.PreventBroadcast slice of functions for controlling what events get broadcasted and to whom.

addresses https://t.me/nip29_temp/303

handlers.go

@@ -205,7 +205,7 @@ func (rl *Relay) HandleWebsocket(w http.ResponseWriter, r *http.Request) {
 							ovw(ctx, &env.Event)
 						}
 						if !skipBroadcast {
-							srl.notifyListeners(&env.Event)
+							srl.notifyListeners(&env.Event, nil)
 						}
 					} else {
 						reason = writeErr.Error()

listener.go

@@ -86,6 +86,11 @@ func (rl *Relay) removeListenerId(ws *WebSocket, id string) {
 func (rl *Relay) notifyListeners(event *nostr.Event) {
 	for _, listener := range rl.listeners {
 		if listener.filter.Matches(event) {
+			for _, pb := range rl.PreventBroadcast {
+				if pb(listener.ws, event) {
+					return
+				}
+			}
 			listener.ws.WriteJSON(nostr.EventEnvelope{SubscriptionID: &listener.subscriptionId, Event: *event})
 		}
 	}

relay.go

@@ -64,6 +64,7 @@ type Relay struct {
 	OnDisconnect              []func(ctx context.Context)
 	OverwriteRelayInformation []func(ctx context.Context, r *http.Request, info nip11.RelayInformationDocument) nip11.RelayInformationDocument
 	OverwriteResponseEvent    []func(ctx context.Context, event *nostr.Event)
+	PreventBroadcast          []func(ws *WebSocket, event *nostr.Event) bool
 
 	// these are used when this relays acts as a router
 	routes                []Route