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Why does a vanilla Drupal 8 site add cache-control: must-revalidate, no-cache, private to all the pages?

A Drupal 7 site adds cache-control: must-revalidate, no-cache.

Is that addition of private for Drupal 8 somehow configurable? I'd like to not have it there.

It turns out that this response header in Drupal 8 is sent when system.performance:cache.page.max_age is set to 0. Setting it to anything greater than 0 (e.g 123) gives me max-age=123, public. The question still remains: Is there a way to get must-revalidate, no-cache?

The reason I want must-revalidate, no-cache without private is that I want browsers to always make requests for pages, and my cache server (fastly) to cache the content. Having private in the response headers bypasses fastly as per their documentation: https://docs.fastly.com/en/guides/cache-control-tutorial#do-not-cache

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    I think you can use the drupal.org/project/http_response_headers module to change the header. – Jdrupal Nov 13 at 9:56
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    Drupal doesn't respond with this header for all pages, only for logged-in users. You can specify different headers in a controller or change the headers of the response before it is delivered, see drupal.stackexchange.com/a/201297/47547 – 4k4 Nov 13 at 10:20
  • @4k4 I do not confirm. I've tested a dozen of Drupal 7 and 8 sites via curl -I on their frontpage. Doing that way means that the request/response doesn't involve a logged in user. – cherouvim Nov 13 at 10:26
  • I get via curl Cache-Control: max-age=x, public, where x is the configured max-age. – 4k4 Nov 13 at 10:30
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    Have you tried the D7/D8 test on the same server? As there's lots of reasons for different headers include your servers configuration. E.g. I can see a hosting provider I use adds this tag by default – Leigh Nov 13 at 10:43
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This is caused by symfony. private is added via vendor/symfony/http-foundation/ResponseHeaderBag.php and as far as I understand it's not possible to not have it when system.performance:cache.page.max_age is set to 0:

protected function computeCacheControlValue() {
  // ...
  if (!isset($this->cacheControl['s-maxage'])) {
    return $header.', private';
  }

Since I don't want to hack symfony, I can remove private via apache mod_header:

Header edit Cache-Control "(, )?private" ""
  • As commented below the question these defaults are only applied if the controller or a response event subscriber doesn't set cache headers. – 4k4 Nov 13 at 12:24
  • My question regards why this has changed from D7 to D8 and how I can remove it. – cherouvim Nov 13 at 12:27
  • My comment is because you've said it's not possible, but it's the opposite, you have full control if you want. – 4k4 Nov 13 at 12:28
  • @4k4: I'm not following you. I don't want to hack symfony to change this behavior. Nor do I want to set max_age to more than 0 because that would break my site. – cherouvim Nov 13 at 12:30
  • Symfony should allow you to return any sensible cache control header. I understand that you don't want max_age >0, but you could set a s-maxage if you want the CDN to store the response. – 4k4 Nov 13 at 12:42

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