ESI issue

BlogController.php

    public function displayAction(Post $post)
    {
        // page caching
        $response = new Response();
        $response->setLastModified($post->getModificationDate());
        $response->setPublic();

        if ($response->isNotModified($this->getRequest())) {
            return $response;
        }

        // ...

        return $this->render('GregoireMBlogBundle:Blog:display.html.twig', array(
            'post' => $post,
            'uid'  => rand(0, 10000),
        ), $response);
    }