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

Question

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!

Answer 1

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)
})
}