A Retrofit Converter.Factory using the Json format from the Kotlin Serialization library, optimized to stream response bodies

JsonStreamingConverterFactory.kt

package be.digitalia.retrofit2

import kotlinx.serialization.DeserializationStrategy
import kotlinx.serialization.ExperimentalSerializationApi
import kotlinx.serialization.SerializationStrategy
import kotlinx.serialization.json.Json
import kotlinx.serialization.json.decodeFromStream
import kotlinx.serialization.serializer
import okhttp3.MediaType.Companion.toMediaType
import okhttp3.RequestBody
import okhttp3.RequestBody.Companion.toRequestBody
import okhttp3.ResponseBody
import retrofit2.Converter
import retrofit2.Retrofit
import java.lang.reflect.Type

/**
 * A Retrofit Converter.Factory using the Json format from the Kotlin Serialization library,
 * optimized to stream response bodies.
 */
@OptIn(ExperimentalSerializationApi::class)
internal class JsonStreamingFactory(
    private val serializer: Json
) : Converter.Factory() {
    override fun responseBodyConverter(
        type: Type,
        annotations: Array<out Annotation>,
        retrofit: Retrofit
    ): Converter<ResponseBody, *> {
        val loader: DeserializationStrategy<Any> = serializer.serializersModule.serializer(type)
        return Converter { responseBody ->
            responseBody.use {
                serializer.decodeFromStream(loader, responseBody.byteStream())
            }
        }
    }

    override fun requestBodyConverter(
        type: Type,
        parameterAnnotations: Array<out Annotation>,
        methodAnnotations: Array<out Annotation>,
        retrofit: Retrofit
    ): Converter<*, RequestBody> {
        val saver: SerializationStrategy<Any> = serializer.serializersModule.serializer(type)
        return Converter<Any, RequestBody> { value ->
            serializer.encodeToString(saver, value).toRequestBody(MEDIA_TYPE)
        }
    }

    companion object {
        private val MEDIA_TYPE = "application/json; charset=UTF-8".toMediaType()
    }
}

@JvmName("create")
fun Json.asStreamingConverterFactory(): Converter.Factory {
    return JsonStreamingFactory(this)
}