Flask server sent events socket exception

Question

I am thinking of using SSE to push new data to the client and using Flot(javascript charting library) display "live" updates. My server runs on python Flask framework and I have figured out how to push the data to the client, but the problem occurs as soon as I leave the page:

Exception happened during processing of request from ('127.0.0.1', 38814)
Traceback (most recent call last):
  File "/usr/lib/python2.7/SocketServer.py", line 582, in process_request_thread
    self.finish_request(request, client_address)
  File "/usr/lib/python2.7/SocketServer.py", line 323, in finish_request
    self.RequestHandlerClass(request, client_address, self)
  File "/usr/lib/python2.7/SocketServer.py", line 640, in __init__
    self.finish()
  File "/usr/lib/python2.7/SocketServer.py", line 693, in finish
    self.wfile.flush()
  File "/usr/lib/python2.7/socket.py", line 303, in flush
    self._sock.sendall(view[write_offset:write_offset+buffer_size])
error: [Errno 32] Broken pipe

I understand why the error occurs - the socket is never closed due the infinite loop serving up "live" data. Question is how do I detect the page change and cleanly close the socket? Can I close the connection on the client side? How do I detect the page change then?

This is the server code skeleton, I would of course replace the text message with json containing the list of objects to display:

def event_stream():
    import time
    while True:
        time.sleep(1)
        yield "data: This is a message number X.\n\n"

@app.route('/stream')
def stream():
    return Response(event_stream(), mimetype="text/event-stream")

Answer 1

You could use either onBeforeUnload or jQuery's window.unload() to make an Ajax call to some tear down method that closes the handle. Something like:

$(window).unload(
    function() {
        $.ajax(type: 'POST',
               async: false,
               url: 'foo.com/client_teardown')
    }
}

There are some inconsistencies with how the unload()/onBeforeUnload() are handled, so you may have some more work to do in something like Chrome.

Answer 2

I have no better answer, but I don't think the above ajax request to server is good.

In flask, SSE use streaming in a Response object, if there is a way to detect the disconnect or pipe broken event in Response, that would be better to handle socket events and release other resources allocated.