Introduction

MediatorK is a coroutine-first Mediator library for Kotlin and Kotlin Multiplatform.

It implements the CQRS and Vertical Slice patterns:

• Every request is routed to exactly one handler
• Every notification fans out to many handlers
• A pipeline of behaviors sits in between (logging, caching, timeout, validation…)

No kotlin-reflect. No annotation processing. No framework required.

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Why MediatorK?

Feature	Description
⚡ Coroutine-native	suspend all the way down — no callbacks, no blocking
🧩 KMP ready	Works on JVM, Android, iOS, Linux, Windows, WASM, and more from one codebase
🌊 Streaming	StreamRequest<T> returns a cold Flow<T> — lazy, incremental, cancellable
🔌 Framework-agnostic	Works with Spring Boot, Ktor, KMP, or plain Kotlin
🪶 Zero magic	No kotlin-reflect, no code generation, no annotation processors
🛡️ Built-in validation	Lightweight RequestValidator DSL with rules { } and rulesFailFast { } — no annotation processing
🔧 Batteries included	6 built-in pipeline behaviors: caching, logging, timeout, timing, error tracking, and more
🧪 Testable by design	buildHandlerTestHarness, FakeMediator, MediatorSpy — no mocking library needed

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Quick Example

// 1. Define a request
data class GetUserQuery(val id: String) : Request<User>

// 2. Implement a handler
class GetUserHandler(private val db: UserRepository) : RequestHandler<GetUserQuery, User> {
    override suspend fun handle(
        mediator: Mediator,
        requestContext: RequestContext,
        request: GetUserQuery
    ): User = db.findById(request.id) ?: error("User not found")
}

// 3. Wire it up
val mediator = MediatorFactory.create(
    registrars = listOf(object : MediatorRegistrar {
        override fun register(registry: HandlerRegistry) {
            registry register GetUserHandler(db)
        }
    })
)

// 4. Use it
val user = mediator.send(GetUserQuery("user-1"))

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Supported Targets

Platform	Targets
JVM	jvm
Android	androidTarget · androidNativeArm32 · androidNativeArm64 · androidNativeX64 · androidNativeX86
iOS	iosArm64 · iosSimulatorArm64 · iosX64
macOS	macosArm64 · macosX64
tvOS	tvosArm64 · tvosSimulatorArm64 · tvosX64
watchOS	watchosArm32 · watchosArm64 · watchosDeviceArm64 · watchosSimulatorArm64 · watchosX64
Linux	linuxArm64 · linuxX64
Windows	mingwX64
Web / Wasm	js · wasmJs · wasmWasi

Ready to start? See the promise MediatorK makes →