protected override async Task Invoke()

in Source/NuGetGallery.Monitoring/HttpMonitor.cs [104:175]
54 lines of code
14 McCabe index (conditional complexity)

        protected override async Task Invoke()
        {
            FlushDnsCache();

            ServicePointManager.DnsRefreshTimeout = 0;
            if (CheckCertificate)
            {
                ServicePointManager.ServerCertificateValidationCallback = CertificateValidationCallBack;
            }

            // Try once with a short timeout, we definitely should be able to get there in ExpectedTimeout
            var requestResult = await MakeSingleRequest(Url, Method, timeout: ExpectedTimeout);
            if (requestResult.IsSuccess && IsSuccessfulResponse(requestResult, ExpectedStatusCode))
            {
                return;
            }

            // Try the known good site
            if (CheckKnownGoodSite)
            {
                var knownGoodResult = await MakeSingleRequest(KnownGoodSite, "GET", timeout: ExpectedTimeout);
                if (!knownGoodResult.IsSuccess || !IsSuccessfulResponse(knownGoodResult, HttpStatusCode.OK))
                {
                    // We can't reach the known-good site either. Report a monitor failure
                    MonitorFailure(String.Format("Failed to reach {0}, but couldn't reach {1} either. Network issues at monitor.",
                        Url.AbsoluteUri,
                        KnownGoodSite.AbsoluteUri));
                }
                else
                {
                    // We reached the known good site.
                    Unhealthy(String.Format("Failed to reach {0} in {1}ms. Still confirming failure.", Url.AbsoluteUri, ExpectedTimeout));
                }
            }

            // If we get here, we failed the initial attempt, try a longer timeout and multiple attempts
            requestResult = await MakeMultipleRequests(Url, Method, NumberOfAttempts, timeout: MaximumTimeout);
            if (requestResult.IsSuccess && IsSuccessfulResponse(requestResult, ExpectedStatusCode))
            {
                Degraded(String.Format("Reached {0} in {1:N2}ms. However, we failed to reach it in the expected time, so this may indicate a potential failure.", Url.AbsoluteUri, requestResult.Time.TotalMilliseconds));
                return;
            }

            // Failed after multiple attempts, check the known good site with a longer timeout.
            if (CheckKnownGoodSite)
            {
                // Check a known good site
                var timing = await MakeSingleRequest(KnownGoodSite, "GET", timeout: MaximumTimeout); // If we can't reach it in MaximumTimeout, the monitor is really hosed
                if (!timing.IsSuccess || !IsSuccessfulResponse(timing, HttpStatusCode.OK))
                {
                    // We can't reach the known-good site either. Report a monitor failure
                    MonitorFailure(String.Format("Failed to reach {0}, but couldn't reach {1} either. Network issues at monitor.",
                        Url.AbsoluteUri,
                        KnownGoodSite.AbsoluteUri));
                    return;
                }
                else
                {
                    // Reached the known good site. Try the target one last time
                    requestResult = await MakeMultipleRequests(Url, Method, NumberOfAttempts, timeout: MaximumTimeout);
                }
            }

            // Final check
            if (requestResult.IsSuccess && IsSuccessfulResponse(requestResult, ExpectedStatusCode))
            {
                return;
            }

            // Phew, we're really sure we can't reach the target now
            await ReportFailure(requestResult);
        }