Halo

Halo [Javanese] is Bonjour [French] is Hello [English]

An implementation of Multicast DNS Service Discovery in Java.

Building from Source

You need JDK-8 or higher to build Halo. Halo can be built with Gradle using the following command:

./gradlew clean build

Tests

Halo is tested with cucumber against JmDNS. Feature files can be found in the src/test/resources folder.

Usage

Service Registration

try (final Halo halo = Halo.allNetworkInterfaces(Clock.systemDefaultZone())) {
    // allowing service instance name to be changed and with a default TTL of 1 hour:
    Registered service = halo.register(RegisterableService.create("Foo Bar", "_http._udp.", 8009).get());
    // registered service is returned:
    System.err.println(service);

    // registering again the service instance and registration type will return a service
    // with an instance name of "Foo Bar (2)":
    service = halo.register(RegisterableService.create("Foo Bar", "_http._udp.", 8010).get());
    System.err.println(service);

    // not allowing service instance name to be changed will throw an IOException at this point:
    halo.register(RegisterableService.create("Foo Bar", "_http._udp.", 8011).get(), false);
    
    // if blocking until the service has been announced is not acceptable:
    ExecutorService es = Executors.newSingleThreadExecutor();
    Future<Registered> future =
            es.submit(() -> halo.register(RegisterableService.create("Future", "_http._udp.", 8009).get()));

    // changing the attributes of a registered service.
    Attributes newAttributes = Attributes.create().with("Changed").get();
    service.changeAttributes(newAttributes);
    // or
    Future<Void> future = es.submit(() -> service.changeAttributes(newAttributes));

}

Service Resolution

try (final Halo halo = Halo.allNetworkInterfaces(Clock.systemDefaultZone())) {
    // default timeout of 6 seconds:
    Optional<ResolvedService> service = halo.resolve("Foo Bar", "_http._udp.");
    // Optional contains the service if it could be resolved, empty otherwise:
    System.err.println(service);
    
    // user defined timeout:
    service = halo.resolve("Foo Bar", "_http._udp.", Duration.ofSeconds(1));
    System.err.println(service);

    // if blocking until the service has been resolved is not acceptable:
    ExecutorService es = Executors.newSingleThreadExecutor();
    Future<Optional<ResolvedService>> future = es.submit(() -> halo.resolved("Foo Bar", "_http._udp."));
}

Services Browsing by Registration Type

try (final Halo halo = Halo.allNetworkInterfaces(Clock.systemDefaultZone())) {
    final ServiceBrowserListener l = new ServiceBrowserListener() {

        @Override
        public final void serviceAdded(final ResolvedService service) {
            System.err.println(service + " has been added to the network!!!!!");
        }

        @Override
        public final void serviceRemoved(final ResolvedService service) {
            System.err.println(service + " has been removed from the network!!!!!");
        }

        @Override
        public final void serviceUpdated(final ResolvedService service) {
            System.err.println(service + " has been updated!!!!!");
        }

    };

    final Browser browser = halo.browse("_http._udp.", l);

    // Wait for some services to be registered on the network...
    Thread.sleep(5000);

    browser.close();
}

Registration Types Browsing

try (final Halo halo = Halo.allNetworkInterfaces(Clock.systemDefaultZone())) {
    final Browser browser = halo.browse(System.err::printLn);

    // Wait for some services to be registered on the network...
    Thread.sleep(5000);

    browser.close();
}

Configuration

The following parameters can be configured by system properties:

Property Key	Description	Default
io.omam.halo.mdns.ipv4	mDNS IPV4 address	224.0.0.251
io.omam.halo.mdns.ipv6	mDNS IPV6 address	FF02::FB
io.omam.halo.mdns.port	mDNS port	5353
io.omam.halo.resolution.timeout	resolution timeout in milliseconds	6000
io.omam.halo.resolution.interval	interval between resolution questions in milliseconds	200
io.omam.halo.probing.timeout	probing timeout in milliseconds	6000
io.omam.halo.probing.interval	interval between probe messages in milliseconds	250
io.omam.halo.probing.number	number of probing messages before announcing a registered service	3
io.omam.halo.announcement.interval	interval between announcement messages in milliseconds	1000
io.omam.halo.announcement.number	number of announcement messages to registered service	2
io.omam.halo.querying.first	delay before transmitting the first browsing query in milliseconds	50
io.omam.halo.querying.delay	interval between consecutive browsing queries in milliseconds	1000
io.omam.halo.querying.increase	increase factor between consecutive browsing queries	2
io.omam.halo.querying.max	maximum interval between consecutive browsing queries in milliseconds	1200000
io.omam.halo.cancellation.interval	interval between goodbye messages in milliseconds	250
io.omam.halo.cancellation.number	number of goodbye messages sent when de-registering a service	3
io.omam.halo.reaper.interval	cache record reaper interval in milliseconds	10000
io.omam.halo.ttl.default	DNS record default time to live in milliseconds	3600000
io.omam.halo.ttl.expiry	DNS record time to live after expiry in milliseconds	1000