Overwrite feature (#7476)

* Overwrite feature

Allow to Overwrite an existing feature in the registry and add package
level function to deal bundle that need to overwrite feature.

This is require by the feature defined in the `add_kubernetes_metadata`
processors, the core ships with a set of default options for the feature
but a specific beats can decide to provide another set of default options.

libbeat/feature/feature.go

@@ -101,11 +101,43 @@ func New(namespace, name string, factory interface{}, stability Stability) *Feat
 // RegisterBundle registers a bundle of features.
 func RegisterBundle(bundle *Bundle) error {
 	for _, f := range bundle.Features() {
-		Registry.Register(f)
+		err := Registry.Register(f)
+		if err != nil {
+			return err
+		}
 	}
 	return nil
 }
 
+// MustRegisterBundle register a new bundle and panic on error.
+func MustRegisterBundle(bundle *Bundle) {
+	err := RegisterBundle(bundle)
+	if err != nil {
+		panic(err)
+	}
+}
+
+// OverwriteBundle register a bundle of feature and replace any existing feature with a new
+// implementation.
+func OverwriteBundle(bundle *Bundle) error {
+	for _, f := range bundle.Features() {
+		err := Registry.Register(f)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// MustOverwriteBundle register a bundle of feature, replace any existing feature with a new
+// implementation and panic on error.
+func MustOverwriteBundle(bundle *Bundle) {
+	err := OverwriteBundle(bundle)
+	if err != nil {
+		panic(err)
+	}
+}
+
 // Register register a new feature on the global registry.
 func Register(feature Featurable) error {
 	return Registry.Register(feature)

libbeat/feature/registry.go

@@ -159,6 +159,19 @@ func (r *registry) LookupAll(namespace string) ([]Featurable, error) {
 	return list, nil
 }
 
+// Overwrite allow to replace an existing feature with a new implementation.
+func (r *registry) Overwrite(feature Featurable) error {
+	_, err := r.Lookup(feature.Namespace(), feature.Name())
+	if err == nil {
+		err := r.Unregister(feature.Namespace(), feature.Name())
+		if err != nil {
+			return err
+		}
+	}
+
+	return r.Register(feature)
+}
+
 // Size returns the number of registered features in the registry.
 func (r *registry) Size() int {
 	r.RLock()

libbeat/feature/registry_test.go

@@ -176,3 +176,33 @@ func TestUnregister(t *testing.T) {
 		assert.Equal(t, 0, r.Size())
 	})
 }
+
+func TestOverwrite(t *testing.T) {
+	t.Run("when the feature doesn't exist", func(t *testing.T) {
+		f := func() {}
+		r := newRegistry()
+		assert.Equal(t, 0, r.Size())
+		r.Overwrite(New("processor", "foo", f, Stable))
+		assert.Equal(t, 1, r.Size())
+	})
+
+	t.Run("overwrite when the feature exists", func(t *testing.T) {
+		f := func() {}
+		r := newRegistry()
+		r.Register(New("processor", "foo", f, Stable))
+		assert.Equal(t, 1, r.Size())
+
+		check := 42
+		r.Overwrite(New("processor", "foo", check, Stable))
+		assert.Equal(t, 1, r.Size())
+
+		feature, err := r.Lookup("processor", "foo")
+		if !assert.NoError(t, err) {
+			return
+		}
+
+		v, ok := feature.Factory().(int)
+		assert.True(t, ok)
+		assert.Equal(t, 42, v)
+	})
+}