Need a simple example on how to consume a HTTP Service with Json unmarshalling

[Mo Batista]

I'm new to Akka-Http please bear with me.

What I'm trying to do is

1. Connect to a Restful service
2. Unmarshall the json payload into the following case class structure

case class ColorBlob(url: String, averageColor: String, classificationColor: String)
case class ColorBlobsResponse(colorBlobs: Map[String, Option[ColorBlob]])

In theory this should be simple, but it turns out that anything on this topic is either outdated or way over my head, as in this article
http://malaw.ski/2016/04/10/hakk-the-planet-implementing-akka-http-marshallers/.

http://doc.akka.io/docs/akka-http/10.0.1/scala/http/common/unmarshalling.html doesn't explain how to actually write an unmarshaller

This is where I got so far:

Issuing the request

val request = HttpRequest(method = HttpMethods.GET, uri = s"https://colorblobs.service.net/ws/colorblobs/en?productCodes=904655")

val future = Http().singleRequest(request)
val result: ColorBlobsResponse = Await.result(future.flatMap(Unmarshal(_).to[ColorBlobsResponse]), Duration.Inf)

Providing the  unmarshaller. This is also where I got stuck

object ColorBlobJsonProtocol extends DefaultJsonProtocol {
  implicit val colorBlobsUnmarshaller = new FromResponseUnmarshaller[ColorBlobsResponse] {
    implicit val colorBlobsFormat = jsonFormat1(ColorBlobsResponse)
    def apply(response: HttpResponse) = try {
      val entity: ResponseEntity = response.entity
??????

    }
  }
}

Now that I have ResponseEntity what would be the next step?

Maybe there is a blog article explaining what  jsonFormat1, DefaultJsonProtocol and FromResponseUnmarshaller actually do?

 I'm using akka-http 10.0.5 btw.


Thanks a lot!

[Konrad Malawski]

On 30 March 2017 at 14:28:34, Mo Batista (mouni...@gmail.com) wrote:

I'm new to Akka-Http please bear with me.

Hello Mo and welcome to Akka :-

What I'm trying to do is

1. Connect to a Restful service
2. Unmarshall the json payload into the following case class structure

It's as simple as these docs really: http://doc.akka.io/docs/akka-http/10.0.5/scala/http/common/unmarshalling.html#using-unmarshallers

So you just need: 

    implicit val colorBlobsFormat = jsonFormat1(ColorBlobsResponse) // this already provided all the needed marshallers

    // implicit materializer in Scope AFAIR too

    import system.dispatcher

Unmarshal(entity).to[ColorBlob]

In theory this should be simple, but it turns out that anything on this topic is either outdated or way over my head, as in this article
http://malaw.ski/2016/04/10/hakk-the-planet-implementing-akka-http-marshallers/

That's about writing custom unmarshallers which is rather advanced - you don't need to do that.

http://doc.akka.io/docs/akka-http/10.0.1/scala/http/common/unmarshalling.html doesn't explain how to actually write an unmarshaller

This is where I got so far:

Issuing the request

val request = HttpRequest(method = HttpMethods.GET, uri = s"https://colorblobs.service.net/ws/colorblobs/en?productCodes=904655")

val future = Http().singleRequest(request)
val result: ColorBlobsResponse = Await.result(future.flatMap(Unmarshal(_).to[ColorBlobsResponse]), Duration.Inf)

Small note here, I would strongly recommend never using Duration.Inf, even in sample code as you might get used to it and in general it simply is a very bad idea to block infinitely.

Put `import scala.concurrent.duration._` and `2.seconds` instead for example.

Providing the  unmarshaller. This is also where I got stuck

You don't need to do any of the manual Unmarshaller building, it's all ready once you did the jsonFormat call :)

Now that I have ResponseEntity what would be the next step?

No need to go so "manual" :-) Check the docs above.

Maybe there is a blog article explaining what  jsonFormat1, DefaultJsonProtocol and FromResponseUnmarshaller actually do?

Again, the docs:

http://doc.akka.io/docs/akka-http/10.0.5/scala/http/common/json-support.html#json-support 

http://doc.akka.io/docs/akka-http/10.0.5/scala/http/common/marshalling.html#http-marshalling-scala 

http://doc.akka.io/docs/akka-http/10.0.5/scala/http/common/unmarshalling.html#http-unmarshalling-scala 

 I'm using akka-http 10.0.5 btw.

Thanks for providing that info, people often forget to and it helps a lot to know that you're on the latest :)

Hope this helps,

-- 
Konrad `ktoso` Malawski
Akka @ Lightbend

[Mo Batista]

package xxx

import akka.actor.ActorSystem
import akka.http.scaladsl.Http
import akka.http.scaladsl.marshallers.sprayjson.SprayJsonSupport
import akka.http.scaladsl.model._
import akka.http.scaladsl.unmarshalling.Unmarshal
import akka.stream.{ActorMaterializer, Materializer}
import org.scalatest.concurrent.ScalaFutures
import org.scalatest.{BeforeAndAfter, FlatSpec, MustMatchers}
import org.scalatest.mock.MockitoSugar
import spray.json.DefaultJsonProtocol
import scala.concurrent.{Await, ExecutionContextExecutor, Future}
import akka.http.scaladsl.server.Directives

case class ColorBlob(url: String, averageColor: String, classificationColor: String)
case class ColorBlobsResponse(colorBlobs: Map[String, Option[ColorBlob]])

trait JsonSupport extends SprayJsonSupport with DefaultJsonProtocol {
  implicit val format1 = jsonFormat3(ColorBlob)
  implicit val format2 = jsonFormat1(ColorBlobsResponse) // this already provided all the needed marshallers
}

class ColorBlobRestTest
  extends FlatSpec
    with MockitoSugar
    with BeforeAndAfter
    with MustMatchers
    with ScalaFutures
    with JsonSupport
    with Directives {

  implicit val system: ActorSystem = ActorSystem()
  implicit val executor: ExecutionContextExecutor = system.dispatcher
  implicit val materializer: Materializer = ActorMaterializer()

  "this" should "work" in {
    val request = HttpRequest(method = HttpMethods.GET, uri = s"https://colorblobs.svc.dglecom.net/ws/colorblobs/de?productCodes=904655")
    val futureResponse: Future[HttpResponse] = Http().singleRequest(request)

    val futureColorBlobResponse: Future[ColorBlobsResponse] = futureResponse.flatMap { response: HttpResponse =>

      val entity: ResponseEntity = response.entity

      Unmarshal(entity).to[ColorBlobsResponse]
    }

    import scala.concurrent.duration._
    val colorBlobsResponse: ColorBlobsResponse = Await.result(futureColorBlobResponse, 1000.millis)

    assert(1==1)

  }
}

Hi Konrad

yes it does !

Here is my working example. I dumbed it down for future reference, if anyone is interested. The solution is indeed much easier than I thought! Thanks again for your help! Yeah, I know the documentation is there, but everything is a little bit hard to follow.

have a good one! :)

[Konrad Malawski]

Glad you worked it out :)

We're working on improving the docs a lot in the very near future, hope that'll help newcomers.

Happy hakking!

-- 
Konrad `ktoso` Malawski
Akka @ Lightbend

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