From 0fe33eecd1dedd56faedb43010c55a517c975f7e Mon Sep 17 00:00:00 2001
From: Tim Donohue <tim.donohue@lyrasis.org>
Date: Wed, 21 Jun 2023 15:36:59 -0500
Subject: [PATCH] Implement basic 301 Redirect when SSR is used.

---
 .../core/data/dso-redirect.service.spec.ts    | 24 +++++++++++++++++++
 src/app/core/data/dso-redirect.service.ts     | 21 +++++++++++++---
 2 files changed, 42 insertions(+), 3 deletions(-)

diff --git a/src/app/core/data/dso-redirect.service.spec.ts b/src/app/core/data/dso-redirect.service.spec.ts
index ca064b5608..64fbd94367 100644
--- a/src/app/core/data/dso-redirect.service.spec.ts
+++ b/src/app/core/data/dso-redirect.service.spec.ts
@@ -27,6 +27,9 @@ describe('DsoRedirectService', () => {
   const requestUUIDURL = `https://rest.api/rest/api/pid/find?id=${dsoUUID}`;
   const requestUUID = '34cfed7c-f597-49ef-9cbe-ea351f0023c2';
   const objectCache = {} as ObjectCacheService;
+  const mockResponse = jasmine.createSpyObj(['redirect']);
+  const mockPlatformBrowser = 'browser';
+  const mockPlatformServer = 'server';
 
   beforeEach(() => {
     scheduler = getTestScheduler();
@@ -58,6 +61,8 @@ describe('DsoRedirectService', () => {
       objectCache,
       halService,
       router,
+      mockResponse,
+      mockPlatformBrowser  // default to CSR except where explicitly SSR below
     );
   });
 
@@ -141,6 +146,25 @@ describe('DsoRedirectService', () => {
       scheduler.flush();
       expect(router.navigate).toHaveBeenCalledWith(['/communities/' + remoteData.payload.uuid]);
     });
+
+    it('should return 301 redirect when SSR is used', () => {
+      service = new DsoRedirectService(
+        requestService,
+        rdbService,
+        objectCache,
+        halService,
+        router,
+        mockResponse,
+        mockPlatformServer  // explicitly SSR mode
+      );
+      remoteData.payload.type = 'item';
+      const redir = service.findByIdAndIDType(dsoHandle, IdentifierType.HANDLE);
+      // The framework would normally subscribe but do it here so we can test navigation.
+      redir.subscribe();
+      scheduler.schedule(() => redir);
+      scheduler.flush();
+      expect(mockResponse.redirect).toHaveBeenCalledWith(301, '/items/' + remoteData.payload.uuid);
+    });
   });
 
   describe('DataService', () => {  // todo: should only test the id/uuid interpolation thingy
diff --git a/src/app/core/data/dso-redirect.service.ts b/src/app/core/data/dso-redirect.service.ts
index 81ce678e43..9b87590f7e 100644
--- a/src/app/core/data/dso-redirect.service.ts
+++ b/src/app/core/data/dso-redirect.service.ts
@@ -6,7 +6,7 @@
  * http://www.dspace.org/license/
  */
 /* eslint-disable max-classes-per-file */
-import { Injectable } from '@angular/core';
+import { Inject, Injectable, Optional, PLATFORM_ID } from '@angular/core';
 import { Router } from '@angular/router';
 import { Observable } from 'rxjs';
 import { tap } from 'rxjs/operators';
@@ -21,6 +21,8 @@ import { getFirstCompletedRemoteData } from '../shared/operators';
 import { DSpaceObject } from '../shared/dspace-object.model';
 import { IdentifiableDataService } from './base/identifiable-data.service';
 import { getDSORoute } from '../../app-routing-paths';
+import { RESPONSE } from '@nguniversal/express-engine/tokens';
+import { isPlatformServer } from '@angular/common';
 
 const ID_ENDPOINT = 'pid';
 const UUID_ENDPOINT = 'dso';
@@ -75,12 +77,20 @@ export class DsoRedirectService {
     protected objectCache: ObjectCacheService,
     protected halService: HALEndpointService,
     private router: Router,
+    @Optional() @Inject(RESPONSE) private response: any,
+    @Inject(PLATFORM_ID) private platformId: any
   ) {
     this.dataService = new DsoByIdOrUUIDDataService(requestService, rdbService, objectCache, halService);
   }
 
   /**
-   * Retrieve a DSpaceObject by
+   * Redirect to a DSpaceObject's path using the given identifier type and ID.
+   * This is used to redirect paths like "/handle/[prefix]/[suffix]" to the object's path (e.g. /items/[uuid]).
+   * See LookupGuard for more examples.
+   *
+   * If this is called server side (via SSR), it performs a 301 Redirect.
+   * If this is called client side (via CSR), it simply uses the Angular router to do the redirect.
+   *
    * @param id              the identifier of the object to retrieve
    * @param identifierType  the type of the given identifier (defaults to UUID)
    */
@@ -94,7 +104,12 @@ export class DsoRedirectService {
           if (hasValue(dso.uuid)) {
             let newRoute = getDSORoute(dso);
             if (hasValue(newRoute)) {
-              this.router.navigate([newRoute]);
+              // If running via SSR, perform a "301 Moved Permanently" redirect for SEO purposes.
+              if (isPlatformServer(this.platformId)) {
+                this.response.redirect(301, newRoute);
+              } else {
+                this.router.navigate([newRoute]);
+              }
             }
           }
         }