def headerSink(headerConfig: HeaderConfig): ZSink[Any, StreamError, Arr[String], Arr[String], List[String]] = (for {
    _ <- skip[Arr[String]](headerConfig.skipBefore)

    result <- headerConfig.headerOverride match {
      case Some((true, list)) =>
        get[Arr[String]] *> ZSink.succeed[Arr[String], List[String]](list)
      case Some((false, list)) =>
        ZSink.succeed[Arr[String], List[String]](list)
      case None =>
        get[Arr[String]].map(_.toList)
    }

    _ <- skip[Arr[String]](headerConfig.skipAfter)
  } yield result).mapError(_ => StreamError.NoHeader())

  // A different way to implement skip.
  def skip[A](n: Long): ZSink[Any, Unit, Nothing, A, Unit] =
    ZSink.foldUntil[Long, A](0L, n)((s, _) => s + 1).flatMap {
      case m if n != m => ZSink.fail(())
      case _           => ZSink.succeed(())
    }
  
  // This is also known as ZSink.identity but it's a weird name.
  def get[A]: ZSink[Any, Unit, A, A, A] =
    ZSink.foldUntil[Option[A], A](None, 1)((_, a) => Some(a)).flatMap {
      case None    => ZSink.fail(())
      case Some(a) => ZSink.succeed(a)
    }