rfc7807-error-handling.scala

case class ErrorResponseBody private(
    `type`: URI,
    title: String
)

// https://doc.akka.io/docs/akka-http/10.1.3/routing-dsl/rejections.html?language=scala#customising-rejection-http-responses
private val rfc7807RejectionHandler = RejectionHandler.default.mapRejectionResponse {
  case res @ HttpResponse(_, _, entity: HttpEntity.Strict, _) =>
    val message = entity.data.utf8String

    res.copy(
      entity = HttpEntity(
        CustomMediaTypes.`application/problem+json`,
        ErrorResponseBody(new URI("about:blank"), message).toJson.prettyPrint
      )
    )
  case x => x
}