Download fails to complete when exception is encountered

[ellykits]

Describe the bug
When an exception occurs while downloading a resource, the com.google.android.fhir.sync.download.DownloaderImpl attempts to emit a com.google.android.fhir.sync.DownloadState.Failure failure in the catch block which results to a FATAL_EXCEPTION.

Component
Core library

To Reproduce
Steps to reproduce the behavior:

1. Attempt downloading a resource that has an exception. (Example in our use case was an Encounter resource missing a coding.code)

Expected behavior
In case of a Resource sync failure com.google.android.fhir.sync.DownloadState.Failure should be emitted with the parameter ResourceSyncException wrapping the sync exception without violating the flow exception transparency.

Error logs

FATAL EXCEPTION: main
                                                                                                    Process: org.smartregister.fhircore.ecbis, PID: 10487
                                                                                                    java.lang.IllegalStateException: Flow exception transparency is violated:
                                                                                                        Previous 'emit' call has thrown exception java.lang.NullPointerException: coding.code must not be null, but then emission attempt of value 'Failure(syncError=ResourceSyncException(resourceType=Encounter, exception=java.lang.NullPointerException: coding.code must not be null))' has been detected.
                                                                                                        Emissions from 'catch' blocks are prohibited in order to avoid unspecified behaviour, 'Flow.catch' operator can be used instead.
                                                                                                        For a more detailed explanation, please refer to Flow documentation.
                                                                                                    	at kotlinx.coroutines.flow.internal.SafeCollector.exceptionTransparencyViolated(SafeCollector.kt:140)
                                                                                                    	at kotlinx.coroutines.flow.internal.SafeCollector.checkContext(SafeCollector.kt:104)
                                                                                                    	at kotlinx.coroutines.flow.internal.SafeCollector.emit(SafeCollector.kt:83)
                                                                                                    	at kotlinx.coroutines.flow.internal.SafeCollector.emit(SafeCollector.kt:66)
                                                                                                    	at com.google.android.fhir.sync.download.DownloaderImpl$download$2.invokeSuspend(DownloaderImpl.kt:56)
                                                                                                    	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
                                                                                                    	at kotlinx.coroutines.flow.internal.SafeCollector.invokeSuspend(SafeCollector.kt:48)
                                                                                                    	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
                                                                                                    	at kotlinx.coroutines.flow.internal.SafeCollector.invokeSuspend(SafeCollector.kt:48)
                                                                                                    	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
                                                                                                    	at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:104)
                                                                                                    	at android.os.Handler.handleCallback(Handler.java:938)
                                                                                                    	at android.os.Handler.dispatchMessage(Handler.java:99)
                                                                                                    	at android.os.Looper.loop(Looper.java:223)
                                                                                                    	at android.app.ActivityThread.main(ActivityThread.java:7656)
                                                                                                    	at java.lang.reflect.Method.invoke(Native Method)
                                                                                                    	at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
                                                                                                    	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
                                                                                                    	Suppressed: kotlinx.coroutines.DiagnosticCoroutineContextException: [StandaloneCoroutine{Cancelling}@1662c1a, Dispatchers.Main.immediate]

Libraries used:
org.jetbrains.kotlinx:kotlinx-coroutines-core:1.6.2
org.jetbrains.kotlinx:kotlinx-coroutines-android:1.6.2

[ellykits]

This exception when you run SyncJob#run method in a try-catch block. Also happens when you use the catch operator on each emitted flow state.

  coroutineScope {
      syncStateFlow
        .onEach {
            //handle sync state
        }
        .catch { throwable -> Timber.e(throwable) }      
        .launchIn(this)
   }

[omarismail94]

@ellykits @maimoonak @f-odhiambo I created a new PR to use the flow catch feature to handle invalid resources, and added unit tests. Please see PR #1917 . From my experimentation, this should catch errors thrown after resources have been successfully downloaded, but cannot be synced into the db

[jingtang10]

@aditya-07 is working on a design right now.