protected function cacheCheck()
    {
        if (is_null($this->etag)) {
            throw \AWonderPHP\FileWrapper\NullPropertyException::propertyIsNull('etag');
        }
        if (isset($this->REQHEADERS['if-none-match'])) {
            $reqETAG=trim($this->REQHEADERS['if-none-match'], '\'"');
            if (strcmp($reqETAG, $this->etag) == 0) {
                $this->cacheok=true;
            }
        } elseif (isset($this->REQHEADERS['if-modified-since'])) {
            $reqLMOD=strtotime(trim($this->REQHEADERS['if-modified-since']));
            if ($reqLMOD == $this->timestamp) {
                $this->cacheok=true;
            }
        }
    }