node/test/parallel/test-dgram-custom-lookup.js

'use strict';
const common = require('../common');
const assert = require('assert');
const dgram = require('dgram');
const dns = require('dns');

{
  // Verify that the provided lookup function is called.
  const lookup = common.mustCall((host, family, callback) => {
    dns.lookup(host, family, callback);
  });

  const socket = dgram.createSocket({ type: 'udp4', lookup });

  socket.bind(common.mustCall(() => {
    socket.close();
  }));
}

{
  // Verify that lookup defaults to dns.lookup().
  const originalLookup = dns.lookup;

  dns.lookup = common.mustCall((host, family, callback) => {
    dns.lookup = originalLookup;
    originalLookup(host, family, callback);
  });

  const socket = dgram.createSocket({ type: 'udp4' });

  socket.bind(common.mustCall(() => {
    socket.close();
  }));
}

{
  // Verify that non-functions throw.
  [null, true, false, 0, 1, NaN, '', 'foo', {}, Symbol()].forEach((value) => {
    assert.throws(() => {
      dgram.createSocket({ type: 'udp4', lookup: value });
    }, common.expectsError({
      code: 'ERR_INVALID_ARG_TYPE',
      type: TypeError,
      message: 'The "lookup" argument must be of type function'
    }));
  });
}