MQTT trigger script template

/**

 * General Trigger Preprocessor Function

 * 

 * ⚠️ IMPORTANT: This preprocessor function is ALWAYS called FIRST, before the main function.

 * 

 * This example assumes the script was triggered by an MQTT event, but the same 

 * preprocessor can handle other trigger types by checking wm_trigger.kind.

 * 

 * Flow: 

 * 1. Trigger event occurs (MQTT message in this example)

 * 2. Preprocessor function is called FIRST

 * 3. Main function is called with the return values from preprocessor

 * 

 * You can transform the raw trigger data here before it reaches your main function.

 * Common transformations include:

 * - Converting binary payload to string or JSON

 * - Extracting metadata from the trigger source

 * - Filtering messages

 * - Adding timestamps or other context

 * 

 * IMPORTANT: The object you return from this preprocessor determines the parameters passed to your main function:

 * - If you return {a: 1, b: 2}, then main will be called as main(a, b)

 * - If you return {payload}, then main will be called as main(payload)

 * 

 * @param wm_trigger - Information about the trigger source (could be MQTT, HTTP, email, etc.)

 * @param payload - The raw data from the trigger (type depends on the trigger kind)

 * @returns An object with the arguments to pass to the main function

 */

export async function preprocessor(

  wm_trigger: {

    kind: 'http' | 'email' | 'webhook' | 'websocket' | 'kafka' | 'nats' | 'postgres' | 'sqs' | 'mqtt',

    mqtt?: {

      topic: string,

      retain: boolean,

      pkid: number,

      qos: number,

      v5?: {

        payload_format_indicator?: number,

        topic_alias?: number,

        response_topic?: string,

        correlation_data?: Array<number>,

        user_properties?: Array<[string, string]>,

        subscription_identifiers?: Array<number>,

        content_type?: string

      }

    }

  },

  /**

 * Each trigger type has its own specific parameters:

 * - For MQTT: 'payload' (Array of raw message bytes)

 * - For SQS: 'msg' (message data)

 * - Other trigger types have their own specific properties

 */

  payload: Array<number>,

) {

  if (wm_trigger.kind === 'mqtt' && wm_trigger.mqtt) {

    // Convert Array<number> to Uint8Array for binary processing

    const uint8Payload = new Uint8Array(payload);

    // Convert the binary payload to a string

    // This assumes the binary data represents a string (e.g., UTF-8 encoded text)

    const payloadAsString = new TextDecoder().decode(uint8Payload);

    return {

      contentType: wm_trigger.mqtt.v5?.content_type,

      payload: uint8Payload,

      payloadAsString

    }

  }

  else {

    return {

      kind: wm_trigger.kind

    }

  }

}

/**

 * Main Function - Handles Trigger Events

 * 

 * ⚠️ This function is called AFTER the preprocessor function.

 * 

 * This example assumes we're handling an MQTT trigger event where the payload is a string.

 * The main function receives arguments based on what the preprocessor returned.

 * 

 * @param contentType - For MQTT: The content type from MQTT v5 properties if available

 * @param payload - The raw binary payload from MQTT

 * @param payloadAsString - The payload as a string (decoded from binary data)

 */

export async function main(payload: Uint8Array, payloadAsString: string, contentType?: string) {

}