Case · Backend · Python
ical-forge: iCalendar (RFC 5545), RRULE and subscription
An iCalendar service in Python (FastAPI + SQLite, no third-party calendar libraries). It builds a valid .ics (line folding, escaping, VTIMEZONE from zoneinfo), validates a foreign file with line numbers, expands recurring events by RRULE and publishes subscription feeds by link with ETag and 304 responses.
- Python
- FastAPI
- uvicorn
- SQLite
- RFC 5545
- ETag
- hypothesis
- mypy --strict
- ruff
- Docker
- GitHub Actions
01 · How it looks
Screenshots
02 · About
What it is and why
An iCalendar service in Python (FastAPI + SQLite, no third-party calendar libraries). It builds a valid .ics (line folding, escaping, VTIMEZONE from zoneinfo), validates a foreign file with line numbers, expands recurring events by RRULE and publishes subscription feeds by link with ETag and 304 responses.
Limitations
SECONDLY, MINUTELY, HOURLY and some of BYWEEKNO, BYYEARDAY, BYHOUR, BYMINUTE, BYSECOND are not expanded: the syntax is accepted, expansion returns an error.
Events with a non-IANA TZID (for example Windows names) are validated but not expanded.
This is a demo store without accounts; the rate limit lives in process memory.
The project runs on a small VPS with demo data: no redundancy or backups.
What is inside
- 28 recurrence examples from RFC 5545 §3.8.5.3 are checked against date lists (BYSETPOS, "second-to-last Monday", Friday the 13th with EXDATE)
- 119 tests; hypothesis: an event → .ics → event round trip over arbitrary Unicode, unfold(fold(x)) == x, lines of at most 75 octets
- POST /api/expand of 500 occurrences in 0.2 s; a feed at about 640 requests per second, p95 45 ms
- The edit key is stored only as a SHA-256, compared in constant time
03 · How to run
Run it locally
git clone <repository on request> ical-forge
cd ical-forge
python -m app04 · Code
The repository is private
The source is in a private repository. Message me on Telegram and I will open access.
Request the code