/**
* Returns an AJAX response to render the toolbar subtrees.
*
* @return \Drupal\Core\Ajax\AjaxResponse
*/
public function subtreesAjax()
{
list($subtrees, $cacheability) = toolbar_get_rendered_subtrees();
$response = new AjaxResponse();
$response->addCommand(new SetSubtreesCommand($subtrees));
// The Expires HTTP header is the heart of the client-side HTTP caching. The
// additional server-side page cache only takes effect when the client
// accesses the callback URL again (e.g., after clearing the browser cache
// or when force-reloading a Drupal page).
$max_age = 365 * 24 * 60 * 60;
$response->setPrivate();
$response->setMaxAge($max_age);
$expires = new \DateTime();
$expires->setTimestamp(REQUEST_TIME + $max_age);
$response->setExpires($expires);
return $response;
}
