Kotlinx.serialization: Custom serializer to keep nested object as plain JSON format

[ClementTroesch]

Hi,

Is there a way to create a custom serializer that would keep a nested object as plain JSON format ?

For instance, I've got the following JSON data:

{
    "id": "v1",
    "index": {
        "data": "value"
    }
}

And the following data class and custom serializer:

@Serializable
data class MyData {

    var id: String = "" // expecting "v1"

    @Serializable(with = IndexSerializer::class)
    var index: String = "" // expecting "{ "data": "value" }"
}

object IndexSerializer : KSerializer<String> {

    override val descriptor: SerialDescriptor
        get() = StringDescriptor.withName("index")

    override fun serialize(output: Encoder, obj: String) {
        // Does nothing for now
    }

    override fun deserialize(input: Decoder): String {
        return "" // Not sure how to retrieve plain JSON
    }
}

But I get the following error:

kotlinx.serialization.json.JsonParsingException: Invalid JSON at 24: Expected string or non-null literal

Any idea on how to avoid this error and retrieve nested JSON ?
Thanks

[sandwwraith]

You can cast input in IndexSerializer to JsonInput and then use .decodeJson to obtain JsonElement. Its .toString() can give you what you want.

[ClementTroesch]

Works great, thanks!