code: public static <ReqT, RespT> Iterator<RespT> blockingServerStreamingCall(
        Channel channel, MethodDescriptor<ReqT, RespT> method, CallOptions callOptions, ReqT req) {
      ThreadlessExecutor executor = new ThreadlessExecutor();
      ClientCall<ReqT, RespT> call = channel.newCall(method, callOptions.withExecutor(executor));
      BlockingResponseStream<RespT> result = new BlockingResponseStream<>(call, executor);
      asyncUnaryRequestCall(call, req, result.listener(), true);
      return result;
    }
docs: TODO(louiscryan): Not clear if we want to use this idiom for 'simple' stubs.