From a7015d9f01e0e94332ee1a50cf33736dc59865b2 Mon Sep 17 00:00:00 2001
From: Alvaro Aleman <alvaroaleman@users.noreply.github.com>
Date: Sun, 21 Apr 2024 13:58:06 +0200
Subject: [PATCH] :sparkles: Add TransformStripManagedFields

This change adds `TransformStripManagedFields` to the Cache, a
transform func that strips off all managed fields for objects. There are
no known issues when using this as a `DefaultTransform` unless there is
explicit code to access objects `ManagedFields` and can lead to a
significant reduction in memory usage.
---
 pkg/cache/cache.go      | 16 ++++++++++++++++
 pkg/cache/cache_test.go | 19 +++++++++++++++++++
 2 files changed, 35 insertions(+)

diff --git a/pkg/cache/cache.go b/pkg/cache/cache.go
index e23045bf40..fa7b392b6e 100644
--- a/pkg/cache/cache.go
+++ b/pkg/cache/cache.go
@@ -201,6 +201,9 @@ type Options struct {
 
 	// DefaultTransform will be used as transform for all object types
 	// unless there is already one set in ByObject or DefaultNamespaces.
+	//
+	// A typical usecase for this is to use TransformStripManagedFields
+	// to reduce the caches memory usage.
 	DefaultTransform toolscache.TransformFunc
 
 	// DefaultWatchErrorHandler will be used to the WatchErrorHandler which is called
@@ -344,6 +347,19 @@ func New(cfg *rest.Config, opts Options) (Cache, error) {
 	return delegating, nil
 }
 
+// TransformStripManagedFields strips the managed fields of an object before it is committed to the cache.
+// If you are not explicitly accessing managedFields from your code, setting this as `DefaultTransform`
+// on the cache can lead to a significant reduction in memory usage.
+func TransformStripManagedFields() toolscache.TransformFunc {
+	return func(in any) (any, error) {
+		if obj, ok := in.(metav1.Object); ok {
+			obj.SetManagedFields(nil)
+		}
+
+		return in, nil
+	}
+}
+
 func optionDefaultsToConfig(opts *Options) Config {
 	return Config{
 		LabelSelector:         opts.DefaultLabelSelector,
diff --git a/pkg/cache/cache_test.go b/pkg/cache/cache_test.go
index 2d88b43ef3..d6c1c4aae4 100644
--- a/pkg/cache/cache_test.go
+++ b/pkg/cache/cache_test.go
@@ -2421,6 +2421,25 @@ func CacheTest(createCacheFunc func(config *rest.Config, opts cache.Options) (ca
 	})
 }
 
+var _ = Describe("TransformStripManagedFields", func() {
+	It("should strip managed fields from an object", func() {
+		obj := &corev1.Pod{ObjectMeta: metav1.ObjectMeta{
+			ManagedFields: []metav1.ManagedFieldsEntry{{
+				Manager: "foo",
+			}},
+		}}
+		transformed, err := cache.TransformStripManagedFields()(obj)
+		Expect(err).NotTo(HaveOccurred())
+		Expect(transformed).To(Equal(&corev1.Pod{ObjectMeta: metav1.ObjectMeta{}}))
+	})
+
+	It("should not trip over an unexpected object", func() {
+		transformed, err := cache.TransformStripManagedFields()("foo")
+		Expect(err).NotTo(HaveOccurred())
+		Expect(transformed).To(Equal("foo"))
+	})
+})
+
 // ensureNamespace installs namespace of a given name if not exists.
 func ensureNamespace(namespace string, client client.Client) error {
 	ns := corev1.Namespace{