Add request.body in CEL notification filtering

This moves the JSON body to request.body from request to allow for
future expansion with the headers.

Add documentation for the CEL functionality to the receivers doc.

Signed-off-by: Kevin McDermott <bigkevmcd@gmail.com>

docs/spec/v1/receivers.md

@@ -700,6 +700,117 @@ resources:
 **Note:** Cross-namespace references [can be disabled for security
 reasons](#disabling-cross-namespace-selectors).
 
+#### Filtering reconciled objects with CEL
+
+To filter the resources that are reconciled you can use [Common Expression Language (CEL)](https://cel.dev/).
+
+For example to trigger `ImageRepositories` on notifications from [Google Artifact Regisry](https://cloud.google.com/artifact-registry/docs/configure-notifications#examples) you can define a receiver.
+
+```yaml
+apiVersion: notification.toolkit.fluxcd.io/v1
+kind: Receiver
+metadata:
+  name: gar-receiver
+  namespace: apps
+spec:
+  type: gcr
+  secretRef:
+    name: flux-gar-token
+  resources:
+    - apiVersion: image.toolkit.fluxcd.io/v1beta2
+      kind: ImageRepository
+      name: "*"
+      matchLabels:
+        registry: gar
+```
+
+This will trigger the reconciliation of all `ImageRepositories` with matching labels `registry: gar`, but if you want to only notify `ImageRepository` resources that are referenced from the incoming hook you can use CEL to filter the resources.
+
+```yaml
+apiVersion: notification.toolkit.fluxcd.io/v1
+kind: Receiver
+metadata:
+  name: gar-receiver
+  namespace: apps
+spec:
+  type: gcr
+  secretRef:
+    name: flux-gar-token
+  resources:
+    - apiVersion: image.toolkit.fluxcd.io/v1beta2
+      kind: ImageRepository
+      name: "*"
+      matchLabels:
+        registry: gar
+  resourceFilter: 'request.body.tag.contains(resource.metadata.name)'
+```
+
+If the body of the incoming hook looks like this:
+
+```json
+{
+  "action":"INSERT",
+  "digest":"us-east1-docker.pkg.dev/my-project/my-repo/hello-world@sha256:6ec128e26cd5...",
+  "tag":"us-east1-docker.pkg.dev/my-project/my-repo/hello-world:1.1"
+}
+```
+
+This simple example would match `ImageRepositories` with the name `hello-world`.
+
+If you want do do more complex processing:
+
+```yaml
+  resourceFilter: has(resource.metadata.annotations) && request.body.tag.split('/').last().split(":").first() == resource.metadata.annotations['update-image']
+```
+
+This would look for an annotation "update-image" on the resource, and match it to the `hello-world` part of the tag name.
+
+**NOTE**: Currently the `resource` value in the CEL expression only provides the object metadata, this means you can access things like `resource.metadata.labels` and `resource.metadata.annotations`.
+
+There are a number of functions available to the CEL expressions beyond the basic CEL functionality.
+
+The [Strings extension](https://github.com/google/cel-go/tree/master/ext#strings) is available.
+
+In addition the notifications-controller CEL implementation provides the following functions:
+
+#### first
+
+Returns the first element of a CEL array expression.
+
+```
+<list<any>>.first() -> <any>
+```
+
+This is syntactic sugar for `['hello', 'mellow'][0]`
+
+Examples:
+
+```
+['hello', 'mellow'].first() // returns 'hello'
+[].first() // returns nil
+'this/test'.split('/').first() // returns 'this'
+```
+
+#### last
+
+Returns the last element of a CEL array expression.
+
+```
+<list<any>>.last() -> <any>
+```
+
+Examples:
+
+```
+['hello', 'mellow'].last() // returns 'mellow'
+[].last() // returns nil
+'this/test'.split('/').last() // returns 'test'
+```
+
+This is syntactic sugar for `['hello', 'mellow'][size(['hello, 'mellow'])-1]`
+
+For zero-length array values, these will both return `nil`.
+
 ### Secret reference
 
 `.spec.secretRef.name` is a required field to specify a name reference to a

internal/server/cel.go

@@ -53,7 +53,9 @@ func newCELEvaluator(expr string, req *http.Request) (resourcePredicate, error)
 
 		out, _, err := prg.Eval(map[string]any{
 			"resource": data,
-			"request":  body,
+			"request": map[string]any{
+				"body": body,
+			},
 		})
 		if err != nil {
 			return nil, fmt.Errorf("expression %v failed to evaluate: %w", expr, err)
@@ -74,7 +76,6 @@ func makeCELEnv() (*cel.Env, error) {
 	mapStrDyn := decls.NewMapType(decls.String, decls.Dyn)
 	return cel.NewEnv(
 		celext.Strings(),
-		celext.Encoders(),
 		notifications(),
 		cel.Declarations(
 			decls.NewVar("resource", mapStrDyn),

internal/server/receiver_handler_test.go

@@ -789,7 +789,7 @@ func Test_handlePayload(t *testing.T) {
 							},
 						},
 					},
-					ResourceFilter: `has(resource.metadata.annotations) && request.tag.split('/').last().split(":").first() == resource.metadata.annotations['update-image']`,
+					ResourceFilter: `has(resource.metadata.annotations) && request.body.tag.split('/').last().split(":").first() == resource.metadata.annotations['update-image']`,
 				},
 				Status: apiv1.ReceiverStatus{
 					WebhookPath: apiv1.ReceiverWebhookPath,
@@ -878,7 +878,7 @@ func Test_handlePayload(t *testing.T) {
 							Name:       "test-resource",
 						},
 					},
-					ResourceFilter: `has(resource.metadata.annotations) && request.tag.split('/').last().split(":").first() == resource.metadata.annotations['update-image']`,
+					ResourceFilter: `has(resource.metadata.annotations) && request.body.tag.split('/').last().split(":").first() == resource.metadata.annotations['update-image']`,
 				},
 				Status: apiv1.ReceiverStatus{
 					WebhookPath: apiv1.ReceiverWebhookPath,