Implementation + Tests

Author: VenkatRamaraju

pkg/predicate/predicate.go

@@ -18,8 +18,8 @@ package predicate
 
 import (
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/labels"
 	"k8s.io/apimachinery/pkg/runtime"
-
 	"sigs.k8s.io/controller-runtime/pkg/event"
 	logf "sigs.k8s.io/controller-runtime/pkg/internal/log"
 )
@@ -270,3 +270,48 @@ func (o or) Generic(e event.GenericEvent) bool {
 	}
 	return false
 }
+
+// LabelSelectorPredicate implements predicate functions and requires a selector that will filter an event by its labels.
+//
+// This predicate will skip reconciliation on all events that have labels that do not match the selector of the predicate.
+// A metav1.LabelSelector is passed as an input parameter while instantiating an LabelSelectorPredicate, and this is (explicitly)
+// converted to a labels.Selector object, and stored within the struct. When a predicate function is evoked, the event labels are checked
+// for a match with the predicate's selector to decide whether an event undergoes reconciliation or not.
+// If the labels match, the event will undergo reconciliation. If the labels do not match, it will skip reconciliation for that particular event.
+
+type LabelSelectorPredicate struct {
+	Funcs
+	Selector labels.Selector
+}
+
+// eventFilter skips reconciliation of events that have labels matching selectors
+func (r LabelSelectorPredicate) eventFilter(eventLabels map[string]string) bool {
+	return r.Selector.Matches(labels.Set(eventLabels))
+}
+
+// NewLabelSelectorPredicate instantiates a new LabelSelectorPredicate with the LabelSelector specified through parameters.
+func NewLabelSelectorPredicate(s metav1.LabelSelector) (Predicate, error) {
+	selectorSpecs, err := metav1.LabelSelectorAsSelector(&s)
+	requirements := LabelSelectorPredicate{Selector: selectorSpecs}
+	return requirements, err
+}
+
+// Update implements default UpdateEvent filter for validating event labels against the predicate selector
+func (r LabelSelectorPredicate) Update(e event.UpdateEvent) bool {
+	return r.eventFilter(e.MetaNew.GetLabels())
+}
+
+// Create implements default CreateEvent filter for validating event labels against the predicate selector
+func (r LabelSelectorPredicate) Create(e event.CreateEvent) bool {
+	return r.eventFilter(e.Meta.GetLabels())
+}
+
+// Delete implements default DeleteEvent filter for validating event labels against the predicate selector
+func (r LabelSelectorPredicate) Delete(e event.DeleteEvent) bool {
+	return r.eventFilter(e.Meta.GetLabels())
+}
+
+// Generic implements default GenericEvent filter for validating event labels against the predicate selector
+func (r LabelSelectorPredicate) Generic(e event.GenericEvent) bool {
+	return r.eventFilter(e.Meta.GetLabels())
+}

pkg/predicate/predicate_test.go

@@ -543,4 +543,31 @@ var _ = Describe("Predicate", func() {
 			})
 		})
 	})
+
+	Describe("When checking a LabelSelectorPredicate", func() {
+		instance, err := predicate.NewLabelSelectorPredicate(*(&metav1.LabelSelector{MatchLabels: map[string]string{"foo": "bar"}}))
+		successLabels := map[string]string{"foo": "bar"}
+		failureLabels := map[string]string{"bar": "foo"}
+		if err != nil {
+			Fail("Improper Label Selector passed during predicate instantiation.")
+		}
+
+		Context("When the Selector does not match the event labels", func() {
+			It("should return false", func() {
+				Expect(instance.Create(event.CreateEvent{Meta: &metav1.ObjectMeta{Labels: failureLabels}})).To(BeFalse())
+				Expect(instance.Delete(event.DeleteEvent{Meta: &metav1.ObjectMeta{Labels: failureLabels}})).To(BeFalse())
+				Expect(instance.Generic(event.GenericEvent{Meta: &metav1.ObjectMeta{Labels: failureLabels}})).To(BeFalse())
+				Expect(instance.Update(event.UpdateEvent{MetaNew: &metav1.ObjectMeta{Labels: failureLabels}})).To(BeFalse())
+			})
+		})
+
+		Context("When the Selector matches the event labels", func() {
+			It("should return true", func() {
+				Expect(instance.Create(event.CreateEvent{Meta: &metav1.ObjectMeta{Labels: successLabels}})).To(BeTrue())
+				Expect(instance.Delete(event.DeleteEvent{Meta: &metav1.ObjectMeta{Labels: successLabels}})).To(BeTrue())
+				Expect(instance.Generic(event.GenericEvent{Meta: &metav1.ObjectMeta{Labels: successLabels}})).To(BeTrue())
+				Expect(instance.Update(event.UpdateEvent{MetaNew: &metav1.ObjectMeta{Labels: successLabels}})).To(BeTrue())
+			})
+		})
+	})
 })