add last-applied strategy for diff

cmd/diff.go

@@ -27,7 +27,7 @@ const (
 )
 
 func init() {
-	diffCmd.PersistentFlags().String(flagDiffStrategy, "all", "Diff strategy, all or subset.")
+	diffCmd.PersistentFlags().String(flagDiffStrategy, "all", "Diff strategy, all, subset or last-applied")
 	diffCmd.PersistentFlags().Bool(flagOmitSecrets, false, "hide secret details when showing diff")
 	RootCmd.AddCommand(diffCmd)
 }

pkg/kubecfg/diff.go

@@ -21,6 +21,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
+	v1 "k8s.io/api/core/v1"
 	"os"
 	"regexp"
 	"sort"
@@ -88,12 +89,7 @@ func (c DiffCmd) Run(ctx context.Context, apiObjects []*unstructured.Unstructure
 			continue
 		}
 
-		liveObjObject := liveObj.Object
-		if c.DiffStrategy == "subset" {
-			liveObjObject = removeMapFields(obj.Object, liveObjObject)
-		}
-
-		liveObjText, _ := json.MarshalIndent(liveObjObject, "", "  ")
+		liveObjText, _ := json.MarshalIndent(c.getLiveObjObject(obj, liveObj), "", "  ")
 		objText, _ := json.MarshalIndent(obj.Object, "", "  ")
 
 		liveObjTextLines, objTextLines, lines := dmp.DiffLinesToChars(string(liveObjText), string(objText))
@@ -119,6 +115,19 @@ func (c DiffCmd) Run(ctx context.Context, apiObjects []*unstructured.Unstructure
 	return nil
 }
 
+func (c DiffCmd) getLiveObjObject(obj *unstructured.Unstructured, liveObj *unstructured.Unstructured) map[string]interface{} {
+	var liveObjObject map[string]interface{}
+	if c.DiffStrategy == "subset" {
+		liveObjObject = removeMapFields(obj.Object, liveObj.Object)
+	} else if c.DiffStrategy == "last-applied" {
+		lastAppliedText := liveObj.GetAnnotations()[v1.LastAppliedConfigAnnotation]
+		json.Unmarshal([]byte(lastAppliedText), &liveObjObject)
+	} else {
+		liveObjObject = liveObj.Object
+	}
+	return liveObjObject
+}
+
 // Formats the supplied Diff as a unified-diff-like text with infinite context and optionally colorizes it.
 func (c DiffCmd) formatDiff(diffs []diffmatchpatch.Diff, color bool, omitchanges bool) string {
 	var buff bytes.Buffer

pkg/kubecfg/diff_test.go

@@ -16,11 +16,84 @@
 package kubecfg
 
 import (
-	"testing"
-
+	"encoding/json"
 	"github.com/stretchr/testify/require"
+	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
+	"testing"
 )
 
+func TestLastAppliedStrategy(t *testing.T) {
+
+	var liveMap map[string]interface{}
+	var expectedMap map[string]interface{}
+
+	c := DiffCmd{}
+	c.DiffStrategy = "last-applied"
+
+	liveText :=
+		`{
+           "apiVersion": "v1",
+           "kind": "Service",
+           "metadata": {
+             "name": "foo",
+             "namespace": "default",
+             "resourceVersion": "288527730",
+             "selfLink": "/api/v1/namespaces/default/services/foo",
+             "uid": "687c86fe-12ec-45d1-a4e8-61db473e2d01",
+             "creationTimestamp": "2021-04-11T13:38:06Z",
+             "annotations":  {
+               "testKey": "testValue",
+               "kubectl.kubernetes.io/last-applied-configuration": "{\"apiVersion\":\"v1\",\"kind\":\"Service\",\"metadata\":{\"annotations\":{\"testKey\": \"testValue\"},\"name\":\"foo\",\"namespace\":\"default\"}, \"spec\":{\"ports\":[{\"name\":\"http\",\"port\":8080}],\"selector\":{\"app\":\"foo\"}}}"
+             }
+           },
+           "spec": {
+             "sessionAffinity": "None",
+             "type": "ClusterIP",
+             "selector": {
+               "app": "foo"
+             },
+             "ports": [
+               {
+                 "name": "http",
+                 "port": 8080,
+                 "protocol": "TCP",
+                 "targetPort": 8080
+               }
+             ]
+           },
+           "status": {
+             "loadBalancer": {}
+           }
+         }`
+	json.Unmarshal([]byte(liveText), &liveMap)
+
+	expectedText :=
+		`{
+           "apiVersion": "v1",
+           "kind": "Service",
+           "metadata": {
+             "name": "foo",
+             "namespace": "default",
+             "annotations":  {
+               "testKey": "testValue"
+             }
+           },
+           "spec": {
+             "selector": {
+               "app": "foo"
+             },
+             "ports": [
+               {
+                 "name": "http",
+                 "port": 8080
+               }
+             ]
+           }
+         }`
+	json.Unmarshal([]byte(expectedText), &expectedMap)
+	require.Equal(t, expectedMap, c.getLiveObjObject(nil, &unstructured.Unstructured{Object: liveMap}))
+}
+
 func TestRemoveListFields(t *testing.T) {
 	for _, tc := range []struct {
 		config, live, expected []interface{}