Discovery

import { Discovery, mdnsMulticast, mdnsUnicast } from '@corewire/core/discovery';

@corewire/core/discovery has its own DNS encoder and decoder, with no dependencies. It sends DNS-SD queries over multicast or unicast from a socket per network interface.

The Discovery class

A Discovery searches for one service type.

import { Discovery } from '@corewire/core/discovery';

const airplay = new Discovery('_airplay._tcp.local');

const all = await airplay.find();
const one = await airplay.findUntil('Living-Room.local');
const byAddress = await airplay.findByAddress('192.168.1.20');

console.log(all.length, one.address, byAddress?.service.port);

Method	Meaning
find(useCache = true)	One multicast scan; a scan less than 30 seconds old is reused
findUntil(id, tries = 10, timeout = 1000)	Scans without cache until the id shows up, waiting timeout ms between tries; throws DiscoveryError after the last try
findByAddress(address, timeout = 4, wakePorts = [])	A unicast query to one address; null when it does not answer
Discovery.findServices(services, useCache = true)	One multicast scan for several service types, as a map
Discovery.clearCache()	Forgets every cached scan
Discovery.wake(address, ports)	Knocks on each port to wake a sleeping device

A DiscoveryResult has the id, address, txt record, fqdn and the service port, protocol and type. The model identifier is in the TXT record, as txt.model or txt.am.

DiscoverOptions ({useCache?: boolean}) lives here once. The discover() of every protocol package and of @corewire/devices takes it.

The service constants live in the protocol packages: AIRPLAY_SERVICE in @corewire/airplay, RAOP_SERVICE in @corewire/airplay/raop and COMPANION_LINK_SERVICE in @corewire/companion-link. Each package also has a discover() of its own.

Raw queries

mdnsMulticast(services, timeout = 4) and mdnsUnicast(hosts, services, timeout = 4, wakePorts = []) return MdnsService records with name, type, address, port and properties. Timeouts are in seconds.

import { mdnsUnicast } from '@corewire/core/discovery';

const services = await mdnsUnicast(['192.168.1.20'], ['_airplay._tcp.local', '_companion-link._tcp.local'], 5, [7000]);

for (const service of services) {
    console.log(service.type, service.port);
}

Advertising

MdnsResponder advertises one service with periodic multicasts and answers queries for its type. It does not fully parse DNS questions, so keep it to quiet test networks.

import { MdnsResponder } from '@corewire/core/discovery';
import { Context } from '@corewire/core/transport';

const responder = new MdnsResponder(new Context('test').logger, {
    instance: 'Test Receiver',
    type: '_airplay._tcp.local',
    host: 'test-receiver.local',
    port: 7000,
    txt: {model: 'AppleTV14,1'}
});

responder.start();