server.js

// Usage:
// node server.js <listen host> <listen port>
const net = require('net');
const process = require('process');

const host = process.argv[2];
const port = +process.argv[3];

const server = net.createServer((socket) => {
    let received = 0;

    console.log(`[${socket.remoteAddress}] connected`);

    socket.on('data', buffer => {
        const data = buffer.toString();
        console.log(`[>] [${++received}] ${data}`);
        if (data === 'ping') {
            console.log(`[<] pong`);
            socket.write('pong');
        }
    });

    socket.on('error', (err) => {
        console.error(err);
        socket.destroy();
    });

    socket.on('timeout', () => {
        socket.destroy();
    });

    socket.on('close', () => {
        console.log(`[${socket.remoteAddress}] disconnected`);
    });
});

server.listen(port, host);