Add Generation variants of kmeta/labels.go (#117)

Unlike `ResourceVersion`, which changes whenever the resource changes at all (including `/status` which can be high churn), `Generation` only changes when the `/spec` of a CRD changes (for CRDs starting in 1.11, right now they are locked at `generation: 1`).

These methods are useful for interacting with K8s resource now, and will be useful for CRDs soon.

Fixes: https://github.com/knative/pkg/issues/116

kmeta/labels.go

@@ -26,6 +26,13 @@ import (
 
 // The methods in this file are used for managing subresources in cases where
 // a controller instantiates different resources for each version of itself.
+// There are two sets of methods available here:
+// * `*VersionLabel*`: these methods act on `metadata.resourceVersion` and
+//  create new labels for EVERY change to the resource (incl. `/status`).
+// * `*GenerationLabel*`: these methods act on `metadata.generation` and
+//  create new labels for changes to the resource's "spec" (typically, but
+//  some K8s resources change `metadata.generation` for annotations as well
+//  e.g. Deployment).
 //
 // For example, if an A might instantiate N B's at version 1 and M B's at
 // version 2 then it can use MakeVersionLabels to decorate each subresource
@@ -66,6 +73,37 @@ func MakeOldVersionLabelSelector(om metav1.ObjectMetaAccessor) labels.Selector {
 	)
 }
 
+// MakeGenerationLabels constructs a set of labels to apply to subresources
+// instantiated at this version of the parent resource, so that we can
+// efficiently select them.
+func MakeGenerationLabels(om metav1.ObjectMetaAccessor) labels.Set {
+	return map[string]string{
+		"controller": string(om.GetObjectMeta().GetUID()),
+		"generation": genStr(om),
+	}
+}
+
+// MakeGenerationLabelSelector constructs a selector for subresources
+// instantiated at this version of the parent resource.  This keys
+// off of the labels populated by MakeGenerationLabels.
+func MakeGenerationLabelSelector(om metav1.ObjectMetaAccessor) labels.Selector {
+	return labels.SelectorFromSet(MakeGenerationLabels(om))
+}
+
+// MakeOldGenerationLabelSelector constructs a selector for subresources
+// instantiated at an older version of the parent resource.  This keys
+// off of the labels populated by MakeGenerationLabels.
+func MakeOldGenerationLabelSelector(om metav1.ObjectMetaAccessor) labels.Selector {
+	return labels.NewSelector().Add(
+		mustNewRequirement("controller", selection.Equals, []string{string(om.GetObjectMeta().GetUID())}),
+		mustNewRequirement("generation", selection.NotEquals, []string{genStr(om)}),
+	)
+}
+
+func genStr(om metav1.ObjectMetaAccessor) string {
+	return fmt.Sprintf("%05d", om.GetObjectMeta().GetGeneration())
+}
+
 // mustNewRequirement panics if there are any errors constructing our selectors.
 func mustNewRequirement(key string, op selection.Operator, vals []string) labels.Requirement {
 	r, err := labels.NewRequirement(key, op, vals)

kmeta/labels_test.go

@@ -114,3 +114,96 @@ func TestMakeOldVersionLabelSelector(t *testing.T) {
 		})
 	}
 }
+
+func TestMakeGenerationLabels(t *testing.T) {
+	tests := []struct {
+		name string
+		om   metav1.ObjectMeta
+		s    string
+	}{{
+		name: "simple translation",
+		om: metav1.ObjectMeta{
+			UID:        "1234",
+			Generation: 5,
+		},
+		s: "controller=1234,generation=00005",
+	}, {
+		name: "another simple translation",
+		om: metav1.ObjectMeta{
+			UID:        "abcd",
+			Generation: 5432,
+		},
+		s: "controller=abcd,generation=05432",
+	}}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			ls := MakeGenerationLabels(&test.om)
+			if want, got := test.s, ls.String(); got != want {
+				t.Errorf("MakeGenerationLabels() = %v, wanted %v", got, want)
+			}
+		})
+	}
+}
+
+func TestMakeGenerationLabelSelector(t *testing.T) {
+	tests := []struct {
+		name string
+		om   metav1.ObjectMeta
+		s    string
+	}{{
+		name: "simple translation",
+		om: metav1.ObjectMeta{
+			UID:        "1234",
+			Generation: 5,
+		},
+		s: "controller=1234,generation=00005",
+	}, {
+		name: "another simple translation",
+		om: metav1.ObjectMeta{
+			UID:        "abcd",
+			Generation: 5432,
+		},
+		s: "controller=abcd,generation=05432",
+	}}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			ls := MakeGenerationLabelSelector(&test.om)
+			if want, got := test.s, ls.String(); got != want {
+				t.Errorf("MakeGenerationLabelSelector() = %v, wanted %v", got, want)
+			}
+		})
+	}
+}
+
+func TestMakeOldGenerationLabelSelector(t *testing.T) {
+	tests := []struct {
+		name string
+		om   metav1.ObjectMeta
+		s    string
+	}{{
+		name: "simple translation",
+		om: metav1.ObjectMeta{
+			UID:        "1234",
+			Generation: 5,
+		},
+		s: "controller=1234,generation!=00005",
+	}, {
+		name: "another simple translation",
+		om: metav1.ObjectMeta{
+			UID:        "abcd",
+			Generation: 5432,
+		},
+		s: "controller=abcd,generation!=05432",
+	}}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			ls := MakeOldGenerationLabelSelector(&test.om)
+			if want, got := test.s, ls.String(); got != want {
+				t.Errorf("MakeOldGenerationLabelSelector() = %v, wanted %v", got, want)
+			}
+		})
+	}
+}