How does WebSockets work?

Let's see how the WebSockets protocol works over HTTP. For a client to establish a connection to a web server using WebSockets, it first performs a WebSocket handshake request, which is very similar to a normal HTTP request, but with the Upgrade header, as follows:

GET /path/to/endpoint HTTP/1.1 
Host: localhost 
Upgrade: websocket 
Connection: Upgrade 
Sec-WebSocket-Key: xqBt3ImNzJbYqRINxEFlkg== 
Origin: http://localhost 
Sec-WebSocket-Version: 13 

As you can see, the upgrade header, with some other WebSockets-related headers, is used to perform what's called a WebSockets handshake. The handshake request asks the server to use the WebSockets protocol.

If the web server supports the WebSockets protocol on this path, it should respond with the following handshake response:

HTTP/1.1 101 Switching Protocols 
Upgrade: websocket 
Connection: Upgrade 
Sec-WebSocket-Accept: K7DJLdLooIwIG/MOpvWFB3y3FE8= 

The connection switches to a bi-directional type, and the connection lasts...