DNS A record filter proxy v2

'use strict';

let dns = require('native-dns');
let server = dns.createUDPServer({ dgram_type: 'udp6' });

function secureExit() {
    try {
        server.close();
    } catch (err) {}
    process.exit(1);
}

function exitWithError(err) {
    console.error(err);
    secureExit();
}

process.once('SIGINT', () => exitWithError('Received SIGINT'));
process.once('SIGTERM', () => exitWithError('Received SIGTERM'));

function beReady(){
    console.log('server listening on', server.address());
    try {
        process.setgid('nogroup');
        process.setuid('nobody');
    } catch (err) {
        exitWithError('can\'t drop privileges');
    }
}

server.on('listening', beReady);
server.on('close', () => console.log('server closed', server.address()));
server.on('error', (err, buff, req, res) => exitWithError(err.stack));
server.on('socketError', (err, socket) => exitWithError(err));

server.serve(53, 'localhost');

let authority = { address: '2001:4860:4860::8888', port: 53, type: 'udp' };

function proxy(question, response, cb) {
    var request = dns.Request({
        question: question, // forwarding the question
        server: authority,  // this is the DNS server we are asking
        timeout: 1000
    });

    // when we get answers, append them to the response
    request.on('message', (err, msg) => {
        msg.answer.forEach(a => {
            if (a.type != 1) {
                response.answer.push(a);
            }
        });
    });

    request.on('end', cb);
    request.send();
}

let async = require('async');

function handleRequest(request, response) {
    let f = []; // array of functions

    // proxy all questions
    // since proxying is asynchronous, store all callbacks
    request.question.forEach(question => {
        f.push(cb => proxy(question, response, cb));
    });

    // do the proxying in parallel
    // when done, respond to the request by sending the response
    async.parallel(f, function() { response.send(); });
}

server.on('request', handleRequest);