  void preConnect(folly::NetworkSocket fd) override {
    VLOG(7) << "client preConnect hook is invoked";
    if (callback_) {
      callback_->preConnect(fd);
    }
  }
  void preConnect(folly::NetworkSocket fd) override {
    VLOG(7) << "client preConnect hook is invoked";
    if (callback_) {
      callback_->preConnect(fd);
    }
  }