Set cache control header for full page cache

[indykoning]

While setting the correct Nginx config will reduce usefulness we can improve speed by setting a cache control header if our page is served from cache, or can be/will be/has been cached

By default Laravel will not set cache control, causing Symfony to always return cache-control: no-cache, private https://github.com/symfony/symfony/blob/6f4f04b98f6134996a57d21d1851d558a34dc45c/src/Symfony/Component/HttpFoundation/ResponseHeaderBag.php#L251

Which honestly is a safe default since Laravel cannot know what can and can't be cached. That is dependent on the page.

However, if Statamic can cache the page statically we can assume a browser and CDN could cache the page too.

https://github.com/statamic/cms/blob/779a92a223d16ee16f6af6de0b6a9acfc95be082/src/StaticCaching/Middleware/Cache.php#L111 https://github.com/statamic/cms/blob/779a92a223d16ee16f6af6de0b6a9acfc95be082/src/StaticCaching/Middleware/Cache.php#L84

These places would need to be updated with

->setPublic(); https://github.com/symfony/symfony/blob/6f4f04b98f6134996a57d21d1851d558a34dc45c/src/Symfony/Component/HttpFoundation/Response.php#L604 ->setMaxAge(); https://github.com/symfony/symfony/blob/6f4f04b98f6134996a57d21d1851d558a34dc45c/src/Symfony/Component/HttpFoundation/Response.php#L788 ->setStaleWhileRevalidate(); https://github.com/symfony/symfony/blob/6f4f04b98f6134996a57d21d1851d558a34dc45c/src/Symfony/Component/HttpFoundation/Response.php#L820

if possible it would be a really nice added bonus to set the Etag https://github.com/symfony/symfony/blob/6f4f04b98f6134996a57d21d1851d558a34dc45c/src/Symfony/Component/HttpFoundation/Response.php#L949

Here's how laravel implements it if you use their cache control middleware https://github.com/laravel/framework/blob/43993ed92af54aa8620d8e779a7dcd658f44364c/src/Illuminate/Http/Middleware/SetCacheHeaders.php#L66 aka ->setEtag(md5($response->getContent())) This will allow the browser and CDN to skip downloading the body if it's still in cache and matches the etag. having set up my Nginx settings as in https://github.com/statamic/docs/pull/1602 and configuring Cloudlfare to generate/pass Etags my "Content download" of a cached page is 2ms