CODEWITHSUNDEEP
jsonscalacircehttp4szio
Developus
Developus

Reputation: 1462

Scala, Circe, Http4s - is it any way to encode Throwable in Circe?

I have created hierarchy of errors:

sealed trait MyError extends Throwable
final case class SecondError(msg: String) extends MyError

Now I could get this kind of error in my http4s routes:

case GET -> Root / "things" => for {
        response <- things.all.foldM(
          error => error match {
            case SecondError(_) => InternalServerError(error)            
          }
...

But I get compiled error:

could not find implicit value for parameter encoder: io.circe.Encoder[Throwable]

Is it possible to encode Throwable with circe and http4s? I tried to do it this way:

implicit def encoderHttpThrowable: EntityEncoder[Env, Throwable] = jsonEncoderOf[Env, Throwable]

But it did not solve a problem.

Upvotes: 2

Views: 764

Answers (1)

pme
pme

Reputation: 14803

It is not possible to encode automatically a Java Hierarchy with Circe (or any other library) (I am pretty sure of this).

So you have 3 possibilities:

  1. Just use the Message of the error:

    case GET -> Root / "things"  =>
    things.all.foldM (
      error => InternalServerError(error.getMessage()),
      Ok(_)
    )

  2. Or get rid of the Throwable:

      sealed trait MyError
  final case class SecondError(msg: String) extends MyError

    And now you can encode the error 

    ...
case GET -> Root / "things"  =>
  things.all.foldM (
    error => InternalServerError(error),
    Ok(_)
  )

  3. Map your Throwable to your own Error (Sealed Trait without Throwable):

    ...
case GET -> Root / "things"  =>
  things.all
    .mapError{
      case ex: IllegalArgumentException => SecondError(ex.getMessage)
      case ex => FirstError(ex.getMessage)
   }
    .foldM (
    error => InternalServerError(error),
    Ok(_)
  )

Upvotes: 1

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