async-caldav

gem "async-caldav", "~> 0.1"

# config.ru
require "async/caldav"

class ForwardAuthMiddleware
  def initialize(app) = @app = app
  def call(env)
    env['dav.user'] = env['HTTP_REMOTE_USER']
    @app.call(env)
  end
end

storage = Async::Caldav::Storage::Filesystem.new("/data")
use ForwardAuthMiddleware
run Async::Caldav::Server.new(storage: storage)

require "async/caldav"

client = Async::Caldav::Client.new("http://localhost:9292", user: "admin")

# Discovery
client.principal           # => "/admin/"
client.calendars           # => [Calendar, ...]
client.addressbooks        # => [Addressbook, ...]

# Create a calendar and add an event
cal = client.create_calendar("work", displayname: "Work")
cal.put_event("meeting.ics", <<~ICAL)
  BEGIN:VCALENDAR
  BEGIN:VEVENT
  UID:meeting-1
  SUMMARY:Team Standup
  DTSTART:20260501T090000Z
  DTEND:20260501T093000Z
  END:VEVENT
  END:VCALENDAR
ICAL

# Retrieve and list events
event = cal.get_event("meeting.ics")
event[:body]    # => "BEGIN:VCALENDAR..."
event[:etag]    # => '"a1b2c3..."'

cal.events      # => [{path:, body:, etag:}, ...]

# Conditional update with ETag
cal.put_event("meeting.ics", new_body, if_match: event[:etag])

# Sync (incremental)
items, token = cal.sync
# ... later ...
changes, token = cal.sync(token: token)

# Addressbook
ab = client.create_addressbook("contacts", displayname: "Contacts")
ab.put_contact("alice.vcf", "BEGIN:VCARD\r\nUID:1\r\nFN:Alice\r\nEND:VCARD")
ab.contacts     # => [{path:, body:, etag:}, ...]

client.close