OpenFeature Kotlin 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

• The Android minSdk version supported is: 21.

Note that this library is intended to be used in a mobile context, and has not been evaluated for use in other types of applications (e.g. server applications).

Install

Maven Central

Installation via Maven Central is preferred, using the following dependency:

dependencies {
    api("dev.openfeature:android-sdk:0.3.2")
}

Usage

coroutineScope.launch(Dispatchers.IO) {
  // configure a provider, wait for it to complete its initialization tasks
  OpenFeatureAPI.setProviderAndWait(customProvider)
  val client = OpenFeatureAPI.getClient()

  // get a bool flag value
  client.getBooleanValue("boolFlag", default = false)
}

🌟 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.
✅	Tracking	Associate user actions with feature flag evaluations.
❌	Logging	Integrate with popular logging packages.
❌	Named clients	Utilize multiple providers in a single application.
✅	Eventing	React to state changes in the provider or flag management system.
✅	Shutdown	Gracefully clean up a provider during application shutdown.
⚠️	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:

OpenFeatureAPI.setProviderAndWait(MyProvider())

Asynchronous API that doesn't wait is also available

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
val evaluationContext = ImmutableContext(
    targetingKey = session.getId,
    attributes = mutableMapOf("region" to Value.String("us-east-1")))
OpenFeatureAPI.setEvaluationContext(evaluationContext)

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
OpenFeatureAPI.addHooks(listOf(ExampleHook()))

// add a hook on this client, to run on all evaluations made by this client
val client = OpenFeatureAPI.getClient()
client.addHooks(listOf(ExampleHook()))

// add a hook for this evaluation only
val retval = client.getBooleanValue(flagKey, false,
    FlagEvaluationOptions(listOf(ExampleHook())))

Tracking

The tracking API allows you to use OpenFeature abstractions to associate user actions with feature flag evaluations. This is essential for robust experimentation powered by feature flags. Note that, unlike methods that handle feature flag evaluations, calling track(...) may throw an IllegalArgumentException if an empty string is passed as the trackingEventName.

Below is an example of how we can track a "Checkout" event with some TrackingDetails.

OpenFeatureAPI.getClient().track(
  "Checkout",
  TrackingEventDetails(
    499.99,
    ImmutableStructure(
      "numberOfItems" to Value.Integer(4),
      "timeInCheckout" to Value.String("PT3M20S")
    )
  )
)

Tracking is optionally implemented by Providers.

Logging

Logging customization is not yet available in the Kotlin SDK.

Named clients

Support for named clients is not yet available in the Kotlin SDK.

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.

Example usage:

viewModelScope.launch {
  OpenFeatureAPI.observe<OpenFeatureEvents.ProviderReady>().collect {
    println(">> ProviderReady event received")
  }
}

viewModelScope.launch {
  OpenFeatureAPI.setProviderAndWait(
    ConfidenceFeatureProvider.create(
      applicationContext,
      clientSecret
    ),
    Dispatchers.IO,
    myEvaluationContext
  )
}

Shutdown

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

OpenFeatureAPI.shutdown()

Extending

Develop a provider

To develop a provider, you need to create a new project and include the OpenFeature SDK as a dependency. You’ll then need to write the provider by implementing the FeatureProvider interface exported by the OpenFeature SDK.

class NewProvider(override val hooks: List<Hook<*>>, override val metadata: Metadata) : FeatureProvider {
    override fun getBooleanEvaluation(
        key: String,
        defaultValue: Boolean,
        context: EvaluationContext?
    ): ProviderEvaluation<Boolean> {
        // resolve a boolean flag value
    }

    override fun getDoubleEvaluation(
        key: String,
        defaultValue: Double,
        context: EvaluationContext?
    ): ProviderEvaluation<Double> {
        // resolve a double flag value
    }

    override fun getIntegerEvaluation(
        key: String,
        defaultValue: Int,
        context: EvaluationContext?
    ): ProviderEvaluation<Int> {
        // resolve an integer flag value
    }

    override fun getObjectEvaluation(
        key: String,
        defaultValue: Value,
        context: EvaluationContext?
    ): ProviderEvaluation<Value> {
        // resolve an object flag value
    }

    override fun getStringEvaluation(
        key: String,
        defaultValue: String,
        context: EvaluationContext?
    ): ProviderEvaluation<String> {
        // resolve a string flag value
    }

    override fun initialize(initialContext: EvaluationContext?) {
        // add context-aware provider initialization
    }

    override fun onContextSet(oldContext: EvaluationContext?, newContext: EvaluationContext) {
        // add necessary changes on context change
    }

    override fun observe(): Flow<OpenFeatureEvents> {
        // return a `Flow` of the Events
    }

    override fun getProviderStatus(): OpenFeatureEvents {
        // return the event representative of the current Provider Status
    }
}

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. Implement your own hook by conforming to the Hook interface exported by the OpenFeature SDK.

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

⭐️ 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 who has already contributed

Made with contrib.rocks.