Flask: stream file upload without form boundary data to file - flask

Question

I want to upload large files using flask. Rather than try to load the entire file into memory, I've implemented the request.stream.read() method to stream the file to disk in chunks, as per the following code, which is very similar to answers given to many similar questions I have found:
#app.route("/uploadData", methods=["POST"])
def uploadData():
filename = uuid.uuid4().hex + '.nc'
filePath = os.path.join("/tmp", filename)
with open(filePath, "wb+") as f:
chunk_size = 4096
while True:
chunk = flask.request.stream.read(chunk_size)
if len(chunk) == 0:
break
f.write(chunk)
return flask.jsonify({'success': True, 'filename': filename})
This works well, except that it "wraps" the file in post data, like the following:
------WebKitFormBoundaryoQ8GPdNkcfUNrKBd
Content-Disposition: form-data; name="inputFile"; filename="some_file_upload.nc"
Content-Type: application/x-netcdf
<Actual File content here>
------WebKitFormBoundaryoQ8GPdNkcfUNrKBd--
How can I stream the file to disk without getting the form boundary stuff?
In theory, I could call flask.request.file or the like to get the file correctly, but as that loads the entire file into memory (or more likely a temporary file), and is quite slow relative to the stream method, I don't like it as a solution.
If it makes a difference, I'm initiating the file upload using the following javascript:
var formData=new FormData($('#fileform')[0])
$.ajax({
url:'/uploadData',
data:formData,
processData:false,
contentType:false,
type:'POST'
})
EDIT: I've managed to work around the issue by using readline() rather than read(), discarding the first four lines, and then checking for chunk starting with "---" to discard the last line, which works. However, this feels both kludgy and fragile, so if there is a better solution, I would love to hear it.