channelnotifier: add InactiveLinkEvent

This commit adds a new event `InactiveLinkEvent` to be used when a link
becomes inactive.

channelnotifier/channelnotifier.go

@@ -47,6 +47,13 @@ type ActiveLinkEvent struct {
 	ChannelPoint *wire.OutPoint
 }
 
+// InactiveLinkEvent represents a new event where the link becomes inactive in
+// the switch.
+type InactiveLinkEvent struct {
+	// ChannelPoint is the channel point for the inactive channel.
+	ChannelPoint *wire.OutPoint
+}
+
 // ActiveChannelEvent represents a new event where a channel becomes active.
 type ActiveChannelEvent struct {
 	// ChannelPoint is the channelpoint for the newly active channel.
@@ -193,6 +200,15 @@ func (c *ChannelNotifier) NotifyActiveChannelEvent(chanPoint wire.OutPoint) {
 	}
 }
 
+// NotifyInactiveLinkEvent notifies the channelEventNotifier goroutine that a
+// link has been removed from the switch.
+func (c *ChannelNotifier) NotifyInactiveLinkEvent(chanPoint wire.OutPoint) {
+	event := InactiveLinkEvent{ChannelPoint: &chanPoint}
+	if err := c.ntfnServer.SendUpdate(event); err != nil {
+		log.Warnf("Unable to send inactive link update: %v", err)
+	}
+}
+
 // NotifyInactiveChannelEvent notifies the channelEventNotifier goroutine that a
 // channel is inactive.
 func (c *ChannelNotifier) NotifyInactiveChannelEvent(chanPoint wire.OutPoint) {

rpcserver.go

@@ -4624,9 +4624,12 @@ func (r *rpcServer) SubscribeChannelEvents(req *lnrpc.ChannelEventSubscription,
 					},
 				}
 
-			// Completely ignore ActiveLinkEvent as this is explicitly not
+			// Completely ignore ActiveLinkEvent and
-			// exposed to the RPC.
+			// InactiveLinkEvent as this is explicitly not exposed
-			case channelnotifier.ActiveLinkEvent:
+			// to the RPC.
+			case channelnotifier.ActiveLinkEvent,
+				channelnotifier.InactiveLinkEvent:
+
 				continue
 
 			case channelnotifier.FullyResolvedChannelEvent:
@@ -7323,6 +7326,8 @@ func (r *rpcServer) SubscribeChannelBackups(req *lnrpc.ChannelBackupSubscription
 				continue
 			case channelnotifier.ActiveLinkEvent:
 				continue
+			case channelnotifier.InactiveLinkEvent:
+				continue
 			}
 
 			// Now that we know the channel state has changed,