code: private void sendGrpcFrame(ChannelHandlerContext ctx, SendGrpcFrameCommand cmd,
        ChannelPromise promise) throws Http2Exception {
      if (cmd.endStream()) {
        closeStreamWhenDone(promise, cmd.streamId());
      }
      // Call the base class to write the HTTP/2 DATA frame.
      encoder().writeData(ctx, cmd.streamId(), cmd.content(), 0, cmd.endStream(), promise);
    }
docs: Sends the given gRPC frame to the client.