dns2/client/tcp.js

A DNS Server and Client Implementation in Pure JavaScript with no dependencies.

const tls = require('node:tls');
const tcp = require('node:net');
const Packet = require('../packet');
const { debuglog } = require('node:util');

const debug = debuglog('dns2');

const makeQuery = ({
  name,
  type = 'A',
  cls = Packet.CLASS.IN,
  clientIp,
  recursive = true,
}) => {
  const packet = new Packet();
  packet.header.rd = recursive ? 1 : 0;

  if (clientIp) {
    packet.additionals.push(
      Packet.Resource.EDNS([Packet.Resource.EDNS.ECS(clientIp)]),
    );
  }

  packet.questions.push({ name, class: cls, type: Packet.TYPE[type] });
  return packet.toBuffer();
};

const sendQuery = (client, message) => {
  const len = Buffer.alloc(2);
  len.writeUInt16BE(message.length);
  client.write(Buffer.concat([len, message]));
};

const protocols = {
  'tcp:': (host, port) => tcp.connect({ host, port }),
  'tls:': (host, port) => tls.connect({ host, port, servername: host }),
};

const TCPClient = ({
  dns,
  protocol = 'tcp:',
  port = protocol === 'tls:' ? 853 : 53,
} = {}) => {
  if (!protocols[protocol]) {
    throw new Error('Protocol must be tcp: or tls:');
  }

  return async (name, type, cls, options = {}) => {
    const message = makeQuery({ name, type, cls, ...options });
    const [host] = dns.split(':');
    const client = protocols[protocol](host, port);
    // The socket outlives the single-message read below — we still end() it —
    // and Packet.readStream releases its own listeners once it has the message.
    // An 'error' with no listener is fatal to the process, so hold one here for
    // the socket's whole life; readStream's rejection reports the failure.
    client.on('error', err => debug('tcp: socket error: %s', err.message));

    sendQuery(client, message);
    const data = await Packet.readStream(client);
    client.end();

    if (!data.length) throw new Error('Empty response');
    return Packet.parse(data);
  };
};

module.exports = TCPClient;