How to serialize a reasonably complex type that is not in my control? I am interested in storing a Google Places API response, but there are a plethora of types that of course aren't marked as `@Serializable`; to avoid adding custom logic for each, is there an easy way to create the serializers as if I the classes had the annotation? Or is the best options to use a reflection based serialzer like gson?

I’m working with a backend returning a

value

attribute as part of a json payload. That attribute can potentially be of any primitive type or null. I started with a custom serializer :

class NullableAnySerializer : KSerializer<Any?> {
    override val descriptor: SerialDescriptor = // What should it be here?

    override fun serialize(encoder: Encoder, value: Any?) {
        when (value) {
            null -> encoder.encodeNull()
            is Float -> encoder.encodeFloat(value)
            is Boolean -> encoder.encodeBoolean(value)
            else -> throw IllegalStateException("unsupported type")
        }
    }

    override fun deserialize(decoder: Decoder): Any? {
        // What should it be here?
    }
}

I’m stuck at the level of

descriptor

and

deserialize()

what should I use in those places?

Will there ever be an easy way to handle

Map<String, Any>

? It's a legitimate use case that seems to have been dismissed outright. Saying "use JsonObject instead" but not providing any guidance is a recipe for frustration and buggy implementations: https://github.com/Kotlin/kotlinx.serialization/issues/296 https://github.com/Kotlin/kotlinx.serialization/issues/746 https://github.com/Kotlin/kotlinx.serialization/issues/1537 https://kotlinlang.slack.com/archives/C7A1U5PTM/p1632495920135600?thread_ts=1632392673.125200&cid=C7A1U5PTM

Is there a way to serialize an object where the type isn’t known at compile time? I’m getting this exception on Kotlin Native -

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

Hi guys, any idea/progress about this? Thanks in advance! https://github.com/Kotlin/kotlinx.serialization/issues/614

Hi there – I’m running into an unusual error linking against an Apple (iOS) framework built from a Kotlin MPP project after adding a dependency to

kotlinx-serialization-json

. The project: – contains

androidMain

,

commonMain

, and

iosMain

sourceSets – built to a framework using the

syncFramework

task created by applying the Cocoapods plugin, and run using a pod post_install hook – already uses

kotlinx-serialization-protobuf

across all source sets already without incident Our Kotlin language version is 1.5.21. The serialization plugin is applied in this manner:

plugins {
    kotlin("multiplatform")
    kotlin("native.cocoapods")
    kotlin("plugin.serialization") version "1.5.21"

And the dependency on kotlinx-serialization-protobuf is defined in this manner:

val commonMain by getting {
            dependsOn(designSystemMain)
            dependencies {
                ...
                implementation("org.jetbrains.kotlin:kotlin-stdlib-common")
                ...
                implementation("org.jetbrains.kotlinx:kotlinx-serialization-protobuf:1.2.1")
                implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.3.1")
            }
        }

A serializable class is defined like so:

@ExperimentalSerializationApi
@Serializable
data class AuthorizerRequestInfo(
    @SerialName("token")
    val token: String,
    @SerialName("client-id")
    val clientId: String,
)

Source in iosMain attempts encodes an instance of the data class in this manner:

Json.encodeToString(
    serializer = serializer(),
    value = AuthorizerRequestInfo(
        token = ...,
        clientId = ...
    )
)

The iOS framework is successfully built using the

syncFramework

command, but a linker issue occurs when statically linking the framework into the application:

Showing All Messages
Ld [redacted]/[redacted].app/[redacted] normal (in target '[redacted]' from project '[redacted]')
    cd 
    ....
Undefined symbols for architecture x86_64:
  "_kfun:kotlinx.serialization.json.JsonClassDiscriminator#<get-discriminator>(){}kotlin.String", referenced from:
      _kfun:kotlinx.serialization.json.internal#classDiscriminator__at__kotlinx.serialization.descriptors.SerialDescriptor(kotlinx.serialization.json.Json){}kotlin.String in [redacted](result.o)
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

We aren’t making use of class discriminator, note how ‘simple’ the

AuthorizerRequestInfo

class in question is, so I’m left kind of stumped. Interestingly, the tasks that compile our

iosTest

source set & links our unit test target for iOS completes successfully – we can spawn a simulator and run a test executable with them, without incident. Does anyone have guidance on how we can debug this further?

How would I go about encoding/decoding one type to another, where the second type just needs a few functions called to insert the elements. e.g: input:

@Serializable
data class ChangeOrderInput(
    val oldProposal: OldProposal,
    val newProposals: List<NewProposal>
)

output:

@Serializable
data class ChangeOrderUnit(
    val oldProposal: SingletonStore<OldProposal>,
    val newProposals: ListDataStore<NewProposal>,
) : RuleUnitData

where

ChangeOrderUnit

will always be deserialized from

ChangeOrderInput

, never the other way around, and where SingletonStore/ListDataStores are created just by calling

oldProposal.set()

or

newProposals.add()

on the stores, with the element. e.g. the only difference between the objects are that the RuleUnit object has the objects contained in stores.

I guess my question above could be better asked. What is the kotlinx-serialization equivalent of Jackson's convertValue function?

How can I convert 

Map<String, Any>

 to a data class using kotlinx.serialization?

I have a closed polymorphic structure like this (only one subclass shown for simplicity):

@Serializable
sealed class Foo<out T> {
  @Serializable
  data class Bar<out T>(
    val value: T?,
  ): Foo<T>()
}

Json.encodeToString(Foo.Bar(true))

works, but if it is wrapped inside another Serializable e.g.:

@Serializable
data class Whatever(val foo: Foo<Boolean>)

Json.encodeToString(Whatever(Foo.Bar(true)))

produces the error:

Exception in thread "main" kotlinx.serialization.SerializationException: Class 'Boolean' is not registered for polymorphic serialization in the scope of 'Any'.
Mark the base class as 'sealed' or register the serializer explicitly.

Hello everybody! So I have this interesting use case that I cannot seem to be able to handle. I have a module with two interfaces,

Base

(which is sealed) and

Data

that extends it, and subclasses of

Data

that cannot be changed, and I have other modules where I can do anything. The comments in the code below should hopefully guide you.

Data

interface should be serialized taking into account only its text property (I use

ConcreteData

for deserializing). The issue is that while I can serialize arbitrary subclasses (represented by

RandomData

) in the context of

Data

, I cannot seem to do it in the context of

Base

. Any help would be greatly appreciated!

Can someone help me with this? https://stackoverflow.com/questions/70164434/how-to-decode-a-json-string-to-a-given-kclass

Hi everybody! Is it possible to parse an empty string to null? Context: I’m trying to parse a response from an external version-check api. If version is up to date it returns a 200 response + empty json body. If the version is outdated it returns HTTP 200 + json body. Here is an oversimplified test:

@Test
    fun test() {
        val voluntary = Json.decodeFromString<SerializableVersionCheckResponse?>("""
        |{
        |  "beheerCode": "VRIJWILLIGE_UPDATE",
        |  "bericht": "App moet geupdate worden"
        |}
        """.trimMargin()
        )
        assertNotNull(voluntary)
        assertEquals("VRIJWILLIGE_UPDATE", voluntary.beheerCode)

        val mandatory = Json.decodeFromString<SerializableVersionCheckResponse?>("""
        |{
        |  "beheerCode": "VERPLICHTE_UPDATE",
        |  "bericht": "Oewe telefoon is oud."
        |}
        """.trimMargin())
        assertNotNull(mandatory)
        assertEquals("VERPLICHTE_UPDATE", mandatory.beheerCode)

        val upToDate = Json.decodeFromString<SerializableVersionCheckResponse?>("")
        assertNull(upToDate)
    }

The last decodeFromString fails with the following message:

kotlinx.serialization.json.internal.JsonDecodingException: Expected start of the object '{', but had 'EOF' instead
JSON input:
    at kotlinx.serialization.json.internal.JsonExceptionsKt.JsonDecodingException(JsonExceptions.kt:24)
	at kotlinx.serialization.json.internal.JsonExceptionsKt.JsonDecodingException(JsonExceptions.kt:32)
	at kotlinx.serialization.json.internal.JsonLexer.fail(JsonLexer.kt:479)

Hi 👋 We have an api that can return

{
  "number": 100
}

or

{
  "number": "none"
}

depending on some conditions, how can I parse this kind of json if I want to have

number: Int?

as a result? If the json responds a

String

I wan’t the number to be

null

Hi everybody! i have a question. Can i use @Serializable annotation for java class?

Hello, is there a way to do JsonDiff (needed for PATCH request) as in library for example https://github.com/beyondeye/kjsonpatch (still mostly in Java). So method with two JSON elements and return value is one JSON element? Or the 3rd party library is the only option. Thanks.

I'm hitting an odd issue where a class can't seem to serialize itself, or at least it's not serializing its backing fields. It's a small class:

@Serializable
class GameState {
    var playerName = "Dougie McDougal"
    @Transient
    var saveFileName = "save1"

    suspend fun save() {
        println("Saving game state $saveFileName.gs.json")
        val gameStateJson = Json.encodeToString(this@GameState)
        val saveFile = applicationVfs["saves/$saveFileName.gs.json"]
        saveFile.write(gameStateJson.toByteArray())
    }
}

The serialized output is just

{}

- empty.

playerName

is not being serialised. Any thoughts?

Does

Json.decodeFromStream(InputStream)

close the inputStream for me or should I wrap in

use {}

?

Is there an open source serializer for

kotlin.time.Duration

somewhere?

hi - new to kotlin here and im trying to use it along with protobufs i have this schema

message JEvent {
  string eventTime = 1;
  string eventType = 2;
  string productId = 3;
  string categoryId = 4;
  string categoryCode = 5;
  string brand = 6;
  string price = 7;
  string userId = 8;
  string userSession = 9;
}

and i generate the class, but when the code compiles i get

/JEventKt.kt: (13, 5): JvmField has no effect on a private property

object JEventKt {
  @kotlin.OptIn(com.google.protobuf.kotlin.OnlyForUseByGeneratedProtoCode::class)
  @com.google.protobuf.kotlin.ProtoDslMarker
  class Dsl private constructor(
    @kotlin.jvm.JvmField private val _builder: io.ipolyzos.models.Event.JEvent.Builder      <------------- COMPLAINS FOR THIS LINE HERE
  ) {
    companion object {
      @kotlin.jvm.JvmSynthetic
      @kotlin.PublishedApi
      internal fun _create(builder: io.ipolyzos.models.Event.JEvent.Builder): Dsl = Dsl(builder)
    }

    @kotlin.jvm.JvmSynthetic
    @kotlin.PublishedApi
    internal fun _build(): io.ipolyzos.models.Event.JEvent = _builder.build()

Is there any way to tell kotlinx.serialization that the class-discriminator for a polymorphic field is defined by a sibling field? i.e.

{"eventType": "MyEventType": "event": { … /*MyEventType fields */ }

or will we need a custom serializer for this?

Hey guys, is it possible to use kotlinx serialization on Android without providing proguard rules in release mode? Something that moshi has with codegen

Well that is interesting

/* In a module of a KMP library */
@Serializable
internal data class GetFileResponse(
    val url: String
)

// In the same module
    override suspend fun getFileUrl(fileId: FileId): String =
        http.get<GetFileResponse>("$baseUrl$file/$fileId") {
            useAuthentication()
        }.url

/* In an iOS app using the aforementioned library */
        val url = try {
            fileApi.getFileUrl(fileId)
        } catch(t: Throwable) {
            log.error("Failed to get file url for file id $fileId: ${t.message}", t)
            return null
        }

/* Logs when running */
ERROR - Failed to get file url for file id blablabla: Fields [name, rating] are required for type with serial name 'whatever.whatever.internal.model.UpsertCandidateEvaluationPayload.CriteriaValue', but they were missing
kotlinx.serialization.MissingFieldException: Fields [name, rating] are required for type with serial name 'whatever.whatever.internal.model.UpsertCandidateEvaluationPayload.CriteriaValue', but they were missing

The model mentioned by the log is completely unrelated and defined in a completely different place in another dependency… wat I just updated to 1.6.0 then 1.6.10 from 1.5.31 so maybe it’s that I don’t know. Super weird bug and not sure what to do. Is it some kind of name/id/hashcode clash or something?

Is it possible to define a deserializer for a class that can deserialize from 2 different unambiguous formats? Example:

{ "createdAt": 11112222333 }
{ "createdAt": { "seconds": 179879, "nanoseconds": 1201800000 } }

class DateTime(....)

@Serializable
class Payload(val createdAt: DateTime)

(serialization is not needed)

Hoping someone has an answer for this one. I have a use case building a Map<String, JsonElement> where the values in the map are all JsonPrimitve from various basic types like String, Int, Float, etc. With a map name of jsonRow, using this:

val json = Json { encodeDefaults = true }
val jsonString = json.encodeToString(JsonObject(jsonRow))

works fine in debug producing correct JSON. But release minified build gets this exception in the encodeToString call:

Serializer for class 'x' is not found.
    Mark the class as @Serializable or provide the serializer explicitly.
    k9.k: Serializer for class 'x' is not found.
    Mark the class as @Serializable or provide the serializer explicitly.

What should I change to correct this? I have proguard rules set up for explicit @Serializable data classes and they work fine. But I have no rule(s) for this "dynamic" encode use case and am not sure what "class 'x'" is so don't know what rule to try. Is it saying that it can't find the serializer for Map (class 'x' minified), even though that is the explicit type required by the JsonObject constructor? Any help/tips are appreciated, my searches for something like this are not finding good hits 🙂 This is serialization 1.3.1 and kotlin 1.6.10.

Is there common multiplatform way to represent a json? I don't need the full serialization stack, I'm just asking about the data-structure. Before I was using https://github.com/stleary/JSON-java for years, but I guess this one does not work in a multiplatform context. I have built my own builder with https://github.com/holgerbrandl/jsonbuilder, but I'd love to migrate it away from JSON-java

Hi, how can I create a serializer for

List<Pair<String, SomeClassWithSerializer>>

(I really need a List of pair, not maps, as I have to change often key names) ? I have this code but it gives me a compiler error :

class SnapshotListPairSerializer<K, V>(private val keySerializer: KSerializer<K>, private val valueSerializer: KSerializer<V>) :
	KSerializer<SnapshotStateList<Pair<K, V>>> {
	override val descriptor: SerialDescriptor = ListSerializer(PairSerializer(keySerializer, valueSerializer)).descriptor
	
	override fun serialize(encoder: Encoder, value: SnapshotStateList<Pair<K, V>>) {
		encoder.encodeSerializableValue(ListSerializer(PairSerializer(keySerializer, valueSerializer)), value as List<Pair<K, V>>)
	}
	
	override fun deserialize(decoder: Decoder): SnapshotStateList<Pair<K, V>> {
		val list = mutableStateListOf<Pair<K, V>>()
		val items = decoder.decodeSerializableValue(ListSerializer(PairSerializer(keySerializer, valueSerializer)))
		list.addAll(items)
		return list
	}
}

PS :

class SnapshotStateList<T> : MutableList<T>

Error in thread

Hi folks, I have a doubt here: why Kotlin Serialization plugin doesn't generate a proguard file with packages/classes to keep? I know this is out of library/plugin scope, but the plugin walk through classes looking for @Serializable annotation. It would be nice reusing this walk phase to "write" to a file or console packages/classes to keep. I think adding something like that will not be weight because can run in parallel with search annotation phase. If it is totally out of scope, how can I to create a compiler plugin to do something like that?

I am getting a new type of errors in 1.3.2:

Receiver class kotlinx.serialization.json.internal.PolymorphismValidator does not define or inherit an implementation of the resolved method 'abstract void polymorphicDefaultDeserializer(kotlin.reflect.KClass, kotlin.jvm.functions.Function1)' of interface kotlinx.serialization.modules.SerializersModuleCollector.
java.lang.AbstractMethodError: Receiver class kotlinx.serialization.json.internal.PolymorphismValidator does not define or inherit an implementation of the resolved method 'abstract void polymorphicDefaultDeserializer(kotlin.reflect.KClass, kotlin.jvm.functions.Function1)' of interface kotlinx.serialization.modules.SerializersModuleCollector.

Does anybody know what could cause this?