Hi Magnus,
the error message is telling you that the `concat` strategy can only flatten
Sources, not Flows. The `map` combinator in your example just emits Flows but
does not connect them to the input that you want to pipe through them; in the
generic, dynamic sense we do not support this currently, you could use groupBy
to achieve this effect. But your use-case is more static anyway, it should be a
perfect fit for using the FlexiRoute
<http://doc.akka.io/api/akka-stream-and-http-experimental/1.0-M1/index.html#akka.stream.scaladsl.FlexiRoute>
junction (see this test suite
<https://github.com/akka/akka/blob/akka-stream-and-http-experimental-1.0-M1/akka-stream-tests/src/test/scala/akka/stream/scaladsl/GraphFlexiRouteSpec.scala>
for inspiration).
Regards,
Roland
> 6 dec 2014 kl. 16:23 skrev Magnus Andersson <magnus.anders...@mollyware.se>:
>
> Hi
>
> I have a flow that I want to conditionally branch off to either one of two
> other flows. Basically I'm looking to "flatMap that shit", but how do I do
> this in the context of Akka streams?
>
> In my current attempt the types will not line up in the flatten step, I get
> the compile error:
>
> polymorphic expression cannot be instantiated to expected type;
> [error] found :
> [T]akka.stream.FlattenStrategy[akka.stream.scaladsl.Source[T],T]
> [error] required:
> akka.stream.FlattenStrategy[akka.stream.scaladsl.Flow[akka.http.model.HttpRequest,akka.http.model.HttpResponse],?]
> [error] }.flatten( FlattenStrategy.concat )
> Relevant code:
>
> val serverBinding = Http( systemRef ).
> bind(
> interface = interface,
> port = port )
>
> val con: OutgoingConnection = Http( systemRef ).outgoingConnection( "akka.io"
> )
>
> val badRequestFlow: Flow[HttpRequest, HttpResponse] =
> Flow[HttpRequest].map( _ ⇒ HttpResponse( BadRequest, entity = "Bad Request"
> ) )
>
> val proxy: Flow[HttpRequest, HttpResponse] = con.flow.concat( Source( () ⇒
> List( HttpRequest( GET, uri = "/" ) ).iterator ) )
>
> val proxyRequest: Flow[HttpRequest, HttpResponse] =
> Flow[HttpRequest].map {
> case HttpRequest( POST, Uri.Path( "/proxy" ), _, _, _ ) ⇒ proxy
> case other ⇒ badRequestFlow
> }.flatten( FlattenStrategy.concat )
> Any hints or examples warmly welcome!
> I'm also wondering about supervision of flows (for error handling) but I will
> put that in a separate post.
>
> /Magnus
>
>
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--
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>>>>>>>>>> Check the FAQ:
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