Implement TestMetadata_Subscriptions E2E test (knative#3324)

* Implement TestMetadata_Subscriptions E2E test

This test verifies the full Knative Eventing flow using func subscribe:
- Creates a producer function that sends CloudEvents to the broker
- Creates a subscriber function that receives events via a Trigger
- Validates the complete event delivery pipeline

Fixes knative#3202

* Fix subscribe command verbose flag compatibility

The subscribe command doesn't support the -v (verbose) flag that newCmd()
automatically adds when FUNC_E2E_VERBOSE=true. This causes test failures.

Changed to use exec.Command directly for the subscribe call to bypass
the automatic verbose flag addition while keeping it for other commands.

* Add Knative Eventing availability check to subscription test

Check for broker-ingress service before running the test to gracefully
skip if Knative Eventing is not installed or not ready yet.

* Add broker-ingress service availability check

The test was failing in CI because it tried to send events before
the broker-ingress service was registered in DNS. This adds a retry
loop to wait for the service to be available before proceeding.

Fixes timing issues in fresh cluster environments.

* fix: improve subscription test with webhook callback verification

- Remove unused sendEventToBroker* functions
- Use callback pattern for reliable event verification
- Clean up comments and reduce code size

* refactor: simplify event subscription e2e test by removing custom producer and callback server, and using stern to verify event reception.

Author: Kunal1522

e2e/e2e_metadata_test.go

@@ -4,14 +4,23 @@
 package e2e
 
 import (
+	"bufio"
 	"bytes"
+	"context"
 	"encoding/json"
 	"fmt"
+	"io"
+	"net/http"
 	"os"
+	"os/exec"
 	"path/filepath"
+	"regexp"
+	"strings"
 	"testing"
+	"time"
 
 	fn "knative.dev/func/pkg/functions"
+	fnhttp "knative.dev/func/pkg/http"
 )
 
 // ---------------------------------------------------------------------------
@@ -552,13 +561,217 @@ func Handle(w http.ResponseWriter, _ *http.Request) {
 	}
 }
 
-// TODO: TestMetadata_Subscriptions ensures that function instances can be
-// subscribed to events.
+// Tests the complete event flow using func subscribe
 func TestMetadata_Subscriptions(t *testing.T) {
-	// TODO
-	// Create a function which emits an event with as much defaults as possible
-	// Create a function which subscribes to those events
-	// Succeed the test as soon as it receives the event
-	// https://github.com/knative/func/issues/3202
-	t.Skip("Subscription E2E tests not yet implemented")
+	brokerName := "default"
+
+	createBrokerWithCheck(t, Namespace, brokerName)
+
+	uniqueEventID := fmt.Sprintf("e2e-test-%d", time.Now().UnixNano())
+
+	eventReceived := waitForEvent(t, uniqueEventID)
+
+	subscriber := "func-e2e-test-subscriber"
+	subscriberName := subscriber
+	subscriberRoot := fromCleanEnv(t, subscriberName)
+	if err := newCmd(t, "init", "-l=go", "-t=cloudevents").Run(); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(subscriberRoot, "handle.go"),
+		[]byte(subscriberCode()), 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	subscribeCmd := exec.Command(Bin, "subscribe", "--filter", "type=test.event")
+	subscribeCmd.Stdout, subscribeCmd.Stderr = os.Stdout, os.Stderr
+	if err := subscribeCmd.Run(); err != nil {
+		t.Fatal(err)
+	}
+
+	f, err := fn.NewFunction(subscriberRoot)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(f.Deploy.Subscriptions) != 1 {
+		t.Fatalf("expected 1 subscription, got %d", len(f.Deploy.Subscriptions))
+	}
+
+	if err := newCmd(t, "deploy").Run(); err != nil {
+		t.Fatal(err)
+	}
+	defer clean(t, subscriberName, Namespace)
+
+	subscriberURL := fmt.Sprintf("http://%s.%s.%s", subscriberName, Namespace, Domain)
+	if !waitFor(t, subscriberURL, withTemplate("cloudevents")) {
+		t.Fatal("subscriber not ready")
+	}
+	waitForTrigger(t, Namespace, subscriberName)
+
+	transport := fnhttp.NewRoundTripper()
+	defer transport.Close()
+	client := http.Client{
+		Transport: transport,
+		Timeout:   30 * time.Second,
+	}
+	url := fmt.Sprintf("http://broker-ingress.knative-eventing.svc/%s/%s", Namespace, brokerName)
+	req, _ := http.NewRequestWithContext(t.Context(), "POST", url, strings.NewReader(`{}`))
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("ce-specversion", "1.0")
+	req.Header.Set("ce-type", "test.event")
+	req.Header.Set("ce-source", "producer")
+	req.Header.Set("ce-id", uniqueEventID)
+
+	resp, err := client.Do(req)
+	if err != nil {
+		t.Fatalf("Failed to invoke producer: %v", err)
+	}
+	body, _ := io.ReadAll(resp.Body)
+	resp.Body.Close()
+	if resp.StatusCode != 202 {
+		t.Fatalf("Broker rejected event: code: %d, body: %q", resp.StatusCode, body)
+	}
+	t.Logf("Broker accepted event %s", uniqueEventID)
+
+	select {
+	case receivedID := <-eventReceived:
+		t.Logf("Event flow verified (received: %s)", receivedID)
+	case <-time.After(60 * time.Second):
+		t.Fatal("Timeout: No callback from subscriber")
+	}
+}
+
+func waitForEvent(t *testing.T, eventId string) <-chan string {
+	t.Helper()
+
+	eventReceived := make(chan string, 10)
+
+	ctx, cancel := context.WithCancel(context.Background())
+	t.Cleanup(cancel)
+
+	pr, pw := io.Pipe()
+	cmd := exec.CommandContext(ctx, "stern", "func-e2e-test-subscriber-.*")
+	cmd.Stderr = io.Discard
+	cmd.Stdout = pw
+	cmd.Env = append(os.Environ(), "KUBECONFIG="+Kubeconfig)
+	err := cmd.Start()
+	if err != nil {
+		t.Fatal(err)
+	}
+	go func() {
+		r := bufio.NewReader(pr)
+		m, e := regexp.MatchReader(`EVENT_RECEIVED: id=`+eventId, r)
+		if e != nil {
+			panic(e)
+		}
+		if m {
+			eventReceived <- "OK"
+			close(eventReceived)
+			cancel()
+		}
+		_, _ = io.Copy(io.Discard, r)
+	}()
+
+	return eventReceived
+}
+
+// CloudEvents handler that logs events
+func subscriberCode() string {
+	return `package function
+
+import (
+	"context"
+	"fmt"
+	"github.com/cloudevents/sdk-go/v2/event"
+)
+
+func Handle(ctx context.Context, e event.Event) (*event.Event, error) {
+	fmt.Printf("EVENT_RECEIVED: id=%s type=%s source=%s\n", e.ID(), e.Type(), e.Source())
+	r := event.New()
+	r.SetID("response-" + e.ID())
+	r.SetSource("subscriber")
+	r.SetType("test.response")
+	r.SetData("application/json", map[string]string{"status": "received"})
+	return &r, nil
+}
+`
+}
+
+// createBrokerWithCheck creates a Knative Broker
+func createBrokerWithCheck(t *testing.T, namespace, name string) {
+	t.Helper()
+
+	brokerYAML := fmt.Sprintf(`apiVersion: eventing.knative.dev/v1
+kind: Broker
+metadata:
+  name: %s
+  namespace: %s
+`, name, namespace)
+
+	cmd := exec.Command("kubectl", "apply", "-f", "-")
+	cmd.Stdin = strings.NewReader(brokerYAML)
+	cmd.Env = append(os.Environ(), "KUBECONFIG="+Kubeconfig)
+
+	output, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("Failed to create broker: %v, output: %s", err, string(output))
+	}
+	t.Cleanup(func() {
+		deleteBroker(t, namespace, name)
+	})
+	t.Logf("Created broker %s in namespace %s", name, namespace)
+
+	waitCmd := exec.Command("kubectl", "wait", "--for=condition=Ready",
+		fmt.Sprintf("broker/%s", name), "-n", namespace, "--timeout=60s")
+	waitCmd.Env = append(os.Environ(), "KUBECONFIG="+Kubeconfig)
+	waitOutput, err := waitCmd.CombinedOutput()
+	if err != nil {
+		t.Logf("Broker not ready: %v, output: %s", err, string(waitOutput))
+	}
+	t.Logf("Broker %s is ready", name)
+
+	// Wait for broker-ingress service to be available
+	t.Log("Waiting for broker-ingress service to be available...")
+	for i := 0; i < 30; i++ {
+		checkCmd := exec.Command("kubectl", "get", "svc", "-n", "knative-eventing", "broker-ingress")
+		checkCmd.Env = append(os.Environ(), "KUBECONFIG="+Kubeconfig)
+		if err := checkCmd.Run(); err == nil {
+			t.Log("broker-ingress service is available")
+			return
+		}
+		time.Sleep(2 * time.Second)
+	}
+	t.Fatal("broker-ingress service check timed out")
+}
+
+// deleteBroker removes a Knative Broker from the given namespace.
+func deleteBroker(t *testing.T, namespace, name string) {
+	t.Helper()
+
+	cmd := exec.Command("kubectl", "delete", "broker", name, "-n", namespace, "--ignore-not-found")
+	cmd.Env = append(os.Environ(), "KUBECONFIG="+Kubeconfig)
+
+	output, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Logf("Warning: could not delete broker: %v, output: %s", err, string(output))
+		return
+	}
+	t.Logf("Deleted broker %s from namespace %s", name, namespace)
+}
+
+// waitForTrigger waits for the function's trigger to become ready.
+func waitForTrigger(t *testing.T, namespace, functionName string) {
+	t.Helper()
+
+	triggerName := fmt.Sprintf("%s-function-trigger-0", functionName)
+
+	cmd := exec.Command("kubectl", "wait", "--for=condition=Ready",
+		fmt.Sprintf("trigger/%s", triggerName), "-n", namespace, "--timeout=60s")
+	cmd.Env = append(os.Environ(), "KUBECONFIG="+Kubeconfig)
+
+	output, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Logf("Warning: trigger may not be ready: %v, output: %s", err, string(output))
+	} else {
+		t.Logf("Trigger %s is ready", triggerName)
+	}
 }