code: func checkFile(filename string) error {
  	info, err := os.Stat(filename)
  	if err != nil {
  		return fmt.Errorf("failed stat on %s: %v", filename, err)
  	}
  	// Check the unix permission bits
  	if info.Mode().Perm()&0377 != 0 {
  		return fmt.Errorf("file (%v) has insecure file permissions (%v)", filename, info.Mode().String())
  	}
  	return nil
  }
docs: // checkFile is a convenience function to check if a file
  // * exists
  // * is mode 0400