title: Spray.io validate json directive
body: <p>Working with Spray.IO, I'm building a service which receives JSON input. 
  I want to validate the JSON payload by checking some of its fields.</p>
  
  <p>I'm not interested in validating JSON schema or parsing errors, but to check field values instead like the real type of a field (i.e: Integer vs Float) </p>
  
  <p>I'm not interested in using Scala <em>require</em> since this would raise an exception, and that would fail to inform the client <strong>ALL</strong> validation errors found on a single request.</p>
  
  <p>Is there a built-in directive / rejection for this?</p>
  
  <p>I've seen something similar in Play (<a href="http://www.playframework.com/documentation/2.2.1/ScalaJsonRequests" rel="nofollow">http://www.playframework.com/documentation/2.2.1/ScalaJsonRequests</a>), and if there's nothing built-in, how would I go to build something myself?</p>