CRDs should support watch of protobuf PartialObjectMetadata

Correctly ensure CRDs can be watched using protobuf when transformed to
PartialObjectMetadata. To do this we add a set of serializers allowed to
be used for "normal" requests (that return CRDs) while the serializers
supported by the infrastructure is broader and includes protobuf. During
negotatiation we check for transformation requests and protobuf is
excluded from non-transform requests.

As part of the change, correct an error message when the server returns
a 406 but the client doesn't accept the format to avoid confusing users
who set impossible Accept rules for CRDs (the dynamic client doesn't
support Protobuf, so if the server responds with a protobuf status the
message from the server is lost and the generic error was confusing).

Kubernetes-commit: 89e752add07f443248f66e4798d160f2d7529a19

pkg/endpoints/handlers/negotiation/negotiate.go

@@ -116,9 +116,10 @@ func isPrettyPrint(req *http.Request) bool {
 // EndpointRestrictions is an interface that allows content-type negotiation
 // to verify server support for specific options
 type EndpointRestrictions interface {
-	// AllowsConversion should return true if the specified group version kind
-	// is an allowed target object.
-	AllowsConversion(target schema.GroupVersionKind, mimeType, mimeSubType string) bool
+	// AllowsMediaTypeTransform returns true if the endpoint allows either the requested mime type
+	// or the requested transformation. If false, the caller should ignore this mime type. If the
+	// target is nil, the client is not requesting a transformation.
+	AllowsMediaTypeTransform(mimeType, mimeSubType string, target *schema.GroupVersionKind) bool
 	// AllowsServerVersion should return true if the specified version is valid
 	// for the server group.
 	AllowsServerVersion(version string) bool
@@ -133,8 +134,8 @@ var DefaultEndpointRestrictions = emptyEndpointRestrictions{}
 
 type emptyEndpointRestrictions struct{}
 
-func (emptyEndpointRestrictions) AllowsConversion(schema.GroupVersionKind, string, string) bool {
-	return false
+func (emptyEndpointRestrictions) AllowsMediaTypeTransform(mimeType string, mimeSubType string, gvk *schema.GroupVersionKind) bool {
+	return gvk == nil
 }
 func (emptyEndpointRestrictions) AllowsServerVersion(string) bool  { return false }
 func (emptyEndpointRestrictions) AllowsStreamSchema(s string) bool { return s == "watch" }
@@ -225,7 +226,7 @@ func acceptMediaTypeOptions(params map[string]string, accepts *runtime.Serialize
 		}
 	}
 
-	if options.Convert != nil && !endpoint.AllowsConversion(*options.Convert, accepts.MediaTypeType, accepts.MediaTypeSubType) {
+	if !endpoint.AllowsMediaTypeTransform(accepts.MediaTypeType, accepts.MediaTypeSubType, options.Convert) {
 		return MediaTypeOptions{}, false
 	}
 

pkg/endpoints/handlers/rest.go

@@ -50,6 +50,11 @@ type RequestScope struct {
 	Serializer runtime.NegotiatedSerializer
 	runtime.ParameterCodec
 
+	// StandardSerializers, if set, restricts which serializers can be used when
+	// we aren't transforming the output (into Table or PartialObjectMetadata).
+	// Used only by CRDs which do not yet support Protobuf.
+	StandardSerializers []runtime.SerializerInfo
+
 	Creater         runtime.ObjectCreater
 	Convertor       runtime.ObjectConvertor
 	Defaulter       runtime.ObjectDefaulter
@@ -78,7 +83,21 @@ func (scope *RequestScope) err(err error, w http.ResponseWriter, req *http.Reque
 	responsewriters.ErrorNegotiated(err, scope.Serializer, scope.Kind.GroupVersion(), w, req)
 }
 
-func (scope *RequestScope) AllowsConversion(gvk schema.GroupVersionKind, mimeType, mimeSubType string) bool {
+func (scope *RequestScope) AllowsMediaTypeTransform(mimeType, mimeSubType string, gvk *schema.GroupVersionKind) bool {
+	// some handlers like CRDs can't serve all the mime types that PartialObjectMetadata or Table can - if
+	// gvk is nil (no conversion) allow StandardSerializers to further restrict the set of mime types.
+	if gvk == nil {
+		if len(scope.StandardSerializers) == 0 {
+			return true
+		}
+		for _, info := range scope.StandardSerializers {
+			if info.MediaTypeType == mimeType && info.MediaTypeSubType == mimeSubType {
+				return true
+			}
+		}
+		return false
+	}
+
 	// TODO: this is temporary, replace with an abstraction calculated at endpoint installation time
 	if gvk.GroupVersion() == metav1beta1.SchemeGroupVersion || gvk.GroupVersion() == metav1.SchemeGroupVersion {
 		switch gvk.Kind {