I would like to serialize this class: ```@Serializ...

# serialization

[Daniele B]

I would like to serialize this class:

@Serializable
data class RpcRequest(
  @SerialName("jsonrpc") val jsonrpc : String,
  @SerialName("id") val id : Int,
  @SerialName("method") val method : String,
  @SerialName("params") val params : List<@Contextual Any>?,
)

where params could be a list of any kind of object

I currently get this error:
Serializer for class 'Any' is not found.
Mark the class as @Serializable or provide the serializer explicitly.

An example of RpcRequest object:

val req = RpcRequest("2.0",2342,"getData",listOf("erwrwee",{"encoding":"base64"}))

How can it be properly serialized?

[itnoles]

What is @Contextual?

[Daniele B]

I just put it there, thinking it would work, but it doesn’t

[Robert Jaros]

Is it compile or runtime error? It does compile for me without error.

[Daniele B]

@Robert Jaros it is a runtime error

[Daniele B]

@Robert Jaros to be precise:
In case I don’t annonate with @Contextual, I get a compile error:
Serializer has not been found for type 'Any'. To use context serializer as fallback, explicitly annotate type or property with @Contextual
If I annotate with @Contextual, I get a runtime error:
Serializer for class 'Any' is not found.
Mark the class as @Serializable or provide the serializer explicitly.

[Robert Jaros]

And do you provide a Serializer for Any within your Json instance?

[Robert Jaros]

This is working for me:

object JsonAnySerializer : KSerializer<Any> {
    override val descriptor: SerialDescriptor = buildClassSerialDescriptor("kotlin.Any")

    override fun deserialize(decoder: Decoder): Any {
        return decoder.decodeString()
    }

    override fun serialize(encoder: Encoder, value: Any) {
        encoder.encodeString(value.toString())
    }
}

val json = Json {
            serializersModule = serializersModuleOf(Any::class, JsonAnySerializer)
}

json.encodeToString(RpcRequest("a", 2, "b", listOf("ABC", 5)))

[Robert Jaros]

Of course the serializer would need to be way more advanced to deserialize anything successfully 😉

[Daniele B]

thanks @Robert Jaros for illustrating this!
I also found another way to encode a list, using `JsonArray`:
https://kotlin.github.io/kotlinx.serialization/kotlinx-serialization-json/kotlinx-ser[…]ation-json/kotlinx.serialization.json/-json-array/index.html

[Daniele B]

so the params field would become:

@SerialName("params") val params : JsonArray?,

[Moritz Post]

There is an issue hoovering around the same problem but with no concrete solution as of yet https://github.com/Kotlin/kotlinx.serialization/issues/746

[Moritz Post]

The Any type should be supported by for basic types imo

[CLOVIS]

It is by design that you can't deserialize Any: https://github.com/Kotlin/kotlinx.serialization/issues/8

You must always explicitly tell the deserializer which class you expect. This is also why interfaces are not supported, but sealed classes are.