Scala and Akka HTTP: Processing form-data requests

Question

Suppose we have the following request:

curl --location --request POST 'localhost:8080/api' \
--header 'Content-Type: multipart/form-data' \
--form 'field1=value1' \
--form 'field2=value2'

The request handler below gets the whole entity, but I am struggling to see how I could instead get value1 and value2.

val requestHandler: Flow[HttpRequest, HttpResponse, _] = Flow[HttpRequest].mapAsync(1) {
  case HttpRequest(HttpMethods.POST, Uri.Path("/api"), _, entity, _) =>
    val entityTextFuture: Future[String] = entity.toStrict(3 seconds).map(_.data.utf8String)
      entityTextFuture.flatMap { text =>
        Future(HttpResponse(
          StatusCodes.OK,
          entity = text
        ))
      }
}

Important: I have to use the Akka HTTP low-level server API, so I cannot use routes.

Many thanks for your time and help in advance!

score 1 · Accepted Answer · answered Apr 28 '20 at 13:15

If all you want are the string values in the form data, you just need to unmarshal to StrictForm, and then unmarshal each of the field values as strings.

Here's a proof of concept Ammonite script that responds to your curl request with value1 & value2:

import $ivy.`com.typesafe.akka::akka-actor:2.6.3`
import $ivy.`com.typesafe.akka::akka-stream:2.6.3`
import $ivy.`com.typesafe.akka::akka-http:10.1.11`

import scala.concurrent.Future

import akka.actor.ActorSystem
import akka.stream.scaladsl.Flow
import akka.http.scaladsl.Http
import akka.http.scaladsl.model._
import akka.http.scaladsl.unmarshalling.Unmarshal
import akka.http.scaladsl.common.StrictForm

implicit val system = ActorSystem()
implicit val ec = system.dispatcher

val requestHandler: Flow[HttpRequest, HttpResponse, _] = Flow[HttpRequest].mapAsync(1) {
  case HttpRequest(HttpMethods.POST, Uri.Path("/api"), _, entity, _) =>
    for {
      strictForm <- Unmarshal(entity).to[StrictForm]
      fieldsSeq <- Future.traverse(strictForm.fields) {
        case (n, v) => Unmarshal(v).to[String].map(n -> _)
      }
      fields = fieldsSeq.toMap
      response = fields("field1") + " & " + fields("field2")
    } yield HttpResponse(StatusCodes.OK, entity = response)
}

Http().bindAndHandle(requestHandler, "localhost", 8080)

Alec it works like a charm! Many thanks for your time and your help! — Stratos K, Apr 28 '20 at 15:52

Scala and Akka HTTP: Processing form-data requests

1 Answers1