Is it possible to add values to a KSerializer? I want to add `error` to an API response I send out s...

# serialization

[Tech]

Is it possible to add values to a KSerializer?
I want to add error to an API response I send out so I thought in the serializer to just add the error field and the only way I got it working was to just make a Surrogate of my error, was wondering if there was a better solution to this than that.

[Adam S]

do you have an example? What will the value of error be?

If you’re using JSON you could try a custom JsonTransformingSerializer, but I suspect that being explicit and creating a new @Serializable class with a specific field is more clear and understandable

[Tech]

Ah sorry for the late response, error will always be true which is why I would prefer to not make another class

[Tech]

internal object RouteErrorSerializer : KSerializer<RouteError> {
    @Serializable
    data class Surrogate(
        val error: Boolean,
        @SerialName("status_code")
        val statusCode: Int,
        val message: String?
    )

    private val surrogateSerializer = Surrogate.serializer()
    override val descriptor = surrogateSerializer.descriptor

    override fun deserialize(decoder: Decoder): RouteError {
        val surrogate = surrogateSerializer.deserialize(decoder)

        return RouteError(
            surrogate.statusCode,
            surrogate.message
        )
    }

    override fun serialize(encoder: Encoder, value: RouteError) {
        surrogateSerializer.serialize(encoder, Surrogate(
            true,
            value.statusCode,
            value.message
        ))
    }
}

[Tech]

I'm sending responses via ktor so I just wanted to apply error onto the JSON object so in the future I can wrap responses in Kotlin's Result

[Adam S]

is RouteError a class that you control? You could just add a @EncodeDefault val error: Boolean = true into the body (not constructor), and maybe annotate it with @Deprecated with the level set to ‘hidden’

[Tech]

Interesting, I didn't even know that was an annotation I'll try it out

[Tech]

yep seems to be working fine, thanks so much

[Adam S]

my pleasure!