CalDAV is an Internet standard allowing a client to access scheduling information on a remote server. It extends WebDAV (HTTP-based protocol for data manipulation) specification and uses iCalendar format for the data. The protocol is defined by RFC 4791.
Horde, specifically the Kronolith and Nag modules for calendaring and tasks management, support CalDAV in two ways: it can be used as a CalDAV server for external calendar clients, providing a central cloud storage for multiple devices of the users. And it can use an external CalDAV server as a calendar client on its own, to display this server's events inside Horde.
Full CalDAV support has been added with Horde 5.1/Kronolith 4.1/Nag 4.1.
The Horde_Dav library is automatically pulled in as a dependency when installing Kronolith or Nag. The necessary database tables can be created as usual from the Horde configuration screen or via horde-db-migrate. The storage backend for all DAV operations has to be enabled in the Horde configuration screen.
Some CalDAV clients support automatic discovery of the CalDAV service end points just by providing the user's email address or a host name. To enable service discovery, redirect aliases have to be set in your web server's configuration. The redirect target is either the horde/rpc/ directory if you have "pretty" URLs enabled in your Horde configuration, or the horde/rpc.php file otherwise. This is an example for Apache web servers:
RedirectPermanent /.well-known/caldav /horde/rpc/
See your web server's documentation about how to set up redirects.
Service Discovery can also be implemented via DNS setup. Please refer to SabreDAV Service Discovery for details.
There are two different kind of CalDAV service end points which may or may not be supported by different clients:
Both types of URLs can be retrieved from the calendars' and task lists' edit forms. In the Kronolith/Nag interface click on the edit icon next to an calendar/task list name and copy the required URL from there.
This is a list of devices known to work with Horde's CalDAV implementation. Please update if you gather new information, or have more detailed knowledge about the supported features or versions.
|Client/Device||Principal URLs||Calendar URLs||Service Discovery||Notes|
|Thunderbird/Lightning||No||Yes||Confirmed with Thunderbird|
|Outlook CalDav Synchronizer (Outlook CalDAV Plugin)||Yes||Yes||Yes|
|Apple iCal||Yes||Yes||Confirmed with iCal 5.0/OS X 10.7|
|BlackBerry||Yes||Yes||Tested with BB10 simulator|