Make Cache in AssignmentFilter configurable

[ruudk]

As opposed to other languages , PHP is stateless. That means that keeping things inside an in memory cache will be cleared at the end of the request. That means that the LRUCache implementation in AssignmentFilter has no value.

The Cache should be made configurable.
While doing that, it's best to allow any PSR-6 cache.

The LRUCache can be dropped and replaced with an ArrayAdapter cache.

https://symfony.com/doc/current/components/cache.html
https://github.com/amplitude/experiment-php-server/blob/main/src/Assignment/LRUCache.php
https://github.com/amplitude/experiment-php-server/blob/main/src/Assignment/AssignmentFilter.php

Currently, we cannot use assignments because we need to make sure the cache is stateful.
It's impossible to define a custom AssignmentFilter. It's not an interface, so we have to extend the existing AssignmentFilter.
But then it's not possible to easily use it because this is initialized here:

experiment-php-server/src/Local/LocalEvaluationClient.php

Line 95 in 0aa016f

new AssignmentFilter($config->cacheCapacity),

Another solution, as opposed to making the Cache configurable, is to make AssignmentFilter an interface, with a DefaultAssignmentFilter implementation that can be swapped.

/cc @bgiori

[ruudk]

I think one solution could be to implement the filtering in the AssignmentTrackingProvider. But I feel that's doing the work twice.

[tyiuhc]

@ruudk Many thanks for raising this issue. This has been prioritized and we are working to address it.

[tyiuhc]

@ruudk, you can now configure a custom AssignmentFilter in v1.2.0. Please let us know if this is not working as expected, thanks!

[ruudk]

Too bad I didn't have time to look at this and it's already tagged. But wouldn't it have been better to make the cache inside the default filter configurable? That way I don't have to create my own filter.

[tyiuhc]

@ruudk To use a custom cache with the default filter, you can create a DefaultAssignmentFilter with your custom cache, then use that as your filter in AssignmentConfig.

We wanted to allow additional flexibility in determining whether an assignment should be tracked. Hope that helps with your use case.

[ruudk]

I understand. But given that much can be configured using a ConfigBuilder, I figured that allowing me to configure the cache there, would make it even easier 😁

[ruudk]

@tyiuhc It's not possible for me to use 1.2.0 because it's locked to symfony/cache ^5.

Could you please widen this to allow all the supported versions? https://symfony.com/releases

[tyiuhc]

@ruudk Apologies for the inconvenience, v1.2.1 will allow additional versions of symfony/cache