Progressive

ProgressiveController.php

<?php

class ProgressiveController
{
  public function progressiveAction($some_id)
  {
    $response = new ProgressiveResponse();

    $response->setHead("Some static data (maybe from twig), or an ESI tag, or whatever");

    $response->setBodyClosure(function($response) {
      heavyProcessing();

      $response->setBody("Other data");
    });

    return $response;
  }
}