Hi, all the `.catch { }` operator of `Flow` should...

# coroutines

[orafaaraujo]

Hi, all
the .catch { } operator of Flow should not get one NPE that might occurs inside it?

[Dico]

Please provide example code, preferably using play.kotlinlang.org, to demonstrate the observation.

[orafaaraujo]

Will do it
While that, I'm getting a NPE and my catch is not getting it
.catch { e -> emit(Result.Error(Exception(e))) }

[orafaaraujo]

I'm sorry
but how can I test Flow in the playground ?

[orafaaraujo]

I'm mocking my scenario but when I do it, the catch works 😞

[orafaaraujo]

Is basically

val myFlow = callbackFlow {
        val json: String? = "aaa"
        val something = json
            ?.let { mapJson("") }
            ?: run { listOf<Any>() }
        offer(something)
    }

    myFlow
        .catch {
            logD { "myFlow catch $it" }
            emit(listOf())
        }
        .collect { logD { "myFlow collect: $it" } }
}

[orafaaraujo]

but here I can get a NPE when the map is wrong because of a bad JSON received

[Dico]

then you're making an incorrect assumption somewhere

[louiscad]

@orafaaraujo You can manually import kotlinx.coroutines.* and kotlinx.coroutines.flow.* on play.kotl.in

[orafaaraujo]

After hours of investigation, I discovered that exceptions launched from inside another lambda (from a library that I'm using here) are not handled by catch
why? no idea 😂

[orafaaraujo]

throw NullPointerException() // handled by catch
val request = searcher.searchable.searchAsync(query) { jsonObject, exception ->
    throw NullPointerException() // not handled by catch
}

[orafaaraujo]

I believe is the same reason why I need to use callbackFlow instead only Flow, to handle with something inside lambdas

[dave08]

If the exception is in a callback you're wrapping and the callback is on another thread, I don't think it'll be handled by catch...

[elizarov]

It depends on if/how searchAsync { … } handles exception. The root cause if there.