Running 'transient' systemd unit files with dbus

transient.py

from __future__ import print_function
import uuid
import functools
import hashlib
# TO-DO: switch to pydbus, currently same code
# with pydbus gives errors.
from dbus import SessionBus, SystemBus, Interface


def rand_name():
    return hashlib.sha256(str(uuid.uuid4())).hexdigest()[:8]


def get_systemd_manager(bus):
    systemd = bus.get_object(
        'org.freedesktop.systemd1', '/org/freedesktop/systemd1'
    )
    manager = Interface(
        systemd, dbus_interface='org.freedesktop.systemd1.Manager'
    )
    return manager


def get_systemd_user():
    return get_systemd_manager(SessionBus())


def get_systemd_system():
    return get_systemd_manager(SystemBus())


def with_systemd_manager(scope='system'):
    def wrap(func):
        @functools.wraps(func)
        def wrapped_func(*args, **kwargs):
            if scope == 'system':
                func(get_systemd_system(), *args, **kwargs)
            elif scope == 'session':
                func(get_systemd_user(), *args, **kwargs)
            else:
                raise RuntimeError('scope must be session or system')

        return wrapped_func

    return wrap


def start_transient(manager, cmd, name=None, mode='replace', props=None):
    if cmd is None:
        raise RuntimeError('no cmd was provided')
    if name is None:
        name = '{0}-{1}.service'.format('transient', rand_name())
    if not isinstance(cmd, list):
        raise RuntimeError('cmd must be a list')
    if props is None:
        properties = [
            ('Description', ' '.join(cmd)),
            ('ExecStart', [(cmd[0], cmd, False)])
        ]
    else:
        properties = props
    job = manager.StartTransientUnit(name, mode, properties, [])
    if not job:
        raise RuntimeError('unable to start transient unit')
    print('job started: {0}'.format(job))
    print('service name: {0}'.format(name))


@with_systemd_manager(scope='session')
def start_user(manager, cmd, mode='replace'):
    start_transient(manager=manager, cmd=cmd, mode=mode)


@with_systemd_manager(scope='system')
def start_system(manager, cmd, mode='replace'):
    start_transient(manager=manager, cmd=cmd, mode=mode)