Understanding the principles of two-way communication with WebSockets

You have probably noticed that the name WebSockets is a direct reference to the traditional concept of sockets in Unix systems. While technically unrelated, they achieve the same goal: to open a communication channel between two applications. As we said in the introduction, HTTP works only on a request-response principle, which makes the implementation of applications that need real-time communication between the client and the server difficult and inefficient.

WebSockets try to solve that by opening a full-duplex communication channel, meaning that messages can be sent in both directions and possibly at the same time. Once the channel is opened, the server can send messages to the client without having to wait for a request from the client.

Even if HTTP and WebSocket are different protocols, WebSockets have been designed to work with HTTP. Indeed, when opening a WebSocket, the connection is first initiated...