AjaxControlToolkit.NoBot.CheckResponseAndStoreState C# (CSharp) 메소드

        void CheckResponseAndStoreState()
        {
            if(NoBotState.InvalidUnknown != _state) return;

            try {
                // Report valid when page first loaded (to avoid breaking pages that unconditionally check IsValid)
                if(!Page.IsPostBack) {
                    _state = NoBotState.Valid;
                    return;
                }

                // Report invalid if response arrives too soon
                var responseTime = (DateTime)ViewState[ResponseTimeKey];
                var utcNow = DateTime.UtcNow;
                if(utcNow < responseTime) {
                    _state = NoBotState.InvalidResponseTooSoon;
                    return;
                }

                // Report invalid if too many responses from same IP address
                // NOTE: The performance of the following code can be improved
                // if performance becomes an issue.
                lock(_pastAddresses) {
                    // Add user address to address cache, taking care not to duplicate keys
                    var userAddress = Page.Request.UserHostAddress;
                    var utcAdd = utcNow;
                    while(_pastAddresses.ContainsKey(utcAdd))
                        utcAdd = utcAdd.AddTicks(1);

                    _pastAddresses.Add(utcAdd, userAddress);
                    // Calculate cutoff window for cached addresses
                    var utcCutoff = utcNow.AddSeconds(-_cutoffWindowSeconds);
                    // Determine number of expired addresses
                    var cutoffs = 0;
                    foreach(var time in _pastAddresses.Keys) {
                        if(time < utcCutoff)
                            cutoffs++;
                        else
                            break;
                    }

                    // Remove expired addresses
                    while(0 < cutoffs) {
                        _pastAddresses.RemoveAt(0);
                        cutoffs--;
                    }
                    // Determine number of instances of user address in cache
                    var instances = 0;
                    foreach(var address in _pastAddresses.Values) {
                        if(userAddress == address)
                            instances++;
                    }

                    // Fail if too many
                    if(_cutoffMaximumInstances < instances) {
                        _state = NoBotState.InvalidAddressTooActive;
                        return;
                    }
                }

                // Report invalid if response is wrong
                var sessionKey = (string)ViewState[SessionKeyKey];
                var requiredResponse = (string)Page.Session[sessionKey];
                Page.Session.Remove(sessionKey);
                if(requiredResponse != _extender.ClientState) {
                    _state = NoBotState.InvalidBadResponse;
                    return;
                }

                // All checks OK, report valid
                _state = NoBotState.Valid;
            }
            catch(NullReferenceException) {
                _state = NoBotState.InvalidBadSession;
            }
        }