sCode</a>)</p><div class="doc"><p>Get Status code from headers
   (and throw an exception if the header does not exist)
</p></div></div><div class="top"><p class="src"><a name="v:getHeader" class="def">getHeader</a> ::  String -&gt; String -&gt; Message m -&gt; IO String</p><div class="doc"><p>Get Generic function to retrieve a header value
   (and throw an exception if the header does not exist):
</p><ul><li> String: Key of the wanted header
</li><li> String: Error message in case there is no such header
<