trait LoggerAPI {
  def log(message: String): Unit
}

case class Foo(id: String)

trait FooRepositoryAPI {
  def add(foo: Foo): Future[Unit]
  def remove(foo: Foo): Future[Unit]
  def getAll(): Future[Set[Foo]]
}

class LoggerAPIImpl extends LoggerAPI {
  override def log(message: String): Unit = println(message)
}

class FooRepositoryAPIImpl extends FooRepositoryAPI {
  var foos: Set[Foo] = Set()

  override def add(foo: Foo): Future[Unit] = this.synchronized {
    foos = foos + foo
    Future() // Acknowledge
  }

  override def remove(foo: Foo): Future[Unit] = this.synchronized {
    foos = foos - foo
    Future() // Acknowledge
  }

  override def getAll(): Future[Set[Foo]] = Future {
    foos
  }
}

val jsonSerializer = // ...
val server = JSONRPCServer(jsonSerializer)
server.bindAPI[LoggerAPI](new LoggerAPIImpl)
server.bindAPI[FooRepositoryAPI](new FooRepositoryAPIImpl)

def onRequestJSONReceived(requestJSON: String): Unit = {
  server.receive(requestJSON).onComplete {
    case Success(Some(responseJSON: String)) => sendResponseJSONToClient(responseJSON)
    case _ =>
  }
}

val jsonSerializer = // ...
val jsonSender = // ...
val client = JSONRPCClient(jsonSerializer, jsonSender)

val loggerAPI = client.createAPI[LoggerAPI]
val fooRepositoryAPI = client.createAPI[FooRepositoryAPI]

loggerAPI.log("Hello, World!")

fooRepositoryAPI.add(Foo("A"))
fooRepositoryAPI.add(Foo("B"))

fooRepositoryAPI.remove(Foo("A"))

fooRepositoryAPI.getAll().onComplete {
  case Success(foos: Set[Foo]) => println(s"Received all the foos: $foos")
  case _ =>
}

def onResponseJSONReceived(responseJSON: String): Unit = {
  client.receive(responseJSON)
}