protected function prepareLocal() {
    // isSmooth: local header will have its general purpose bit set
    // => empty values in local header
    // => append data descriptor
    if ($this->isSmooth()) return;

    $size = filesize($this->path);
    $this->setSize($size);
    if (!$this->hasDeflation()) $this->setDeflatedSize($size);
    $this->setRawCrc(hash_file('crc32b', $this->path, TRUE));
  }