code: public function getHostInfo()
      {
          if ($this->_hostInfo === null) {
              $secure = $this->getIsSecureConnection();
              $http = $secure ? 'https' : 'http';
              if (isset($_SERVER['HTTP_HOST'])) {
                  $this->_hostInfo = $http . '://' . $_SERVER['HTTP_HOST'];
              } else {
                  $this->_hostInfo = $http . '://' . $_SERVER['SERVER_NAME'];
                  $port = $secure ? $this->getSecurePort() : $this->getPort();
                  if (($port !== 80 && !$secure) || ($port !== 443 && $secure)) {
                      $this->_hostInfo .= ':' . $port;
                  }
              }
          }
  
          return $this->_hostInfo;
      }
docs: Returns the schema and host part of the current request URL.
  The returned URL does not have an ending slash.
  By default this is determined based on the user request information.
  You may explicitly specify it by setting the [[setHostInfo()|hostInfo]] property.
  @return string schema and hostname part (with port number if needed) of the request URL (e.g. `http://www.yiiframework.com`)
  @see setHostInfo()