Generate RSS2 Feeds (and Newsletters) from Google Calendar

In 2015 Google dropped support for RSS feeds from its Calendar product. I am bad at Internet searches and was not able to find the dozen projects that replace this functionality, so I wrote my own.

This is a script that is intended to be run from a cronjob. It is written in Python 3 with lots of helper modules (requests, jinja2, dateutil ...). Note that since Google dropped support for its goo.gl shortening service, we are now using the pyshorteners library for URL shortening. This library is licensed under the GPL3 (which should be okay, since the Apache 2.0 license is GPL3-compatible).

There is a second script called gen_newsletter.py which will create the body of a plaintext email. You can use this to send newsletters about your events. There is a third script for generating HTML bullet lists of events, but you probably do not want to use that one.

There is a third script that is called schedule_event_tweets.py. This sends out tweets at random times about upcoming events. It is moderately dangerous: first it generates tweet text and schedules them using the at command. Then the at command launches a second script which (blindly!) tweets out the contents of the text. Don't use this one in an untrusted environment.

There is a fourth script called gen_sidebar.py which generates an HTML bullet list. This is probably not helpful for you, but it can be used to embed events on a webpage.

Deployment

Local

• Generate a Google Calendar API key, as described below.
• Use virtualenv to set up a Python 3 environment: virtualenv -p /usr/bin/python3 venv
• Activate the environment: source venv/bin/activate
• Install dependencies: pip install -r requirements.txt
• Copy config.py.example to config.py and customize it to your needs.
• Run gen_rss.py or gen_newsletter.py or gen_sidebar.py or schedule_event_tweets.py

Generating an API key

• Log into https://console.developers.google.com with a Google account (preferably the one that owns the Google calendar in question, but it does not really matter).
• Create a new project.
• Click on Enable API (or Library). Select the URL Shortener API and enable it. Do the same for the Google Calendar API.
• Click on Credentials, and then Create Credentials.
• Create an API Key. Give it an appropriate name ("RSS/Newsletter key"). Set the restriction to be IP Addresses, and enter the IP address of the host that will be running the scripts.

Production

• Copy config.py.example to config.py and customize it to your liking
• Build the docker image with docker build -t gcal-rss .
• Run the container and generate the files into a named volume: docker run --rm -v gcal-rss-data:/data gcal-rss

Caveats

• The code is probably not production ready (but we are deploying it anyways). Among other things there is not much test coverage. There are no error messages.
• Because it uses an API key, you can only generate feeds for public calendars.
• This project is colonialist: it has only been tested in English, in the America/Toronto timezone.
• This project sources a file config.py that the end user can specify on the commandline. This is really dangerous unless you trust everybody who can run this script.
• If you use a person's default calendar the title of the newsletter will be the same as their email. The person will have to edit the name of the calendar in order for the scripts to display something sensible. (This is the "summary" field returned by the API.)
• By default we use the da.gd link shortener for newsletters.