private class CountingSource(source: Source) : ForwardingSource(source) {
    var bytesRead = 0L

    override fun read(
      sink: Buffer,
      byteCount: Long,
    ): Long {
      val result = delegate.read(sink, byteCount)
      if (result == -1L) return -1L
      bytesRead += result
      return result
    }
  }