docs: def fetch_file_handler(unused_build_context, target, fetch, package_dir, tar):
      """Handle remote downloadable file URI.
  
      Download the file and cache it under the private builer workspace
      (unless already downloaded), and add it to the package tar.
  
      TODO(itamar): Support re-downloading if remote changed compared to local.
      """
      dl_dir = join(package_dir, fetch.name) if fetch.name else package_dir
      fetch_url(fetch.uri,
                join(dl_dir, basename(urlparse(fetch.uri).path)),
                dl_dir)
      tar.add(package_dir, arcname=split_name(target.name))