title: Check ContentLength of a large response before downloading content
body: <p>I'm using HttpWebRequest and want to check the ContentLength of the response before the entire response is downloaded. But when calling:</p>
  
  <pre><code>var res = request.GetResponse(); // entire response is being downloaded
  var len = res.ContentLegth; // need only this value 
  </code></pre>
  
  <p>How can this be achived in C# ?</p>