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How to implement a WebSocket server using Tornado?

WebSocket in Python: Here, we are going to learn how to implement a WebSocket server using Tornado?
Submitted by Sapna Deraje Radhakrishna, on September 17, 2019

What is Tornado?

Tornado is a python web framework and asynchronous networking library. It is scalable and non-blocking. It specializes in dealing with event-driven networking. As tornado supports concurrent connections, naturally, a server can take advantage of this behavior and handle a lot of web socket connections within a single node.

What is Websocket?

WebSocket is a protocol that provides full-duplex communication channels over a single TCP connection. The behavior of the open socket makes a web connection stateless and facilitates the real-time data transfer to and from the server.

WebSockets are designed to be used in web-browsers and servers. A connection is opened once and messages can travel to-fro multiple times before the connection is closed.

Install Tornado

Installing the tornado is rather simple in a virtual environment using pip.

• Create a virtual environment
  python3 -m venv /path/to/virtual/environment
  >> python3 -m venv venv
• Source the virtual environment
  >> source venv/bin/activate
• Install the websocket-client using pip
  >> (venv) pip3 install tornado

  Using cached https://files.pythonhosted.org/packages/30/78/2d2823598496127b21423baffaa186b668f73cd91887fcef78b6eade136b/tornado-6.0.3.tar.gz
Requirement already satisfied: six in ./venv/lib/python3.7/site-packages (from websocket_client==0.56.0->-r requirements.txt (line 1)) (1.12.0)
Installing collected packages: tornado
  Running setup.py install for tornado ... done
Successfully installed tornado-6.0.3

Python example to start a web socket server using Tornado library

'''
    This module hosts a websocket server using tornado
    libraries
'''

import tornado.web
import tornado.httpserver
import tornado.ioloop
import tornado.websocket as ws
from tornado.options import define, options
import time

define('port', default=4041, help='port to listen on')

class web_socket_handler(ws.WebSocketHandler):
    '''
    This class handles the websocket channel
    '''
    @classmethod
    def route_urls(cls):
        return [(r'/',cls, {}),]
    
    def simple_init(self):
        self.last = time.time()
        self.stop = False
    
    def open(self):
        '''
            client opens a connection
        '''
        self.simple_init()
        print("New client connected")
        self.write_message("You are connected")
        
    def on_message(self, message):
        '''
            Message received on the handler
        '''
        print("received message {}".format(message))
        self.write_message("You said {}".format(message))
        self.last = time.time()
    
    def on_close(self):
        '''
            Channel is closed
        '''
        print("connection is closed")
        self.loop.stop()
    
    def check_origin(self, origin):
        return True

def initiate_server():
    #create a tornado application and provide the urls
    app = tornado.web.Application(web_socket_handler.route_urls())
    
    #setup the server
    server = tornado.httpserver.HTTPServer(app)
    server.listen(options.port)
    
    #start io/event loop
    tornado.ioloop.IOLoop.instance().start()


if __name__ == '__main__':
    initiate_server()

The above code will start the server on localhost and port as 4041.

Connect to the server using a websocket client code (example below),

from websocket import create_connection

def short_lived_connection():

    ws = create_connection("ws://localhost:4040/")
    print("Sending 'Hello Server'...")
    ws.send("Hello, Server")
    print("Sent")
    print("Receiving...")
    result =  ws.recv()
    print("Received '%s'" % result)
    ws.close()

if __name__ == '__main__':
    short_lived_connection()

Output (Client side):

>>Sending 'Hello, Server'...
>>Sent
>>Receiving...
>>Received 'You are connected'

Output (Server side):

>>New client connected
>>received message Hello, Server
>>connection is closed

References:

• Tornado
• WebSocket