apiextensions: ignore ObjectMeta from webhook converted objects other than labels and annotations

[sttts]

Fixes #72160

Specified in kubernetes/enhancements#1063.

TODOs:

• unit tests
• webhook integration test

In CRD webhook conversion ignore changes to metadata other than for labels and annotations.

[sttts]

/assign @liggitt @jpbetz

[fejta-bot]

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[jpbetz]

As a FYI, As part of #77756 I'll be adding integration tests for converters that do invalid things (return various illegal responses). I've taken notes to include metadata label and annotations test cases.

[liggitt]

a few comments, nothing major

[sttts]

Rebased

@liggitt @jpbetz please take a look.

[sttts]

/retest

empty verify log

[liggitt]

/lgtm
/approve

[k8s-ci-robot]

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[jpbetz]

/lgtm

[liggitt]

/retest

[tedyu]

It seems these 5 lines can be rewritten as:

diff --git a/staging/src/k8s.io/apiextensions-apiserver/pkg/apiserver/conversion/webhook_converter.go b/staging/src/k8s.io/apiextensions-apiserver/pkg/apiserver/conversion/webhook_converter.go
index 8cc7e78e22..121654846d 100644
--- a/staging/src/k8s.io/apiextensions-apiserver/pkg/apiserver/conversion/webhook_converter.go
+++ b/staging/src/k8s.io/apiextensions-apiserver/pkg/apiserver/conversion/webhook_converter.go
@@ -317,7 +317,11 @@ func restoreObjectMeta(original, converted *unstructured.Unstructured) error {
                return fmt.Errorf("invalid metadata of type %T in input object", obj)
        }

-       for _, fld := range []string{"labels", "annotations"} {
+       type validatorType = func(map[string]string, *field.Path) field.ErrorList
+       fldToValidator := make(map[string]validatorType)
+       fldToValidator["labels"] = metav1validation.ValidateLabels
+       fldToValidator["annotations"] = apivalidation.ValidateAnnotations
+       for fld, validator := range fldToValidator {
                obj, found := responseMetaData[fld]
                if !found || obj == nil {
                        delete(convertedMetaData, fld)
@@ -349,11 +353,7 @@ func restoreObjectMeta(original, converted *unstructured.Unstructured) error {
                                stringMap[k] = v.(string)
                        }
                        var errs field.ErrorList
-                       if fld == "labels" {
-                               errs = metav1validation.ValidateLabels(stringMap, field.NewPath("metadata", "labels"))
-                       } else {
-                               errs = apivalidation.ValidateAnnotations(stringMap, field.NewPath("metadata", "annotation"))
-                       }
+                       errs = validator(stringMap, field.NewPath("metadata", "labels"))
                        if len(errs) > 0 {
                                return errs.ToAggregate()
                        }

The above is expandable: it is trivial to add more supported fields.