Executing non pubsub command after unsubscribe

[quard8]

I'm trying to implement simple long-polling chat and have strange situation. When adding new message, message id will be pushed to channel. On updates handler I subscribing to that channel. But I can't execute any commands, because I got exception

RequestError (on ZRANGEBYSCORE [('messages', '22', '22'), {}]): Calling not pub/sub command during subscribed state

I'm doing like this:

    @tornado.web.asynchronous
    @tornado.gen.engine
    def on_pubsub_message(self, message):
        if message.kind == 'message':
            yield tornado.gen.Task(self.client.unsubscribe, 'chat_messages')
            messages = yield tornado.gen.Task(self.client.zrangebyscore, 'messages', message.body, message.body)
            result = []
            for m in messages:
                result.append(json.loads(m[0]))

            response = {
                'm': result[::-1]
            }
            self.set_header('Content-Type', 'application/json')
            self.finish(json.dumps(response))

So you can see that I'm unsubscribing and still get error. What I'm missing?

[leporo]

Here are my suggestions:

• Use a single global Client instance for zrangebyscope commands and create a Client instance for each Pub/Sub channel (or connected client).
• Consider using the synchronous redis-py library instead of tornado-redis for zrangebyscope calls.
• Do not wrap your message handler with @tornado.gen.engine and @tornado.web.asynchronous decorators, it should be as simple and fast as possible. Set IOLoop callback (http://www.tornadoweb.org/en/stable/ioloop.html?highlight=ioloop#tornado.ioloop.IOLoop.add_callback) to run an asynchronous code on receiving a message.
• Consider using the sockjs transport for your application. You may find the sockjs-tornado library here: https://github.com/MrJoes/sockjs-tornado. Use this websockets demo application: https://github.com/leporo/tornado-redis/tree/master/demos/websockets as a starting point. Just inherit your connection handlers from the sockjs.tornado.SockJSConnection class instead of the tornado.websocket.WebSocketHandler class.

[quard8]

Thanks for quick answer! I will try to use global Client.

WebSocket's are great, but for iOS application it still painfull to check connections on app close.

Thanks, anyway!

[leporo]

Oh, I didn't mentioned in my previous answer that you may use long-polling connections with sockjs.

Please check the documentation and client source code here: https://github.com/sockjs/sockjs-client#sockjs-client-api. May be it would me easier to implement sockjs connection protocol in your iOS application and get the websocket connection support (to be used by Android or web applications) "for free"?

However, it's only a suggestion. Thank you.