How to create a lagom server with grpc service implementation only?

Question

I am trying to create a grpc service using Lagom framework following this documentation . Here the hello service also exposes rest API besides grpc service.

Now while creating lagom server in the ApplicationLoader we assign grpc service impl as additionalRouter like so:

abstract class HelloApplication(context: LagomApplicationContext)
  extends LagomApplication(context)
    with AhcWSComponents {

  // Bind the service that this server provides
  override lazy val lagomServer =
    serverFor[HelloService](wire[HelloServiceImpl])
    .additionalRouter(wire[HelloGrpcServiceImpl])

}

Its all fine for the purpose of demo but we may not need to always create a REST endpoint besides gRPC endpoint. In that case I won't need either HelloService or HelloServiceImpl . The problem is how would you create lagom server with only HelloGrpcServiceImpl ? I can't see to find a way either any documentation or the APIs itself to be able to achieve this!

Please suggest.

Answer 1

Based on the answer in the link I provided as a comment to my question, the solution would look something like this:

trait PrimeGeneratorService extends Service {
  override def descriptor: Descriptor = named("prime-generator")
}

class PrimeGeneratorServiceImpl() extends PrimeGeneratorService

abstract class PrimeGeneratorApplication(context: LagomApplicationContext)
  extends LagomApplication(context) with AhcWSComponents {

  override lazy val lagomServer: LagomServer = {
    serverFor[PrimeGeneratorService](wire[PrimeGeneratorServiceImpl])
      .additionalRouter(wire[PrimeGeneratorGrpcServiceImpl])
  }

}

class PrimeGeneratorLoader extends LagomApplicationLoader {
  override def load(context: LagomApplicationContext): LagomApplication =
    new PrimeGeneratorApplication(context) {
      override def serviceLocator: ServiceLocator = NoServiceLocator
    }

  override def loadDevMode(context: LagomApplicationContext): LagomApplication =
    new PrimeGeneratorApplication(context) with LagomDevModeComponents

  override def describeService = Some(readDescriptor[PrimeGeneratorService])
}

Here we have to create dummy service trait and implementation, namely, PrimeGeneratorService and PrimeGeneratorServiceImpl , respectively.

Don't forget to add following in the loader class:

override def describeService = Some(readDescriptor[PrimeGeneratorService])