flipt_client 1.0.0

Flipt Client Evaluation SDK for Dart **Note:** As of 1.0.0, `FliptEvaluationClient` has been renamed to `FliptClient` for consistency with other SDKs and Dart idioms. Update your code accordingly. 0. [...]

Flipt Client Dart

The flipt-client-dart library contains the Dart source code for the Flipt client-side evaluation client.

Installation

Add this to your package's pubspec.yaml file:

dependencies:
  flipt_client: ^1.0.0

Then run dart pub get to install the package.

How Does It Work?

The flipt-client-dart library is a wrapper around the flipt-engine-ffi library.

All evaluation happens within the SDK, using the shared library built from the flipt-engine-ffi library.

Because the evaluation happens within the SDK, the SDKs can be used in environments where the Flipt server is not available or reachable after the initial data is fetched.

Data Fetching

Upon instantiation, the flipt-client-dart library will fetch the flag state from the Flipt server and store it in memory. This means that the first time you use the SDK, it will make a request to the Flipt server.

Polling (Default)

By default, the SDK will poll the Flipt server for new flag state at a regular interval. This interval can be configured using the updateInterval option when constructing a client. The default interval is 120 seconds.

Streaming (Flipt Cloud/Flipt v2)

Flipt Cloud and Flipt v2 users can use the streaming fetch method to stream flag state changes from the Flipt server to the SDK.

When in streaming mode, the SDK will connect to the Flipt server and open a persistent connection that will remain open until the client is closed. The SDK will then receive flag state changes in real-time.

Retries

The SDK will automatically retry fetching (or initiating streaming) flag state if the client is unable to reach the Flipt server temporarily.

The SDK will retry up to 3 times with an exponential backoff interval between retries. The base delay is 1 second and the maximum delay is 30 seconds.

Retriable errors include:

• 429 Too Many Requests
• 502 Bad Gateway
• 503 Service Unavailable
• 504 Gateway Timeout
• Other potential transient network or DNS errors

Supported Architectures

This SDK currently supports the following OSes/architectures:

• Linux x86_64
• Linux arm64
• MacOS arm64
• Windows x86_64
• Android arm64
• iOS arm64 ⚠️ See iOS Integration
• iOS arm64 (simulator) ⚠️ See iOS Integration

Migration Notes

Pre-1.0.0 -> 1.0.0

This section is for users who are migrating from a previous (pre-1.0.0) version of the SDK.

• FliptEvaluationClient has been renamed to FliptClient.
• Options now accept namespace and environment as optional parameters.
• requestTimeout and updateInterval in Options are now Duration types instead of int (seconds). Update your code to use Duration(seconds: ...).
• MacOS x86_64 is no longer supported as pub.dev enforces a file size limit of published packages so we cannot include every architecture in the SDK.

Usage

import 'package:flipt_client/flipt_client.dart';

void main() {
  // Initialize the client
  final client = FliptClient(
    options: Options.withClientToken(
      'your-token',
      url: 'http://localhost:8080',
      requestTimeout: Duration(seconds: 10),
      updateInterval: Duration(minutes: 2),
    ),
  );

  // Evaluate a variant flag
  final result = client.evaluateVariant(
    flagKey: 'flag1',
    entityId: 'someentity',
    context: {'fizz': 'buzz'},
  );

  print('Variant: ${result.variantKey}');

  // Evaluate a boolean flag
  final result = client.evaluateBoolean(
    flagKey: 'flag2',
    entityId: 'user123',
    context: {'key': 'value'},
  );

  print('Enabled: ${result.enabled}');

  // Don't forget to close the client when you're done
  client.close();
}

Client Options

The FliptClient initializer accepts several options that can be used to configure the client. The available options are:

• environment: The environment (Flipt v2) to fetch flag state from. If not provided, the client will default to the default environment.
• namespace: The namespace to fetch flag state from. If not provided, the client will default to the default namespace.
• url: The URL of the upstream Flipt instance. If not provided, the client will default to http://localhost:8080.
• requestTimeout: The timeout as a Duration for total request time to the upstream Flipt instance. If not provided, the client will default to no timeout. Note: this only affects polling mode. Streaming mode will have no timeout set.
• updateInterval: The interval as a Duration in which to fetch new flag state. If not provided, the client will default to Duration(seconds: 120).
• authentication: The authentication strategy to use when communicating with the upstream Flipt instance. If not provided, the client will default to no authentication. See the Authentication section for more information.
• reference: The reference to use when fetching flag state. If not provided, reference will not be used.
• fetchMode: The fetch mode to use when fetching flag state. If not provided, the client will default to polling.
• errorStrategy: The error strategy to use when fetching flag state. If not provided, the client will default to fail. See the Error Strategies section for more information.
• snapshot: The initial snapshot to use when instantiating the client. See the Snapshotting section for more information.

Authentication

The FliptClient supports the following authentication strategies:

• No Authentication (default)
• Client Token Authentication
• JWT Authentication

Error Strategies

The client supports the following error strategies:

• fail: The client will throw an error if the flag state cannot be fetched. This is the default behavior.
• fallback: The client will maintain the last known good state and use that state for evaluation in case of an error.

Snapshotting

The client supports snapshotting of flag state as well as seeding the client with a snapshot for evaluation. This is helpful if you want to use the client in an environment where the Flipt server is not guaranteed to be available or reachable on startup.

To get the snapshot for the client, you can use the getSnapshot method. This returns a base64 encoded JSON string that represents the flag state for the client.

You can set the snapshot for the client using the snapshot option when constructing a client.

Note: You most likely will want to also set the errorStrategy to fallback when using snapshots. This will ensure that you wont get an error if the Flipt server is not available or reachable even on the initial fetch.

You also may want to store the snapshot in a local file so that you can use it to seed the client on startup.

Important

If the Flipt server becomes reachable after the setting the snapshot, the client will replace the snapshot with the new flag state from the Flipt server.

iOS Integration 📱

The flipt-client-dart library can be used in a Flutter iOS app but requires a few additional steps to integrate.

We're working on making this easier in the future.

Podfile

Open your app's ios/Podfile and comment out the following lines in the target 'Runner' do block:

# use_frameworks!
# use_modular_headers!

Troubleshooting

Missing x86_64

If you see errors about missing x86_64, add the following to the post_install block of your Podfile:

post_install do |installer|
  installer.pods_project.targets.each do |target|
    flutter_additional_ios_build_settings(target)
    # Exclude x86_64 for simulator builds (Apple Silicon only)
    target.build_configurations.each do |config|
      config.build_settings['EXCLUDED_ARCHS[sdk=iphonesimulator*]'] = 'x86_64'
    end
  end
end

You may also need to add the following User Defined Setting to your Xcode project. Do this in the Build Settings tab for your project, not the target!

VALID_ARCHS = arm64

[User Defined Settings]

Development

Install Dependencies

To install the dependencies, run:

dart pub get

Generate JSON Serialization Code

To generate the JSON serialization code (found in lib/src/models.g.dart), run:

dart run build_runner build --delete-conflicting-outputs

Generate FFI Bindings

To generate the FFI bindings (found in lib/ffi/bindings.dart), run:

cp ../flipt-engine-ffi/include/flipt_engine.h ffi/flipt_engine.h
dart run ffigen --config ffigen.yaml

Contributing

Contributions are welcome! Please feel free to open an issue or submit a Pull Request.

License

This project is licensed under the MIT License.