Marshal akka `HttpResponse` as Argonaut `Json`

Question

I'm trying to marshal an akka HttpResponse as such:

{
  "code": 200,
  "headers": [],
  "body": "{\"data\": \"Yes!\"}"
}

If I write an Argonaut EncodeJson for this Instance, it might look like this:

implicit def httpResponseEncodeJson: EncodeJson[HttpResponse] =
  EncodeJson(
    (res: HttpResponse) ⇒ {
      ("code" := res._1.value) ->:
      ("headers" := res._2.toList) ->:
      ("body" := res._3) ->: jEmptyObject
    }
  )

I have managed to marshal the headers as json. The only problem is with the body, i.e., the ResponseEntity. Since it is an akka stream, it can only return a future, if I use .toStrict.

Can anybody guide me as to how I might marshal it?

score 0 · Accepted Answer · answered Jan 19 '17 at 14:32

If possible, I would keep the marshalled value as a Future, to preserve the asynchrony of the entity extraction.

I would start by having something along the lines of

  case class StrictHttpResponse(code: String, headers: List[HttpHeader], body: String)

  def toStrictResponse(response: HttpResponse): Future[StrictHttpResponse] = response.entity.dataBytes.runFold(ByteString(""))(_ ++ _).map { bs =>
    StrictHttpResponse(response.status.value, response.headers.toList, bs.utf8String)
  }

  implicit def httpResponseEncodeJson: EncodeJson[StrictHttpResponse] =
    EncodeJson(
      (res: StrictHttpResponse) ⇒ {
        ("code" := res.code) ->:
          ("headers" := res.headers) ->:
          ("body" := res.body) ->: jEmptyObject
      }
    )

  def encodeResponse(response: HttpResponse): Future[Json] = toStrictResponse(response).map(_.jencode)

and then - e.g. - handle the result of encodeResponse by providing a callback.

Thanks a lot for your answer. I think I did nearly the same thing. Can you review my answer? — Yash Srivastav, Jan 20 '17 at 15:25

score 0 · Answer 2 · answered Jan 20 '17 at 15:17

I ultimately used this:

  implicit def httpResponseListMarshal: ToEntityMarshaller[List[HttpResponse]] =
Marshaller { implicit ec ⇒ (responses: List[HttpResponse]) ⇒

    // Sink for folding Source of ByteString into 1 single huge ByteString
    val sink = Sink.fold[ByteString, ByteString](ByteString.empty)(_ ++ _)

    // A List of Future Json obtained by folding Source[ByteString]
    // and mapping appropriately
    val listFuture: List[Future[Json]] = for {
      res ← responses
    } yield for {
      byteString ← res._3.dataBytes runWith sink
      string = byteString.utf8String
    } yield ("code" := res._1.intValue) ->:
      ("headers" := res._2.toList) ->:
      ("body" := string) ->: jEmptyObject


    // Convert List[Future[Json]] to Future[List[Json]]
    val futureList: Future[List[Json]] = Future.sequence(listFuture)

    // ToEntityMarshaller is essentially a   Future[List[Marshalling[RequestEntity]]]
    for {
      list ← futureList
      json = jArray(list).nospaces
    } yield List(
      Marshalling.Opaque[RequestEntity](() ⇒
        HttpEntity(`application/json`, json)
    ).asInstanceOf[Marshalling[RequestEntity]]
  )
}

The full code and sample usage can be found here: https://github.com/yashsriv/akka-http-batch-api/blob/argonaut/src/main/scala/org.yashsriv/json/Batch.scala

Marshal akka `HttpResponse` as Argonaut `Json`

2 Answers2