title: download file with PHP through varnish generating them directly on the output buffer
body: <p>the scenario is:
  Download a file that is generate directly onto <code>php://output</code> write into it.</p>
  
  <p>Without varnish the behavior is the file is downloaded properly while the server writing on the buffer.</p>
  
  <p>with varnish the client is waiting until the whole file is generated and then download the file.</p>
  
  <p>Is there a particular configuration for varnish to accomplish the start immediatly download the file instead of waiting the full generated file?</p>
  
  <p>I already try to pass the URL (Varnish rule to skip the caching mechanism) where the file is generated, but writing into the buffer it doesn't make sense, doesn it?</p>
  
  <p><strong>EDIT</strong></p>
  
  <p>from a perspective PHP view, It open a filestream on <code>php://output</code> and write into that stream </p>
  
  <pre><code>$out = fopen( 'php://output', 'w' );
  fputcsv( $out, $whatever ); // or fwrite
  </code></pre>