/**
   * Process HTTP request.
   *
   * @param act Action.
   * @param req Http request.
   * @param res Http response.
   */
  private void processRequest(String act, HttpServletRequest req, HttpServletResponse res) {
    res.setContentType("application/json");
    res.setCharacterEncoding("UTF-8");

    GridRestCommand cmd = command(req);

    if (cmd == null) {
      res.setStatus(HttpServletResponse.SC_BAD_REQUEST);

      return;
    }

    if (!authChecker.apply(req.getHeader("X-Signature"))) {
      res.setStatus(HttpServletResponse.SC_UNAUTHORIZED);

      return;
    }

    GridRestResponse cmdRes;

    Map<String, Object> params = parameters(req);

    try {
      GridRestRequest cmdReq = createRequest(cmd, params, req);

      if (log.isDebugEnabled()) log.debug("Initialized command request: " + cmdReq);

      cmdRes = hnd.handle(cmdReq);

      if (cmdRes == null)
        throw new IllegalStateException("Received null result from handler: " + hnd);

      byte[] sesTok = cmdRes.sessionTokenBytes();

      if (sesTok != null) cmdRes.setSessionToken(U.byteArray2HexString(sesTok));

      res.setStatus(HttpServletResponse.SC_OK);
    } catch (Throwable e) {
      res.setStatus(HttpServletResponse.SC_OK);

      U.error(log, "Failed to process HTTP request [action=" + act + ", req=" + req + ']', e);

      cmdRes = new GridRestResponse(STATUS_FAILED, e.getMessage());

      if (e instanceof Error) throw (Error) e;
    }

    String json;

    try {
      json = jsonMapper.writeValueAsString(cmdRes);
    } catch (JsonProcessingException e1) {
      U.error(log, "Failed to convert response to JSON: " + cmdRes, e1);

      GridRestResponse resFailed = new GridRestResponse(STATUS_FAILED, e1.getMessage());

      try {
        json = jsonMapper.writeValueAsString(resFailed);
      } catch (JsonProcessingException e2) {
        json = "{\"successStatus\": \"1\", \"error:\" \"" + e2.getMessage() + "\"}}";
      }
    }

    try {
      if (log.isDebugEnabled()) log.debug("Parsed command response into JSON object: " + json);

      res.getWriter().write(json);

      if (log.isDebugEnabled())
        log.debug(
            "Processed HTTP request [action=" + act + ", jsonRes=" + cmdRes + ", req=" + req + ']');
    } catch (IOException e) {
      U.error(log, "Failed to send HTTP response: " + json, e);
    }
  }
  /**
   * Grabs local events and detects if events was lost since last poll.
   *
   * @param ignite Target grid.
   * @param evtOrderKey Unique key to take last order key from node local map.
   * @param evtThrottleCntrKey Unique key to take throttle count from node local map.
   * @param evtTypes Event types to collect.
   * @param evtMapper Closure to map grid events to Visor data transfer objects.
   * @return Collections of node events
   */
  public static Collection<VisorGridEvent> collectEvents(
      Ignite ignite,
      String evtOrderKey,
      String evtThrottleCntrKey,
      final int[] evtTypes,
      IgniteClosure<Event, VisorGridEvent> evtMapper) {
    assert ignite != null;
    assert evtTypes != null && evtTypes.length > 0;

    ConcurrentMap<String, Long> nl = ignite.cluster().nodeLocalMap();

    final long lastOrder = getOrElse(nl, evtOrderKey, -1L);
    final long throttle = getOrElse(nl, evtThrottleCntrKey, 0L);

    // When we first time arrive onto a node to get its local events,
    // we'll grab only last those events that not older than given period to make sure we are
    // not grabbing GBs of data accidentally.
    final long notOlderThan = System.currentTimeMillis() - EVENTS_COLLECT_TIME_WINDOW;

    // Flag for detecting gaps between events.
    final AtomicBoolean lastFound = new AtomicBoolean(lastOrder < 0);

    IgnitePredicate<Event> p =
        new IgnitePredicate<Event>() {
          /** */
          private static final long serialVersionUID = 0L;

          @Override
          public boolean apply(Event e) {
            // Detects that events were lost.
            if (!lastFound.get() && (lastOrder == e.localOrder())) lastFound.set(true);

            // Retains events by lastOrder, period and type.
            return e.localOrder() > lastOrder
                && e.timestamp() > notOlderThan
                && F.contains(evtTypes, e.type());
          }
        };

    Collection<Event> evts = ignite.events().localQuery(p);

    // Update latest order in node local, if not empty.
    if (!evts.isEmpty()) {
      Event maxEvt = Collections.max(evts, EVTS_ORDER_COMPARATOR);

      nl.put(evtOrderKey, maxEvt.localOrder());
    }

    // Update throttle counter.
    if (!lastFound.get())
      nl.put(evtThrottleCntrKey, throttle == 0 ? EVENTS_LOST_THROTTLE : throttle - 1);

    boolean lost = !lastFound.get() && throttle == 0;

    Collection<VisorGridEvent> res = new ArrayList<>(evts.size() + (lost ? 1 : 0));

    if (lost) res.add(new VisorGridEventsLost(ignite.cluster().localNode().id()));

    for (Event e : evts) {
      VisorGridEvent visorEvt = evtMapper.apply(e);

      if (visorEvt != null) res.add(visorEvt);
    }

    return res;
  }