Here’s the initial implementation of the D-Bus API for the scheduling
daemon, plus a dummy scheduling algorithm which allows everything when
the network connection is unmetered, and denies everything otherwise. We
use GLib’s definition of ‘metered’, which is very coarse grained and
probably wrong most of the time.

The D-Bus API is implemented manually, rather than using gdbus-codegen,
as that allows us to implement permissions checks for API calls
(gdbus-codegen doesn’t). In future, we might want to lock down the API
more finely using polkit, which has similar requirements for not using
gdbus-codegen.

There are two D-Bus objects implemented to begin with:
 • com.endlessm.DownloadManager1.Scheduler, which exposes the scheduler
   and allows new schedule entries to be created. It can be accessed by
   any peer who has access to the service at all.
 • com.endlessm.DownloadManager1.ScheduleEntry, which represents a
   single schedule entry (download) for the lifetime of that download,
   including any time before the download is first allowed to start. It
   can only be accessed by the peer which created the entry.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

https://phabricator.endlessm.com/T20420