fix: avoid enrChangeCh panic on Stop() timeout and make stopWithTimeout a method

Address review on #1306:
- Only close enrChangeCh once wg.Wait() completes; on timeout leave it open
  to avoid a send-on-closed-channel panic from still-running node goroutines.
- Convert stopWithTimeout to a *WakuNode method using w.log (per review).
- Reword the cancel comment to not reference a non-existent processLoop symbol.

Signed-off-by: kblinichkin <kirill.blinichkin@gmail.com>

waku/v2/node/wakunode2.go

@@ -527,11 +527,11 @@ func (w *WakuNode) Stop() {
 		return
 	}
 
-	// Cancel the node context before stopping protocols: once processLoop sees
-	// ctx.Done() it stops draining its channels, so a later send would block.
+	// Cancel the node context before stopping protocols: node goroutines that
+	// observe ctx.Done() stop draining their channels, so a later send would block.
 	w.cancel()
 
-	stopWithTimeout(w.bcaster.Stop, "bcaster", 5*time.Second, w.log)
+	w.stopWithTimeout(w.bcaster.Stop, "bcaster", 5*time.Second)
 
 	defer w.connectionNotif.Close()
 	defer w.addressChangesSub.Close()
@@ -540,32 +540,35 @@ func (w *WakuNode) Stop() {
 
 	// Each Stop() calls wg.Wait() internally and can block on a goroutine stuck
 	// writing to a dead connection; the timeout keeps Stop() bounded.
-	stopWithTimeout(w.relay.Stop, "relay", 10*time.Second, w.log)
-	stopWithTimeout(w.lightPush.Stop, "lightPush", 5*time.Second, w.log)
-	stopWithTimeout(w.legacyStore.Stop, "legacyStore", 5*time.Second, w.log)
-	stopWithTimeout(w.filterFullNode.Stop, "filterFullNode", 5*time.Second, w.log)
-	stopWithTimeout(w.filterLightNode.Stop, "filterLightNode", 5*time.Second, w.log)
+	w.stopWithTimeout(w.relay.Stop, "relay", 10*time.Second)
+	w.stopWithTimeout(w.lightPush.Stop, "lightPush", 5*time.Second)
+	w.stopWithTimeout(w.legacyStore.Stop, "legacyStore", 5*time.Second)
+	w.stopWithTimeout(w.filterFullNode.Stop, "filterFullNode", 5*time.Second)
+	w.stopWithTimeout(w.filterLightNode.Stop, "filterLightNode", 5*time.Second)
 
 	if w.opts.enableDiscV5 {
-		stopWithTimeout(w.discoveryV5.Stop, "discoveryV5", 5*time.Second, w.log)
+		w.stopWithTimeout(w.discoveryV5.Stop, "discoveryV5", 5*time.Second)
 	}
-	stopWithTimeout(w.peerExchange.Stop, "peerExchange", 5*time.Second, w.log)
-	stopWithTimeout(w.rendezvous.Stop, "rendezvous", 5*time.Second, w.log)
-	stopWithTimeout(w.peerConnector.Stop, "peerConnector", 5*time.Second, w.log)
-	stopWithTimeout(func() { _ = w.stopRlnRelay() }, "rlnRelay", 5*time.Second, w.log)
-	stopWithTimeout(w.timesource.Stop, "timesource", 5*time.Second, w.log)
+	w.stopWithTimeout(w.peerExchange.Stop, "peerExchange", 5*time.Second)
+	w.stopWithTimeout(w.rendezvous.Stop, "rendezvous", 5*time.Second)
+	w.stopWithTimeout(w.peerConnector.Stop, "peerConnector", 5*time.Second)
+	w.stopWithTimeout(func() { _ = w.stopRlnRelay() }, "rlnRelay", 5*time.Second)
+	w.stopWithTimeout(w.timesource.Stop, "timesource", 5*time.Second)
 
 	// Bound the wait: goroutines select on ctx.Done() and should exit promptly.
 	waitDone := make(chan struct{})
 	go func() { w.wg.Wait(); close(waitDone) }()
 	select {
 	case <-waitDone:
+		// All node goroutines have exited, so it is safe to close the channels
+		// they send on.
+		close(w.enrChangeCh)
 	case <-time.After(5 * time.Second):
-		w.log.Error("timed out waiting for node goroutines to stop")
+		// Some goroutines may still be running; leave enrChangeCh open, otherwise
+		// a pending send would panic with "send on closed channel".
+		w.log.Error("timed out waiting for node goroutines to stop; leaving enrChangeCh open")
 	}
 
-	close(w.enrChangeCh)
-
 	// host.Close() can block indefinitely draining dead sockets; bound it too.
 	hostClosed := make(chan struct{})
 	go func() { w.host.Close(); close(hostClosed) }()
@@ -580,13 +583,13 @@ func (w *WakuNode) Stop() {
 
 // stopWithTimeout runs fn and returns once it completes or timeout elapses,
 // logging a warning on timeout so one stuck component cannot hang Stop().
-func stopWithTimeout(fn func(), name string, timeout time.Duration, log *zap.Logger) {
+func (w *WakuNode) stopWithTimeout(fn func(), name string, timeout time.Duration) {
 	done := make(chan struct{})
 	go func() { fn(); close(done) }()
 	select {
 	case <-done:
 	case <-time.After(timeout):
-		log.Warn("timed out stopping component", zap.String("component", name))
+		w.log.Warn("timed out stopping component", zap.String("component", name))
 	}
 }