code: @Override
    public void getTopChannels(
        GetTopChannelsRequest request, StreamObserver<GetTopChannelsResponse> responseObserver) {
      InternalChannelz.RootChannelList rootChannels
          = channelz.getRootChannels(request.getStartChannelId(), maxPageSize);
  
      GetTopChannelsResponse resp;
      try {
        resp = ChannelzProtoUtil.toGetTopChannelResponse(rootChannels);
      } catch (StatusRuntimeException e) {
        responseObserver.onError(e);
        return;
      }
  
      responseObserver.onNext(resp);
      responseObserver.onCompleted();
    }
docs: Returns top level channel aka {@link io.grpc.ManagedChannel}.