(Non-compiling) example for "ToResponseMarshaller application problem ( https://groups.google.com/forum/#!topic/spray-user/05SxKaBDU6s ) thread on spray-user mailing list.

Ping.scala

package example

import akka.actor._
import akka.actor.ActorDSL._
import akka.io.IO
import akka.pattern.ask
import akka.util.Timeout
import scala.concurrent.duration._
import spray.can.Http
import spray.http.StatusCodes
import spray.httpx.SprayJsonSupport._
import spray.routing.HttpServiceActor
import spray.json._
import spray.routing._
import spray.http._
import DefaultJsonProtocol._

case class Pong(ping: String)

object Ping extends App {

  implicit val system = ActorSystem("demo")

  val model = actor(new Act {
    become {
      case req: String => sender ! Pong(req)
    }
  })

  val service = system.actorOf(Props(new Service(model)))

  IO(Http) ! Http.Bind(service, interface = "localhost", port = 8080)
}

class Service(model: ActorRef) extends HttpServiceActor {
  import context.dispatcher

  implicit val resFmt = jsonFormat1(Pong)
  implicit val timeout = Timeout(1.second)

  def receive = runRoute(
    path(Segment) { segment =>
      get {
        complete {
          (model ? segment).map {
            case Pong(x) if x == "bad" => StatusCodes.Conflict -> Pong("BAD REQUEST")
            case r @ Pong(_) => StatusCodes.OK -> r
          }
        }
      }
    })
}