Adds an Ignore option for Metadata (#44)

Author: john-a-joyce

Diff for: README.md

@@ -65,6 +65,7 @@ To help in these scenarios there are the following options to be used when calcu
 - `IgnoreStatusFields`
 - `IgnoreVolumeClaimTemplateTypeMetaAndStatus`
 - `IgnorePDBSelector`
+- `IgnoreField("field-name-to-ignore")`
 
 Example:
 ```
@@ -91,6 +92,11 @@ This CalculateOption clears volumeClaimTemplate fields from both objects before
 Checks `selector` fields of PDB objects before comparing and removes them if they match. `reflect.DeepEquals` is used for the equality check. 
 This is required because map fields using `patchStrategy:"replace"` will always diff regardless if they are otherwise equal.
 
+#### IgnoreField("field-name-to-ignore")
+
+This CalculateOption removes the field provided (as a string) in the call before comparing them. A common usage might be to remove the metadata fields by using the `IgnoreField("metadata")` option.
+
+
 ## Contributing
 
 If you find this project useful here's how you can help:

Diff for: patch/deletenull.go

@@ -41,6 +41,22 @@ func IgnoreStatusFields() CalculateOption {
 	}
 }
 
+func IgnoreField(field string) CalculateOption {
+	return func(current, modified []byte) ([]byte, []byte, error) {
+		current, err := deleteDataField(current, field)
+		if err != nil {
+			return []byte{}, []byte{}, errors.Wrap(err, "could not delete the field from current byte sequence")
+		}
+
+		modified, err = deleteDataField(modified, field)
+		if err != nil {
+			return []byte{}, []byte{}, errors.Wrap(err, "could not delete the field from modified byte sequence")
+		}
+
+		return current, modified, nil
+	}
+}
+
 func IgnoreVolumeClaimTemplateTypeMetaAndStatus() CalculateOption {
 	return func(current, modified []byte) ([]byte, []byte, error) {
 		current, err := deleteVolumeClaimTemplateFields(current)
@@ -173,6 +189,21 @@ func deleteNullInSlice(m []interface{}) ([]interface{}, error) {
 	return filteredSlice, nil
 }
 
+func deleteDataField(obj []byte, fieldName string) ([]byte, error) {
+	var objectMap map[string]interface{}
+	err := json.Unmarshal(obj, &objectMap)
+	if err != nil {
+		return []byte{}, errors.Wrap(err, "could not unmarshal byte sequence")
+	}
+	delete(objectMap, fieldName)
+	obj, err = json.ConfigCompatibleWithStandardLibrary.Marshal(objectMap)
+	if err != nil {
+		return []byte{}, errors.Wrap(err, "could not marshal byte sequence")
+	}
+
+	return obj, nil
+}
+
 func deleteStatusField(obj []byte) ([]byte, error) {
 	var objectMap map[string]interface{}
 	err := json.Unmarshal(obj, &objectMap)

Diff for: tests/integration_test.go

@@ -725,6 +725,27 @@ func TestIntegration(t *testing.T) {
 			n := i.(*appsv1.StatefulSet)
 			n.Spec.Template.ObjectMeta.Labels = map[string]string{"c": "d"}
 		}),
+		NewTestMatch("Ignore Metadata field",
+			&v1.Pod{
+
+				ObjectMeta: standardObjectMeta(),
+				Spec: v1.PodSpec{
+					Containers: []v1.Container{
+						{
+							Name:    "test-container",
+							Image:   "test-image",
+						},
+					},
+				},
+			}).
+			withRemoteChange(func(i interface{}) {
+			pod := i.(*v1.Pod)
+			pod.Labels = map[string]string{"a": "b"}
+		}).
+			withLocalChange(func(i interface{}) {
+				pod := i.(*v1.Pod)
+				pod.Labels = map[string]string{"c": "d"}
+		}),
 	}
 	runAll(t, tests)
 }
@@ -748,7 +769,12 @@ func runAll(t *testing.T, tests []*TestItem) {
 		if testing.Verbose() {
 			log.Printf("> %s", test.name)
 		}
-		err := testMatchOnObject(test)
+		var err error
+		if test.name == "Ignore Metadata field" {
+			err = testMatchOnObject(test, "metadata")
+		} else {
+			err = testMatchOnObject(test, "")
+		}
 		if err != nil {
 			if *failonerror {
 				t.Fatalf("Test '%s' failed: %s %s", test.name, err, errors.GetDetails(err))

Diff for: tests/main_test.go

@@ -186,13 +186,14 @@ func (t *TestItem) withIgnoreVersions(v []string) *TestItem {
 	return t
 }
 
-func testMatchOnObject(testItem *TestItem) error {
+func testMatchOnObject(testItem *TestItem, ignoreField string) error {
 	var existing metav1.Object
 	var err error
 	opts := []patch.CalculateOption{
 		patch.IgnoreStatusFields(),
 		patch.IgnoreVolumeClaimTemplateTypeMetaAndStatus(),
 		patch.IgnorePDBSelector(),
+		patch.IgnoreField(ignoreField),
 	}
 
 	newObject := testItem.object