node/test/parallel/test-net-autoselectfamily-ipv4first.js

'use strict';

const common = require('../common');
const { parseDNSPacket, writeDNSPacket } = require('../common/dns');

const assert = require('assert');
const dgram = require('dgram');
const { Resolver } = require('dns');
const { createConnection, createServer } = require('net');

// Test that happy eyeballs algorithm is properly implemented when a A record is returned first.

function _lookup(resolver, hostname, options, cb) {
  resolver.resolve(hostname, 'ANY', (err, replies) => {
    assert.notStrictEqual(options.family, 4);

    if (err) {
      return cb(err);
    }

    const hosts = replies
      .map((r) => ({ address: r.address, family: r.type === 'AAAA' ? 6 : 4 }));

    if (options.all === true) {
      return cb(null, hosts);
    }

    return cb(null, hosts[0].address, hosts[0].family);
  });
}

function createDnsServer(ipv6Addr, ipv4Addr, cb) {
  // Create a DNS server which replies with a AAAA and a A record for the same host
  const socket = dgram.createSocket('udp4');

  socket.on('message', common.mustCall((msg, { address, port }) => {
    const parsed = parseDNSPacket(msg);
    const domain = parsed.questions[0].domain;
    assert.strictEqual(domain, 'example.org');

    socket.send(writeDNSPacket({
      id: parsed.id,
      questions: parsed.questions,
      answers: [
        { type: 'A', address: ipv4Addr, ttl: 123, domain: 'example.org' },
        { type: 'AAAA', address: ipv6Addr, ttl: 123, domain: 'example.org' },
      ]
    }), port, address);
  }));

  socket.bind(0, () => {
    const resolver = new Resolver();
    resolver.setServers([`127.0.0.1:${socket.address().port}`]);

    cb({ dnsServer: socket, lookup: _lookup.bind(null, resolver) });
  });
}

// Test that IPV6 is NOT reached if IPV4 is sorted first
if (common.hasIPv6) {
  createDnsServer('::1', '127.0.0.1', common.mustCall(function({ dnsServer, lookup }) {
    const ipv4Server = createServer((socket) => {
      socket.on('data', common.mustCall(() => {
        socket.write('response-ipv4');
        socket.end();
      }));
    });

    const ipv6Server = createServer((socket) => {
      socket.on('data', common.mustNotCall(() => {
        socket.write('response-ipv6');
        socket.end();
      }));
    });

    ipv4Server.listen(0, '127.0.0.1', common.mustCall(() => {
      const port = ipv4Server.address().port;

      ipv6Server.listen(port, '::1', common.mustCall(() => {
        const connection = createConnection({
          host: 'example.org',
          port,
          lookup,
          autoSelectFamily: true,
        });

        let response = '';
        connection.setEncoding('utf-8');

        connection.on('data', (chunk) => {
          response += chunk;
        });

        connection.on('end', common.mustCall(() => {
          assert.strictEqual(response, 'response-ipv4');
          ipv4Server.close();
          ipv6Server.close();
          dnsServer.close();
        }));

        connection.write('request');
      }));
    }));
  }));
}