refactor(MQTT Node): Refactor, fix duplicate triggers, and add Unit tests (#9847)

Co-authored-by: Elias Meire <elias@meire.dev>

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

@@ -0,0 +1,53 @@
+import { connectAsync, type IClientOptions, type MqttClient } from 'mqtt';
+import { randomString } from 'n8n-workflow';
+import { formatPrivateKey } from '@utils/utilities';
+
+interface BaseMqttCredential {
+	protocol: 'mqtt' | 'mqtts' | 'ws';
+	host: string;
+	port: number;
+	username: string;
+	password: string;
+	clean: boolean;
+	clientId: string;
+	passwordless?: boolean;
+}
+
+type NonSslMqttCredential = BaseMqttCredential & {
+	ssl: false;
+};
+
+type SslMqttCredential = BaseMqttCredential & {
+	ssl: true;
+	ca: string;
+	cert: string;
+	key: string;
+	rejectUnauthorized?: boolean;
+};
+export type MqttCredential = NonSslMqttCredential | SslMqttCredential;
+
+export const createClient = async (credentials: MqttCredential): Promise<MqttClient> => {
+	const { protocol, host, port, clean, clientId, username, password } = credentials;
+
+	const clientOptions: IClientOptions = {
+		protocol,
+		host,
+		port,
+		clean,
+		clientId: clientId || `mqttjs_${randomString(8).toLowerCase()}`,
+	};
+
+	if (username && password) {
+		clientOptions.username = username;
+		clientOptions.password = password;
+	}
+
+	if (credentials.ssl) {
+		clientOptions.ca = formatPrivateKey(credentials.ca);
+		clientOptions.cert = formatPrivateKey(credentials.cert);
+		clientOptions.key = formatPrivateKey(credentials.key);
+		clientOptions.rejectUnauthorized = credentials.rejectUnauthorized;
+	}
+
+	return await connectAsync(clientOptions);
+};