server.js

const { Server } = require('net');

const host = '0.0.0.0';
const END = 'END';

const connections = new Map();

const error = (message) => {
    console.error(message);
    process.exit(1);
}

const sendMessage = (message, origin) =>{
    //Mandar a todos menos a origin el message
    for (socket of connections.keys()) {
        if (socket !== origin){
            socket.write(message);
        }
    }
}

const listen = (port) => {
    const server = new Server();

    server.on("connection", (socket) => {
        const remoteSocket = `${socket.remoteAddress}: ${socket.remotePort}`;
        console.log(`New connection from ${remoteSocket}`);

        socket.setEncoding('utf-8');

        socket.on("data", (message) => {
            if(!connections.has(socket)){
                console.log(`Username ${message} set for connection ${remoteSocket}`);
                connections.set(socket, message);
            } else if (message === END) {
                socket.end();
                connections.delete(socket);
            } else {
                //Enviar mensaje al resto de clientes
                const fullMessage = `[${connections.get(socket)}]:  ${message}`
                console.log(`${remoteSocket} => ${fullMessage}`);
                sendMessage(fullMessage, socket);
            }
        })

        socket.on("error", (err) => error(err.message));

        socket.on("close", () => {
            console.log(`Connection with ${remoteSocket} has ended.`);
        })
    })

    server.listen({ port, host }, () => {
        console.log(`Listening on port: ${port}`)
    });

    server.on("error", (err) => error(err.message));
}

const main = () => {
    if (process.argv.length !== 3) {
        error(`Usage: node ${__filename} <port_number>`)
    }
    let port = process.argv[2];
    if (isNaN(port)) {
        error(`Invalid port: '${port}'. Must be a number`);
    }
    port = Number(port)
    listen(port);
}

if (require.main === module) {
    main();
}