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<h1 class="lined-header"><span>cowboy_websocket(3)</span></h1>
<h2 id="_name">Name</h2>
<p>cowboy_websocket - Websocket</p>
<h2 id="_description">Description</h2>
<p>The module <code>cowboy_websocket</code> implements Websocket as a Ranch protocol. It also defines a callback interface for handling Websocket connections.</p>
<h2 id="_callbacks">Callbacks</h2>
<p>Websocket handlers must implement the following callback interface:</p>
<div class="listingblock"><div class="content"><!-- Generator: GNU source-highlight 3.1.8
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><b><font color="#000000">init</font></b>(<font color="#009900">Req</font>, <font color="#009900">State</font>)
<font color="#990000">-></font> {<font color="#FF6600">cowboy_websocket</font>, <font color="#009900">Req</font>, <font color="#009900">State</font>}
| {<font color="#FF6600">cowboy_websocket</font>, <font color="#009900">Req</font>, <font color="#009900">State</font>, <font color="#009900">Opts</font>}
<b><font color="#000000">websocket_init</font></b>(<font color="#009900">State</font>) <font color="#990000">-></font> <font color="#009900">CallResult</font> <i><font color="#9A1900">%% optional</font></i>
<b><font color="#000000">websocket_handle</font></b>(<font color="#009900">InFrame</font>, <font color="#009900">State</font>) <font color="#990000">-></font> <font color="#009900">CallResult</font>
<b><font color="#000000">websocket_info</font></b>(<font color="#009900">Info</font>, <font color="#009900">State</font>) <font color="#990000">-></font> <font color="#009900">CallResult</font>
<b><font color="#000000">terminate</font></b>(<font color="#009900">Reason</font>, <font color="#009900">PartialReq</font>, <font color="#009900">State</font>) <font color="#990000">-></font> <font color="#FF6600">ok</font> <i><font color="#9A1900">%% optional</font></i>
<font color="#009900">Req</font> <font color="#990000">::</font> <b><font color="#000000">cowboy_req:req</font></b>()
<font color="#009900">PartialReq</font> <font color="#990000">::</font> <b><font color="#000000">map</font></b>()
<font color="#009900">State</font> <font color="#990000">::</font> <b><font color="#000000">any</font></b>()
<font color="#009900">Opts</font> <font color="#990000">::</font> <b><font color="#000000">cowboy_websocket:opts</font></b>()
<font color="#009900">InFrame</font> <font color="#990000">::</font> {<font color="#FF6600">text</font> | <b><font color="#000080">binary</font></b> | <font color="#FF6600">ping</font> | <font color="#FF6600">pong</font>, <b><font color="#000080">binary</font></b>()}
<font color="#009900">OutFrame</font> <font color="#990000">::</font> <b><font color="#000000">cow_ws:frame</font></b>() <i><font color="#9A1900">%% see types below</font></i>
<font color="#009900">Info</font> <font color="#990000">::</font> <b><font color="#000000">any</font></b>()
<font color="#009900">CallResult</font> <font color="#990000">::</font> {<font color="#FF6600">ok</font>, <font color="#009900">State</font>}
| {<font color="#FF6600">ok</font>, <font color="#009900">State</font>, <font color="#FF6600">hibernate</font>}
| {<font color="#FF6600">reply</font>, <font color="#009900">OutFrame</font> | [<font color="#009900">OutFrame</font>], <font color="#009900">State</font>}
| {<font color="#FF6600">reply</font>, <font color="#009900">OutFrame</font> | [<font color="#009900">OutFrame</font>], <font color="#009900">State</font>, <font color="#FF6600">hibernate</font>}
| {<font color="#FF6600">stop</font>, <font color="#009900">State</font>}
<font color="#009900">Reason</font> <font color="#990000">::</font> <b><font color="#000080">normal</font></b> | <font color="#FF6600">stop</font> | <font color="#FF6600">timeout</font>
| <font color="#FF6600">remote</font> | {<font color="#FF6600">remote</font>, <b><font color="#000000">cow_ws:close_code</font></b>(), <b><font color="#000080">binary</font></b>()}
| {<font color="#FF6600">error</font>, <font color="#FF6600">badencoding</font> | <font color="#FF6600">badframe</font> | <font color="#FF6600">closed</font> | <b><font color="#000080">atom</font></b>()}
| {<font color="#FF6600">crash</font>, <font color="#FF6600">error</font> | <b><font color="#000080">exit</font></b> | <b><font color="#000080">throw</font></b>, <b><font color="#000000">any</font></b>()}</tt></pre>
</div></div>
<p>The <code>init/2</code> callback is common to all handlers. To upgrade the connection to Websocket, it must return <code>cowboy_websocket</code> as the first element of the tuple.</p>
<p>Any operation requiring the HTTP request must be done in the <code>init/2</code> function, as the Req object will not be available after it returns. Websocket sub-protocol selection should therefore be done in this function.</p>
<p>The optional <code>websocket_init/1</code> callback will be called once the connection has been upgraded to Websocket. It can be used to perform any required initialization of the handler.</p>
<p>Note that the <code>init/2</code> function does not run in the same process as the Websocket callbacks. Any Websocket-specific initialization must be done in <code>websocket_init/1</code>.</p>
<p>The <code>websocket_handle/2</code> callback will be called for every frame received. The <code>websocket_info/2</code> callback will be called for every Erlang message received.</p>
<p>All three Websocket callbacks may send one or more frames back to the client (by returning a <code>reply</code> tuple) or terminate the connection (by sending a <code>close</code> frame or returning a <code>stop</code> tuple).</p>
<p>The optional <code>terminate/3</code> callback will ultimately be called with the reason for the termination of the connection. This callback is common to all handlers. Note that Websocket will not provide the full Req object by default, to save memory.</p>
<p>Cowboy will terminate the process right after closing the Websocket connection. This means that there is no need to perform any cleanup in the <code>terminate/3</code> callback.</p>
<p>The following terminate reasons are defined for Websocket connections:</p>
<dl><dt>normal</dt>
<dd><p>The connection was closed normally before establishing a Websocket connection. This typically happens if an <code>ok</code> tuple is returned from the <code>init/2</code> callback.</p>
</dd>
<dt>remote</dt>
<dd><p>The remote endpoint closed the connection without giving any further details.</p>
</dd>
<dt>{remote, Code, Payload}</dt>
<dd><p>The remote endpoint closed the connection with the given <code>Code</code> and <code>Payload</code> as the reason.</p>
</dd>
<dt>stop</dt>
<dd><p>The handler requested to close the connection, either by returning a <code>stop</code> tuple or by sending a <code>close</code> frame.</p>
</dd>
<dt>timeout</dt>
<dd><p>The connection has been closed due to inactivity. The timeout value can be configured from <code>init/2</code>.</p>
</dd>
<dt>{crash, Class, Reason}</dt>
<dd><p>A crash occurred in the handler. <code>Class</code> and <code>Reason</code> can be used to obtain more information about the crash. The function <code>erlang:get_stacktrace/0</code> can also be called to obtain the stacktrace of the process when the crash occurred.</p>
</dd>
<dt>{error, badencoding}</dt>
<dd><p>A text frame was sent by the client with invalid encoding. All text frames must be valid UTF-8.</p>
</dd>
<dt>{error, badframe}</dt>
<dd><p>A protocol error has been detected.</p>
</dd>
<dt>{error, closed}</dt>
<dd><p>The socket has been closed brutally without a close frame being received first.</p>
</dd>
<dt>{error, Reason}</dt>
<dd><p>A socket error ocurred.</p>
</dd>
</dl>
<h2 id="_types">Types</h2>
<h4 id="_cow_ws_frame">cow_ws:frame()</h4>
<div class="listingblock"><div class="content"><!-- Generator: GNU source-highlight 3.1.8
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><b><font color="#000000">frame</font></b>() <font color="#990000">::</font> {<font color="#FF6600">text</font>, <b><font color="#000000">iodata</font></b>()}
| {<b><font color="#000080">binary</font></b>, <b><font color="#000000">iodata</font></b>()}
| <font color="#FF6600">ping</font> | {<font color="#FF6600">ping</font>, <b><font color="#000000">iodata</font></b>()}
| <font color="#FF6600">pong</font> | {<font color="#FF6600">pong</font>, <b><font color="#000000">iodata</font></b>()}
| <font color="#FF6600">close</font> | {<font color="#FF6600">close</font>, <b><font color="#000000">iodata</font></b>()} | {<font color="#FF6600">close</font>, <b><font color="#000000">close_code</font></b>(), <b><font color="#000000">iodata</font></b>()}
<b><font color="#000000">close_code</font></b>() <font color="#990000">::</font> <font color="#993399">1000</font><font color="#990000">..</font><font color="#993399">1003</font> | <font color="#993399">1006</font><font color="#990000">..</font><font color="#993399">1011</font> | <font color="#993399">3000</font><font color="#990000">..</font><font color="#993399">4999</font></tt></pre>
</div></div>
<p>Websocket frames that can be sent as a response.</p>
<p>Note that there is no need to send pong frames back as Cowboy does it automatically for you.</p>
<h3 id="_opts">opts()</h3>
<div class="listingblock"><div class="content"><!-- Generator: GNU source-highlight 3.1.8
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><b><font color="#000000">opts</font></b>() <font color="#990000">::</font> #{
<font color="#0000FF">compress</font> <font color="#990000">=></font> <b><font color="#000000">boolean</font></b>(),
<font color="#0000FF">idle_timeout</font> <font color="#990000">=></font> <b><font color="#000000">timeout</font></b>(),
<font color="#0000FF">req_filter</font> <font color="#990000">=></font> <b><font color="#0000FF">fun</font></b>((<b><font color="#000000">cowboy_req:req</font></b>()) <font color="#990000">-></font> <b><font color="#000000">map</font></b>())
}</tt></pre>
</div></div>
<p>Websocket handler options.</p>
<p>This configuration is passed to Cowboy from the <code>init/2</code> function:</p>
<div class="listingblock"><div class="content"><!-- Generator: GNU source-highlight 3.1.8
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><b><font color="#000000">init</font></b>(<font color="#009900">Req</font>, <font color="#009900">State</font>) <font color="#990000">-></font>
<font color="#009900">Opts</font> <font color="#990000">=</font> #{<font color="#0000FF">compress</font> <font color="#990000">=></font> <font color="#000080">true</font>},
{<font color="#FF6600">cowboy_websocket</font>, <font color="#009900">Req</font>, <font color="#009900">State</font>, <font color="#009900">Opts</font>}<font color="#990000">.</font></tt></pre>
</div></div>
<p>The default value is given next to the option name:</p>
<dl><dt>compress (false)</dt>
<dd><p>Whether to enable the Websocket frame compression extension. Frames will only be compressed for the clients that support this extension.</p>
</dd>
<dt>idle_timeout (60000)</dt>
<dd><p>Time in milliseconds that Cowboy will keep the connection open without receiving anything from the client.</p>
</dd>
<dt>req_filter</dt>
<dd><p>A function applied to the Req to compact it and only keep required information. The Req is only given back in the <code>terminate/3</code> callback. By default it keeps the method, version, URI components and peer information.</p>
</dd>
</dl>
<h2 id="_changelog">Changelog</h2>
<ul><li><strong>2.0</strong>: The Req object is no longer passed to Websocket callbacks.
</li>
<li><strong>2.0</strong>: The callback <code>websocket_terminate/3</code> was removed in favor of <code>terminate/3</code>.
</li>
<li><strong>1.0</strong>: Protocol introduced.
</li>
</ul>
<h2 id="_see_also">See also</h2>
<p><a href="..">cowboy(7)</a>, <a href="../cowboy_handler">cowboy_handler(3)</a>, <a href="../cowboy_http">cowboy_http(3)</a>, <a href="../cowboy_http2">cowboy_http2(3)</a></p>
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