Issues using dbus in strict

[Sergey Borovkov]

Hi. I am running a couple of daemons (daemon: simple) and they interact
between each other using dbus. Unfortunately I've ran into the issue when
porting them from devmode to strict, I am getting this backtrace just
trying to obtain SystemBus in python:

Mar 31 12:44:02 localhost.localdomain snap[1466]: GLib.Error:
g-io-error-quark: Could not connect: Permission denied (14)
Mar 31 12:44:02 localhost.localdomain snap[1466]: return Gio.bus_get_sync(type,
None).pydbus
Mar 31 12:44:02 localhost.localdomain snap[1466]: File "/snap/screenly-
client/165/lib/python3.5/site-packages/pydbus/bus.py", line 19, in bus_get
Mar 31 12:44:02 localhost.localdomain snap[1466]: return bus_get(Bus.Type.
SYSTEM)
Mar 31 12:44:02 localhost.localdomain snap[1466]: File "/snap/screenly-
client/165/lib/python3.5/site-packages/pydbus/bus.py", line 57, in SystemBus
Mar 31 12:44:02 localhost.localdomain snap[1466]: self.bus = SystemBus()
Mar 31 12:44:02 localhost.localdomain kernel: audit: type=1400
audit(1490964242.523:72): apparmor="DENIED" operation="connect" profile=
"snap.screenly-client.websocket" name="/run/dbus/system_bus_socket"
pid=1466 comm="python3" req
Mar 31 12:44:02 localhost.localdomain audit[1466]: AVC apparmor="DENIED"
operation="connect" profile="snap.screenly-client.websocket" name="/
run/dbus/system_bus_socket" pid=1466 comm="python3" requested_mask="wr"
denied_mask="wr"

I am not sure if I need to use some additional interfaces - to get it
working under devmode I've used the following code (And I can't find
anything relevant in wiki):

  playlist:
    command: usr/bin/playlist-service.sh
    daemon: simple
    plugs: [network-bind, network]
    slots: [playlist-dbus-server]

  websocket:
    command: usr/bin/websocket-service.sh
    daemon: simple
    plugs: [network-bind, network, playlist-dbus-client]

slots:
  playlist-dbus-server:
    interface: dbus
    name: com.screenly.playlist
    bus: system

plugs:
  playlist-dbus-client:
    interface: dbus
    name: com.screenly.playlist
    bus: system