code: @SuppressWarnings("unchecked")
    private void handleRequest(long requestId, Object request) {
      HandlerHolder holder = handlers.get(request.getClass());
      if (holder == null) {
        connection.handleResponseError(requestId, new ConnectException("no handler registered"));
        return;
      }
  
      Function<Object, CompletableFuture<Object>> handler = (Function<Object, CompletableFuture<Object>>) holder.handler;
  
      try {
        holder.context.executor().execute(() -> {
          if (open && connection.open) {
            CompletableFuture<Object> responseFuture = handler.apply(request);
            if (responseFuture != null) {
              responseFuture.whenComplete((response, error) -> {
                if (!open || !connection.open) {
                  connection.handleResponseError(requestId, new ConnectException("connection closed"));
                } else if (error == null) {
                  connection.handleResponseOk(requestId, response);
                } else {
                  connection.handleResponseError(requestId, error);
                }
              });
            }
          } else {
            connection.handleResponseError(requestId, new ConnectException("connection closed"));
          }
        });
      } catch (RejectedExecutionException e) {
        connection.handleResponseError(requestId, new ConnectException("connection closed"));
      }
    }
docs: Receives a message.