node-tcp-server.js

const net = require('net');
const server = net.createServer();
const config = {
    host: '0.0.0.0',
    port: 9670,
    exclusive: true,
}

server.on('connection', (socket) => {
    console.log('New client connected')
    socket.on('data', (data) => {
        const code = data.toString().slice(0,3);
        switch (code) {
            case '404':
                return socket.write(`Code ${code}: Not found, used when user request for a resource or page that does not exist.\n`);
            case '500':
                return socket.write(`Code ${code}: Internal Server, used when web server has an unxpected error.\n`);
            default:
                return socket.write(`I dont know about code "${code}" mate, or I am yet to learn about it \n`);
        }
    });

    socket.on('error', (err) => {
        console.log({ error: `error in connection ${err}` });
        socket.destroy(JSON.stringify({
            error: 'connection error',
            code: 500,
        }));
        socket.end();
    });
});

// Start server
server.listen(config);

// server running
server.on('listening', () => {
    console.log('server is listening on %j', config.port);
});

// Restart server if port or address is under use
server.on('error', (err) => {
    if (err.code === 'EADDRINUSE') {
        console.log('Address or Port in use, retrying...');
        setTimeout(() => {
            server.close();
            server.listen(config);
        }, 5000);
    } else {
        console.log({ err: `Server error ${err}` });
    }
});

module.exports = server;