'use strict';

const net = require('node:net');

const PORT = Number(process.env.PORT || 19090);
const HOST = process.env.HOST || '0.0.0.0';

if (Number.isNaN(PORT)) {
  throw new Error('PORT must be a number');
}

const server = net.createServer((socket) => {
  socket.setKeepAlive(true, 15000);

  socket.on('data', (buf) => {
    const msg = buf.toString('utf8').trim();
    if (msg === 'ping') {
      socket.write('pong\n');
    }
  });
});

server.listen(PORT, HOST, () => {
  console.log(`[probe] listening on ${HOST}:${PORT}`);
});