throw IndexOutOfBoundsException()
    }
    var mutablePos = pos
    var mutableByteCount = byteCount

    while (mutableByteCount > 0L) {
      val bytesWritten = fileChannel.transferFrom(source, mutablePos, mutableByteCount)
      mutablePos += bytesWritten
      mutableByteCount -= bytesWritten
    }
  }

  /**
   * Copy [byteCount] bytes from the file at [pos] into `sink`. It is the