kotlinlang #serialization

I'm experimenting with writing my own serialization format. How would I best handle it, if the underlying format can handle certain types (like for example a Timestamp) natively? Would I detect this type in

Encoder#encodeSerializableValue

and act accordingly?

Stylianos Gakis

10/13/2020, 9:34 PM

I decided to try out Kotlin Serialization in a Jetpack Compose project and I am experiencing some issues. Basically the moment I include the "@Serializable" annotation over a data class, the compilation never goes over the app:compileDebugKotlin step, it's stuck there infinitely. If I just remove that one line it compiles just fine. Is there a template somewhere that I can follow to file this as a potential bug?

aleksey.tomin

10/14/2020, 1:12 PM

I try to use kotlin.serialization (1.0.0) with ktor (1.4.1) and kotlin (1.4.10) I have too classes:

@Serializable
class Holder<T> (val value: T)

@Serializable
class StringHolderDirect (val value: String)

The both work with Json directly

Json.encodeToString(StringHolderDirect(""))
    Json.encodeToString(Holder(""))}

but with ktor works only the second, the first produces an error:

val client = HttpClient(CIO) {
        this.install(JsonFeature) { serializer = KotlinxSerializer() }
    }
    <http://client.post|client.post><String>(URL) {
        contentType(ContentType.Application.Json)
        body = Holder("")
    }

On run:

Exception in thread "main" kotlinx.serialization.SerializationException: Serializer for class 'Holder' is not found.
Mark the class as @Serializable or provide the serializer explicitly.
        at kotlinx.serialization.internal.Platform_commonKt.serializerNotRegistered(Platform.common.kt:91)
        at kotlinx.serialization.SerializersKt__SerializersKt.serializer(Serializers.kt:130)
        at kotlinx.serialization.SerializersKt.serializer(Unknown Source)
        at io.ktor.client.features.json.serializer.KotlinxSerializerKt.buildSerializer(KotlinxSerializer.kt:77)

What do I wrong?

aarjav

10/14/2020, 2:00 PM

Given a class

data class Node<T: Any>(val id: String, val type: String, val value: T)

, is it possible to deserialize

value

based on the

type

field?

Tomas Kormanak

10/14/2020, 2:16 PM

Is there a way how to deserialize JSON into dynamic object? For example I have a data class, but I don't know the structure of prop2

@Serializable
data class (
val prop1:String
val prop2:dynamic
)

and JSON:

{
  "prop1": "somestring",
  "prop2": {
    "a": 1,
    "b": 2
  }
}

Olaf Gottschalk

10/14/2020, 2:57 PM

I wanted to switch from Jackson to kotlinx serialization. But in my project I use two aspects heavily:

@JsonRawValue

for a string that already IS a valid Json string that needs to be put into the encoded result without any intervention, no escaping, nothing - and secondly I always work on unknown structures using

Map<String, Any?>

as my data values. How can kotlinx-serialization do these two things?

👍 1

Big Chungus

10/15/2020, 2:57 PM

Hi guys, is it possible to deserialize json into unknown class (class provided by library consumer) like in gson for example via

Gson().fromJson(<str>, <any java class>.class)

jaqxues

10/15/2020, 6:38 PM

Hello, I previously used Gson and used the "Type" parameter pretty often, to serialize more complex elements. When i now wanted to switch to kotlinx.serialization, this was the thing that ended up not working for me.

@OptIn(InternalSerializationApi::class)
fun main() {
    val pairJson = """
        { 
          "first": "a",
          "second": 0
        }
    """.trimIndent()
    println(Json.decodeFromString(serializer<Pair<String, Int>>(), pairJson))

    println(Json.decodeFromString(serializer(object : TypeToken<Pair<String, Int>>() {}.type), pairJson))
}

As you can see, when using reified types, it works just fine, but as soon as i try to use type:

kotlinx.serialization.SerializationException: Serializer for class 'Pair' is not found.

Now, I know that TypeToken is a class and weird type generic stuff from Gson, so I am not necessarily asking for a fix. I just do not know what would be the best way to handle this problem. I suppose implementing the full kotlin reflection library and using

createType

to create generic KTypes? The type has to be stored in a property, so imagine a

Data

container that needs the type

class Data {
    // Allow KClass for simpler JsonElements to be deserialized
    val type: Either<KClass<*>, KType<*>>

    fun deserialize() { ... }
}

manlan

10/16/2020, 9:34 AM

kotlinx.serialization.SerializationException: Serializer for class 'UUID' is not found.

Mark the class as @Serializable or provide the serializer explicitly.

I know UUID is not serializable. How do I do provide a serializer in Ktor?

KamilH

10/16/2020, 9:55 AM

Does anyone else faces following problem

e: Compilation failed: Deserializer for declaration public kotlinx.serialization/UpdateMode|null[0] is not found

when running

compileKotlinIos

task? I’m using

kotlinx-serialization-core:1.0.0

1.0.0-RC2

it was working properly

KamilH

10/16/2020, 10:06 AM

Another issue: I’m working on a multiplatform library and I’m using both

ktor 1.4.1

and

serialization 1.0.0

. When I’m building and publishing it is works fine, but when I’m trying to use it in another project I’m getting a lot of “duplication” errors:

Duplicate class kotlinx.serialization.BinaryFormat found in modules jetified-kotlinx-serialization-core-jvm-1.0.0.jar (org.jetbrains.kotlinx:kotlinx-serialization-core-jvm:1.0.0) and jetified-kotlinx-serialization-runtime-0.20.0.jar (org.jetbrains.kotlinx:kotlinx-serialization-runtime:0.20.0)

I found some message that suggest to exclude it in a following way:

implementation(io.ktor:ktor-client-serialization:1.4.1) {
    exclude(group = "org.jetbrains.kotlinx", module = "kotlinx-serialization-runtime")
}

but it doesn’t help

Big Chungus

10/17/2020, 12:34 AM

Has anyone writen a serial format lib for XML yet?

kartik1712

10/18/2020, 7:34 AM

e: java.lang.IllegalStateException: Cannot get FQ name of local class: class <no name provided> : at.yawk.javap.model.ConfigProperty.Choice<kotlin.String?> defined in private final val propertyLanguageVersion: <no name provided> defined in at.yawk.javap.model.ConfigProperties
	at org.jetbrains.kotlin.serialization.DescriptorAwareStringTable$DefaultImpls.getFqNameIndex(DescriptorAwareStringTable.kt:26)
	at org.jetbrains.kotlin.serialization.StringTableImpl.getFqNameIndex(StringTableImpl.kt:25)
	at org.jetbrains.kotlin.serialization.DescriptorSerializer.getClassifierId(DescriptorSerializer.kt:729)
	at org.jetbrains.kotlin.serialization.DescriptorSerializer.fillFromPossiblyInnerType(DescriptorSerializer.kt:601)
	at org.jetbrains.kotlin.serialization.DescriptorSerializer.type$serialization(DescriptorSerializer.kt:568)
	at org.jetbrains.kotlin.serialization.DescriptorSerializer.typeId(DescriptorSerializer.kt:535)
	at org.jetbrains.kotlin.serialization.DescriptorSerializer.propertyProto(DescriptorSerializer.kt:252)
	at org.jetbrains.kotlin.serialization.DescriptorSerializer.classProto(DescriptorSerializer.kt:113)
	at org.jetbrains.kotlin.cli.metadata.MetadataSerializer$PackageSerializer.serializeClasses(MetadataSerializer.kt:149)
	at org.jetbrains.kotlin.cli.metadata.MetadataSerializer$PackageSerializer.run(MetadataSerializer.kt:133)
	at org.jetbrains.kotlin.cli.metadata.MetadataSerializer$performSerialization$1.visitClassOrObject(MetadataSerializer.kt:86)
	at org.jetbrains.kotlin.psi.KtVisitorVoid.visitClassOrObject(KtVisitorVoid.java:465)
	at org.jetbrains.kotlin.psi.KtVisitorVoid.visitClassOrObject(KtVisitorVoid.java:21)
	at org.jetbrains.kotlin.psi.KtVisitor.visitObjectDeclaration(KtVisitor.java:37)
	at org.jetbrains.kotlin.psi.KtVisitorVoid.visitObjectDeclaration(KtVisitorVoid.java:413)
	at org.jetbrains.kotlin.psi.KtVisitorVoid.visitObjectDeclaration(KtVisitorVoid.java:1013)
	at org.jetbrains.kotlin.psi.KtVisitorVoid.visitObjectDeclaration(KtVisitorVoid.java:21)
	at org.jetbrains.kotlin.psi.KtObjectDeclaration.accept(KtObjectDeclaration.kt:63)
	at org.jetbrains.kotlin.psi.KtElementImplStub.accept(KtElementImplStub.java:59)
	at org.jetbrains.kotlin.cli.metadata.MetadataSerializer.performSerialization(MetadataSerializer.kt:60)
	at org.jetbrains.kotlin.cli.metadata.MetadataSerializer.serialize(MetadataSerializer.kt:48)
	at org.jetbrains.kotlin.cli.metadata.K2MetadataCompiler.doExecute(K2MetadataCompiler.kt:111)
	at org.jetbrains.kotlin.cli.metadata.K2MetadataCompiler.doExecute(K2MetadataCompiler.kt:40)
	at org.jetbrains.kotlin.cli.common.CLICompiler.execImpl(CLICompiler.kt:86)
	at org.jetbrains.kotlin.cli.common.CLICompiler.execImpl(CLICompiler.kt:44)
	at org.jetbrains.kotlin.cli.common.CLITool.exec(CLITool.kt:98)
	at org.jetbrains.kotlin.daemon.CompileServiceImpl.compile(CompileServiceImpl.kt:1549)
	at jdk.internal.reflect.GeneratedMethodAccessor164.invoke(Unknown Source)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:564)
	at java.rmi/sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:359)
	at java.rmi/sun.rmi.transport.Transport$1.run(Transport.java:200)
	at java.rmi/sun.rmi.transport.Transport$1.run(Transport.java:197)
	at java.base/java.security.AccessController.doPrivileged(AccessController.java:691)
	at java.rmi/sun.rmi.transport.Transport.serviceCall(Transport.java:196)
	at java.rmi/sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:587)
	at java.rmi/sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:828)
	at java.rmi/sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.lambda$run$0(TCPTransport.java:705)
	at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
	at java.rmi/sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:704)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:630)
	at java.base/java.lang.Thread.run(Thread.java:832)

Matthew Bartos

10/20/2020, 7:50 AM

Hey, hey! 👋 I’m trying to convince my team to switch to the

kotlinx.serialization

and I want to show them the performance comparison between

GSON

and

kotlinx.serialization

Can anyone show me some proper benchmarks?

Alec Muffett

10/20/2020, 3:48 PM

Hi Everyone! I am a Kotlin noob (but have about 21 years of Java on-and-off, so I got that goin for me which is nice) — and I am playing with serialisation of immutable, signed objects to send over the network. I am starting to read up on Kotlin serialisation but - in parallel with that - I was wondering if anyone had enough experience of Square.com's "Wire" library (https://square.github.io/wire/ - see

Wire Kotlin

section) which I've used in Java before to provide elegant/ish cross-platform serialisation. What I am seeking is: perspective on whether the problems which Wire addresses for Java, are still an issue with native Kotlin protobuf support and/or serialisation? Typically Java coders who like Wire are looking for generation of lightweight (field-not-getter) code for Java - to reduce method proliferation - and simpler syntax. Wire has Kotlin support, but given Kotlin's pragmatism, I am wondering how necessary it is, please?

Javier

10/21/2020, 10:05 AM

Should avoid

@Serializer

in companion objects?

christophsturm

10/21/2020, 11:08 AM

when i upgrade my project from 1.4.0 to 1.4.10 i get this error with the IR backend:

Unbound public symbol for public kotlinx.serialization.json/JsonElementSerializer.patch

andyg

10/22/2020, 9:19 AM

is it possible to write a custom serializer (kotlinx.serialization) for serializing only, and not overriding deserialize? I get an error if I don't specifically override deserialize too. Alternatively, how can I write the deserialize method to use the default or built-in deserializer? (this is for a data class, not a primitive). There's no

super

to leverage. Thank you.

savrov

10/23/2020, 4:38 PM

Hi, I have followed a tutorial to create a custom serialization for my generic class. But i am still stacked with error:

SerializationException: Serializer for class 'ApiResponse' is not found. Mark the class as @Serializable or provide the serializer explicitly.

ApiResponse

class looks like this:

@Serializable(with = ApiResponseSerializer::class)
class ApiResponse<T>(
    @SerialName("data")
    val data: T? = null,
    @SerialName("error")
    val error: ApiError? = null
)

And

ApiResponseSerializer

, that is used in annotation above is:

class ApiResponseSerializer<T>(private val dataSerializer: KSerializer<T>) : KSerializer<ApiResponse<T>> {
    
    override val descriptor: SerialDescriptor = buildClassSerialDescriptor("ApiResponseDataSerializer") {
        val dataDescriptor = dataSerializer.descriptor
        element("data", dataDescriptor)
        element("error", ApiError.serializer().descriptor)
    }
    
    override fun deserialize(decoder: Decoder): ApiResponse<T> =
        decoder.decodeStructure(descriptor) {
            var data: T? = null
            var error: ApiError? = null
            loop@ while (true) {
                when (val i = decodeElementIndex(descriptor)) {
                    0 -> data = decodeSerializableElement(descriptor, i, dataSerializer)
                    1 -> error = decodeSerializableElement(descriptor, i, ApiError.serializer())
                    CompositeDecoder.DECODE_DONE -> break
                    else -> throw SerializationException("Unknown index $i")
                }
            }
            ApiResponse(data, error)
        }
        
    override fun serialize(encoder: Encoder, value: ApiResponse<T>) {
        encoder.encodeStructure(descriptor) {
            encodeNullableSerializableElement(descriptor, 0, dataSerializer, value.data)
            encodeNullableSerializableElement(descriptor, 1, ApiError.serializer(), value.error)
        }
    }
}

Then, when i’m trying to serialise my data object, i receive an exception I’ve mentioned above.

Json.encodeToString(ApiResponse(data = response.data))
---- OR ----
Json.encodeToString(ApiResponse.serializer(T::class.serializer()), ApiResponse(data = response.data))

Can someone tell me where i’m wrong? Thank you.

jaqxues

10/24/2020, 3:39 PM

The gradle plugin is freezing

app:compileDebugKotlin

for me now, is that a known issue or what is going on?

Paul Griffith

10/26/2020, 11:43 PM

Is there a way to require the type-discriminator's presence during serialization, even if the serialization case doesn't actually need discriminating? That is, I'm putting a specific member of a sealed class inside a sealed class, and, for the API's sake, I want to include the

type

key, but if I type the field in the data class to the specific sealed class member, it just serializes the different properties and does not include the type discriminator (by design, surely - but I'm hoping to avoid it anyways)

Tatum Alenko

10/27/2020, 7:07 AM

This might sound like a silly question but does anyone mind explaining what characterizes kotlinx.serialization to be considered "reflectionless"?

Evilthreads669966

10/27/2020, 8:59 AM

I'm trying to serialize lambdas into a Room database table. I've been working on it for a week and have switched from Gson to kotlinx serialization. Has anyone ever come across this. I've tried doing SAM, FunctionalInteface from jdk, and an open class with an open function. Kotlin states that lambdas are serializable by default. I'm performing the serialization for the function types inside of a Converters class

😔 1

😮 1

kingsley

10/27/2020, 10:33 AM

🙏

Nikky

10/27/2020, 12:03 PM

so.. serializable classes with fields default values having dependencies on other fields is not working well.. what workarounds would you recommend for that?

starsep

10/28/2020, 12:06 PM

Is it possible to try deserializing String to one of types provided?

FooResponse

is sealed class, I don't control response and therefore cannot add type discriminator as described in https://github.com/Kotlin/kotlinx.serialization/blob/master/docs/polymorphism.md#sealed-classes At the moment I use this ugly code, is there a better way?

val jsonData = jsonSerializer.parseToJsonElement(responseData)

try {
    Json.decodeFromJsonElement<FooResponse.SuccessData>(jsonData)
} catch (e: SerializationException) {
    try {
        Json.decodeFromJsonElement<FooResponse.AnotherCase>(jsonData)
    } catch (e: SerializationException) {
        Json.decodeFromJsonElement<FooResponse.ErrorData>(jsonData)
    }
}

Jovan

10/28/2020, 12:42 PM

Hi guys. I need some help.

val module = SerializersModule {
    polymorphic(Project::class) {
        subclass(OwnedProject::class)
    }
}

So, I was looking into Open polymorphism and can’t get it working for me. For some reason it only works when I have two levels, like in the example from above. How to init SerializersModule in case I have 3+ levels (e.g. OwnedProject is parent of OwnedChildeProject)?

rnentjes

10/28/2020, 3:17 PM

Hi, documentation for serialization seems to be out of date, is that correct? For example: https://github.com/Kotlin/kotlinx.serialization/blob/master/docs/polymorphism.md This doesn't work anymore with 1.0.0:

val module = SerializersModule {
    polymorphic(Project::class) {
        subclass(OwnedProject::class)
    }
}

Is there up to date documentation somewhere?

Joaquim Ley

10/28/2020, 3:23 PM

(I’ve initially posted this in #ktor but it feels like it might make more sense to ask here: ---- Hello fellow kotliners, I’m haivng an issue where my ktor client is not parsing the response correctly.. The body “ends” unexpectedly, looking at the logs is simply stops “parsing the json” from the response. I’ve double checked with postman and the response from the API is correct.

[14:55] kotlinx.serialization.json.internal.JsonDecodingException: Unexpected JSON token at offset 82: Expected string literal with quotes.

For some context the body seems to be cut randomly and the rest of the response is not parsed, using latest versions for both ktor and kotlinx.serialisation

rnentjes

10/28/2020, 3:36 PM

Anyone run into this one yet?:

java.lang.NoSuchMethodError: kotlinx.serialization.internal.AbstractPolymorphicSerializer.findPolymorphicSerializerOrNull(Lkotlinx/serialization/encoding/Encoder;Ljava/lang/Object;)Lkotlinx/serialization/SerializationStrategy;
	at kotlinx.serialization.PolymorphicSerializerKt.findPolymorphicSerializer(PolymorphicSerializer.kt:96)
	at kotlinx.serialization.json.internal.PolymorphicKt.findActualSerializer(Polymorphic.kt:29)
	at kotlinx.serialization.json.internal.PolymorphicKt.access$findActualSerializer(Polymorphic.kt:1)
	at kotlinx.serialization.json.internal.StreamingJsonEncoder.encodeSerializableValue(StreamingJsonEncoder.kt:226)
	at kotlinx.serialization.encoding.AbstractEncoder.encodeSerializableElement(AbstractEncoder.kt:81)
	at kotlinx.serialization.internal.MapLikeSerializer.serialize(CollectionSerializers.kt:123)
	at kotlinx.serialization.json.internal.StreamingJsonEncoder.encodeSerializableValue(StreamingJsonEncoder.kt:223)
	at kotlinx.serialization.encoding.AbstractEncoder.encodeSerializableElement(AbstractEncoder.kt:81)

This is KMM with serialization plugin 1.4.10 and dependency 'kotlinx-serialization-json:1.0.0' in common. The error happens on the jvm with a sealed class.

Title

rnentjes

10/28/2020, 3:36 PM

Anyone run into this one yet?:

java.lang.NoSuchMethodError: kotlinx.serialization.internal.AbstractPolymorphicSerializer.findPolymorphicSerializerOrNull(Lkotlinx/serialization/encoding/Encoder;Ljava/lang/Object;)Lkotlinx/serialization/SerializationStrategy;
	at kotlinx.serialization.PolymorphicSerializerKt.findPolymorphicSerializer(PolymorphicSerializer.kt:96)
	at kotlinx.serialization.json.internal.PolymorphicKt.findActualSerializer(Polymorphic.kt:29)
	at kotlinx.serialization.json.internal.PolymorphicKt.access$findActualSerializer(Polymorphic.kt:1)
	at kotlinx.serialization.json.internal.StreamingJsonEncoder.encodeSerializableValue(StreamingJsonEncoder.kt:226)
	at kotlinx.serialization.encoding.AbstractEncoder.encodeSerializableElement(AbstractEncoder.kt:81)
	at kotlinx.serialization.internal.MapLikeSerializer.serialize(CollectionSerializers.kt:123)
	at kotlinx.serialization.json.internal.StreamingJsonEncoder.encodeSerializableValue(StreamingJsonEncoder.kt:223)
	at kotlinx.serialization.encoding.AbstractEncoder.encodeSerializableElement(AbstractEncoder.kt:81)

This is KMM with serialization plugin 1.4.10 and dependency 'kotlinx-serialization-json:1.0.0' in common. The error happens on the jvm with a sealed class.

sandwwraith

10/28/2020, 6:30 PM

maybe you have old version (1.0.0-RC or 0.20.0) included somewhere in the classpath

rnentjes

10/28/2020, 7:24 PM

Thx, you are right, there was another version included through a ktor dependency.

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