Registration and Discovery

Server applications need to advertise what services they provide and clients of server application services need to know what implementations of the services exist. This happens through Apparc's application registration file system.

Application registration files have a table in which applications can list the service UIDs that they implement. For each service UID listed, there is an associated opaque (i.e. not interpreted by the framework) data field which indicates how the service is implemented by that application. The opaque data field is accessed through an LLINK into a resource elsewhere in the application registration file group. The meaning of this opaque data field is not known to the framework, it will vary according to the service. For some services the opaque data field may be a name intended for user display, for others it may be structured data that the service's client-side code can interpret.

Clients of a service can discover which applications implement a particular service by using RApaLsSession. This has a number of APIs for retrieving an application list, filtered to only include applications that implement a particular service. RApaLsSession can also return other information about server applications, including how the services are implemented as described by the opaque data field. If a service uses the opaque data field to store localised strings to describe implementations, these can be shown to the user. If a service uses structured data, a resource reader can be created over the opaque data field to extract the data.