Sending messages actively from Tornado WebSocket server

Question

I have a Python WebSocket server. This can return a response when it receives a message.

import tornado.web
import tornado.websocket
import tornado.ioloop

class WebSocketHandler(tornado.websocket.WebSocketHandler):

    def open(self):
        print("New client connected")
        self.write_message("You are connected")

    def on_message(self, message):
        self.write_message(u"You said: " + message)

    def on_close(self):
        print("Client disconnected")

    def check_origin(self, origin):
        return True

application = tornado.web.Application([
        (r"/", WebSocketHandler),
])


if __name__ == "__main__":
    application.listen(8888)
    tornado.ioloop.IOLoop.instance().start()

However, this can't send messages before it receives one. How do I send a message actively? For example, it measures time and if it didn't receive messages for 10 sec, it send "Are you sleeping?".

I want to make chatbot using WebSocket. I use tornado and websocket because I only know this, and I would be interested if you know of better methods to use in this regard.

Answer 1

You can add a schedule with tornado.ioloop.PeriodicCallback and simply check if there has been activity or not based on time, like the following (I adapted from your code and this answer):

import tornado.web
import tornado.websocket
import tornado.ioloop
import time

class WebSocketHandler(tornado.websocket.WebSocketHandler):
    def simple_init(self):
        self.last = time.time()
        self.stop = False

    def open(self):
        self.simple_init()
        print("New client connected")
        self.write_message("You are connected")
        self.loop = tornado.ioloop.PeriodicCallback(self.check_ten_seconds, 1000, io_loop=tornado.ioloop.IOLoop.instance())
        self.loop.start()

    def on_message(self, message):
        self.write_message(u"You said: " + message)
        self.last = time.time()

    def on_close(self):
        print("Client disconnected")
        self.loop.stop()

    def check_origin(self, origin):
        return True

    def check_ten_seconds(self):
        print("Just checking")
        if (time.time() - self.last > 10):
            self.write_message("You sleeping mate?")
            self.last = time.time()

Now with a client alternating between idling and writing (adapted from here):

class Client(object):
    def __init__(self, url, timeout):
        self.url = url
        self.timeout = timeout
        self.ioloop = IOLoop.instance()
        self.ws = None
        self.connect()
        PeriodicCallback(self.keep_alive, 20000, io_loop=self.ioloop).start()
        self.ioloop.start()

    @gen.coroutine
    def connect(self):
        print("trying to connect")
        try:
            self.ws = yield websocket_connect(self.url)
        except Exception as e:
            print("connection error")
        else:
            print("connected")
            self.run()

    @gen.coroutine
    def run(self):
        once = False
        while True:
            msg = yield self.ws.read_message()
            print(msg)
            if once:
                time.sleep(11)
                once = False
            else:
                time.sleep(1)
                once = True
            self.ws.write_message("Hello matey")
            if msg is None:
                print("connection closed")
                self.ws = None
                break

    def keep_alive(self):
        if self.ws is None:
            self.connect()
        else:
            self.ws.write_message("keep alive")

We obtain the expected output:

trying to connect
connected
You are connected
You said: Hello matey
You sleeping mate?
You said: Hello matey
You said: Hello matey
You sleeping mate?