Merge pull request #71542 from smarterclayton/endpoints_cleanup

Ensure all response object modification happens in one place

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

@@ -158,6 +158,19 @@ func ExtractList(obj runtime.Object) ([]runtime.Object, error) {
 // objectSliceType is the type of a slice of Objects
 var objectSliceType = reflect.TypeOf([]runtime.Object{})
 
+// LenList returns the length of this list or 0 if it is not a list.
+func LenList(list runtime.Object) int {
+	itemsPtr, err := GetItemsPtr(list)
+	if err != nil {
+		return 0
+	}
+	items, err := conversion.EnforcePtr(itemsPtr)
+	if err != nil {
+		return 0
+	}
+	return items.Len()
+}
+
 // SetList sets the given list object's Items member have the elements given in
 // objects.
 // Returns an error if list is not a List type (does not have an Items member),

staging/src/k8s.io/apiserver/pkg/endpoints/handlers/create.go

@@ -70,6 +70,11 @@ func createHandler(r rest.NamedCreater, scope RequestScope, admit admission.Inte
 
 		ctx := req.Context()
 		ctx = request.WithNamespace(ctx, namespace)
+		outputMediaType, _, err := negotiation.NegotiateOutputMediaType(req, scope.Serializer, &scope)
+		if err != nil {
+			scope.err(err, w, req)
+			return
+		}
 
 		gv := scope.Kind.GroupVersion()
 		s, err := negotiation.NegotiateInputSerializer(req, false, scope.Serializer)
@@ -77,6 +82,7 @@ func createHandler(r rest.NamedCreater, scope RequestScope, admit admission.Inte
 			scope.err(err, w, req)
 			return
 		}
+
 		decoder := scope.Serializer.DecoderToVersion(s.Serializer, scope.HubGroupVersion)
 
 		body, err := readBody(req)
@@ -144,17 +150,6 @@ func createHandler(r rest.NamedCreater, scope RequestScope, admit admission.Inte
 		}
 		trace.Step("Object stored in database")
 
-		requestInfo, ok := request.RequestInfoFrom(ctx)
-		if !ok {
-			scope.err(fmt.Errorf("missing requestInfo"), w, req)
-			return
-		}
-		if err := setSelfLink(result, requestInfo, scope.Namer); err != nil {
-			scope.err(err, w, req)
-			return
-		}
-		trace.Step("Self-link added")
-
 		// If the object is partially initialized, always indicate it via StatusAccepted
 		code := http.StatusCreated
 		if accessor, err := meta.Accessor(result); err == nil {
@@ -168,7 +163,7 @@ func createHandler(r rest.NamedCreater, scope RequestScope, admit admission.Inte
 		}
 
 		scope.Trace = trace
-		transformResponseObject(ctx, scope, req, w, code, result)
+		transformResponseObject(ctx, scope, req, w, code, outputMediaType, result)
 	}
 }
 

staging/src/k8s.io/apiserver/pkg/endpoints/handlers/delete.go

@@ -64,6 +64,12 @@ func DeleteResource(r rest.GracefulDeleter, allowsOptions bool, scope RequestSco
 		ae := request.AuditEventFrom(ctx)
 		admit = admission.WithAudit(admit, ae)
 
+		outputMediaType, _, err := negotiation.NegotiateOutputMediaType(req, scope.Serializer, &scope)
+		if err != nil {
+			scope.err(err, w, req)
+			return
+		}
+
 		options := &metav1.DeleteOptions{}
 		if allowsOptions {
 			body, err := readBody(req)
@@ -160,23 +166,10 @@ func DeleteResource(r rest.GracefulDeleter, allowsOptions bool, scope RequestSco
 					Kind: scope.Kind.Kind,
 				},
 			}
-		} else {
-			// when a non-status response is returned, set the self link
-			requestInfo, ok := request.RequestInfoFrom(ctx)
-			if !ok {
-				scope.err(fmt.Errorf("missing requestInfo"), w, req)
-				return
-			}
-			if _, ok := result.(*metav1.Status); !ok {
-				if err := setSelfLink(result, requestInfo, scope.Namer); err != nil {
-					scope.err(err, w, req)
-					return
-				}
-			}
 		}
 
 		scope.Trace = trace
-		transformResponseObject(ctx, scope, req, w, status, result)
+		transformResponseObject(ctx, scope, req, w, status, outputMediaType, result)
 	}
 }
 
@@ -204,6 +197,12 @@ func DeleteCollection(r rest.CollectionDeleter, checkBody bool, scope RequestSco
 		ctx = request.WithNamespace(ctx, namespace)
 		ae := request.AuditEventFrom(ctx)
 
+		outputMediaType, _, err := negotiation.NegotiateOutputMediaType(req, scope.Serializer, &scope)
+		if err != nil {
+			scope.err(err, w, req)
+			return
+		}
+
 		listOptions := metainternalversion.ListOptions{}
 		if err := metainternalversion.ParameterCodec.DecodeParameters(req.URL.Query(), scope.MetaGroupVersion, &listOptions); err != nil {
 			err = errors.NewBadRequest(err.Error())
@@ -304,17 +303,9 @@ func DeleteCollection(r rest.CollectionDeleter, checkBody bool, scope RequestSco
 					Kind: scope.Kind.Kind,
 				},
 			}
-		} else {
-			// when a non-status response is returned, set the self link
-			if _, ok := result.(*metav1.Status); !ok {
-				if _, err := setListSelfLink(result, ctx, req, scope.Namer); err != nil {
-					scope.err(err, w, req)
-					return
-				}
-			}
 		}
 
 		scope.Trace = trace
-		transformResponseObject(ctx, scope, req, w, http.StatusOK, result)
+		transformResponseObject(ctx, scope, req, w, http.StatusOK, outputMediaType, result)
 	}
 }

staging/src/k8s.io/apiserver/pkg/endpoints/handlers/get.go

@@ -33,6 +33,7 @@ import (
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/fields"
 	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/apiserver/pkg/endpoints/handlers/negotiation"
 	"k8s.io/apiserver/pkg/endpoints/metrics"
 	"k8s.io/apiserver/pkg/endpoints/request"
 	"k8s.io/apiserver/pkg/registry/rest"
@@ -58,24 +59,21 @@ func getResourceHandler(scope RequestScope, getter getterFunc) http.HandlerFunc
 		ctx := req.Context()
 		ctx = request.WithNamespace(ctx, namespace)
 
-		result, err := getter(ctx, name, req, trace)
+		outputMediaType, _, err := negotiation.NegotiateOutputMediaType(req, scope.Serializer, &scope)
 		if err != nil {
 			scope.err(err, w, req)
 			return
 		}
-		requestInfo, ok := request.RequestInfoFrom(ctx)
-		if !ok {
-			scope.err(fmt.Errorf("missing requestInfo"), w, req)
-			return
-		}
-		if err := setSelfLink(result, requestInfo, scope.Namer); err != nil {
+
+		result, err := getter(ctx, name, req, trace)
+		if err != nil {
 			scope.err(err, w, req)
 			return
 		}
 
 		trace.Step("About to write a response")
 		scope.Trace = trace
-		transformResponseObject(ctx, scope, req, w, http.StatusOK, result)
+		transformResponseObject(ctx, scope, req, w, http.StatusOK, outputMediaType, result)
 		trace.Step("Transformed response object")
 	}
 }
@@ -187,6 +185,12 @@ func ListResource(r rest.Lister, rw rest.Watcher, scope RequestScope, forceWatch
 		ctx := req.Context()
 		ctx = request.WithNamespace(ctx, namespace)
 
+		outputMediaType, _, err := negotiation.NegotiateOutputMediaType(req, scope.Serializer, &scope)
+		if err != nil {
+			scope.err(err, w, req)
+			return
+		}
+
 		opts := metainternalversion.ListOptions{}
 		if err := metainternalversion.ParameterCodec.DecodeParameters(req.URL.Query(), scope.MetaGroupVersion, &opts); err != nil {
 			err = errors.NewBadRequest(err.Error())
@@ -267,22 +271,9 @@ func ListResource(r rest.Lister, rw rest.Watcher, scope RequestScope, forceWatch
 			return
 		}
 		trace.Step("Listing from storage done")
-		numberOfItems, err := setListSelfLink(result, ctx, req, scope.Namer)
-		if err != nil {
-			scope.err(err, w, req)
-			return
-		}
-		trace.Step("Self-linking done")
-		// Ensure empty lists return a non-nil items slice
-		if numberOfItems == 0 && meta.IsListType(result) {
-			if err := meta.SetList(result, []runtime.Object{}); err != nil {
-				scope.err(err, w, req)
-				return
-			}
-		}
 
 		scope.Trace = trace
-		transformResponseObject(ctx, scope, req, w, http.StatusOK, result)
-		trace.Step(fmt.Sprintf("Writing http response done (%d items)", numberOfItems))
+		transformResponseObject(ctx, scope, req, w, http.StatusOK, outputMediaType, result)
+		trace.Step(fmt.Sprintf("Writing http response done (%d items)", meta.LenList(result)))
 	}
 }

staging/src/k8s.io/apiserver/pkg/endpoints/handlers/patch.go

@@ -88,6 +88,12 @@ func PatchResource(r rest.Patcher, scope RequestScope, admit admission.Interface
 		ctx := req.Context()
 		ctx = request.WithNamespace(ctx, namespace)
 
+		outputMediaType, _, err := negotiation.NegotiateOutputMediaType(req, scope.Serializer, &scope)
+		if err != nil {
+			scope.err(err, w, req)
+			return
+		}
+
 		patchJS, err := readBody(req)
 		if err != nil {
 			scope.err(err, w, req)
@@ -190,19 +196,8 @@ func PatchResource(r rest.Patcher, scope RequestScope, admit admission.Interface
 		}
 		trace.Step("Object stored in database")
 
-		requestInfo, ok := request.RequestInfoFrom(ctx)
-		if !ok {
-			scope.err(fmt.Errorf("missing requestInfo"), w, req)
-			return
-		}
-		if err := setSelfLink(result, requestInfo, scope.Namer); err != nil {
-			scope.err(err, w, req)
-			return
-		}
-		trace.Step("Self-link added")
-
 		scope.Trace = trace
-		transformResponseObject(ctx, scope, req, w, http.StatusOK, result)
+		transformResponseObject(ctx, scope, req, w, http.StatusOK, outputMediaType, result)
 	}
 }
 

staging/src/k8s.io/apiserver/pkg/endpoints/handlers/response.go

@@ -27,160 +27,85 @@ import (
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	metav1beta1 "k8s.io/apimachinery/pkg/apis/meta/v1beta1"
 	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/apimachinery/pkg/runtime/schema"
 	"k8s.io/apiserver/pkg/endpoints/handlers/negotiation"
 	"k8s.io/apiserver/pkg/endpoints/handlers/responsewriters"
 )
 
 // transformResponseObject takes an object loaded from storage and performs any necessary transformations.
 // Will write the complete response object.
-func transformResponseObject(ctx context.Context, scope RequestScope, req *http.Request, w http.ResponseWriter, statusCode int, result runtime.Object) {
-	// TODO: fetch the media type much earlier in request processing and pass it into this method.
-	trace := scope.Trace
-	mediaType, _, err := negotiation.NegotiateOutputMediaType(req, scope.Serializer, &scope)
-	if err != nil {
-		status := responsewriters.ErrorToAPIStatus(err)
-		trace.Step("Writing raw JSON response")
-		responsewriters.WriteRawJSON(int(status.Code), status, w)
+func transformResponseObject(ctx context.Context, scope RequestScope, req *http.Request, w http.ResponseWriter, statusCode int, mediaType negotiation.MediaTypeOptions, result runtime.Object) {
+	// status objects are ignored for transformation
+	if _, ok := result.(*metav1.Status); ok {
+		responsewriters.WriteObject(statusCode, scope.Kind.GroupVersion(), scope.Serializer, result, w, req)
 		return
 	}
 
-	// If conversion was allowed by the scope, perform it before writing the response
-	if target := mediaType.Convert; target != nil {
-		switch {
-
-		case target.Kind == "PartialObjectMetadata" && target.GroupVersion() == metav1beta1.SchemeGroupVersion:
-			if meta.IsListType(result) {
-				// TODO: this should be calculated earlier
-				err = newNotAcceptableError(fmt.Sprintf("you requested PartialObjectMetadata, but the requested object is a list (%T)", result))
-				scope.err(err, w, req)
-				return
-			}
-			m, err := meta.Accessor(result)
-			if err != nil {
-				scope.err(err, w, req)
-				return
-			}
-			partial := meta.AsPartialObjectMetadata(m)
-			partial.GetObjectKind().SetGroupVersionKind(metav1beta1.SchemeGroupVersion.WithKind("PartialObjectMetadata"))
-
-			// renegotiate under the internal version
-			_, info, err := negotiation.NegotiateOutputMediaType(req, metainternalversion.Codecs, &scope)
-			if err != nil {
-				scope.err(err, w, req)
-				return
-			}
-			encoder := metainternalversion.Codecs.EncoderForVersion(info.Serializer, metav1beta1.SchemeGroupVersion)
-			trace.Step(fmt.Sprintf("Serializing response as type %s", info.MediaType))
-			responsewriters.SerializeObject(info.MediaType, encoder, w, req, statusCode, partial)
-			return
-
-		case target.Kind == "PartialObjectMetadataList" && target.GroupVersion() == metav1beta1.SchemeGroupVersion:
-			if !meta.IsListType(result) {
-				// TODO: this should be calculated earlier
-				err = newNotAcceptableError(fmt.Sprintf("you requested PartialObjectMetadataList, but the requested object is not a list (%T)", result))
-				scope.err(err, w, req)
-				return
-			}
-			list := &metav1beta1.PartialObjectMetadataList{}
-			trace.Step("Processing list items")
-			err := meta.EachListItem(result, func(obj runtime.Object) error {
-				m, err := meta.Accessor(obj)
-				if err != nil {
-					return err
-				}
-				partial := meta.AsPartialObjectMetadata(m)
-				partial.GetObjectKind().SetGroupVersionKind(metav1beta1.SchemeGroupVersion.WithKind("PartialObjectMetadata"))
-				list.Items = append(list.Items, partial)
-				return nil
-			})
-			if err != nil {
-				scope.err(err, w, req)
-				return
-			}
-
-			// renegotiate under the internal version
-			_, info, err := negotiation.NegotiateOutputMediaType(req, metainternalversion.Codecs, &scope)
-			if err != nil {
-				scope.err(err, w, req)
-				return
-			}
-			encoder := metainternalversion.Codecs.EncoderForVersion(info.Serializer, metav1beta1.SchemeGroupVersion)
-			trace.Step(fmt.Sprintf("Serializing response as type %s", info.MediaType))
-			responsewriters.SerializeObject(info.MediaType, encoder, w, req, statusCode, list)
-			return
-
-		case target.Kind == "Table" && target.GroupVersion() == metav1beta1.SchemeGroupVersion:
-			// TODO: relax the version abstraction
-			// TODO: skip if this is a status response (delete without body)?
-
-			opts := &metav1beta1.TableOptions{}
-			trace.Step("Decoding parameters")
-			if err := metav1beta1.ParameterCodec.DecodeParameters(req.URL.Query(), metav1beta1.SchemeGroupVersion, opts); err != nil {
-				scope.err(err, w, req)
-				return
-			}
-
-			trace.Step("Converting to table")
-			table, err := scope.TableConvertor.ConvertToTable(ctx, result, opts)
-			if err != nil {
-				scope.err(err, w, req)
-				return
-			}
-
-			trace.Step("Processing rows")
-			for i := range table.Rows {
-				item := &table.Rows[i]
-				switch opts.IncludeObject {
-				case metav1beta1.IncludeObject:
-					item.Object.Object, err = scope.Convertor.ConvertToVersion(item.Object.Object, scope.Kind.GroupVersion())
-					if err != nil {
-						scope.err(err, w, req)
-						return
-					}
-				// TODO: rely on defaulting for the value here?
-				case metav1beta1.IncludeMetadata, "":
-					m, err := meta.Accessor(item.Object.Object)
-					if err != nil {
-						scope.err(err, w, req)
-						return
-					}
-					// TODO: turn this into an internal type and do conversion in order to get object kind automatically set?
-					partial := meta.AsPartialObjectMetadata(m)
-					partial.GetObjectKind().SetGroupVersionKind(metav1beta1.SchemeGroupVersion.WithKind("PartialObjectMetadata"))
-					item.Object.Object = partial
-				case metav1beta1.IncludeNone:
-					item.Object.Object = nil
-				default:
-					// TODO: move this to validation on the table options?
-					err = errors.NewBadRequest(fmt.Sprintf("unrecognized includeObject value: %q", opts.IncludeObject))
-					scope.err(err, w, req)
-				}
-			}
-
-			// renegotiate under the internal version
-			_, info, err := negotiation.NegotiateOutputMediaType(req, metainternalversion.Codecs, &scope)
-			if err != nil {
-				scope.err(err, w, req)
-				return
-			}
-			encoder := metainternalversion.Codecs.EncoderForVersion(info.Serializer, metav1beta1.SchemeGroupVersion)
-			trace.Step(fmt.Sprintf("Serializing response as type %s", info.MediaType))
-			responsewriters.SerializeObject(info.MediaType, encoder, w, req, statusCode, table)
-			return
-
-		default:
-			// this block should only be hit if scope AllowsConversion is incorrect
-			accepted, _ := negotiation.MediaTypesForSerializer(metainternalversion.Codecs)
-			err := negotiation.NewNotAcceptableError(accepted)
-			status := responsewriters.ErrorToAPIStatus(err)
-			trace.Step("Writing raw JSON response")
-			responsewriters.WriteRawJSON(int(status.Code), status, w)
-			return
-		}
+	// ensure the self link and empty list array are set
+	if err := setObjectSelfLink(ctx, result, req, scope.Namer); err != nil {
+		scope.err(err, w, req)
+		return
 	}
 
-	trace.Step("Writing response")
-	responsewriters.WriteObject(statusCode, scope.Kind.GroupVersion(), scope.Serializer, result, w, req)
+	trace := scope.Trace
+
+	// If conversion was allowed by the scope, perform it before writing the response
+	switch target := mediaType.Convert; {
+
+	case target == nil:
+		trace.Step("Writing response")
+		responsewriters.WriteObject(statusCode, scope.Kind.GroupVersion(), scope.Serializer, result, w, req)
+
+	case target.Kind == "PartialObjectMetadata" && target.GroupVersion() == metav1beta1.SchemeGroupVersion:
+		partial, err := asV1Beta1PartialObjectMetadata(result)
+		if err != nil {
+			scope.err(err, w, req)
+			return
+		}
+
+		if err := writeMetaInternalVersion(partial, statusCode, w, req, &scope, target.GroupVersion()); err != nil {
+			scope.err(err, w, req)
+			return
+		}
+
+	case target.Kind == "PartialObjectMetadataList" && target.GroupVersion() == metav1beta1.SchemeGroupVersion:
+		trace.Step("Processing list items")
+		partial, err := asV1Beta1PartialObjectMetadataList(result)
+		if err != nil {
+			scope.err(err, w, req)
+			return
+		}
+
+		if err := writeMetaInternalVersion(partial, statusCode, w, req, &scope, target.GroupVersion()); err != nil {
+			scope.err(err, w, req)
+			return
+		}
+
+	case target.Kind == "Table" && target.GroupVersion() == metav1beta1.SchemeGroupVersion:
+		opts := &metav1beta1.TableOptions{}
+		trace.Step("Decoding parameters")
+		if err := metav1beta1.ParameterCodec.DecodeParameters(req.URL.Query(), metav1beta1.SchemeGroupVersion, opts); err != nil {
+			scope.err(err, w, req)
+			return
+		}
+
+		table, err := asV1Beta1Table(ctx, result, opts, scope)
+		if err != nil {
+			scope.err(err, w, req)
+			return
+		}
+
+		if err := writeMetaInternalVersion(table, statusCode, w, req, &scope, target.GroupVersion()); err != nil {
+			scope.err(err, w, req)
+			return
+		}
+
+	default:
+		// this block should only be hit if scope AllowsConversion is incorrect
+		accepted, _ := negotiation.MediaTypesForSerializer(metainternalversion.Codecs)
+		err := negotiation.NewNotAcceptableError(accepted)
+		scope.err(err, w, req)
+	}
 }
 
 // errNotAcceptable indicates Accept negotiation has failed
@@ -204,3 +129,91 @@ func (e errNotAcceptable) Status() metav1.Status {
 		Message: e.Error(),
 	}
 }
+
+func asV1Beta1Table(ctx context.Context, result runtime.Object, opts *metav1beta1.TableOptions, scope RequestScope) (runtime.Object, error) {
+	trace := scope.Trace
+
+	trace.Step("Converting to table")
+	table, err := scope.TableConvertor.ConvertToTable(ctx, result, opts)
+	if err != nil {
+		return nil, err
+	}
+
+	trace.Step("Processing rows")
+	for i := range table.Rows {
+		item := &table.Rows[i]
+		switch opts.IncludeObject {
+		case metav1beta1.IncludeObject:
+			item.Object.Object, err = scope.Convertor.ConvertToVersion(item.Object.Object, scope.Kind.GroupVersion())
+			if err != nil {
+				return nil, err
+			}
+		// TODO: rely on defaulting for the value here?
+		case metav1beta1.IncludeMetadata, "":
+			m, err := meta.Accessor(item.Object.Object)
+			if err != nil {
+				return nil, err
+			}
+			// TODO: turn this into an internal type and do conversion in order to get object kind automatically set?
+			partial := meta.AsPartialObjectMetadata(m)
+			partial.GetObjectKind().SetGroupVersionKind(metav1beta1.SchemeGroupVersion.WithKind("PartialObjectMetadata"))
+			item.Object.Object = partial
+		case metav1beta1.IncludeNone:
+			item.Object.Object = nil
+		default:
+			// TODO: move this to validation on the table options?
+			err = errors.NewBadRequest(fmt.Sprintf("unrecognized includeObject value: %q", opts.IncludeObject))
+			return nil, err
+		}
+	}
+
+	return table, nil
+}
+
+func asV1Beta1PartialObjectMetadata(result runtime.Object) (runtime.Object, error) {
+	if meta.IsListType(result) {
+		// TODO: this should be calculated earlier
+		err := newNotAcceptableError(fmt.Sprintf("you requested PartialObjectMetadata, but the requested object is a list (%T)", result))
+		return nil, err
+	}
+	m, err := meta.Accessor(result)
+	if err != nil {
+		return nil, err
+	}
+	partial := meta.AsPartialObjectMetadata(m)
+	partial.GetObjectKind().SetGroupVersionKind(metav1beta1.SchemeGroupVersion.WithKind("PartialObjectMetadata"))
+	return partial, nil
+}
+
+func asV1Beta1PartialObjectMetadataList(result runtime.Object) (runtime.Object, error) {
+	if !meta.IsListType(result) {
+		// TODO: this should be calculated earlier
+		return nil, newNotAcceptableError(fmt.Sprintf("you requested PartialObjectMetadataList, but the requested object is not a list (%T)", result))
+	}
+	list := &metav1beta1.PartialObjectMetadataList{}
+	err := meta.EachListItem(result, func(obj runtime.Object) error {
+		m, err := meta.Accessor(obj)
+		if err != nil {
+			return err
+		}
+		partial := meta.AsPartialObjectMetadata(m)
+		partial.GetObjectKind().SetGroupVersionKind(metav1beta1.SchemeGroupVersion.WithKind("PartialObjectMetadata"))
+		list.Items = append(list.Items, partial)
+		return nil
+	})
+	if err != nil {
+		return nil, err
+	}
+	return list, nil
+}
+
+func writeMetaInternalVersion(obj runtime.Object, statusCode int, w http.ResponseWriter, req *http.Request, restrictions negotiation.EndpointRestrictions, target schema.GroupVersion) error {
+	// renegotiate under the internal version
+	_, info, err := negotiation.NegotiateOutputMediaType(req, metainternalversion.Codecs, restrictions)
+	if err != nil {
+		return err
+	}
+	encoder := metainternalversion.Codecs.EncoderForVersion(info.Serializer, target)
+	responsewriters.SerializeObject(info.MediaType, encoder, w, req, statusCode, obj)
+	return nil
+}

staging/src/k8s.io/apiserver/pkg/endpoints/handlers/rest.go

@@ -280,23 +280,26 @@ func checkName(obj runtime.Object, name, namespace string, namer ScopeNamer) err
 	return nil
 }
 
-// setListSelfLink sets the self link of a list to the base URL, then sets the self links
-// on all child objects returned. Returns the number of items in the list.
-func setListSelfLink(obj runtime.Object, ctx context.Context, req *http.Request, namer ScopeNamer) (int, error) {
+// setObjectSelfLink sets the self link of an object as needed.
+func setObjectSelfLink(ctx context.Context, obj runtime.Object, req *http.Request, namer ScopeNamer) error {
 	if !meta.IsListType(obj) {
-		return 0, nil
+		requestInfo, ok := request.RequestInfoFrom(ctx)
+		if !ok {
+			return fmt.Errorf("missing requestInfo")
+		}
+		return setSelfLink(obj, requestInfo, namer)
 	}
 
 	uri, err := namer.GenerateListLink(req)
 	if err != nil {
-		return 0, err
+		return err
 	}
 	if err := namer.SetSelfLink(obj, uri); err != nil {
 		klog.V(4).Infof("Unable to set self link on object: %v", err)
 	}
 	requestInfo, ok := request.RequestInfoFrom(ctx)
 	if !ok {
-		return 0, fmt.Errorf("missing requestInfo")
+		return fmt.Errorf("missing requestInfo")
 	}
 
 	count := 0
@@ -304,7 +307,14 @@ func setListSelfLink(obj runtime.Object, ctx context.Context, req *http.Request,
 		count++
 		return setSelfLink(obj, requestInfo, namer)
 	})
-	return count, err
+
+	if count == 0 {
+		if err := meta.SetList(obj, []runtime.Object{}); err != nil {
+			return err
+		}
+	}
+
+	return err
 }
 
 func summarizeData(data []byte, maxLength int) string {

staging/src/k8s.io/apiserver/pkg/endpoints/handlers/update.go

@@ -64,6 +64,12 @@ func UpdateResource(r rest.Updater, scope RequestScope, admit admission.Interfac
 		ctx := req.Context()
 		ctx = request.WithNamespace(ctx, namespace)
 
+		outputMediaType, _, err := negotiation.NegotiateOutputMediaType(req, scope.Serializer, &scope)
+		if err != nil {
+			scope.err(err, w, req)
+			return
+		}
+
 		body, err := readBody(req)
 		if err != nil {
 			scope.err(err, w, req)
@@ -174,24 +180,13 @@ func UpdateResource(r rest.Updater, scope RequestScope, admit admission.Interfac
 		}
 		trace.Step("Object stored in database")
 
-		requestInfo, ok := request.RequestInfoFrom(ctx)
-		if !ok {
-			scope.err(fmt.Errorf("missing requestInfo"), w, req)
-			return
-		}
-		if err := setSelfLink(result, requestInfo, scope.Namer); err != nil {
-			scope.err(err, w, req)
-			return
-		}
-		trace.Step("Self-link added")
-
 		status := http.StatusOK
 		if wasCreated {
 			status = http.StatusCreated
 		}
 
 		scope.Trace = trace
-		transformResponseObject(ctx, scope, req, w, status, result)
+		transformResponseObject(ctx, scope, req, w, status, outputMediaType, result)
 	}
 }