http4k is a lightweight but fully-featured HTTP toolkit written in pure Kotlin that enables the serving and consuming of HTTP services in a functional and consistent way. http4k applications are just Kotlin functions. For example, here's a simple echo server:

val app: HttpHandler = { request: Request -> Response(OK).body(request.body) }
val server = app.asServer(SunHttp(8000)).start()

You can read about the rationale and ethos of http4k here

The http4k platform consists of the following main ecosystems, all released under a single version:

• http4k-core consists of a lightweight core library providing a base HTTP implementation and Server/Client implementations based on the JDK classes. Further servers, clients, serverless, templating, websockets capabilities are then implemented in add-on modules. http4k apps can be simply mounted into a running Server, Serverless platform, or compiled to GraalVM and run as a super-lightweight binary.
• http4k-connect is a lightweight API Client toolkit which includes libraries for connecting to popular third-party cloud services and AI backends using http4k compatible APIs, along with Fake implementations for usage during local testing.

You can find out all about the project on the http4k site.

dependencies {
    // install the platform...
    implementation(platform("org.http4k:http4k-bom:<LATEST_VERSION>"))

    // ...then choose any moduless but at least the core
    implementation("org.http4k:http4k-core")
}

• Dan Bodart's utterlyidle
• Ivan Moore for pairing on the original hackday project - Barely Magical.
• You can see the amazing people and companies who have helped us to make http4k here.