Message Queue in Google Apps Script

Implementation of a Message Queue in Google Apps Script.

Google Apps Script is an environment for light-weight application development around Google's G Suite set of tools. It runs JavaScript on the server side and provides access to the Spreadsheet for example. Scripts can be exposed as Web App and return arbitrary text-content as part of the Content Service.

Can Google Apps Script therefore be used to build a web application backend? This proof-of-concept shows an implementation of a message queue, using a spreadsheet for persistence and a HTTP API for access. It looks like this:

Limitations

Race conditions are likely to occur when concurrently consuming messages. There does not seem to be a way to lock the spreadsheet. For the producer, the sheet.appendRow() method looks like an atomic operation, although the documentation does not mention anything specific about it.

How to Install

1. Create a new spreadsheet and create two columns "Data" (A1) and "Reader" (A2)
2. Go to Tools -> Script Editor
3. Create MessageQueue.js using the sources provided here
4. In the script editor, expose the script as Web App via Publish -> Deploy as web app. Expose as "Who has access to the app: Anyone, even anonymous"
5. Copy the "Current web app URL" and paste it into consumer.js and producer.js as script_url