File is empty after saving flask uploads

Question

I\'ve been trying to upload a file using Flask and HTML forms. Now I can save an uploaded file but it shows up empty (0 bytes). After that I store the form entries in a database

Answer 1

I realized that flask has a habit of including one empty file upload with the exact same name and details as one of the file attachments(usually the first attachment) WHEN you use the 'multiple' attribute in your form.

My workaround was to

1. create a temporary random filename and save the file upload
2. use os.stat(temp_filename).st_size to check if the file is empty
3. if the file is empty, delete it with os.remove, otherwise, rename the file to your preferred [secure] filename

an example...

# ...

def upload_file(req):
    if req.method != 'POST': return

    # file with 'multiple' attribute is 'uploads'
    files = req.files.getlist("uploads")

    # get other single file attachments
    if req.files:
        for f in req.files: files.append(req.files[f])

    for f in files:

        if not f.filename: continue

        tmp_fname = YOUR_TEMPORARY_FILENAME
        while os.path.isfile(tmp_fname):
            # you can never rule out the possibility of similar random 
            # names
            tmp_fname = NEW_TEMPORARY_FILENAME

        # TEMP_FPATH is he root temporary directory
        f.save(os.path.join(TEMP_FPATH, tmp_fname))

        # and here comes the trick
        if os.stat(os.path.join(TEMP_FPATH, tmp_fname)).st_size:
            os.system("mv \"{}\" \"{}\" > /dev/null 2> /dev/null".format(
                os.path.join(TEMP_FPATH, tmp_fname),
                os.path.join(ACTUAL_FILEPATH, f.filename))
            ))
        else:
            # cleanup
            os.remove(os.path.join(TEMP_FPATH, tmp_fname))
            pass

@app.route("/upload", methods=["POST"])
def upload():
    upload_files(request)

    return "files are uploaded!"

# ...