khatru: add and remove listener hooks.

khatru/listener.go

@@ -100,10 +100,14 @@ func (d *dispatcher) addSubscription(sub subscription) int {
 	return ssid
 }
 
-func (d *dispatcher) removeSubscription(ssid int) {
+func (d *dispatcher) removeSubscription(ssid int) nostr.Filter {
+	var filter nostr.Filter
+
 	d.subscriptions.Compute(ssid, func(sub subscription, loaded bool) (subscription, bool) {
 		indexed := false
 
+		filter = sub.filter
+
 		if sub.filter.Authors != nil {
 			indexed = true
 			for _, author := range sub.filter.Authors {
@@ -150,6 +154,8 @@ func (d *dispatcher) removeSubscription(ssid int) {
 
 		return sub, true
 	})
+
+	return filter
 }
 
 func (d *dispatcher) candidates(event nostr.Event) iter.Seq[subscription] {
@@ -305,6 +311,10 @@ func (rl *Relay) addListener(
 			cancel: cancel,
 			sid:    id,
 		})
+
+		if rl.OnListenerAdded != nil {
+			rl.OnListenerAdded(ws, ssid, id, filter)
+		}
 	}
 }
 
@@ -319,7 +329,12 @@ func (rl *Relay) removeListenerId(ws *WebSocket, id string) {
 		for _, spec := range specs {
 			if spec.sid == id {
 				spec.cancel(ErrSubscriptionClosedByClient)
-				rl.dispatcher.removeSubscription(spec.ssid)
+				filter := rl.dispatcher.removeSubscription(spec.ssid)
+
+				if rl.OnListenerRemoved != nil {
+					rl.OnListenerRemoved(ws, spec.ssid, id, filter)
+				}
+
 				continue
 			}
 			kept = append(kept, spec)

khatru/relay.go

@@ -84,6 +84,8 @@ type Relay struct {
 	RejectConnection          func(r *http.Request) bool
 	OnConnect                 func(ctx context.Context)
 	OnDisconnect              func(ctx context.Context)
+	OnListenerAdded           func(ws *WebSocket, ssid int, id string, filter nostr.Filter)
+	OnListenerRemoved         func(ws *WebSocket, ssid int, id string, filter nostr.Filter)
 	OverwriteRelayInformation func(ctx context.Context, r *http.Request, info nip11.RelayInformationDocument) nip11.RelayInformationDocument
 	PreventBroadcast          func(ws *WebSocket, filter nostr.Filter, event nostr.Event) bool