Deserialize a child whether it's an Element or an Attribute

[hyphenrf]

Is it currently possible to ignore child type and deserialize it just for the fact it's a child? Here's a minimal setup:

val xml = XML { }

@Serializable
data class Data(val child : String)

// Should be able to do both
xml.decodeFromString(Data.serializer(), "<Data child='child1'/>") // OK
xml.decodeFromString(Data.serializer(), "<Data><child>child1</child></Data>") // NOPE

For reference, I'm trying to interface with a server I don't control and it sometimes returns the first format, sometimes the second, depending on the running version (with no indication of the running version in the response!)

[pdvrieze]

You should be able to use either @XmlValue otherChildren: List<Node> or @XmlValue otherChildren: List<CompactFragment>

[pdvrieze]

But the format doesn't support this fallback automatically. You could try a custom recovery in the policy.

[hyphenrf]

Before asking this question, I checked if one of the policy attributes could've helped me achieve my goal, and I couldn't figure it out. I suppose what you're suggesting is that I implement a XmlSerializationPolicy instead? Or even override the default one? Or do you provide a shortcut that I'm not aware of, like unknownChildHandler?

Thanks for your guidance

[pdvrieze]

I am suggesting unknown child handler (this doesn't require updating the policy), as you can return the resolved property. I haven't tested it though in terms of whether it is able to ignore the input kind (tag vs attribute). An alternative would be to transform the input.

[hyphenrf]

Transforming the input to "normalize" it, converting child elements to attrs (and in the process dropping their own attrs) was what I went for.

I think I had trouble doing it via the unknownChildHandler because I didn't know if what I was doing was correct. Here's what I tried for posterity:

UnknownChildHandler { input, kind, _, qname, candidates ->
    if (kind == InputKind.Element)
        candidates
            .filterIsInstance<PolyInfo>()
            .filter { it.tagName == qname }
            .map { XML.ParsedData(it.index, input.allText() }
    else
        emptyList()
}

I'm not too familiar with the API (first time using it) and I couldn't find docs/examples for how the handler is used. Maybe there's something wrong with doing it this way. I did some guessing, some source reading, some testing, and it seemed to work. I was hesitant to go for it nonetheless. This snippet is public domain. feel free to include in the examples if you deem it correct and worth including.

[pdvrieze]

@hyphenrf (and readers) the most important consideration for recovery is to leave the input in a valid state. In this case I would go for .single/.singleOrNull instead of .filter for a bit more robustness (although you should only have a single element in the list anyway - the alternative would break decoding in many ways).