Handling Circular Dependency: Injecting a Service into an HTTP Interceptor in AngularJS

I'm currently working on developing an HTTP interceptor for my AngularJS application to manage authentication.

Although the code I have is functional, I am wary of manually injecting a service as I believed Angular is designed to handle this process automatically:

    app.config(['$httpProvider', function ($httpProvider) {
    $httpProvider.interceptors.push(function ($location, $injector) {
        return {
            'request': function (config) {
                //manually injected to resolve circular dependency issue.
                var AuthService = $injector.get('AuthService');
                console.log(AuthService);
                console.log('in request interceptor');
                if (!AuthService.isAuthenticated() && $location.path != '/login') {
                    console.log('user is not logged in.');
                    $location.path('/login');
                }
                return config;
            }
        };
    })
}]);

Initially, I attempted a different approach but encountered circular dependency challenges:

    app.config(function ($provide, $httpProvider) {
    $provide.factory('HttpInterceptor', function ($q, $location, AuthService) {
        return {
            'request': function (config) {
                console.log('in request interceptor.');
                if (!AuthService.isAuthenticated() && $location.path != '/login') {
                    console.log('user is not logged in.');
                    $location.path('/login');
                }
                return config;
            }
        };
    });

    $httpProvider.interceptors.push('HttpInterceptor');
});

Furthermore, observing the documentation section about $http in the Angular Docs revealed a method for injecting dependencies in a more conventional manner within an Http interceptor. Refer to the sample code listed under "Interceptors":

// registering the interceptor as a service
$provide.factory('myHttpInterceptor', function($q, dependency1, dependency2) {
  return {
    // optional method
    'request': function(config) {
      // perform actions upon success
      return config || $q.when(config);
    },

    // optional method
   'requestError': function(rejection) {
      // execute actions upon error
      if (canRecover(rejection)) {
        return responseOrNewPromise
      }
      return $q.reject(rejection);
    },



    // optional method
    'response': function(response) {
      // perform actions upon success
      return response || $q.when(response);
    },

    // optional method
   'responseError': function(rejection) {
      // execute actions upon error
      if (canRecover(rejection)) {
        return responseOrNewPromise
      }
      return $q.reject(rejection);
    };
  }
});

$httpProvider.interceptors.push('myHttpInterceptor');

Specifically where should the above code implementation be placed?

Essentially, my query revolves around determining the correct procedure for accomplishing this task.

Thank you, and I trust that my inquiry was articulated clearly enough.

Answer №1

Here is the solution I came up with:

  .config(['$httpProvider', function ($httpProvider) {
        //enable cors
        $httpProvider.defaults.useXDomain = true;

        $httpProvider.interceptors.push(['$location', '$injector', '$q', function ($location, $injector, $q) {
            return {
                'request': function (config) {

                    //injected manually to avoid circular dependency issue.
                    var AuthService = $injector.get('Auth');

                    if (!AuthService.isAuthenticated()) {
                        $location.path('/login');
                    } else {
                        //add session_id as a bearer token in header of all outgoing HTTP requests.
                        var currentUser = AuthService.getCurrentUser();
                        if (currentUser !== null) {
                            var sessionId = AuthService.getCurrentUser().sessionId;
                            if (sessionId) {
                                config.headers.Authorization = 'Bearer ' + sessionId;
                            }
                        }
                    }

                    //add headers
                    return config;
                },
                'responseError': function (rejection) {
                    if (rejection.status === 401) {

                        //injected manually to avoid circular dependency issue.
                        var AuthService = $injector.get('Auth');

                        //if server returns 401 despite user being authenticated on app side, it means session timed out on server
                        if (AuthService.isAuthenticated()) {
                            AuthService.appLogOut();
                        }
                        $location.path('/login');
                        return $q.reject(rejection);
                    }
                }
            };
        }]);
    }]);

Note: It is important to keep the $injector.get calls within the methods of the interceptor to prevent circular dependency errors in JavaScript.

Answer №2

Your AuthService and $http are caught in a circular dependency loop.

One way to break this cycle is by utilizing the $injector service to delay $http's dependency on AuthService, effectively solving the issue.

In my opinion, your solution is the most straightforward approach to resolving this problem.

Alternative methods include:

  • Delaying interceptor registration by placing it in a run() block instead of a config() block. However, there is no guarantee that $http hasn't already been called.
  • Manually injecting $http into AuthService during interceptor registration by calling AuthService.setHttp() or similar method.
  • ...

Answer №3

I believe that utilizing the $injector directly is not a recommended practice.

To avoid a circular dependency, one approach is to utilize an event system: Instead of directly injecting $state, inject $rootScope. Rather than performing a direct redirection, you can do

this.$rootScope.$emit("unauthorized");

and

angular
    .module('bar')
    .run(function($rootScope, $state) {
        $rootScope.$on('unauthorized', () => {
            $state.transitionTo('login');
        });
    });

Answer №4

Illogical reasoning leading to unexpected outcomes

When it comes to determining whether a user is authorized or not in an HTTP Interceptor, the key is to consolidate all your HTTP requests into a single .service (or .factory, or .provider). By doing so, you can easily check if the user is logged in before allowing the request to be sent. This approach ensures that regardless of where the request originates from within your Angular application, proper authorization checks are in place.

The core issue at hand lies in the interaction between myHttpInterceptor and the $httpProvider instance. The AuthService relies on $http or $resource, creating a potential for dependency recursion or circular dependency. Removing this dependency from the AuthService will resolve the error.


As mentioned by @Pieter Herroelen, another workaround could involve placing the interceptor in your module's module.run. However, this should be considered more of a temporary fix rather than a permanent solution.

If you strive for clean and self-explanatory code, adhering to SOLID principles, particularly the Single Responsibility principle, can greatly aid in navigating such complex scenarios.

Answer №5

To streamline the process of checking for the Auth state (isAuthorized()), it is recommended to create a separate module called "Auth". This module will solely manage the state without directly utilizing $http.

app.config(['$httpProvider', function ($httpProvider) {
  $httpProvider.interceptors.push(function ($location, Auth) {
    return {
      'request': function (config) {
        if (!Auth.isAuthenticated() && $location.path != '/login') {
          console.log('user is not logged in.');
          $location.path('/login');
        }
        return config;
      }
    }
  })
}])

The Auth Module structure:

angular
  .module('app')
  .factory('Auth', Auth)

function Auth() {
  var $scope = {}
  $scope.sessionId = localStorage.getItem('sessionId')
  $scope.authorized = $scope.sessionId !== null
  //... other auth relevant data

  $scope.isAuthorized = function() {
    return $scope.authorized
  }

  return $scope
}

(I utilized localStorage to store the sessionId on the client side in this example, but you can also implement this within your AuthService post a $http request)

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