Always unwrap a JSON response key using Retrofit/Moshi/Kotlin

response_unwrap.kt

// for parsing "data" out of every response object
// https://stackoverflow.com/questions/23070298/get-nested-json-object-with-gson-using-retrofit/40691739#40691739
class ItemTypeAdapterFactory : TypeAdapterFactory {
    override fun <T> create(gson: Gson, type: TypeToken<T>): TypeAdapter<T> {

        val delegate = gson.getDelegateAdapter(this, type)
        val elementAdapter = gson.getAdapter(JsonElement::class.java)

        return object : TypeAdapter<T>() {
            override fun write(out: JsonWriter, value: T) {
                delegate.write(out, value)
            }

            override fun read(`in`: JsonReader): T {
                var jsonElement = elementAdapter.read(`in`)
                if (jsonElement.isJsonObject) {
                    val jsonObject = jsonElement.asJsonObject
                    if (jsonObject.has("data")) {
                        jsonElement = jsonObject.get("data")
                    }
                }

                return delegate.fromJsonTree(jsonElement)
            }
        }.nullSafe()
    }
}

        // request builder
        private val client = OkHttpClient().newBuilder()
            .addInterceptor(authInterceptor)
            .build()

        // handle unwrapping
        var gson = GsonBuilder()
            .registerTypeAdapterFactory(ItemTypeAdapterFactory())  // unwraps "data" object
            .create()

        // API factory
        fun retrofit(baseURL: String) : Retrofit = Retrofit.Builder()
            .client(client)
            .baseUrl(baseURL)
            .addConverterFactory(GsonConverterFactory.create(gson))
            .addConverterFactory(MoshiConverterFactory.create())  // handle serialization and deserialization
            .addCallAdapterFactory(CoroutineCallAdapterFactory())
            .build()