Changes to sharing in sabre/dav 3.2

We are currently working on sabre/dav 3.2. A first beta has been released. This release includes major changes to the sharing system.

If you are a user of sabre/dav and have never done any deep modifications to the sharing system, this simply means that from that version onward, there's a new calendar sharing feature.

To take advantage of that feature, you can just upgrade and then turn on the sharing plugin:

$server->addPlugin(new Sabre\DAV\Sharing\Plugin());

And to allow Apple clients and BusyCal to modify the list of who can access your calendar, add the following second plugin:

$server->addPlugin(new Sabre\CalDAV\SharingPlugin());

Now if you're completely new to this, you can stop reading this article right here. However, if you did stuff with sharing before, read on.

The old situation

Preliminary support for sharing was added to sabre/dav in version 1.7, which was released back in 2012. However, this release only ever shipped with the interfaces to allow an implementor to write a custom backend for this.

There were only a few people that have actually done that. This guide is for those people.

The specification we used back then were 2 apple proprietary specifications:

  1. caldav-sharing.
  2. caldav-notifications.

The internal sabre/dav API's match the terminology from those specifications. The API's allowed someone to write an implementation that allows a user to invite another user to their calendar. The others get the invitation and can accept or decline the invite.

New standardization effort

In 2014 the sabre/dav project and a couple of other vendors started on a new effort, with the following primary goals:

  1. Standardize the proprietary spec.
  2. Extend the specification to also allow CardDAV (addressbook) sharing to be implemented.

To do this, we've split the standard into 4 separate specifications:

  1. draft-pot-webdav-notifications.
  2. draft-pot-webdav-resource-sharing.
  3. draft-pot-caldav-sharing.
  4. And a future carddav sharing spec.

So in this process we're not only creating a separate CardDAV and CalDAV spec, but also adding a generic 'WebDAV sharing' spec that can be used by WebDAV file sharing systems, such as ownCloud.

On a high level the data-model is similar, but almost everywhere new XML documents have been defined that are more descriptive, more generic or just better for aesthetic reasons.

The state of sharing in sabre/dav 3.2

The first place where the new specifications will be integrated, is CalDAV. So 3.2 is also the first place where we actually ship a working implementation.

However, to do this properly, some big changes were made:

  1. The internal API is 100% rewritten. All the properties and classes use terminology matching the new specs and not the old specs.
  2. A lot of the code has been moved from the Sabre\CalDAV to the Sabre\DAV\Sharing namespace.

But, another thing is really important. The new sharing specification allows two workflows for sharing:

  1. Sharing with a notification system. In this approach you can invite someone to a share, and that person then gets an opportunity to accept, decline or ignore the invite.
  2. Instant sharing. In this workflow you invite someone, and then that person immediately has access to the share.

The old spec only has support for the first model, and this is true as well for the sabre/dav implementation.

However, in sabre/dav 3.2 we initially only support model #2. So if you require the notification system, you can't yet do an upgrade.

We think model #1 is probably more appropriate for public consumer systems, and #2 works better for systems supporting small teams.

Getting support for the old specifications

One drawback of using the new specs, is that old clients don't yet understand them. So we've added a plugin to handle this.

If you add the Sabre\CalDAV\SharingPlugin plugin, this plugin supports the old apple spec and automatically maps all incoming request to the new model.

This plugin can therefore only work if Sabre\DAV\Sharing\Plugin is also up and running.

The old and the new classes

This table gives you an idea of the old classes and interfaces, and which classes and interfaces you now need to look at for similar functionality.

Sabre\CalDAV\SharingPlugin

This class split in two:

  • Sabre\DAV\Sharing\Plugin
  • Sabre\CalDAV\SharingPlugin

Sabre\CalDAV\ISharableCalendar and `Sabre\CalDAV\ISharedCalendar

The old sabre/dav had two node types for shared calendars, one for the original and one for the shared instances.

The new sabre/dav combines this into a single Sabre\DAV\Sharing\ISharedNode. Which is used for 'all instances'.

However, there is still Sabre\CalDAV\ISharedCalendar which extends both Sabre\DAV\Sharing\ISharedNode and Sabre\CalDAV\ICalendar.

Sabre\CalDAV\SharedCalendar and Sabre\CalDAV\ShareableCalendar

Like the interfaces, the concrete classes also had two distinct nodes. In the new system, there is just Sabre\CalDAV\SharedCalendar.

Sabre\CalDAV\Notifications

This entire namespace must not be used in sabre/dav 3.2. It doesn't work and it will go away.

Sabre\CalDAV\Backend\SharingSupport

This interface still exists and still has the same goal, but it went through a number of structual changes. It also no longer requires Sabre\CalDAV\Backend\NotificationSupport as well.

The future

The plan is to implement the notifications engine again, but take a different approach than we originally did in old sabre/dav versions. The new system should be better separated from CalDAV and support notifications for different subsystems (CardDAV, CalDAV, etc).

We will also add support for CardDAV (addressbook) sharing soon.

Hopefully these releases will all be rolled out in 3.3 and 3.4 releases.

My advice for people that require the notification subsystem for now is to stick to 3.1 until we have a complete replacement. Some shifts will likely happen until we land on a design we're actually happy with.

Tags: dav, carddav, caldav, sharing