Implement retryWhen logic

Question

I have an app which requires session (cookies) to process web calls. Im using Retrofit+RxJava. However, session could expire (Retrofit error with 401 Unauthorized status) and i want to reauthenticate (to get fresh cookies) and retry previous call in this case. How would i do it with RxJava?

My example:

getServerApi().getDialogs(offset, getCookies())
     .subscribeOn(Schedulers.newThread())
     .observeOn(AndroidSchedulers.mainThread())
     .retryWhen(observable -> {...}) // Need some logic
     .subscribe(dialogsEnvelope -> getView().setDialogs(dialogsEnvelope),
                throwable -> getView().setError(processFail(throwable)));

Answer 1

While an Interceptor may be a better solution for this particular problem, the question specifically asked for a solution using retryWhen, so here is is one way to do it:

retryWhen(new Func1<Observable<Throwable>, Observable<?>>(){

    @Override
    public void Observable<?> call(Observable<Throwable>> attempts) {
        return attempts.flatMap(new Func1<Throwable, Observable<?>>() {

            @Override
            public Observable<?> call(Throwable throwable) {
                 if (throwable instanceof RetrofitError) {
                     RetrofitError retrofitError = (RetrofitError) throwable;
                     if (retrofitError.getKind() == RetrofitError.Kind.HTTP && retrofitError.getResponse().getStatus() == 401) {
                         // this is the error we care about - to trigger a retry we need to emit anything other than onError or onCompleted
                         return Observable.just(new Object());
                     } else {
                         // some other kind of error: just pass it along and don't retry
                         return Observable.error(throwable);
                     }
                 } else {
                     // some other kind of error: just pass it along and don't retry
                     return Observable.error(throwable);
                 }
             }
        });
    }
})

However, your getCookies would not be called again in the case of a simple retry. That would just resubscribe to the same Observable but getCookies was called before the creation of that Observable. So I think you would have to wrap the creation of the source Observable in a defer.

Answer 2

Use OkHttp's extremely powerful Interceptor.

public class RecoverInterceptor implements Interceptor {
  String getAuth() {
    // check if we have auth, if not, authorize
    return "Bearer ...";
  }

  void clearAuth() {
    // clear everything
  }

  @Override public Response intercept(Chain chain) throws IOException {
    final Request request = chain.request();
    if (request.urlString().startsWith("MY ENDPOINT")) {
      final Request signed = request.newBuilder()
          .header("Authorization", getAuth())
          .build();
      final Response response = chain.proceed(signed);
      if (response.code() == 401) {
        clearAuth();
        return intercept(chain);
      } else {
        return response;
      }
    } else {
      return chain.proceed(request);
    }
  }
}

Remember to synchronize your auth process code, so that two concurrent requests do not invoke it at the same time.