add function to upgrade managedfields CSA to SSA

Kubernetes-commit: 27cd307e23df3a2d508d52ff10ac8f46bf3bcea3

util/csaupgrade/upgrade.go

@@ -0,0 +1,134 @@
+package csaupgrade
+
+import (
+	"encoding/json"
+	"fmt"
+
+	"k8s.io/apimachinery/pkg/api/meta"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/apiserver/pkg/endpoints/handlers/fieldmanager"
+	"sigs.k8s.io/structured-merge-diff/v4/fieldpath"
+)
+
+// Upgrades the Manager information for fields managed with CSA
+// Prepares fields owned by `csaManager` for 'Update' operations for use now
+// with the given `ssaManager` for `Apply` operations
+//
+// csaManager - Name of FieldManager formerly used for `Update` operations
+// ssaManager - Name of FieldManager formerly used for `Apply` operations
+// subResource - Name of subresource used for api calls or empty string for main resource
+func UpgradeManagedFields(
+	obj runtime.Object,
+	csaManager string,
+	ssaManager string,
+	subResource string,
+) (runtime.Object, error) {
+	accessor, err := meta.Accessor(obj)
+	if err != nil {
+		return nil, fmt.Errorf("error accessing object metadata: %w", err)
+	}
+
+	managed, error := fieldmanager.DecodeManagedFields(accessor.GetManagedFields())
+	if error != nil {
+		return nil, fmt.Errorf("failed to decode managed fields: %w", error)
+	}
+	// If SSA manager  exists:
+	//		find CSA manager of same version, union. discard the rest
+	// Else SSA manager does not exist:
+	//		find most recent CSA manager. convert to Apply operation
+
+	ssaIdentifier, err := fieldmanager.BuildManagerIdentifier(&metav1.ManagedFieldsEntry{
+		Manager:     ssaManager,
+		Operation:   metav1.ManagedFieldsOperationApply,
+		Subresource: subResource,
+	})
+	if err != nil {
+		return nil, fmt.Errorf("failed to build manager identifier for ssa manager")
+	}
+
+	ssaMan, ssaExists := managed.Fields()[ssaIdentifier]
+
+	// Collect all relevant CSA managers before operating on them
+	csaManagers := map[string]fieldpath.VersionedSet{}
+	for name, entry := range managed.Fields() {
+		if entry.Applied() {
+			// Not interested in SSA managed fields entries
+			continue
+		}
+
+		// Manager string is a JSON representation of encoded entry
+		// Pull manager name and subresource from it
+		encodedVersionedSet := &metav1.ManagedFieldsEntry{}
+		err = json.Unmarshal([]byte(name), encodedVersionedSet)
+		if err != nil {
+			return nil, fmt.Errorf("error unmarshalling manager identifier %v: %v", name, err)
+		}
+
+		if encodedVersionedSet.Manager != csaManager ||
+			encodedVersionedSet.Subresource != subResource {
+			continue
+		}
+
+		csaManagers[name] = entry
+	}
+
+	if len(csaManagers) == 0 {
+		return obj, nil
+	}
+
+	if ssaExists {
+		for name, entry := range csaManagers {
+			if entry.APIVersion() == ssaMan.APIVersion() {
+				// Merge entries if they are compatible versions
+				ssaMan = fieldpath.NewVersionedSet(
+					ssaMan.Set().Union(entry.Set()),
+					entry.APIVersion(),
+					true,
+				)
+				managed.Fields()[ssaIdentifier] = ssaMan
+			}
+
+			// Discard entry in all cases:
+			//	if it has the wrong version we discard since managed fields versions
+			//		cannot be converted
+			//	if it has the correct version its fields were moved into the
+			//		ssaManager's fieldSet
+			delete(managed.Fields(), name)
+		}
+	} else {
+		// Loop through sorted CSA managers. Take the first one we care about
+		firstName := ""
+		for _, entry := range accessor.GetManagedFields() {
+			if entry.Manager == csaManager &&
+				entry.Subresource == subResource &&
+				entry.Operation == metav1.ManagedFieldsOperationUpdate {
+
+				if len(firstName) == 0 {
+					ident, err := fieldmanager.BuildManagerIdentifier(&entry)
+					if err != nil {
+						return nil, fmt.Errorf("failed to build manager identifier: %w", err)
+					}
+
+					firstName = ident
+					break
+				}
+			}
+		}
+
+		managed.Fields()[ssaIdentifier] = csaManagers[firstName]
+
+		for name := range csaManagers {
+			delete(managed.Fields(), name)
+		}
+	}
+
+	now := metav1.Now()
+	managed.Times()[ssaIdentifier] = &now
+
+	copied := obj.DeepCopyObject()
+	if err := fieldmanager.EncodeObjectManagedFields(copied, managed); err != nil {
+		return nil, err
+	}
+	return copied, nil
+}