Angular 4.3 HttpClient : Intercept response

olivier houssin picture olivier houssin · Aug 8, 2017 · Viewed 57.8k times · Source

In the documentation about the new HttpClientModule included in the new version of Angular 4.3, the mechanism to intercept requests is explained very well. There is also mention of the response interceptor mechanism however I cannot find anything about it.

Does anyone have an idea about how to intercept a response in order to modify the body message before it is sent to the service?

Thanks.

Answer

A T picture A T · Aug 29, 2017

I suppose you can use do as @federico-scamuzzi suggested, or you can use map and catch like so:

import { Injectable } from '@angular/core';
import {
  HttpErrorResponse,
  HttpEvent,
  HttpHandler,
  HttpInterceptor,
  HttpRequest,
  HttpResponse
} from '@angular/common/http';

import { Observable } from 'rxjs/Observable';
import 'rxjs/add/operator/map';
import 'rxjs/add/operator/catch';
import 'rxjs/add/observable/throw';

@Injectable()
export class AuthInterceptor implements HttpInterceptor {
  intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
    console.info('req.headers =', req.headers, ';');
    return next.handle(req)
      .map((event: HttpEvent<any>) => {
        if (event instanceof HttpResponse && ~~(event.status / 100) > 3) {
          console.info('HttpResponse::event =', event, ';');
        } else console.info('event =', event, ';');
        return event;
      })
      .catch((err: any, caught) => {
        if (err instanceof HttpErrorResponse) {
          if (err.status === 403) {
            console.info('err.error =', err.error, ';');
          }
          return Observable.throw(err);
        }
      });
  }
}

EDIT: @LalitKushwah was asking about redirecting if(!loggedIn). I use Route Guards, specifically:

import { Injectable } from '@angular/core';
import { ActivatedRouteSnapshot, CanActivate, Router, RouterStateSnapshot
       } from '@angular/router';

import { Observable } from 'rxjs/Observable';

import { AuthService } from '../../api/auth/auth.service';
import { AlertsService } from '../alerts/alerts.service';

@Injectable()
export class AuthGuard implements CanActivate {
  constructor(private router: Router,
              private alertsService: AlertsService) {}

  canActivate(next: ActivatedRouteSnapshot,
              state: RouterStateSnapshot
              ): Observable<boolean> | Promise<boolean> | boolean {
    if (AuthService.loggedIn()) return true;

    const url: string = state.url;

    this.alertsService.add(`Auth required to view ${url}`);
    this.router
      .navigate(['/auth'], { queryParams: { redirectUrl: url } })
      .then(() => {});
    return false;
  }
}

Then I can simply add that as an argument to my route:

{
  path: 'dashboard', loadChildren:'app/dashboard/dashboard.module#DashboardModule',
  canActivate: [AuthGuard]
}