sniffer.js

const net = require('net');

function printFatal (message) {
  process.stdout.write(message);
  process.exit(1);
}

function printSuccess (message) {
  process.stdout.write(message);
  process.exit(0);
}

function getParamsFromArguments () {
  if (process.argv.includes('--help')) {
    printSuccessHelp();
  }
  if (!process.argv.includes('--host')) {
    printFatal('Host is required, e.g. "--host 8.8.8.8"');
  }
  return process.argv
    .slice(2)
    .join(' ')
    .split(/\s?--/)
    .reduce(function (acc, str) {
      if (!str) return acc;
      const [key, value] = str.split(' ');
      switch (key) {
        case 'help':
          break;
        case 'host':
          if (!value) {
            printFatal('Host value must be provided, e.g. "--host 8.8.8.8"');
          }
          acc[key] = value;
          break;
        case 'ports':
          if (!value) {
            printFatal('Ports value must be provided, e.g. "--ports 300-1024"');
          }
          if (!value.includes('-')) {
            printFatal('Ports format invalid, must be e.g. "--ports 300-1024"');
          } else {
            const [startPort, endPort] = value.split('-').map(port => parseInt(port, 10));
            if (isNaN(startPort) || startPort < 0) {
              printFatal('Start port format invalid');
            }
            if (isNaN(endPort) || endPort < 0) {
              printFatal('End port format invalid');
            }
            if (endPort > 65535) {
              printFatal('End port must be between 0-65535');
            }
            if (startPort > endPort) {
              printFatal('End port must be bigger then start port');
            }
            acc.startPort = startPort;
            acc.endPort = endPort;
          }
          break;
        default:
          acc[key] = value;
      }
      return acc;
    }, {});
}

function printSuccessHelp () {
  printSuccess(`NAME
    TCP sniffer - scans open ports on specific host.

OPTIONS
    --help
        Output a usage message and exit.

    --host
        Set a host for scan.
        E.g. "--host 127.0.0.1".

    --ports
        Set ports to scan.
        E.g. "--ports 300-1024".
        Default values: 0-65535.

EXAMPLES
    node sniffer.js --host localhost
    node sniffer.js --host localhost --ports 300-1024
`);
}

function sniffConnectionAvailabilityAsync (port, host) {
  return new Promise(function (resolve, reject) {
    const socket = new net.Socket();
    socket.setTimeout(300);

    socket.on('connect', function () {
      socket.destroy();
      resolve();
    });
    socket.on('timeout', function () {
      socket.destroy();
      reject(new Error('timeout'));
    });
    socket.on('error', function (err) {
      socket.destroy();
      reject(err);
    });

    socket.connect(port, host);
  });
}

async function scanAsync (host, port, portLimit, availablePorts = []) {
  if (port > portLimit) {
    return availablePorts;
  }
  try {
    await sniffConnectionAvailabilityAsync(port, host);
    process.stdout.write('.');
    availablePorts.push(port);
  } catch (e) {}
  return scanAsync(host, port + 1, portLimit, availablePorts);
}

(async function () {
  const { host, startPort = 0, endPort = 65535 } = getParamsFromArguments();
  const openedPorts = await scanAsync(host, startPort, endPort);
  const result = openedPorts.length ? `\n${openedPorts.join(',')} ports are opened` : `\nNo open ports on host: ${host}`;
  printSuccess(result);
})();