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<h1 class="lined-header"><span>cowboy_req:parse_header(3)</span></h1>
<h2 id="_name">Name</h2>
<p>cowboy_req:parse_header - Parse the given HTTP header</p>
<h2 id="_description">Description</h2>
<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">parse_header</font></b>(<font color="#009900">Name</font>, <font color="#009900">Req</font>) <font color="#990000">-></font> <font color="#009900">ParsedValue</font> | <font color="#009900">Default</font>
<b><font color="#000000">parse_header</font></b>(<font color="#009900">Name</font>, <font color="#009900">Req</font>, <font color="#009900">Default</font>) <font color="#990000">-></font> <font color="#009900">ParsedValue</font> | <font color="#009900">Default</font>
<font color="#009900">Name</font> <font color="#990000">::</font> <b><font color="#000080">binary</font></b>()
<font color="#009900">Req</font> <font color="#990000">::</font> <b><font color="#000000">cowboy_req:req</font></b>()
<font color="#009900">ParsedValue</font> <font color="#990000">::</font> <b><font color="#000000">any</font></b>()
<font color="#009900">Default</font> <font color="#990000">::</font> <b><font color="#000000">any</font></b>()</tt></pre>
</div></div>
<p>Parse the given HTTP header.</p>
<p>The header name must be given as a lowercase binary string. While header names are case insensitive, Cowboy requires them to be given as lowercase to function properly.</p>
<p>The type of the parsed value varies depending on the header. Similarly, the default value when calling <code>cowboy_req:parse_header/2</code> differs depending on the header.</p>
<h2 id="_arguments">Arguments</h2>
<dl><dt>Name</dt>
<dd><p>Desired HTTP header name as a lowercase binary string.</p>
</dd>
<dt>Req</dt>
<dd><p>The Req object.</p>
</dd>
<dt>Default</dt>
<dd><p>Default value returned when the header is missing.</p>
</dd>
</dl>
<h2 id="_return_value">Return value</h2>
<p>The parsed header value varies depending on the header. When the header is missing, the default argument is returned.</p>
<h2 id="_headers">Headers</h2>
<p>The following snippets detail the types returned by the different headers. Unless mentioned otherwise, the default value when the header is missing will be <code>undefined</code>:</p>
<div class="listingblock"><div class="title">accept</div>
<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">parse_header</font></b>(<font color="#990000"><<</font><font color="#FF0000">"accept"</font><font color="#990000">>></font>, <font color="#009900">Req</font>)
<font color="#990000">-></font> [{{<font color="#009900">Type</font>, <font color="#009900">SubType</font>, <font color="#009900">Params</font>}, <font color="#009900">Quality</font>, <font color="#009900">AcceptExt</font>}]
<font color="#009900">Type</font> <font color="#990000">::</font> <b><font color="#000080">binary</font></b>() <i><font color="#9A1900">%% case insensitive</font></i>
<font color="#009900">SubType</font> <font color="#990000">::</font> <b><font color="#000080">binary</font></b>() <i><font color="#9A1900">%% case insensitive</font></i>
<font color="#009900">Params</font> <font color="#990000">::</font> [{<font color="#009900">Key</font>, <font color="#009900">Value</font>}]
<font color="#009900">Quality</font> <font color="#990000">::</font> <font color="#993399">0</font><font color="#990000">..</font><font color="#993399">1000</font>
<font color="#009900">AcceptExt</font> <font color="#990000">::</font> [<font color="#009900">Key</font> | {<font color="#009900">Key</font>, <font color="#009900">Value</font>}]
<font color="#009900">Key</font> <font color="#990000">::</font> <b><font color="#000080">binary</font></b>() <i><font color="#9A1900">%% case insensitive</font></i>
<font color="#009900">Value</font> <font color="#990000">::</font> <b><font color="#000080">binary</font></b>() <i><font color="#9A1900">%% case sensitive</font></i></tt></pre>
</div></div>
<div class="listingblock"><div class="title">accept-charset, accept-encoding and accept-language</div>
<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">parse_header</font></b>(<font color="#009900">Name</font>, <font color="#009900">Req</font>) <font color="#990000">-></font> [{<font color="#009900">Value</font>, <font color="#009900">Quality</font>}]
<font color="#009900">Name</font> <font color="#990000">::</font> <font color="#990000"><<</font><font color="#FF0000">"accept-charset"</font><font color="#990000">>></font>
| <font color="#990000"><<</font><font color="#FF0000">"accept-encoding"</font><font color="#990000">>></font>
| <font color="#990000"><<</font><font color="#FF0000">"accept-language"</font><font color="#990000">>></font>
<font color="#009900">Value</font> <font color="#990000">::</font> <b><font color="#000080">binary</font></b>() <i><font color="#9A1900">%% case insensitive</font></i>
<font color="#009900">Quality</font> <font color="#990000">::</font> <font color="#993399">0</font><font color="#990000">..</font><font color="#993399">1000</font></tt></pre>
</div></div>
<div class="listingblock"><div class="title">authorization</div>
<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">parse_header</font></b>(<font color="#990000"><<</font><font color="#FF0000">"authorization"</font><font color="#990000">>></font>, <font color="#009900">Req</font>)
<font color="#990000">-></font> {<font color="#FF6600">basic</font>, <font color="#009900">Username</font> <font color="#990000">::</font> <b><font color="#000080">binary</font></b>(), <font color="#009900">Password</font> <font color="#990000">::</font> <b><font color="#000080">binary</font></b>()}
| {<font color="#FF6600">bearer</font>, <font color="#009900">Token</font> <font color="#990000">::</font> <b><font color="#000080">binary</font></b>()}
| {<font color="#FF6600">digest</font>, [{<font color="#009900">Key</font> <font color="#990000">::</font> <b><font color="#000080">binary</font></b>(), <font color="#009900">Value</font> <font color="#990000">::</font> <b><font color="#000080">binary</font></b>()}]}</tt></pre>
</div></div>
<!-- @todo Currently also parses connection. Do we want this? Should it be documented? Use case?-->
<div class="listingblock"><div class="title">content-length</div>
<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">parse_header</font></b>(<font color="#990000"><<</font><font color="#FF0000">"content-length"</font><font color="#990000">>></font>, <font color="#009900">Req</font>) <font color="#990000">-></font> <b><font color="#000000">non_neg_integer</font></b>()</tt></pre>
</div></div>
<p>When the content-length header is missing, <code>0</code> is returned.</p>
<div class="listingblock"><div class="title">content-type</div>
<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">parse_header</font></b>(<font color="#990000"><<</font><font color="#FF0000">"content-type"</font><font color="#990000">>></font>, <font color="#009900">Req</font>)
<font color="#990000">-></font> {<font color="#009900">Type</font>, <font color="#009900">SubType</font>, <font color="#009900">Params</font>}
<font color="#009900">Type</font> <font color="#990000">::</font> <b><font color="#000080">binary</font></b>() <i><font color="#9A1900">%% case insensitive</font></i>
<font color="#009900">SubType</font> <font color="#990000">::</font> <b><font color="#000080">binary</font></b>() <i><font color="#9A1900">%% case insensitive</font></i>
<font color="#009900">Params</font> <font color="#990000">::</font> [{<font color="#009900">Key</font>, <font color="#009900">Value</font>}]
<font color="#009900">Key</font> <font color="#990000">::</font> <b><font color="#000080">binary</font></b>() <i><font color="#9A1900">%% case insensitive</font></i>
<font color="#009900">Value</font> <font color="#990000">::</font> <b><font color="#000080">binary</font></b>() <i><font color="#9A1900">%% case sensitive;</font></i></tt></pre>
</div></div>
<p>Note that the value for the charset parameter is case insensitive and returned as a lowercase binary string.</p>
<div class="listingblock"><div class="title">cookie</div>
<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">parse_header</font></b>(<font color="#990000"><<</font><font color="#FF0000">"cookie"</font><font color="#990000">>></font>, <font color="#009900">Req</font>) <font color="#990000">-></font> [{<font color="#009900">Name</font>, <font color="#009900">Value</font>}]
<font color="#009900">Name</font> <font color="#990000">::</font> <b><font color="#000080">binary</font></b>() <i><font color="#9A1900">%% case sensitive</font></i>
<font color="#009900">Value</font> <font color="#990000">::</font> <b><font color="#000080">binary</font></b>() <i><font color="#9A1900">%% case sensitive</font></i></tt></pre>
</div></div>
<p>When the cookie header is missing, <code>[]</code> is returned.</p>
<p>While an empty cookie header is not valid, some clients do send it. Cowboy will in this case also return <code>[]</code>.</p>
<div class="listingblock"><div class="title">expect</div>
<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">parse_header</font></b>(<font color="#990000"><<</font><font color="#FF0000">"expect"</font><font color="#990000">>></font>, <font color="#009900">Req</font>) <font color="#990000">-></font> <font color="#FF6600">continue</font></tt></pre>
</div></div>
<div class="listingblock"><div class="title">if-match and if-none-match</div>
<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">parse_header</font></b>(<font color="#009900">Name</font>, <font color="#009900">Req</font>)
<font color="#990000">-></font> <font color="#FF6600">'*'</font> | [{<font color="#FF6600">weak</font> | <font color="#FF6600">strong</font>, <font color="#009900">OpaqueTag</font>}]
<font color="#009900">Name</font> <font color="#990000">::</font> <font color="#990000"><<</font><font color="#FF0000">"if-match"</font><font color="#990000">>></font>
| <font color="#990000"><<</font><font color="#FF0000">"if-none-match"</font><font color="#990000">>></font>
<font color="#009900">OpaqueTag</font> <font color="#990000">::</font> <b><font color="#000080">binary</font></b>() <i><font color="#9A1900">%% case sensitive</font></i></tt></pre>
</div></div>
<div class="listingblock"><div class="title">if-modified-since and if-unmodified-since</div>
<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">parse_header</font></b>(<font color="#009900">Name</font>, <font color="#009900">Req</font>) <font color="#990000">-></font> <b><font color="#000000">calendar:datetime</font></b>()</tt></pre>
</div></div>
<div class="listingblock"><div class="title">range</div>
<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">parse_header</font></b>(<font color="#990000"><<</font><font color="#FF0000">"range"</font><font color="#990000">>></font>, <font color="#009900">Req</font>) <font color="#990000">-></font> {<font color="#009900">From</font>, <font color="#009900">To</font>} | <font color="#009900">Final</font>
<font color="#009900">From</font> <font color="#990000">::</font> <b><font color="#000000">non_neg_integer</font></b>()
<font color="#009900">To</font> <font color="#990000">::</font> <b><font color="#000000">non_neg_integer</font></b>() | <font color="#FF6600">infinity</font>
<font color="#009900">Final</font> <font color="#990000">::</font> <b><font color="#000000">neg_integer</font></b>()</tt></pre>
</div></div>
<div class="listingblock"><div class="title">sec-websocket-extensions</div>
<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">parse_header</font></b>(<font color="#990000"><<</font><font color="#FF0000">"sec-websocket-extensions"</font><font color="#990000">>></font>, <font color="#009900">Req</font>)
<font color="#990000">-></font> [{<font color="#009900">Extension</font>, <font color="#009900">Params</font>}]
<font color="#009900">Extension</font> <font color="#990000">::</font> <b><font color="#000080">binary</font></b>() <i><font color="#9A1900">%% case sensitive</font></i>
<font color="#009900">Params</font> <font color="#990000">::</font> [<font color="#009900">Key</font> | {<font color="#009900">Key</font>, <font color="#009900">Value</font>}]
<font color="#009900">Key</font> <font color="#990000">::</font> <b><font color="#000080">binary</font></b>() <i><font color="#9A1900">%% case sensitive</font></i>
<font color="#009900">Value</font> <font color="#990000">::</font> <b><font color="#000080">binary</font></b>() <i><font color="#9A1900">%% case sensitive</font></i></tt></pre>
</div></div>
<div class="listingblock"><div class="title">sec-websocket-protocol and upgrade</div>
<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">parse_header</font></b>(<font color="#009900">Name</font>, <font color="#009900">Req</font>) <font color="#990000">-></font> [<font color="#009900">Token</font>]
<font color="#009900">Name</font> <font color="#990000">::</font> <font color="#990000"><<</font><font color="#FF0000">"sec-websocket-protocol"</font><font color="#990000">>></font>
| <font color="#990000"><<</font><font color="#FF0000">"upgrade"</font><font color="#990000">>></font>
<font color="#009900">Token</font> <font color="#990000">::</font> <b><font color="#000080">binary</font></b>() <i><font color="#9A1900">%% case insensitive</font></i></tt></pre>
</div></div>
<div class="listingblock"><div class="title">x-forwarded-for</div>
<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">parse_header</font></b>(<font color="#990000"><<</font><font color="#FF0000">"x-forwarded-for"</font><font color="#990000">>></font>, <font color="#009900">Req</font>) <font color="#990000">-></font> [<font color="#009900">Token</font>]
<font color="#009900">Token</font> <font color="#990000">::</font> <b><font color="#000080">binary</font></b>() <i><font color="#9A1900">%% case sensitive</font></i></tt></pre>
</div></div>
<div class="listingblock"><div class="title">Unknown headers</div>
<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">parse_header</font></b>(<font color="#990000">_</font>, <font color="#009900">Req</font>) <font color="#990000">-></font> {<font color="#000080">undefined</font>, <font color="#009900">RawValue</font>}</tt></pre>
</div></div>
<h2 id="_changelog">Changelog</h2>
<ul><li><strong>2.0</strong>: Only the parsed header value is returned, it is no longer wrapped in a tuple.
</li>
<li><strong>1.0</strong>: Function introduced.
</li>
</ul>
<h2 id="_examples">Examples</h2>
<div class="listingblock"><div class="title">Parse the accept header with a custom default value</div>
<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><i><font color="#9A1900">%% Accept everything when header is missing.</font></i>
<font color="#009900">Accept</font> <font color="#990000">=</font> <b><font color="#000000">cowboy_req:parse_header</font></b>(<font color="#990000"><<</font><font color="#FF0000">"accept"</font><font color="#990000">>></font>, <font color="#009900">Req</font>,
[{{ <font color="#990000"><<</font><font color="#FF0000">"*"</font><font color="#990000">>></font>, <font color="#990000"><<</font><font color="#FF0000">"*"</font><font color="#990000">>></font>, []}, <font color="#993399">1000</font>, []}])<font color="#990000">.</font></tt></pre>
</div></div>
<div class="listingblock"><div class="title">Parse the content-length header</div>
<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><i><font color="#9A1900">%% Default content-length is 0.</font></i>
<font color="#009900">Length</font> <font color="#990000">=</font> <b><font color="#000000">cowboy_req:header</font></b>(<font color="#990000"><<</font><font color="#FF0000">"content-length"</font><font color="#990000">>></font>, <font color="#009900">Req</font>)<font color="#990000">.</font></tt></pre>
</div></div>
<h2 id="_see_also">See also</h2>
<p><a href="../cowboy_req">cowboy_req(3)</a>, <a href="../cowboy_req.header">cowboy_req:header(3)</a>, <a href="../cowboy_req.headers">cowboy_req:headers(3)</a></p>
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