fix: race condition with host in relay

waku/v2/protocol/relay/waku_relay.go

@@ -51,6 +51,7 @@ type WakuRelay struct {
 
 	minPeersToPublish int
 
+	hostMutex              sync.Mutex
 	topicValidatorMutex    sync.RWMutex
 	topicValidators        map[string][]validatorFn
 	defaultTopicValidators []validatorFn
@@ -103,25 +104,31 @@ func NewWakuRelay(bcaster Broadcaster, minPeersToPublish int, timesource timesou
 }
 
 func (w *WakuRelay) peerScoreInspector(peerScoresSnapshots map[peer.ID]*pubsub.PeerScoreSnapshot) {
-	if w.host == nil {
+	w.hostMutex.Lock()
+	host := w.host
+	w.hostMutex.Unlock()
+
+	if host == nil {
 		return
 	}
 
 	for pid, snap := range peerScoresSnapshots {
 		if snap.Score < w.peerScoreThresholds.GraylistThreshold {
 			// Disconnect bad peers
-			err := w.host.Network().ClosePeer(pid)
+			err := host.Network().ClosePeer(pid)
 			if err != nil {
 				w.log.Error("could not disconnect peer", logging.HostID("peer", pid), zap.Error(err))
 			}
 		}
-		_ = w.host.Peerstore().(wps.WakuPeerstore).SetScore(pid, snap.Score)
+		_ = host.Peerstore().(wps.WakuPeerstore).SetScore(pid, snap.Score)
 	}
 }
 
 // SetHost sets the host to be able to mount or consume a protocol
 func (w *WakuRelay) SetHost(h host.Host) {
+	w.hostMutex.Lock()
 	w.host = h
+	w.hostMutex.Unlock()
 }
 
 // Start initiates the WakuRelay protocol
@@ -155,8 +162,8 @@ func (w *WakuRelay) PubSub() *pubsub.PubSub {
 
 // Topics returns a list of all the pubsub topics currently subscribed to
 func (w *WakuRelay) Topics() []string {
-	defer w.topicsMutex.RUnlock()
 	w.topicsMutex.RLock()
+	defer w.topicsMutex.RUnlock()
 
 	var result []string
 	for topic := range w.topics {