Give validation errors on unknown config fields

[kke]

Signed-off-by: Kimmo Lehto klehto@mirantis.com

As mentioned in #1237 (comment) - the unknown field validation has not been working as intended since the move to https://sigs.k8s.io/yaml

Seems what breaks it is the UnmarshalJSON function which runs basic json.Unmarshal, which will lose the strictness. This PR makes it use the DisallowUnknownFields JSON decoder option.

[kke]

I don't know what the "UnmarshalStrictIgnoringFields" was made for, apparently a field called "interval" has caused problems, maybe telemetry related.

[kke]

There's also decoder.DisallowUnknownFields() for json 🤔

[trawler]

the yaml package already turns DisallowUnknownFields on. Will turning it on here solve our issue?
https://github.com/kubernetes-sigs/yaml/blob/39f74b9b8a135185d095704ab98c760ca031a9f8/yaml.go#L63-L64

[kke]

Yes. The json.Unmarshal in the UnmarshalJSON function creates a new decoder that doesn't know anything about the DisallowUnknownFields set by the yaml thing.

[trawler]

Seems what breaks it is the UnmarshalJSON function which runs basic json.Unmarshal, which will lose the strictness. This PR makes it use the DisallowUnknownFields JSON decoder option.

The yaml.Unmarshalstrict is already turning on the DisallowUnknownFields option for the json unmarshaller. If this is not working as intended, I think a better route would be to submit a fix upstream.

[kke]

I think a better route would be to submit a fix upstream.

I don't think it's possible to fix in upstream. The UnmarshalJSON function does not work like UnmarshalYAML, it does not receive a function to be called to do the unmarshaling:

func (c *Config) UnmarshalYAML(unmarshal func(interface{}) error) error {
  	// do stuff
  	
  	if err := unmarshal(yc); err != nil { // this function can inherit options from the original decoder
		return err
	}
	
	return nil
}

func (c *Config) UnmarshalJSON(data []byte) error {
  	// do stuff

	if err := json.Unmarshal(data, c); err != nil { // this can not
		return err
	}

	return nil
}

[kke]

Btw, I think the DisallowUnknownFields only works case-insensitively. The json decoder, I think, will accept "aPiVeRSiON": "k0s.k0sproject.io/v1beta1" and put it in the APIVersion struct field without any errors.

[trawler]

Btw, I think the DisallowUnknownFields only works case-insensitively. The json decoder, I think, will accept "aPiVeRSiON": "k0s.k0sproject.io/v1beta1" and put it in the APIVersion struct field without any errors.

Yes, that is correct. There is an issue about this same problem already open upstream: kubernetes-sigs/yaml#15