Merge remote-tracking branch 'origin/main' into more-eslint

src/app/core/server-check/server-check.guard.ts

@@ -2,13 +2,16 @@ import { Injectable } from '@angular/core';
 import {
   ActivatedRouteSnapshot,
   CanActivateChild,
+  NavigationStart,
   Router,
   RouterStateSnapshot,
+  UrlTree,
 } from '@angular/router';
 import { Observable } from 'rxjs';
 import {
+  filter,
+  map,
   take,
-  tap,
 } from 'rxjs/operators';
 
 import { getPageInternalServerErrorRoute } from '../../app-routing-paths';
@@ -30,17 +33,38 @@ export class ServerCheckGuard implements CanActivateChild {
    */
   canActivateChild(
     route: ActivatedRouteSnapshot,
-    state: RouterStateSnapshot): Observable<boolean> {
+    state: RouterStateSnapshot,
+  ): Observable<boolean | UrlTree> {
 
     return this.rootDataService.checkServerAvailability().pipe(
       take(1),
-      tap((isAvailable: boolean) => {
+      map((isAvailable: boolean) => {
         if (!isAvailable) {
-          this.rootDataService.invalidateRootCache();
-          this.router.navigateByUrl(getPageInternalServerErrorRoute());
+          return this.router.parseUrl(getPageInternalServerErrorRoute());
+        } else {
+          return true;
         }
       }),
     );
+  }
 
+  /**
+   * Listen to all router events. Every time a new navigation starts, invalidate the cache
+   * for the root endpoint. That way we retrieve it once per routing operation to ensure the
+   * backend is not down. But if the guard is called multiple times during the same routing
+   * operation, the cached version is used.
+   */
+  listenForRouteChanges(): void {
+    // we'll always be too late for the first NavigationStart event with the router subscribe below,
+    // so this statement is for the very first route operation. A `find` without using the cache,
+    // rather than an invalidateRootCache, because invalidating as the app is bootstrapping can
+    // break other features
+    this.rootDataService.findRoot(false);
+
+    this.router.events.pipe(
+      filter(event => event instanceof NavigationStart),
+    ).subscribe(() => {
+      this.rootDataService.invalidateRootCache();
+    });
   }
 }