Serialising case class with Either to JSON in play framework 2.1 scala

gistfile1.scala

package models

import play.api.libs.json._
import play.api.libs.json.Json._
import play.api.libs.functional.syntax._
import org.apache.commons.codec.binary.Base64

/**
 * Created with IntelliJ IDEA.
 * User: arturas
 * Date: 2/21/13
 * Time: 9:13 PM
 * To change this template use File | Settings | File Templates.
 */
object Js {

  /**
   * @param data Either Left(length of the binary data for stub) or
   *             Right(binary data)
   */
  case class Attachment(
    contentType: String, data: Either[Int, Array[Byte]]
  ) {
    val stub = data.isLeft
  }

  implicit val attachmentFormat = new Format[Attachment] {
    def reads(json: JsValue): JsResult[Attachment] = {
      val reads = (
        (__ \ "content_type").read[String] ~
        (__ \ "stub_data_length").read[Int]
      ) { (contentType: String, stubDataLength: Int) =>
        Attachment(contentType, Left(stubDataLength))
      } | (
        (__ \ "content_type").read[String] ~
        (__ \ "data").read[String]
      ) { (contentType: String, base64Data: String) =>
        val data = Base64.decodeBase64(base64Data.getBytes)
        Attachment(contentType, Right(data))
      }
      reads.reads(json)
    }

    def writes(o: Attachment): JsValue = obj(
      "content_type" -> o.contentType,
      o.data.fold(
        length => "stub_data_length" -> length,
        bytes => "data" -> new String(Base64.encodeBase64(bytes))
      )
    )
  }
}

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