Implement forwarding to instances for events

Implement forward to instance for Event messages.

client.js

@@ -297,6 +297,20 @@ class InstanceConnection extends link.Link {
 		link.attachAllMessages(this);
 	}
 
+	async forwardEventToInstance(message, event) {
+		let instanceId = message.data.instance_id;
+		if (!this.slave.instanceInfos.has(instanceId)) {
+			// Instance is probably on another slave
+			await this.slave.forwardEventToMaster(message, event);
+			return;
+		}
+
+		let instanceConnection = this.slave.instanceConnections.get(instanceId);
+		if (!instanceConnection) { return; }
+
+		event.send(instanceConnection, message.data);
+	}
+
 	async forwardEventToMaster(message, event) {
 		event.send(this.slave, message.data);
 	}
@@ -388,6 +402,16 @@ class Slave extends link.Link {
 		return await request.send(instanceConnection, message.data);
 	}
 
+	async forwardEventToInstance(message, event) {
+		let instanceId = message.data.instance_id;
+		if (!this.instanceInfos.has(instanceId)) { return; }
+
+		let instanceConnection = this.instanceConnections.get(instanceId);
+		if (!instanceConnection) { return; }
+
+		event.send(instanceConnection, message.data);
+	}
+
 	async broadcastEventToInstance(message, event) {
 		for (let instanceConnection of this.instanceConnections.values()) {
 			event.send(instanceConnection, message.data);

lib/link/messages.js

@@ -311,8 +311,9 @@ class Event {
 	 *     Links this event is valid on.  Takes an array of strings
 	 *     containing "<source>-<target>" specifications.
 	 * @param {?string} forwardTo -
-	 *     Optional target to forward this request to.  Only 'master' is
-	 *     currently supported.
+	 *     Optional target to forward this request to.  Supported values are
+	 *     'master' and 'instance'.  If set to 'instance' an instance_id
+	 *     property is implicity added to eventProperties.
 	 * @param {?string} broadcastTo -
 	 *     Optional target to broadcast this event to.  Only 'instance' is
 	 *     currently supported.  An event will only be broadcast towards
@@ -329,7 +330,12 @@ class Event {
 		this.forwardTo = forwardTo;
 		this.broadcastTo = broadcastTo;
 
-		if (forwardTo !== 'master' && forwardTo !== null) {
+		if (forwardTo === 'instance') {
+			eventProperties = Object.assign(
+				{"instance_id": { type: "integer" }}, eventProperties
+			);
+
+		} else if (forwardTo !== 'master' && forwardTo !== null) {
 			throw new Error(`Invalid forwardTo value ${forwardTo}`);
 		}
 
@@ -358,10 +364,11 @@ class Event {
 	 * for the event.
 	 *
 	 * If forwardTo was set to 'master' the `forwardEventToMaster` method on
-	 * the link is used as the default handler.
+	 * the link is used as the default handler.  If it was set to 'instance'
+	 * the `forwardEventToInstance` method on the link is used by default.
 	 *
 	 * If broadcastTo was set to 'instance' the `broadcastEventToInstance`
-	 * method on the link is invoked before the handler.  BUT HOW?
+	 * method on the link is invoked before the handler.
 	 *
 	 * Does nothing if the link is not a target for this event.
 	 *
@@ -376,7 +383,9 @@ class Event {
 		if (this.links.includes(`${link.target}-${link.source}`)) {
 			// Use forwarder if handler is not present.
 			if (!handler) {
-				if (this.forwardTo === 'master') {
+				if (this.forwardTo === 'instance') {
+					handler = link.forwardEventToInstance;
+				} else if (this.forwardTo === 'master') {
 					handler = link.forwardEventToMaster;
 				}
 			}

master.js

@@ -268,6 +268,16 @@ class BaseConnection extends link.Link {
 		return await request.send(connection, message.data);
 	}
 
+	async forwardEventToInstance(message, event) {
+		let instance = db.instance.get(message.data.instance_id);
+		if (!instance) { return; }
+
+		let connection = slaveConnection.get(instance.slaveId);
+		if (!connection) { return; }
+
+		event.send(connection, message.data);
+	}
+
 	async broadcastEventToInstance(message, event) {
 		for (let slaveConnection of slaveConnections.values()) {
 			if (slaveConnection === this) {