code: private void sendRequest(Object request, ContextualFuture future) {
      if (open && connection.open) {
        long requestId = ++this.requestId;
        futures.put(requestId, future);
        connection.handleRequest(requestId, request);
      } else {
        future.context.executor().execute(() -> future.completeExceptionally(new ConnectException("connection closed")));
      }
  
      if (request instanceof ReferenceCounted) {
        ((ReferenceCounted<?>) request).release();
      }
    }
docs: Sends a request.