Add warnings capability for admission webhooks

pkg/apis/admission/types.go

@@ -138,6 +138,12 @@ type AdmissionResponse struct {
 	// the admission webhook to add additional context to the audit log for this request.
 	// +optional
 	AuditAnnotations map[string]string
+	// warnings is a list of warning messages to return to the requesting API client.
+	// Warning messages describe a problem the client making the API request should correct or be aware of.
+	// Limit warnings to 120 characters if possible.
+	// Warnings over 256 characters and large numbers of warnings may be truncated.
+	// +optional
+	Warnings []string
 }
 
 // PatchType is the type of patch being used to represent the mutated object

staging/src/k8s.io/api/admission/v1/types.go

@@ -140,6 +140,13 @@ type AdmissionResponse struct {
 	// the admission webhook to add additional context to the audit log for this request.
 	// +optional
 	AuditAnnotations map[string]string `json:"auditAnnotations,omitempty" protobuf:"bytes,6,opt,name=auditAnnotations"`
+
+	// warnings is a list of warning messages to return to the requesting API client.
+	// Warning messages describe a problem the client making the API request should correct or be aware of.
+	// Limit warnings to 120 characters if possible.
+	// Warnings over 256 characters and large numbers of warnings may be truncated.
+	// +optional
+	Warnings []string `json:"warnings,omitempty" protobuf:"bytes,7,rep,name=warnings"`
 }
 
 // PatchType is the type of patch being used to represent the mutated object

staging/src/k8s.io/api/admission/v1beta1/types.go

@@ -145,6 +145,13 @@ type AdmissionResponse struct {
 	// the admission webhook to add additional context to the audit log for this request.
 	// +optional
 	AuditAnnotations map[string]string `json:"auditAnnotations,omitempty" protobuf:"bytes,6,opt,name=auditAnnotations"`
+
+	// warnings is a list of warning messages to return to the requesting API client.
+	// Warning messages describe a problem the client making the API request should correct or be aware of.
+	// Limit warnings to 120 characters if possible.
+	// Warnings over 256 characters and large numbers of warnings may be truncated.
+	// +optional
+	Warnings []string `json:"warnings,omitempty" protobuf:"bytes,7,rep,name=warnings"`
 }
 
 // PatchType is the type of patch being used to represent the mutated object

staging/src/k8s.io/apiserver/pkg/admission/plugin/webhook/mutating/dispatcher.go

@@ -43,6 +43,7 @@ import (
 	webhookrequest "k8s.io/apiserver/pkg/admission/plugin/webhook/request"
 	auditinternal "k8s.io/apiserver/pkg/apis/audit"
 	webhookutil "k8s.io/apiserver/pkg/util/webhook"
+	"k8s.io/apiserver/pkg/warning"
 	utiltrace "k8s.io/utils/trace"
 )
 
@@ -267,6 +268,9 @@ func (a *mutatingDispatcher) callAttrMutatingHook(ctx context.Context, h *admiss
 			klog.Warningf("Failed to set admission audit annotation %s to %s for mutating webhook %s: %v", key, v, h.Name, err)
 		}
 	}
+	for _, w := range result.Warnings {
+		warning.AddWarning(ctx, "", w)
+	}
 
 	if !result.Allowed {
 		return false, &webhookutil.ErrWebhookRejection{Status: webhookerrors.ToStatusErr(h.Name, result.Result)}

staging/src/k8s.io/apiserver/pkg/admission/plugin/webhook/request/admissionreview.go

@@ -36,6 +36,7 @@ type AdmissionResponse struct {
 	Patch            []byte
 	PatchType        admissionv1.PatchType
 	Result           *metav1.Status
+	Warnings         []string
 }
 
 // VerifyAdmissionResponse checks the validity of the provided admission review object, and returns the
@@ -93,6 +94,7 @@ func VerifyAdmissionResponse(uid types.UID, mutating bool, review runtime.Object
 			Patch:            patch,
 			PatchType:        patchType,
 			Result:           r.Response.Result,
+			Warnings:         r.Response.Warnings,
 		}, nil
 
 	case *admissionv1beta1.AdmissionReview:
@@ -118,6 +120,7 @@ func VerifyAdmissionResponse(uid types.UID, mutating bool, review runtime.Object
 			Patch:            patch,
 			PatchType:        patchType,
 			Result:           r.Response.Result,
+			Warnings:         r.Response.Warnings,
 		}, nil
 
 	default:

staging/src/k8s.io/apiserver/pkg/admission/plugin/webhook/validating/dispatcher.go

@@ -33,6 +33,7 @@ import (
 	"k8s.io/apiserver/pkg/admission/plugin/webhook/generic"
 	webhookrequest "k8s.io/apiserver/pkg/admission/plugin/webhook/request"
 	webhookutil "k8s.io/apiserver/pkg/util/webhook"
+	"k8s.io/apiserver/pkg/warning"
 	"k8s.io/klog/v2"
 	utiltrace "k8s.io/utils/trace"
 )
@@ -227,6 +228,9 @@ func (d *validatingDispatcher) callHook(ctx context.Context, h *v1.ValidatingWeb
 			klog.Warningf("Failed to set admission audit annotation %s to %s for validating webhook %s: %v", key, v, h.Name, err)
 		}
 	}
+	for _, w := range result.Warnings {
+		warning.AddWarning(ctx, "", w)
+	}
 	if result.Allowed {
 		return nil
 	}

staging/src/k8s.io/apiserver/pkg/endpoints/filters/warning.go

@@ -17,10 +17,13 @@ limitations under the License.
 package filters
 
 import (
+	"fmt"
 	"net/http"
 	"sync"
+	"unicode/utf8"
 
 	"k8s.io/apimachinery/pkg/util/net"
+	utilruntime "k8s.io/apimachinery/pkg/util/runtime"
 	"k8s.io/apiserver/pkg/warning"
 )
 
@@ -33,10 +36,34 @@ func WithWarningRecorder(handler http.Handler) http.Handler {
 	})
 }
 
+var (
+	truncateAtTotalRunes = 4 * 1024
+	truncateItemRunes    = 256
+)
+
+type recordedWarning struct {
+	agent string
+	text  string
+}
+
 type recorder struct {
-	lock     sync.Mutex
+	// lock guards calls to AddWarning from multiple threads
+	lock sync.Mutex
+
+	// recorded tracks whether AddWarning was already called with a given text
 	recorded map[string]bool
-	writer   http.ResponseWriter
+
+	// ordered tracks warnings added so they can be replayed and truncated if needed
+	ordered []recordedWarning
+
+	// written tracks how many runes of text have been added as warning headers
+	written int
+
+	// truncating tracks if we have already exceeded truncateAtTotalRunes and are now truncating warning messages as we add them
+	truncating bool
+
+	// writer is the response writer to add warning headers to
+	writer http.ResponseWriter
 }
 
 func (r *recorder) AddWarning(agent, text string) {
@@ -47,6 +74,11 @@ func (r *recorder) AddWarning(agent, text string) {
 	r.lock.Lock()
 	defer r.lock.Unlock()
 
+	// if we've already exceeded our limit and are already truncating, return early
+	if r.written >= truncateAtTotalRunes && r.truncating {
+		return
+	}
+
 	// init if needed
 	if r.recorded == nil {
 		r.recorded = map[string]bool{}
@@ -57,13 +89,45 @@ func (r *recorder) AddWarning(agent, text string) {
 		return
 	}
 	r.recorded[text] = true
+	r.ordered = append(r.ordered, recordedWarning{agent: agent, text: text})
 
-	// TODO(liggitt): track total message characters written:
-	// * if this takes us over 4k truncate individual messages to 256 chars and regenerate headers
-	// * if we're already truncating truncate this message to 256 chars
-	// * if we're still over 4k omit this message
+	// truncate on a rune boundary, if needed
+	textRuneLength := utf8.RuneCountInString(text)
+	if r.truncating && textRuneLength > truncateItemRunes {
+		text = string([]rune(text)[:truncateItemRunes])
+		textRuneLength = truncateItemRunes
+	}
 
-	if header, err := net.NewWarningHeader(299, agent, text); err == nil {
+	// compute the header
+	header, err := net.NewWarningHeader(299, agent, text)
+	if err != nil {
+		return
+	}
+
+	// if this fits within our limit, or we're already truncating, write and return
+	if r.written+textRuneLength <= truncateAtTotalRunes || r.truncating {
+		r.written += textRuneLength
 		r.writer.Header().Add("Warning", header)
+		return
+	}
+
+	// otherwise, enable truncation, reset, and replay the existing items as truncated warnings
+	r.truncating = true
+	r.written = 0
+	r.writer.Header().Del("Warning")
+	utilruntime.HandleError(fmt.Errorf("exceeded max warning header size, truncating"))
+	for _, w := range r.ordered {
+		agent := w.agent
+		text := w.text
+
+		textRuneLength := utf8.RuneCountInString(text)
+		if textRuneLength > truncateItemRunes {
+			text = string([]rune(text)[:truncateItemRunes])
+			textRuneLength = truncateItemRunes
+		}
+		if header, err := net.NewWarningHeader(299, agent, text); err == nil {
+			r.written += textRuneLength
+			r.writer.Header().Add("Warning", header)
+		}
 	}
 }

staging/src/k8s.io/apiserver/pkg/endpoints/filters/warning_test.go

@@ -98,3 +98,35 @@ func Test_recorder_AddWarning(t *testing.T) {
 		})
 	}
 }
+
+func TestTruncation(t *testing.T) {
+	originalTotalRunes, originalItemRunes := truncateAtTotalRunes, truncateItemRunes
+	truncateAtTotalRunes, truncateItemRunes = 25, 5
+	defer func() {
+		truncateAtTotalRunes, truncateItemRunes = originalTotalRunes, originalItemRunes
+	}()
+
+	responseRecorder := httptest.NewRecorder()
+	warningRecorder := &recorder{writer: responseRecorder}
+
+	// add items longer than the individual length
+	warningRecorder.AddWarning("", "aaaaaaaaaa")  // long item
+	warningRecorder.AddWarning("-", "aaaaaaaaaa") // duplicate item
+	warningRecorder.AddWarning("", "bb")          // short item
+	warningRecorder.AddWarning("", "ccc")         // short item
+	warningRecorder.AddWarning("", "Iñtërnâtiô")  // long item
+	// check they are preserved
+	if e, a := []string{`299 - "aaaaaaaaaa"`, `299 - "bb"`, `299 - "ccc"`, `299 - "Iñtërnâtiô"`}, responseRecorder.Header()["Warning"]; !reflect.DeepEqual(e, a) {
+		t.Errorf("expected\n%#v\ngot\n%#v", e, a)
+	}
+	// add an item that exceeds the length and triggers truncation, reducing existing items to 15 runes
+	warningRecorder.AddWarning("", "e")          // triggering item, 16 total
+	warningRecorder.AddWarning("", "ffffffffff") // long item to get truncated, 21 total
+	warningRecorder.AddWarning("", "ffffffffff") // duplicate item
+	warningRecorder.AddWarning("", "gggggggggg") // item to get truncated, 26 total
+	warningRecorder.AddWarning("", "h")          // item to get ignored since we're over our limit
+	// check that existing items are truncated, and order preserved
+	if e, a := []string{`299 - "aaaaa"`, `299 - "bb"`, `299 - "ccc"`, `299 - "Iñtër"`, `299 - "e"`, `299 - "fffff"`, `299 - "ggggg"`}, responseRecorder.Header()["Warning"]; !reflect.DeepEqual(e, a) {
+		t.Errorf("expected\n%#v\ngot\n%#v", e, a)
+	}
+}

test/images/agnhost/webhook/convert.go

@@ -75,6 +75,7 @@ func convertAdmissionResponseToV1(r *v1beta1.AdmissionResponse) *v1.AdmissionRes
 		Patch:            r.Patch,
 		PatchType:        pt,
 		Result:           r.Result,
+		Warnings:         r.Warnings,
 	}
 }
 
@@ -91,6 +92,7 @@ func convertAdmissionResponseToV1beta1(r *v1.AdmissionResponse) *v1beta1.Admissi
 		Patch:            r.Patch,
 		PatchType:        pt,
 		Result:           r.Result,
+		Warnings:         r.Warnings,
 	}
 }
 

test/integration/apiserver/admissionwebhook/admission_test.go

@@ -169,6 +169,8 @@ type holder struct {
 
 	t *testing.T
 
+	warningHandler *warningHandler
+
 	recordGVR       metav1.GroupVersionResource
 	recordOperation string
 	recordNamespace string
@@ -203,6 +205,7 @@ func (h *holder) reset(t *testing.T) {
 	h.expectOldObject = false
 	h.expectOptionsGVK = schema.GroupVersionKind{}
 	h.expectOptions = false
+	h.warningHandler.reset()
 
 	// Set up the recorded map with nil records for all combinations
 	h.recorded = map[webhookOptions]*admissionRequest{}
@@ -231,6 +234,7 @@ func (h *holder) expect(gvr schema.GroupVersionResource, gvk, optionsGVK schema.
 	h.expectOldObject = oldObject
 	h.expectOptionsGVK = optionsGVK
 	h.expectOptions = options
+	h.warningHandler.reset()
 
 	// Set up the recorded map with nil records for all combinations
 	h.recorded = map[webhookOptions]*admissionRequest{}
@@ -314,13 +318,15 @@ func (h *holder) verify(t *testing.T) {
 	defer h.lock.Unlock()
 
 	for options, value := range h.recorded {
-		if err := h.verifyRequest(options.converted, value); err != nil {
+		if err := h.verifyRequest(options, value); err != nil {
 			t.Errorf("version: %v, phase:%v, converted:%v error: %v", options.version, options.phase, options.converted, err)
 		}
 	}
 }
 
-func (h *holder) verifyRequest(converted bool, request *admissionRequest) error {
+func (h *holder) verifyRequest(webhookOptions webhookOptions, request *admissionRequest) error {
+	converted := webhookOptions.converted
+
 	// Check if current resource should be exempted from Admission processing
 	if admissionExemptResources[gvr(h.recordGVR.Group, h.recordGVR.Version, h.recordGVR.Resource)] {
 		if request == nil {
@@ -357,6 +363,10 @@ func (h *holder) verifyRequest(converted bool, request *admissionRequest) error
 		return fmt.Errorf("unexpected options: %#v", request.Options.Object)
 	}
 
+	if !h.warningHandler.hasWarning(makeWarning(webhookOptions.version, webhookOptions.phase, webhookOptions.converted)) {
+		return fmt.Errorf("no warning received from webhook")
+	}
+
 	return nil
 }
 
@@ -384,6 +394,34 @@ func (h *holder) verifyOptions(options runtime.Object) error {
 	return nil
 }
 
+type warningHandler struct {
+	lock     sync.Mutex
+	warnings map[string]bool
+}
+
+func (w *warningHandler) reset() {
+	w.lock.Lock()
+	defer w.lock.Unlock()
+	w.warnings = map[string]bool{}
+}
+func (w *warningHandler) hasWarning(warning string) bool {
+	w.lock.Lock()
+	defer w.lock.Unlock()
+	return w.warnings[warning]
+}
+func makeWarning(version string, phase string, converted bool) string {
+	return fmt.Sprintf("%v/%v/%v", version, phase, converted)
+}
+
+func (w *warningHandler) HandleWarningHeader(code int, agent string, message string) {
+	if code != 299 || len(message) == 0 {
+		return
+	}
+	w.lock.Lock()
+	defer w.lock.Unlock()
+	w.warnings[message] = true
+}
+
 // TestWebhookAdmissionWithWatchCache tests communication between API server and webhook process.
 func TestWebhookAdmissionWithWatchCache(t *testing.T) {
 	testWebhookAdmission(t, true)
@@ -399,6 +437,7 @@ func testWebhookAdmission(t *testing.T, watchCache bool) {
 	// holder communicates expectations to webhooks, and results from webhooks
 	holder := &holder{
 		t:                 t,
+		warningHandler:    &warningHandler{warnings: map[string]bool{}},
 		gvrToConvertedGVR: map[metav1.GroupVersionResource]metav1.GroupVersionResource{},
 		gvrToConvertedGVK: map[metav1.GroupVersionResource]schema.GroupVersionKind{},
 	}
@@ -451,6 +490,7 @@ func testWebhookAdmission(t *testing.T, watchCache bool) {
 	clientConfig := rest.CopyConfig(server.ClientConfig)
 	clientConfig.Impersonate.UserName = testClientUsername
 	clientConfig.Impersonate.Groups = []string{"system:masters", "system:authenticated"}
+	clientConfig.WarningHandler = holder.warningHandler
 	client, err := clientset.NewForConfig(clientConfig)
 	if err != nil {
 		t.Fatalf("unexpected error: %v", err)
@@ -1265,6 +1305,9 @@ func newV1beta1WebhookHandler(t *testing.T, holder *holder, phase string, conver
 		review.Kind = ""
 		review.Response.UID = ""
 
+		// test plumbing warnings back to the client
+		review.Response.Warnings = []string{makeWarning("v1beta1", phase, converted)}
+
 		// If we're mutating, and have an object, return a patch to exercise conversion
 		if phase == mutation && len(review.Request.Object.Raw) > 0 {
 			review.Response.Patch = []byte(`[{"op":"add","path":"/foo","value":"test"}]`)
@@ -1355,6 +1398,9 @@ func newV1WebhookHandler(t *testing.T, holder *holder, phase string, converted b
 			Allowed: true,
 			UID:     review.Request.UID,
 			Result:  &metav1.Status{Message: "admitted"},
+
+			// test plumbing warnings back
+			Warnings: []string{makeWarning("v1", phase, converted)},
 		}
 		// If we're mutating, and have an object, return a patch to exercise conversion
 		if phase == mutation && len(review.Request.Object.Raw) > 0 {