static byte[] doPostBinary(String urlParameters, URLConnection conn) throws IOException {
  // connect and do POST
  setHeaders(conn);
  conn.setDoOutput(true);

  OutputStreamWriter writer = new OutputStreamWriter(conn.getOutputStream());
  writer.write(urlParameters);
  writer.flush();

  byte[] contents = loadBinaryPage_noHeaders(conn);
  writer.close();
  return contents;
}