feat: Add OpenFeature Provider support

[typotter]

Summary

Implements OpenFeature Provider for Eppo SDK to enable standardized feature flag evaluation through the vendor-neutral OpenFeature API.

Key Features

• ✅ Full OpenFeature Provider interface compliance - Complete implementation of all required methods
• ✅ All flag types supported - boolean, string, number, and object flags
• ✅ Context mapping - Automatic conversion from OpenFeature format to Eppo attributes
• ✅ Bandit evaluation support - Special handling for bandit evaluations through object flags
• ✅ Comprehensive error handling - Proper error mapping and graceful fallbacks
• ✅ Provider lifecycle management - Initialization, status tracking, and cleanup
• ✅ Event system integration - OpenFeature provider events support
• ✅ Full backward compatibility - Maintains all existing Eppo SDK functionality

Implementation Details

Core Components Added

• EppoOpenFeatureProvider - Main provider class implementing OpenFeature Provider interface
• getOpenFeatureProvider() - Factory function to create provider from existing Eppo client
• Context transformation - Maps targetingKey → subjectKey, flattens nested objects for attributes
• Flag type handling - Routes to appropriate Eppo SDK methods based on flag type
• Bandit support - Detects actions in context to trigger bandit evaluation

Files Added/Modified

• 📄 src/openfeature-provider.ts - Complete provider implementation
• 📄 src/index.ts - Added getOpenFeatureProvider() method and exports
• 📄 package.json - Added @openfeature/server-sdk dependency
• 🧪 src/openfeature-provider.spec.ts - Comprehensive unit tests
• 🧪 src/openfeature-integration.spec.ts - Integration tests with OpenFeature API
• 📖 examples/openfeature-example.ts - Complete usage examples
• 📖 README-OpenFeature.md - Full documentation and migration guide

Usage Example

import { OpenFeature } from '@openfeature/server-sdk';
import { init, getOpenFeatureProvider } from '@eppo/node-server-sdk';

// 1. Initialize Eppo SDK as usual
await init({
  apiKey: 'your-api-key',
  assignmentLogger: { logAssignment: (assignment) => console.log(assignment) }
});

// 2. Get OpenFeature provider and set it
const provider = getOpenFeatureProvider();
OpenFeature.setProvider(provider);

// 3. Use standardized OpenFeature API
const client = OpenFeature.getClient();
const result = await client.getBooleanValue('my-flag', false, {
  targetingKey: 'user-123',
  email: '[email protected]'
});

Test Plan

• Unit Tests - Complete test coverage for all provider methods
• Integration Tests - End-to-end testing with OpenFeature SDK
• Error Handling - Tests for all error scenarios and fallbacks
• Context Transformation - Tests for nested object flattening and attribute mapping
• Bandit Support - Tests for bandit evaluation through object flags
• TypeScript Compilation - All code compiles without errors
• Lint Checks - Code follows project linting standards

Manual Testing

• Example code runs successfully
• All flag types evaluate correctly
• Context mapping works for complex nested objects
• Error handling provides appropriate fallbacks
• Bandit evaluations work through object flags

Benefits

For Developers

• Standardization - Use vendor-neutral OpenFeature API across different feature flag systems
• Migration Path - Gradual migration from direct SDK usage to OpenFeature
• Ecosystem - Access to OpenFeature's growing ecosystem of tools and integrations
• Flexibility - Easy switching between feature flag providers in the future

For the Eppo Ecosystem

• Market Reach - Makes Eppo accessible to OpenFeature users
• Standards Compliance - Aligns with industry-standard feature flag API
• Integration - Enables integration with OpenFeature-compatible tools
• Future-Proofing - Positions Eppo for emerging OpenFeature ecosystem

Compatibility & Migration

Full Backward Compatibility

• All existing Eppo SDK usage continues to work unchanged
• No breaking changes to existing APIs
• Direct SDK and OpenFeature usage can coexist

Migration Strategy

// Existing code (continues to work)
const eppoClient = getInstance();
const result = eppoClient.getBooleanAssignment('flag', 'user', {}, false);

// New OpenFeature code (gradually adopted)
const client = OpenFeature.getClient();
const result = await client.getBooleanValue('flag', false, { targetingKey: 'user' });

🤖 Generated with Claude Code