hey all, I'm having some trouble with dynamic deserialization on kotlin native. i've included releva...

# serialization

[Ryan Simon]

hey all, I'm having some trouble with dynamic deserialization on kotlin native. i've included relevant code in the thread. would appreciate some help on this one, thank you in advance!

[Ryan Simon]

private fun <ResponseType> deserializeBaseResponse(
        body: String,
        responseDeserializer: KSerializer<ResponseType>
    ): Pair<HttpStatusCode, ResponseType?> {
        val response = json.decodeFromString(BaseResponse.serializer(responseDeserializer), body)
        return Pair(response.code.toHttpStatusCode(), response.response)
    }

Here's where I'm trying to do some dynamic deserialization. I have a data type that is wrapped by BaseResponse. Here's the BaseResponse data class:

@Serializable
data class BaseResponse<T>(
    @SerialName("code")
    val code: Int,

    @SerialName("response")
    var response: T? = null
)

[Ryan Simon]

crash from ios

Uncaught Kotlin exception: kotlin.native.concurrent.InvalidMutabilityException: mutation attempt of frozen kotlin.collections.HashMap@322768
    at 0   Shared                              0x000000010aaba050 ThrowInvalidMutabilityException + 208
    at 1   Shared                              0x000000010aaaf647 <kfun:kotlin.collections.HashMap#addKey(1:0){}kotlin.Int> + 1447
    at 2   Shared                              0x000000010aaabe0a <kfun:kotlin.collections.HashMap#put(1:0;1:1){}1:1>? + 106
    at 3   Shared                              0x000000010ab85fba <kfun:kotlinx.serialization.json.internal.DescriptorSchemaCache#getOrPut(kotlinx.serialization.descriptors.SerialDescriptor;kotlinx.serialization.json.internal.DescriptorSchemaCache.Key><0:0>;kotlin.Function0<0:0>){0§<kotlin.Any>}0:0 + 474
    at 4   Shared                              0x000000010ab879d5 <kfun:kotlinx.serialization.json.internal.StreamingJsonDecoder#decodeElementIndex(kotlinx.serialization.descriptors.SerialDescriptor){}kotlin.Int> + 2597
    at 5   Shared                              0x000000010abe2f7a <kfun:app.shred.kmp.shared.network.BaseResponse>.$serializer#deserialize(kotlinx.serialization.encoding.Decoder){}app.shred.kmp.shared.network.BaseResponse<2:0> + 538
    at 6   Shared                              0x000000010ab8429e <kfun:kotlinx.serialization.json.internal#[e-mail](kotlinx.serialization.DeserializationStrategy><0:0>){0§<kotlin.Any?>}0:0 + 382
    at 7   Shared                              0x000000010ab7347a <kfun:kotlinx.serialization.json.Json#decodeFromString(kotlinx.serialization.DeserializationStrategy><0:0>;kotlin.String){0§<kotlin.Any?>}0:0 + 330
    at 8   Shared                              0x000000010abe42c3

[bsimmons]

It looks like the json object you are using to decode with is being shared between threads. Hence the mutability exception. Try creating a new json for each thread. Or do it all on one thread.

[Ryan Simon]

oh interesting, yeah, i was using the same instance of Json across all of my classes

[Ryan Simon]

so i should make a new one for each instance of my class then?

[bsimmons]

These days you can just use Json.decodeFromString(string) and not even create an instance at all, I think.

[bsimmons]

That works for version 1.1.0

[Ryan Simon]

well i want there to be some common settings setup for the Json instance like ignoreUnknownKeys=true

[bsimmons]

Oh true, yeah, then I'd create a new one for each class / scope should be fine.

[Ryan Simon]

great, will give that a try, thank you 🙏🏻

[Ryan Simon]

quick update on this. the way i fixed this was by using extension functions and always spinning up a new Json instance like so

private fun getJson() = Json { ignoreUnknownKeys = true }

internal fun <T> String.fromJson(deserializer: DeserializationStrategy<T>): T {
    return getJson().decodeFromString(
        deserializer,
        this
    )
}