storeAndRedirect.scala

import akka.actor.ActorSystem
import akka.http.scaladsl.Http
import akka.stream.ActorMaterializer
import java.io.PrintWriter

import akka.http.scaladsl.server.Directives._
import akka.http.scaladsl.model.{StatusCodes, HttpResponse, HttpRequest, HttpEntity}
import akka.http.scaladsl.model.headers.Location
import scala.concurrent.{Future, Await}
import scala.concurrent.duration._


implicit val system = ActorSystem()
implicit val materializer = ActorMaterializer()
implicit val executionContext = system.dispatcher

def storeAndRedirect(response: HttpResponse): HttpResponse = response
  .entity.contentLengthOption match {
    case Some(length) if length > 10 => HttpResponse(
      status = StatusCodes.PermanentRedirect,
      headers = Location("http://example.com") :: Nil,
      entity = HttpEntity.Empty
    )

    case _ => response
  }

val routes = mapResponse(storeAndRedirect)(get {
  complete("Hello World")
})

val binding: Future[Http.ServerBinding] =
  Http().bindAndHandle(routes, "127.0.0.1", 8080)

val madeRequest = Http()
  .singleRequest(HttpRequest(uri = "http://127.0.0.1:8080"))

val madeRequestResult = Await.result(madeRequest, 1.seconds)

println(madeRequestResult)

Await.result(binding, 1.seconds)
  .terminate(hardDeadline = 1.seconds)
  .flatMap { _ =>
    system.terminate()
  }