feat: Add Support For Feature Flag Payloads

[elliottlawson]

This PR enables support for retrieving the payloads of feature flags, by leveraging the .../decide/?v=3 query parameter.

The decide version can now be customized by passing a version number in the options parameter when initializing PostHog. This enables the decide call to return the featureFlagPayloads object in the payload. The version defaults to 2 if no value is specified.

Usage:

PostHog::init(
    apiKey: '...',
    options: [
        'decide_version' => 3,
    ],
);

PostHog::getFeatureFlagPayload('payload-flag', 'distinct-id');

 

Tests

Tests are included for the following scenarios

• Feature flag disabled - payload should be null
• Feature flag enabled - json payload
• Feature flag enabled - integer payload
• Feature flag enabled - string payload

[neilkakkar]

I just realised my review from a few months ago is still sitting in 'pending' and you can't actually see it 🤦 - sorry about this!

[neilkakkar]

Hey Elliot, instead of making this an option, force update everything to version 3, I'll make a major version release for PHP with your PR, since we are meant to move off of v2 anyway.

[neilkakkar]

The only thing blocking a merge here is support for local evaluation -> since getFeatureFlag supports local evaluation, the payload should too.

You can copy the exact code from python: https://github.com/PostHog/posthog-python/blob/master/posthog/client.py#L602 - and compare the get_feature_flag function to the PHP equivalent - they're exactly the same (with some language specific quirks)

You can also then copy all the tests below this line: https://github.com/PostHog/posthog-python/pull/81/files#diff-0e2fa9949bd8d80eecebfa2ff9b994a1bc528fbb003c7e80d104e6d5b3c5f07fR1379-R1384 to make sure it works fine.

Let me know if any questions! :) If this is too much for your bandwidth, let me know too.