Hi guys!
How do you throttle Flow in the latest Akka (2.4.6) ? I'd like to throttle
Http client flow to limit number of requests to 3 requests per second. I
found following example online but it's for old Akka and akka-streams ApI
changed so much that I can't figure out how to rewrite it.
def throttled[T](rate: FiniteDuration): Flow[T, T] = {
val tickSource: Source[Unit] = TickSource(rate, rate, () => ())
val zip = Zip[T, Unit]
val in = UndefinedSource[T]
val out = UndefinedSink[T]
PartialFlowGraph { implicit builder =>
import FlowGraphImplicits._
in ~> zip.left ~> Flow[(T, Unit)].map { case (t, _) => t } ~> out
tickSource ~> zip.right
}.toFlow(in, out)}
here is my best attempt so far
def throttleFlow[T](rate: FiniteDuration) = Flow.fromGraph(GraphDSL.create() {
implicit builder =>
import GraphDSL.Implicits._
val ticker = Source.tick(rate, rate, Unit)
val zip = builder.add(Zip[T, Unit.type])
val map = Flow[(T, Unit.type)].map { case (value, _) => value }
val messageExtractor = builder.add(map)
val in = Inlet[T]("Req.in")
val out = Outlet[T]("Req.out")
out ~> zip.in0
ticker ~> zip.in1
zip.out ~> messageExtractor.in
FlowShape.of(in, messageExtractor.out)})
it throws exception in my main flow though :) It looks like this
private val queueHttp = Source.queue[(HttpRequest, (Any,
Promise[(Try[HttpResponse], Any)]))](1000, OverflowStrategy.backpressure)
.via(throttleFlow(rate))
.via(poolClientFlow)
.mapAsync(4) {
case (util.Success(resp), any) =>
val strictFut = resp.entity.toStrict(5 seconds)
strictFut.map(ent => (util.Success(resp.copy(entity = ent)), any))
case other =>
Future.successful(other)
}
.toMat(Sink.foreach({
case (triedResp, (value: Any, p: Promise[(Try[HttpResponse], Any)])) =>
p.success(triedResp -> value)
case _ =>
throw new RuntimeException()
}))(Keep.left)
.run
where poolClientFlow is
Http()(system).cachedHostConnectionPool[Any](baseDomain)
Exception is:
Caused by: java.lang.IllegalArgumentException: requirement failed: The output
port [Req.out] is not part of the underlying graph.
at scala.Predef$.require(Predef.scala:219)
at akka.stream.impl.StreamLayout$Module$class.wire(StreamLayout.scala:204)
It's totally confusing to me. How do I get connected inlet and outlet ? I
thought Akka is supposed to connect them when I use my flow in .via() call.
Thanks!
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