reflection: accept interface instead of grpc.Server struct in Register() (#4340)

reflection/serverreflection.go

@@ -54,9 +54,19 @@ import (
 	"google.golang.org/grpc/status"
 )
 
+// GRPCServer is the interface provided by a gRPC server. It is implemented by
+// *grpc.Server, but could also be implemented by other concrete types. It acts
+// as a registry, for accumulating the services exposed by the server.
+type GRPCServer interface {
+	grpc.ServiceRegistrar
+	GetServiceInfo() map[string]grpc.ServiceInfo
+}
+
+var _ GRPCServer = (*grpc.Server)(nil)
+
 type serverReflectionServer struct {
 	rpb.UnimplementedServerReflectionServer
-	s *grpc.Server
+	s GRPCServer
 
 	initSymbols  sync.Once
 	serviceNames []string
@@ -64,7 +74,7 @@ type serverReflectionServer struct {
 }
 
 // Register registers the server reflection service on the given gRPC server.
-func Register(s *grpc.Server) {
+func Register(s GRPCServer) {
 	rpb.RegisterServerReflectionServer(s, &serverReflectionServer{
 		s: s,
 	})