extract_entry

# File lib/rubygems/package/tar_input.rb, line 147
  def extract_entry(destdir, entry, expected_md5sum = nil)
    if entry.directory? then
      dest = File.join destdir, entry.full_name

      if File.directory? dest then
        FileUtils.chmod entry.header.mode, dest, :verbose => false
      else
        FileUtils.mkdir_p dest, :mode => entry.header.mode, :verbose => false
      end

      fsync_dir dest
      fsync_dir File.join(dest, "..")

      return
    end

    # it's a file
    md5 = Digest::MD5.new if expected_md5sum
    destdir = File.join destdir, File.dirname(entry.full_name)
    FileUtils.mkdir_p destdir, :mode => 0755, :verbose => false
    destfile = File.join destdir, File.basename(entry.full_name)
    FileUtils.chmod 0600, destfile, :verbose => false rescue nil # Errno::ENOENT

    open destfile, "wb", entry.header.mode do |os|
      loop do
        data = entry.read 4096
        break unless data
        # HACK shouldn't we check the MD5 before writing to disk?
        md5 << data if expected_md5sum
        os.write(data)
      end

      os.fsync
    end

    FileUtils.chmod entry.header.mode, destfile, :verbose => false
    fsync_dir File.dirname(destfile)
    fsync_dir File.join(File.dirname(destfile), "..")

    if expected_md5sum && expected_md5sum != md5.hexdigest then
      raise Gem::Package::BadCheckSum
    end
  end