Akka flow for multiple http requests - scala

Question

In a project of mine I have an akka actor for sending post requests to my google fcm server. The actor takes a list of ids and should make as many requests as there are in the list. I print out the response from the server in runForeach(println(_)) but I only get one printout for a whole list of ids. Why does this happen?
class FCMActor(val key: String) extends Actor{
import fcm.FCMActor._
import akka.pattern.pipe
import context.dispatcher
private implicit def system: ActorSystem = ActorSystem()
final implicit val materializer: ActorMaterializer = ActorMaterializer(ActorMaterializerSettings(context.system))
def buildBody(id: Option[String]): String = {
Json.obj(
"to" -> id,
"priority" -> "high",
"data" -> Json.obj("message" -> "Firebase Clud Message"),
"time_to_live" -> 60
).toString()
}
def buildHttpRequest(body: String): HttpRequest = {
HttpRequest(method = HttpMethods.POST,
uri = s"/fcm/send",
entity = HttpEntity(MediaTypes.`application/json`, body),
headers = List(RawHeader("Authorization", s"key=$key")))
}
val connectionFlow: Flow[HttpRequest, HttpResponse, Future[Http.OutgoingConnection]] = {
Http().outgoingConnection("fcm.googleapis.com")
}
def send(ids: List[Option[String]]) = {
val httpRequests: List[HttpRequest] = ids.map(buildBody).map(buildHttpRequest)
println(httpRequests)
Source(httpRequests).via(connectionFlow).runForeach(println(_)) // << here I only get one println
}
override def receive: Receive = {
case SendToIds(ids: List[Option[String]]) =>
send(ids)
}
}

Answer 1

You are not consuming the response entity that the server sends you. To understand why this is important, check out the related docs page.
A quick code change to try and fix this is:
... .runForeach{ response =>
response.discardEntityBytes()
println(response)
}
Or, if you're actually interested in the entity, something along the lines of
... .runForeach{ _.entity.dataBytes
.runFold(ByteString.empty) { case (acc, b) => acc ++ b }
.map(println(_))
}