feat: Add flipt provider with PSR-16 caching support

[legoheld]

This PR

Adds a provider for https://www.flipt.io/ with PSR-16 caching support.

How to test

How to run tests is documented in the README.md

[markphelps]

minor things, looks good otherwise from a Flipt perspective! thanks @legoheld !!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (13ebc3c) 57.58% compared to head (41f4474) 57.58%.

Additional details and impacted files

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  Coverage   57.58%   57.58%           
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  Files          28       28           
  Lines         422      422           
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  Misses        179      179           

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[tcarrio]

Thanks for the pull request! It's looking pretty good so far, mostly have questions around the caching provided thus far.

[tcarrio]

This should never happen, in which case if it did, it should be an error not nullng the value.

[legoheld]

Im not sure if this is an issue as I use this only when I get a successfull response from the client:

if( $result->getReason() == ResponseReasons::MATCH_EVALUATION_REASON || $result->getReason() == ResponseReasons::DEFAULT_EVALUATION_REASON ) {
   $result = ResolutionDetailsFactory::fromSuccess( $this->castResult( $result, $flagType ) );
}

And the I suppose a correct value. But you are in a way right if the response value is somewhat invalid I should throw an error. What do you propose here?

[tcarrio]

This introduces race conditions for distributed storage caches like Redis or Memcached. You can atomically interact with the cache per key if you utilize a key prefix instead.

Suggested change

	$entries = $this->cache->get( self::CACHE_KEY, []);
	$entries[ $key ] = $value;
	$this->cache->set( self::CACHE_KEY, $entries );
	$this->cache->set($key, $value);

This does not fix the issue I mentioned below about the collisions. To resolve both, you would still need a different solution.

[tcarrio]

Or, utilize a sufficiently large range hash function to avoid collisions. This might be something to consider being a configurable setting, e.g. raw JSON encoded keys or md5 or sha256 would all be valid strategies, to give you the overall safety necessary for the application.

[legoheld]

Now this is the hard part. With PSR-16 there is no way to delete all keys with a certain cache key prefix.
So I have two ways to solve that either the way you have seen ( all entries under one key ) or I store the keys to delete under a separate cache key. But the later is probably more efficient.

But with both ways you have racing conditions as you mentioned.

I actually dont know how to solve that with PSR-16. Maybe just by documenting that this is not ready to use with a distributed caching storage.

[legoheld]

Dedicated cahce storage -> clear will clear all keys.

[legoheld]

Thank you @tcarrio for this very detailed feedback!

[markphelps]

should this be this repo? or our (Flipt's) website?

[legoheld]

Remove the homepage as its optional. We do it like the other providers.

[tcarrio]

A few things I noticed after we talked @legoheld :

• unit tests exist but do not run in CI. Include the Flipt provider package in the matrix for testing in GH Actions
• I will need to create the corresponding repository this will "deploy" through before we merge. We gitsplit the packages to individual repos hosted under @open-feauture-php

[tcarrio]

The new repository has been created.

You will need to point the gitsplit config for the new Flipt provider to it in the .gitsplit.yml file

[markphelps]

👋🏻 Is there anything I can do to help get this across the line? much appreciated @legoheld and @tcarrio !!

[tcarrio]

@legoheld Just reaching out to see if this is something you still wanted to continue with. If so, then the commits would need to be assigned in order to contribute the work.

Let me know! 👋

[legoheld]

Thanks for the reminder @tcarrio.

Im quite busy with projects and havent caught up with the flip progress.
@markphelps would you like to take over?

[markphelps]

Thanks for the reminder @tcarrio.

Im quite busy with projects and havent caught up with the flip progress. @markphelps would you like to take over?

Yes I will take over. Thank you @legoheld !!

[tcarrio]

No worries, that works fine @legoheld. If the work is being continued from your branch then you should sign off the commits for the DCO.

If you have questions @markphelps throw them in the thread and I'll get to it as soon as I can 👋