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<h1 class="lined-header"><span>cowboy_tracer_h(3)</span></h1>
<h2 id="_name">Name</h2>
<p>cowboy_tracer_h - Tracer stream handler</p>
<h2 id="_description">Description</h2>
<p>The module <code>cowboy_tracer_h</code> can be used to conditionally trace streams based on information found in the request. Trace messages are given to the configured callback.</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">tracer_callback</font> <font color="#990000">=></font> <font color="#009900">Callback</font>,
<font color="#0000FF">tracer_flags</font> <font color="#990000">=></font> [<b><font color="#000080">atom</font></b>()],
<font color="#0000FF">tracer_match_specs</font> <font color="#990000">=></font> [<font color="#009900">MatchSpec</font>]
}
<font color="#009900">Callback</font> <font color="#990000">::</font> <b><font color="#0000FF">fun</font></b>((<font color="#FF6600">init</font> | <font color="#FF6600">terminate</font> | <b><font color="#000000">tuple</font></b>(), <font color="#009900">State</font>) <font color="#990000">-></font> <font color="#009900">State</font>)
<font color="#009900">MatchSpec</font> <font color="#990000">::</font> <font color="#009900">MatchPredicate</font>
| {<font color="#FF6600">method</font>, <b><font color="#000080">binary</font></b>()}
| {<font color="#FF6600">host</font>, <b><font color="#000080">binary</font></b>()}
| {<font color="#FF6600">path</font>, <b><font color="#000080">binary</font></b>()}
| {<font color="#FF6600">path_start</font>, <b><font color="#000080">binary</font></b>()}
| {<font color="#FF6600">header</font>, <b><font color="#000080">binary</font></b>()}
| {<font color="#FF6600">header</font>, <b><font color="#000080">binary</font></b>(), <b><font color="#000080">binary</font></b>()}
| {<font color="#FF6600">peer_ip</font>, <b><font color="#000000">inet:ip_address</font></b>()}
<font color="#009900">MatchPredicate</font> <font color="#990000">::</font> <b><font color="#0000FF">fun</font></b>((<b><font color="#000000">cowboy_stream:streamid</font></b>(),
<b><font color="#000000">cowboy_req:req</font></b>(),
<b><font color="#000000">cowboy:opts</font></b>()) <font color="#990000">-></font> <b><font color="#000000">boolean</font></b>())
}</tt></pre>
</div></div>
<p>Configuration for the tracer stream handler.</p>
<p>This module will not set trace patterns. Those must be set by the user directly, either from the callback's <code>init</code> or, preferably, in advance.</p>
<dl><dt>tracer_callback</dt>
<dd><p>The function that will be called for each trace events. It will also be called before any trace event with an argument <code>init</code>, and when the stream is terminated with an argument <code>terminate</code>.</p>
<p>This option is required for tracing to be enabled. The tracer stream handler does nothing otherwise.</p>
</dd>
<dt>tracer_flags</dt>
<dd><p>Trace flags to enable. See the documentation of <code>erlang:trace/3</code> for details. Note that all trace flags are allowed except for the <code>tracer</code> flag.</p>
</dd>
<dt>tracer_match_specs</dt>
<dd><p>A list of match conditions that must all be fulfilled for the stream to be traced. Cowboy will compare these with the information found in the request and only enable tracing if all matches succeed.</p>
<p>This option is required for tracing to be enabled. The tracer stream handler does nothing otherwise.</p>
</dd>
</dl>
<h2 id="_events">Events</h2>
<p>The tracer 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_metrics_h">cowboy_metrics_h(3)</a>, <a href="../cowboy_stream_h">cowboy_stream_h(3)</a></p>
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<h3>
Cowboy
2.7
Function Reference
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<li><a href="/docs/en/cowboy/2.7/manual">Function Reference</a></li>
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