Hello, I decompiled a java class inside my kmp jar...

# multiplatform

[Raphael TEYSSANDIER]

Hello, I decompiled a java class inside my kmp jar. But I see some weird things

public final Object connectLocal(@NotNull final Credential.LocalMode credential, @NotNull final List features, @NotNull final Function1 configuration, @NotNull Continuation $completion) {
      return FlowKt.callbackFlow((Function2)(new Function2((Continuation)null) {
    ...
};

The last argument isn’t used, but in callbackFlow we pass null instead of the completion. Any idea ?

[Rick Clephas]

Not quite sure why a null continuation is provided. However callbackFlow itself isn’t a suspend function, therefor it doesn’t accept a continuation (which is why the last argument isn’t used). The block parameter of the callbackFlow is a suspend function, which is why it should receive a continuation from the Flow implementation (I am guessing that that’s probably why you are seeing this continuation argument).

[Raphael TEYSSANDIER]

Hummm ok, seems logic. But I try to call my function in a Java code. But nothing is happening.

XXXX.INSTANCE.connectLocal(
                new Credential.LocalMode(""),
                Feature.Companion.getDefaultFeatures(),
                XXXXHelper.createSessionDefinition(
                        new Server(
                                Server.Scheme.HTTPS,
                                "<http://xxx.com|xxx.com>",
                                Server.Endpoint.defaultOnlineEndpoint()
                        )
                ),
                new Continuation<Flow<? extends InitStep>>() {
                    @NotNull
                    @Override
                    public CoroutineContext getContext() {
                        return EmptyCoroutineContext.INSTANCE;
                    }

                    @Override
                    public void resumeWith(@NotNull Object o) {

                    }
                }
        );

[Rick Clephas]

Looking at the implementation of connectLocal it just returns the Flow from callbackFlow.
callbackFlow returns a cold flow, so you would need to collect it before any code inside the block is executed.

[Raphael TEYSSANDIER]

Yes, I do that after

if (test instanceof Flow) {
            ((Flow<?>) test).collect(
                    (FlowCollector<Object>) (o, continuation) -> null,
                    new Continuation<Unit>() {
                        @NotNull
                        @Override
                        public CoroutineContext getContext() {
                            return EmptyCoroutineContext.INSTANCE;
                        }

                        @Override
                        public void resumeWith(@NotNull Object o) {
                            System.out.println(o);
                        }
                    }
            );
        }

But nothing is printed

[Rick Clephas]

Do you have the Kotlin code for the connectLocal functions? I am starting to wonder why it accepts a continuation if it returns the Flow directly 🤔

[Raphael TEYSSANDIER]

I did it, so yeah 😄

suspend fun connectLocal(
		credential: Credential.LocalMode,
		features: List<Feature> = Feature.getDefaultFeatures(),
		configuration: LocalSessionConfiguration.() -> Unit
	): Flow<InitStep> = callbackFlow {
		val uuid = EPPlatform.randomUUID()
		val config = LocalSessionConfiguration().apply(configuration)
		val parentJob = Job() // improve for better error handling -> Todo for later
		val session = Session.create(uuid, SessionMode.LOCAL)
		val scope = session.scope
		val client: HttpClient = buildClient(
			config = config, localConfiguration = config.localConfiguration
		)

		scope.declare(client)
		koinApp.koin.declare(LoginAndSessionService(client = client))
		scope.baseDI(client = client)

		val sortedFeatures = scope.initFeatures(features, client, config)

		scope.get<GatewayRepository>()
			.setLocalToken(credential.token)
			.exceptionOrNull()

        trySend(InitStep.Authenticated)
        initFetchFeatures(sortedFeatures, scope, config.mode, parentJob).join()
        success(session = session, startPoller = config.startPoller)
        awaitClose { parentJob.complete() }
    }

[Rick Clephas]

Alright. Where is your test variable comming from? Could you verify if resumeWith for your connectLocal call is being called with a Flow? Also is the code inside the callbackFlow ever called?

[Raphael TEYSSANDIER]

test variable is just the return of connectLocal . I don’t how to verify, I can put break point inside the decompiled class. Yeah, the method is working in a Android App

[Rick Clephas]

I would try and print test to verify you are actually receiving the Flow.
If test is indeed the Flow then I think the only remaining issue is in the other print statement.
You are currently printing the result of the collect. Which is probably not going to be called (I don't see any close call inside the callbackFlow). Try logging o from the first argument (FlowCollector).

[Rick Clephas]

Also it might be worth checking the coroutines rx libraries: https://github.com/Kotlin/kotlinx.coroutines/tree/master/reactive/kotlinx-coroutines-rx3

[Raphael TEYSSANDIER]

test = block[kotlinx.coroutines.channels.ProducerScope<com.modulotech.epos.session.InitStep>.() -> kotlin.Unit] -> CallbackFlowBuilder[capacity=-2]
The flow collector is not called, nothing is print out.

I would like to stay full kotlin.

[Rick Clephas]

Hmm that's not what I would expect from a Flow type. How about the o inside resumeWith of the connectLocal call?

[Raphael TEYSSANDIER]

test instanceOf Flow is true .
I have put in every resumeWith a println, but nothing is printed.
Maybe it’s because it’s not launch in a Coroutine ?

[Rick Clephas]

Yeah these things are tricky. If you don't want to use something like rx, you could create a "wrapper function" in Kotlin that collects the flow and invokes a callback instead:

fun connectLocal(...., onItem: (InitStep) -> Unit) {
    coroutineScope.launch {
        connectLocal(....).collect { onItem(it) }
    }
}

[Raphael TEYSSANDIER]

I really don’t want to go that way, but seems like I have no choice... The module is based on coroutine, so if I can find a way to make it work, it would be better.
Thank’s for helping