fix broken URLs and automate broken URL checks #70

This commit:
- Fixes broken URLs using archive.org or other references.
- Replaces tenforums.com URLs with better documentation as they tend to return HTTP status code 403 to tests and also are low quality source.
- Changes all insecure http sources to https alternatives
- Adds integration tests to check for broken URLs
  - There's logic implemented for having a delay inbetween when sending requests to same domains, however it's not used as the sources can respond to totally parallelized requests.
- Run test pipeline weekly to get notified about broken URls without commits

tests/integration/application/collections/StatusChecker/ExponentialBackOffRetryHandler.ts

@@ -0,0 +1,44 @@
+import { sleepAsync } from '@/infrastructure/Threading/AsyncSleep';
+import { IUrlStatus } from './IUrlStatus';
+
+const DefaultBaseRetryIntervalInMs = 5 /* sec */ * 1000;
+
+export async function retryWithExponentialBackOffAsync(
+    action: () => Promise<IUrlStatus>,
+    baseRetryIntervalInMs: number = DefaultBaseRetryIntervalInMs,
+    currentRetry = 1): Promise<IUrlStatus> {
+    const maxTries: number = 3;
+    const status = await action();
+    if (shouldRetry(status)) {
+        if (currentRetry <= maxTries) {
+            const exponentialBackOffInMs = getRetryTimeoutInMs(currentRetry, baseRetryIntervalInMs);
+            // tslint:disable-next-line: no-console
+            console.log(`Retrying (${currentRetry}) in ${exponentialBackOffInMs / 1000} seconds`, status);
+            await sleepAsync(exponentialBackOffInMs);
+            return retryWithExponentialBackOffAsync(action, baseRetryIntervalInMs, currentRetry + 1);
+        }
+    }
+    return status;
+}
+
+function shouldRetry(status: IUrlStatus) {
+    if (status.error) {
+        return true;
+    }
+    return isTransientError(status.statusCode)
+        || status.statusCode === 429; // Too Many Requests
+}
+
+function isTransientError(statusCode: number) {
+    return statusCode >= 500 && statusCode <= 599;
+}
+
+function getRetryTimeoutInMs(currentRetry: number, baseRetryIntervalInMs: number = DefaultBaseRetryIntervalInMs) {
+    const retryRandomFactor = 0.5;  // Retry intervals are between 50% and 150%
+                                    // of the exponentially increasing base amount
+    const minRandom = 1 - retryRandomFactor;
+    const maxRandom = 1 + retryRandomFactor;
+    const randomization = (Math.random() * (maxRandom - minRandom)) + maxRandom;
+    const exponential = Math.pow(2, currentRetry - 1);
+    return Math.ceil(exponential * baseRetryIntervalInMs * randomization);
+}