If I have a custom ```JsonTransformingSerializer<String>(String.serializer())``` How can I add...

# serialization

[spand]

If I have a custom

JsonTransformingSerializer<String>(String.serializer())

How can I add this to a json format, serializer module or whatever so it applies to all String in the serialized type ? ie. I want to transform all strings

[ephemient]

which property serializers are used by a class's serializer is determined when it is built (except in the case of @Contextual or polymorphic, in which case it retrieves the serializer from the serializersModule)

[ephemient]

tl;dr you can't do it for all strings in a format, you have to use @Serializable(with = ...) String at all the use sites

[spand]

Is there any other hook then where I can transform all strings then ? I have browsed most of the json code but everything seems internal. (ie. JsonEncoder, JsonWriter etc.)

[ephemient]

not easily. a custom format that changes decodeString could, but that would break things like polymorphic type discriminators

[ephemient]

what are you trying to do?

[spand]

For reasons I need to transform multibyte characters to their "escape" sequence ie. Curaçao -> Cura\u00e7ao

[ephemient]

ah, you could do that as a post-processing step

[spand]

You mean in-place replacement in the serialized json bytes ?

[ephemient]

yeah, if you're just replacing non-ASCII characters with escaped variants, you can just do that on the String

[ephemient]

it won't change anything about the JSON structure

[ephemient]

you could file a feature request for this to be a feature in the JSON format, but I don't think it's a common need

[spand]

Yeah it could work. A bit out of the box and I will have to switch away from the streaming encoder.

[spand]

Thanks for the response !

[Adam S]

maybe try a value class.

@JvmInline
@Serializable(with = MultibyteStringSerializer::class)
value class MultibyteString(val value: String): CharSequence by value

object MultibyteStringSerializer : KSerializer<MultibyteString> {
   // encode/decode...
}

then you can use MultibyteString instead of String in your DTOs

[ephemient]

that doesn't really help though. you don't have a way of writing that serializer to produce the desired output

[ephemient]

if it performs escaping, the Json format will escape those escapes, resulting in \\ in the output

[Adam S]

oh I didn’t realise that was the case. Outputting that sort of raw string should be possible in KxS 1.5, with JsonUnquotedLiteral

[ephemient]

to be released soon, hopefully