code: public static long length(URL url) throws IOException {
  	HTTPResponse http = HTTPEngine.head(url, null, null, -1, true, null, Constants.NAME, null, null);
  	long len = http.getContentLength();
  	HTTPEngine.closeEL(http);
  	return len;
      }
docs: return the length of a file defined by a url.
  
  @param dataUrl
  @return
  @throws IOException