avahi: Control with HOST_DISCOVERABILITY

The host config variable HOST_DISCOVERABILITY can be set to
true or false, controlling the state of the avahi service. This
determines if the device advertises it's presence over mDNS.

Change-type: patch
Signed-off-by: Cameron Diver <cameron@balena.io>
Signed-off-by: Rich Bayliss <rich@balena.io>

src/config/schema-type.ts

@@ -170,6 +170,10 @@ export const schemaTypes = {
 		type: t.string,
 		default: NullOrUndefined,
 	},
+	hostDiscoverability: {
+		type: PermissiveBoolean,
+		default: true,
+	},
 
 	// Function schema types
 	// The type should be the value that the promise resolves

src/config/schema.ts

@@ -190,6 +190,11 @@ export const schema = {
 		mutable: true,
 		removeIfNull: false,
 	},
+	hostDiscoverability: {
+		source: 'db',
+		mutable: true,
+		removeIfNull: false,
+	},
 };
 
 export type Schema = typeof schema;

src/device-config.ts

@@ -127,6 +127,11 @@ export class DeviceConfig {
 			varType: 'string',
 			defaultValue: 'off',
 		},
+		hostDiscoverability: {
+			envVarName: 'HOST_DISCOVERABILITY',
+			varType: 'bool',
+			defaultValue: 'true',
+		},
 	};
 
 	public static validKeys = [

src/lib/avahi.ts

@@ -0,0 +1,32 @@
+import * as config from '../config';
+import * as dbus from './dbus';
+
+import log from './supervisor-console';
+
+export const initialized = (async () => {
+	await config.initialized;
+
+	config.on('change', (conf) => {
+		if (conf.hostDiscoverability != null) {
+			switchDiscoverability(conf.hostDiscoverability);
+		}
+	});
+
+	await switchDiscoverability(await config.get('hostDiscoverability'));
+})();
+
+async function switchDiscoverability(discoverable: boolean) {
+	try {
+		if (discoverable) {
+			log.info('Setting host to discoverable');
+			await dbus.startService('avahi-daemon');
+			await dbus.startSocket('avahi-daemon');
+		} else {
+			log.info('Setting host to undiscoverable');
+			await dbus.stopService('avahi-daemon');
+			await dbus.stopSocket('avahi-daemon');
+		}
+	} catch (e) {
+		log.error('There was an error switching host discoverability:', e);
+	}
+}

src/lib/dbus.ts

@@ -35,6 +35,15 @@ export async function getLoginManagerInterface() {
 	}
 }
 
+async function startUnit(unitName: string) {
+	const systemd = await getSystemdInterface();
+	try {
+		systemd.StartUnit(unitName, 'fail');
+	} catch (e) {
+		throw new DbusError(e);
+	}
+}
+
 export async function restartService(serviceName: string) {
 	const systemd = await getSystemdInterface();
 	try {
@@ -45,21 +54,28 @@ export async function restartService(serviceName: string) {
 }
 
 export async function startService(serviceName: string) {
+	return startUnit(`${serviceName}.service`);
+}
+
+export async function startSocket(socketName: string) {
+	return startUnit(`${socketName}.socket`);
+}
+
+async function stopUnit(unitName: string) {
 	const systemd = await getSystemdInterface();
 	try {
-		systemd.StartUnit(`${serviceName}.service`, 'fail');
+		systemd.StopUnit(unitName, 'fail');
 	} catch (e) {
 		throw new DbusError(e);
 	}
 }
 
 export async function stopService(serviceName: string) {
-	const systemd = await getSystemdInterface();
-	try {
-		systemd.StopUnit(`${serviceName}.service`, 'fail');
-	} catch (e) {
-		throw new DbusError(e);
-	}
+	return stopUnit(`${serviceName}.service`);
+}
+
+export async function stopSocket(socketName: string) {
+	return stopUnit(`${socketName}.socket`);
 }
 
 export async function enableService(serviceName: string) {

src/supervisor.ts

@@ -12,6 +12,7 @@ import SupervisorAPI from './supervisor-api';
 import log from './lib/supervisor-console';
 import version = require('./lib/supervisor-version');
 
+import * as avahi from './lib/avahi';
 import * as firewall from './lib/firewall';
 
 const startupConfigFields: config.ConfigKey[] = [
@@ -61,6 +62,7 @@ export class Supervisor {
 		await db.initialized;
 		await config.initialized;
 		await eventTracker.initialized;
+		await avahi.initialized;
 		log.debug('Starting logging infrastructure');
 		await logger.initialized;
 

test/05-device-state.spec.ts

@@ -42,6 +42,7 @@ const testTarget1 = {
 		config: {
 			HOST_CONFIG_gpu_mem: '256',
 			HOST_FIREWALL_MODE: 'off',
+			HOST_DISCOVERABILITY: 'true',
 			SUPERVISOR_CONNECTIVITY_CHECK: 'true',
 			SUPERVISOR_DELTA: 'false',
 			SUPERVISOR_DELTA_APPLY_TIMEOUT: '0',
@@ -129,6 +130,7 @@ const testTargetWithDefaults2 = {
 		config: {
 			HOST_CONFIG_gpu_mem: '512',
 			HOST_FIREWALL_MODE: 'off',
+			HOST_DISCOVERABILITY: 'true',
 			SUPERVISOR_CONNECTIVITY_CHECK: 'true',
 			SUPERVISOR_DELTA: 'false',
 			SUPERVISOR_DELTA_APPLY_TIMEOUT: '0',

test/13-device-config.spec.ts

@@ -192,6 +192,7 @@ describe('Device Backend Config', () => {
 		const conf = deviceConfig.getDefaults();
 		return expect(conf).to.deep.equal({
 			HOST_FIREWALL_MODE: 'off',
+			HOST_DISCOVERABILITY: 'true',
 			SUPERVISOR_VPN_CONTROL: 'true',
 			SUPERVISOR_POLL_INTERVAL: '60000',
 			SUPERVISOR_LOCAL_MODE: 'false',