code: function hashFile(filename, callback) {
  
      var calledBack = false,
          md5sum = crypto.createHash('md5'),
          stream = fs.ReadStream(filename);
  
      stream.on('data', function (data) {
        md5sum.update(data);
      });
  
      stream.on('end', function () {
        var hash = md5sum.digest('hex');
        callback(null, hash);
      });
  
      stream.on('error', function(err) {
        handleResponse(err);
      });
  
      function handleResponse(err, hash) {
        if (calledBack) {
          return;
        }
  
        calledBack = true;
        callback(err, hash);
      }
    }
docs: Used to MD5 a file, useful when checking against already uploaded assets