WIP: Support webhooks

mockkubeapiserver/admissionhooks/webhooks.go

@@ -0,0 +1,379 @@
+/*
+Copyright 2024 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package admissionhooks
+
+import (
+	"bytes"
+	"context"
+	"crypto/tls"
+	"crypto/x509"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"strings"
+	"sync"
+
+	jsonpatch "github.com/evanphx/json-patch/v5"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
+	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/apimachinery/pkg/runtime/schema"
+	"k8s.io/klog/v2"
+	admissionv1 "sigs.k8s.io/kubebuilder-declarative-pattern/mockkubeapiserver/internal/api/admission/v1"
+	admissionregistrationv1 "sigs.k8s.io/kubebuilder-declarative-pattern/mockkubeapiserver/internal/api/admissionregistration/v1"
+	"sigs.k8s.io/kubebuilder-declarative-pattern/mockkubeapiserver/storage"
+)
+
+// Webhooks manages our kubernetes admission webhooks (both validating and mutating)
+type Webhooks struct {
+	// TODO: Replace with a copy-on-write mechanism
+	mutex          sync.Mutex
+	mutatingByName map[string]*mutatingWebhookRecord
+}
+
+// New constructs an instance of Webhooks.
+func New() *Webhooks {
+	h := &Webhooks{}
+	h.mutatingByName = make(map[string]*mutatingWebhookRecord)
+	return h
+}
+
+// OnWatchEvent is called by the storage system for any change.
+// We observe changes to webhook objects and set up webhooks
+func (s *Webhooks) OnWatchEvent(ev *storage.WatchEvent) {
+	switch ev.GroupKind() {
+	case schema.GroupKind{Group: "admissionregistration.k8s.io", Kind: "MutatingWebhookConfiguration"}:
+
+		// TODO: Deleted / changed webhooks
+
+		u := ev.Unstructured()
+
+		webhook := &admissionregistrationv1.MutatingWebhookConfiguration{}
+		if err := runtime.DefaultUnstructuredConverter.FromUnstructured(u.Object, webhook); err != nil {
+			klog.Fatalf("failed to parse webhook: %v", err)
+		}
+
+		if err := s.update(webhook); err != nil {
+			klog.Fatalf("failed to update webhook: %v", err)
+		}
+	}
+}
+
+// update is called when a mutating webhook changes; we record the webhook details.
+func (w *Webhooks) update(obj *admissionregistrationv1.MutatingWebhookConfiguration) error {
+	w.mutex.Lock()
+	defer w.mutex.Unlock()
+
+	name := obj.GetName()
+	existing := w.mutatingByName[name]
+	if existing != nil {
+		existing.obj = obj
+	} else {
+		existing = &mutatingWebhookRecord{obj: obj}
+		w.mutatingByName[name] = existing
+	}
+
+	existing.webhooks = make([]*mutatingWebhook, 0, len(obj.Webhooks))
+	for i := range obj.Webhooks {
+		webhookObj := &obj.Webhooks[i]
+		existing.webhooks = append(existing.webhooks, &mutatingWebhook{webhook: webhookObj})
+	}
+
+	return nil
+}
+
+// BeforeCreate should be invoked before any object is created.
+// We will invoke validating and mutating webhooks on the object.
+func (w *Webhooks) BeforeCreate(ctx context.Context, resource storage.ResourceInfo, obj *unstructured.Unstructured) (*unstructured.Unstructured, error) {
+	subresource := ""
+	gvr := resource.GVR()
+
+	matchingWebhooks, err := w.findMatchingWebhooks(admissionregistrationv1.Create, gvr, subresource)
+	if err != nil {
+		return nil, err
+	}
+	if len(matchingWebhooks) == 0 {
+		return obj, nil
+	}
+
+	req := newAdmissionRequest(obj, admissionv1.Create, gvr)
+	updated, err := w.invoke(ctx, matchingWebhooks, req, obj)
+	if err != nil {
+		return nil, err
+	}
+	if updated != nil {
+		obj = updated
+		// TODO: Looping if object changes
+	}
+	return obj, nil
+}
+
+// findMatchingWebhooks returns the webhooks that we need to call.
+func (w *Webhooks) findMatchingWebhooks(operation admissionregistrationv1.OperationType, gvr schema.GroupVersionResource, subresource string) ([]*mutatingWebhook, error) {
+	w.mutex.Lock()
+	defer w.mutex.Unlock()
+
+	var allMatches []*mutatingWebhook
+	for _, webhookSet := range w.mutatingByName {
+		for _, webhook := range webhookSet.webhooks {
+			isMatch, err := webhook.isMatch(operation, gvr, subresource)
+			if err != nil {
+				return nil, err
+			}
+			if isMatch {
+				allMatches = append(allMatches, webhook)
+			}
+		}
+	}
+	return allMatches, nil
+}
+
+// invoke makes the webhook requests to a chain of webhooks.
+func (w *Webhooks) invoke(ctx context.Context, matches []*mutatingWebhook, req *admissionRequest, original *unstructured.Unstructured) (*unstructured.Unstructured, error) {
+	for _, match := range matches {
+		updated, err := match.invoke(ctx, req, original)
+		if err != nil {
+			return nil, err
+		}
+		if updated != nil {
+			return updated, nil
+		}
+	}
+	return nil, nil
+}
+
+// mutatingWebhookRecord is our tracking data structure for a mutatingWebhook
+type mutatingWebhookRecord struct {
+	obj      *admissionregistrationv1.MutatingWebhookConfiguration
+	webhooks []*mutatingWebhook
+}
+
+type mutatingWebhook struct {
+	webhook *admissionregistrationv1.MutatingWebhook
+}
+
+func (w *mutatingWebhook) isMatch(operation admissionregistrationv1.OperationType, gvr schema.GroupVersionResource, subresource string) (bool, error) {
+	webhook := w.webhook
+	if webhook.NamespaceSelector != nil {
+		return false, fmt.Errorf("webhook namespaceSelector not implemented")
+	}
+	if webhook.ObjectSelector != nil {
+		return false, fmt.Errorf("webhook objectSelector not implemented")
+	}
+	if webhook.MatchPolicy != nil {
+		return false, fmt.Errorf("webhook matchPolicy not implemented")
+	}
+	for _, rule := range webhook.Rules {
+		if rule.Scope != nil {
+			return false, fmt.Errorf("webhook scope not implemented")
+		}
+
+		matchOperations := false
+		for _, op := range rule.Operations {
+			if op == "*" {
+				matchOperations = true
+			} else if op == operation {
+				matchOperations = true
+			}
+		}
+		if !matchOperations {
+			continue
+		}
+
+		matchGroup := false
+		for _, group := range rule.APIGroups {
+			if group == "*" {
+				matchGroup = true
+			} else if group == gvr.Group {
+				matchGroup = true
+			}
+		}
+		if !matchGroup {
+			continue
+		}
+		matchResource := false
+		for _, resource := range rule.Resources {
+			tokens := strings.Split(resource, "/")
+			if len(tokens) == 1 {
+				if resource == "" {
+					// Empty-string ("") means "all resources, but not subresources"
+					matchResource = subresource == ""
+				} else if tokens[0] == gvr.Resource {
+					matchResource = subresource == ""
+				}
+			} else if len(tokens) == 2 {
+				if resource == "/*" {
+					// `/*` means "all resources, and their subresources"
+					matchResource = true
+				} else if tokens[0] == gvr.Resource {
+					if tokens[1] == "" || tokens[1] == gvr.Resource {
+						matchResource = true
+					}
+				} else if tokens[0] == "" {
+					if tokens[1] == subresource {
+						matchResource = true
+					}
+				}
+			}
+		}
+		if !matchResource {
+			continue
+		}
+
+		return true, nil
+	}
+
+	return false, nil
+}
+
+// admissionRequest holds the data for an admission webhook call.
+type admissionRequest struct {
+	req *admissionv1.AdmissionReview
+}
+
+// newAdmissionRequest constructs an admissionRequest object.
+func newAdmissionRequest(obj *unstructured.Unstructured, op admissionv1.Operation, gvr schema.GroupVersionResource) *admissionRequest {
+	gvk := obj.GroupVersionKind()
+
+	req := &admissionv1.AdmissionReview{}
+	req.APIVersion = "admission.k8s.io/v1"
+	req.Kind = "AdmissionReview"
+	req.Request = &admissionv1.AdmissionRequest{}
+	req.Request.Kind = metav1.GroupVersionKind{
+		Group:   gvk.Group,
+		Version: gvk.Version,
+		Kind:    gvk.Kind,
+	}
+	req.Request.Resource = metav1.GroupVersionResource{
+		Group:    gvk.Group,
+		Version:  gvk.Version,
+		Resource: gvr.Resource,
+	}
+	req.Request.Name = obj.GetName()
+	req.Request.Namespace = obj.GetNamespace()
+	req.Request.Operation = op
+	req.Request.Object = runtime.RawExtension{Object: obj}
+
+	r := &admissionRequest{req: req}
+
+	return r
+}
+
+func (r *admissionRequest) requestJSON() ([]byte, error) {
+	body, err := json.Marshal(r.req)
+	if err != nil {
+		return nil, fmt.Errorf("building webhook request: %w", err)
+	}
+	return body, nil
+}
+
+// invoke makes the webhook request to a specific webhook.
+func (c *mutatingWebhook) invoke(ctx context.Context, req *admissionRequest, u *unstructured.Unstructured) (*unstructured.Unstructured, error) {
+	clientConfig := c.webhook.ClientConfig
+
+	tlsConfig := &tls.Config{}
+	if len(clientConfig.CABundle) != 0 {
+		caBundle := x509.NewCertPool()
+		if ok := caBundle.AppendCertsFromPEM(clientConfig.CABundle); !ok {
+			return nil, fmt.Errorf("no CA certificates found in caBundle")
+		}
+		tlsConfig.RootCAs = caBundle
+	}
+
+	url := ""
+	if clientConfig.URL != nil {
+		url = *clientConfig.URL
+	}
+	if clientConfig.Service != nil {
+		return nil, fmt.Errorf("webhook clientConfig.Service not implemented")
+	}
+	if url == "" {
+		return nil, fmt.Errorf("cannot determine URL for webhook")
+	}
+
+	client := http.Client{
+		Transport: &http.Transport{
+			TLSClientConfig: tlsConfig,
+		},
+	}
+	httpRequestBody, err := req.requestJSON()
+	if err != nil {
+		return nil, fmt.Errorf("building webhook request: %w", err)
+	}
+	klog.Infof("sending webhook request: %v", string(httpRequestBody))
+
+	httpRequest, err := http.NewRequestWithContext(ctx, "POST", url, bytes.NewReader(httpRequestBody))
+	if err != nil {
+		return nil, fmt.Errorf("building http request: %w", err)
+	}
+	httpRequest.Header.Set("Content-Type", "application/json")
+	httpRequest.Header.Set("Accept", "application/json")
+
+	httpResponse, err := client.Do(httpRequest)
+	if err != nil {
+		return nil, fmt.Errorf("calling webhook: %w", err)
+	}
+	defer httpResponse.Body.Close()
+
+	if httpResponse.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("webhook returned unexpected status %q", httpResponse.Status)
+	}
+
+	httpResponseBody, err := io.ReadAll(httpResponse.Body)
+	if err != nil {
+		return nil, fmt.Errorf("reading webhook response body: %w", err)
+	}
+
+	admissionResponse := admissionv1.AdmissionReview{}
+	if err := json.Unmarshal(httpResponseBody, &admissionResponse); err != nil {
+		return nil, fmt.Errorf("parsing webhook response: %w", err)
+	}
+	if admissionResponse.Response == nil {
+		return nil, fmt.Errorf("webhook response is nil")
+	}
+	klog.Infof("admission response: %v", string(httpResponseBody))
+	if !admissionResponse.Response.Allowed {
+		return nil, fmt.Errorf("webhook blocked request")
+	}
+
+	if admissionResponse.Response.Patch != nil {
+		if admissionResponse.Response.PatchType == nil || *admissionResponse.Response.PatchType != admissionv1.PatchTypeJSONPatch {
+			return nil, fmt.Errorf("unhandled webhook patchType %q", *admissionResponse.Response.PatchType)
+		}
+		patch, err := jsonpatch.DecodePatch(admissionResponse.Response.Patch)
+		if err != nil {
+			return nil, fmt.Errorf("decoding webhook patch: %w", err)
+		}
+		beforePatch, err := json.Marshal(u)
+		if err != nil {
+			return nil, fmt.Errorf("building json for object: %w", err)
+		}
+		afterPatch, err := patch.Apply(beforePatch)
+		if err != nil {
+			return nil, fmt.Errorf("applying webhook patch: %w", err)
+		}
+
+		u2 := &unstructured.Unstructured{}
+		if err := json.Unmarshal(afterPatch, u2); err != nil {
+			return nil, fmt.Errorf("unmarshalling patched object: %w", err)
+		}
+		klog.Infof("after patch: %v", u2)
+		return u2, nil
+	}
+	return nil, nil
+}