Automatic get parameters generator from case class for spray routing

Main.scala

package example

import scala.language.existentials

import shapeless._; import record._; import ops.record._; import ops.hlist._

import spray.routing.SimpleRoutingApp

trait AutoGetParametersModule { self: SimpleRoutingApp =>
  import spray.routing.{ Directive, Directive1, Directive0, HListDeserializer }
  import spray.routing.directives._

  // mimic partial inference
  trait AsBuilder[L <: HList] {
    def apply[A](ds: HListDeserializer[L, A]): Directive1[A]
  }

  // mimic partial inference
  class ParamsBuilder[A] {
    def apply[Repr <: HList, O <: HList, L <: HList](implicit
      lgen: LabelledGeneric.Aux[A, Repr],
      names: Names.Aux[Repr, O],
      folder: LeftFolder.Aux[O, Directive0, ParamDefMagnet2.MapReduce.type, Directive[L]]
    ): AsBuilder[L] = new AsBuilder[L] {
      def apply[A](ds: HListDeserializer[L, A]) =
        parameters(names.apply).as(ds)
    }
  }

  def params[A] = new ParamsBuilder[A]

  /* type class for building an HList of NameReceptacle from a LabelledGeneric */
  trait Names[L <: HList] extends DepFn0 { type Out <: HList }

  object Names {
    def apply[L <: HList](implicit names: Names[L]): Aux[L, names.Out] = names

    type Aux[L <: HList, Out0 <: HList] = Names[L] { type Out = Out0 }

    implicit def hnilNames[L <: HNil]: Aux[L, HNil] =
      new Names[L] {
        type Out = HNil
        def apply(): Out = HNil
      }

    implicit def hlistNames[K <: Symbol, V, T <: HList](implicit wk: Witness.Aux[K], nt: Names[T]): Aux[FieldType[K, V] :: T, NameReceptacle[V] :: nt.Out] =
      new Names[FieldType[K, V] :: T] {
        type Out = NameReceptacle[V] :: nt.Out
        def apply(): Out = {
          NameReceptacle[V](wk.value.name) :: nt()
        }
      }
  }
}

object Main extends App with SimpleRoutingApp with AutoGetParametersModule {
  implicit val system = akka.actor.ActorSystem("foo")

  case class Foo(x: Option[String], y: Option[Boolean])

  val fooParams = params[Foo].apply

  startServer(interface = "localhost", port = 8080) {
    path("foo") {
      fooParams(Foo) { foo =>
        complete(foo.toString)
      }
    }
  }
}

Test with

curl http://127.0.0.1:8080/foo?x=foo&y=true

produces

Foo(Some(foo),Some(true))

also, Option fields in the case class, can be left out

curl http://127.0.0.1:8080/foo?x=foo

produces

Foo(Some(foo), None)