Merge pull request #2248 from 4Science/feature/CST-5729

Implement Signposting on angular side

server.ts

@@ -26,7 +26,6 @@ import * as ejs from 'ejs';
 import * as compression from 'compression';
 import * as expressStaticGzip from 'express-static-gzip';
 /* eslint-enable import/no-namespace */
-
 import axios from 'axios';
 import LRU from 'lru-cache';
 import isbot from 'isbot';
@@ -34,7 +33,7 @@ import { createCertificate } from 'pem';
 import { createServer } from 'https';
 import { json } from 'body-parser';
 
-import { existsSync, readFileSync } from 'fs';
+import { readFileSync } from 'fs';
 import { join } from 'path';
 
 import { enableProdMode } from '@angular/core';
@@ -180,6 +179,15 @@ export function app() {
     changeOrigin: true
   }));
 
+  /**
+   * Proxy the linksets
+   */
+  router.use('/signposting**', createProxyMiddleware({
+    target: `${environment.rest.baseUrl}`,
+    pathRewrite: path => path.replace(environment.ui.nameSpace, '/'),
+    changeOrigin: true
+  }));
+
   /**
    * Checks if the rateLimiter property is present
    * When it is present, the rateLimiter will be enabled. When it is undefined, the rateLimiter will be disabled.

src/app/bitstream-page/bitstream-download-page/bitstream-download-page.component.spec.ts

@@ -11,6 +11,9 @@ import { ActivatedRoute, Router } from '@angular/router';
 import { getForbiddenRoute } from '../../app-routing-paths';
 import { TranslateModule } from '@ngx-translate/core';
 import { CommonModule } from '@angular/common';
+import { SignpostingDataService } from '../../core/data/signposting-data.service';
+import { ServerResponseService } from '../../core/services/server-response.service';
+import { PLATFORM_ID } from '@angular/core';
 
 describe('BitstreamDownloadPageComponent', () => {
   let component: BitstreamDownloadPageComponent;
@@ -24,6 +27,20 @@ describe('BitstreamDownloadPageComponent', () => {
   let router;
 
   let bitstream: Bitstream;
+  let serverResponseService: jasmine.SpyObj<ServerResponseService>;
+  let signpostingDataService: jasmine.SpyObj<SignpostingDataService>;
+
+  const mocklink = {
+    href: 'http://test.org',
+    rel: 'test',
+    type: 'test'
+  };
+
+  const mocklink2 = {
+    href: 'http://test2.org',
+    rel: 'test',
+    type: 'test'
+  };
 
   function init() {
     authService = jasmine.createSpyObj('authService', {
@@ -44,8 +61,8 @@ describe('BitstreamDownloadPageComponent', () => {
     bitstream = Object.assign(new Bitstream(), {
       uuid: 'bitstreamUuid',
       _links: {
-        content: {href: 'bitstream-content-link'},
+        content: { href: 'bitstream-content-link' },
-        self: {href: 'bitstream-self-link'},
+        self: { href: 'bitstream-self-link' },
       }
     });
 
@@ -54,10 +71,21 @@ describe('BitstreamDownloadPageComponent', () => {
         bitstream: createSuccessfulRemoteDataObject(
           bitstream
         )
+      }),
+      params: observableOf({
+        id: 'testid'
       })
     };
 
     router = jasmine.createSpyObj('router', ['navigateByUrl']);
+
+    serverResponseService = jasmine.createSpyObj('ServerResponseService', {
+      setHeader: jasmine.createSpy('setHeader'),
+    });
+
+    signpostingDataService = jasmine.createSpyObj('SignpostingDataService', {
+      getLinks: observableOf([mocklink, mocklink2])
+    });
   }
 
   function initTestbed() {
@@ -65,12 +93,15 @@ describe('BitstreamDownloadPageComponent', () => {
       imports: [CommonModule, TranslateModule.forRoot()],
       declarations: [BitstreamDownloadPageComponent],
       providers: [
-        {provide: ActivatedRoute, useValue: activatedRoute},
+        { provide: ActivatedRoute, useValue: activatedRoute },
-        {provide: Router, useValue: router},
+        { provide: Router, useValue: router },
-        {provide: AuthorizationDataService, useValue: authorizationService},
+        { provide: AuthorizationDataService, useValue: authorizationService },
-        {provide: AuthService, useValue: authService},
+        { provide: AuthService, useValue: authService },
-        {provide: FileService, useValue: fileService},
+        { provide: FileService, useValue: fileService },
-        {provide: HardRedirectService, useValue: hardRedirectService},
+        { provide: HardRedirectService, useValue: hardRedirectService },
+        { provide: ServerResponseService, useValue: serverResponseService },
+        { provide: SignpostingDataService, useValue: signpostingDataService },
+        { provide: PLATFORM_ID, useValue: 'server' }
       ]
     })
       .compileComponents();
@@ -107,6 +138,9 @@ describe('BitstreamDownloadPageComponent', () => {
       it('should redirect to the content link', () => {
         expect(hardRedirectService.redirect).toHaveBeenCalledWith('bitstream-content-link');
       });
+      it('should add the signposting links', () => {
+        expect(serverResponseService.setHeader).toHaveBeenCalled();
+      });
     });
     describe('when the user is authorized and logged in', () => {
       beforeEach(waitForAsync(() => {
@@ -134,7 +168,7 @@ describe('BitstreamDownloadPageComponent', () => {
         fixture.detectChanges();
       });
       it('should navigate to the forbidden route', () => {
-        expect(router.navigateByUrl).toHaveBeenCalledWith(getForbiddenRoute(), {skipLocationChange: true});
+        expect(router.navigateByUrl).toHaveBeenCalledWith(getForbiddenRoute(), { skipLocationChange: true });
       });
     });
     describe('when the user is not authorized and not logged in', () => {

src/app/bitstream-page/bitstream-download-page/bitstream-download-page.component.ts

@@ -1,8 +1,8 @@
-import { Component, OnInit } from '@angular/core';
+import { Component, Inject, OnInit, PLATFORM_ID } from '@angular/core';
 import { filter, map, switchMap, take } from 'rxjs/operators';
 import { ActivatedRoute, Router } from '@angular/router';
 import { hasValue, isNotEmpty } from '../../shared/empty.util';
-import { getRemoteDataPayload} from '../../core/shared/operators';
+import { getRemoteDataPayload } from '../../core/shared/operators';
 import { Bitstream } from '../../core/shared/bitstream.model';
 import { AuthorizationDataService } from '../../core/data/feature-authorization/authorization-data.service';
 import { FeatureID } from '../../core/data/feature-authorization/feature-id';
@@ -13,8 +13,11 @@ import { HardRedirectService } from '../../core/services/hard-redirect.service';
 import { getForbiddenRoute } from '../../app-routing-paths';
 import { RemoteData } from '../../core/data/remote-data';
 import { redirectOn4xx } from '../../core/shared/authorized.operators';
-import { Location } from '@angular/common';
+import { isPlatformServer, Location } from '@angular/common';
 import { DSONameService } from '../../core/breadcrumbs/dso-name.service';
+import { SignpostingDataService } from '../../core/data/signposting-data.service';
+import { ServerResponseService } from '../../core/services/server-response.service';
+import { SignpostingLink } from '../../core/data/signposting-links.model';
 
 @Component({
   selector: 'ds-bitstream-download-page',
@@ -28,7 +31,6 @@ export class BitstreamDownloadPageComponent implements OnInit {
   bitstream$: Observable<Bitstream>;
   bitstreamRD$: Observable<RemoteData<Bitstream>>;
 
-
   constructor(
     private route: ActivatedRoute,
     protected router: Router,
@@ -38,8 +40,11 @@ export class BitstreamDownloadPageComponent implements OnInit {
     private hardRedirectService: HardRedirectService,
     private location: Location,
     public dsoNameService: DSONameService,
+    private signpostingDataService: SignpostingDataService,
+    private responseService: ServerResponseService,
+    @Inject(PLATFORM_ID) protected platformId: string
   ) {
-
+    this.initPageLinks();
   }
 
   back(): void {
@@ -89,4 +94,26 @@ export class BitstreamDownloadPageComponent implements OnInit {
       }
     });
   }
+
+  /**
+   * Create page links if any are retrieved by signposting endpoint
+   *
+   * @private
+   */
+  private initPageLinks(): void {
+    if (isPlatformServer(this.platformId)) {
+      this.route.params.subscribe(params => {
+        this.signpostingDataService.getLinks(params.id).pipe(take(1)).subscribe((signpostingLinks: SignpostingLink[]) => {
+          let links = '';
+
+          signpostingLinks.forEach((link: SignpostingLink) => {
+            links = links + (isNotEmpty(links) ? ', ' : '') + `<${link.href}> ; rel="${link.rel}"` + (isNotEmpty(link.type) ? ` ; type="${link.type}" ` : ' ');
+            links = links + (isNotEmpty(links) ? ', ' : '') + `<${link.href}> ; rel="${link.rel}" ; type="${link.type}" `;
+          });
+
+          this.responseService.setHeader('Link', links);
+        });
+      });
+    }
+  }
 }

src/app/core/data/signposting-data.service.spec.ts

@@ -0,0 +1,97 @@
+import { fakeAsync, TestBed, tick } from '@angular/core/testing';
+import { SignpostingDataService } from './signposting-data.service';
+import { DspaceRestService } from '../dspace-rest/dspace-rest.service';
+import { HALEndpointService } from '../shared/hal-endpoint.service';
+import { of } from 'rxjs';
+import { SignpostingLink } from './signposting-links.model';
+
+describe('SignpostingDataService', () => {
+  let service: SignpostingDataService;
+  let restServiceSpy: jasmine.SpyObj<DspaceRestService>;
+  let halServiceSpy: jasmine.SpyObj<HALEndpointService>;
+  const mocklink = {
+    href: 'http://test.org',
+    rel: 'test',
+    type: 'test'
+  };
+
+  const mocklink2 = {
+    href: 'http://test2.org',
+    rel: 'test',
+    type: 'test'
+  };
+
+  const mockResponse: any = {
+    statusCode: 200,
+    payload: [mocklink, mocklink2]
+  };
+
+  const mockErrResponse: any = {
+    statusCode: 500
+  };
+
+  beforeEach(() => {
+    const restSpy = jasmine.createSpyObj('DspaceRestService', ['get', 'getWithHeaders']);
+    const halSpy = jasmine.createSpyObj('HALEndpointService', ['getRootHref']);
+
+    TestBed.configureTestingModule({
+      providers: [
+        SignpostingDataService,
+        { provide: DspaceRestService, useValue: restSpy },
+        { provide: HALEndpointService, useValue: halSpy }
+      ]
+    });
+
+    service = TestBed.inject(SignpostingDataService);
+    restServiceSpy = TestBed.inject(DspaceRestService) as jasmine.SpyObj<DspaceRestService>;
+    halServiceSpy = TestBed.inject(HALEndpointService) as jasmine.SpyObj<HALEndpointService>;
+  });
+
+  it('should be created', () => {
+    expect(service).toBeTruthy();
+  });
+
+  it('should return signposting links', fakeAsync(() => {
+    const uuid = '123';
+    const baseUrl = 'http://localhost:8080';
+
+    halServiceSpy.getRootHref.and.returnValue(`${baseUrl}/api`);
+
+    restServiceSpy.get.and.returnValue(of(mockResponse));
+
+    let result: SignpostingLink[];
+
+    const expectedResult: SignpostingLink[] = [mocklink, mocklink2];
+
+    service.getLinks(uuid).subscribe((links) => {
+      result = links;
+    });
+
+    tick();
+
+    expect(result).toEqual(expectedResult);
+    expect(halServiceSpy.getRootHref).toHaveBeenCalled();
+    expect(restServiceSpy.get).toHaveBeenCalledWith(`${baseUrl}/signposting/links/${uuid}`);
+  }));
+
+  it('should handle error and return an empty array', fakeAsync(() => {
+    const uuid = '123';
+    const baseUrl = 'http://localhost:8080';
+
+    halServiceSpy.getRootHref.and.returnValue(`${baseUrl}/api`);
+
+    restServiceSpy.get.and.returnValue(of(mockErrResponse));
+
+    let result: any;
+
+    service.getLinks(uuid).subscribe((data) => {
+      result = data;
+    });
+
+    tick();
+
+    expect(result).toEqual([]);
+    expect(halServiceSpy.getRootHref).toHaveBeenCalled();
+    expect(restServiceSpy.get).toHaveBeenCalledWith(`${baseUrl}/signposting/links/${uuid}`);
+  }));
+});

src/app/core/data/signposting-data.service.ts

@@ -0,0 +1,38 @@
+import { Injectable } from '@angular/core';
+
+import { catchError, map } from 'rxjs/operators';
+import { Observable, of as observableOf } from 'rxjs';
+
+import { DspaceRestService } from '../dspace-rest/dspace-rest.service';
+import { HALEndpointService } from '../shared/hal-endpoint.service';
+import { RawRestResponse } from '../dspace-rest/raw-rest-response.model';
+import { SignpostingLink } from './signposting-links.model';
+
+/**
+ * Service responsible for handling requests related to the Signposting endpoint
+ */
+@Injectable({
+  providedIn: 'root'
+})
+export class SignpostingDataService {
+
+  constructor(private restService: DspaceRestService, protected halService: HALEndpointService) {
+  }
+
+  /**
+   * Retrieve the list of signposting links related to the given resource's id
+   *
+   * @param uuid
+   */
+  getLinks(uuid: string): Observable<SignpostingLink[]> {
+    const baseUrl = this.halService.getRootHref().replace('/api', '');
+
+    return this.restService.get(`${baseUrl}/signposting/links/${uuid}`).pipe(
+      catchError((err) => {
+        return observableOf([]);
+      }),
+      map((res: RawRestResponse) => res.statusCode === 200 ? res.payload as SignpostingLink[] : [])
+    );
+  }
+
+}

src/app/core/data/signposting-links.model.ts

@@ -0,0 +1,8 @@
+/**
+ * Represents the link object received by the signposting endpoint
+ */
+export interface SignpostingLink {
+    href?: string,
+    rel?: string,
+    type?: string
+}

src/app/core/services/server-hard-redirect.service.ts

@@ -46,6 +46,7 @@ export class ServerHardRedirectService extends HardRedirectService {
       }
 
       console.log(`Redirecting from ${this.req.url} to ${url} with ${status}`);
+
       this.res.redirect(status, url);
       this.res.end();
       // I haven't found a way to correctly stop Angular rendering.

src/app/core/services/server-response.service.ts

@@ -1,7 +1,11 @@
 import { RESPONSE } from '@nguniversal/express-engine/tokens';
 import { Inject, Injectable, Optional } from '@angular/core';
+
 import { Response } from 'express';
 
+/**
+ * Service responsible to provide method to manage the response object
+ */
 @Injectable()
 export class ServerResponseService {
   private response: Response;
@@ -10,6 +14,12 @@ export class ServerResponseService {
     this.response = response;
   }
 
+  /**
+   * Set a status code to response
+   *
+   * @param code
+   * @param message
+   */
   setStatus(code: number, message?: string): this {
     if (this.response) {
       this.response.statusCode = code;
@@ -20,19 +30,51 @@ export class ServerResponseService {
     return this;
   }
 
+  /**
+   * Set Unauthorized status
+   *
+   *  @param message
+   */
   setUnauthorized(message = 'Unauthorized'): this {
     return this.setStatus(401, message);
   }
 
+  /**
+   * Set Forbidden status
+   *
+   *  @param message
+   */
   setForbidden(message = 'Forbidden'): this {
     return this.setStatus(403, message);
   }
 
+  /**
+   * Set Not found status
+   *
+   *  @param message
+   */
   setNotFound(message = 'Not found'): this {
     return this.setStatus(404, message);
   }
 
+  /**
+   * Set Internal Server Error status
+   *
+   *  @param message
+   */
   setInternalServerError(message = 'Internal Server Error'): this {
     return this.setStatus(500, message);
   }
+
+  /**
+   * Set a response's header
+   *
+   * @param header
+   * @param content
+   */
+  setHeader(header: string, content: string) {
+    if (this.response) {
+      this.response.setHeader(header, content);
+    }
+  }
 }

src/app/item-page/full/full-item-page.component.spec.ts

@@ -2,7 +2,7 @@ import { ComponentFixture, fakeAsync, TestBed, waitForAsync } from '@angular/cor
 import { ItemDataService } from '../../core/data/item-data.service';
 import { TranslateLoader, TranslateModule } from '@ngx-translate/core';
 import { TranslateLoaderMock } from '../../shared/mocks/translate-loader.mock';
-import { ChangeDetectionStrategy, NO_ERRORS_SCHEMA } from '@angular/core';
+import { ChangeDetectionStrategy, NO_ERRORS_SCHEMA, PLATFORM_ID } from '@angular/core';
 import { TruncatePipe } from '../../shared/utils/truncate.pipe';
 import { FullItemPageComponent } from './full-item-page.component';
 import { MetadataService } from '../../core/metadata/metadata.service';
@@ -20,6 +20,9 @@ import { createPaginatedList } from '../../shared/testing/utils.test';
 import { AuthorizationDataService } from '../../core/data/feature-authorization/authorization-data.service';
 import { createRelationshipsObservable } from '../simple/item-types/shared/item.component.spec';
 import { RemoteData } from '../../core/data/remote-data';
+import { ServerResponseService } from '../../core/services/server-response.service';
+import { SignpostingDataService } from '../../core/data/signposting-data.service';
+import { LinkHeadService } from '../../core/services/link-head.service';
 
 const mockItem: Item = Object.assign(new Item(), {
   bundles: createSuccessfulRemoteDataObject$(createPaginatedList([])),
@@ -55,8 +58,21 @@ describe('FullItemPageComponent', () => {
   let routeStub: ActivatedRouteStub;
   let routeData;
   let authorizationDataService: AuthorizationDataService;
+  let serverResponseService: jasmine.SpyObj<ServerResponseService>;
+  let signpostingDataService: jasmine.SpyObj<SignpostingDataService>;
+  let linkHeadService: jasmine.SpyObj<LinkHeadService>;
 
+  const mocklink = {
+    href: 'http://test.org',
+    rel: 'test',
+    type: 'test'
+  };
 
+  const mocklink2 = {
+    href: 'http://test2.org',
+    rel: 'test',
+    type: 'test'
+  };
 
   beforeEach(waitForAsync(() => {
     authService = jasmine.createSpyObj('authService', {
@@ -76,6 +92,19 @@ describe('FullItemPageComponent', () => {
       isAuthorized: observableOf(false),
     });
 
+    serverResponseService = jasmine.createSpyObj('ServerResponseService', {
+      setHeader: jasmine.createSpy('setHeader'),
+    });
+
+    signpostingDataService = jasmine.createSpyObj('SignpostingDataService', {
+      getLinks: observableOf([mocklink, mocklink2]),
+    });
+
+    linkHeadService = jasmine.createSpyObj('LinkHeadService', {
+      addTag: jasmine.createSpy('setHeader'),
+      removeTag: jasmine.createSpy('removeTag'),
+    });
+
     TestBed.configureTestingModule({
       imports: [TranslateModule.forRoot({
         loader: {
@@ -90,8 +119,11 @@ describe('FullItemPageComponent', () => {
         { provide: MetadataService, useValue: metadataServiceStub },
         { provide: AuthService, useValue: authService },
         { provide: AuthorizationDataService, useValue: authorizationDataService },
+        { provide: ServerResponseService, useValue: serverResponseService },
+        { provide: SignpostingDataService, useValue: signpostingDataService },
+        { provide: LinkHeadService, useValue: linkHeadService },
+        { provide: PLATFORM_ID, useValue: 'server' }
       ],
-
       schemas: [NO_ERRORS_SCHEMA]
     }).overrideComponent(FullItemPageComponent, {
       set: { changeDetection: ChangeDetectionStrategy.Default }
@@ -143,6 +175,11 @@ describe('FullItemPageComponent', () => {
       const objectLoader = fixture.debugElement.query(By.css('.full-item-info'));
       expect(objectLoader.nativeElement).not.toBeNull();
     });
+
+    it('should add the signposting links', () => {
+      expect(serverResponseService.setHeader).toHaveBeenCalled();
+      expect(linkHeadService.addTag).toHaveBeenCalledTimes(2);
+    });
   });
   describe('when the item is withdrawn and the user is not an admin', () => {
     beforeEach(() => {
@@ -167,6 +204,11 @@ describe('FullItemPageComponent', () => {
       const objectLoader = fixture.debugElement.query(By.css('.full-item-info'));
       expect(objectLoader).not.toBeNull();
     });
+
+    it('should add the signposting links', () => {
+      expect(serverResponseService.setHeader).toHaveBeenCalled();
+      expect(linkHeadService.addTag).toHaveBeenCalledTimes(2);
+    });
   });
 
   describe('when the item is not withdrawn and the user is not an admin', () => {
@@ -179,5 +221,10 @@ describe('FullItemPageComponent', () => {
       const objectLoader = fixture.debugElement.query(By.css('.full-item-info'));
       expect(objectLoader).not.toBeNull();
     });
+
+    it('should add the signposting links', () => {
+      expect(serverResponseService.setHeader).toHaveBeenCalled();
+      expect(linkHeadService.addTag).toHaveBeenCalledTimes(2);
+    });
   });
 });

src/app/item-page/full/full-item-page.component.ts

@@ -1,5 +1,5 @@
 import { filter, map } from 'rxjs/operators';
-import { ChangeDetectionStrategy, Component, OnDestroy, OnInit } from '@angular/core';
+import { ChangeDetectionStrategy, Component, Inject, OnDestroy, OnInit, PLATFORM_ID } from '@angular/core';
 import { ActivatedRoute, Data, Router } from '@angular/router';
 
 import { BehaviorSubject, Observable } from 'rxjs';
@@ -16,7 +16,9 @@ import { hasValue } from '../../shared/empty.util';
 import { AuthService } from '../../core/auth/auth.service';
 import { Location } from '@angular/common';
 import { AuthorizationDataService } from '../../core/data/feature-authorization/authorization-data.service';
-
+import { ServerResponseService } from '../../core/services/server-response.service';
+import { SignpostingDataService } from '../../core/data/signposting-data.service';
+import { LinkHeadService } from '../../core/services/link-head.service';
 
 /**
  * This component renders a full item page.
@@ -43,13 +45,19 @@ export class FullItemPageComponent extends ItemPageComponent implements OnInit,
 
   subs = [];
 
-  constructor(protected route: ActivatedRoute,
+  constructor(
-              router: Router,
+    protected route: ActivatedRoute,
-              items: ItemDataService,
+    protected router: Router,
-              authService: AuthService,
+    protected items: ItemDataService,
-              authorizationService: AuthorizationDataService,
+    protected authService: AuthService,
-              private _location: Location) {
+    protected authorizationService: AuthorizationDataService,
-    super(route, router, items, authService, authorizationService);
+    protected _location: Location,
+    protected responseService: ServerResponseService,
+    protected signpostingDataService: SignpostingDataService,
+    protected linkHeadService: LinkHeadService,
+    @Inject(PLATFORM_ID) protected platformId: string,
+  ) {
+    super(route, router, items, authService, authorizationService, responseService, signpostingDataService, linkHeadService, platformId);
   }
 
   /*** AoT inheritance fix, will hopefully be resolved in the near future **/

src/app/item-page/simple/item-page.component.spec.ts

@@ -2,7 +2,7 @@ import { ComponentFixture, TestBed, waitForAsync } from '@angular/core/testing';
 import { TranslateLoader, TranslateModule } from '@ngx-translate/core';
 import { TranslateLoaderMock } from '../../shared/mocks/translate-loader.mock';
 import { ItemDataService } from '../../core/data/item-data.service';
-import { ChangeDetectionStrategy, NO_ERRORS_SCHEMA } from '@angular/core';
+import { ChangeDetectionStrategy, NO_ERRORS_SCHEMA, PLATFORM_ID } from '@angular/core';
 import { ItemPageComponent } from './item-page.component';
 import { ActivatedRoute, Router } from '@angular/router';
 import { ActivatedRouteStub } from '../../shared/testing/active-router.stub';
@@ -22,6 +22,10 @@ import {
 import { AuthService } from '../../core/auth/auth.service';
 import { createPaginatedList } from '../../shared/testing/utils.test';
 import { AuthorizationDataService } from '../../core/data/feature-authorization/authorization-data.service';
+import { ServerResponseService } from '../../core/services/server-response.service';
+import { SignpostingDataService } from '../../core/data/signposting-data.service';
+import { LinkDefinition, LinkHeadService } from '../../core/services/link-head.service';
+import { SignpostingLink } from '../../core/data/signposting-links.model';
 
 const mockItem: Item = Object.assign(new Item(), {
   bundles: createSuccessfulRemoteDataObject$(createPaginatedList([])),
@@ -36,11 +40,28 @@ const mockWithdrawnItem: Item = Object.assign(new Item(), {
   isWithdrawn: true
 });
 
+const mocklink = {
+  href: 'http://test.org',
+  rel: 'rel1',
+  type: 'type1'
+};
+
+const mocklink2 = {
+  href: 'http://test2.org',
+  rel: 'rel2',
+  type: undefined
+};
+
+const mockSignpostingLinks: SignpostingLink[] = [mocklink, mocklink2];
+
 describe('ItemPageComponent', () => {
   let comp: ItemPageComponent;
   let fixture: ComponentFixture<ItemPageComponent>;
   let authService: AuthService;
   let authorizationDataService: AuthorizationDataService;
+  let serverResponseService: jasmine.SpyObj<ServerResponseService>;
+  let signpostingDataService: jasmine.SpyObj<SignpostingDataService>;
+  let linkHeadService: jasmine.SpyObj<LinkHeadService>;
 
   const mockMetadataService = {
     /* eslint-disable no-empty,@typescript-eslint/no-empty-function */
@@ -60,6 +81,18 @@ describe('ItemPageComponent', () => {
     authorizationDataService = jasmine.createSpyObj('authorizationDataService', {
       isAuthorized: observableOf(false),
     });
+    serverResponseService = jasmine.createSpyObj('ServerResponseService', {
+      setHeader: jasmine.createSpy('setHeader'),
+    });
+
+    signpostingDataService = jasmine.createSpyObj('SignpostingDataService', {
+      getLinks: observableOf([mocklink, mocklink2]),
+    });
+
+    linkHeadService = jasmine.createSpyObj('LinkHeadService', {
+      addTag: jasmine.createSpy('setHeader'),
+      removeTag: jasmine.createSpy('removeTag'),
+    });
 
     TestBed.configureTestingModule({
       imports: [TranslateModule.forRoot({
@@ -76,6 +109,10 @@ describe('ItemPageComponent', () => {
         { provide: Router, useValue: {} },
         { provide: AuthService, useValue: authService },
         { provide: AuthorizationDataService, useValue: authorizationDataService },
+        { provide: ServerResponseService, useValue: serverResponseService },
+        { provide: SignpostingDataService, useValue: signpostingDataService },
+        { provide: LinkHeadService, useValue: linkHeadService },
+        { provide: PLATFORM_ID, useValue: 'server' },
       ],
 
       schemas: [NO_ERRORS_SCHEMA]
@@ -126,6 +163,33 @@ describe('ItemPageComponent', () => {
       const objectLoader = fixture.debugElement.query(By.css('ds-listable-object-component-loader'));
       expect(objectLoader.nativeElement).toBeDefined();
     });
+
+    it('should add the signposting links', () => {
+      expect(serverResponseService.setHeader).toHaveBeenCalled();
+      expect(linkHeadService.addTag).toHaveBeenCalledTimes(2);
+    });
+
+
+    it('should add link tags correctly', () => {
+
+      expect(comp.signpostingLinks).toEqual([mocklink, mocklink2]);
+
+      // Check if linkHeadService.addTag() was called with the correct arguments
+      expect(linkHeadService.addTag).toHaveBeenCalledTimes(mockSignpostingLinks.length);
+      let expected: LinkDefinition = mockSignpostingLinks[0] as LinkDefinition;
+      expect(linkHeadService.addTag).toHaveBeenCalledWith(expected);
+      expected = {
+        href: 'http://test2.org',
+        rel: 'rel2'
+      };
+      expect(linkHeadService.addTag).toHaveBeenCalledWith(expected);
+    });
+
+    it('should set Link header on the server', () => {
+
+      expect(serverResponseService.setHeader).toHaveBeenCalledWith('Link', '<http://test.org> ; rel="rel1" ; type="type1" , <http://test2.org> ; rel="rel2" ');
+    });
+
   });
   describe('when the item is withdrawn and the user is not an admin', () => {
     beforeEach(() => {
@@ -150,6 +214,11 @@ describe('ItemPageComponent', () => {
       const objectLoader = fixture.debugElement.query(By.css('ds-listable-object-component-loader'));
       expect(objectLoader.nativeElement).toBeDefined();
     });
+
+    it('should add the signposting links', () => {
+      expect(serverResponseService.setHeader).toHaveBeenCalled();
+      expect(linkHeadService.addTag).toHaveBeenCalledTimes(2);
+    });
   });
 
   describe('when the item is not withdrawn and the user is not an admin', () => {
@@ -162,6 +231,11 @@ describe('ItemPageComponent', () => {
       const objectLoader = fixture.debugElement.query(By.css('ds-listable-object-component-loader'));
       expect(objectLoader.nativeElement).toBeDefined();
     });
+
+    it('should add the signposting links', () => {
+      expect(serverResponseService.setHeader).toHaveBeenCalled();
+      expect(linkHeadService.addTag).toHaveBeenCalledTimes(2);
+    });
   });
 
 });

src/app/item-page/simple/item-page.component.ts

@@ -1,8 +1,9 @@
-import { ChangeDetectionStrategy, Component, OnInit } from '@angular/core';
+import { ChangeDetectionStrategy, Component, Inject, OnDestroy, OnInit, PLATFORM_ID } from '@angular/core';
 import { ActivatedRoute, Router } from '@angular/router';
+import { isPlatformServer } from '@angular/common';
 
 import { Observable } from 'rxjs';
-import { map } from 'rxjs/operators';
+import { map, take } from 'rxjs/operators';
 
 import { ItemDataService } from '../../core/data/item-data.service';
 import { RemoteData } from '../../core/data/remote-data';
@@ -15,6 +16,11 @@ import { getItemPageRoute } from '../item-page-routing-paths';
 import { redirectOn4xx } from '../../core/shared/authorized.operators';
 import { AuthorizationDataService } from '../../core/data/feature-authorization/authorization-data.service';
 import { FeatureID } from '../../core/data/feature-authorization/feature-id';
+import { ServerResponseService } from '../../core/services/server-response.service';
+import { SignpostingDataService } from '../../core/data/signposting-data.service';
+import { SignpostingLink } from '../../core/data/signposting-links.model';
+import { isNotEmpty } from '../../shared/empty.util';
+import { LinkDefinition, LinkHeadService } from '../../core/services/link-head.service';
 
 /**
  * This component renders a simple item page.
@@ -28,7 +34,7 @@ import { FeatureID } from '../../core/data/feature-authorization/feature-id';
   changeDetection: ChangeDetectionStrategy.OnPush,
   animations: [fadeInOut]
 })
-export class ItemPageComponent implements OnInit {
+export class ItemPageComponent implements OnInit, OnDestroy {
 
   /**
    * The item's id
@@ -57,13 +63,23 @@ export class ItemPageComponent implements OnInit {
 
   itemUrl: string;
 
+  /**
+   * Contains a list of SignpostingLink related to the item
+   */
+  signpostingLinks: SignpostingLink[] = [];
+
   constructor(
     protected route: ActivatedRoute,
-    private router: Router,
+    protected router: Router,
-    private items: ItemDataService,
+    protected items: ItemDataService,
-    private authService: AuthService,
+    protected authService: AuthService,
-    private authorizationService: AuthorizationDataService
+    protected authorizationService: AuthorizationDataService,
+    protected responseService: ServerResponseService,
+    protected signpostingDataService: SignpostingDataService,
+    protected linkHeadService: LinkHeadService,
+    @Inject(PLATFORM_ID) protected platformId: string
   ) {
+    this.initPageLinks();
   }
 
   /**
@@ -82,4 +98,42 @@ export class ItemPageComponent implements OnInit {
     this.isAdmin$ = this.authorizationService.isAuthorized(FeatureID.AdministratorOf);
 
   }
+
+  /**
+   * Create page links if any are retrieved by signposting endpoint
+   *
+   * @private
+   */
+  private initPageLinks(): void {
+    this.route.params.subscribe(params => {
+      this.signpostingDataService.getLinks(params.id).pipe(take(1)).subscribe((signpostingLinks: SignpostingLink[]) => {
+        let links = '';
+        this.signpostingLinks = signpostingLinks;
+
+        signpostingLinks.forEach((link: SignpostingLink) => {
+          links = links + (isNotEmpty(links) ? ', ' : '') + `<${link.href}> ; rel="${link.rel}"` + (isNotEmpty(link.type) ? ` ; type="${link.type}" ` : ' ');
+          let tag: LinkDefinition = {
+            href: link.href,
+            rel: link.rel
+          };
+          if (isNotEmpty(link.type)) {
+            tag = Object.assign(tag, {
+              type: link.type
+            });
+          }
+          this.linkHeadService.addTag(tag);
+        });
+
+        if (isPlatformServer(this.platformId)) {
+          this.responseService.setHeader('Link', links);
+        }
+      });
+    });
+  }
+
+  ngOnDestroy(): void {
+    this.signpostingLinks.forEach((link: SignpostingLink) => {
+      this.linkHeadService.removeTag(`href='${link.href}'`);
+    });
+  }
 }

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

@@ -38,7 +38,7 @@ export class ServerInitService extends InitService {
     protected metadata: MetadataService,
     protected breadcrumbsService: BreadcrumbsService,
     protected themeService: ThemeService,
-    protected menuService: MenuService,
+    protected menuService: MenuService
   ) {
     super(
       store,