How to calculate to web latency in torando?

Question

I'm using tornado web sockets and would like to calculate web socket latency to the client. I have seen using ping/pong in tornado but I didn't understand it clearly and there is no good example.

Is there any simple example code to send ping/pong response and calculate web response?

Answer 1

I have used this below code to calculate the WebSocket latency. Ping will send a timestamp. In pong, we receive the ping timestamp and calculate the latency by subtracting ping timestamp from the current time.

class EchoWebSocket(tornado.websocket.WebSocketHandler):

    def open(self):
        ping_errors = 0

        # Send a ping packet with the timestamp
        def send_ping():
            global ping_errors
            timestamp = time.time()
            try:
                self.ping(str(timestamp).encode('utf-8'))
                ping_errors = 0
            except tornado.websocket.WebSocketClosedError:
                msg = "Web socket closed. Stopped ping."
                logger.info(msg)
                pinger.stop()
            except Exception:
                ping_errors += 1
                msg = "Ping failed to send."
                logger.error(msg, exc_info=True)

                if ping_errors > 3:
                    msg = "Stopping ping."
                    logger.error(msg, exc_info=True)
                    pinger.stop()

        interval = 10000 #ms
        pinger = tornado.ioloop.PeriodicCallback(send_ping, interval)
        pinger.start()

    def on_pong(self, timestamp):
        curr_time = time.time()
        time_diff  = curr_time - float(timestamp)

        if time_diff < 0:
            logger.info("Lost a ping packet")
            return
        logger.info("WebSocket Latency: {0}ms".format(
            int(ceil(time_diff * 1000))))

    def on_close(self):
        print("WebSocket closed")

In handlers,

handlers = [
             ...,
             (r'/ping', EchoWebSocket),
           ]

In javascript,

protocol = (location.protocol === 'https:') ? 'wss://' : 'ws://';
ping_ws_url = protocol + window.location.host + "/ping";
ping_ws = new WebSocket(ping_ws_url);