Sample streaming response with akka http

numbers-as-a-service.scala

import akka.actor.ActorSystem
import akka.http.scaladsl.Http
import akka.http.scaladsl.marshalling.{Marshaller, ToResponseMarshaller}
import akka.http.scaladsl.model.HttpEntity.ChunkStreamPart
import akka.http.scaladsl.model.{HttpEntity, HttpResponse, MediaTypes}
import akka.http.scaladsl.server.Directives._
import akka.stream.ActorMaterializer
import akka.stream.scaladsl.Source


object StreamNumbers extends App {
  implicit val system = ActorSystem("my-system")
  implicit val materializer = ActorMaterializer()

  implicit val toResponseMarshaller: ToResponseMarshaller[Source[Int, Any]] =
    Marshaller.opaque { items =>
      val data = items.map(item => ChunkStreamPart(item.toString + "\n"))
      HttpResponse(entity = HttpEntity.Chunked(MediaTypes.`text/plain`, data))
    }

  def newDataStream(): Stream[Int] = Stream.from(1)

  val route =
    path("numbers") {
      get {
        complete {
          Source(() => newDataStream().toIterator)
        }
      }
    }

  val bindingFuture = Http().bindAndHandle(route, "localhost", 8080)

  println(s"Server online at http://localhost:8080/\nPress RETURN to stop...")
  Console.readLine()

  import system.dispatcher // for the future transformations
  bindingFuture
    .flatMap(_.unbind()) // trigger unbinding from the port
    .onComplete(_ ⇒ system.shutdown()) // and shutdown when done

}