Shallow copy Kubernetes objects in API Server before encoding them

This works around a race condition present in the encoder for
Kubernetes objects, as detailed in
kubernetes/kubernetes#82497

Uses the fix from kubernetes/kubernetes#101123

Fixes googleforgames#2086

pkg/util/apiserver/apiserver.go

@@ -19,6 +19,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"net/http"
+	"reflect"
 	"strings"
 
 	"agones.dev/agones/pkg/util/https"
@@ -167,8 +168,9 @@ func (as *APIServer) addSerializedHandler(pattern string, m k8sruntime.Object) {
 				return err
 			}
 
+			shallowCopy := shallowCopyObjectForTargetKind(m)
 			w.Header().Set(ContentTypeHeader, info.MediaType)
-			err = Codecs.EncoderForVersion(info.Serializer, unversionedVersion).Encode(m, w)
+			err = Codecs.EncoderForVersion(info.Serializer, unversionedVersion).Encode(shallowCopy, w)
 			if err != nil {
 				return errors.New("error marshalling")
 			}
@@ -180,6 +182,16 @@ func (as *APIServer) addSerializedHandler(pattern string, m k8sruntime.Object) {
 	}))
 }
 
+// shallowCopyObjectForTargetKind ensures obj is unique by performing a shallow copy
+// of the struct Object points to (all Object must be a pointer to a struct in a scheme).
+// Copied from https://github.com/kubernetes/kubernetes/pull/101123 until the referenced PR is merged
+func shallowCopyObjectForTargetKind(obj k8sruntime.Object) k8sruntime.Object {
+	v := reflect.ValueOf(obj).Elem()
+	copied := reflect.New(v.Type())
+	copied.Elem().Set(v)
+	return copied.Interface().(k8sruntime.Object)
+}
+
 // AcceptedSerializer takes the request, and returns a serialiser (if it exists)
 // for the given codec factory and
 // for the Accepted media types.  If not found, returns error

pkg/util/apiserver/apiserver_test.go

@@ -158,13 +158,57 @@ func TestAPIServerAddAPIResourceDiscovery(t *testing.T) {
 		_, _, err = info.Serializer.Decode(b, &gvk, list)
 		assert.NoError(t, err)
 
-		// not testing for version/kind, seems not to come through. Strange.
-		// we're not building anything that needs this, so not our issue.
+		assert.Equal(t, "v1", list.TypeMeta.APIVersion)
+		assert.Equal(t, "APIResourceList", list.TypeMeta.Kind)
 		assert.Equal(t, gv.String(), list.GroupVersion)
 		assert.Equal(t, resource, list.APIResources[0])
 	})
 }
 
+func TestAPIServerAddAPIResourceDiscoveryParallel(t *testing.T) {
+	t.Parallel()
+	mux := http.NewServeMux()
+	ts := httptest.NewUnstartedServer(mux)
+	api := NewAPIServer(mux)
+
+	api.AddAPIResource(gv.String(), resource, func(_ http.ResponseWriter, _ *http.Request, _ string) error {
+		return nil
+	})
+
+	ts.Start()
+	defer ts.Close()
+
+	t.Run("Parallel Tests", func(t *testing.T) {
+		// Run 10 concurrent requests to exercise multithreading
+		for i := 0; i < 10; i++ {
+			t.Run("Accept */*", func(t *testing.T) {
+				t.Parallel()
+				client := ts.Client()
+				path := ts.URL + "/apis/allocation.agones.dev/v1"
+				request, err := http.NewRequest(http.MethodGet, path, nil)
+				assert.NoError(t, err)
+
+				request.Header.Set("Accept", "*/*")
+				resp, err := client.Do(request)
+				assert.NoError(t, err)
+				if resp != nil {
+					defer resp.Body.Close() // nolint: errcheck
+				}
+				assert.Equal(t, k8sruntime.ContentTypeJSON, resp.Header.Get("Content-Type"))
+
+				list := &metav1.APIResourceList{}
+				err = json.NewDecoder(resp.Body).Decode(list)
+				assert.NoError(t, err)
+
+				assert.Equal(t, "v1", list.TypeMeta.APIVersion)
+				assert.Equal(t, "APIResourceList", list.TypeMeta.Kind)
+				assert.Equal(t, gv.String(), list.GroupVersion)
+				assert.Equal(t, resource, list.APIResources[0])
+			})
+		}
+	})
+}
+
 func TestSplitNameSpaceResource(t *testing.T) {
 	type expected struct {
 		namespace string