Phone Auth crashes with "Already resumed" in DefaultVerifier.onVerificationCompleted

[tatuas]

Environment

• Devices: multiple devices
• Android versions: 11–17
• FirebaseUI Auth: 10.0.0-beta03
• Firebase Auth: 24.0.1

Description

Our Android app crashes during Phone Authentication when Firebase automatically completes verification after detecting the SMS verification code.

The crash is fatal on the main thread and prevents affected users from signing in with SMS.

Steps to reproduce

1. Configure FirebaseUI Phone Auth:

   AuthProvider.Phone(
       defaultNumber = null,
       defaultCountryCode = "<country>",
       allowedCountries = listOf("<country>"),
   )

2. Start phone number verification.

3. Receive the verification SMS.

4. In affected cases, Firebase automatically detects the SMS code and completes verification.

5. The app crashes.

Observed result

Fatal Exception: java.lang.IllegalStateException: Already resumed
    at kotlin.coroutines.SafeContinuation.resumeWith(SafeContinuationJvm.kt:44)
    at com.firebase.ui.auth.configuration.auth_provider.AuthProvider$Phone$DefaultVerifier$verifyPhoneNumber$2$options$1.onVerificationCompleted(AuthProvider.kt:418)
    at com.google.firebase.auth.zzl.onVerificationCompleted(com.google.firebase:firebase-auth@@24.0.1:6)
    at com.google.android.gms.internal.firebase-auth-api.zzaga.onVerificationCompleted(com.google.firebase:firebase-auth@@24.0.1:8)
    at com.google.android.gms.internal.firebase-auth-api.zzafi.zza(com.google.firebase:firebase-auth@@24.0.1:2)
    at com.google.android.gms.internal.firebase-auth-api.zzafn.run(com.google.firebase:firebase-auth@@24.0.1:4)

DefaultVerifier wraps Phone Auth callbacks with a single suspendCoroutine continuation. It resumes that continuation from onVerificationCompleted, onVerificationFailed, and onCodeSent.

The exception indicates that onVerificationCompleted attempted to resume a continuation that had already been completed by another callback. This may occur when onCodeSent is followed by SMS auto-retrieval.

Expected result

Phone verification should either complete automatically or transition to manual code entry without crashing. Any callback received after a terminal result should be safely ignored.

[demolaf]

Hi @tatuas thanks for the detailed report. Currently investigating, I'll keep this issue updated.

[tatuas]

As a temporary mitigation, we have set timeout = 0L for AuthProvider.Phone:

AuthProvider.Phone(
    defaultNumber = null,
    defaultCountryCode = region.country,
    allowedCountries = listOf(region.country),
    timeout = 0L,
)

This disables SMS auto-retrieval and requires users to enter the SMS verification code manually in most cases. It appears to avoid the crash path in our app, and we have not received further reports of this crash so far.

We understand that this is a workaround rather than a fix for the underlying FirebaseUI issue. We will keep monitoring and would appreciate a library-level fix when available.

[demolaf]

@tatuas yes that would work. I was able to reproduce the issue, currently working on a fix.