fix(MQTT Node): Close connection if connection attempt fails (#10873)

packages/nodes-base/nodes/MQTT/GenericFunctions.ts

@@ -1,5 +1,6 @@
 import { connect, type IClientOptions, type MqttClient } from 'mqtt';
 import { ApplicationError, randomString } from 'n8n-workflow';
+
 import { formatPrivateKey } from '@utils/utilities';
 
 interface BaseMqttCredential {
@@ -62,6 +63,10 @@ export const createClient = async (credentials: MqttCredential): Promise<MqttCli
 		const onError = (error: Error) => {
 			client.removeListener('connect', onConnect);
 			client.removeListener('error', onError);
+			// mqtt client has an automatic reconnect mechanism that will
+			// keep trying to reconnect until it succeeds unless we
+			// explicitly close the client
+			client.end();
 			reject(new ApplicationError(error.message));
 		};
 

packages/nodes-base/nodes/MQTT/Mqtt.node.ts

@@ -8,6 +8,7 @@ import {
 	type INodeType,
 	type INodeTypeDescription,
 	NodeConnectionType,
+	ensureError,
 } from 'n8n-workflow';
 
 import { createClient, type MqttCredential } from './GenericFunctions';
@@ -116,10 +117,12 @@ export class Mqtt implements INodeType {
 				try {
 					const client = await createClient(credentials);
 					client.end();
-				} catch (error) {
+				} catch (e) {
+					const error = ensureError(e);
+
 					return {
 						status: 'Error',
-						message: (error as Error).message,
+						message: error.message,
 					};
 				}
 				return {

packages/nodes-base/nodes/MQTT/test/GenericFunctions.test.ts

@@ -1,19 +1,20 @@
-import { MqttClient } from 'mqtt';
 import { mock } from 'jest-mock-extended';
+import { MqttClient } from 'mqtt';
+import { ApplicationError } from 'n8n-workflow';
 
 import { createClient, type MqttCredential } from '../GenericFunctions';
 
 describe('createClient', () => {
-	const mockConnect = jest.spyOn(MqttClient.prototype, 'connect').mockImplementation(function (
-		this: MqttClient,
-	) {
-		setImmediate(() => this.emit('connect', mock()));
-		return this;
-	});
-
 	beforeEach(() => jest.clearAllMocks());
 
 	it('should create a client with minimal credentials', async () => {
+		const mockConnect = jest.spyOn(MqttClient.prototype, 'connect').mockImplementation(function (
+			this: MqttClient,
+		) {
+			setImmediate(() => this.emit('connect', mock()));
+			return this;
+		});
+
 		const credentials = mock<MqttCredential>({
 			protocol: 'mqtt',
 			host: 'localhost',
@@ -35,4 +36,31 @@ describe('createClient', () => {
 			clientId: 'testClient',
 		});
 	});
+
+	it('should reject with ApplicationError on connection error and close connection', async () => {
+		const mockConnect = jest.spyOn(MqttClient.prototype, 'connect').mockImplementation(function (
+			this: MqttClient,
+		) {
+			setImmediate(() => this.emit('error', new Error('Connection failed')));
+			return this;
+		});
+		const mockEnd = jest.spyOn(MqttClient.prototype, 'end').mockImplementation();
+
+		const credentials: MqttCredential = {
+			protocol: 'mqtt',
+			host: 'localhost',
+			port: 1883,
+			clean: true,
+			clientId: 'testClientId',
+			username: 'testUser',
+			password: 'testPass',
+			ssl: false,
+		};
+
+		const clientPromise = createClient(credentials);
+
+		await expect(clientPromise).rejects.toThrow(ApplicationError);
+		expect(mockConnect).toBeCalledTimes(1);
+		expect(mockEnd).toBeCalledTimes(1);
+	});
 });