System.Net.Cache.FtpRequestCacheValidator.RevalidateCache C# (CSharp) Method

        protected internal override CacheValidationStatus RevalidateCache()
        {
            if (HttpProxyMode)
                return base.RevalidateCache();


            if (Policy.Level >= RequestCacheLevel.Reload)
            {
                // For those policies cache is never returned
                GlobalLog.Assert("RevalidateCache()", "This validator should not be called for policy = " + Policy.ToString());
                if(Logging.On)Logging.PrintError(Logging.RequestCache, SR.GetString(SR.net_log_cache_validator_invalid_for_policy, Policy.ToString()));
                return CacheValidationStatus.DoNotTakeFromCache;
            }

            // First check is do we still hold on a cached entry?
            if (CacheStream == Stream.Null)
            {
                return CacheValidationStatus.DoNotTakeFromCache;
            }

            //
            // This is a second+ time validation after receiving at least one response
            //

            CacheValidationStatus result = CacheValidationStatus.DoNotTakeFromCache;

            FtpWebResponse resp = Response as FtpWebResponse;
            if (resp == null)
            {
                // This will result to an application error
                return CacheValidationStatus.DoNotTakeFromCache;
            }

            if (resp.StatusCode == FtpStatusCode.FileStatus)
            {
                if(Logging.On) Logging.PrintInfo(Logging.RequestCache, SR.GetString(SR.net_log_cache_response_last_modified, resp.LastModified.ToUniversalTime().ToString("r", CultureInfo.InvariantCulture), resp.ContentLength));
                if(Logging.On) Logging.PrintInfo(Logging.RequestCache, SR.GetString(SR.net_log_cache_cache_last_modified, CacheEntry.LastModifiedUtc.ToString("r", CultureInfo.InvariantCulture), CacheEntry.StreamSize));

                if (CacheStreamOffset != 0L && CacheEntry.IsPartialEntry)
                {
                    //should never happen
                    if(Logging.On) Logging.PrintError(Logging.RequestCache, SR.GetString(SR.net_log_cache_partial_and_non_zero_content_offset, CacheStreamOffset.ToString(CultureInfo.InvariantCulture))); 
                    result = CacheValidationStatus.DoNotTakeFromCache;
                }

                if (resp.LastModified.ToUniversalTime() == CacheEntry.LastModifiedUtc)
                {
                    if (CacheEntry.IsPartialEntry)
                    {
                        // A caller will need to use Validator.CacheEntry.StreamSize to figure out what the restart point is

                        if (resp.ContentLength > 0)
                            this.CacheStreamLength = resp.ContentLength;
                        else
                            this.CacheStreamLength = -1;

                        result = CacheValidationStatus.CombineCachedAndServerResponse;
                    }
                    else if (resp.ContentLength == CacheEntry.StreamSize)
                    {
                        result = CacheValidationStatus.ReturnCachedResponse;
                    }
                    else
                        result = CacheValidationStatus.DoNotTakeFromCache;
                }
                else
                    result = CacheValidationStatus.DoNotTakeFromCache;
            }
            else
            {
                result =  CacheValidationStatus.DoNotTakeFromCache;
            }

            return result;
        }