[libical] Adding support for VALARM extensions

[Robert Norris]

Hi all,

The Cyrus project is currently adding CalDAV & CardDAV support to Cyrus
IMAP, using libical as a base. We're interested in implementing some of
the extensions from draft-daboo-valarm-extensions-04[1], mostly to
support ACTION:URI VALARMs for SMS sending.

As far as we've been able to tell, there's really no way to add
attributes to libical without breaking ABI compatibility. We tried
storing the raw (pre-parse) properties in XLICERROR properties so the
application can handle them specially, but that stops strip_errors
working sanely. Hacky workarounds to preserve ABI compatibility aren't
going to work.

So unless anyone has a better idea (that's either trivial or backed up
with working code), we're going to fork libical into cyrus-ical, for our
own use. We'll do a name change to avoid conflicts but that's all for
the moment. If there's time and inclination down the track we'd like to
rework a few things so that stuff can be added without breaking the ABI,
but that's not necessary for us right now.

We don't really want to fork, but neither do we want to contribute
patches that break the world for everyone else. Tracking upstream
shouldn't be too difficult given the lack of activity.

Happy to discuss further!

Cheers,
Rob N.

1. http://tools.ietf.org/html/draft-daboo-valarm-extensions-04