Android Dagger2 + OkHttp + Retrofit dependency cycle error

Question

Hey there I am using Dagger2, Retrofit and OkHttp and I am facing dependency cycle issue.

When providing OkHttp :

@Provides
@ApplicationScope
OkHttpClient provideOkHttpClient(TokenAuthenticator auth,Dispatcher dispatcher){
    return new OkHttpClient.Builder()
            .connectTimeout(Constants.CONNECT_TIMEOUT, TimeUnit.SECONDS)
            .readTimeout(Constants.READ_TIMEOUT,TimeUnit.SECONDS)
            .writeTimeout(Constants.WRITE_TIMEOUT,TimeUnit.SECONDS)
            .authenticator(auth)
            .dispatcher(dispatcher)
            .build();
}

When providing Retrofit :

@Provides
@ApplicationScope
Retrofit provideRetrofit(Resources resources,Gson gson, OkHttpClient okHttpClient){
    return new Retrofit.Builder()
            .baseUrl(resources.getString(R.string.base_api_url))
            .addConverterFactory(GsonConverterFactory.create(gson))
            .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
            .client(okHttpClient)
            .build();
}

When providing APIService :

@Provides
@ApplicationScope
APIService provideAPI(Retrofit retrofit) {
    return retrofit.create(APIService.class);
}

My APIService interface :

public interface  APIService {
@FormUrlEncoded
@POST("token")
Observable<Response<UserTokenResponse>> refreshUserToken();

--- other methods like login, register ---

}

My TokenAuthenticator class :

@Inject
public TokenAuthenticator(APIService mApi,@NonNull ImmediateSchedulerProvider mSchedulerProvider) {
    this.mApi= mApi;
    this.mSchedulerProvider=mSchedulerProvider;
    mDisposables=new CompositeDisposable();
}

@Override
public  Request authenticate(Route route, Response response) throws IOException {

    request = null;

    mApi.refreshUserToken(...)
            .subscribeOn(mSchedulerProvider.io())
            .observeOn(mSchedulerProvider.ui())
            .doOnSubscribe(d -> mDisposables.add(d))
            .subscribe(tokenResponse -> {
                if(tokenResponse.isSuccessful()) {
                    saveUserToken(tokenResponse.body());
                    request = response.request().newBuilder()
                            .header("Authorization", getUserAccessToken())
                            .build();
                } else {
                    logoutUser();
                }
            },error -> {

            },() -> {});

    mDisposables.clear();
    stop();
    return request;

}

My logcat :

Error:(55, 16) error: Found a dependency cycle:
com.yasinkacmaz.myapp.service.APIService is injected at com.yasinkacmaz.myapp.darkvane.modules.NetworkModule.provideTokenAuthenticator(…, mApi, …)
com.yasinkacmaz.myapp.service.token.TokenAuthenticator is injected at
com.yasinkacmaz.myapp.darkvane.modules.NetworkModule.provideOkHttpClient(…, tokenAuthenticator, …)
okhttp3.OkHttpClient is injected at
com.yasinkacmaz.myapp.darkvane.modules.NetworkModule.provideRetrofit(…, okHttpClient)
retrofit2.Retrofit is injected at
com.yasinkacmaz.myapp.darkvane.modules.NetworkModule.provideAPI(retrofit)
com.yasinkacmaz.myapp.service.APIService is provided at
com.yasinkacmaz.myapp.darkvane.components.ApplicationComponent.exposeAPI()

So my question: My TokenAuthenticator class is depends on APIService but I need to provide TokenAuthenticator when creating APIService. This causes dependency cycle error. How do I beat this , is there anyone facing this issue ? Thanks in advance.

Answer 1

Your problem is:

1. Your OKHttpClient depends on your Authenticator
2. Your Authenticator depends on a Retrofit Service
3. Retrofit depends on an OKHttpClient (as in point 1)

Hence the circular dependency.

One possible solution here is for your TokenAuthenticator to depend on an APIServiceHolder rather than a APIService. Then your TokenAuthenticator can be provided as a dependency when configuring OKHttpClient regardless of whether the APIService (further down the object graph) has been instantiated or not.

A very simple APIServiceHolder:

public class APIServiceHolder {

    private APIService apiService;

    @Nullable
    APIService apiService() {
        return apiService;
    }

    void setAPIService(APIService apiService) {
        this.apiService = apiService;
    }
}

Then refactor your TokenAuthenticator:

@Inject
public TokenAuthenticator(@NonNull APIServiceHolder apiServiceHolder, @NonNull ImmediateSchedulerProvider schedulerProvider) {
    this.apiServiceHolder = apiServiceHolder;
    this.schedulerProvider = schedulerProvider;
    this.disposables = new CompositeDisposable();
}

@Override
public  Request authenticate(Route route, Response response) throws IOException {

    if (apiServiceHolder.get() == null) {
         //we cannot answer the challenge as no token service is available

         return null //as per contract of Retrofit Authenticator interface for when unable to contest a challenge
    }    

    request = null;            

    TokenResponse tokenResponse = apiServiceHolder.get().blockingGet()

    if (tokenResponse.isSuccessful()) {
        saveUserToken(tokenResponse.body());
        request = response.request().newBuilder()
                     .header("Authorization", getUserAccessToken())
                     .build();
    } else {
       logoutUser();
    }

    return request;
}

Note that the code to retrieve the token should be synchronous. This is part of the contract of Authenticator. The code inside the Authenticator will run off the main thread.

Of course you will need to write the @Provides methods for the same:

@Provides
@ApplicationScope
apiServiceHolder() {
    return new APIServiceHolder();
}

And refactor the provider methods:

@Provides
@ApplicationScope
APIService provideAPI(Retrofit retrofit, APIServiceHolder apiServiceHolder) {
    APIService apiService = retrofit.create(APIService.class);
    apiServiceHolder.setAPIService(apiService);
    return apiService;
}

Note that mutable global state is not usually a good idea. However, if you have your packages organised well you may be able to use access modifiers appropriately to avoid unintended usages of the holder.

Answer 2

Using the Lazy interface of Dagger 2 is the solution here. In your TokenAuthenticator replace APIService mApi with Lazy<APIService> mApiLazyWrapper

@Inject
public TokenAuthenticator(Lazy<APIService> mApiLazyWrapper,@NonNull ImmediateSchedulerProvider mSchedulerProvider) {
    this.mApiLazyWrapper= mApiLazyWrapper;
    this.mSchedulerProvider=mSchedulerProvider;
    mDisposables=new CompositeDisposable();
}

And to get the APIService instance from wrapper use mApiLazyWrapper.get()

In case mApiLazyWrapper.get() returns null, return null from the authenticate method of TokenAuthenticator as well.

Answer 3

Big thanks to @Selvin and @David. I have two approach, one of them is David's answer and the other one is :

Creating another OkHttp or Retrofit or another library which will handle our operations inside TokenAuthenticator class.

If you want to use another OkHttp or Retrofit instance you must use Qualifier annotation.

For example :

@Qualifier
public @interface ApiClient {}


@Qualifier
public @interface RefreshTokenClient {}

then provide :

@Provides
@ApplicationScope
@ApiClient
OkHttpClient provideOkHttpClientForApi(TokenAuthenticator tokenAuthenticator, TokenInterceptor tokenInterceptor, Dispatcher dispatcher){
    return new OkHttpClient.Builder()
            .connectTimeout(Constants.CONNECT_TIMEOUT, TimeUnit.SECONDS)
            .readTimeout(Constants.READ_TIMEOUT,TimeUnit.SECONDS)
            .writeTimeout(Constants.WRITE_TIMEOUT,TimeUnit.SECONDS)
            .authenticator(tokenAuthenticator)
            .addInterceptor(tokenInterceptor)
            .dispatcher(dispatcher)
            .build();
}

@Provides
@ApplicationScope
@RefreshTokenClient
OkHttpClient provideOkHttpClientForRefreshToken(Dispatcher dispatcher){
    return new OkHttpClient.Builder()
            .connectTimeout(Constants.CONNECT_TIMEOUT, TimeUnit.SECONDS)
            .readTimeout(Constants.READ_TIMEOUT,TimeUnit.SECONDS)
            .writeTimeout(Constants.WRITE_TIMEOUT,TimeUnit.SECONDS)
            .dispatcher(dispatcher)
            .build();
}

@Provides
@ApplicationScope
@ApiClient
Retrofit provideRetrofitForApi(Resources resources, Gson gson,@ApiClient OkHttpClient okHttpClient){
    return new Retrofit.Builder()
            .baseUrl(resources.getString(R.string.base_api_url))
            .addConverterFactory(GsonConverterFactory.create(gson))
            .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
            .client(okHttpClient)
            .build();
}

@Provides
@ApplicationScope
@RefreshTokenClient
Retrofit provideRetrofitForRefreshToken(Resources resources, Gson gson,@RefreshTokenClient OkHttpClient okHttpClient){
    return new Retrofit.Builder()
            .baseUrl(resources.getString(R.string.base_api_url))
            .addConverterFactory(GsonConverterFactory.create(gson))
            .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
            .client(okHttpClient)
            .build();
}

Then we can provide our seperated interfaces :

@Provides
@ApplicationScope
public APIService provideApi(@ApiClient Retrofit retrofit) {
    return retrofit.create(APIService.class);
}

@Provides
@ApplicationScope
public RefreshTokenApi provideRefreshApi(@RefreshTokenClient Retrofit retrofit) {
    return retrofit.create(RefreshTokenApi.class);
}

When providing our TokenAuthenticator :

@Provides
@ApplicationScope
TokenAuthenticator provideTokenAuthenticator(RefreshTokenApi mApi){
    return new TokenAuthenticator(mApi);
}

Advantages : You have two seperated api interfaces which means you can maintain them independently. Also you can use plain OkHttp or HttpUrlConnection or another library.

Disadvantages : You will have two different OkHttp and Retrofit instance.

P.S : Make sure you make syncronous calls inside Authenticator class.

Answer 4

You can inject the service dependency into your authenticator via the Lazy type. This way you will avoid the cyclic dependency on instantiation.

Check this link on how Lazy works.