code: public void setLocalActive() throws ClientException, IOException {
          if (session.serverAddress == null) {
              throw new ClientException(ClientException.CALL_PASSIVE_FIRST);
          }
          try {
              localServer.setActive(session.serverAddress);
          } catch (java.net.UnknownHostException e) {
              throw new ClientException(ClientException.UNKNOWN_HOST);
          }
      }
docs: Starts local server in active server mode.