MQTT trigger script template

/**

 * General Trigger Preprocessor

 * 

 * ⚠️ This function runs BEFORE the main function.

 * 

 * It processes raw trigger data (e.g., MQTT, HTTP, SQS) before passing it to `main()`.

 * Common tasks:

 * - Convert binary payloads to string/JSON

 * - Extract metadata

 * - Filter messages

 * - Add timestamps/context

 * 

 * The returned object determines `main()` parameters:

 * - `{a: 1, b: 2}` → `main(a, b)`

 * - `{payload}` → `main(payload)`

 * 

 * @param event - Trigger data (e.g., MQTT, HTTP)

 * @returns Processed data for `main()`

 */

export async function preprocessor(

  event: {

    kind: 'mqtt',

    payload: string, // base 64 encoded payload

    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

    }

  },

) {

  if (event.kind === 'mqtt') {

    const payloadAsString = atob(event.payload);

    return {

      contentType: event.v5?.content_type,

      payload: event.payload,

      payloadAsString

    };

  }

  // We assume the script is triggered by an MQTT message, which is why an error is thrown for other trigger kinds.

  // If the script is intended to support other triggers, update this logic to handle the respective trigger kind.

  throw new Error(`Expected mqtt trigger kind got: ${event.kind}`)

}

/**

 * Main Function - Handles processed trigger events

 * 

 * ⚠️ Called AFTER `preprocessor()`, with its return values.

 * 

 * @param payload - Raw base64 encoded payload

 * @param payloadAsString - Decoded string payload

 * @param contentType - MQTT v5 content type (if available)

 */

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

}