How to detect when stream_with_context is aborted by user in Flask?

Question

Right now I am serving a file with stream_with_context and a generator. If go to the /download endpoint in my browser, and allow the download to complete, then the 'Loop complete' print statement is reached. However, if I request the download, then cancel it (in my browser), then the print statement is not reached.

The code below is simplified. I am actually trying to make a database call AFTER the download is completed or aborted by the user. But when the user aborts the download, the statement is never reached.

@app.route('/download', methods=['GET'])
def download():
    if request.method == 'GET':
        def generate():
            for i in range(100):
                yield i # simplified code
            print('Loop complete') # this statement is only reached when the download is completed

        return Response(stream_with_context(generate()), mimetype='video/MP2T')

@jordanm placing a try/finally inside of the generate function worked. Thank you very much — Arman, Dec 14 '19 at 01:30

Arman · Accepted Answer · 2019-12-21T00:34:30.660

As @jordanm suggests, placing a try/finally block in the generate function fixed the problem.

Example:

@app.route('/download', methods=['GET'])
def download():
    if request.method == 'GET':
        def generate():
            try:
                for i in range(100):
                    yield i
            finally:
                print('Complete')

        return Response(stream_with_context(generate()), mimetype='video/MP2T')

How to detect when stream_with_context is aborted by user in Flask?

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