title: How to show a progress bar while generating a PDF file for download, without IE "download" warnings
body: <p>I've got a communication between client and server. The process is simple:</p>
  
  <ol>
  <li>I'm making an AJAX POST request to a controller which generates a pdf in the file system</li>
  <li>On success of the above request a form GET request is made to get the pdf back and the standard browser "save or open" dialog box opens up</li>
  </ol>
  
  <p>The reason I'm having a two step process is because I need to have a progress bar while the pdf is being generated.</p>
  
  <p>The reason of the second request being a form submit rather than part of the AJAX request is because I can't get the standard browser "save or open" dialog box.</p>
  
  <p>The problem with this approach is that IE7 &amp; IE8 pop up a their annoying notification bar notifying the user that the it is dangerous to download the content and I don't want that.</p>
  
  <p>So:</p>
  
  <ol>
  <li>I need the progress bar.</li>
  <li>If I go for an AJAX request only I need a way to pop up the "save or open" dialog box.</li>
  <li>If I go for the a form GET submit I need a way of knowing when the file has been generated in order to stop the progress bar, something like a shared flag between server and client. </li>
  </ol>
  
  <p>Any help appreciated.</p>