Interceptor not intercepting http requests (Angular 6)

Question

I'm in the proces of adding an interceptor to my angular 6 project. To make calls to my API, I need to add a bearer token to all calls. Unfortunately the interceptor does not seem to be called. My code:

import { Injectable } from "@angular/core";
import { HttpInterceptor, HttpRequest, HttpHandler, HttpEvent } from "@angular/common/http";
import { Observable } from "rxjs";

@Injectable()
export class AuthInterceptor implements HttpInterceptor {

    intercept(req: HttpRequest<any>,
              next: HttpHandler): Observable<HttpEvent<any>> {

        //Retrieve accesstoken from local storage
        const accessToken = localStorage.getItem("access_token");

        //Check if accesToken exists, else send request without bearer token
        if (accessToken) {
            const cloned = req.clone({
                headers: req.headers.set("Authorization",
                    "Bearer " + accessToken)
            });

            console.log('Token added to HTTP request');

            return next.handle(cloned);
        }
        else {
            //No token; proceed request without bearer token
            console.log('No token added to HTTP request');
            return next.handle(req);
        }
    }
}

Does anyone know what could be causing this issue? Thanks in advance.

Answer 1

In my case interceptor wasn't getting involved for service calls because I had imported HttpClientModule multiple times, for different modules.

Later I found that HttpClientModule must be imported only once. Doc ref

Hope this helps!

Answer 2

You use the right way to intercept.

For people who use interceptor, you need to do 2 modifications :

Interceptor in service

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

import { Observable } from 'rxjs/Observable';
import 'rxjs/add/operator/do';

@Injectable()
export class MyInterceptor implements HttpInterceptor {
  intercept(
    req: HttpRequest<any>,
    next: HttpHandler
  ): Observable<HttpEvent<any>> {

    return next.handle(req).do(evt => {
      if (evt instanceof HttpResponse) {
        console.log('---> status:', evt.status);
        console.log('---> filter:', req.params.get('filter'));
      }
    });

  }
}

Provide HTTP_INTERCEPTOR

import { HttpClientModule, HTTP_INTERCEPTORS } from '@angular/common/http';
(...)
  providers: [
    { provide: HTTP_INTERCEPTORS, useClass: MyInterceptor, multi: true }
  ],

Read this article for more details. It's pretty good

Answer 3

If you have a providers array for a module then you have to define the HTTP_INTERCEPTORS too for that module then only it will intercept the requests under that module.

e.g:

providers: [ 
// singleton services
PasswordVerifyService,
{ provide: HTTP_INTERCEPTORS, useClass: AppInterceptor, multi: true },
{ provide: HTTP_INTERCEPTORS, useClass: ErrorInterceptorService, multi: true }
]

Answer 4

In my case, I had to import both HTTP_INTERCEPTORS, HttpClientModule in same module.