Retrofit converter for wrapped responses

[enriquebautista]

Hi, can provide some examples how to handle wrapping responses please.

I need help to parse this json response:

{
"statusCode:" 0,
"statusMessage": "OK",
"resultset": {}
}

data class GenericErrorResponse(
    val statusCode: Int,
    val statusMessage: String
)

data class ApiWrappedResponse<T>(
    val statusCode: Int,
    val statusMessage: String,
    val resultset: T
)

@GET("/")
suspend fun fetchActionRules(): ApiResult<List<ActionRule>, GenericErrorResponse>

object DeEnvelopingConverter : Converter.Factory() {
    override fun responseBodyConverter(
        type: Type,
        annotations: Array<out Annotation>,
        retrofit: Retrofit
    ): Converter<ResponseBody, *>? {
       // This returns a `@ResultType` instance that can be used to get the error type via toType()
        val (errorType, nextAnnotations) = annotations.errorType() ?: return null
        val delegateConverter = retrofit.nextResponseBodyConverter<ApiWrappedResponse<Any>>(this, errorType.toType(), nextAnnotations)
        return ResponseBodyConverter(delegateConverter)
    }
}

private class ResponseBodyConverter<T>(private val delegate: Converter<ResponseBody, ApiWrappedResponse<T>>) : Converter<ResponseBody, T> {
    override fun convert(responseBody: ResponseBody): T? {
        return delegate.convert(responseBody)?.let {
            if (it.statusCode == 0) it.resultset else throw ApiException(GenericErrorResponse(it.statusCode, it.statusMessage))
        }
    }
}

========
This return ApiResult.Failure.UnknownFailure
cause -> java.lang.ClassCastException: GenericErrorResponse cannot be cast to ApiWrappedResponse

I found some information in Retrofit
square/retrofit#2179

https://medium.com/hackernoon/retrofit-converter-for-wrapped-responses-8919298a549c

[ZacSweers]

I don't think a custom converter is the right layer for that. I'd suggest using a Moshi adapter to unwrap that type instead. Check out @Wrapped in moshi-lazy-adapters: https://github.com/serj-lotutovici/moshi-lazy-adapters#wrapped

[enriquebautista]

Thanks for the response.
For that i have one utility, wich removes unwanted wrapping envelopes.

import com.google.gson.Gson
import com.google.gson.TypeAdapter
import com.google.gson.reflect.TypeToken
import okhttp3.ResponseBody
import retrofit2.Converter
import retrofit2.Retrofit
import java.lang.reflect.Type

private const val PAYLOAD_NAME = "resultset"

/**
 * A [retrofit2.Converter.Factory] which removes unwanted wrapping envelopes from API responses.
 */
class DeEnvelopingConverter(private val gson: Gson) : Converter.Factory() {

    override fun responseBodyConverter(
        type: Type,
        annotations: Array<out Annotation>,
        retrofit: Retrofit
    ): Converter<ResponseBody, Any> {

        val adapter: TypeAdapter<*> = gson.getAdapter(TypeToken.get(type))

        return Converter { body: ResponseBody ->
            gson.newJsonReader(body.charStream()).use { jsonReader ->
                jsonReader.beginObject()
                while (jsonReader.hasNext()) {
                    if (PAYLOAD_NAME == jsonReader.nextName()) {
                        return@use adapter.read(jsonReader)
                    } else {
                        jsonReader.skipValue()
                    }
                }
                return@use null
            }
        }
    }
}

But i want to return ApiResult.Failure when statusCode != 0 using EitherNet.

throw ApiException(GenericErrorResponse(it.statusCode, it.statusMessage)

Like you suggest in this part
Plugability