Add slave update subscriptions

Allow the web interface to listen for updates to the slave list and
apply it live to the places where slaves are shown in the web interface.

packages/master/src/ControlConnection.js

@@ -39,6 +39,11 @@ class ControlConnection extends BaseConnection {
 		 */
 		this.user = user;
 
+		this.slaveSubscriptions = {
+			all: false,
+			slave_ids: [],
+		};
+
 		this.instanceSubscriptions = {
 			all: false,
 			instance_ids: [],
@@ -107,6 +112,19 @@ class ControlConnection extends BaseConnection {
 		return { list };
 	}
 
+	async setSlaveSubscriptionsRequestHandler(message) {
+		this.slaveSubscriptions = message.data;
+	}
+
+	slaveUpdated(slave, update) {
+		if (
+			this.slaveSubscriptions.all
+			|| this.slaveSubscriptions.slave_ids.includes(slave.id)
+		) {
+			libLink.messages.slaveUpdate.send(this, update);
+		}
+	}
+
 	generateSlaveToken(slaveId) {
 		return jwt.sign({ aud: "slave", slave: slaveId }, this._master.config.get("master.auth_secret"));
 	}