Handling of 'inv-by' aka cache dependencies should be done by another subsystem

[evert]

Lets say we have 2 resources:

• Resource A
• Resource B

If resource A returns a link header like this:

Link: </resource-b>; rel="inv-by"

This lets Resource A say: "If Resource B expires, then I also expire".

This feature is currently handled by Ketting inside the 'cache middleware'. The issue with this is that it can only automatically expire resource A, if expiring resource B was done as the result of a HTTP request.

Sometimes users expire things manually or they use other systems to trigger expiries (such as websocket). Typically this is done by calling something like:

client.cache.delete('/resource-b')
// or
resourceB.clearCache();

Clearning caches that way does not trigger the cache middleware, so the cache of resource A does not get cleared for those cases.

To fix this, the 'cache dependencies' handling system needs to move somewhere else, probably the classes in src/cache