Akka-http process requests with Stream - scala

Question

I try write some simple akka-http and akka-streams based application, that handle http requests, always with one precompiled stream, because I plan to use long time processing with back-pressure in my requestProcessor stream
My application code:
import akka.actor.{ActorSystem, Props}
import akka.http.scaladsl._
import akka.http.scaladsl.server.Directives._
import akka.http.scaladsl.server._
import akka.stream.ActorFlowMaterializer
import akka.stream.actor.ActorPublisher
import akka.stream.scaladsl.{Sink, Source}
import scala.annotation.tailrec
import scala.concurrent.Future
object UserRegisterSource {
def props: Props = Props[UserRegisterSource]
final case class RegisterUser(username: String)
}
class UserRegisterSource extends ActorPublisher[UserRegisterSource.RegisterUser] {
import UserRegisterSource._
import akka.stream.actor.ActorPublisherMessage._
val MaxBufferSize = 100
var buf = Vector.empty[RegisterUser]
override def receive: Receive = {
case request: RegisterUser =>
if (buf.isEmpty && totalDemand > 0)
onNext(request)
else {
buf :+= request
deliverBuf()
}
case Request(_) =>
deliverBuf()
case Cancel =>
context.stop(self)
}
#tailrec final def deliverBuf(): Unit =
if (totalDemand > 0) {
if (totalDemand <= Int.MaxValue) {
val (use, keep) = buf.splitAt(totalDemand.toInt)
buf = keep
use foreach onNext
} else {
val (use, keep) = buf.splitAt(Int.MaxValue)
buf = keep
use foreach onNext
deliverBuf()
}
}
}
object Main extends App {
val host = "127.0.0.1"
val port = 8094
implicit val system = ActorSystem("my-testing-system")
implicit val fm = ActorFlowMaterializer()
implicit val executionContext = system.dispatcher
val serverSource: Source[Http.IncomingConnection, Future[Http.ServerBinding]] = Http(system).bind(interface = host, port = port)
val mySource = Source.actorPublisher[UserRegisterSource.RegisterUser](UserRegisterSource.props)
val requestProcessor = mySource
.mapAsync(1)(fakeSaveUserAndReturnCreatedUserId)
.to(Sink.head[Int])
.run()
val route: Route =
get {
path("test") {
parameter('test) { case t: String =>
requestProcessor ! UserRegisterSource.RegisterUser(t)
???
}
}
}
def fakeSaveUserAndReturnCreatedUserId(param: UserRegisterSource.RegisterUser): Future[Int] =
Future.successful {
1
}
serverSource.to(Sink.foreach {
connection =>
connection handleWith Route.handlerFlow(route)
}).run()
}
I found solution about how create Source that can dynamically accept new items to process, but I can found any solution about how than obtain result of stream execution in my route

Answer 1

The direct answer to your question is to materialize a new Stream for each HttpRequest and use Sink.head to get the value you're looking for. Modifying your code:
val requestStream =
mySource.map(fakeSaveUserAndReturnCreatedUserId)
.to(Sink.head[Int])
//.run() - don't materialize here
val route: Route =
get {
path("test") {
parameter('test) { case t: String =>
//materialize a new Stream here
val userIdFut : Future[Int] = requestStream.run()
requestProcessor ! UserRegisterSource.RegisterUser(t)
//get the result of the Stream
userIdFut onSuccess { case userId : Int => ...}
}
}
}
However, I think your question is ill posed. In your code example the only thing you're using an akka Stream for is to create a new UserId. Futures readily solve this problem without the need for a materialized Stream (and all the accompanying overhead):
val route: Route =
get {
path("test") {
parameter('test) { case t: String =>
val user = RegisterUser(t)
fakeSaveUserAndReturnCreatedUserId(user) onSuccess { case userId : Int =>
...
}
}
}
}
If you want to limit the number of concurrent calls to fakeSaveUserAndReturnCreateUserId then you can create an ExecutionContext with a defined ThreadPool size, as explained in the answer to this question, and use that ExecutionContext to create the Futures:
val ThreadCount = 10 //concurrent queries
val limitedExecutionContext =
ExecutionContext.fromExecutor(Executors.newFixedThreadPool(ThreadCount))
def fakeSaveUserAndReturnCreatedUserId(param: UserRegisterSource.RegisterUser): Future[Int] =
Future { 1 }(limitedExecutionContext)