so i have been experimenting with kotlinx.serilaizazion for ktor-client . <https://gist.github.com/N...

# ktor

[Nikky]

so i have been experimenting with kotlinx.serilaizazion for ktor-client . https://gist.github.com/NikkyAI/2e2891ccf67d423c523311f0b43ca57b
it seems to be a mess currently, registering classes for read/write mapper seems to make using generics like `List`s impossible
this could work if the ktor-client Framework could pass reified types down instead of assuming the Json serializer can handle Any
PS: sorry for the many edits, slack keeps cutting out and not actually saving

[enleur]

I would return just plain text from call and do serialization work somewhere else

[Nikky]

thats what i ended up doing for the List at least

[Deactivated User]

I haven’t tried myself yet. I think I’m going to try so I can help more.
Have you used the @Serializable annotation?
https://github.com/Kotlin/kotlinx.serialization

I would expect that to work out of the box. But since I haven’t tried yet, maybe it is not the case.

Also there is a #serialization channel for doubts/feedback (if the issue is not related to ktor directly)

[Nikky]

yes, i can deserialize it by hand just fine when i turn it into a String first
I tried to make my own kotlinXSerializer for jsonFeature and it seems like fun write(data: Any): OutgoingContent is just not enough type info 😛

[Nikky]

yes i know of the channel but this is relatede ktor-client JsonFeature for it, i think

[Deactivated User]

I have used kotlinx.serialization alone but not the client feature.

Looking at the code, I guess that makes sense.

[Deactivated User]

@e5l

[Deactivated User]

I guess, you can register not your own serializer, but your own serialization feature that gets type information.

Though can you use data::class to get a class instance and then get the type to serialize?

[Nikky]

i think the issue might be that lists are only supported when nested within a serializable class ?
in that case it would be a question for #serialization

[Deactivated User]

https://github.com/ktorio/ktor/blob/master/ktor-client/ktor-client-core/src/io/ktor/client/call/TypeInfo.kt

[Deactivated User]

That class doesn’t help? I guess it was created for that topic.

[Nikky]

it seems to e only available for parsing json

[Deactivated User]

Also, are you sending [] directly? without being wrapped by an object? That’s valid json?

[Nikky]

it was for just about every other library i used, including jackson

[Deactivated User]

Can’t you wrap the array in an object, and then strip the initial part and the tailing as a dirty, dirty workaround?

[Nikky]

i could probably make a wrapper and some String templating to work around it

[Deactivated User]

I’m suggesting it so you are not blocked, but I think that it is something we should look at. So if you can, I would add an issue with the problem here: https://github.com/ktorio/ktor/issues

[Nikky]

solution that works:
@Serializable class ListWrapper(val list: List<AddonFile>)

val content = client.get<String>(url)
return json.parse<ListWrapper>("{ \"list\": $content }").list

[e5l]

Kotlinx.serializer feature supports only type mappers from the feature configuration for now.

[Nikky]

is that being worked on and a hard problem or do you think it would be worth giving it a try to adapt a custom JsonFeature ?

[e5l]

It’s easy task for jvm and quite hard for ios. If you use jvm only client consider using gson serializer.

[Nikky]

either way i think the fact that RequestPipeline is effectively untyped is the root cause here.. i assume changing that would break on native platforms though unless you made heavy use of inline reified

[Deactivated User]

can’t you use a KClass instance to get a serializer/deserializer?

edit: I used clazz.serializer here and it worked https://github.com/mmo-poc/mmo-poc/blob/2d7d82d9bec0ef95c93bb90447caf20e3a0d6038/mmo/common/src/mmo/protocol/serial.kt#L17

but maybe I’m missing something

[Nikky]

i think you are right.. i was mixing up multiple issues and getting confused

[Nikky]

and no that does not work

https://i.imgur.com/oIooQaC.png▾

[Deactivated User]

you need type information

[Deactivated User]

1 sec

[Nikky]

which the Pipeline does not contain as far as i can see

[Nikky]

and thats why the current implementation has to register them all by class
and then looks up the mappers

[Deactivated User]

have you tried to do some casts?

[Deactivated User]

I have tried:

fun <T : Any> serializePacket(obj: T, clazz: KClass<T>): String {
    //return JSON.stringify(Packet(clazz.serialName, JSON.stringify(clazz.serializer(), obj)))
    return serializePacket(obj)
}

fun serializePacket(obj: Any): String {
    val clazz: KClass<*> = obj::class
    val serializer = clazz.serializer()
    @Suppress("UNCHECKED_CAST")
    return JSON.stringify(Packet(clazz.serialName, JSON.stringify(serializer as SerializationStrategy<Any>, obj)))
}

it compiles at least. (Though not testest)

[Deactivated User]

edit: tested. It works. No reified required. Just an instance + ::class + .serializer and some unsafe casts

[Nikky]

where does SerializationStrategy come from ?

[Deactivated User]

kotlinx-serialization-runtime

[Nikky]

weird.. i seem to not have that class

[Deactivated User]

and KSerializer?

[Deactivated User]

well check the JSON.stringify arguments and cast to whatever it requests, it works because of the type erasure

[Deactivated User]

so you can place the generic you need to match the one of the instance

[Nikky]

KSerializer works then i hope

[Deactivated User]

You can also do this:

val clazz: KClass<Any> = obj::class as KClass<Any>
val serializer = clazz.serializer()

the problem is that obj::class returns KClass<out T> and you don’t need an out generic, but the specific one. Since the generic is erased, it is ok.

[Nikky]

it WORKS.. i will do a PR to the kotlinxSerializer

[Nikky]

now i just need to find where that code lives

[Nikky]

opinion on the constructorß https://gist.github.com/NikkyAI/6ed96fd2794269a8c29d829743494793

[Nikky]

i am not sure if i should just allow to pass in a JSON object with default value

[Nikky]

i am not even sure if this would work on non-jvm platforms.. it only depnds on common code as far as i can tell..

[Deactivated User]

Looks fine to me. I would change the as KSerializer<Any> to the second trick: val clazz: KClass<Any> = obj::class as KClass<Any> since KClass is way more stable API than KSerializer. But that’s a minor observation

[bdawg.io]

The hard part about reified types is type Erasure when creating the KClass via ::class so you would only have a List<*> which isn't much better than Any IMO

[sandwwraith]

The ::class.serializer() will likely work for plain user types, but not for generic containers (like List<T>), because there are no information about T to get serializer for it. I suggest to use mentioned TypeInfo in conjuction with this method: https://github.com/Kotlin/kotlinx.serialization/blob/master/runtime/jvm/src/main/kotlin/kotlinx/serialization/Resolving.kt#L60

[Nikky]

well if it had any type info.. https://github.com/ktorio/ktor/blob/master/ktor-client/ktor-client-features/ktor-client-json/src/io/ktor/client/features/json/JsonSerializer.kt#L8

[Nikky]

and bare lists seems to be a seperate issue for kotlinx-serialization, did not work for me, i had to wrap it in some text and deserialize as a class, just to take the list from it then

[sandwwraith]

It is a known limitation that serializers for some classes (generic ones) can not be obtained from KClass. It is induced by reflectionless design and hard to change in the runtime itself.