direct-method-mqtt-client

TypeScript/Node.js MQTT client implementation - part of the Direct Method Library.

Installation

npm install direct-method-mqtt-client

Quick Start

import { DirectMethodMqttClient } from 'direct-method-mqtt-client';

const client = new DirectMethodMqttClient('localhost', 1883, 'test/topic');

// Set up message handler
client.onMessageReceived((topic, message) => {
  console.log(`Received: ${message} on topic: ${topic}`);
});

// Connect and start using the client
async function main() {
  try {
    await client.connect();
    await client.subscribe();
    await client.publish('Hello from TypeScript!');
    
    // Keep the application running to receive messages
    // In a real application, you might want to handle this differently
    setTimeout(async () => {
      await client.disconnect();
    }, 5000);
    
  } catch (error) {
    console.error('Error:', error);
  }
}

main();

API Reference

Constructor

new DirectMethodMqttClient(brokerHost, brokerPort?, topic, clientId?)

• brokerHost (string): MQTT broker hostname or IP address
• brokerPort (number, optional): MQTT broker port (default: 1883)
• topic (string): Topic to subscribe and publish to
• clientId (string, optional): Unique client identifier (auto-generated if not provided)

Methods

connect(): Promise<void>

Connect to the MQTT broker.

disconnect(): Promise<void>

Disconnect from the MQTT broker.

publish(message: string): Promise<void>

Publish a message to the configured topic.

subscribe(): Promise<void>

Subscribe to the configured topic.

onMessageReceived(callback: MessageCallback): void

Set a callback function to handle received messages.

• callback: Function that receives (topic: string, message: string) => void

getConnectionStatus(): boolean

Get the current connection status.

getTopic(): string

Get the configured topic.

getBrokerInfo(): { host: string; port: number }

Get the broker connection details.

Error Handling

The client includes comprehensive error handling:

try {
  await client.connect();
  await client.publish('test message');
} catch (error) {
  console.error('MQTT operation failed:', error.message);
}

Common errors:

• Connection failures (broker unreachable, wrong credentials)
• Publish/subscribe failures (not connected, invalid topic)
• Invalid constructor parameters

Advanced Usage

Custom Client ID

const client = new DirectMethodMqttClient(
  'mqtt.example.com', 
  1883, 
  'sensors/temperature',
  'my-unique-client-id'
);

Message Handling with Context

class MqttHandler {
  constructor(private deviceId: string) {}
  
  handleMessage = (topic: string, message: string) => {
    console.log(`Device ${this.deviceId} received: ${message} on ${topic}`);
    // Process message here
  }
}

const handler = new MqttHandler('device-001');
client.onMessageReceived(handler.handleMessage);

Requirements

• Node.js 18.0.0 or higher
• TypeScript 5.0.0 or higher (for development)

License

MIT License - see the LICENSE file for details.

Contributing

This is part of the Direct Method Library demo project. See the main repository for contribution guidelines.