OpenFeature Dart Server SDK

⚠️ This repository is a work in progress repository for an implementation of the dart-server-sdk.

OpenFeature is an open specification that provides a vendor-agnostic, community-driven API for feature flagging that works with your favorite feature flag management tool.

🚀 Quick start

Requirements

Dart language version: 3.7.2

Note

The OpenFeature DartServer SDK only supports the latest currently maintained Dart language versions.

Install

dependencies:
  openfeature_dart_server_sdk: ^0.0.6

Then run:

dart pub get

Usage

import 'dart:async';
import 'package:openfeature_dart_server_sdk/client.dart';
import 'package:openfeature_dart_server_sdk/open_feature_api.dart';
import 'package:openfeature_dart_server_sdk/feature_provider.dart';
import 'package:openfeature_dart_server_sdk/evaluation_context.dart';
import 'package:openfeature_dart_server_sdk/hooks.dart';

void main() async {
  // Register your feature flag provider
  final api = OpenFeatureAPI();
  api.setProvider(InMemoryProvider({
    'new-feature': true,
    'welcome-message': 'Hello, OpenFeature!'
  }));

  // Create a client
  final client = FeatureClient(
    metadata: ClientMetadata(name: 'my-app'),
    hookManager: HookManager(),
    defaultContext: EvaluationContext(attributes: {}),
  );

  // Evaluate your feature flags
  final newFeatureEnabled = await client.getBooleanFlag(
    'new-feature',
    defaultValue: false,
  );

  // Use the returned flag value
  if (newFeatureEnabled) {
    print('New feature is enabled!');

    final welcomeMessage = await client.getStringFlag(
      'welcome-message',
      defaultValue: 'Welcome!',
    );

    print(welcomeMessage);
  }
}

API Reference

See here for the complete API documentation.

🌟 Features

Status	Features	Description
✅	Providers	Integrate with a commercial, open source, or in-house feature management tool.
✅	Targeting	Contextually-aware flag evaluation using evaluation context.
✅	Hooks	Add functionality to various stages of the flag evaluation life-cycle.
✅	Logging	Integrate with popular logging packages.
✅	Domains	Logically bind clients with providers.
✅	Eventing	React to state changes in the provider or flag management system.
✅	Shutdown	Gracefully clean up a provider during application shutdown.
✅	Transaction Context Propagation	Set a specific evaluation context for a transaction (e.g. an HTTP request or a thread)
✅	Extending	Extend OpenFeature with custom providers and hooks.

_{Implemented: ✅ | In-progress: ⚠️ | Not implemented yet: ❌}

Providers

Providers are an abstraction between a flag management system and the OpenFeature SDK. Look here for a complete list of available providers. If the provider you're looking for hasn't been created yet, see the develop a provider section to learn how to build it yourself.

Once you've added a provider as a dependency, it can be registered with OpenFeature like this:

final api = OpenFeatureAPI();
api.setProvider(MyProvider());

Targeting

Sometimes, the value of a flag must consider some dynamic criteria about the application or user, such as the user's location, IP, email address, or the server's location. In OpenFeature, we refer to this as targeting. If the flag management system you're using supports targeting, you can provide the input data using the evaluation context.

// Set a value to the global context
final api = OpenFeatureAPI();
api.setGlobalContext(OpenFeatureEvaluationContext({
  'region': 'us-east-1-iah-1a',
}));

// Create a client with a specific evaluation context
final client = FeatureClient(
  metadata: ClientMetadata(name: 'my-app'),
  hookManager: HookManager(),
  defaultContext: EvaluationContext(attributes: {
    'version': '1.4.6',
  }),
);

// Set a value to the invocation context
final result = await client.getBooleanFlag(
  'feature-flag',
  defaultValue: false,
  context: EvaluationContext(attributes: {
    'user': 'user-123',
    'company': 'Initech',
  }),
);

Hooks

Hooks allow for custom logic to be added at well-defined points of the flag evaluation life-cycle Look here for a complete list of available hooks. If the hook you're looking for hasn't been created yet, see the develop a hook section to learn how to build it yourself.

Once you've added a hook as a dependency, it can be registered at the global, client, or flag invocation level.

// Add a hook globally, to run on all evaluations
final api = OpenFeatureAPI();
api.addHooks([MyGlobalHook()]);

// Add a hook on this client, to run on all evaluations made by this client
final hookManager = HookManager();
hookManager.addHook(MyClientHook());

final client = FeatureClient(
  metadata: ClientMetadata(name: 'my-app'),
  hookManager: hookManager,
  defaultContext: EvaluationContext(attributes: {}),
);

// Create a hook for a specific evaluation
final myHook = MyHook();
// You can use the hook with a specific evaluation

Tracking

The tracking API allows you to use OpenFeature abstractions and objects to associate user actions with feature flag evaluations. This is essential for robust experimentation powered by feature flags. For example, a flag enhancing the appearance of a UI component might drive user engagement to a new feature; to test this hypothesis, telemetry collected by a hook or provider can be associated with telemetry reported in the client's track function.

Note that some providers may not support tracking; check the documentation for your provider for more information.

Logging

Note that in accordance with the OpenFeature specification, the SDK doesn't generally log messages during flag evaluation.

Logging Hook

The Dart SDK includes a LoggingHook, which logs detailed information at key points during flag evaluation, using TBD structured logging API. This hook can be particularly helpful for troubleshooting and debugging; simply attach it at the global, client or invocation level and ensure your log level is set to "debug".

Usage example

import 'package:logging/logging.dart';
import 'package:openfeature_dart_server_sdk/hooks.dart';

// Configure logging
Logger.root.level = Level.ALL;
Logger.root.onRecord.listen((record) {
  print('${record.time} [${record.level.name}] ${record.message}');
});

// Create a logging hook
final loggingHook = LoggingHook();

// Add the hook to your hook manager
final hookManager = HookManager();
hookManager.addHook(loggingHook);

// Create a client using this hook manager
final client = FeatureClient(
  metadata: ClientMetadata(name: 'test-client'),
  hookManager: hookManager,
  defaultContext: EvaluationContext(attributes: {}),
);

// Evaluate a flag
final result = await client.getBooleanFlag('my-flag', defaultValue: false);

Output

{"time":"2024-10-23T13:33:09.8870867+03:00","level":"DEBUG","msg":"Before stage","domain":"test-client","provider_name":"InMemoryProvider","flag_key":"not-exist","default_value":true}
{"time":"2024-10-23T13:33:09.8968242+03:00","level":"ERROR","msg":"Error stage","domain":"test-client","provider_name":"InMemoryProvider","flag_key":"not-exist","default_value":true,"error_message":"error code: FLAG_NOT_FOUND: flag for key not-exist not found"}

See hooks for more information on configuring hooks.

Domains

Clients can be assigned to a domain. A domain is a logical identifier that can be used to associate clients with a particular provider. If a domain has no associated provider, the default provider is used.

import 'package:openfeature_dart_server_sdk/domain_manager.dart';
import 'package:openfeature_dart_server_sdk/feature_provider.dart';
import 'package:openfeature_dart_server_sdk/open_feature_api.dart';

// Get the OpenFeature API instance
final api = OpenFeatureAPI();

// Register the default provider
api.setProvider(InMemoryProvider({'default-flag': true}));

// Register a domain-specific provider
api.bindClientToProvider('cache-domain', 'CachedProvider');

// Client backed by default provider
api.evaluateBooleanFlag('my-flag', 'default-client');

// Client backed by CachedProvider
api.evaluateBooleanFlag('my-flag', 'cache-domain');

Eventing

Events allow you to react to state changes in the provider or underlying flag management system, such as flag definition changes, provider readiness, or error conditions. Initialization events (PROVIDER_READY on success, PROVIDER_ERROR on failure) are dispatched for every provider. Some providers support additional events, such as PROVIDER_CONFIGURATION_CHANGED.

Please refer to the documentation of the provider you're using to see what events are supported.

import 'package:openfeature_dart_server_sdk/open_feature_api.dart';
import 'package:openfeature_dart_server_sdk/open_feature_event.dart';

// Get the OpenFeature API instance
final api = OpenFeatureAPI();

// Listen for provider change events
api.events.listen((event) {
  if (event.type == OpenFeatureEventType.providerChanged) {
    print('Provider changed: ${event.message}');
  }
});

// Listen for flag evaluation events
api.events.listen((event) {
  if (event.type == OpenFeatureEventType.flagEvaluated) {
    print('Flag evaluated: ${event.data['flagKey']} = ${event.data['result']}');
  }
});

Shutdown

The OpenFeature API provides mechanisms to perform a cleanup of all registered providers. This should only be called when your application is in the process of shutting down.

import 'package:openfeature_dart_server_sdk/open_feature_api.dart';
import 'package:openfeature_dart_server_sdk/shutdown_manager.dart';

// Get the OpenFeature API instance
final api = OpenFeatureAPI();

// Register shutdown hooks
final shutdownManager = ShutdownManager();
shutdownManager.registerHook(ShutdownHook(
  name: 'provider-cleanup',
  phase: ShutdownPhase.PROVIDER_SHUTDOWN,
  execute: () async {
    // Clean up provider resources
    await api.dispose();
  },
));

// During application shutdown
await shutdownManager.shutdown();

Transaction Context Propagation

Transaction context is a container for transaction-specific evaluation context (e.g. user id, user agent, IP). Transaction context can be set where specific data is available (e.g. an auth service or request handler), and by using the transaction context propagator, it will automatically be applied to all flag evaluations within a transaction (e.g. a request or thread).

import 'package:openfeature_dart_server_sdk/transaction_context.dart';

// Create a transaction context manager
final transactionManager = TransactionContextManager();

// Set the transaction context
final context = TransactionContext(
  transactionId: 'request-123',
  attributes: {
    'user': 'user-456',
    'region': 'us-west-1',
  },
);
transactionManager.pushContext(context);

// The transaction context will automatically be applied to flag evaluations
await client.getBooleanFlag('my-flag', defaultValue: false);

// Execute code with a specific transaction context
await transactionManager.withContext(
  'transaction-id',
  {'user': 'user-123'},
  () async {
    await client.getBooleanFlag('my-flag', defaultValue: false);
  },
);

// When the transaction is complete, pop the context
transactionManager.popContext();

Extending

Develop a provider

To develop a provider, you need to create a new project and include the OpenFeature SDK as a dependency. This can be a new repository or included in the existing contrib repository available under the OpenFeature organization. You’ll then need to write the provider by implementing the FeatureProvider interface exported by the OpenFeature SDK.

import 'dart:async';
import 'package:openfeature_dart_server_sdk/feature_provider.dart';

class MyCustomProvider implements FeatureProvider {
  @override
  String get name => 'MyCustomProvider';

  @override
  ProviderState get state => ProviderState.READY;

  @override
  ProviderConfig get config => ProviderConfig();

  @override
  Future<void> initialize([Map<String, dynamic>? config]) async {
    // Initialize your provider
  }

  @override
  Future<void> connect() async {
    // Connection logic if needed
  }

  @override
  Future<void> shutdown() async {
    // Clean up resources
  }

  @override
  Future<FlagEvaluationResult<bool>> getBooleanFlag(
    String flagKey,
    bool defaultValue, {
    Map<String, dynamic>? context,
  }) async {
    // Evaluate boolean flag
    return FlagEvaluationResult(
      flagKey: flagKey,
      value: true, // Your implementation here
      evaluatedAt: DateTime.now(),
      evaluatorId: name,
    );
  }

  @override
  Future<FlagEvaluationResult<String>> getStringFlag(
    String flagKey,
    String defaultValue, {
    Map<String, dynamic>? context,
  }) async {
    // Evaluate string flag
    return FlagEvaluationResult(
      flagKey: flagKey,
      value: 'value', // Your implementation here
      evaluatedAt: DateTime.now(),
      evaluatorId: name,
    );
  }

  @override
  Future<FlagEvaluationResult<int>> getIntegerFlag(
    String flagKey,
    int defaultValue, {
    Map<String, dynamic>? context,
  }) async {
    // Evaluate integer flag
    return FlagEvaluationResult(
      flagKey: flagKey,
      value: 42, // Your implementation here
      evaluatedAt: DateTime.now(),
      evaluatorId: name,
    );
  }

  @override
  Future<FlagEvaluationResult<double>> getDoubleFlag(
    String flagKey,
    double defaultValue, {
    Map<String, dynamic>? context,
  }) async {
    // Evaluate double flag
    return FlagEvaluationResult(
      flagKey: flagKey,
      value: 3.14, // Your implementation here
      evaluatedAt: DateTime.now(),
      evaluatorId: name,
    );
  }

  @override
  Future<FlagEvaluationResult<Map<String, dynamic>>> getObjectFlag(
    String flagKey,
    Map<String, dynamic> defaultValue, {
    Map<String, dynamic>? context,
  }) async {
    // Evaluate object flag
    return FlagEvaluationResult(
      flagKey: flagKey,
      value: {'key': 'value'}, // Your implementation here
      evaluatedAt: DateTime.now(),
      evaluatorId: name,
    );
  }
}

Built a new provider? Let us know so we can add it to the docs!

Develop a hook

To develop a hook, you need to create a new project and include the OpenFeature SDK as a dependency. This can be a new repository or included in the existing contrib repository available under the OpenFeature organization. Implement your own hook by conforming to the Hook interface. To satisfy the interface, all methods (Before/After/Finally/Error) need to be defined. To avoid defining empty functions make use of the UnimplementedHook struct (which already implements all the empty functions).

import 'dart:async';
import 'package:openfeature_dart_server_sdk/hooks.dart';

class MyCustomHook extends BaseHook {
  MyCustomHook()
    : super(metadata: HookMetadata(name: 'MyCustomHook'));

  @override
  Future<void> before(HookContext context) async {
    // Code to run before flag evaluation
    print('Before evaluating flag: ${context.flagKey}');
  }

  @override
  Future<void> after(HookContext context) async {
    // Code to run after successful flag evaluation
    print('After evaluating flag: ${context.flagKey}, result: ${context.result}');
  }

  @override
  Future<void> error(HookContext context) async {
    // Code to run when an error occurs during flag evaluation
    print('Error evaluating flag: ${context.flagKey}, error: ${context.error}');
  }

  @override
  Future<void> finally_(
    HookContext context,
    EvaluationDetails? evaluationDetails, [
    HookHints? hints,
  ]) async {
    // Code to run regardless of success or failure
    print('Finished evaluating flag: ${context.flagKey}');
  }
}

Built a new hook? Let us know so we can add it to the docs!

Testing

The SDK provides a NewTestProvider which allows you to set flags for the scope of a test. The TestProvider is thread-safe and can be used in tests that run in parallel.

Call testProvider.UsingFlags(t, tt.flags) to set flags for a test, and clean them up with testProvider.Cleanup()

import 'package:test/test.dart';
import 'package:openfeature_dart_server_sdk/open_feature_api.dart';
import 'package:openfeature_dart_server_sdk/feature_provider.dart';

void main() {
  late OpenFeatureAPI api;
  late InMemoryProvider testProvider;

  setUp(() {
    api = OpenFeatureAPI();
    testProvider = InMemoryProvider({
      'test-flag': true,
      'string-flag': 'test-value',
    });
    api.setProvider(testProvider);
  });

  tearDown(() {
    OpenFeatureAPI.resetInstance();
  });

  test('evaluates boolean flag correctly', () async {
    final client = api.getClient('test-client');
    final result = await client.getBooleanFlag('test-flag', defaultValue: false);
    expect(result, isTrue);
  });

  test('evaluates string flag correctly', () async {
    final client = api.getClient('test-client');
    final result = await client.getStringFlag('string-flag', defaultValue: 'default');
    expect(result, equals('test-value'));
  });
}

⭐️ Support the project

• Give this repo a ⭐️!
• Follow us on social media:
  • Twitter: @openfeature
  • LinkedIn: OpenFeature
• Join us on Slack
• For more, check out our community page

🤝 Contributing

Interested in contributing? Great, we'd love your help! To get started, take a look at the CONTRIBUTING guide.

Thanks to everyone that has already contributed

Made with contrib.rocks.