Developer Guide

The mDNS module is intended exclusively for developer needs. It provides some terminal commands, but they serve mostly exploratory and test purposes.

Getting Notifications

Any service topology changes are communicated to the higher levels using the EventAdmin with the following events:

• com.prosyst.mbs.services.mdns.MDNSConstants.TOPIC_SERVICE_INSTANCE_ADDED which equals the following string com/prosyst/mbs/services/mdns/ServiceInstance/ADDED and is sent whenever a record for a new service is received and its data is not fully loaded yet
• com.prosyst.mbs.services.mdns.MDNSConstants.TOPIC_SERVICE_INSTANCE_RESOLVED which equals the following string com/prosyst/mbs/services/mdns/ServiceInstance/RESOLVED and is sent whenever all of the data for some new service is received and processed and whenever service data is updated
• com.prosyst.mbs.services.mdns.MDNSConstants.TOPIC_SERVICE_INSTANCE_REMOVED which equals the following string com/prosyst/mbs/services/mdns/ServiceInstance/REMOVED and is sent whenever a service is removed

To get notified for these events you need to register normal OSGi event handlers.

Registering own Service

In case you need to announce some functionality in the network, you can register your own service. Thus your functionality will be discoverable via mDNS and will be available for the other devices in the network. This can be done by providing all required information in the ServiceInstance object passed to the register method. Since the success of the registration depends on the underlying mDNS implementations and the network, this method is asynchronous and the registration completes with a TOPIC_SERVICE_INSTANCE_ADDED event notification. This method returns and instance of ServiceInstanceRegistration hook object that can be used to verify the state of the service and especially when one wants to stop announcing a given service.

Finding a Service

There are several methods that can be used in order to find some specific service.

• browse(type, domain) - Initiates a full search for all services of the given type and returns immediately. All services found during the search are reported using the event notifications.
• browse(type, domain, timeout) - Initiates a full search for all services of the given type, collects the data received during the specified timeout and provides it as result.
• list(type, domain) - Provides a list of all currently known services of the given type and domain and returns immediately. This method does not initiate any search.
• getServiceTypes() - Provides a list of all currently known fully qualified service types.
• getServiceInstance(name, type, domain) - if there is a service with the specified name, type and domain, than it is provided as result. This method does not block and returns immediately, without initiating any search.

Depending on your needs and knowledge, various combinations of these methods can be used to find the service needed by your application.

For example, you can use just the getServiceInstance method, if you are sure the service is already known. You can list the service instances of a given type and manually search for the one you need.

If this approach is not successful, you could initiate a network search for the service in question using some of the browse methods. In addition to the browse methods, event subscriptions will ensure you get further notifications.

Updating Service Information

If the information for a given service is outdated you can use some of the resolve methods. They behave very similarly to the browse methods and event subscriptions will provide further notifications.

These methods can also be used for checking service presence.