code: protected void logExtended(HttpRequest request,
                                 HttpResponse response,
                                 Writer log)
          throws IOException
      {
          String referer = request.getField(HttpFields.__Referer);
          if(referer==null)
              log.write("\"-\" ");
          else
          {
              log.write('"');
              log.write(referer);
              log.write("\" ");
          }
          
          String agent = request.getField(HttpFields.__UserAgent);
          if(agent==null)
              log.write("\"-\"");
          else
          {
              log.write('"');
              log.write(agent);
              log.write('"');
          }
          
  
      }
docs: Log Extended fields.
  This method can be extended by a derived class to add extened fields to
  each log entry.  It is called by the log method after all standard
  fields have been added, but before the line terminator.
  Derived implementations should write extra fields to the Writer
  provided.
  The default implementation writes the referer and user agent.
  @param request The request to log.
  @param response The response to log.
  @param log The writer to write the extra fields to.
  @exception IOException Problem writing log