python bottle server sent events - one way to handle client disconnects


A Lot of people including me wonder how to handle client disconnections when using Server Sent Events (SSE). This example shows one way of doing it in bottle.

There is a stack overflow question I asked about this here

Note that for my purposes, I don't care if events are 'lost' when there is no client present, but you may care. If so, then take advantage of the SSE ID: record as discussed on Simon Baynes's blog post

How it works:

This seems like a merry dance, and it is. But I have not found a way as yet to be notified when a client has 'gone away' in bottle. I suspect it is possible by attaching to the internal bottle event handler in some way. However, for my particular case the code below works well. With a little tidy up and testing it can be put into proper service.

    class EventDispatcher:
        def __init__(self, main_queue):
            self.main_queue = main_queue
            self.clients = weakref.WeakSet()

        def register_client(self, queue):
            logging.debug("Registering client queue %s", queue)

        def start(self):

            class EnqueueThread:
                def __init__(self, main_queue, clients):
                    self.main_queue = main_queue
                    self.clients = clients

                def __call__(self):
                    while True:
                        msg = self.main_queue.get()
                        logging.debug("Got message. There are %d clients", len(self.clients))
                        for x in self.clients:
                            logging.debug("Delivering message to client %s", x)
                            except Queue.Full:
                                logging.error("Client %s queue is full, message dropped", x)  

            self.enqueue_thread = EnqueueThread(self.main_queue, self.clients)
            threading.Thread(None, self.enqueue_thread).start()