shaunlim shaunlim - 4 months ago 143
Javascript Question

AngularJS: Injecting service into a HTTP interceptor (Circular dependency)

I'm trying to write a HTTP interceptor for my AngularJS app to handle authentication.

This code works, but I'm concerned about manually injecting a service since I thought Angular is supposed to handle this automatically:

app.config(['$httpProvider', function ($httpProvider) {
$httpProvider.interceptors.push(function ($location, $injector) {
return {
'request': function (config) {
//injected manually to get around circular dependency problem.
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;
}
};
})
}]);


What I started out doing, but ran into circular dependency problems:

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');
});


Another reason why I'm concerned is that the section on $http in the Angular Docs seem to show a way to get dependencies injected the "regular way" into a Http interceptor. See their code snippet under "Interceptors":

// register the interceptor as a service
$provide.factory('myHttpInterceptor', function($q, dependency1, dependency2) {
return {
// optional method
'request': function(config) {
// do something on success
return config || $q.when(config);
},

// optional method
'requestError': function(rejection) {
// do something on error
if (canRecover(rejection)) {
return responseOrNewPromise
}
return $q.reject(rejection);
},



// optional method
'response': function(response) {
// do something on success
return response || $q.when(response);
},

// optional method
'responseError': function(rejection) {
// do something on error
if (canRecover(rejection)) {
return responseOrNewPromise
}
return $q.reject(rejection);
};
}
});

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


Where should the above code go?

I guess my question is what's the right way to go about doing this?

Thanks, and I hope my question was clear enough.

Answer

You have a circular dependency between $http and your AuthService.

What you are doing by using the $injector service is solving the chicken-and-egg problem by delaying the dependency of $http on the AuthService.

I believe that what you did is actually the simplest way of doing it.

You could also do this by:

  • Registering the interceptor later (doing so in a run() block instead of a config() block might already do the trick). But can you guarantee that $http hasn't been called already?
  • "Injecting" $http manually into the AuthService when you're registering the interceptor by calling AuthService.setHttp() or something.
  • ...