scodec.codecs.VariableSizeCodec.scala Maven / Gradle / Ivy

package scodec
package codecs

import scalaz.\/._
import scodec.bits.BitVector

private[codecs] final class VariableSizeCodec[A](sizeCodec: Codec[Int], valueCodec: Codec[A], sizePadding: Int = 0) extends Codec[A] {

  private val decoder = sizeCodec flatZip { sz => fixedSizeBits(sz - sizePadding, valueCodec) }

  override def encode(a: A) = for {
    encA <- valueCodec.encode(a)
    encSize <- encA.intSize.map { n => sizeCodec.encode(n + sizePadding).leftMap { fail(a, _) } }
                           .getOrElse(left(fail(a, s"${encA.size} exceeds maximum 32-bit integer value ${Int.MaxValue}")))
  } yield encSize ++ encA

  private def fail(a: A, msg: String): String =
    s"[$a] is too long to be encoded: $msg"

  override def decode(buffer: BitVector) =
    decoder.decode(buffer).map { case (rest, (sz, value)) => (rest, value) }

  override def toString = s"variableSizeBits($sizeCodec, $valueCodec)"
}