Handling 401s globally with Angular

Question

In my Angular 2 project I make API calls from services that return an Observable. The calling code then subscribes to this observable. For example:

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Answer 1

To avoid the cyclic referencing issue that is caused by having services like "Router" being injected into an Http derived class, one must use the post-constructor Injector method. The following code is a working implementation of an Http service that redirects to Login route each time a REST API returns "Token_Expired". Note that it can be used as a substitution to the regular Http and as such, doesn't require to change anything in your application's already existing components or services.

app.module.ts

  providers: [  
    {provide: Http, useClass: ExtendedHttpService },
    AuthService,
    PartService,
    AuthGuard
  ],

extended-http.service.ts

import { Injectable, Injector } from '@angular/core';
import { Request, XHRBackend, RequestOptions, Response, Http, RequestOptionsArgs, Headers } from '@angular/http';
import { Observable } from 'rxjs/Observable';
import { Router } from '@angular/router';
import { AuthService } from './auth.service';
import 'rxjs/add/operator/catch';
import 'rxjs/add/observable/throw';

@Injectable()
export class ExtendedHttpService extends Http {
    private router; 
    private authService;

  constructor(  backend: XHRBackend, defaultOptions: RequestOptions, private injector: Injector) {
    super(backend, defaultOptions);
  }

  request(url: string | Request, options?: RequestOptionsArgs): Observable {
 
    if (typeof url === 'string') {
      if (!options) {
        options = { headers: new Headers() };
      }
      this.setHeaders(options);
    } else {
      this.setHeaders(url);
    }
    console.log("url: " + JSON.stringify(url) +", Options:" + options);

    return super.request(url, options).catch(this.catchErrors());
  }

  private catchErrors() {

    return (res: Response) => {
        if (this.router == null) {
            this.router = this.injector.get(Router);
        }
        if (res.status === 401 || res.status === 403) {
            //handle authorization errors
            //in this example I am navigating to login.
            console.log("Error_Token_Expired: redirecting to login.");
            this.router.navigate(['signin']);
        }
        return Observable.throw(res);
    };
  }

  private setHeaders(objectToSetHeadersTo: Request | RequestOptionsArgs) {
      
      if (this.authService == null) {
            this.authService = this.injector.get(AuthService);
      }
    //add whatever header that you need to every request
    //in this example I could set the header token by using authService that I've created
     //objectToSetHeadersTo.headers.set('token', this.authService.getToken());
  }
}