code: protected function _toHtml() // @codingStandardsIgnoreLine - required by parent class
      {
          if ($this->config->isGeoIpEnabled() == false || $this->config->isFastlyEnabled() == false) {
              return parent::_toHtml();
          }
  
          /** @var string $actionUrl */
          $actionUrl = $this->getUrl('fastlyCdn/geoip/getaction');
  
          // This page has an esi tag, set x-esi header if it is not already set
          $header = $this->response->getHeader('x-esi');
          if (empty($header)) {
              $this->response->setHeader("x-esi", "1");
          }
  
          // HTTPS ESIs are not supported so we need to turn them into HTTP
          return sprintf(
              '<esi:include src=\'%s\' />',
              preg_replace("/^https/", "http", $actionUrl)
          );
      }
docs: Renders ESI GeoIp block
  
  @return string