Kotlin Multiplatform fails on iOS while calling Kt...

# multiplatform

[BollywoodVillain]

Kotlin Multiplatform fails on iOS while calling Ktor suspend functions. The error is kotlin.native.concurrent.InvalidMutabilityException: mutation attempt of frozen. It works fine on Android and gets the network data without issues. I created a brand new MPP project using Android Studio MPP template and added the Ktor network code from Ktor-sample/client-mpp repo. What could be the problem?

The complete project is on Github at: https://github.com/samkhawase/Kotlin_MPP_Demo.

I’m using ktor 1.4.2, Kotlin 1.4, Kotlin plugin 1.4.20-release-Studio4.1.1, and KMM plugin 0.2.0-release-65-Studio4.1.
Here’s a snapshot of my sourceSets from build.gradle.kt (:shared)

val ktor_version = "1.4.2"
    sourceSets {
        val commonMain by getting {
            dependencies {
                implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.0.1")
                implementation("io.ktor:ktor-client-core:$ktor_version")
                implementation("io.ktor:ktor-client-serialization:$ktor_version")
            }
        }
        val commonTest by getting {
            dependencies {
                //... 
                implementation("io.ktor:ktor-client-core:$ktor_version")
            }
        }
        val androidMain by getting {
            dependencies {
                //... 
                implementation("io.ktor:ktor-client-android:$ktor_version")
                implementation("io.ktor:ktor-client-serialization-jvm:$ktor_version")
            }
        }
        val androidTest by getting {
            dependencies {
                //... 
                implementation("io.ktor:ktor-client-android:$ktor_version")
            }
        }
        val iosMain by getting {
            dependencies {
                implementation("io.ktor:ktor-client-ios:$ktor_version")
                implementation("io.ktor:ktor-client-serialization:$ktor_version")
            }
        }
        val iosTest by getting {
            dependencies {
                implementation("io.ktor:ktor-client-ios:$ktor_version")
                implementation("io.ktor:ktor-client-serialization:$ktor_version")
            }
        }
    }

Here’s the failing Swift code

func getLocations() {
        let apiService = ApiService()
        apiService.about { (htmlString) in
            print("🦋 htmlString:\n \(htmlString)")
        }
}

struct ContentView: View {
    var body: some View {
        Text(greet()).onAppear {
            print("isMainThread: \(Thread.isMainThread)")
            getLocations()
        }
    }
}

Here’s the complete stacktrace from the iOS app.

[Cicero]

isMainThread: true
Function doesn't have or inherit @Throws annotation and thus exception isn't propagated from Kotlin to Objective-C/Swift as NSError.

[Cicero]

I believe you forgot this annotation at the top of your functions

[Cicero]

@Throws(Exception::class)
suspend fun getMeIOS(token: String): Me? {
    return client.get<Me> {
        url("https://")
        accept(ContentType.Application.Json)
        contentType(ContentType.Application.Json)
        header(
            "Authorization",
            token
        )
    }
}

[BollywoodVillain]

Interesting, In the ktor client-mpp sample it’s not there. Let me try it out

[Cicero]

That’s the error that’s popping at least

[BollywoodVillain]

in fact the function doesn’t even say suspend in the ktor-samples

[Cicero]

weird

[Cicero]

let me give you a sample of how I unwrap this on my front

[BollywoodVillain]

here’s what it says in the ktor github

package io.ktor.samples.mpp.client
import io.ktor.client.*
import io.ktor.client.request.*
import io.ktor.http.*
import kotlinx.coroutines.*

internal expect val ApplicationDispatcher: CoroutineDispatcher

class ApplicationApi {
    private val client = HttpClient()

    var address = Url("<https://tools.ietf.org/rfc/rfc1866.txt>")

    fun about(callback: (String) -> Unit) {
        GlobalScope.apply {
            launch(ApplicationDispatcher) {
                val result: String = client.get {
                    url([e-mail]())
                }
                callback(result)
            }
        }
    }
}

[Cicero]

And you believe them?

[Cicero]

🙂

[BollywoodVillain]

let me give you a sample of how I unwrap this on my front

much appreciated! I was banging my head traversing the interwebz for this error

[BollywoodVillain]

And you believe them?

Us newbies have no other choice 😅

[Cicero]

let login = common.LoginModel(email: emailTextfield.text, password: passwordTextField.text, userType: String(describing:UserType.professional))
     
    *if*(login.isNotNullOrEmpty()){
      common.PostLoginKt.postLoginIOS(login: login, completionHandler: {
        login, error in
         
        *if*(login != “”){
          if let token = login {
          }
        }
      }
      }

[Cicero]

something like this to unwrap

[Cicero]

I believe there may be some extra }

[BollywoodVillain]

However the error occur when I initialize the ApiService class, not when I call the suspend func. Let me check once

[BollywoodVillain]

yes, the error is \*not\* on function call, but on the instantiation of the ApiService variable on Swift.

[Cicero]

k

[Arkadii Ivanov]

I think the code should not crash, so there is no need for @Throws annotation. The error says that it could mutate the frozen ApiService object. You can add ensureNeverFrozen() into its init section, so you will get a stack trace of the place, where it is actually gets frozen.

[Cicero]

let me see what I have here

[Cicero]

Funny, I just read your article @Arkadii Ivanov

[Cicero]

This is my sourceSet

sourceSets {
    val ktorVersion = "1.4.2"
    val serializationVersion = "1.0.0-RC"
    val coroutineVersion = "1.3.9-native-mt-2"

    val commonMain by getting {
        val commonCore = "io.ktor:ktor-client-core:$ktorVersion"
        val commonJson = "io.ktor:ktor-client-json:$ktorVersion"
        val commonSerialization = "io.ktor:ktor-client-serialization:$ktorVersion"
        val commonSerializationCore = "org.jetbrains.kotlinx:kotlinx-serialization-core:$serializationVersion"
        val common = "org.jetbrains.kotlinx:kotlinx-coroutines-core:$coroutineVersion"

        dependencies {
            implementation(commonCore)
            implementation(commonSerializationCore)
            implementation(commonJson)
            implementation(commonSerialization)
            implementation(common)
        }
    }
    val androidMain by getting {
        val ktorAndroid = "io.ktor:ktor-client-android:${ktorVersion}"
        dependencies {
            implementation(ktorAndroid)
        }
    }
    val iosMain by getting{
        val ktoriOS = "io.ktor:ktor-client-ios:${ktorVersion}"
        dependencies {
            implementation(ktoriOS)
        }
    }
}

[Cicero]

private val json = Json {
    isLenient = true; ignoreUnknownKeys = true; coerceInputValues = true; useArrayPolymorphism =
    true
}

internal val client = HttpClient() {
    install(JsonFeature) {
        serializer = KotlinxSerializer(json)
    }
}

[Arkadii Ivanov]

Looks like HttpClient lambda freezes the captured ApiService object. Try to avoid the json field, create the JSON directly in HttpClient lambda

[Cicero]

Hm, maybe you’re trying to do something different of what I did but, this is what I used to run Ktor

[BollywoodVillain]

ok, so you mean this line in ApiService.kt is the culprit:

url([e-mail]())

[Cicero]

Why do you initialise your Api inside swift?

[Cicero]

and not inside of common?

[BollywoodVillain]

I am just trying to call the network service from the swift side

[BollywoodVillain]

(I am totally new to Kotlin Multiplatform so doing things by trial and error)

[Cicero]

Hm

[Cicero]

If you try out the samples I posted it should work

[BollywoodVillain]

Ok, I got several pointers let me try one by one and see which works

[Cicero]

I only make a common.myFucntionCall from iOS side

[Arkadii Ivanov]

Untitled

[Arkadii Ivanov]

Could you try this?

[BollywoodVillain]

Looks like HttpClient lambda freezes the captured ApiService object. Try to avoid the json field, create the JSON directly in HttpClient lambda

That’s what I’m trying. Thanks

[BollywoodVillain]

You can add ensureNeverFrozen() into its init section

strangely android studio can’t find ensureNeverFrozen()  reference when I do this:

class ApiService {
    init {
        ensureNeverFrozen()
    }
//...
}

[Arkadii Ivanov]

You need expect/actual it

[BollywoodVillain]

Wow it worked! damn it feels good 😄

[BollywoodVillain]

Thanks a lot guys, much appreciated!

[BollywoodVillain]

You need expect/actual it

Do you have any pointers on how to do this?

[BollywoodVillain]

This hands-on doc doesn’t say anything about expect/actual

[Arkadii Ivanov]

Absolutely, here is the native actual part.

[Arkadii Ivanov]

Non-native variants are just no-ops

[BollywoodVillain]

Ah ok, thanks will take a look. TBH this expect/actual is quite cool, much better than what I had to do to get C++ interop with iOS/Android.

[Arkadii Ivanov]

So when you see an InvalidMutabilityException , it's shows you the place where the mutation attempt of a frozen object happened. If you you add ensureNeverFrozen to that class, you will get another exception earlier, on freeze attempt.

[nrobi]

Also if you’re using Ktor, there is preventFreeze(), which is essentially the same expect/actual and uses ensureNeverFrozen on the native part

[BollywoodVillain]

I see, I’ll add that to me notes now. Quite a different array of tools we’ve got here

[Cicero]

I’m a little bit lost now about the difference in my approach and hist and the advantages of both 🤔

[Michal Klimczak]

@BollywoodVillain did you eventually succeed? Because I have exactly the same issue.

private val kotlinxSerializer = KotlinxSerializer(jsonConfig)
   
    private val httpClient: HttpClient = HttpClient {
        install(JsonFeature) {
            serializer = kotlinxSerializer
        }
    }

If I remove serializer = kotlinxSerializer, it doesn't crash.

(Also if I add preventFreeze, the project doesn't compile at all with Command PhaseScriptExecution failed with a nonzero exit code )

I have all ktor dependencies on 1.4.2 and corotuines at 1.4.2-native-mt.

[Michal Klimczak]

found this config here, but it crashes with the same error

val ktorVersion = "1.4.1" //"1.4.2"
        val coroutineVersion = "1.3.9-native-mt-2" //"1.4.2-native-mt-2"
        val kotlinxSerialization = "1.0.0-RC2" //"1.0.1"

[BollywoodVillain]

@Michal Klimczak A bit late to reply but I fixed the issue by moving the Json formatter inside the KotlinXSerializer init(). You can find the final working source code here:
https://github.com/samkhawase/Kotlin_MPP_Demo

[Michal Klimczak]

thanks, I'll try that. I wonder why it crashes for us but is apparently not a big deal for anyone else.

[BollywoodVillain]

There’s a slight difference in your code and mine. I init the KotlinxSerializer inside the install(JsonFeatue){ block. You can see my ApiSErvice.kt file for reference.

[Michal Klimczak]

yes, I just tried that and it works that way. But I also looked at this code (not mine) https://github.com/joreilly/galway-bus-android/blob/5925fa3c5b6e9f4d9e8101976dac3b[…]nMain/kotlin/com/surrus/galwaybus/common/remote/GalwayBusApi.kt

[Michal Klimczak]

not a big deal but I find it strange - somehow this Galway app works "the right way" apparently

[Michal Klimczak]

anyway, thank you very much for help 🙂