1. https://flask-socketio.readthedocs.io/en/latest/
2. https://www.npmjs.com/package/socket.io
3. https://github.com/yingshaoxo/Web-Math-Chat
4. https://socket.io/get-started/chat/
5. https://flask-socketio.readthedocs.io/en/latest/#flask_socketio.SocketIO