Unable to resolve host error on first launch: `UnknownErrorException: Unable to resolve host`

This issue respects the following points:

• I have read the FAQ
• I have searched for existing issues
• The issue affects the Notes Android app, neither the Notes server app nor the Nextcloud Android app.

Describe the bug

Steps to reproduce the bug:

1. Open Notes app on Android Phone.
2. Notice 'Synchronization error' bar at the bottom of the app

Expected behavior

No 'Synchronization error'

Notes Android version

4.2.1

Notes server version

4.10.1

Nextcloud Android version

3.29.1

Nextcloud version

28.0.7

Device

Realme 6i and Realme P1 Pro 5G

Android Version

14 and 11

App Store

• Google Play Store
• F-Droid
• Huawei App Gallery

Stacktrace

App Version: 4.2.1

App Version Code: 40020190

App Flavor: fdroid

Files App Version Code: 30290190 (PROD)

---

OS Version: 5.10.198-android12-9-o-g31299f4e1e15(U.R4T2.189bc1a_40579_40578)

OS API Level: 34

Device: RE5C84L1

Manufacturer: realme

Model (and Product): RMX3844 (RMX3844IN)

---

java.lang.RuntimeException: com.nextcloud.android.sso.exceptions.UnknownErrorException: Unable to resolve host "<hostname>": No address associated with hostname

    at io.reactivex.internal.util.ExceptionHelper.wrapOrThrow(ExceptionHelper.java:46)

    at io.reactivex.internal.observers.BlockingMultiObserver.blockingGet(BlockingMultiObserver.java:93)

    at io.reactivex.Maybe.blockingGet(Maybe.java:2321)

    at io.reactivex.Observable.blockingSingle(Observable.java:5381)

    at it.niedermann.owncloud.notes.persistence.NotesServerSyncTask.pullRemoteChanges(NotesServerSyncTask.java:219)

    at it.niedermann.owncloud.notes.persistence.NotesServerSyncTask.run(NotesServerSyncTask.java:96)

    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:487)

    at java.util.concurrent.FutureTask.run(FutureTask.java:264)

    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)

    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:644)

    at java.lang.Thread.run(Thread.java:1012)

Caused by: com.nextcloud.android.sso.exceptions.UnknownErrorException: Unable to resolve host "<hostname>": No address associated with hostname

    at com.nextcloud.android.sso.api.AidlNetworkRequest.performNetworkRequestV2(AidlNetworkRequest.java:189)

    at com.nextcloud.android.sso.api.NextcloudAPI.performNetworkRequestV2(NextcloudAPI.java:165)

    at com.nextcloud.android.sso.api.NextcloudAPI.lambda$performRequestObservableV2$0(NextcloudAPI.java:105)

    at com.nextcloud.android.sso.api.NextcloudAPI.$r8$lambda$2CK7Y9lXWWrtN8jgT_iNTMeTrHU(Unknown Source:0)

    at com.nextcloud.android.sso.api.NextcloudAPI$$ExternalSyntheticLambda0.subscribe(Unknown Source:6)

    at io.reactivex.internal.operators.observable.ObservableFromPublisher.subscribeActual(ObservableFromPublisher.java:31)

    at io.reactivex.Observable.subscribe(Observable.java:12284)

    at io.reactivex.internal.operators.observable.ObservableSingleMaybe.subscribeActual(ObservableSingleMaybe.java:31)

    at io.reactivex.Maybe.subscribe(Maybe.java:4290)

    at io.reactivex.Maybe.blockingGet(Maybe.java:2320)

    ... 8 more

Note: Nextcloud server is hosted on public cloud and is reachable via public domain name.

Start with NotesServerSyncTask.java, especially pullRemoteChanges at line 219 and run at line 96, then trace the reported Android SSO network exception. Reproduce the first-launch synchronization against the public server hostname and verify that synchronization completes without the error bar.