Socket.io with TLS

Socket.io with TLS

After the last article, this place has not been updated for a long time. In order to avoid being a shopping list blog, I try to write some useful information or at least, provide some learning journeys. In the last article, I want to build an on-line game for interactive RPG, you can spell some magics or attack to the enemy. However, if the interaction is time-sensitive, the server has to push events to the client, i.e., our web page to ensure the operation works. Moreover, the communication between the server and the client must be in secure. Therefore, I want to use websocket over TLS to achieve those goals.
Nevertheless, websocket still has some shortages like group management. If the function of the game becomes more growing, e.g., multi-player fight together with the same enemy. The game server must have a more comprehensive solution to handle the group management. The final approach is socket.io.

Socket.io is a protocol based on websocket, and in addition, socket.io also applies the room concept to deal with emitting a message to multiple receivers.

First of all, I have no idea about the https, and I don’t know what is the certificate and what is the CA. So, this article will not introduce those details about the protocol, I will focus on how to build a workable server.

Now, you have a private key(server.key) and a certificate(server.crt). The suffix is no meaning, you can use what you want. If you get a file from somewhere, and you don’t know what it is, you can open it via the text editor, and then, you will see the purpose at the first line.

How to build a socket.io server

There is a great example written in python at the flask socket.io. The example/app.py demonstrates how to join/leave a room, broadcast a message, and be a echoed server. Nevertheless, this example does not tell you how to enable the TLS and become a https server. The reason behind it is very simple, you only need the original function in flask. If you want to enable the TLS, you have to replace the line:

socketio.run(app, debug=True)

to:

socketio.run(app, debug=True, ssl_context=(‘server.crt’, ‘server.key’))

Then, the server will run in https. However, you maybe want to improve the scalability for this server by using asynchronous mechanism. You can install the gevent and gevent-websocket. It is worth noting that you have to replace the mentioned line to:

socketio.run(app, debug=True, certfile=’server.crt’, keyfile=’server.key’)

Because the gevent cannot support the parameter, ssl_context. Things are almost done. Finally, you can use gunicorn and nginx to further expand the scalability and reliably like:

gunicorn -k geventwebsocket.gunicorn.workers.GeventWebSocketWorker -w 1 — certfile server.crt — keyfile server.key -b 127.0.0.1:3000 app:app

I will introduce how to benchmark the socket.io next time, especially the amount of concurrent clients. See you.

Originally published on Medium