Getting signals working on PulseAudio's DBus interface?

Question

I'm trying to get a D-Bus signal handler to be called whenever the state of a sink changes in PulseAudio (e.g. becomes inactive). Unfortunately, it isn't being called and I frankly am not sure why.

import dbus
import dbus.mainloop.glib
from gi.repository import GObject


dbus.mainloop.glib.DBusGMainLoop(set_as_default=True)
bus = dbus.SessionBus()


def signal_handler(*args, **kwargs):
    print('sig: ', args, kwargs)


def connect():
    import os
    if 'PULSE_DBUS_SERVER' in os.environ:
        address = os.environ['PULSE_DBUS_SERVER']
    else:
        bus = dbus.SessionBus()
        server_lookup = bus.get_object("org.PulseAudio1", "/org/pulseaudio/server_lookup1")
        address = server_lookup.Get("org.PulseAudio.ServerLookup1", "Address", dbus_interface="org.freedesktop.DBus.Properties")

    return dbus.connection.Connection(address)


conn = connect()
core = conn.get_object(object_path='/org/pulseaudio/core1')
core.connect_to_signal('StateUpdated', signal_handler)
core.ListenForSignal('org.PulseAudio.Core1.Device.StateUpdated', dbus.Array(signature='o'), dbus_interface='org.PulseAudio.Core1')
loop = GObject.MainLoop()
loop.run()

Answer 1

Try this, works for me.

import dbus
import os
from dbus.mainloop.glib import DBusGMainLoop
import gobject
def pulse_bus_address():
    if 'PULSE_DBUS_SERVER' in os.environ:
        address = os.environ['PULSE_DBUS_SERVER']
    else:
        bus = dbus.SessionBus()
        server_lookup = bus.get_object("org.PulseAudio1", "/org/pulseaudio/server_lookup1")
        address = server_lookup.Get("org.PulseAudio.ServerLookup1", "Address", dbus_interface="org.freedesktop.DBus.Properties")
        print(address)

    return address

def sig_handler(state):
    print("State changed to %s" % state)
    if state == 0:
        print("Pulseaudio running.")
    elif state == 1:
        print("Pulseaudio idle.")
    elif state == 2:
        print("Pulseaudio suspended")

# setup the glib mainloop

DBusGMainLoop(set_as_default=True)

loop = gobject.MainLoop()

pulse_bus = dbus.connection.Connection(pulse_bus_address())
pulse_core = pulse_bus.get_object(object_path='/org/pulseaudio/core1')
pulse_core.ListenForSignal('org.PulseAudio.Core1.Device.StateUpdated', dbus.Array(signature='o'), dbus_interface='org.PulseAudio.Core1')

pulse_bus.add_signal_receiver(sig_handler, 'StateUpdated')
loop.run()

Requires pulseaudio's default.pa to have the following:

.ifexists module-dbus-protocol.so
load-module module-dbus-protocol
.endif

Edit: for those wondering about @conf-f-use's question concerning the application name. It turns out that they answered this issue themselves and posted the answer here: https://askubuntu.com/questions/906160/is-there-a-way-to-detect-whether-a-skype-call-is-in-progress-dbus-pulseaudio
Stealing a section of @con-f-use's code and applying to my code above, we get a monitor that tracks what the state is and is able to tell you the application name, the artist, title and name of what is playing.
Cheers @con-f-use :)

import dbus
import os
from dbus.mainloop.glib import DBusGMainLoop
import gobject
def pulse_bus_address():
    if 'PULSE_DBUS_SERVER' in os.environ:
        address = os.environ['PULSE_DBUS_SERVER']
    else:
        bus = dbus.SessionBus()
        server_lookup = bus.get_object("org.PulseAudio1", "/org/pulseaudio/server_lookup1")
        address = server_lookup.Get("org.PulseAudio.ServerLookup1", "Address", dbus_interface="org.freedesktop.DBus.Properties")
        print(address)

    return address

# convert byte array to string
def dbus2str(db):
    if type(db)==dbus.Struct:
        return str(tuple(dbus2str(i) for i in db))
    if type(db)==dbus.Array:
        return "".join([dbus2str(i) for i in db])
    if type(db)==dbus.Dictionary:
        return dict((dbus2str(k), dbus2str(v)) for k, v in db.items())
    if type(db)==dbus.String:
        return db+''
    if type(db)==dbus.UInt32:
        return str(db+0)
    if type(db)==dbus.Byte:
        return chr(db)
    if type(db)==dbus.Boolean:
        return db==True
    if type(db)==dict:
        return dict((dbus2str(k), dbus2str(v)) for k, v in db.items())
    return "(%s:%s)" % (type(db), db)

def sig_handler(state):
    print("State changed to %s" % state)
    if state == 0:
        print("Pulseaudio running.")
    elif state == 1:
        print("Pulseaudio idle.")
    elif state == 2:
        print("Pulseaudio suspended")

    dbus_pstreams = (
        dbus.Interface(
            pulse_bus.get_object(object_path=path),
            dbus_interface='org.freedesktop.DBus.Properties'
        ) for path in pulse_core.Get(
            'org.PulseAudio.Core1',
            'PlaybackStreams',
            dbus_interface='org.freedesktop.DBus.Properties' )
        )
    pstreams = {}
    for pstream in dbus_pstreams:
        try:
            pstreams[pstream.Get('org.PulseAudio.Core1.Stream', 'Index')] =  pstream
        except dbus.exceptions.DBusException:
            pass
    if pstreams:
        for stream in pstreams.keys():
            plist = pstreams[stream].Get('org.PulseAudio.Core1.Stream', 'PropertyList')
            appname = dbus2str(plist.get('application.name', None))
            artist = dbus2str(plist.get('media.artist', None))
            title = dbus2str(plist.get('media.title', None))
            name = dbus2str(plist.get('media.name', None))
            print appname,artist,title,name


# setup the glib mainloop

DBusGMainLoop(set_as_default=True)

loop = gobject.MainLoop()

pulse_bus = dbus.connection.Connection(pulse_bus_address())
pulse_core = pulse_bus.get_object(object_path='/org/pulseaudio/core1')
#pulse_clients = pulse_bus.get_object(object_path='/org/pulseaudio/core1/Clients')
#print dir(pulse_clients)
pulse_core.ListenForSignal('org.PulseAudio.Core1.Device.StateUpdated', dbus.Array(signature='o'), dbus_interface='org.PulseAudio.Core1')

pulse_bus.add_signal_receiver(sig_handler, 'StateUpdated')
loop.run()

Answer 2

I my environment, I have dbus and pulseaudio running, however the discovered address does not exist:

>>> import dbus
>>> import dbus.mainloop.glib
>>> from gi.repository import GObject
>>> dbus.mainloop.glib.DBusGMainLoop(set_as_default=True)
<dbus.mainloop.NativeMainLoop object at 0x7f3c98ffd4e0>
>>> bus = dbus.SessionBus()
>>> server_lookup = bus.get_object("org.PulseAudio1", "/org/pulseaudio/server_lookup1")
>>> address = server_lookup.Get("org.PulseAudio.ServerLookup1", "Address", dbus_interface="org.freedesktop.DBus.Properties")
>>> address
dbus.String('unix:path=/run/user/1000/pulse/dbus-socket', variant_level=1)


$ dbus-monitor --address 'unix:path=/run/user/1000/pulse/dbus-socket'
Failed to open connection to unix:path=/run/user/1000/pulse/dbus-socket: Failed to connect to socket /run/user/1000/pulse/dbus-socket: No such file or directory

$ ls /run/user/1000/pulse/
cli  native  pid

I don't know if my configuration is default, but it seems dbus integration is just not there!