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<h1 class="lined-header"><span>cowboy_metrics_h(3)</span></h1>

<h2 id="_name">Name</h2>
<p>cowboy_metrics_h - Metrics stream handler</p>
<h2 id="_description">Description</h2>
<p>The module <code>cowboy_metrics_h</code> gathers metrics and other information about a stream. It then calls the configured callback with this data.</p>
<h2 id="_types">Types</h2>
<h3 id="_metrics">metrics()</h3>
<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">metrics</font></b>() <font color="#990000">::</font> #{
    <i><font color="#9A1900">%% The identifier for this listener.</font></i>
    <font color="#FF6600">ref</font> <font color="#990000">:=</font> <b><font color="#000000">ranch:ref</font></b>(),

    <i><font color="#9A1900">%% The pid for this connection.</font></i>
    <font color="#FF6600">pid</font> <font color="#990000">:=</font> <b><font color="#000080">pid</font></b>(),

    <i><font color="#9A1900">%% The streamid also indicates the total number of requests on</font></i>
    <i><font color="#9A1900">%% this connection (StreamID div 2 + 1).</font></i>
    <font color="#FF6600">streamid</font> <font color="#990000">:=</font> <b><font color="#000000">cowboy_stream:streamid</font></b>(),

    <i><font color="#9A1900">%% The terminate reason is always useful.</font></i>
    <font color="#FF6600">reason</font> <font color="#990000">:=</font> <b><font color="#000000">cowboy_stream:reason</font></b>(),

    <i><font color="#9A1900">%% A filtered Req object or a partial Req object</font></i>
    <i><font color="#9A1900">%% depending on how far the request got to.</font></i>
    <font color="#0000FF">req</font> <font color="#990000">=&gt;</font> <b><font color="#000000">cowboy_req:req</font></b>(),
    <font color="#0000FF">partial_req</font> <font color="#990000">=&gt;</font> <b><font color="#000000">cowboy_stream:partial_req</font></b>(),

    <i><font color="#9A1900">%% Response status.</font></i>
    <font color="#FF6600">resp_status</font> <font color="#990000">:=</font> <b><font color="#000000">cowboy:http_status</font></b>(),

    <i><font color="#9A1900">%% Filtered response headers.</font></i>
    <font color="#FF6600">resp_headers</font> <font color="#990000">:=</font> <b><font color="#000000">cowboy:http_headers</font></b>(),

    <i><font color="#9A1900">%% Start/end of the processing of the request.</font></i>
    <i><font color="#9A1900">%%</font></i>
    <i><font color="#9A1900">%% This represents the time from this stream handler's init</font></i>
    <i><font color="#9A1900">%% to terminate.</font></i>
    <font color="#0000FF">req_start</font> <font color="#990000">=&gt;</font> <b><font color="#000080">integer</font></b>(),
    <font color="#0000FF">req_end</font> <font color="#990000">=&gt;</font> <b><font color="#000080">integer</font></b>(),

    <i><font color="#9A1900">%% Start/end of the receiving of the request body.</font></i>
    <i><font color="#9A1900">%% Begins when the first packet has been received.</font></i>
    <font color="#0000FF">req_body_start</font> <font color="#990000">=&gt;</font> <b><font color="#000080">integer</font></b>(),
    <font color="#0000FF">req_body_end</font> <font color="#990000">=&gt;</font> <b><font color="#000080">integer</font></b>(),

    <i><font color="#9A1900">%% Start/end of the sending of the response.</font></i>
    <i><font color="#9A1900">%% Begins when we send the headers and ends on the final</font></i>
    <i><font color="#9A1900">%% packet of the response body. If everything is sent at</font></i>
    <i><font color="#9A1900">%% once these values are identical.</font></i>
    <font color="#0000FF">resp_start</font> <font color="#990000">=&gt;</font> <b><font color="#000080">integer</font></b>(),
    <font color="#0000FF">resp_end</font> <font color="#990000">=&gt;</font> <b><font color="#000080">integer</font></b>(),

    <i><font color="#9A1900">%% For early errors all we get is the time we received it.</font></i>
    <font color="#0000FF">early_error_time</font> <font color="#990000">=&gt;</font> <b><font color="#000080">integer</font></b>(),

    <i><font color="#9A1900">%% Start/end of spawned processes. This is where most of</font></i>
    <i><font color="#9A1900">%% the user code lies, excluding stream handlers. On a</font></i>
    <i><font color="#9A1900">%% default Cowboy configuration there should be only one</font></i>
    <i><font color="#9A1900">%% process: the request process.</font></i>
    <font color="#0000FF">procs</font> <font color="#990000">=&gt;</font> <font color="#009900">ProcMetrics</font>,

    <i><font color="#9A1900">%% Informational responses sent before the final response.</font></i>
    <font color="#0000FF">informational</font> <font color="#990000">=&gt;</font> [<font color="#009900">InformationalMetrics</font>],

    <i><font color="#9A1900">%% Length of the request and response bodies. This does</font></i>
    <i><font color="#9A1900">%% not include the framing.</font></i>
    <font color="#0000FF">req_body_length</font> <font color="#990000">=&gt;</font> <b><font color="#000000">non_neg_integer</font></b>(),
    <font color="#0000FF">resp_body_length</font> <font color="#990000">=&gt;</font> <b><font color="#000000">non_neg_integer</font></b>(),

    <i><font color="#9A1900">%% Additional metadata set by the user.</font></i>
    <font color="#0000FF">user_data</font> <font color="#990000">=&gt;</font> <b><font color="#000000">map</font></b>()
}

<font color="#009900">InformationalMetrics</font> <font color="#990000">::</font> #{
    <i><font color="#9A1900">%% Informational response status.</font></i>
    <font color="#FF6600">status</font> <font color="#990000">:=</font> <b><font color="#000000">cowboy:http_status</font></b>(),

    <i><font color="#9A1900">%% Headers sent with the informational response.</font></i>
    <font color="#FF6600">headers</font> <font color="#990000">:=</font> <b><font color="#000000">cowboy:http_headers</font></b>(),

    <i><font color="#9A1900">%% Time when the informational response was sent.</font></i>
    <font color="#FF6600">time</font> <font color="#990000">:=</font> <b><font color="#000080">integer</font></b>()
}

<font color="#009900">ProcMetrics</font> <font color="#990000">::</font> #{<b><font color="#000080">pid</font></b>() <font color="#990000">=&gt;</font> #{
    <i><font color="#9A1900">%% Time at which the process spawned.</font></i>
    <font color="#FF6600">spawn</font> <font color="#990000">:=</font> <b><font color="#000080">integer</font></b>(),

    <i><font color="#9A1900">%% Time at which the process exited.</font></i>
    <b><font color="#000080">exit</font></b> <font color="#990000">=&gt;</font> <b><font color="#000080">integer</font></b>(),

    <i><font color="#9A1900">%% Reason for the process exit.</font></i>
    <font color="#0000FF">reason</font> <font color="#990000">=&gt;</font> <b><font color="#000000">any</font></b>()
}}</tt></pre>
</div></div>
<p>Metrics given to the callback function.</p>
<p>Depending on the life of the stream the metrics may include more or less information.</p>
<p>The <code>set_options</code> command can be used to add additional metadata in the <code>user_data</code> metric. This can be used for example to add the handler module which was selected by the router. The option to be set is <code>metrics_user_data</code>. It takes a map which will be merged in the existing <code>user_data</code> map.</p>
<h2 id="_options">Options</h2>
<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">opts</font></b>() <font color="#990000">::</font> #{
    <font color="#0000FF">metrics_callback</font> <font color="#990000">=&gt;</font> <b><font color="#0000FF">fun</font></b>((<b><font color="#000000">metrics</font></b>()) <font color="#990000">-&gt;</font> <b><font color="#000000">any</font></b>()),
    <font color="#0000FF">metrics_req_filter</font> <font color="#990000">=&gt;</font> <b><font color="#0000FF">fun</font></b>((<b><font color="#000000">cowboy_req:req</font></b>()) <font color="#990000">-&gt;</font> <b><font color="#000000">map</font></b>()),
    <font color="#0000FF">metrics_resp_headers_filter</font> <font color="#990000">=&gt;</font> <b><font color="#0000FF">fun</font></b>((<b><font color="#000000">cowboy:http_headers</font></b>()) <font color="#990000">-&gt;</font> <b><font color="#000000">cowboy:http_headers</font></b>())
}</tt></pre>
</div></div>
<p>Configuration for the metrics stream handler.</p>
<dl><dt>metrics_callback - mandatory</dt>
<dd><p>The function that will be called upon completion of the stream. It only takes a single argument, the <code>metrics()</code>.</p>
</dd>
<dt>metrics_req_filter</dt>
<dd><p>A function applied to the Req to compact it and only keep required information. By default no filtering is done.</p>
</dd>
<dt>metrics_resp_headers_filter</dt>
<dd><p>A function applied to the response headers to filter them and only keep required information. By default no filtering is done.</p>
</dd>
</dl>
<h2 id="_events">Events</h2>
<p>The metrics stream handler does not produce any event.</p>
<h2 id="_changelog">Changelog</h2>
<ul><li><strong>2.7</strong>: Module introduced.
</li>
</ul>
<h2 id="_see_also">See also</h2>
<p><a href="..">cowboy(7)</a>, <a href="../cowboy_stream">cowboy_stream(3)</a>, <a href="../cowboy_compress_h">cowboy_compress_h(3)</a>, <a href="../cowboy_stream_h">cowboy_stream_h(3)</a>, <a href="../cowboy_tracer_h">cowboy_tracer_h(3)</a></p>






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<h3>
	Cowboy
	2.8
	Function Reference
	
</h3>

<ul>
	
		<li><a href="/docs/en/cowboy/2.8/guide">User Guide</a></li>
	
	
		<li><a href="/docs/en/cowboy/2.8/manual">Function Reference</a></li>
	
	
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<h4 id="docs-nav">Navigation</h4>

<h4>Version select</h4>
<ul>
	
	
	
		<li><a href="/docs/en/cowboy/2.9/manual">2.9</a></li>
	
		<li><a href="/docs/en/cowboy/2.8/manual">2.8</a></li>
	
		<li><a href="/docs/en/cowboy/2.7/manual">2.7</a></li>
	
		<li><a href="/docs/en/cowboy/2.6/manual">2.6</a></li>
	
		<li><a href="/docs/en/cowboy/2.5/manual">2.5</a></li>
	
		<li><a href="/docs/en/cowboy/2.4/manual">2.4</a></li>
	
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