How to disable HTML error responses when using Action(parse.json)?

Question

In a REST API implemented with Play Framework (2.4), I'm using Action(parse.json) to parse JSON from incoming POST request body.

With my current code (see below),

• Posting valid JSON with missing fields (e.g. {"foo": ""}) produces 400 with the response body {"error":"Missing input fields"}. This is fine and expected. 👍

• Posting completely invalid JSON (such as {,,,} or {\00}) produces 400 with a long HTML response body. 👎 This comes from somewhere within parse.json.

In the latter case, how to get rid of the HTML response body? I'd like the response body to either contain a short JSON error message (such as {"error":"Invalid JSON input"}), or nothing at all. Does Play have a config option for this, or would I need to create a custom Action? What is the simplest way?

Controller method:

def test = Action(parse.json) { request =>
  request.body.validate[Input].map(i => {
    Ok(i.foo)
  }).getOrElse(BadRequest(errorJson("Missing input fields")))
}

Other stuff used above:

case class Input(foo: String, bar: String)

object Input {
  implicit val reads = Json.reads[Input]
}

case class ErrorJson(error: String)

object ErrorJson {
  implicit val writes = Json.writes[ErrorJson]
}

private def errorJson(message: String) = Json.toJson(ErrorJson(message))

Answer 1

The long html is produced by the default HttpErrorHandler. You can provide your own by following this guide. Quoting the example code:

class ErrorHandler extends HttpErrorHandler {

  def onClientError(request: RequestHeader, statusCode: Int, message: String) = {
    Future.successful(
      Status(statusCode)("A client error occurred: " + message)
    )
  }

  def onServerError(request: RequestHeader, exception: Throwable) = {
    Future.successful(
      InternalServerError("A server error occurred: " + exception.getMessage)
    )
  }
}

Note: if you manage your dependencies without Guice, you will have to provide your custom HttpErrorHandler in the ApplicationLoader