code: public function getUrl()
      {
          if ($this->_url === null) {
              $this->_url = $this->resolveRequestUri();
          }
  
          return $this->_url;
      }
docs: Returns the currently requested relative URL.
  This refers to the portion of the URL that is after the [[hostInfo]] part.
  It includes the [[queryString]] part if any.
  @return string the currently requested relative URL. Note that the URI returned may be URL-encoded depending on the client.
  @throws InvalidConfigException if the URL cannot be determined due to unusual server configuration