good morning, I’m sorry if this is a recurring or a trivial question but it’s my first time I had to write custom serializer/deserializer for a project and i’m a little confused. I have to migrate an old GSON Deserializer for a data class that look like this:

@Serializable(with = PaymentInfoSerializer::class)

data class PaymentInfo(

val id: PaymentId,

val amount: Float,

val paidAt: String?,

val productId: ProductId

)

The last field is a typealias for a Int type but it’s actually an evaluated one. The field is a field taken from an inner Json Object like this:

"product":{"id":74}

so the value is just the id field. The entire json is like this one:

"id":22,"paidAt":null,"amount":720.0,"description":null,"product":{"id":74}

So my problem is that I can’t use simple deserilization with dataclass because I have to keep the code working but i can’t figure out how a map object is actually descripted inside a desirializer. I’have written a descriptor like this but i’m not sure how ti could work as I have no way to tell it to take just the id field inside the map:

override val descriptor: SerialDescriptor =

buildClassSerialDescriptor("PaymentInfo") {

element<PaymentId>("id")

element<Float>("amount")

element<String?>("paidAt", isOptional = true)

element<Map<String, Int>>("product")

}

At the end, i’ve to find a way to tell serilization to do something like this in GSON:

productId = jsonObject.get("product").asJsonObject.get("id").asInt

I've read the doc but I can't find some example that actually seems to fit and since I have to migrate a lot of this custom serializer I'm tring to start with the correct structure. Is there someone who could help? Thanks

[Resolved] I’ve started seeing this error on iOS recently

* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x8)

`frame #0: 0x000000010d014d10 MyFramework`kfun:kotlinx.serialization.json.Json#encodeToString(kotlinx.serialization.SerializationStrategy<0:0&gt;;0:0){0§<kotlin.Any?>}kotlin.String [inlined] Composer at Composers.kt:13:9` I’m using a standard

json.encodeToString(Model.serializer(), model)

using

private val json = Json {
    isLenient = true
    ignoreUnknownKeys = true
}

Everything works fine on Android, but fails on iOS. What should I be looking for?

Hi folks, I’m trying to find my way around R8 / ProGuard config. I’m just using a dummy test project with

minifyEnabled true

on the release build. My question is, is it necessary to configure ProGuard for Kotlin serialization, if you always provide a serializer explicitly? So I mean, in every case I call it like this:

serializer.decodeFromString(MyData.serializer(), json)
// or
serializer.encodeToString(MyData.serializer(), myObj)

On observation, my program seems to work fine with obfuscation enabled, without any ProGuard configuration, if I am passing the serializer like this. This seems to contradict the docs:

The library works on Android, but, if you’re using ProGuard, you need to add rules to your

<http://proguard-rules.pro|proguard-rules.pro>

configuration to cover all classes that are serialized at runtime.

Why variable that starts with

is

is omitted while serialization? I have data class

@Serializable
public data class Config(
    val isVariable: String,
    val anotherVariable: String
)

Config("omit", "value")

Output will be:

{anotherVariable:"value"}

P.S. isVariable should be boolean, I know, anyway it should be a String in my case

Hello! Are there any plans to fix this: https://github.com/Kotlin/kotlinx.serialization/issues/1051 It’s a real pain in the neck. Unfortunately, it is the reason to reject using kotlin.serialization in systems with money involved

Is there a better way to get the serializer for a generic type if it’s not reified but you have its class?

class Generic<T : Any>(
    private val clazz: KClass<out T>,
) {

    init {
        require(clazz.hasAnnotation<Serializable>())
    }

    fun serialize(value: T): String {
        val type = clazz.createType()
        val serializer = Json.serializersModule.serializer(type)
        return Json.encodeToString(serializer, value)
    }

}

How experimental is

SerializersModule.getContextual(...)

? I’ve got a library that uses this behavior. I’m fine to ship a new release if this function’s signature changes, but I’m in deep trouble if the feature goes away altogether!

ALSO! I’m looking forward to stable APIs for

Json.decodeFromDynamic

+

Json.encodeToDynamic

. On the JS engine I’m using (QuickJS) using these APIs has a massive performance advantage over doing encoding with Kotlin/JS and StringBuilder. (QuickJS doesn’t use ropes internally in its strings, so

StringBuilder

is sloooow!) Any ETA on stability here? Would y’all accept a pull request to remove

@ExperimentalSerializationApi

on these?

What is this?

java.lang.VerifyError: class kotlinx.serialization.json.internal.StreamingJsonDecoder overrides final method kotlinx.serialization.encoding.AbstractDecoder.decodeSerializableElement(Lkotlinx/serialization/descriptors/SerialDescriptor;ILkotlinx/serialization/DeserializationStrategy;Ljava/lang/Object;)Ljava/lang/Object;

I have an arrow Either deserializer that I found in a thread here, that I’ve slightly modified, but for some reason it fails if my object has a different class discriminator, even if I specify a specific one just for the deserializer. no clue what’s going on. anyone?

class EitherSerializer<R>(
    private val leftSerializer: KSerializer<PricingError>,
    private val rightSerializer: KSerializer<R>,
) : KSerializer<Either<PricingError, R>> {
    override val descriptor: SerialDescriptor
        get() = rightSerializer.descriptor

    private val errorJson = Json {
        ignoreUnknownKeys = true
        isLenient = true
        encodeDefaults = true
    }

    override fun deserialize(decoder: Decoder): Either<PricingError, R> {
        require(decoder is JsonDecoder) { "only works in JSON format" }
        val element = Either.catch {
            decoder.decodeJsonElement()
        }.mapLeft { PricingError.SerializationError(it.localizedMessage) }
        return when (element) {
            is Either.Left -> element
            is Either.Right -> {
                try {
                    decoder.json.decodeFromJsonElement(rightSerializer, element.value).right()
                } catch (_: SerializationException) {
                    errorJson.decodeFromJsonElement(leftSerializer, element.value).left() // fails here with error in thread
                }
            }
        }
    }

    override fun serialize(encoder: Encoder, value: Either<PricingError, R>) {
        TODO("Not yet implemented")
    }
}

i have a public interface with properties in module A, a private data class implementing the interface in module B, and in module C (the only one I control) i need to create a serializer for the interface type (for encoding only). Are my only options a manually-written serializer for the interface or a surrogate? i really would like to avoid having to maintain a hand-written serializer but also would like the serialize without extra allocation of surrogates for every instance in the outgoing tree. My dream would be external seriazation generation through

@Serializer(forClass=)

but for an interface where the generated decoder throws UOE, or I could manually override decode and throw UOE

Hi I'm trying to deserialize json to a sealed class, but it fails with a decoding exception that says

Exception in thread "main" kotlinx.serialization.json.internal.JsonDecodingException: Expected JsonPrimitive at self, found {"href":"<https://horizon.stellar.org/operations/122511124621283329>"}

. Could anyone take a look and tell me if I'm missing something obvious?. I'll put the code in the replies.

👋 A question on proto-buff data-store in android. I realised tool like flipper doesn’t support proto-buff yet. I was writing a flipper plugin for it and the approach i took was - from client/consumer end i am converting the protobuff to json and then sending it to the flipper Android plugin, which reads it and send it’s to the desktop flipper plugin. Was wondering if there is a better approach in proto-buff world, where i can avoid converting it to json and sending it as string, as any client/server needs the

proto

schema for serialising or deserialising it.

Hello, a question on use

@SerialInfo

annotation on Java annotations: we have a Kotlin library which is depend on our Java library and use some of the Java annotations. I want to use some of the Java annotations during Kotlin serialization process. In order to do this, I have to 1) add

@SerialInfo

on the Java annotations, and 2) define an inner class

Impl

inside of my Java annotation for the Kotlin complier plugin. The working code is like below:

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.FIELD, ElementType.METHOD})
@SerialInfo  //<--------------------------------------------------------- Add this line
@kotlin.annotation.Target(allowedTargets = AnnotationTarget.PROPERTY)
public @interface ServerTimestamp {

  final class Impl implements ServerTimestamp { // <--------------------- Add this block
    @Override
    public Class<? extends Annotation> annotationType() {
      return (Class<? extends Annotation>) ServerTimestamp.class;
    }
  }
}

My question is will the complier plugin always looking for the

Impl

inner class in the future? How stable this mechanism is going to be? Thank you~

Another conjugate question: What is the process if I want to apply

@Serializable (with = customJavaSerializer.class)

annotation on a Java class? (I want to have both the class itself and the custom serializer defined in Java, but use them in Kotlin) I have tried define a Java class

Hello

, and then define a custom serializer

HelloSerializer

in Java. What is the field name or method name (like the

Impl

in the previous annotation example) should I give, so that the complier plugin can get access to my custom java serializer with

@Serializable

? Thank you very much.

Hello! How would I create a

JsonContentPolymorphicSerializer

for the following class hierarchy? I want it to select the proper serializer by checking the value of the "ok" key in the JSON and if it's true, return a

ApiResponse.Success

serializer and if false return the

ApiResponse.Error

serializer.

@Serializable
internal sealed class ApiResponse {

    @SerialName("ok") abstract val ok: Boolean

    @Serializable
    class Success<T>(
        override val ok: Boolean,
        @SerialName("result") val result: T
    ) : ApiResponse()

    @Serializable
    class Error(
        override val ok: Boolean,
        @SerialName("error_code") val errorCode: Int,
        @SerialName("description") val description: String
    ) : ApiResponse()
}

Is there any builtin datetime serialization? Or do I have to make a serializer myself?

What would be the recommended way to serialize/deserialize money amounts? I'm getting a decimal amount of money from an API and

BigDecimal

doesn't have a default serializer. Is the best thing to do creating a serializer for

BigDecimal

?

I'm parsing some JSON API responses returns an empty object

{}

if a list is empty I've written a custom serializer to handle this, and set

contextual(List::class)

in the

SerializersModule

, but I forgetting to add

@Contextual

to all the list properties. Is there a way to hardcode 'use my

EmptyListEmptyObjectSerializer

for all `List<>`s' in a

SerializersModule

?

I got an interface

Action

with normal subclass

class SomeAction : Action

and another interface subclass of type

interface ServerAction : Action

which itself has implementations like

class SpecificServerAction : ServerAction

. I’ve been trying to think of how I need to setup my SerializersModule to make all of this work. From what I understand since my interface is not sealed, I need to do something like this

polymorphic(Action::class) {
    subclass(ServerAction::class, //??)
    subclass(NavigationPushAction::class, NavigationPushAction.serializer())
    subclass(NavigationPopAction::class, NavigationPopAction.serializer())
    subclass(VoidAction::class, VoidAction.serializer())
}

but how do I do this for the ServerAction? Optimally I’d like to be able to define my ServerAction hierarchy the same way by providing all the subclasses, but I don’t see a way that the dsl allows me to do this? I could probably do this by creating my own

object ServerActionSerializer : KSerializer<ServerAction> {

and implementing it, but I’d rather not if possible? I like this subclass approach which can take care of it for me. Am I missing something, any ideas maybe? Some part of the api I can be using that I am not?

Hello, I have a Java library and a Koltin library is depending on the Java library. In the java library I have a class,

Foo.java

, Is that possible I can to mark it

@Serializable (with = ContextualSerializer<Foo>.class)

in side of Java, then use this

Foo.java

in my Kotlin library as it is

Serializable

, where inside of the Kotlin library, I define the

SerializerModule

(build a contextual serializer for Foo.java class and also a list of other classes), and then pass the

SerializerModule

to my custom ktxEncoder/ktxDecoder; The key point for me to doing this is to avoid define a Kotlin serializer for

Foo.java

in my Java library (we are trying to have at least Kotlin file in the Java lib as possible). Also trying to avoid the

@Contextual

annotation for my customers;

Is there a way to configure JSON serialization that, when deserializing, it should populate any encountered but unknown keys into some 'extras'

Map<String, JsonElement>

in the object? I've seen this feature exist in other frameworks e.g. Jackson. It can be used to afford a certain degree of future proofing to information-oriented API's e.g. the data could still be presented to the user and re-serialized as original.

So I'm implementing a format for kxs (knbt). Is there a recommended way to run tests on a format? My first thought is that it would be cool if there were some kind of "test-suite-for-3rd-party-kxs-formats" dependency I could pull in, maybe abstract test suites for

BinaryFormat

and

StringFormat

that could be extended, overriding some format-specific details (like instantiation?) Otherwise I'm thinking of using the json tests as a starting point. I think my format is already well tested, I'm just worried I've got some small oversights. I'm also looking to implement support for polymorphism which I'm less comfortable with so knowing I've got all my bases covered would be reassuring :)

What guidelines do you use for schema evolution to have forward and backward compatibility? How do you test it? I can't find anything in the docs about how older code might read a newer format and what guarantees I get

kotlinx-serialization 1.4.0-RC makes unsigned types a stable feature, so explicit opt-in is no longer required: https://github.com/Kotlin/kotlinx.serialization/pull/1962 But why the core interfaces such as Encoder/Decoder still don’t have specific

encodeU...

/

decodeU...

methods for unsigned types, so generic

encodeSerializable…

/

decodeSerializable…

methods that require explicit serializer for the value have to be used when dealing with unsigned values?

Using Kotlin 1.7.10, kotlinx.serialization 1.3.3 I'm stuck on this error, I don't know what it means. I don't know what it's looking for exactly.

> Task :linkPodDebugFrameworkIosArm64 FAILED
e: Could not find "org.jetbrains.kotlinx:kotlinx-serialization-core" in [/Users/ribesg/Projects/events, /Users/ribesg/.konan/klib, /Users/ribesg/.konan/kotlin-native-prebuilt-macos-aarch64-1.7.10/klib/common, /Users/ribesg/.konan/kotlin-native-prebuilt-macos-aarch64-1.7.10/klib/platform/ios_arm64]

If I try with kotlinx.serialization 1.4.0-RC I get this:

> Task :linkPodDebugFrameworkIosArm64 FAILED
e: Compilation failed: Expecting descriptor for kotlinx.serialization/MissingFieldException.<init>|399804788095754142[0]

 * Source files:
 * Compiler version info: Konan: 1.7.10 / Kotlin: 1.7.20
 * Output kind: STATIC_CACHE

e: java.lang.IllegalStateException: Expecting descriptor for kotlinx.serialization/MissingFieldException.<init>|399804788095754142[0]
        at org.jetbrains.kotlin.backend.konan.serialization.KonanIrLinker$KonanCachedLibraryModuleDeserializer.deserializeIrSymbol(KonanIrlinker.kt:635)
        at org.jetbrains.kotlin.backend.common.serialization.FileDeserializationState$symbolDeserializer$3.invoke(IrFileDeserializer.kt:88)
        at org.jetbrains.kotlin.backend.common.serialization.FileDeserializationState$symbolDeserializer$3.invoke(IrFileDeserializer.kt:77)
        at org.jetbrains.kotlin.backend.common.serialization.IrSymbolDeserializer.deserializeIrSymbolData(IrSymbolDeserializer.kt:67)

Hi, I’ve a use case wherein I want to parse two different attributes from a json into a single variable. It is guaranteed that I’ll be getting only one of such attribute at a time. For example my json will either be:

{"id1" : "1", "name" : "xyz"}

or

{"id2" : "1", "name" : "xyz"}

and my DTO is

data class MyObj(val id: String, val name: String)

. Is it possible to address such a use case using kotlinx serialization?

Hey guys, what the meaning of this error

kotlinx.serialization compiler plugin is not applied to the module, so this annotation would not be processed. Make sure that you've setup your buildscript correctly and re-import project.