Android Cloud Firestore task's return successfully when there is no internet connection. How?

Question

I'm messing around with Cloud Firestore.

I would like to simply get a callback when reading from DB fails, so I can show a dialog to the user about he has no internet connection. Of course, this would need sophisticated exception handling, but first things first, I would like to just simply get a callback when the app cannot reach the server.

HOWEVER, whenever I test my application with an emulator which has no internet connection, I still get successful callbacks.

This is the log:

Logging_: onSuccess
Logging_: onComplete
Logging_: Task was successful without an internet connection, how?

How is it possible? Am I thinking right that Cloud Firestore is simply not available for this use case since it was built to provide cached data and aggressive syncing in order to provide a seamless user experience even when there is no internet connection?

I would just need a way to just KNOW whether the DB is reachable. (a.k.a - Is there an internet connection problem?)

---

Code is really simple, it just tries to reach for the current account's characters.

  db.collection("users")
                .document(accountId)
                .collection("characters")
                .get()
                .addOnCanceledListener(new OnCanceledListener() {
                    @Override
                    public void onCanceled() {
                        Log.i("Logging_", "onCanceled");
                    }
                })
                .addOnFailureListener(new OnFailureListener() {
                    @Override
                    public void onFailure(@NonNull Exception e) {
                        Log.i("Logging_", "onFailure");
                    }
                })
                .addOnSuccessListener(new OnSuccessListener<QuerySnapshot>() {
                    @Override
                    public void onSuccess(QuerySnapshot queryDocumentSnapshots) {
                        Log.i("Logging_", "onSuccess");
                    }
                })
                .addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
                    @Override
                    public void onComplete(@NonNull Task<QuerySnapshot> task) {

                        Log.i("Logging_", "onComplete");

                        if (task.isSuccessful()) {
                            Log.i("Logging_", "Task was successful without internet connection, how?");
                        } else {
                            Log.i("Logging_", "Task wasn't successful.");
                        }
                    }
                });

Answer 1

I would like to simply get a callback when reading from DB fails, so I can show a dialog to the user about whether he has no internet connection.

The Firestore SDK doesn't throw an error when there is no internet connection, and it makes sense since Firestore is designed to work offline. Behind the scenes, Firestore SDK tries to reconnect until the devices regain connectivity. So not having an internet connection cannot be considered a failure. If you want to check for internet connectivity, the following answer might help:

• How to verify if user has network access and show a pop-up alert when there isn't

Please notice that Firestore has a built-in mechanism that can help know when an error occurs. So the failure callback occurs when Firestore servers reject the request due to a security rule issue.

There is a solution in which you can force the retrieval of data only from the cache or from the server. Here is the official documentation regarding source options:

• https://firebase.google.com/docs/firestore/query-data/get-data#source_options

Answer 2

Firestore has built in caching that is enabled by default for reading from a database on Apple and Android devices. If you want to disable being able to read the cached data, you can do something like this:

FirebaseFirestoreSettings settings = new FirebaseFirestoreSettings.Builder()
    .setPersistenceEnabled(false)
    .build();
db.setFirestoreSettings(settings);

I think what you may want to do instead is listen to network events in Android which would allow you to update the user if they try to perform an action while there is no network available.

This might be a bug. I have logged the tracking info here on GitHub