code: public void appendExtraServerInformation(HashMap<String, String> map)
      {
          List<HandlerBase> handlers = getClientHandlerList();
          for (HandlerBase handler : handlers)
              handler.appendExtraServerInformation(map);
      }
docs: This method gives our handlers a chance to add any information to the ping message
  which the client sends (repeatedly) to the server while the agents are assembling.
  This message is guaranteed to get through to the server, so it is a good place to
  communicate.
  (NOTE this is called BEFORE addExtraHandlers - but that mechanism is provided to allow
  the *server* to add extra handlers on the *client* - so the server should already know
  whatever the extra handlers might want to tell it!)
  @param map the map of data passed to the server