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

<h2 id="_name">Name</h2>
<p>cowboy_constraints - Constraints</p>
<h2 id="_description">Description</h2>
<p>The module <code>cowboy_constraints</code> defines the built-in constraints in Cowboy and provides an interface for manipulating these constraints.</p>
<p>Constraints are functions that define what type of input is allowed. They are used throughout Cowboy, from the router to query strings to cookies.</p>
<h2 id="_exports">Exports</h2>
<p>Built-in constraints:</p>
<ul><li><a href="../cowboy_constraints.int">cowboy_constraints:int(3)</a> - Integer constraint
</li>
<li><a href="../cowboy_constraints.nonempty">cowboy_constraints:nonempty(3)</a> - Non-empty constraint
</li>
</ul>
<h2 id="_types">Types</h2>
<h3 id="_constraint">constraint()</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">constraint</font></b>() <font color="#990000">::</font> <font color="#FF6600">int</font> | <font color="#FF6600">nonempty</font> | <b><font color="#0000FF">fun</font></b>()</tt></pre>
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<p>A constraint function.</p>
<p>The atom constraints are built-in, see the corresponding function in the exports list above.</p>
<h3 id="_reason">reason()</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">reason</font></b>() <font color="#990000">::</font> {<b><font color="#000000">constraint</font></b>(), <font color="#009900">Reason</font>, <font color="#009900">Value</font>}

<font color="#009900">Reason</font> <font color="#990000">::</font> <b><font color="#000000">any</font></b>()
<font color="#009900">Value</font>  <font color="#990000">::</font> <b><font color="#000000">any</font></b>()</tt></pre>
</div></div>
<p>Reason for the constraint failure.</p>
<p>It includes the constraint function in question, a machine-readable error reason and the value that made the constraint fail.</p>
<h2 id="_see_also">See also</h2>
<p><a href="..">cowboy(7)</a>, <a href="../cowboy">cowboy(3)</a>, <a href="../cowboy_router">cowboy_router(3)</a>, <a href="../cowboy_req.match_cookies">cowboy_req:match_cookies(3)</a>, <a href="../cowboy_req.match_qs">cowboy_req:match_qs(3)</a></p>






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