title: Tornado - empty json when angularjs upload image
body: <p>In my Html file:</p>
  
  <pre><code> &lt;div class="col-sm-10"&gt;
            &lt;div ngf-drop ngf-select ng-model="files" class="drop-box" 
              ngf-drag-over-class="'dragover'" ngf-multiple="true" ngf-allow-dir="true"
              accept="image/*,application/pdf" 
              ngf-pattern="'image/*,application/pdf'"&gt;Drop pdfs or images here or click to upload&lt;/div&gt;
          &lt;div ngf-no-file-drop&gt;File Drag/Drop is not supported for this browser&lt;/div&gt;
          &lt;/div&gt;
  </code></pre>
  
  <p>In my Angularjs file:</p>
  
  <pre><code>app.controller('registerController', ['$scope', '$http', 'Upload', '$timeout', function($scope, $http, Upload, $timeout) {
    $scope.$watch('files', function() {
      $scope.upload($scope.files);
    })
  
    $scope.$watch('file', function () {
        if ($scope.file != null) {
          $scope.files = [$scope.file]; 
      }
  });
  
    $scope.upload = function (files) {
      if (files &amp;&amp; files.length) {
          for (var i = 0; i &lt; files.length; i++) {
            var file = files[i];
            if (!file.$error) {
              Upload.http({
                  method: 'POST',
                  url: '/upload',
                  data: {
                     username: 'Testing',
                     file: file
                  }                    
              }).then(function (response) {
                  console.log(response)
              }, function errorCallback(response) {
                console.log('Error: ' + response)
              });
            }
          }
      }
  };
  </code></pre>
  
  <p>In my python file:</p>
  
  <pre><code>class UploadHandle(tornado.web.RequestHandler):
      def post(self):
          userData = json.loads(self.request.body)
          print userData
  </code></pre>
  
  <p>Then, my result of python is showing 
  {"username":"testing","file":{}}</p>
  
  <p>I can get the username, but why my file is return empty value?</p>