Codesleeve\AssetPipeline\Filters\ClientCacheFilter::get PHP Method

    public function get($key)
    {
        $lastModified = $this->getLastTimeModified($key);
        $modifiedSince = isset($_SERVER['HTTP_IF_MODIFIED_SINCE']) ? $_SERVER['HTTP_IF_MODIFIED_SINCE'] : 0;
        header('Last-Modified: ' . $lastModified);
        if ($modifiedSince >= $lastModified) {
            header('HTTP/1.0 304 Not Modified');
            exit;
        }
        return $this->cache->get($key);
    }