iOS v10.20.0-beta.2 Flexible sync: subscriptions.update crashes after token expiry

[Joelfrewy]

How frequently does the bug occur?

All the time

Description

Initialising realm subscriptions with flexible sync on iOS results in a crash. This crash only occurs roughly 30 mins after initially logging in (surely due to token expiration?). running refreshCustomData() before updating subscriptions fixes the issue, however this function requires internet access which could brick an offline app.

Stacktrace & log output

OS Version: iOS 15.3.1 (19D52)
Report Version: 104

Exception Type: EXC_BAD_ACCESS (SIGBUS)
Exception Codes: BUS_NOOP
Crashed Thread: 7

Application Specific Information:
ZTUM >
Attempted to dereference null pointer.

Thread 7 Crashed:
0   app   0x2030f16dc   realm::sync::Session::on_new_flx_sync_subscription
1   app   0x2030424a0   realm::util::UniqueFunction<T>::make_impl<T>::SpecificImpl::call
2   app   0x2030424a0   realm::util::UniqueFunction<T>::make_impl<T>::SpecificImpl::call
3   app   0x203132720   realm::sync::MutableSubscriptionSet::commit
4   app   0x202f10ae0   realm::js::SubscriptionSetClass<T>::update
5   app   0x202f10774   realm::js::wrap<T>

Can you reproduce the bug?

Yes, always

Reproduction Steps

const initialise = async () => {
  const appConfig = {
    id: '<app id>',
    timeout: 10000,
  };
  const app = new Realm.App(appConfig);
  let user = app.currentUser;
  if (!user || user?.state !== 'active') {
    const credentials = Realm.Credentials.anonymous();
    user = await app.logIn(credentials);
  }
  // await app.currentUser?.refreshCustomData();      <-- This line fixes the null pointer issue but requires internet
  const realm = new Realm({
    schema: [...],
    sync: {
      user: app.currentUser,
      flexible: true,
    },
  });
  realm.subscriptions.update(mutableSubscriptions => {
    realm.schema.forEach(schema => {
      mutableSubscriptions.add(
        realm.objects(schema.name).filtered('userId = $0', user!.id),
        {
          name: schema.name,
        },
      );
    });
  });
}

Version

v10.20.0-beta.2 Hermes

What SDK flavour are you using?

MongoDB Realm (i.e. Sync, auth, functions)

Are you using encryption?

No, not using encryption

Platform OS and version(s)

iOS 15.3.1

Build environment

Release Mode

Cocoapods version

1.11.2

[fronck]

@Joelfrewy Thank you for reporting this issue.
We will investigate how to address it.

[rklubenspies]

We're experiencing a similar issue on realm-swift v10.24.1.

[danieltabacaru]

Hi @Joelfrewy. Thanks for filling the bug. We identified the problem and it will be fixed by #5343.

[tomduncalf]

Waiting on new core release to get this fix into Realm JS