code: void callback(boolean ask) {
          if (viStatusCallback != null) {
              if (states.remove(callState.toString().toLowerCase())) {
                  if (logger.isInfoEnabled()) {
                      logger.info("About to execute viStatusCallback: " + viStatusCallback.toString());
                  }
                  if (viStatusCallbackMethod == null) {
                      viStatusCallbackMethod = "POST";
                  }
                  final List<NameValuePair> parameters = parameters();
                  requestCallback = new HttpRequestDescriptor(viStatusCallback, viStatusCallbackMethod, parameters);
                  if (!ask) {
                      downloader.tell(requestCallback, null);
                  } else if (ask) {
                      final Timeout timeout = new Timeout(Duration.create(5, TimeUnit.SECONDS));
                      Future<Object> future = (Future<Object>) ask(downloader, requestCallback, timeout);
                      DownloaderResponse downloaderResponse = null;
                      try {
                          downloaderResponse = (DownloaderResponse) Await.result(future, Duration.create(10, TimeUnit.SECONDS));
                      } catch (Exception e) {
                          logger.error("Exception during callback with ask pattern");
                      }
                  }
              } else {
                  if (logger.isInfoEnabled()) {
                      logger.info("Status Callback has been already executed for state: ",callState.toString());
                  }
              }
          } else if(logger.isInfoEnabled()){
              logger.info("status callback is null");
          }
  
      }
docs: Downloader finish with this callback before shutdown everything. Issue https://github.com/Mobicents/RestComm/issues/437