Scala and Akka HTTP: Request inside a request & issue with threads

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I am new to learning Scala, Akka Streams and Akka HTTP, so apologies beforehand if the question is too basic.

I want to do an HTTP request inside an HTTP request, just like in the following piece of code:

  implicit val system = ActorSystem("ActorSystem")
  implicit val materializer = ActorMaterializer
  import system.dispatcher

  val requestHandler: Flow[HttpRequest, HttpResponse, _] = Flow[HttpRequest].map {
    case HttpRequest(HttpMethods.GET, Uri.Path("/api"), _, _, _) =>
      val responseFuture = Http().singleRequest(HttpRequest(uri = "http://www.google.com"))
      responseFuture.onComplete {
        case Success(response) =>
          response.discardEntityBytes()
          println(s"The request was successful")
        case Failure(ex) =>
          println(s"The request failed with: $ex")
      }
      //Await.result(responseFuture, 10 seconds)
      println("Reached HttpResponse")
      HttpResponse(
        StatusCodes.OK
      )
  }

  Http().bindAndHandle(requestHandler, "localhost", 8080)

But in the above case the result looks like this, meaning that Reached HttpResponse is reached first before completing the request:

Reached HttpResponse
The request was successful

I tried using Await.result(responseFuture, 10 seconds) (currently commented out) but it made no difference.

What am I missing here? Any help will be greatly appreciated!

Many thanks in advance!

akka-stream akka-http httprequest httpresponse scala
1 Answers

map is a function that takes request and produces a response:

HttpRequest => HttpResponse

The challenge is that response is a type of Future. Therefore, you need a function that deals with it. The function that takes HttpRequest and returns Future of HttpResponse.

HttpRequest => Future[HttpResponse]

And voila, mapAsync is exactly what you need:

val requestHandler: Flow[HttpRequest, HttpResponse, _] = Flow[HttpRequest].mapAsync(2) {
  case HttpRequest(HttpMethods.GET, Uri.Path("/api"), _, _, _) =>
    Http().singleRequest(HttpRequest(uri = "http://www.google.com")).map (resp => {
      resp.discardEntityBytes()
      println(s"The request was successful")
      HttpResponse(StatusCodes.OK)
    })
}
user_13247090
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