Restrict supported media types for new apiservers.

This is to prevent the enablement of new data formats (CBOR) in the early stages of phased
implementation.

staging/src/k8s.io/apiserver/pkg/server/config.go

@@ -724,6 +724,12 @@ func (c *RecommendedConfig) Complete() CompletedConfig {
 	return c.Config.Complete(c.SharedInformerFactory)
 }
 
+var allowedMediaTypes = []string{
+	runtime.ContentTypeJSON,
+	runtime.ContentTypeYAML,
+	runtime.ContentTypeProtobuf,
+}
+
 // New creates a new server which logically combines the handling chain with the passed server.
 // name is used to differentiate for logging. The handler chain in particular can be difficult as it starts delegating.
 // delegationTarget may not be nil.
@@ -731,6 +737,18 @@ func (c completedConfig) New(name string, delegationTarget DelegationTarget) (*G
 	if c.Serializer == nil {
 		return nil, fmt.Errorf("Genericapiserver.New() called with config.Serializer == nil")
 	}
+	for _, info := range c.Serializer.SupportedMediaTypes() {
+		var ok bool
+		for _, mt := range allowedMediaTypes {
+			if info.MediaType == mt {
+				ok = true
+				break
+			}
+		}
+		if !ok {
+			return nil, fmt.Errorf("refusing to create new apiserver %q with support for media type %q (allowed media types are: %s)", name, info.MediaType, strings.Join(allowedMediaTypes, ", "))
+		}
+	}
 	if c.LoopbackClientConfig == nil {
 		return nil, fmt.Errorf("Genericapiserver.New() called with config.LoopbackClientConfig == nil")
 	}

staging/src/k8s.io/apiserver/pkg/server/config_test.go

@@ -26,6 +26,7 @@ import (
 	"testing"
 	"time"
 
+	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/util/json"
 	"k8s.io/apimachinery/pkg/util/sets"
 	"k8s.io/apimachinery/pkg/util/wait"
@@ -362,3 +363,21 @@ func (b *testBackend) ProcessEvents(events ...*auditinternal.Event) bool {
 	b.events = append(b.events, events...)
 	return true
 }
+
+func TestNewErrorForbiddenSerializer(t *testing.T) {
+	config := CompletedConfig{
+		&completedConfig{
+			Config: &Config{
+				Serializer: runtime.NewSimpleNegotiatedSerializer(runtime.SerializerInfo{
+					MediaType: "application/cbor",
+				}),
+			},
+		},
+	}
+	_, err := config.New("test", NewEmptyDelegate())
+	if err == nil {
+		t.Error("successfully created a new server configured with cbor support")
+	} else if err.Error() != `refusing to create new apiserver "test" with support for media type "application/cbor" (allowed media types are: application/json, application/yaml, application/vnd.kubernetes.protobuf)` {
+		t.Errorf("unexpected error: %v", err)
+	}
+}