Play2/Scala Custom JSON field validation

Question

Let's say I have this model, in which I defined a custom case class IPAddress address with specific JSON formats. This class holds a String representation of an IPv4 and havs a validation in the Constructor that raises an IllegalArgumentException if the input string is not valid.

case class Node(id: UUID, name: String, ip: IPAddress)

case class IPAddress(s: String) {
  val rx = """^([01]?\d\d?|2[0-4]\d|25[0-5])\.([01]?\d\d?|2[0-4]\d|25[0-5])\.([01]?\d\d?|2[0-4]\d|25[0-5])\.([01]?\d\d?|2[0-4]\d|25[0-5])$""".r
  require(rx.pattern.matcher(s).matches())

  val ip = s
  override def toString = ip
}


object JsonNodeFormat {
  import play.api.libs.json.Json

  implicit val midWrite: Writes[FMMid] = Writes {
    (mid: FMMid) => JsString(mid.toString)
  }
  implicit val midRead: Reads[FMMid] = JsPath.read[String].map(FMMid(_))

  implicit val NodeFormat = Json.format[Node]
}

Then I have my controller with an action that creates a new Node and write it in the database (in my case I'm using ReactiveMongo, but this is irrelevant)

class Nodes extends Controller with MongoController {
  def collection: JSONCollection = db.collection[JSONCollection]("nodes")

  import models._
  import models.JsonNodeFormat._

  def createTest = Action.async(parse.json) {
    request =>
      request.body.validate[Node].map {
        node =>
          collection.insert(node).map {
            lastError =>
              Created(s"Node Created")
          }
      }.getOrElse(Future.successful(BadRequest("invalid json")))
  }
}

If make a request with valid json

{
    "id": "0879d4be-78bb-4cc0-810b965b",
    "ip": "192.168.0.10",
    "name": "node1"
}

everything works fine. The object is correctly added to the db. I would like the controller return a BadRequest response when an invalid IP address is passed. On the contrary, if I pass a Json with an invalid IP address

{
    "id": "0879d4be-78bb-4cc0-810b965b",
    "ip": "192.168.0.foo",
    "name": "node1"
}

it causes an internal server error with all the stack printed on the console (because nobody catches the constructor exception). I would like that when an invalid IPAddress is passed, the request.body.validate function fails and the execution falls in the getOrElse statement.

Also note that passing an invalid UUID doesn't generate an error but a BadRequest reply.

What's missing in my IPAddress class?

Have you thought about returning Try[String] instead of String? You could wrap the ip validation so you can react in case you have a validation problem. — Carlos Vilchez
Yes, this is absolutely a solution. But I wanted to demand to the body.validate all the work, so that I wouldn't need another code block and consequently an additional nesting level. I'm just wondering because everything works as expected in with the UUID. — tano
Play gives you the option to decide how to reply to a particular exception. You can override the definition of the function onError inside the object Global. There you can get the exception and you will be able to return the BadRequest code. — Carlos Vilchez
That's the solution I'm currently adopting. The weakness of this approach is that you lose the information about which specific validation has failed. — tano
In that case I would get rid of the require and use another function like findFirstIn. Then you can process the Option[String] — Carlos Vilchez

tano tano · Accepted Answer · 2015-04-30T15:33:05

Eventually I found a solution. I discovered that between other Reads validation helpers there is one called pattern that matches the a String with a Regex. So I changed my Json Reads as

  implicit val midRead: Reads[FMMid] = JsPath.read[String](pattern("""^5\.([01]?\d\d?|2[0-4]\d|25[0-5])\.([01]?\d\d?|2[0-4]\d|25[0-5])\.([01]?\d\d?|2[0-4]\d|25[0-5])$""".r)).map(FMMid(_))

and everything started working as I expected.

P.S. still can't understand how UUID works without any custom validator.

Play2/Scala Custom JSON field validation

1 Answers