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OpenFeature Android SDK

SpecificationRelease
StatusMavenCentral

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:0.4.1")
}

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​

StatusFeaturesDescription
✅ProvidersIntegrate with a commercial, open source, or in-house feature management tool.
✅TargetingContextually-aware flag evaluation using evaluation context.
✅HooksAdd functionality to various stages of the flag evaluation life-cycle.
✅TrackingAssociate user actions with feature flag evaluations.
❌LoggingIntegrate with popular logging packages.
❌Named clientsUtilize multiple providers in a single application.
✅EventingReact to state changes in the provider or flag management system.
✅ShutdownGracefully clean up a provider during application shutdown.
⚠️ExtendingExtend 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:

coroutineScope.launch(Dispatchers.IO) {
    OpenFeatureAPI.setProviderAndWait(MyProvider())
}

Asynchronous API that doesn't wait is also available. It's useful when you want to set a provider and continue with other tasks.

However, flag evaluations are only possible after the provider is Ready.

OpenFeatureAPI.setProvider(MyProvider()) // can pass a dispatcher here
// The provider initialization happens on a coroutine launched on the IO dispatcher. 
val status = OpenFeatureAPI.getStatus()
// When status is Ready, flag evaluations can be made

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.

It is possible to write and inject logging Hooks to log events at different stages of the flag evaluation life-cycle.

Named clients​

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

Eventing​

Events from the Provider allow the SDK to react to state changes in the provider or underlying flag management system, such as flag definition changes, provider readiness, or error conditions. Events are optional which mean that not all Providers will emit them and it is not a must have. 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().collect {
    println(">> Provider event received")
  }
}

viewModelScope.launch {
  OpenFeatureAPI.setProviderAndWait(
    MyFeatureProvider(),
    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()

Sample app​

In the repo there is also a sample app currently under development. The sample app can be used to try out development of a Provider, a Hook or to validate changes to the SDK itself.

The sample app should not be used as a reference implementation of how to use the OpenFeature SDK in an Android app.

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

    override suspend fun onContextSet(oldContext: EvaluationContext?, newContext: EvaluationContext) {
        // add necessary changes on context change
    }
  
    override fun track(
      trackingEventName: String,
      context: EvaluationContext?,
      details: TrackingEventDetails?
    ) {
      // Optionally track an event
    }
  
    override fun observe(): Flow<OpenFeatureProviderEvents> {
        // Optionally return a `Flow` of OpenFeatureProviderEvents
    }
}

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!