How to create a generic GRPC server start function in Go

Question

I'm trying to abstract the start of a GRPC server

The original main function is the following:

func main() {
    lis, err := net.Listen("tcp", port)
    if err != nil {
        log.Fatalf("failed to listen: %v", err)
    }

    s := grpc.NewServer()
    pb.RegisterCollectionServer(s, &server.Server{})
    // Register reflection service on gRPC server.
    reflection.Register(s)
    if err := s.Serve(lis); err != nil {
        log.Fatalf("failed to serve: %v", err)
    }
}

My goal is to have something like this:

func startService(sr func(*grpc.Server, interface{}), srv interface{}) error {
    lis, err := net.Listen("tcp", port)
    if err != nil {
        return err
    }
    s := grpc.NewServer()
    sr(s, srv)
    reflection.Register(s)
    return s.Serve(lis)
}

func main() {
    err := startService(pb.RegisterCollectionServer, &server.Server{})

    if err != nil {
        log.Fatalf("failed to start Service: %v", err)
    }
}

But this gives me the following error:

cannot use collection_api.RegisterCollectionServer (type func(*grpc.Server, collection_api.CollectionServer)) as type func(*grpc.Server, interface {}) in argument to startServicego

It seems that collection_api.CollectionServer is not a valid interface{} type.

Any idea how to make this work?

Answer 1

In your setup the function signature of collector_api.RegisterCollectionServer must match exactly func(*grpc.Server, interface{}), there is no "is-kind-of" in Go as there is in other languages.

If you want to keep the startService function independent of the collection_api types, you can use a anonymous function in main(). If you know that you what ever you are registering is always dependent on the implementation of the anonymous function (in this case &server.Server{}), then you can leave this detail out of the function signature of startService and put it into the anonymous function:

func startService(sr func(*grpc.Server)) error {
    lis, err := net.Listen("tcp", port)
    if err != nil {
        return err
    }
    s := grpc.NewServer()
    sr(s)
    reflection.Register(s)
    return s.Serve(lis)
}

func main() {
    err := startService(func(grpcServer *grpc.Server) {
            pb.RegisterCollectionServer(grpcServer, &server.Server{})
        }, &server.Server{})

    if err != nil {
        log.Fatalf("failed to start Service: %v", err)
    }
}