Scala spray-client define implicits for AKKA ActorRefFactory

Question

I'm trying to write a simple HTTP client using Scala and spray-client. I'm basing my client on the examples given on Spray docs.

My issue is that the example is creating a new implicit ActorSystem i.e.

implicit val system = ActorSystem()

but I want my client to be reusable and not create a new ActorSystem.

Here's the gist of my code.

trait WebClient {
  def get(url: String)(implicit system: ActorSystem): Future[String]
}

object SprayWebClient extends WebClient {
  val pipeline: HttpRequest => Future[HttpResponse] = sendReceive

  def get(url: String): Future[String] = {
    val r = pipeline (Get("http://some.url/"))
    r.map(_.entity.asString)
  }

}

But I am getting two compiler errors regarding implicits

implicit ActorRefFactory required: if outside of an Actor you need an implicit ActorSystem, inside of an actor this should be the implicit ActorContext WebClient.scala ...

and

not enough arguments for method sendReceive: (implicit refFactory: akka.actor.ActorRefFactory, implicit executionContext: scala.concurrent.ExecutionContext, implicit futureTimeout: akka.util.Timeout)spray.http.HttpRequest => scala.concurrent.Future[spray.http.HttpResponse]. Unspecified value parameters refFactory, executionContext.   WebClient.scala...

How should I change the API definitions?

Answer 1

Here's one solution:

import akka.actor.ActorSystem
import spray.http.{HttpRequest, HttpResponse}
import scala.concurrent.Future
import spray.client.pipelining._

trait WebClient {
  def get(url: String): Future[String]
}

class SprayWebClient(implicit system: ActorSystem) extends WebClient {
  import system.dispatcher

  val pipeline: HttpRequest => Future[HttpResponse] = sendReceive

  def get(url: String): Future[String] = {
    val r = pipeline (Get("http://some.url/"))
    r.map(_.entity.asString)
  }
}

and here's another that keeps the original WebClient.get signature:

import akka.actor.ActorSystem
import spray.http.{HttpRequest, HttpResponse}
import scala.concurrent.Future
import spray.client.pipelining._

trait WebClient {
  def get(url: String)(implicit system: ActorSystem): Future[String]
}

object SprayWebClient extends WebClient {
  def get(url: String)(implicit system: ActorSystem): Future[String] = {
    import system.dispatcher

    val pipeline: HttpRequest => Future[HttpResponse] = sendReceive
    val r = pipeline (Get("http://some.url/"))
    r.map(_.entity.asString)
  }
}

The second one is a bit more expensive because the pipeline is created anew every time even if it is theoretically static per ActorSystem. I would prefer the first solution and try to find a way to propagate the WebClient through your application (by using the cake pattern, by passing it around explicitly, or by using other dependency injection techniques).