A Retrofit ConverterFactory which lazily serializes the RequestBody handled by the next factory to ensure serialization does not occur on the main thread

LazyRequestBodyConverterFactory.kt

package be.digitalia.retrofit2

import okhttp3.MediaType
import okhttp3.RequestBody
import okio.BufferedSink
import retrofit2.Converter
import retrofit2.Retrofit
import java.lang.reflect.Type

/**
 * A ConverterFactory which lazily serializes the RequestBody handled by the next factory
 * to ensure serialization does not occur on the main thread.
 */
object LazyRequestBodyConverterFactory : Converter.Factory() {
    override fun requestBodyConverter(
        type: Type,
        parameterAnnotations: Array<out Annotation>,
        methodAnnotations: Array<out Annotation>,
        retrofit: Retrofit
    ): Converter<*, RequestBody> {
        val delegate = retrofit.nextRequestBodyConverter<Any>(
            this,
            type,
            parameterAnnotations,
            methodAnnotations
        )
        return Converter<Any, RequestBody> { value ->
            LazyRequestBody {
                requireNotNull(delegate.convert(value))
            }
        }
    }
}

class LazyRequestBody(initializer: () -> RequestBody) : RequestBody() {
    private val delegate: RequestBody by lazy(initializer)

    override fun contentType(): MediaType? = delegate.contentType()

    override fun contentLength(): Long = delegate.contentLength()

    override fun writeTo(sink: BufferedSink) = delegate.writeTo(sink)

    override fun isDuplex(): Boolean = delegate.isDuplex()

    override fun isOneShot(): Boolean = delegate.isOneShot()
}