Handling of misformatted JSON #424

Description

I'm working on a client library for an API product of some multibillion dollar company, that seems to use some proprietary server software, probably from another multibillion dollar company. Neither of them seem to give a .... have the necessary diligence, to make their products fully JSON specification compatible. Or some other top secret business reasons, like not enough budget for some programmer hours, to fix it.

Anyways, what I want to say, it's something that probably won't change and is something the client side will have to live and deal with. And it's probably something, that shouldn't be too uncommon to be found out there in the "wild".

What you irregularly find in these API results is "null" instead of null, "123" instead of 123, "123.45" instead of 123.45and so on. Of course not consistently, some response fields have the erroneous quotation always, some occasionally, and some are encoded correctly. So far the best approach I found to deal with it, is this:

import msgspec

class IntStr(int):
    pass
    
class FloatStr(float):
    pass


def encode_quoted(obj):
    if isinstance(obj, int):
        return int(obj)
    if isinstance(obj, float):
        return float(obj)
    raise TypeError(f"Unencodable type: {type(obj).__name__}: {obj}")


def decode_quoted(type_, obj):
    if type_ is IntStr:
        if isinstance(obj, int):
            return IntStr(obj)
        if obj == "null":
            return IntStr(0)
        return IntStr(obj.strip("'\" "))
    if type_ is FloatStr:
        if isinstance(obj, (float, int)):
            return FloatStr(obj)
        if obj == "null":
            return FloatStr("nan")
        return FloatStr(obj.strip("'\" "))
    raise TypeError(f"Undecodable type: {type(obj).__name__}: {obj}. Expected type: {type_.__name__}")

Now, unfortunately this only partly does, what it's supposed to do. I can declare IntStr fields, and they get parsed to an IntStr object. Ideally, I'd like to have them plain int, but this doesn't work. If I try to return int instead of IntStr from the decode hook, I get a TypeError

Also it has issues with optional values:

>>> msgspec.json.decode(b'"123"', type=IntStr, dec_hook=decode_quoted)
123
>>> msgspec.json.decode(b'"null"', type=Optional[IntStr], dec_hook=decode_quoted)
0

Ideally, I'd like to have None here, but again, I get a TypeError, if I try to return some other type than IntStr.

So far I also failed to define a Union as a custom type for the decode hook. If there is any possibility, that would already be a big help.

I'm not sure what I should suggest as a best solution for this. Maybe another keyword to msgspec.field and msgspec.Meta like attempt_unquote=? Or the possibility of decode_hook to return other types, than the ones that were specified in the type definition?