meta.EachListItem should support runtime.Unstructured

Allows callers to iterate over that construct.

staging/src/k8s.io/apimachinery/pkg/api/meta/help.go

@@ -67,6 +67,9 @@ func GetItemsPtr(list runtime.Object) (interface{}, error) {
 // EachListItem invokes fn on each runtime.Object in the list. Any error immediately terminates
 // the loop.
 func EachListItem(obj runtime.Object, fn func(runtime.Object) error) error {
+	if unstructured, ok := obj.(runtime.Unstructured); ok {
+		return unstructured.EachListItem(fn)
+	}
 	// TODO: Change to an interface call?
 	itemsPtr, err := GetItemsPtr(obj)
 	if err != nil {

staging/src/k8s.io/apimachinery/pkg/apis/meta/v1/unstructured/unstructured.go

@@ -69,6 +69,39 @@ func (obj *Unstructured) IsList() bool {
 }
 func (obj *UnstructuredList) IsList() bool { return true }
 
+func (obj *Unstructured) EachListItem(fn func(runtime.Object) error) error {
+	if obj.Object == nil {
+		return fmt.Errorf("content is not a list")
+	}
+	field, ok := obj.Object["items"]
+	if !ok {
+		return fmt.Errorf("content is not a list")
+	}
+	items, ok := field.([]interface{})
+	if !ok {
+		return nil
+	}
+	for _, item := range items {
+		child, ok := item.(map[string]interface{})
+		if !ok {
+			return fmt.Errorf("items member is not an object")
+		}
+		if err := fn(&Unstructured{Object: child}); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (obj *UnstructuredList) EachListItem(fn func(runtime.Object) error) error {
+	for i := range obj.Items {
+		if err := fn(&obj.Items[i]); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
 func (obj *Unstructured) UnstructuredContent() map[string]interface{} {
 	if obj.Object == nil {
 		obj.Object = make(map[string]interface{})

staging/src/k8s.io/apimachinery/pkg/runtime/interfaces.go

@@ -242,10 +242,14 @@ type Unstructured interface {
 	// IsUnstructuredObject is a marker interface to allow objects that can be serialized but not introspected
 	// to bypass conversion.
 	IsUnstructuredObject()
-	// IsList returns true if this type is a list or matches the list convention - has an array called "items".
-	IsList() bool
 	// UnstructuredContent returns a non-nil, mutable map of the contents of this object. Values may be
 	// []interface{}, map[string]interface{}, or any primitive type. Contents are typically serialized to
 	// and from JSON.
 	UnstructuredContent() map[string]interface{}
+	// IsList returns true if this type is a list or matches the list convention - has an array called "items".
+	IsList() bool
+	// EachListItem should pass a single item out of the list as an Object to the provided function. Any
+	// error should terminate the iteration. If IsList() returns false, this method should return an error
+	// instead of calling the provided function.
+	EachListItem(func(Object) error) error
 }