public function setCacheControl(array $cacheControl)
    {
        //validate headers
        foreach ($cacheControl as $k => $v) {
            if (!$this->validateCacheControlHeader($k)) {
                throw new ResponseException('Invalid cache control header "' . $v . '".');
            }
        }

        $this->cacheControl = $this->arr($cacheControl);

        return $this;
    }