Forcing browser caching on custom controller / full page cache disables browser caching

Question

I have a custom controller which should serve some more or less static HTML block, with this code:

use Magento\Framework\App\Action\HttpGetActionInterface;
use Magento\Framework\App\Response\HttpFactory;
use Magento\Framework\App\ResponseInterface;
use Magento\Framework\Controller\ResultInterface;
use Magento\Framework\Exception\NotFoundException;
use Magento\Framework\View\Element\Template;
use Magento\Framework\View\Result\PageFactory;
class Entries implements HttpGetActionInterface
{
 public function __construct(
 private Navigation $navigation,
 private readonly PageFactory $resultPageFactory,
 private readonly HttpFactory $httpResponseFactory
 )
 {
 }
 /**
 * Execute action based on request and return result
 *
 * @return ResultInterface|ResponseInterface
 * @throws NotFoundException
 */
 public function execute()
 {
 $resultPage = $this->resultPageFactory->create();
 $categories = $this->navigation->getNavigation(5);
 $content = $resultPage->getLayout()
 ->createBlock(Template::class)
 ->setTemplate('Magento_Theme::html/header/topmenu/menu.phtml')
[...]
 ->toHtml();
 $response = $this->httpResponseFactory->create();
 $response->setContent($content);
 $response->setPublicHeaders(3600);
 return $response;
 }
}

setPublicHeader should set a max-age and force browser caching.

 $this->setHeader('pragma', 'cache', true);
 $this->setHeader('cache-control', 'public, max-age=' . $ttl . ', s-maxage=' . $ttl, true);
 $this->setHeader('expires', $this->getExpirationHeader('+' . $ttl . ' seconds'), true);

But it doesn't.

$ http -ph https://example.local/theme/menu/entries
HTTP/1.1 200 OK
Cache-Control: max-age=0, must-revalidate, no-cache, no-store

Is this expected behavior, when the full page cache is on? I tried to debug and in Magento the headers seem to be overwritten, but did not fully understand what's happening here with the full page cache.

EDIT:

More debugging:

\Magento\Framework\App\FrontController::processRequest calls

$this->response->setNoCacheHeaders();

When reaching

\Magento\PageCache\Model\App\FrontController\BuiltinPlugin::addDebugHeaders

Also cache control contains max-age=0

Much later \Magento\PageCache\Model\Layout\LayoutPlugin::afterGenerateElements sets the plugic header, because the layout is cacheable.

Then this code again sets no cache headers: \Magento\Framework\App\PageCache\Kernel::process

 public function process(\Magento\Framework\App\Response\Http $response)
 {
 if (preg_match('/public.*s-maxage=(\d+)/', $response->getHeader('Cache-Control')->getFieldValue(), $matches)) {
 $maxAge = $matches[1];
 $response->setNoCacheHeaders(); ### trying to comment out
 if (($response->getHttpResponseCode() == 200 || $response->getHttpResponseCode() == 404)

Which I don't understand, because it's actually matching for public which means "cacheable".

If I comment out this line in the above snipped, it would be cached - so literally the full page cache is disabling the browser cache.

So it boils down to this line:

https://github.com/magento/magento2/blob/984630670aa9ffb711b3169f1c1a15ea5cc4f052/lib/internal/Magento/Framework/App/PageCache/Kernel.php#L154

Why did the inventors put that here :-) ?

Answer 1

Partial answer:

I now understand, why this line was put there:

s-maxage is for the shared cached, which is the FPC, see Mozilla dev docs.

Unfortunately there seems currently no simple way to

• Cache in the FPC
• and additionally cache in the browser

That really is a pity.