title: Multiple file upload with md5 check before upload
body: <p>I am building a webpage for which I need a multi-file upload implementation that can hash a file before uploading it to the server.</p>
  
  <p>The idea is that users can upload files that may or may not exist on the server already. To save bandwidth I want to hash the file before uploading it to the server, send the hash via POST, and only proceed with upload if the server responds that it does not have a file with this hash.</p>
  
  <p>Are there any free Flash-based implementations (I suppose that JavaScript won't be able to load the file and hash it) that may work for me?</p>