Flask large file download

Memory Error occurs when downloading a file from Flask. The size of the file is about 100 megabytes. How can I fix it?

Flask Download Code

return send_from_directory(s_trash_path, s_zip_name, mimetype='zip', as_attachment=True)

Error Code

[2018-07-21 16:11:22,328] ERROR in app: Exception on /ec-fileupload/download/select [POST]
Traceback (most recent call last):
  File "/home/venv_ec_fileupload/lib/python3.6/site-packages/flask/app.py", line 1982, in wsgi_app
    response = self.full_dispatch_request()
  File "/home/venv_ec_fileupload/lib/python3.6/site-packages/flask/app.py", line 1615, in full_dispatch_request
    return self.finalize_request(rv)
  File "/home/venv_ec_fileupload/lib/python3.6/site-packages/flask/app.py", line 1632, in finalize_request
    response = self.process_response(response)
  File "/home/venv_ec_fileupload/lib/python3.6/site-packages/flask/app.py", line 1856, in process_response
    response = handler(response)
  File "./app/__init__.py", line 170, in after_request
    s_data = resp.get_data()
  File "/home/venv_ec_fileupload/lib/python3.6/site-packages/werkzeug/wrappers.py", line 987, in get_data
    rv = b''.join(self.iter_encoded())
MemoryError

Solution

Since your file is large and dynamically generated, I'd suggest you not to use send_from_directory() to send files.

Check out the flask streaming documentation on how to stream files (sending small chunks of data instead of a full file) : http://flask.pocoo.org/docs/1.0/patterns/streaming/

from flask import Response

@app.route('/large.csv')
def generate_large_csv():
    def generate():
        for row in iter_all_rows():
            yield ','.join(row) + '\n'
    return Response(generate(), mimetype='text/csv')

The above code is a snippet for how to stream csv files using flask.

However, if your file is static, then Flask recommends using nginx for deployment.