internal/event: fix log processor race (#5401)

The cloud events formatter Process function would call
the signer without protecting it, which was racy with the Rotate
function.

internal/event/cloudevents_formatter_node.go

@@ -113,6 +113,15 @@ func (f *cloudEventsFormatterFilter) Rotate(w wrapping.Wrapper, _ ...Option) err
 	return nil
 }
 
+func (f *cloudEventsFormatterFilter) Process(ctx context.Context, e *eventlogger.Event) (*eventlogger.Event, error) {
+	// The embedded FormatterFilter's Process function calls the signer, but doesn't know
+	// about the lock, leading to a potential race condition. We take the lock here to ensure
+	// that the signer is only accessed by one goroutine at a time.
+	f.l.RLock()
+	defer f.l.RUnlock()
+	return f.FormatterFilter.Process(ctx, e)
+}
+
 func newPredicate(allow, deny []*filter) func(ctx context.Context, ce any) (bool, error) {
 	return func(ctx context.Context, ce any) (bool, error) {
 		if len(allow) == 0 && len(deny) == 0 {

internal/event/cloudevents_formatter_node_test.go

@@ -8,6 +8,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"net/url"
+	"sync"
 	"testing"
 	"time"
 
@@ -395,3 +396,36 @@ func Test_cloudEventsFormatter_Rotate(t *testing.T) {
 		})
 	}
 }
+
+func Test_cloudEventsFormatter_Race(t *testing.T) {
+	testUrl, err := url.Parse("https://[::1]")
+	require.NoError(t, err)
+
+	testNode, err := newCloudEventsFormatterFilter(testUrl, cloudevents.FormatJSON, WithSchema(testUrl))
+	require.NoError(t, err)
+
+	start := make(chan struct{})
+	wg := new(sync.WaitGroup)
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		<-start
+		for i := 0; i < 10; i++ {
+			_ = testNode.Rotate(testWrapper(t))
+		}
+	}()
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		<-start
+		for i := 0; i < 10; i++ {
+			_, _ = testNode.Process(context.Background(), &eventlogger.Event{
+				Type:      "test",
+				CreatedAt: time.Now(),
+				Payload:   "test-data",
+			})
+		}
+	}()
+	close(start)
+	wg.Wait()
+}