Example of using scodec to decode a document of fields

document.scala

package foo

import scodec.bits._
import scodec._
import scodec.codecs._

case class Document(fields: Vector[(String, Field)])

sealed trait Field
case class IntField(value: Int) extends Field
case class StringField(value: String) extends Field

object Document {
  val field: Codec[(String, Field)] = {
    discriminated[(String, Field)].by(uint8).
      subcaseO(1) { case (nme, fld: IntField) => Some(nme -> fld); case _ => None } (cstring ~ int32.as[IntField]).
      subcaseO(2) { case (nme, fld: StringField) => Some(nme -> fld); case _ => None } (cstring ~ cstring.as[StringField])
  }

  def nullTerminated[A](c: Codec[A]): Codec[A] = new Codec[A] {
    def sizeBound = c.sizeBound + SizeBound.exact(8)
    def encode(a: A) = c.encode(a).map { _ ++ hex"00".bits }
    def decode(b: BitVector) = {
      if (b.takeRight(8) == hex"00".bits)
        c.decode(b.dropRight(8))
      else Attempt.failure(Err("Was not null terminated!"))
    }
  }

  val codec: Codec[Document] = {
    nullTerminated(variableSizeBytes(int32, vector(field), 4).as[Document])
  }
}