Stop processing Flask route if request aborted
There is a potentially... hacky solution to your problem. Flask has the ability to stream content back to the user via a generator. The hacky part would be streaming blank data as a check to see if the connection is still open and then when your content is finished the generator could produce the actual image. Your generator could check to see if processing is done and return None
or ""
or whatever if it's not finished.
from flask import Response@app.route('/image')def generate_large_image(): def generate(): while True: if not processing_finished(): yield "" else: yield get_image() return Response(generate(), mimetype='image/jpeg')
I don't know what exception you'll get if the client closes the connection but I'm willing to bet its error: [Errno 32] Broken pipe
I was just attempting to do this same thing in a project and I found that with my stack of uWSGI and nginx that when a streaming response was interrupted on the client's end that the following errors occurred
SIGPIPE: writing to a closed pipe/socket/fd (probably the client disconnected) on requestuwsgi_response_write_body_do(): Broken pipe [core/writer.c line 404] during GETIOError: write error
and I could just use a regular old try
and except
like below
try: for chunk in iter(process.stdout.readline, ''): yield chunk process.wait() except: app.logger.debug('client disconnected, killing process') process.terminate() process.wait()
This gave me:
- Instant streaming of data using Flask's generator functionality
- No zombie processes on cancelled connection
As far as I know you can't know if a connection was closed by the client during the execution because the server is not testing if the connection is open during the execution. I know that you can create your custom request_handler
in your Flask application for detecting if after the request is processed the connection was "dropped".
For example:
from flask import Flaskfrom time import sleepfrom werkzeug.serving import WSGIRequestHandlerapp = Flask(__name__)class CustomRequestHandler(WSGIRequestHandler): def connection_dropped(self, error, environ=None): print 'dropped, but it is called at the end of the execution :('@app.route("/")def hello(): for i in xrange(3): print i sleep(1) return "Hello World!"if __name__ == "__main__": app.run(debug=True, request_handler=CustomRequestHandler)
Maybe you want to investigate a bit more and as your custom request_handler
is created when a request comes you can create a thread in the __init__
that checks the status of the connection every second and when it detects that the connection is closed ( check this thread ) then stop the image processing. But I think this is a bit complicated :(.