implementors who are not taking part in the

discussions are likely to find the specification changing out from

under them in incompatible ways.</strong> 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.</p>

</div>

<p>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>.</p>

<p>Notifications of changes to this specification are sent along

with notifications of changes to related specifications using the

following mechanisms:</p>

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

<p>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>.

</p>

<p>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.</p>

<p>This specification is being developed in conjunction with an

RFC for a wire protocol, the WebSocket Protocol,

available from the following location:</p>

<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><p>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>.</p>

<p>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>.</p>

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

<p>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"><span class="secno">1 </span>Introduction</a></li>

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

<ol>

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

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

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

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

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

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

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

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

<li><a href="#garbage-collection"><span class="secno">9 </span>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"><span class="secno">1 </span>Introduction</h2>

<p><i>This section is non-normative.</i></p>

<p>To enable Web applications to maintain bidirectional

<p>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.</p>

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

<p class="note">This interface does not allow for raw access to the

<p class="note">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.</p>

server.</p>

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

<p>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.</p>

<p>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></p>

<p>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.</p>

<p>Some conformance requirements are phrased as requirements on

attributes, methods or objects. Such requirements are to be

interpreted as requirements on user agents.</p>

<p>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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  <div class="head" id="head">
   <p><a href="http://www.w3.org/"><img alt="W3C" height="48" src="http://www.w3.org/Icons/w3c_home" width="72"></a></p>

   <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>
<!-- :ZZZ -->
    <dt>Editor:</dt>
    <dd><a href="mailto:ian@hixie.ch">Ian Hickson</a>, Google, Inc.</dd>
   </dl><p class="copyright"><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><sup>&reg;</sup> (<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.</p>


   <!-- UNDER NO CIRCUMSTANCES IS THE FOLLOWING PARAGRAPH TO BE REMOVED OR EDITED WITHOUT TALKING TO IAN FIRST -->
   <p class="alt">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.</p>
   <!-- UNDER NO CIRCUMSTANCES IS THE PRECEDING PARAGRAPH TO BE REMOVED OR EDITED WITHOUT TALKING TO IAN FIRST -->


  </div>

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

  <p>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.</p>

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

  
  

  <p><em>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 <!-- DO NOT CHANGE THIS BACK TO THE STANDARD BOILERPLATE, AS IT IS INACCURATE -->

  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/.</em></p>


  

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  following mechanisms:</p>
  <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>

  <p>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>.
  </p>

<p>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.</p>

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

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

  <p>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>.</p>

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

<p>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"><span class="secno">1 </span>Introduction</a></li>
 <li><a href="#conformance-requirements"><span class="secno">2 </span>Conformance requirements</a>
  <ol>
   <li><a href="#dependencies"><span class="secno">2.1 </span>Dependencies</a></ol></li>
 <li><a href="#terminology"><span class="secno">3 </span>Terminology</a></li>
 <li><a href="#the-websocket-interface"><span class="secno">4 </span>The <code>WebSocket</code> interface</a></li>
 <li><a href="#feedback-from-the-protocol"><span class="secno">5 </span>Feedback from the protocol</a></li>
 <li><a href="#ping-and-pong-frames"><span class="secno">6 </span>Ping and Pong frames</a></li>
 <li><a href="#parsing-websocket-urls"><span class="secno">7 </span>Parsing WebSocket URLs</a></li>
 <li><a href="#event-definitions"><span class="secno">8 </span>Event definitions</a></li>
 <li><a href="#garbage-collection"><span class="secno">9 </span>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"><span class="secno">1 </span>Introduction</h2>

  <p><i>This section is non-normative.</i></p>

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

  <p class="note">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.</p>


  

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

  <p>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.</p>

  <p>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></p>

  <p>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.</p>

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

  <p>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.)</p>

  <p>The only conformance class defined by this specification is user
  agents.</p>

  <p>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.</p>

  <p>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.</p>


  <h3 id="dependencies"><span class="secno">2.1 </span>Dependencies</h3>

  <p>This specification relies on several other underlying
  specifications.</p>

  <dl><dt>HTML</dt>

   <dd>

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

   </dd>

   <dt>WebIDL</dt>

   <dd>

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

   </dd>

  </dl><h2 id="terminology"><span class="secno">3 </span>Terminology</h2>

  <p>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>".</p>

  <p>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></p>

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



  <h2 id="the-websocket-interface"><span class="secno">4 </span>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>(<span>ArrayBuffer</span> data);
  void <a href="#dom-websocket-send" title="dom-WebSocket-send">send</a>(<span>ArrayBufferView</span> data);
};</pre>

  <p>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></p>

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

  <ol><li><p><i><a href="#parse-a-websocket-url-s-components">Parse a WebSocket URL's components</a></i> 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><p>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>

    <p>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.)</p>

    

    <p>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.</p>
    

   </li>

   <li>

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

    <p>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.</p>

   </li>

   <li><p>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><p>Let <var title="">origin</var> be the <span title="ASCII
   serialization of an origin">ASCII serialization</span> 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><p>Return a new <code><a href="#websocket">WebSocket</a></code> object, and continue
   these steps in the background (without blocking scripts).</li>

   <li>

    <p><i>Establish a WebSocket connection</i> 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 <i>headers to send
    appropriate cookies</i> must be a <code title="http-Cookie">Cookie</code> header whose value is the
    <i>cookie-string</i> computed from the user's cookie store and the
    URL <var title="">url</var>; for these purposes this is
    <em>not</em> a "non-HTTP" API. <a href="#refsWSP">[WSP]</a> <a href="#refsCOOKIES">[COOKIES]</a></p>

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

    <p class="warning">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.</p>
    

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

   </li>

  </ol><p>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.</p>

  <hr><p>The <dfn id="dom-websocket-url" title="dom-WebSocket-url"><code>url</code></dfn>
  attribute must return the result of <span title="resolve a
  url">resolving</span> 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>.)</p>

  <p>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:</p>

  <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><i>The WebSocket connection is established</i> 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><p>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).</p>

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

  <p class="note">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.)</p>

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

  <p class="note">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.</p>

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

  <ol><li><p>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>

    <p>If the method's second argument is present, then run these
    substeps:</p>

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

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

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

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

    <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>

      <p>Do nothing.</p>

      <p class="note">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>.</p>

     </dd>


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

     <dd>

      <p><i>Fail the WebSocket connection</i> 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></p>

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

     </dd>


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

     <dd>

      <p><i>Start the WebSocket closing handshake</i> 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></p>

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

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

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

     </dd>


     <dt>Otherwise</dt>

     <dd>

      <p>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).</p>

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

     </dd>

    </dl></li>

  </ol><hr><p>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 <span title="concept-task">task</span>, 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).</p>

  <div class="example">

   <p>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 <em>can</em> handle, if that is too
   fast.</p>

   <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>

   <p>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.</p>

  </div>

  <hr><p>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.</p>

  <p class="note">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.</p>

  <p>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:</p>

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

   <dd>

    <p>Let <var title="">data</var> be the result of <span title="convert a DOMString to a sequence of Unicode
    characters">converting the <var title="">data</var> argument to a
    sequence of Unicode characters</span>. If <i>the WebSocket
    connection is established</i> and <i title="the WebSocket closing
    handshake is started">the WebSocket closing handshake has not yet
    started</i>, then the user agent must <i>send a WebSocket
    Message</i> 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
    <i>close the WebSocket connection</i> <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></p>

   </dd>


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

   <dd>

    <p>If <i>the WebSocket connection is established</i>, and <i title="the WebSocket closing handshake is started">the WebSocket
    closing handshake has not yet started</i>, then the user agent
    must <i>send a WebSocket Message</i> 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 <i>close the WebSocket
    connection</i> <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></p>

   </dd>


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

   <dd>

    <p>If <i>the WebSocket connection is established</i>, and <i title="the WebSocket closing handshake is started">the WebSocket
    closing handshake has not yet started</i>, then the user agent
    must <i>send a WebSocket Message</i> 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 <i>close the WebSocket
    connection</i> <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></p>

   </dd>


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

   <dd>

    <p>If <i>the WebSocket connection is established</i>, and <i title="the WebSocket closing handshake is started">the WebSocket
    closing handshake has not yet started</i>, then the user agent
    must <i>send a WebSocket Message</i> 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 <i>close the WebSocket
    connection</i> <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></p>

   </dd>

  </dl><hr><p>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:</p>

  <table><thead><tr><th><span title="event handlers">Event handler</span> <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"><span class="secno">5 </span>Feedback from the protocol</h2>

  <p>When <i>the WebSocket connection is established</i>, 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:</p>

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

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

   <li><p>Act as if the user agent had <span title="receives a
   set-cookie-string">received a set-cookie-string</span> consisting
   of the <i>cookies set during the server's opening handshake</i>,
   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><p><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.</p>

  </ol><hr><p>When <i>a WebSocket message has been received</i> 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></p>

  <ol><li>

    <p>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.</p>

   </li>

   <li>

    <p>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>
    
    </p>

   </li>

   <li><p>Initialize <var title="">event</var>'s <code title="dom-MessageEvent-origin">origin</code> attribute to the
   <span title="Unicode serialization of an origin">Unicode
   serialization</span> 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>

    <p>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>.

    <p>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></p>

    <p>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></p>

   </li>

   <li>

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

   </li>

  </ol><p class="note">User agents are encouraged to check if they can
  perform the above steps efficiently before they run the task,
  picking tasks from other <span title="task queue">task queues</span>
  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 <span title="concept-task">task</span> 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 <span title="concept-task">task</span> so as to avoid stalling the main
  thread while it created the <code>ArrayBuffer</code> object.</p>

  <div class="example">

   <p>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:</p>

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

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

  </div>

  <hr><p>When <i>the WebSocket closing handshake is started</i>, 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></p>

  <hr><p id="closeWebSocket">When <i>the WebSocket connection is
  closed</i>, possibly <i title="">cleanly</i>, 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:</p>

  <ol><li><p>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><p>If the user agent was required to <i>fail the WebSocket
   connection</i> or <i>the WebSocket connection is closed</i> <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><p>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 <i title="">cleanly</i> and false
   otherwise, whose <code title="dom-CloseEvent-code"><a href="#dom-closeevent-code">code</a></code>
   attribute is initialized to <i>the WebSocket connection close code</i>, and
   whose <code title="dom-CloseEvent-reason"><a href="#dom-closeevent-reason">reason</a></code> attribute
   is initialized to <i>the WebSocket connection close reason</i>
   <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">

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

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

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

   <p class="note">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).</p>

  </div>

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


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

  <p>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.</p>

  <p>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.</p>

  


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

  <p>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.</p>

  <ol><li><p>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>

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

    <p class="note">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.</p>

   </li>

   <li><p>If <var title="">url</var> does not have a <span title="url-scheme">&lt;scheme&gt;</span> 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><p>If <var title="">url</var> has a <span title="url-fragment">&lt;fragment&gt;</span> component, then fail
   this algorithm.</li>

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

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

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

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

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

   <li><p>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"><span class="secno">8 </span>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>

  <p>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.</p>

  <p>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.</p>

  <p>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.</p>



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

  <p>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 <span title="concept-task">task</span> 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.</p>

  <p>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 <span title="concept-task">task</span> 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.</p>

  <p>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
  <span title="concept-task">task</span> 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.</p>

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

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

  <hr><p>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:</p>

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

   <dd>

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

   </dd>


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

   <dd>

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

   </dd>


   <dt>Otherwise</dt>

   <dd>

    <p>Do nothing.</p>

   </dd>

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

  <p>All references are normative unless marked "Non-normative".</p>

  

  <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>

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

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  <div class="head" id="head">
   <p><a href="http://www.w3.org/"><img width="72" src="http://www.w3.org/Icons/w3c_home" alt="W3C" height="48"></a></p>

   <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>
<!-- :ZZZ -->
    <dt>Editor:</dt>
    <dd><a href="mailto:ian@hixie.ch">Ian Hickson</a>, Google, Inc.</dd>
   </dl><p class="copyright"><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><sup>&reg;</sup> (<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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   and <a href="http://www.w3.org/Consortium/Legal/copyright-documents">document
   use</a> rules apply.</p>


   <!-- UNDER NO CIRCUMSTANCES IS THE FOLLOWING PARAGRAPH TO BE REMOVED OR EDITED WITHOUT TALKING TO IAN FIRST -->
   <p class="alt">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.</p>
   <!-- UNDER NO CIRCUMSTANCES IS THE PRECEDING PARAGRAPH TO BE REMOVED OR EDITED WITHOUT TALKING TO IAN FIRST -->


  </div>

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

  <p>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.</p>

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

  
  

  <p><em>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 <!-- DO NOT CHANGE THIS BACK TO THE STANDARD BOILERPLATE, AS IT IS INACCURATE -->

  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/.</em></p>


  

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

  
  <p>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.</p>

  
  <p>Implementors should be aware that this specification is not
  stable. <strong>Implementors who are not taking part in the
  discussions are likely to find the specification changing out from
  under them in incompatible ways.</strong> 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.</p>

  <div id="multipage-common">
  </div>

   <p>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>.</p>

  <p>Notifications of changes to this specification are sent along
  with notifications of changes to related specifications using the
  following mechanisms:</p>
  <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><p>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 4 June 2014 Editor's Draft.
  </p>


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

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

  
  
  <p>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>.</p>


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

<ol class="toc">
 <li><a href="#network-intro"><span class="secno">1 </span>Introduction</a></li>
 <li><a href="#conformance-requirements"><span class="secno">2 </span>Conformance requirements</a>
  <ol>
   <li><a href="#dependencies"><span class="secno">2.1 </span>Dependencies</a></ol></li>
 <li><a href="#terminology"><span class="secno">3 </span>Terminology</a></li>
 <li><a href="#the-websocket-interface"><span class="secno">4 </span>The <code>WebSocket</code> interface</a></li>
 <li><a href="#feedback-from-the-protocol"><span class="secno">5 </span>Feedback from the protocol</a></li>
 <li><a href="#ping-and-pong-frames"><span class="secno">6 </span>Ping and Pong frames</a></li>
 <li><a href="#parsing-websocket-urls"><span class="secno">7 </span>Parsing WebSocket URLs</a></li>
 <li><a href="#the-closeevent-interfaces"><span class="secno">8 </span>The <code>CloseEvent</code> interfaces</a></li>
 <li><a href="#garbage-collection"><span class="secno">9 </span>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"><span class="secno">1 </span>Introduction</h2>

  <p><i>This section is non-normative.</i></p>

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

  <p class="note">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.</p>


  

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

  <p>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.</p>

  <p>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></p>

  <p>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.</p>

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

  <p>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.)</p>

  <p>The only conformance class defined by this specification is user
  agents.</p>

  <p>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.</p>

  <p>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.</p>


  <h3 id="dependencies"><span class="secno">2.1 </span>Dependencies</h3>

  <p>This specification relies on several other underlying
  specifications.</p>

  <dl><dt>HTML</dt>

   <dd>

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

   </dd>

   <dt>WebIDL</dt>

   <dd>

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

   </dd>

  </dl><h2 id="terminology"><span class="secno">3 </span>Terminology</h2>

  <p>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>".</p>

  <p>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 specifications. <a href="#refsDOM">[DOM]</a></p>

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



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

  <pre class="idl">enum <dfn id="binarytype">BinaryType</dfn> { "<span title="dom-BinaryType-blob">blob</span>", "<span title="dom-BinaryType-arraybuffer">arraybuffer</span>" };
[<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> : <span>EventTarget</span> {
  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 <span>EventHandler</span> <a href="#handler-websocket-onopen" title="handler-WebSocket-onopen">onopen</a>;
           attribute <span>EventHandler</span> <a href="#handler-websocket-onerror" title="handler-WebSocket-onerror">onerror</a>;
           attribute <span>EventHandler</span> <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 <span>EventHandler</span> <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>(<span>Blob</span> data);
  void <a href="#dom-websocket-send" title="dom-WebSocket-send">send</a>(<span>ArrayBuffer</span> data);
  void <a href="#dom-websocket-send" title="dom-WebSocket-send">send</a>(<span>ArrayBufferView</span> data);
};</pre>

  <p>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 <span>URL</span> 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></p>

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

  <ol><li><p><i><a href="#parse-a-websocket-url-s-components">Parse a WebSocket URL's components</a></i> 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><p>If <var title="">secure</var> is false but the <span>origin</span> specified by the
   <span>entry settings object</span> 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>

    <p>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.)</p>
    

    <p>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.</p>
    

   </li>

   <li>

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

    <p>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.</p>

   </li>

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

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

   <li><p>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>

    <p><i>Establish a WebSocket connection</i> 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 <i>headers to send appropriate cookies</i> must be a <code title="http-Cookie">Cookie</code> header whose value is the <i>cookie-string</i> computed from
    the user's cookie store and the URL <var title="">url</var>; for these purposes this is
    <em>not</em> a "non-HTTP" API. <a href="#refsWSP">[WSP]</a> <a href="#refsCOOKIES">[COOKIES]</a></p>

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

    <p class="warning">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.</p>
    

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

   </li>

  </ol><hr><p>The <dfn id="dom-websocket-url" title="dom-WebSocket-url"><code>url</code></dfn> attribute must return the result of
  <span title="resolve a url">resolving</span> the <span>URL</span> 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 <span>absolute URL</span>.)</p>

  <p>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:</p>

  <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><i>The WebSocket connection is established</i> 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><p>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).</p>

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

  <p class="note">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.)</p>

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

  <p class="note">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.</p>

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

  <ol><li><p>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>

    <p>If the method's second argument is present, then run these substeps:</p>

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

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

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

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

    <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>

      <p>Do nothing.</p>

      <p class="note">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>.</p>

     </dd>


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

     <dd>

      <p><i>Fail the WebSocket connection</i> 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></p>

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

     </dd>


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

     <dd>

      <p><i>Start the WebSocket closing handshake</i> 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></p>

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

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

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

     </dd>


     <dt>Otherwise</dt>

     <dd>

      <p>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).</p>

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

     </dd>

    </dl></li>

  </ol><p class="note">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.</p> 

  <hr><p>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
  <span>event loop</span> 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).</p>

  <div class="example">

   <p>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 <em>can</em> handle, if that is
   too fast.</p>

   <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>

   <p>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.</p>

  </div>

  <hr><p>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, the user agent must set the IDL attribute to the new value.</p>

  <p class="note">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.</p>

  <p>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:</p>

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

   <dd>

    <p>Let <var title="">data</var> be the result of <span title="convert a DOMString to a
    sequence of Unicode characters">converting the <var title="">data</var> argument to a sequence
    of Unicode characters</span>. If <i>the WebSocket connection is established</i> and <i title="the WebSocket closing handshake is started">the WebSocket closing handshake has not yet
    started</i>, then the user agent must <i>send a WebSocket Message</i> 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 <i>close the
    WebSocket connection</i>. 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></p>

   </dd>


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

   <dd>

    <p>If <i>the WebSocket connection is established</i>, and <i title="the WebSocket closing
    handshake is started">the WebSocket closing handshake has not yet started</i>, then the user
    agent must <i>send a WebSocket Message</i> 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 <i>close the WebSocket connection</i>. 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></p>

   </dd>


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

   <dd>

    <p>If <i>the WebSocket connection is established</i>, and <i title="the WebSocket closing
    handshake is started">the WebSocket closing handshake has not yet started</i>, then the user
    agent must <i>send a WebSocket Message</i> 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 <i>close the WebSocket connection</i>. 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></p>

   </dd>


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

   <dd>

    <p>If <i>the WebSocket connection is established</i>, and <i title="the WebSocket closing
    handshake is started">the WebSocket closing handshake has not yet started</i>, then the user
    agent must <i>send a WebSocket Message</i> 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 <i>close the WebSocket connection</i>. 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></p>

   </dd>

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

  <table><thead><tr><th><span title="event handlers">Event handler</span> <th><span>Event handler event type</span>
   <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"><span class="secno">5 </span>Feedback from the protocol</h2>

  <p>When <i>the WebSocket connection is established</i>, the user agent must <span>queue a
  task</span> to run these steps:</p>

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

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

   <li><p>Act as if the user agent had <span title="receives a set-cookie-string">received a
   set-cookie-string</span> consisting of the <i>cookies set during the server's opening
   handshake</i>, 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><p><span>Fire a simple event</span> named <code title="event-open">open</code> at the
   <code><a href="#websocket">WebSocket</a></code> object.</p>

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

  <ol><li>

    <p>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.</p>

   </li>

   <li>

    <p>Let <var title="">event</var> be a newly created <span title="concept-events-trusted">trusted</span> 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>
    
    </p>

   </li>

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

   <li>

    <p>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>.

    <p>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></p>

    <p>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></p>

   </li>

   <li>

    <p><span title="concept-event-dispatch">Dispatch</span> <var title="">event</var> at the
    <code><a href="#websocket">WebSocket</a></code> object.</p>

   </li>

  </ol><p class="note">User agents are encouraged to check if they can perform the above steps
  efficiently before they run the task, picking tasks from other <span title="task queue">task
  queues</span> 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 <span title="concept-task">task</span> 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 <span title="concept-task">task</span> so as to avoid stalling the main thread while
  it created the <code>ArrayBuffer</code> object.</p>

  <div class="example">

   <p>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:</p>

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

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

  </div>

  <hr><p>When <i>the WebSocket closing handshake is started</i>, the user agent must <span>queue a
  task</span> 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></p>

  <hr><p id="closeWebSocket">When <i>the WebSocket connection is closed</i>, possibly <i title="">cleanly</i>, the user agent must <span>queue a task</span> to run the following
  substeps:</p>

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

   <li><p>Create a <span title="concept-events-trusted">trusted</span> 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 <i title="">cleanly</i> and false otherwise, whose <code title="dom-CloseEvent-code"><a href="#dom-closeevent-code">code</a></code> attribute is initialised to <i>the WebSocket connection
   close code</i>, and whose <code title="dom-CloseEvent-reason"><a href="#dom-closeevent-reason">reason</a></code> attribute is
   initialised to the result of applying the <span>UTF-8 decoder</span> to <i>the WebSocket
   connection close reason</i>, and <span title="concept-event-dispatch">dispatch</span> the event
   at the <code><a href="#websocket">WebSocket</a></code> object. <a href="#refsWSP">[WSP]</a></li>

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

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

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

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

   <p class="note">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).</p>

  </div>

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


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

  <p>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.</p>

  <p>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.</p>

  


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

  <p>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.</p>

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

   <li>

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

    <p class="note">It doesn't matter what it is resolved relative to, since we already know it is
    an <span>absolute URL</span> at this point.</p>

   </li>

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

   <li><p>If the resulting <span>parsed URL</span> has a non-null <span title="concept-url-fragment">fragment</span> component, then fail this algorithm.</li>

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

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

   <li><p>If the resulting <span>parsed URL</span> has a <span title="concept-url-port">port</span>
   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><p>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><p>Let <var title="">resource name</var> be the value of the resulting <span>parsed
   URL</span>'s <span title="concept-url-path">path</span> component (which might be
   empty).</li> 

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

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

   <li><p>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"><span class="secno">8 </span>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> : <span>Event</span> {
  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> : <span>EventInit</span> {
  boolean wasClean;
  unsigned short code;
  DOMString reason;
};</pre>

  <p>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.</p>

  <p>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.</p>

  <p>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.</p>



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


  <p>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 <span>event loop</span> 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.</p>

  <p>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 <span>event loop</span> 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.</p>

  <p>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 <span>event loop</span> reached step 1 must not be garbage collected if there are
  any event listeners registered for <code title="event-error">error</code> or <code title="event-close">close</code> events.</p>

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

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

  <hr><p>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:</p>

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

   <dd>

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

   </dd>


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

   <dd>

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

   </dd>


   <dt>Otherwise</dt>

   <dd>

    <p>Do nothing.</p>

   </dd>

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

  <p>All references are normative unless marked "Non-normative".</p>

  

  <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>

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