NATS trigger script with preprocessor example

/**

 * General Trigger Preprocessor

 *

 * ⚠️ This function runs BEFORE the main function.

 *

 * It processes raw trigger data (e.g., MQTT, HTTP, SQS, WebSocket, Kafka, NATS) 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)

 * - {msg} → main(msg)

 *

 * @param event - Trigger data (e.g., MQTT, HTTP, SQS, WebSocket, Kafka, NATS)

 * @returns Processed data for main()

 */

export async function preprocessor(

  event: {

    kind: 'nats',

    payload: string, // base64 encoded payload

    servers: string[],

    subject: string,

    headers?: Record<string, string[]>,

    status?: number,

    description?: string,

    length: number

  },

) {

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

    try {

      const msg = atob(event.payload)

      // Assuming the message received is a JSON value

      const data = JSON.parse(msg);

      return {

        msg,

        data,

        nats: event.headers

      };

    } catch (error) {

      throw new Error("Failed to parse NATS message as JSON");

    }

  }

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

}

/**

 * Main Function - Handles processed trigger events

 *

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

 *

 * @param msg - Decoded message content

 * @param data - Parsed JSON data from the NATS message

 * @param headers - messages headers

 */

export async function main(

  msg: string,

  data: any,

  headers?: Record<string, string[]>

) {

  // Implement the main function logic here

}