FlagPole

Feature flag handling for PHP. Simple, framework-agnostic, and lightweight.

Installation

Install via Composer:

composer require phred/flagpole

Quick start

use FlagPole\FeatureManager;
use FlagPole\Context;
use FlagPole\Repository\InMemoryFlagRepository;

require __DIR__ . '/vendor/autoload.php';

$repo = InMemoryFlagRepository::fromArray([
    'new-dashboard' => [
        'enabled' => null,               // not a hard on/off
        'rolloutPercentage' => 25,       // 25% gradual rollout
        'allowList' => ['user_1'],       // always on for specific users
    ],
    'hard-off' => [ 'enabled' => false ],
    'hard-on'  => [ 'enabled' => true ],
]);

$flags = new FeatureManager($repo);

$context = Context::fromArray(['userId' => 'user_42']);

if ($flags->isEnabled('new-dashboard', $context, false)) {
    // show the new dashboard
} else {
    // keep the old dashboard
}

Concepts

• Flag: has a name and optional strategies:
  • enabled: explicit boolean on/off overrides everything.
  • rolloutPercentage: 0-100 gradual rollout based on a stable hash of the flag name + user key.
  • allowList: list of user keys that always get the flag enabled.
• Context: attributes about the subject (e.g. userId, email) used for evaluation.
• Repository: source of truth for flags. Provided: InMemoryFlagRepository. You can implement your own.

Targeting key

Evaluator looks for a stable key in the context in this order: key, userId, id, email.

Rollout hashing and boundary behavior

• Stable bucketing uses crc32(flagName:key) normalized to an unsigned 32-bit integer, then mapped to buckets 0..99.
• This guarantees consistent behavior across 32-bit and 64-bit platforms.
• Boundary rules:
  • 0% rollout always evaluates to false when a targeting key is present.
  • 100% rollout always evaluates to true when a targeting key is present.
  • If no targeting key is present in the Context, percentage rollout falls back to the default you pass to isEnabled().

Precedence semantics

When evaluating a flag, the following precedence applies:

1. allowList — if the targeting key is in the allow-list, the flag is enabled.
2. enabled — explicit on/off overrides percentage rollout and defaults.
3. rolloutPercentage — uses stable bucketing over the targeting key.
4. Fallback — returns the provided default when none of the above apply.

Framework integration

FlagPole is framework-agnostic. Wrap FeatureManager in your framework's container and bind a repository suitable for your environment.

License

MIT