CodecQuestion

Code:

import scodec._
import scodec.bits._
import codecs._
import scalaz._
import Scalaz._

object Messages {
  sealed trait MessageType
  case object Buy  extends MessageType
  case object Sell extends MessageType

  case class Message(id:Int, clientName: String, mt: MessageType) 

  val messageTypeCodec : Codec[MessageType] = mappedEnum(uint8, Buy -> 1, Sell -> 2)
  val messageCodec = (int32 :: ascii :: messageTypeCodec).as[Message]
}

Session:

scala> import Messages._
import Messages._

scala> Message(90,"c",Buy)
res1: Messages.Message = Message(90,c,Buy)

scala> messageCodec.encode(res1)
res2: scodec.Attempt[scodec.bits.BitVector] = Successful(BitVector(48 bits, 0x0000005a6301))

scala> res2.flatMap(messageCodec.decode)
res3: scodec.Attempt[scodec.DecodeResult[Messages.Message]] = Failure(cannot acquire 8 bits from a vector that contains 0 bits)