FreedomBox/plinth/dbus.py

#
# This file is part of FreedomBox.
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as
# published by the Free Software Foundation, either version 3 of the
# License, or (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU Affero General Public License for more details.
#
# You should have received a copy of the GNU Affero General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
#
"""
Expose some API over D-Bus.
"""

import logging
import threading

from plinth.utils import import_from_gi

from . import setup

glib = import_from_gi('GLib', '2.0')
gio = import_from_gi('Gio', '2.0')

logger = logging.getLogger(__name__)

_thread = None
_server = None
_main_loop = None


class PackageHandler():
    """D-Bus service to listen for messages when apt cache is updated."""

    introspection_xml = '''
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE node PUBLIC "-//freedesktop//DTD D-BUS Object Introspection 1.0//EN"
  "http://www.freedesktop.org/standards/dbus/1.0/introspect.dtd">
<node name="/org/freedombox/Service/PackageHandler">
  <interface name="org.freedombox.Service.PackageHandler">
    <method name="CacheUpdated"/>
  </interface>
</node>
'''

    def register(self, connection):
        """Register the object in D-Bus connection."""
        introspection_data = gio.DBusNodeInfo.new_for_xml(
            self.introspection_xml)
        interface_info = gio.DBusNodeInfo.lookup_interface(
            introspection_data, 'org.freedombox.Service.PackageHandler')
        connection.register_object('/org/freedombox/Service/PackageHandler',
                                   interface_info, self.on_method_call, None,
                                   None)

    def on_method_call(self, _connection, _sender, _object_path,
                       _interface_name, method_name, _parameters, invocation):
        """Handle method being called.

        No need to check all the incoming parameters as D-Bus will validate all
        the incoming parameters using introspection data.

        """
        if method_name == 'CacheUpdated':
            self.on_cache_updated()
            invocation.return_value()

    @staticmethod
    def on_cache_updated():
        """Called when system package cache is updated."""
        logger.info('Apt package cache updated.')

        # Run in a new thread because we don't want to block the thread running
        # Glib main loop.
        threading.Thread(target=setup.on_package_cache_updated).start()


class DBusServer():
    """Abstraction over a connection to D-Bus."""

    def __init__(self):
        """Initialize the server object."""
        self.package_handler = None

    def connect(self):
        """Connect to bus with well-known name."""
        gio.bus_own_name(gio.BusType.SYSTEM, 'org.freedombox.Service',
                         gio.BusNameOwnerFlags.NONE, self.on_bus_acquired,
                         self.on_name_acquired, self.on_name_lost)

    def on_bus_acquired(self, connection, name):
        """Callback when connection to D-Bus has been acquired."""
        logger.info('D-Bus connection acquired: %s', name)
        self.package_handler = PackageHandler()
        self.package_handler.register(connection)

    @staticmethod
    def on_name_acquired(_connection, name):
        """Callback when service name on D-Bus has been acquired."""
        logger.info('D-Bus name acquired: %s', name)

    @staticmethod
    def on_name_lost(_connection, name):
        """Callback when service name or DBus connection is closed."""
        logger.info('D-Bus connection lost: %s', name)

        # XXX: Reconnect after a while
        #
        # Such as by doing:
        # connection.set_exit_on_close(False)
        # gio.timeout_add(10000, self.connect)
        #
        # However, perhaps due to some cleanup issues, reconnection is not
        # happening if it is does after an incoming method call.
        #
        # If D-Bus connection is lost due to daemon restart, FreedomBox service
        # will receive a SIGTERM and exit. systemd should then restart the
        # service again.


def run():
    """Run a glib main loop forever in a thread."""
    global _thread
    _thread = threading.Thread(target=_run)
    _thread.start()


def stop():
    """Exit glib main loop and end the thread."""
    if _main_loop:
        logger.info('Exiting main loop for D-Bus services')
        _main_loop.quit()


def _run():
    """Connect to D-Bus and run main loop."""
    logger.info('Started new thread for D-Bus services')

    global _server
    _server = DBusServer()
    _server.connect()

    global _main_loop
    _main_loop = glib.MainLoop()
    _main_loop.run()
    _main_loop = None

    logger.info('D-Bus services thread exited.')