protected function _passThrough($request, $response, $server)
    {
        $source = $server->getSource();
        $path = $server->getSourcePath($this->_path);

        $resource = $source->readStream($path);
        if ($resource === false) {
            throw new ResponseException();
        }
        $stream = new Stream($resource);

        $contentType = $source->getMimetype($path);
        $contentLength = $source->getSize($path);

        return (new Response())->withBody($stream)
            ->withHeader('Content-Type', $contentType)
            ->withHeader('Content-Length', $contentLength);
    }