For legacy reasons I need to talk to API:s that re...

# ktor

[Niclas Kron]

For legacy reasons I need to talk to API:s that return both success and error body as http 200. How can i parse/approach that with ktor+kotlinx.serialization?

If deserialization fails I get a JsonConvertException and not a ResponseException with the HttpResponse that I can parse into a different structure..

[Aleksei Tirman [JB]]

Can you share an example of both success and error responses?

[Niclas Kron]

Sure, I'm trying to achieve something like this; but it seems not to be possible since if .body<ConsentResponse> throws a JsonConvertException with cause MissingFieldException

/**
 *  {"errorCode": "42", "message": "something went wrong"}
 */
@Serializable
data class ErrorResponse(
    val errorCode: String,
    val message: String
)

/**
 *  {"hasGivenConsent": false}
 */
@Serializable
data class ConsentResponse(
    val hasGivenConsent: Boolean
)

sealed class Result<out T, out E> {
    data class Success<T>(val value: T) : Result<T, Nothing>()
    data class Failure<E>(val error: E) : Result<Nothing, E>()
}

fun main(): Unit = runBlocking {
    val client = HttpClient()

    val result: Result<ConsentResponse, ErrorResponse> = try {
        Result.Success(client.get("<https://example.com/v1/consent>").body<ConsentResponse>())
    } catch (e: ResponseException) {
        val errorResponse = e.response.body<ErrorResponse>()
        Result.Failure(errorResponse)
    }
    
    println("result: $result")
}

[Niclas Kron]

(I have many such cases with different success/error responses so im looking for a somewhat generic way of solving it)

[Aleksei Tirman [JB]]

You can write a custom serializer to delegate deserialization to either a success or an error serializer, depending on the shape of the JSON. Serializers for concrete success types can be registered in the serializer module. Here is a complete example:

[Aleksei Tirman [JB]]

client.kt.cpp

client.kt.cpp

[Niclas Kron]

oh interesting, thank you very much Aleksei I'll take a look 🙏