Basic akka http client post not working - scala

Question

I am trying to make a basic http client posting some data to a REST API with Akka HTTP but I cannot make the following code work :
def sendData(e : GenericEvent): Future[Either[(String,StatusCode),(GenericEvent,StatusCode)]] = {
val request = Marshal(e).to[RequestEntity]
val responseFuture: Future[HttpResponse] = request map { req =>
Source.single(HttpRequest(method = HttpMethods.POST, uri = s"/data-ingest", headers = List(auth), entity = req))
.via(dataIngestFlow)
.runWith(Sink.head)
}
responseFuture.flatMap { response =>
response.status match {
case OK => Unmarshal(response.entity).to[GenericEvent].map(Right(_, response.status))
case BadRequest => Future.successful(Left(s"$e.data: incorrect data", response.status))
case _ => Unmarshal(response.entity).to[String].flatMap { entity =>
val error = s"generic event ingest failed with status code ${response.status} and entity $entity"
logger.error(error)
Future.failed(new IOException(error))
}
}
}
I got the following error
polymorphic expression cannot be instantiated to expected type;
[error] found :
[T]akka.stream.scaladsl.Sink[T,scala.concurrent.Future[T]]
[error] required:
akka.stream.Graph[akka.stream.SinkShape[akka.http.scaladsl.model.HttpResponse],akka.http.scaladsl.model.HttpResponse]
[error] .runWith(Sink.head)
Here is the code for the dataIngestFlow
val dataIngestFlow = Http().outgoingConnection(config.endpointUrl,config.endpointPort)
Here is the code on server side :
val routes = {
logRequestResult("akka-http-microservice") {
path("event-ingest") {
post {
entity(as[GenericEvent]) { eventIngest =>
log.info(s"Ingesting {} and publishing event to Kafka topic {}.", eventIngest.eventType,config.kafkaTopic)
kafka ! eventIngest
complete {
eventIngest
}
}~
entity(as[List[GenericEvent]]) { eventIngestList =>
eventIngestList.foreach{ eventIngest=>
log.info(s"Ingesting {} and publishing event List to Kafka topic {}.", eventIngest.eventType,config.kafkaTopic)
kafka ! eventIngest
}
complete {
eventIngestList
}
}
}
}
}
}
I tried another simple client, it builds well but the ingestion stop after 160 events, the server doesn't receive anymore events.

Answer 1

The first problem I see with your example is that RequestEntity does not have a map function. Therefore, the following line
val responseFuture: Future[HttpResponse] = request map { ...
should not compile.
Further, if request is actually a Future (which I infer from the map) then responseFuture is actually of type Future[Future[HttpResponse]] because the stream materializes into its own Future. To solve this problem you can use Future.flatMap instead of map. Namely:
val responseFuture: Future[HttpResponse] = request flatMap { req =>
This is the monadic bind operation within Futures.