Move informer_factory to staging

Kubernetes-commit: a91a2cdad62f673ebfaa947af85153002a25d418

Author: cici37

pkg/informerfactory/informer_factory.go

@@ -0,0 +1,56 @@
+/*
+Copyright 2019 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package informerfactory
+
+import (
+	"k8s.io/apimachinery/pkg/runtime/schema"
+	"k8s.io/client-go/informers"
+	"k8s.io/client-go/metadata/metadatainformer"
+)
+
+// InformerFactory creates informers for each group version resource.
+type InformerFactory interface {
+	ForResource(resource schema.GroupVersionResource) (informers.GenericInformer, error)
+	Start(stopCh <-chan struct{})
+}
+
+type informerFactory struct {
+	typedInformerFactory    informers.SharedInformerFactory
+	metadataInformerFactory metadatainformer.SharedInformerFactory
+}
+
+func (i *informerFactory) ForResource(resource schema.GroupVersionResource) (informers.GenericInformer, error) {
+	informer, err := i.typedInformerFactory.ForResource(resource)
+	if err != nil {
+		return i.metadataInformerFactory.ForResource(resource), nil
+	}
+	return informer, nil
+}
+
+func (i *informerFactory) Start(stopCh <-chan struct{}) {
+	i.typedInformerFactory.Start(stopCh)
+	i.metadataInformerFactory.Start(stopCh)
+}
+
+// NewInformerFactory creates a new InformerFactory which works with both typed
+// resources and metadata-only resources
+func NewInformerFactory(typedInformerFactory informers.SharedInformerFactory, metadataInformerFactory metadatainformer.SharedInformerFactory) InformerFactory {
+	return &informerFactory{
+		typedInformerFactory:    typedInformerFactory,
+		metadataInformerFactory: metadataInformerFactory,
+	}
+}