title: Can one receive a Google Cloud Messaging (GCM) message in a Google Apps Script
body: <p>I'm trying to write an application where most of the logic sits in a Google Apps Script attached to a Google Sheet. I need some clients to periodically send a message to this script/sheet. Is this possible? I know I'd be able to send messages from the Sheets Script to the clients using an HTTP request, but I need the Sheets script to receive messages too.</p>