WIP: Fix usage of symfony cache with shared max age 0

[alexander-schranz]

Q	A
Bug fix?	yes
New feature?	no
BC breaks?	no
Deprecations?	no
License	MIT

What's in this PR?

Fix usage of symfony cache with shared max age 0.

Why?

Symfony will not cache if shared max age is set and 0 because of $response->getMaxAge() in $response->isCacheable() will return at first s-max-age.

Example Usage

sulu_http_cache:
    handlers:
        public:
            max_age: 100 
            shared_max_age: 0

[danrot]

I would move that logic into the HttpCache component from Symfony, because I would like to have the s-maxage header set to whatever is set in the config for external browsers/proxies. Therefore the validate method of the HttpCache component could be overridden, which will store the response in case the default implementation didn't. That means we would have to introduce another check in the validate method.

[alexander-schranz]

@danrot did have a look at it but seems the validate method is not the only case where isCacheable is called or where logic is based on the getMaxAge function of the Response.

[alexander-schranz]

Maybe obsolute after the changes in: symfony/symfony#26532

[danrot]

What does "maybe" mean? 🙂 Can we close this PR?