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<h1 class="lined-header"><span>cowboy_handler(3)</span></h1>
<h2 id="_name">Name</h2>
<p>cowboy_handler - Plain HTTP handlers</p>
<h2 id="_description">Description</h2>
<p>The <code>cowboy_handler</code> middleware executes the handler selected by the router or any other preceding middleware.</p>
<p>This middleware takes the handler module and initial state from the <code>handler</code> and <code>handler_opts</code> environment values, respectively. On completion, it adds a <code>result</code> value to the middleware environment, containing the return value of the <code>terminate/3</code> callback (if defined) and <code>ok</code> otherwise.</p>
<p>This module also defines a callback interface for handling HTTP requests.</p>
<h2 id="_callbacks">Callbacks</h2>
<p>Plain HTTP handlers implement the following interface:</p>
<div class="listingblock"><div class="content"><!-- Generator: GNU source-highlight 3.1.9
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">ok</font>, <font color="#009900">Req</font>, <font color="#009900">State</font>}
<b><font color="#000000">terminate</font></b>(<font color="#009900">Reason</font>, <font color="#009900">Req</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">State</font> <font color="#990000">::</font> <b><font color="#000000">any</font></b>()
<font color="#009900">Reason</font> <font color="#990000">::</font> <b><font color="#000080">normal</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>These two callbacks are common to all handlers.</p>
<p>Plain HTTP handlers do all their work in the <code>init/2</code> callback. Returning <code>ok</code> terminates the handler. If no response is sent, Cowboy will send a <code>204 No Content</code>.</p>
<p>The optional <code>terminate/3</code> callback will ultimately be called with the reason for the termination of the handler. Cowboy will terminate the process right after this. There is no need to perform any cleanup in this callback.</p>
<p>The following terminate reasons are defined for plain HTTP handlers:</p>
<dl><dt>normal</dt>
<dd><p>The connection was closed normally.</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>
</dl>
<h2 id="_exports">Exports</h2>
<p>The following function should be called by modules implementing custom handlers to execute the optional terminate callback:</p>
<ul><li><a href="../cowboy_handler.terminate">cowboy_handler:terminate(3)</a> - Terminate the handler
</li>
</ul>
<h2 id="_see_also">See also</h2>
<p><a href="..">cowboy(7)</a></p>
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