How do I turn all rejections into custom json in spray?

Question

When spray (spray.io) produces a rejection, it responds with a string body. Since all my API clients will assume that my API only returns json, I'd like globally make every rejection a valid json object that conforms to our error object format. How can I make this happen?

The error object format looks like this

{
    'details' : 'Something happened in the app. boooo!',
    'errorType' : 'Unknown'
}

The errorType is my internal enum-style list of values like UserNotFound and NeedPaidAccount

Answer 1

If you just want to turn all of the rejections into your custom json format, you can create a rejection handler. For example, I'll put this in my ServiceActor and do the following:

class ApiServiceActor extends Actor with HttpServiceActor with ApiServices {
  def jsonify(response: HttpResponse): HttpResponse = {
    response.withEntity(HttpBody(ContentType.`application/json`,
      JSONObject(Map(
        "details" -> response.entity.asString.toJson,
        "errorType" -> ApiErrorType.Unknown.toJson
      )).toString()))
  }

  implicit val apiRejectionHandler = RejectionHandler {
    case rejections => mapHttpResponse(jsonify) {
      RejectionHandler.Default(rejections)
    }
  }

  def receive = runRoute {
    yourRoute ~ yourOtherRoute ~ someOtherRoute
  }
}