private static async Task <List <AppleFeedback> > _feedbackReadResponse(Internal.APNSConnection connection)
        {
            var rtn = new List <AppleFeedback>();

            byte[] msg;

            while ((msg = await connection.Receive(6, true)) != null)
            {
                var timestamp   = (msg[0] << 24) | (msg[1] << 16) | (msg[2] << 8) | (msg[3]);
                var deviceToken = await connection.Receive((msg[4] << 8) | (msg[5]), false);

                rtn.Add(new AppleFeedback(timestamp, deviceToken));
            }

            return(rtn);
        }
        private async Task                        _receiveResponceAsync()
        {
            byte[] msg = null;
            List <Notification> notifications;

            try {
                msg = await _connection.Receive(6, true);

                lock (_lockObject) {
                    notifications  = _notifications;
                    _notifications = null;
                }

                _close();
            }
            catch (Exception err) {
                bool connected;

                lock (_lockObject) {
                    notifications  = _notifications;
                    _notifications = null;
                    connected      = _connection != null;
                    _close();
                }

                if (connected)
                {
                    Service.Error(new PushNotificationServiceException("Receive response from APNS failed.", err));
                }
            }

            if (msg != null && msg[0] == 0x08)
            {
                var ni = (msg[2] << 24) | (msg[3] << 16) | (msg[4] << 8) | (msg[5]);

                if (ni >= 0 && ni == _notificationIdentifier - 1 && notifications[ni] == null)
                {
                    notifications = null;
                }
                else
                {
                    if (ni >= 0 && ni < _notificationIdentifier)
                    {
                        var n = notifications[ni];

                        if (n != null)
                        {
                            Service.Error((msg[1] == 0x08)
                                            ? new PushNotificationInvalidDeviceException(n)
                                            : new PushNotificationException(n, "Submit notification to '" + n.DeviceAddress + "' failed error #" + msg[1] + "."));
                        }
                    }

                    for (int i = 0; i <= ni && i < _notificationIdentifier; ++i)
                    {
                        notifications[i] = null;
                    }
                }

                Service.ConnectionClosed(this, notifications);
            }
            else
            {
                Service.NotificationDropped(notifications, new Exception("Connection dropped by APSN."));
                Service.ConnectionClosed(this);
            }
        }