sized decoder for http4s

sized.scala

  case class Sized[T](bytes: Long, value: T)

  object Sized {
    implicit def sizedEntityDecoder[F[_] : FlatMap, T](implicit dec: EntityDecoder[F, T], F: Sync[F]): EntityDecoder[F, Sized[T]] =
      new EntityDecoder[F, Sized[T]] {
        override def decode(msg: Message[F], strict: Boolean): DecodeResult[F, Sized[T]] = {
          EitherT(
            for {
              counter <- F.delay {
                new LongAdder()
              }
              wrappedmsg <- F.delay {
                msg.withEntity(msg.body.chunks.observe1(c => F.delay(counter.add(c.size.toLong))))
              }
              result <- dec.decode(wrappedmsg, strict).value
              sum <- F.delay {
                counter.sum()
              }
            } yield result.map(x => Sized(sum, x))
          )
        }
        override def consumes: Set[MediaRange] = dec.consumes
      }
  }