JavaScript DNS-SD implementation using multicast-dns

demo.js

// 
// Author: sskaje (https://sskaje.me)
// 
// https://sskaje.me/2020/05/javascript-dns-sd
// 

const dnssd_query_name = '_protocol._tcp.local'
const dnssd_sd_query_name = '_services._dns-sd._udp.local'
const dnssd_service_name = 'My Services'
const dnssd_host_name = 'test.local'

const dnssd_services = {
    answers: [
        {
            name: dnssd_query_name,
            type: 'PTR',
            ttl : 4500,
            data: dnssd_service_name + '.' + dnssd_query_name
        }
    ],
    additionals: [
        {
            name: dnssd_service_name + '.' + dnssd_query_name,
            type: 'SRV',
            data: {
                port    : http_port,
                weight  : 0,
                priority: 0,
                target  : dnssd_host_name
            },
            ttl: 120,
            flush: 1,
        },
        {
            name: dnssd_service_name + '.' + dnssd_query_name,
            type: 'TXT',
            data: [
                "use_https=false",
                "http_port="+http_port,
                "mqtt_port="+mqtt_port,
                "server_ip="+server_ip,
            ],
            ttl: 4500,
            flush: 1,
        },
        {
            name: dnssd_host_name,
            type: 'A',
            ttl : 120,
            data: server_ip,
            flush: 1,
        }
    ]
};

let mdns = require('multicast-dns')({interface: server_ip});
mdns.on('warning', function (err) {
    console.log("Warning: ", err.stack)
})

//mdns.on('response', function (response) {
//    console.log('got a response packet:', response)
//})

mdns.on('query', function (query) {
    //console.log('got a query packet:', query)

    query.questions.forEach(function (q) {

        if (q.type === 'PTR' && q.name === dnssd_sd_query_name) {
            mdns.respond({
                answers: [
                    {
                        name: dnssd_sd_query_name,
                        type: 'PTR',
                        ttl : 3600,
                        data: dnssd_query_name
                    }
                ]
            })
        } else if (q.type === 'PTR' && q.name === dnssd_query_name) {
            mdns.respond(JSON.parse(JSON.stringify(dnssd_services)))
        }
    })
})