ical-to-caldav

iCal-to-CalDAV bridge daemon. Converts public iCal (ICS) subscription URLs into a CalDAV server, so calendar clients like DankCalendar, khal, Evolution, and Thunderbird/Lightning can consume any public .ics feed without proprietary API locks.

Apache2 licensed.

Why

Many calendar providers only offer iCal subscription URLs (Google Calendar free/busy, academic calendars, government ICS feeds) but no CalDAV. Desktop clients prefer CalDAV for bidirectional sync. This daemon bridges that gap:

iCal URL (Google free/busy, academic .ics, etc.)
        │
        ▼
  ical-to-caldav
  (fetches + parses + caches)
        │
        ▼
CalDAV server (:8080)
        │
        ▼
DankCalendar / khal / Evolution / Thunderbird

Quick start

# Build
make build

# Configure
cp ical-to-caldav.yaml.example ical-to-caldav.yaml
$EDITOR ical-to-caldav.yaml

# Run
./icaltocaldav --config ical-to-caldav.yaml

# In DankCalendar: dcal account add caldav
#   URL: http://localhost:8080/caldav/sources/<source-id>/

Config example

listen: ":8080"
data_dir: "~/.local/share/ical-to-caldav"
refresh_interval: "30m"

sources:
  - id: google-freebusy
    name: "Google Free/Busy"
    url: "https://calendar.google.com/calendar/ical/.../public/basic.ics"
    color: "#1a73e8"
  - id: university
    name: "University Calendar"
    url: "https://example.edu/calendar.ics"
    color: "#34a853"
    refresh_interval: "1h"

Tech stack

Layer	Choice
Language	Go 1.23+
HTTP	chi
iCal parsing	github.com/jszwec/ics
Cache	Badger (embedded KV)
License	Apache 2.0

Architecture

ical-to-caldav/
├── cmd/icaltocaldav/     # main entrypoint
├── internal/
│   ├── source/          # fetcher + iCal parser
│   ├── caldav/          # CalDAV HTTP server (RFC 4791)
│   ├── store/           # Badger persistence
│   └── config/          # YAML config
└── Makefile

CalDAV compliance

Implements the subset of RFC 4791 needed for read-only calendar access:

• PROPFIND on calendar-home-set and calendar collections
• REPORT calendar-query with time-range filter
• GET on calendar object resources (.ics files)

Write operations (PUT, DELETE) are out of scope for v1 — the daemon is a read-only bridge.

Contributing

Issues and PRs welcome. Follow the LOUST contribution standards.

Related

• DankMaterialShell — desktop shell
• DankCalendar — calendar daemon + QML UI
• khal — CLI calendar client (CalDAV/iCal)
• vdirsyncer — CalDAV/iCal sync