feat: Multiplatform OFREP provider (#6)

## This PR
Implements an [OFREP](https://openfeature.dev/specification/appendix-c)
provider for Kotlin Multiplatform. The implementation was initially
based on @thomaspoignant's [OFREP
implementation](https://github.com/thomaspoignant/go-feature-flag/tree/main/openfeature/providers/kotlin-provider/gofeatureflag-kotlin-provider/src/main/java/org/gofeatureflag/openfeature/ofrep),
then I made a bunch of changes to make it compatible with multiple
platforms:
* Replaced Java APIs with Kotlin APIs
* Replaced jUnit with kotlin-test
* Replaced OkHttp with Ktor
* Replaced GSON with kotlinx-serialization
* Replaced the Java Timer with Kotlin Coroutines
* ...

Now the project is compatible with multiple platforms, and can be easily
extended to other ones by changing the targets in the
`build.gradle.kts`:


| Supported | Platform | Supported versions |

|-----------|----------------------|--------------------------------------------------------------------------------|
| ✅ | Android | |
| ✅ | JVM | JDK 11+ |
| ✅ | Native | Linux x64 |
| ❌ | Native | [Other native
targets](https://kotlinlang.org/docs/native-target-support.html) |
| ✅ | Javascript (Node.js) | |
| ✅ | Javascript (Browser) | |
| ❌ | Wasm | |

### Notes
I have based these changes on the unmerged
open-feature/kotlin-sdk#148, which brings in
multiplatform support for the SDK.

### Prerequisites
- [x] Merge open-feature/kotlin-sdk#148 first

### How to test
<!-- if applicable, add testing instructions under this section -->

For manual testing: set up a local OFREP provider and try out various
evaluations.

---------

Signed-off-by: Bence Hornák <[email protected]>

Author: bencehornak

buildSrc/build.gradle.kts

@@ -8,6 +8,7 @@ dependencies {
     implementation(plugin(libs.plugins.kotlin.multiplatform))
     implementation(plugin(libs.plugins.dokka))
     implementation(plugin(libs.plugins.vanniktech.maven.publish))
+    implementation(plugin(libs.plugins.android.library))
 }
 
 /**
@@ -16,4 +17,4 @@ dependencies {
  * https://docs.gradle.org/current/userguide/version_catalogs.html#sec:buildsrc-version-catalog
  */
 private fun DependencyHandlerScope.plugin(plugin: Provider<PluginDependency>) =
-    plugin.map { "${it.pluginId}:${it.pluginId}.gradle.plugin:${it.version}" }
+    plugin.map { "${it.pluginId}:${it.pluginId}.gradle.plugin:${it.version}" }

gradle.properties

@@ -1,5 +1,6 @@
 version=0.1.0
 org.gradle.configuration-cache=true
+org.gradle.jvmargs=-Xmx1g "-XX:MaxMetaspaceSize=768m
 
 # This seems to be necessary for Coroutines to work on JS. Otherwise getting the following error:
 #   > Task :providers:env-var:compileTestDevelopmentExecutableKotlinJs FAILED

gradle/libs.versions.toml

@@ -2,8 +2,16 @@
 kotlin = "2.2.10"
 kotlinx-coroutines = "1.10.2"
 open-feature-kotlin-sdk = "0.6.2"
+android = "8.10.1"
+ktor = "3.1.3"
 
 [libraries]
+ktor-core = { module="io.ktor:ktor-client-core", version.ref="ktor" }
+ktor-cio = { module="io.ktor:ktor-client-cio", version.ref="ktor" }
+ktor-js = { module="io.ktor:ktor-client-js", version.ref="ktor" }
+ktor-client-content-negotiation = { module="io.ktor:ktor-client-content-negotiation", version.ref="ktor" }
+ktor-serialization-kotlinx-json = { module="io.ktor:ktor-serialization-kotlinx-json", version.ref="ktor" }
+ktor-client-mock = { module="io.ktor:ktor-client-mock", version.ref="ktor" }
 openfeature-kotlin-sdk = { group="dev.openfeature", name="kotlin-sdk", version.ref="open-feature-kotlin-sdk" }
 kotlin-test = { group="org.jetbrains.kotlin", name="kotlin-test", version.ref="kotlin" }
 kotlinx-coroutines-core = { group="org.jetbrains.kotlinx", name="kotlinx-coroutines-core", version.ref="kotlinx-coroutines" }
@@ -13,7 +21,10 @@ kotlinx-coroutines-test = { group="org.jetbrains.kotlinx", name="kotlinx-corouti
 dokka = { id="org.jetbrains.dokka", version="2.0.0" }
 kotlin-multiplatform = { id="org.jetbrains.kotlin.multiplatform", version.ref="kotlin" }
 kotlinx-atomicfu = { id="org.jetbrains.kotlinx.atomicfu", version="0.29.0" }
+kotlinx-serialization = { id="org.jetbrains.kotlin.plugin.serialization", version="2.1.21" }
 ktlint = { id="org.jlleitschuh.gradle.ktlint", version="13.1.0" }
 nexus-publish = { id="io.github.gradle-nexus.publish-plugin", version="2.0.0" }
 binary-compatibility-validator = { id="org.jetbrains.kotlinx.binary-compatibility-validator", version="0.18.1" }
 vanniktech-maven-publish = { id="com.vanniktech.maven.publish", version="0.34.0" }
+android-library = { id="com.android.library", version.ref="android" }
+docker-compose = { id="com.avast.gradle.docker-compose", version="0.17.12" }

kotlin-js-store/yarn.lock

@@ -0,0 +1,32 @@
+# Kotlin OFREP Provider
+
+This provider is designed to use the [OpenFeature Remote Evaluation Protocol (OFREP)](https://openfeature.dev/specification/appendix-c).
+
+## Supported platforms
+
+| Supported | Platform             | Supported versions                                                             |
+|-----------|----------------------|--------------------------------------------------------------------------------|
+| ✅         | Android              |                                                                                |
+| ✅         | JVM                  | JDK 11+                                                                        |
+| ✅         | Native               | Linux x64                                                                      |
+| ❌         | Native               | [Other native targets](https://kotlinlang.org/docs/native-target-support.html) |
+| ✅         | Javascript (Node.js) |                                                                                |
+| ✅         | Javascript (Browser) |                                                                                |
+| ❌         | Wasm                 |                                                                                |
+
+
+## Installation
+
+```kotlin
+implementation("dev.openfeature.kotlin.contrib.providers:ofrep:0.1.0")
+```
+
+## Usage
+
+To use the `OfrepProvider` create an instance and use it as a provider:
+
+```kotlin
+val options = OfrepOptions(endpoint="https://localhost:8080")
+val provider = OfrepProvider(options)
+OpenFeatureAPI.setProviderAndWait(provider)
+```

providers/ofrep/README.md

@@ -0,0 +1,42 @@
+public final class dev/openfeature/kotlin/contrib/providers/ofrep/OfrepProvider : dev/openfeature/kotlin/sdk/FeatureProvider {
+	public fun <init> (Ldev/openfeature/kotlin/contrib/providers/ofrep/bean/OfrepOptions;)V
+	public fun getBooleanEvaluation (Ljava/lang/String;ZLdev/openfeature/kotlin/sdk/EvaluationContext;)Ldev/openfeature/kotlin/sdk/ProviderEvaluation;
+	public fun getDoubleEvaluation (Ljava/lang/String;DLdev/openfeature/kotlin/sdk/EvaluationContext;)Ldev/openfeature/kotlin/sdk/ProviderEvaluation;
+	public fun getHooks ()Ljava/util/List;
+	public fun getIntegerEvaluation (Ljava/lang/String;ILdev/openfeature/kotlin/sdk/EvaluationContext;)Ldev/openfeature/kotlin/sdk/ProviderEvaluation;
+	public fun getMetadata ()Ldev/openfeature/kotlin/sdk/ProviderMetadata;
+	public fun getObjectEvaluation (Ljava/lang/String;Ldev/openfeature/kotlin/sdk/Value;Ldev/openfeature/kotlin/sdk/EvaluationContext;)Ldev/openfeature/kotlin/sdk/ProviderEvaluation;
+	public fun getStringEvaluation (Ljava/lang/String;Ljava/lang/String;Ldev/openfeature/kotlin/sdk/EvaluationContext;)Ldev/openfeature/kotlin/sdk/ProviderEvaluation;
+	public fun initialize (Ldev/openfeature/kotlin/sdk/EvaluationContext;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
+	public fun observe ()Lkotlinx/coroutines/flow/Flow;
+	public fun onContextSet (Ldev/openfeature/kotlin/sdk/EvaluationContext;Ldev/openfeature/kotlin/sdk/EvaluationContext;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
+	public fun shutdown ()V
+	public fun track (Ljava/lang/String;Ldev/openfeature/kotlin/sdk/EvaluationContext;Ldev/openfeature/kotlin/sdk/TrackingEventDetails;)V
+}
+
+public final class dev/openfeature/kotlin/contrib/providers/ofrep/bean/OfrepOptions {
+	public synthetic fun <init> (Ljava/lang/String;JIJLjava/util/Map;JLio/ktor/client/engine/HttpClientEngine;Lkotlinx/coroutines/CoroutineDispatcher;ILkotlin/jvm/internal/DefaultConstructorMarker;)V
+	public synthetic fun <init> (Ljava/lang/String;JIJLjava/util/Map;JLio/ktor/client/engine/HttpClientEngine;Lkotlinx/coroutines/CoroutineDispatcher;Lkotlin/jvm/internal/DefaultConstructorMarker;)V
+	public final fun component1 ()Ljava/lang/String;
+	public final fun component2-UwyO8pc ()J
+	public final fun component3 ()I
+	public final fun component4-UwyO8pc ()J
+	public final fun component5 ()Ljava/util/Map;
+	public final fun component6-UwyO8pc ()J
+	public final fun component7 ()Lio/ktor/client/engine/HttpClientEngine;
+	public final fun component8 ()Lkotlinx/coroutines/CoroutineDispatcher;
+	public final fun copy-Sx1y28s (Ljava/lang/String;JIJLjava/util/Map;JLio/ktor/client/engine/HttpClientEngine;Lkotlinx/coroutines/CoroutineDispatcher;)Ldev/openfeature/kotlin/contrib/providers/ofrep/bean/OfrepOptions;
+	public static synthetic fun copy-Sx1y28s$default (Ldev/openfeature/kotlin/contrib/providers/ofrep/bean/OfrepOptions;Ljava/lang/String;JIJLjava/util/Map;JLio/ktor/client/engine/HttpClientEngine;Lkotlinx/coroutines/CoroutineDispatcher;ILjava/lang/Object;)Ldev/openfeature/kotlin/contrib/providers/ofrep/bean/OfrepOptions;
+	public fun equals (Ljava/lang/Object;)Z
+	public final fun getEndpoint ()Ljava/lang/String;
+	public final fun getHeaders ()Ljava/util/Map;
+	public final fun getHttpClientEngine ()Lio/ktor/client/engine/HttpClientEngine;
+	public final fun getKeepAliveDuration-UwyO8pc ()J
+	public final fun getMaxIdleConnections ()I
+	public final fun getPollingDispatcher ()Lkotlinx/coroutines/CoroutineDispatcher;
+	public final fun getPollingInterval-UwyO8pc ()J
+	public final fun getTimeout-UwyO8pc ()J
+	public fun hashCode ()I
+	public fun toString ()Ljava/lang/String;
+}
+

providers/ofrep/api/android/ofrep.api

@@ -0,0 +1,42 @@
+public final class dev/openfeature/kotlin/contrib/providers/ofrep/OfrepProvider : dev/openfeature/kotlin/sdk/FeatureProvider {
+	public fun <init> (Ldev/openfeature/kotlin/contrib/providers/ofrep/bean/OfrepOptions;)V
+	public fun getBooleanEvaluation (Ljava/lang/String;ZLdev/openfeature/kotlin/sdk/EvaluationContext;)Ldev/openfeature/kotlin/sdk/ProviderEvaluation;
+	public fun getDoubleEvaluation (Ljava/lang/String;DLdev/openfeature/kotlin/sdk/EvaluationContext;)Ldev/openfeature/kotlin/sdk/ProviderEvaluation;
+	public fun getHooks ()Ljava/util/List;
+	public fun getIntegerEvaluation (Ljava/lang/String;ILdev/openfeature/kotlin/sdk/EvaluationContext;)Ldev/openfeature/kotlin/sdk/ProviderEvaluation;
+	public fun getMetadata ()Ldev/openfeature/kotlin/sdk/ProviderMetadata;
+	public fun getObjectEvaluation (Ljava/lang/String;Ldev/openfeature/kotlin/sdk/Value;Ldev/openfeature/kotlin/sdk/EvaluationContext;)Ldev/openfeature/kotlin/sdk/ProviderEvaluation;
+	public fun getStringEvaluation (Ljava/lang/String;Ljava/lang/String;Ldev/openfeature/kotlin/sdk/EvaluationContext;)Ldev/openfeature/kotlin/sdk/ProviderEvaluation;
+	public fun initialize (Ldev/openfeature/kotlin/sdk/EvaluationContext;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
+	public fun observe ()Lkotlinx/coroutines/flow/Flow;
+	public fun onContextSet (Ldev/openfeature/kotlin/sdk/EvaluationContext;Ldev/openfeature/kotlin/sdk/EvaluationContext;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
+	public fun shutdown ()V
+	public fun track (Ljava/lang/String;Ldev/openfeature/kotlin/sdk/EvaluationContext;Ldev/openfeature/kotlin/sdk/TrackingEventDetails;)V
+}
+
+public final class dev/openfeature/kotlin/contrib/providers/ofrep/bean/OfrepOptions {
+	public synthetic fun <init> (Ljava/lang/String;JIJLjava/util/Map;JLio/ktor/client/engine/HttpClientEngine;Lkotlinx/coroutines/CoroutineDispatcher;ILkotlin/jvm/internal/DefaultConstructorMarker;)V
+	public synthetic fun <init> (Ljava/lang/String;JIJLjava/util/Map;JLio/ktor/client/engine/HttpClientEngine;Lkotlinx/coroutines/CoroutineDispatcher;Lkotlin/jvm/internal/DefaultConstructorMarker;)V
+	public final fun component1 ()Ljava/lang/String;
+	public final fun component2-UwyO8pc ()J
+	public final fun component3 ()I
+	public final fun component4-UwyO8pc ()J
+	public final fun component5 ()Ljava/util/Map;
+	public final fun component6-UwyO8pc ()J
+	public final fun component7 ()Lio/ktor/client/engine/HttpClientEngine;
+	public final fun component8 ()Lkotlinx/coroutines/CoroutineDispatcher;
+	public final fun copy-Sx1y28s (Ljava/lang/String;JIJLjava/util/Map;JLio/ktor/client/engine/HttpClientEngine;Lkotlinx/coroutines/CoroutineDispatcher;)Ldev/openfeature/kotlin/contrib/providers/ofrep/bean/OfrepOptions;
+	public static synthetic fun copy-Sx1y28s$default (Ldev/openfeature/kotlin/contrib/providers/ofrep/bean/OfrepOptions;Ljava/lang/String;JIJLjava/util/Map;JLio/ktor/client/engine/HttpClientEngine;Lkotlinx/coroutines/CoroutineDispatcher;ILjava/lang/Object;)Ldev/openfeature/kotlin/contrib/providers/ofrep/bean/OfrepOptions;
+	public fun equals (Ljava/lang/Object;)Z
+	public final fun getEndpoint ()Ljava/lang/String;
+	public final fun getHeaders ()Ljava/util/Map;
+	public final fun getHttpClientEngine ()Lio/ktor/client/engine/HttpClientEngine;
+	public final fun getKeepAliveDuration-UwyO8pc ()J
+	public final fun getMaxIdleConnections ()I
+	public final fun getPollingDispatcher ()Lkotlinx/coroutines/CoroutineDispatcher;
+	public final fun getPollingInterval-UwyO8pc ()J
+	public final fun getTimeout-UwyO8pc ()J
+	public fun hashCode ()I
+	public fun toString ()Ljava/lang/String;
+}
+

providers/ofrep/api/jvm/ofrep.api

@@ -0,0 +1,107 @@
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+import org.jetbrains.kotlin.gradle.tasks.KotlinTest
+
+plugins {
+    id("com.android.library")
+    id("dev.openfeature.provider-conventions")
+    alias(libs.plugins.kotlinx.serialization)
+    // Needed for the JS coroutine support for the tests
+    alias(libs.plugins.kotlinx.atomicfu)
+    alias(libs.plugins.docker.compose)
+}
+
+kotlin {
+    androidTarget()
+    jvm {
+        compilations.all {
+            compileTaskProvider.configure {
+                compilerOptions {
+                    jvmTarget.set(JvmTarget.JVM_11)
+                }
+            }
+        }
+    }
+    linuxX64 {}
+    js {
+        nodejs {}
+        browser {
+            testTask {
+                useKarma {
+                    useChromeHeadless()
+                }
+            }
+        }
+    }
+
+    sourceSets {
+        val commonMain by getting {
+            dependencies {
+                api(libs.openfeature.kotlin.sdk)
+
+                api(libs.kotlinx.coroutines.core)
+                api(libs.ktor.core)
+                implementation(libs.ktor.client.content.negotiation)
+                implementation(libs.ktor.serialization.kotlinx.json)
+            }
+        }
+        commonTest.dependencies {
+            implementation(libs.kotlin.test)
+            implementation(libs.kotlinx.coroutines.test)
+            implementation(libs.ktor.client.mock)
+        }
+        val nonJsMain by creating {
+            dependsOn(commonMain)
+            dependencies {
+                implementation(libs.ktor.cio)
+            }
+        }
+        androidMain.get().dependsOn(nonJsMain)
+        jvmMain.get().dependsOn(nonJsMain)
+        linuxX64Main.get().dependsOn(nonJsMain)
+
+        jsMain.dependencies {
+            implementation(libs.ktor.js)
+        }
+    }
+}
+
+android {
+    namespace = "dev.openfeature.kotlin.contrib.providers.ofrep"
+    compileSdk = 35
+
+    defaultConfig {
+        minSdk = 21
+    }
+
+    compileOptions {
+        sourceCompatibility = JavaVersion.VERSION_11
+        targetCompatibility = JavaVersion.VERSION_11
+    }
+
+    publishing {
+        singleVariant("release") {
+            withJavadocJar()
+            withSourcesJar()
+        }
+    }
+
+    testOptions {
+        unitTests {
+            isIncludeAndroidResources = true
+        }
+    }
+}
+
+// Launch test container for IntegrationTest.kt
+dockerCompose {
+    useComposeFiles = listOf("src/integrationTest/docker-compose.yaml")
+}
+// Note: some Kotlin test targets extend the Test (e.g. JVM), some others the KotlinTest class (e.g. Native, JS)
+tasks.withType(Test::class) {
+    dependsOn(tasks.named("composeUp"))
+    finalizedBy(tasks.named("composeDown"))
+}
+tasks.withType(KotlinTest::class) {
+    dependsOn(tasks.named("composeUp"))
+    finalizedBy(tasks.named("composeDown"))
+}

providers/ofrep/build.gradle.kts

@@ -0,0 +1,2 @@
+# Disable the default source set hierarchy to allow creating the nonJsMain source set
+kotlin.mpp.applyDefaultHierarchyTemplate=false