function retrieveCacheFirst($url, $accept = false, $forcestring = false, $channel = false)
    {
        $cachefile = $this->config->get('cache_dir') . DIRECTORY_SEPARATOR .
            md5($url) . 'rest.cachefile';

        if (file_exists($cachefile)) {
            return unserialize(implode('', file($cachefile)));
        }

        return $this->retrieveData($url, $accept, $forcestring, $channel);
    }