Add option for custom status readers

This commit adds the `CustomStatusReadersFactoryFunc` option to the
StatusPoller's `Poll` method options so that consumers can provide
custom status readers for certain GroupKinds (esp. CRDs).

It also changes the `NewGenericStatusReader` func so that it accepts a
statusFunc parameter so that consumers only have to implement that
single func and use the genericStatusReader for all the boilerplate
stuff (like fetching an object from the API).

refs #382

pkg/kstatus/polling/polling.go

@@ -14,6 +14,7 @@ import (
 	"sigs.k8s.io/cli-utils/pkg/kstatus/polling/engine"
 	"sigs.k8s.io/cli-utils/pkg/kstatus/polling/event"
 	"sigs.k8s.io/cli-utils/pkg/kstatus/polling/statusreaders"
+	"sigs.k8s.io/cli-utils/pkg/kstatus/status"
 	"sigs.k8s.io/cli-utils/pkg/object"
 	"sigs.k8s.io/controller-runtime/pkg/client"
 )
@@ -38,10 +39,20 @@ type StatusPoller struct {
 // back on the event channel returned. The statusPollerRunner can be cancelled at any time by cancelling the
 // context passed in.
 func (s *StatusPoller) Poll(ctx context.Context, identifiers []object.ObjMetadata, options Options) <-chan event.Event {
+	statusReaderFactory := createStatusReaders
+	if options.CustomStatusReadersFactoryFunc != nil {
+		statusReaderFactory = func(reader engine.ClusterReader, mapper meta.RESTMapper) (map[schema.GroupKind]engine.StatusReader, engine.StatusReader) {
+			readers, defaultReader := createStatusReaders(reader, mapper)
+			for gk, r := range options.CustomStatusReadersFactoryFunc(reader, mapper) {
+				readers[gk] = r
+			}
+			return readers, defaultReader
+		}
+	}
 	return s.engine.Poll(ctx, identifiers, engine.Options{
 		PollInterval:             options.PollInterval,
 		ClusterReaderFactoryFunc: clusterReaderFactoryFunc(options.UseCache),
-		StatusReadersFactoryFunc: createStatusReaders,
+		StatusReadersFactoryFunc: statusReaderFactory,
 	})
 }
 
@@ -56,6 +67,8 @@ type Options struct {
 	// all needed resources before each polling cycle. If this is set to false,
 	// then each resource will be fetched when needed with GET calls.
 	UseCache bool
+
+	CustomStatusReadersFactoryFunc func(engine.ClusterReader, meta.RESTMapper) map[schema.GroupKind]engine.StatusReader
 }
 
 // createStatusReaders creates an instance of all the statusreaders. This includes a set of statusreaders for
@@ -64,7 +77,7 @@ type Options struct {
 // TODO: We should consider making the registration more automatic instead of having to create each of them
 // here. Also, it might be worth creating them on demand.
 func createStatusReaders(reader engine.ClusterReader, mapper meta.RESTMapper) (map[schema.GroupKind]engine.StatusReader, engine.StatusReader) {
-	defaultStatusReader := statusreaders.NewGenericStatusReader(reader, mapper)
+	defaultStatusReader := statusreaders.NewGenericStatusReader(reader, mapper, status.Compute)
 
 	replicaSetStatusReader := statusreaders.NewReplicaSetStatusReader(reader, mapper, defaultStatusReader)
 	deploymentStatusReader := statusreaders.NewDeploymentResourceReader(reader, mapper, replicaSetStatusReader)

pkg/kstatus/polling/statusreaders/generic.go

@@ -14,14 +14,16 @@ import (
 	"sigs.k8s.io/cli-utils/pkg/object"
 )
 
-func NewGenericStatusReader(reader engine.ClusterReader, mapper meta.RESTMapper) engine.StatusReader {
+type StatusFunc func(u *unstructured.Unstructured) (*status.Result, error)
+
+func NewGenericStatusReader(reader engine.ClusterReader, mapper meta.RESTMapper, statusFunc StatusFunc) engine.StatusReader {
 	return &baseStatusReader{
 		reader: reader,
 		mapper: mapper,
 		resourceStatusReader: &genericStatusReader{
 			reader:     reader,
 			mapper:     mapper,
-			statusFunc: status.Compute,
+			statusFunc: statusFunc,
 		},
 	}
 }
@@ -36,7 +38,7 @@ type genericStatusReader struct {
 	reader engine.ClusterReader
 	mapper meta.RESTMapper
 
-	statusFunc func(u *unstructured.Unstructured) (*status.Result, error)
+	statusFunc StatusFunc
 }
 
 var _ resourceTypeStatusReader = &genericStatusReader{}