code: func normalizeURL(dest string) (string, error) {
  	u, err := url.Parse(dest)
  	if err != nil {
  		return "", err
  	}
  	// Note: '//host/path' is a location on a server named 'host'.
  	if u.IsAbs() || !strings.HasPrefix(u.Path, "/") || strings.HasPrefix(u.Path, "//") {
  		return "", errBadDestinationURL
  	}
  	// path.Clean removes trailing slash. It matters for URLs though. Keep it.
  	keepSlash := strings.HasSuffix(u.Path, "/")
  	u.Path = path.Clean(u.Path)
  	if !strings.HasSuffix(u.Path, "/") && keepSlash {
  		u.Path += "/"
  	}
  	if !strings.HasPrefix(u.Path, "/") {
  		return "", errBadDestinationURL
  	}
  	return u.String(), nil
  }
docs: ////
  // normalizeURL verifies URL is parsable and that it is relative.