Getting an empty ImmutableMultiDict object from jQuery request data

问题

Trying to upload a file to server but the ImmutableMultiDict object is returning empty.

upload.html

<html>
 <head>
  <title>Upload File Ajax</title>
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.min.js"></script>
<script type="text/javascript">
$(function() {
    $('#upload-file-btn').click(function() {
        var form_data = new FormData($('#upload-file')[0]);
        form_data.append('file', $('input[type=file]')[0].files[0]);
        console.log(form_data)
        $.ajax({
            url: '/uploadajax',
            data: form_data,
            type: 'POST',
            contentType: false,
            cache: false,
            processData: false,
            async: false,
            success: function(data) {
                console.log('Success!');
                // console.log(data);
            },
        });
    });
});

</script>

 </head>
 <body>
<form action="" name="upload-file" id="upload-file" method="post" enctype="multipart/form-data">
    <fieldset>
        <label for="file">Select a file</label>
        <input name="file" id="file" type="file">
    </fieldset>
    <fieldset>
        <button id="upload-file-btn" type="button">Upload</button>
    </fieldset>
</form>

 </body>
</html>

Flask

app = Flask(__name__)

@app.route('/')
def index():
  return render_template("upload.html")


@app.route('/uploadajax', methods = ['POST'])
def upldfile():
  logging.debug('request.method : %s',  request.method)
  logging.debug('request.files : %s', request.files)
  logging.debug('request.args : %s', request.args)
  logging.debug('request.form : %s', request.form)
  logging.debug('request.values : %s', request.values)
  logging.debug('request.headers : %s', request.headers
  logging.debug('request.data : %s', request.data)

  upload_files = request.files.getlist("file")

  logging.debug('upload_files : %s', upload_files)

  file_val = request.files

  for k, v in file_val.items() :logging.debug('key : %s -- value : %s ', k, v)


  # if request.method == 'POST':file_val = request.files['file']
  return render_template('upload.html')


if __name__ == '__main__': 
  app.run(host='127.0.0.1', debug=True, port=2345, use_reloader=True)

This is the log data

    016-05-03 00:05:30,500 - root - DEBUG - request.method : POST
    2016-05-03 00:05:30,500 - root - DEBUG - request.files : ImmutableMultiDict([])
    2016-05-03 00:05:30,500 - root - DEBUG - request.args : ImmutableMultiDict([])
    2016-05-03 00:05:30,501 - root - DEBUG - request.form : ImmutableMultiDict([])
    2016-05-03 00:05:30,501 - root - DEBUG - request.values : CombinedMultiDict([ImmutableMultiDict([]), ImmutableMultiDict([])])
    2016-05-03 00:05:30,501 - root - DEBUG - request.headers : Referer: http://127.0.0.1:2345/
    Origin: http://127.0.0.1:2345
    Content-Length: 368
    User-Agent: Mozilla/5.0....
    Connection: keep-alive
    X-Requested-With: XMLHttpRequest
    Host: 127.0.0.1:2345
    Accept: */*
    Accept-Language: en-US,en;q=0.8
    Content-Type: false
    Accept-Encoding: gzip, deflate2016-05-03 03:13:58,236 - root - DEBUG - request.data : ------WebKitFormBoundaryA8jmfBTRKGJFtMS
Content-Disposition: form-data; name="file"; filename="test_upload.txt"
Content-Type: text/plain

qbcdefgh
abcdefgh
------WebKitFormBoundaryA8jmfBTRKGJFtMS
Content-Disposition: form-data; name="file"; filename="test_upload.txt"
Content-Type: text/plain

qbcdefgh
abcdefgh
------WebKitFormBoundaryA8jmfBTRKGJFtMS--


2016-05-03 00:05:30,501 - root - DEBUG - upload_files : []