tcp-echo-cli.mjs

import * as net from 'net';
import * as rl from 'readline';
import assert from 'assert/strict';

const [ COMMAND, PORT, HOST ] = process.argv.splice(2);

try {
  assert.strictEqual(
    ['open', 'host'].includes(COMMAND),
    true,
    'Valid commands: "host <port>", "open <port> <host?>"'
  );

  const run = { open, host };

  run[COMMAND]();

} catch (err) {
  process.stderr.write(err.message + '\n');
}

function open () {
  const client = net.createConnection({ host: HOST | 'localhost', port: Number(PORT) });
  const readline = rl.createInterface({ input: process.stdin });

  client
    .on('connect', handleOpen)
    .on('data', handleData)
    .on('error', handleError)
    .once('end', handleClose);

  readline.on('line', line => client.write(line));

  function handleOpen () {
    process.stdout.write('connected!' + '\n');
  };

  function handleData (data) {
    process.stdout.write('> ' + data + '\n');
  };

  function handleError (err) {
    process.stderr.write('connection error: ' + err.message + '\n');
    process.exit(1);
  };

  function handleClose () {
    process.stdout.write('disonnected!' + '\n');
  };
}

function host () {
  const server = net.createServer();

  const handler = socket => {
    var addr = socket.remoteAddress + ':' + socket.remotePort;
    process.stdout.write('new connection: ' + addr + '\n');

    socket
      .on('data', handleData)
      .on('error', handleError)
      .on('close', handleClose);

    function handleData (data) {
      process.stdout.write('echo: ' + data + '\n');
      socket.write(data);
    };

    function handleError (err) {
      process.stdout.write('error: ' + err.message + '\n');
    };

    function handleClose () {
      process.stdout.write('connection closed: ' + addr + '\n');
    };
  };

  server
    .on('connection', handler)
    .on('error', console.error);

  server.listen(
    Number(PORT) || 9000,
    () => console.info('server listening on', PORT || 9000)
  );
}

node tcp-echo-cli.mjs host 1234
node tcp-echo-cli.mjs open 1234

node tcp-echo-cli.mjs host 1234
ngrok tcp 1234
node tcp-echo-cli.mjs open <ngrok_port> <ngrok_host>