static Map<S, L<S>> getURLHeadersByHEAD(String url) ctex {
  url = absoluteURL(url);
  if (!networkAllowanceTest(url)) fail("Not allowed: " + url);
  HttpURLConnection conn = null;
  InputStream in = null;
  try {
    conn = (HttpURLConnection) new URL(url).openConnection();
    conn.setRequestMethod("HEAD");
    conn.setRequestProperty("X-No-Cookies", "1");
    in = conn.getInputStream();
    ret toCIMap(conn.getHeaderFields());
  } finally {
    closeURLConnection(conn, in);
  }
}

Began life as a copy of #1002941