static InputStream urlConnection_getInputStream(URLConnection con) throws IOException {
  UnknownHostException lastException = null;
  repeat 2 {
    try {
      if (con cast HttpURLConnection)
        if (con.getResponseCode() == 500)
          throw new IOException(joinNemptiesWithColonSpace("Server code 500", tryToReadErrorStreamFromURLConnection(con)));
      ret con.getInputStream();
    } catch (UnknownHostException e) {
      lastException = e;
      print("Retrying because of: " + e);
      continue;
    }
  }
  throw lastException;
}