Google Drive Watch: Push Notifications with Apps Script

Introduction
Keeping a close eye on modifications to critical files in Google Drive can save teams from costly errors and missed deadlines. Google’s push notification service, combined with Apps Script, lets you receive real‑time alerts whenever a file is created, edited, or deleted. This article walks you through the entire setup: from configuring a Google Cloud project and enabling the Drive API, to writing the Apps Script that registers a watch on a specific file or folder, creating a lightweight webhook receiver, and finally testing and troubleshooting the whole pipeline. By the end, you’ll have a reliable, server‑less solution that automatically notifies you (or downstream systems) the moment a change occurs in your Drive assets.

Create a Google Cloud Project and Enable the Drive API

Before any script can subscribe to change events, Google needs a project that owns the credentials used for the watch request. Follow these steps:

• Open the Google Cloud Console and click **New Project**. Give it a descriptive name such as “Drive‑Change‑Watcher”.
• Enable the Drive API under APIs & Services → Library. Search for “Google Drive API” and click **Enable**.
• Create OAuth 2.0 client credentials (type: Web application). Add the Apps Script URL (e.g., https://script.google.com) to the authorized JavaScript origins and redirect URIs.
• Note the client ID and client secret. You’ll need them when the script requests authorization to act on your Drive.

These credentials give the Apps Script the permission to call drive.changes.watch on your behalf, which is the core of the push‑notification flow.

Write an Apps Script that Subscribes to Drive Changes

With the project ready, open a new Apps Script bound to a Google Sheet (or a standalone script) and add the following logic:

• Authorize the script using the OAuth scopes https://www.googleapis.com/auth/drive and https://www.googleapis.com/auth/script.external_request.
• Identify the target – either a single file ID or a folder ID you want to monitor.
• Call the Watch endpoint using the Drive API’s changes.watch method. Supply a channelId (a UUID you generate), a type of web_hook, and the URL of your webhook receiver (created in the next section).
• Store the watch details (channel ID, expiration timestamp, resource ID) in the script’s PropertiesService so you can renew or cancel the watch later.

Example snippet (simplified for clarity):

function startWatch() {
  var fileId = ‘YOUR_FILE_OR_FOLDER_ID’;
  var channelId = Utilities.getUuid();
  var webhookUrl = ‘https://YOUR_SCRIPT_URL/exec’;
  var request = {
    id: channelId,
    type: ‘web_hook’,
    address: webhookUrl
  };
  var response = Drive.Changes.watch(request, fileId);
  PropertiesService.getScriptProperties().setProperties({
    channelId: channelId,
    resourceId: response.resourceId,
    expiration: response.expiration
  });
}

Deploy a Webhook Receiver with Apps Script

The webhook URL you supplied in the previous step must point to an endpoint that can accept POST requests from Google’s notification service. Apps Script can act as that endpoint by publishing a Web App:

• In the script editor, choose **Publish → Deploy as web app**.
• Set Execute the app as to “Me (your email)”.
• Set Who has access to “Anyone, even anonymous” – Google’s notification service does not carry an OAuth token.
• Implement a doPost(e) function that parses the JSON payload, verifies the channelId against the stored value, and then triggers your desired action (e.g., send an email, post to Slack, update a spreadsheet).

Sample doPost handler:

function doPost(e) {
  var payload = JSON.parse(e.postData.contents);
  var stored = PropertiesService.getScriptProperties().getProperty(‘channelId’);
  if (payload.channelId !== stored) return; // ignore stray calls
  // Example action: log the change and notify
  Logger.log(‘Change detected on resource: ‘ + payload.resourceId);
  MailApp.sendEmail(‘[email protected]’, ‘Drive file changed’, ‘A monitored file was updated.’);
  return ContentService.createTextOutput(‘OK’);
}

Because the web app runs on Google’s infrastructure, you do not need an external server, making the whole solution lightweight and cost‑free.

Verify, Test, and Maintain the Notification Flow

After deployment, you must ensure the watch is active and that notifications are being received correctly:

• Check the watch status by calling Drive.Channels.stop with the stored channelId and resourceId. If the call succeeds, the watch existed.
• Trigger a change – edit the monitored file, rename it, or add a new file to the watched folder. Observe the email or log entry generated by doPost.
• Renew before expiration. Watches expire (usually after 7 days). Schedule a time‑driven Apps Script function that reads the stored expiration timestamp and re‑creates the watch a few hours before it lapses.
• Handle failures gracefully. Google may resend a notification if your endpoint returns a non‑200 status. Ensure doPost always returns a 200 response after processing, and implement exponential back‑off if you need to retry external actions.

By following these verification steps, you guarantee a robust, low‑maintenance monitoring system that scales with the number of files or folders you need to watch.

Conclusion
Enabling push notifications for Google Drive changes with Apps Script transforms a passive file repository into an actively monitored workspace. Starting with a properly configured Cloud project, you grant the script the rights to subscribe to change events, then write concise code that registers a watch and deploys a serverless webhook receiver. Once the webhook processes incoming alerts, you can route them to any downstream system—email, chat, or custom dashboards—while a simple renewal routine keeps the watch alive indefinitely. This end‑to‑end approach eliminates the need for constant polling, reduces latency, and leverages Google’s native infrastructure, giving you a reliable, cost‑effective solution for real‑time Drive oversight.