Fix infinite route-loader spinner from per-navigation root cache inva…

src/modules/app/browser-init.service.spec.ts

@@ -0,0 +1,44 @@
+/**
+ * The contents of this file are subject to the license and copyright
+ * detailed in the LICENSE and NOTICE files at the root of the source
+ * tree and available online at
+ *
+ * http://www.dspace.org/license/
+ */
+import { NavigationStart } from '@angular/router';
+import { Subject } from 'rxjs';
+
+import { BrowserInitService } from './browser-init.service';
+
+describe('BrowserInitService', () => {
+  describe('listenForRouteChanges', () => {
+    let service: BrowserInitService;
+    let rootDataServiceSpy;
+    let routerEvents$: Subject<any>;
+
+    beforeEach(() => {
+      rootDataServiceSpy = jasmine.createSpyObj('rootDataService', ['invalidateRootCache']);
+      routerEvents$ = new Subject();
+
+      service = new BrowserInitService(
+        null, null, null, null, null, null, null, null, null, null, null, null, null, null,
+        rootDataServiceSpy,
+        { events: routerEvents$.asObservable() } as any,
+        null, null, null, null,
+      );
+
+      (service as any).listenForRouteChanges();
+    });
+
+    it('should invalidate the root endpoint cache once, at init', () => {
+      expect(rootDataServiceSpy.invalidateRootCache).toHaveBeenCalledTimes(1);
+    });
+
+    it('should not invalidate the root endpoint cache again on subsequent NavigationStart events', () => {
+      routerEvents$.next(new NavigationStart(1, '/some-route'));
+      routerEvents$.next(new NavigationStart(2, '/another-route'));
+
+      expect(rootDataServiceSpy.invalidateRootCache).toHaveBeenCalledTimes(1);
+    });
+  });
+});

src/modules/app/browser-init.service.ts

@@ -10,10 +10,7 @@ import {
   Injectable,
   TransferState,
 } from '@angular/core';
-import {
-  NavigationStart,
-  Router,
-} from '@angular/router';
+import { Router } from '@angular/router';
 import {
   APP_CONFIG,
   APP_CONFIG_STATE,
@@ -226,21 +223,18 @@ export class BrowserInitService extends InitService {
   }
 
   /**
-   * 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.
+   * Invalidate the cache for the root endpoint once, at startup, so the first request for it
+   * is guaranteed to hit the backend rather than serve a value cached before the app booted.
+   *
+   * This used to also run on every `NavigationStart`, but the root endpoint map does not change
+   * between navigations, so that repeated invalidation was unnecessary. Worse, it could mark the
+   * root request stale while {@link HALEndpointService} was still resolving it for an in-flight
+   * data request; the stale value is filtered out of the endpoint map and the retry for it can
+   * lose the race with the next invalidation, so `getEndpoint()` never resolves and the route
+   * that depends on it never finishes loading.
    */
   protected 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.
     this.rootDataService.invalidateRootCache();
-
-    this.router.events.pipe(
-      filter(event => event instanceof NavigationStart),
-    ).subscribe(() => {
-      this.rootDataService.invalidateRootCache();
-    });
   }
 
 }