Add connection events for control connections

Add hooks for plugins to be able to handle connection state changes for
control connections on the master server and in the web interface.

packages/lib/plugin.js

@@ -329,6 +329,43 @@ class BaseMasterPlugin {
 	 */
 	onSlaveConnectionEvent(connection, event) { }
 
+	/**
+	 * Called when an avent on a control connection happens
+	 *
+	 * The event param may be one of connect, drop, resume and close and has
+	 * the following meaning:
+	 *
+	 * ##### connect
+	 *
+	 * Invoked when a new connection to the control has been established.
+	 *
+	 * ##### drop
+	 *
+	 * Invoked when a connection loss is detected between the master and a
+	 * control.  Plugins should respond to this event by throtteling
+	 * messages it is sending to the given control connection to an absolute
+	 * minimum.
+	 *
+	 * Messages sent over a dropped control connection will get queued up in
+	 * memory on the master and sent all in one go when the connection is
+	 * re-established again.
+	 *
+	 * ##### resume
+	 *
+	 * Invoked when a connection that had previously been dropped is
+	 * re-established.
+	 *
+	 * ##### close
+	 *
+	 * Invoked when the connection to the control has been closed.
+	 *
+	 * @param {module:master/master~ControlConnection} connection -
+	 *     The connection the event occured on.
+	 * @param {string} event - one of connect, drop, resume, and close.
+	 */
+	onControlConnectionEvent(connection, event) { }
+
+
 	/**
 	 * Called when a slave is preparing to disconnect from the master
 	 *
@@ -505,6 +542,42 @@ class BaseWebPlugin {
 	 * Called immediately after the class is instantiated.
 	 */
 	async init() { }
+
+	/**
+	 * Called when an event on the master connection happens
+	 *
+	 * The event param may be one of connect, drop, resume and close and has
+	 * the following meaning:
+	 *
+	 * ##### connect
+	 *
+	 * Invoked when a new connection to the master has been established.
+	 *
+	 * ##### drop
+	 *
+	 * Invoked when a connection loss is detected between the control link
+	 * and the master.  Plugins should respond to this event by throtteling
+	 * messages it is sending to the master to an absolute minimum.
+	 *
+	 * Messages sent over a dropped master connection will get queued up in
+	 * memory in the browser and sent all in one go when the connection is
+	 * re-established again.
+	 *
+	 * ##### resume
+	 *
+	 * Invoked when the connection that had previously dropped is
+	 * re-established.
+	 *
+	 * ##### close
+	 *
+	 * Invoked when the connection to the master has been closed.  This
+	 * typically means the master server has shut down.  Plugins should not
+	 * send any messages that goes to or via the master server after the
+	 * connection has been closed and before a new one is established.
+	 *
+	 * @param {string} event - one of connect, drop, resume and close
+	 */
+	onMasterConnectionEvent(event) { }
 }
 
 /**

packages/master/master.js

@@ -696,6 +696,14 @@ class ControlConnection extends BaseConnection {
 				debugEvents.off("message", this.ws_dumper);
 			}
 		});
+
+		for (let event of ["connect", "drop", "resume", "close"]) {
+			this.connector.on(event, () => {
+				for (let masterPlugin of masterPlugins.values()) {
+					masterPlugin.onControlConnectionEvent(this, event);
+				}
+			});
+		}
 	}
 
 	async getMasterConfigRequestHandler() {

packages/web_ui/src/util/websocket.jsx

@@ -73,6 +73,14 @@ export class Control extends libLink.Link {
 		this.connector.on("close", () => {
 			this.accountName = null;
 		});
+
+		for (let event of ["connect", "drop", "resume", "close"]) {
+			this.connector.on(event, () => {
+				for (let plugin of this.plugins.values()) {
+					plugin.onMasterConnectionEvent(event);
+				}
+			});
+		}
 	}
 
 	async logMessageEventHandler(message) {