broker.py

# Copyright (c) 2015 Nicolas JOUANIN
#
# See the file license.txt for copying permission.
import logging
import ssl
import websockets
import asyncio
import sys
import re
from asyncio import CancelledError
from collections import deque

from functools import partial
from transitions import Machine, MachineError
from hbmqtt.session import Session
from hbmqtt.mqtt.protocol.broker_handler import BrokerProtocolHandler
from hbmqtt.errors import HBMQTTException, MQTTException
from hbmqtt.utils import format_client_message, gen_client_id
from hbmqtt.adapters import (
    StreamReaderAdapter,
    StreamWriterAdapter,
    ReaderAdapter,
    WriterAdapter,
    WebSocketsReader,
    WebSocketsWriter)
from .plugins.manager import PluginManager, BaseContext


_defaults = {
    'timeout-disconnect-delay': 2,
    'auth': {
        'allow-anonymous': True,
        'password-file': None
    },
}

EVENT_BROKER_PRE_START = 'broker_pre_start'
EVENT_BROKER_POST_START = 'broker_post_start'
EVENT_BROKER_PRE_SHUTDOWN = 'broker_pre_shutdown'
EVENT_BROKER_POST_SHUTDOWN = 'broker_post_shutdown'
EVENT_BROKER_CLIENT_CONNECTED = 'broker_client_connected'
EVENT_BROKER_CLIENT_DISCONNECTED = 'broker_client_disconnected'
EVENT_BROKER_CLIENT_SUBSCRIBED = 'broker_client_subscribed'
EVENT_BROKER_CLIENT_UNSUBSCRIBED = 'broker_client_unsubscribed'
EVENT_BROKER_MESSAGE_RECEIVED = 'broker_message_received'


class BrokerException(BaseException):
    pass


class RetainedApplicationMessage:

    __slots__ = ('source_session', 'topic', 'data', 'qos')

    def __init__(self, source_session, topic, data, qos=None):
        self.source_session = source_session
        self.topic = topic
        self.data = data
        self.qos = qos


class Server:
    def __init__(self, listener_name, server_instance, max_connections=-1, loop=None):
        self.logger = logging.getLogger(__name__)
        self.instance = server_instance
        self.conn_count = 0
        self.listener_name = listener_name
        if loop is not None:
            self._loop = loop
        else:
            self._loop = asyncio.get_event_loop()

        self.max_connections = max_connections
        if self.max_connections > 0:
            self.semaphore = asyncio.Semaphore(self.max_connections, loop=self._loop)
        else:
            self.semaphore = None

    @asyncio.coroutine
    def acquire_connection(self):
        if self.semaphore:
            yield from self.semaphore.acquire()
        self.conn_count += 1
        if self.max_connections > 0:
            self.logger.info("Listener '%s': %d/%d connections acquired" %
                             (self.listener_name, self.conn_count, self.max_connections))
        else:
            self.logger.info("Listener '%s': %d connections acquired" %
                             (self.listener_name, self.conn_count))

    def release_connection(self):
        if self.semaphore:
            self.semaphore.release()
        self.conn_count -= 1
        if self.max_connections > 0:
            self.logger.info("Listener '%s': %d/%d connections acquired" %
                             (self.listener_name, self.conn_count, self.max_connections))
        else:
            self.logger.info("Listener '%s': %d connections acquired" %
                             (self.listener_name, self.conn_count))

    @asyncio.coroutine
    def close_instance(self):
        if self.instance:
            self.instance.close()
            yield from self.instance.wait_closed()


class BrokerContext(BaseContext):
    """
    BrokerContext is used as the context passed to plugins interacting with the broker.
    It act as an adapter to broker services from plugins developed for HBMQTT broker
    """
    def __init__(self, broker):
        super().__init__()
        self.config = None
        self._broker_instance = broker

    @asyncio.coroutine
    def broadcast_message(self, topic, data, qos=None):
        yield from self._broker_instance.internal_message_broadcast(topic, data, qos)

    def retain_message(self, topic_name, data, qos=None):
        self._broker_instance.retain_message(None, topic_name, data, qos)

    @property
    def sessions(self):
        for k, session in self._broker_instance._sessions.items():
            yield session[0]

    @property
    def retained_messages(self):
        return self._broker_instance._retained_messages

    @property
    def subscriptions(self):
        return self._broker_instance._subscriptions


class Broker:
    """
    MQTT 3.1.1 compliant broker implementation

    :param config: Example Yaml config
    :param loop: asyncio loop to use. Defaults to ``asyncio.get_event_loop()`` if none is given
    :param plugin_namespace: Plugin namespace to use when loading plugin entry_points. Defaults to ``hbmqtt.broker.plugins``

    """
    states = ['new', 'starting', 'started', 'not_started', 'stopping', 'stopped', 'not_stopped', 'stopped']

    def __init__(self, config=None, loop=None, plugin_namespace=None):
        self.logger = logging.getLogger(__name__)
        self.config = _defaults
        if config is not None:
            self.config.update(config)
        self._build_listeners_config(self.config)

        if loop is not None:
            self._loop = loop
        else:
            self._loop = asyncio.get_event_loop()

        self._servers = dict()
        self._init_states()
        self._sessions = dict()
        self._subscriptions = dict()
        self._retained_messages = dict()
        self._broadcast_queue = asyncio.Queue(loop=self._loop)

        self._broadcast_task = None

        # Init plugins manager
        context = BrokerContext(self)
        context.config = self.config
        if plugin_namespace:
            namespace = plugin_namespace
        else:
            namespace = 'hbmqtt.broker.plugins'
        self.plugins_manager = PluginManager(namespace, context, self._loop)

    def _build_listeners_config(self, broker_config):
        self.listeners_config = dict()
        try:
            listeners_config = broker_config['listeners']
            defaults = listeners_config['default']
            for listener in listeners_config:
                config = dict(defaults)
                config.update(listeners_config[listener])
                self.listeners_config[listener] = config
        except KeyError as ke:
            raise BrokerException("Listener config not found invalid: %s" % ke)

    def _init_states(self):
        self.transitions = Machine(states=Broker.states, initial='new')
        self.transitions.add_transition(trigger='start', source='new', dest='starting')
        self.transitions.add_transition(trigger='starting_fail', source='starting', dest='not_started')
        self.transitions.add_transition(trigger='starting_success', source='starting', dest='started')
        self.transitions.add_transition(trigger='shutdown', source='started', dest='stopping')
        self.transitions.add_transition(trigger='stopping_success', source='stopping', dest='stopped')
        self.transitions.add_transition(trigger='stopping_failure', source='stopping', dest='not_stopped')
        self.transitions.add_transition(trigger='start', source='stopped', dest='starting')

    @asyncio.coroutine
    def start(self):
        """
            Start the broker to serve with the given configuration

            Start method opens network sockets and will start listening for incoming connections.

            This method is a *coroutine*.
        """
        try:
            self._sessions = dict()
            self._subscriptions = dict()
            self._retained_messages = dict()
            self.transitions.start()
            self.logger.debug("Broker starting")
        except (MachineError, ValueError) as exc:
            # Backwards compat: MachineError is raised by transitions < 0.5.0.
            self.logger.warning("[WARN-0001] Invalid method call at this moment: %s" % exc)
            raise BrokerException("Broker instance can't be started: %s" % exc)

        yield from self.plugins_manager.fire_event(EVENT_BROKER_PRE_START)
        try:
            # Start network listeners
            for listener_name in self.listeners_config:
                listener = self.listeners_config[listener_name]

                if 'bind' not in listener:
                    self.logger.debug("Listener configuration '%s' is not bound" % listener_name)
                else:
                    # Max connections
                    try:
                        max_connections = listener['max_connections']
                    except KeyError:
                        max_connections = -1

                    # SSL Context
                    sc = None

                    # accept string "on" / "off" or boolean
                    ssl_active = listener.get('ssl', False)
                    if isinstance(ssl_active, str):
                        ssl_active = ssl_active.upper() == 'ON'

                    if ssl_active:
                        try:
                            sc = ssl.create_default_context(
                                ssl.Purpose.CLIENT_AUTH,
                                cafile=listener.get('cafile'),
                                capath=listener.get('capath'),
                                cadata=listener.get('cadata')
                            )
                            sc.load_cert_chain(listener['certfile'], listener['keyfile'])
                            sc.verify_mode = ssl.CERT_OPTIONAL
                        except KeyError as ke:
                            raise BrokerException("'certfile' or 'keyfile' configuration parameter missing: %s" % ke)
                        except FileNotFoundError as fnfe:
                            raise BrokerException("Can't read cert files '%s' or '%s' : %s" %
                                                  (listener['certfile'], listener['keyfile'], fnfe))

                    address, s_port = listener['bind'].split(':')
                    port = 0
                    try:
                        port = int(s_port)
                    except ValueError as ve:
                        raise BrokerException("Invalid port value in bind value: %s" % listener['bind'])

                    if listener['type'] == 'tcp':
                        cb_partial = partial(self.stream_connected, listener_name=listener_name)
                        instance = yield from asyncio.start_server(cb_partial,
                                                                   address,
                                                                   port,
                                                                   reuse_address=True,
                                                                   ssl=sc,
                                                                   loop=self._loop)
                        self._servers[listener_name] = Server(listener_name, instance, max_connections, self._loop)
                    elif listener['type'] == 'ws':
                        cb_partial = partial(self.ws_connected, listener_name=listener_name)
                        instance = yield from websockets.serve(cb_partial, address, port, ssl=sc, loop=self._loop,
                                                               subprotocols=['mqtt'])
                        self._servers[listener_name] = Server(listener_name, instance, max_connections, self._loop)

                    self.logger.info("Listener '%s' bind to %s (max_connections=%d)" %
                                     (listener_name, listener['bind'], max_connections))

            self.transitions.starting_success()
            yield from self.plugins_manager.fire_event(EVENT_BROKER_POST_START)

            #Start broadcast loop
            self._broadcast_task = asyncio.ensure_future(self._broadcast_loop(), loop=self._loop)

            self.logger.debug("Broker started")
        except Exception as e:
            self.logger.error("Broker startup failed: %s" % e)
            self.transitions.starting_fail()
            raise BrokerException("Broker instance can't be started: %s" % e)

    @asyncio.coroutine
    def shutdown(self):
        """
            Stop broker instance.

            Closes all connected session, stop listening on network socket and free resources.
        """
        try:
            self._sessions = dict()
            self._subscriptions = dict()
            self._retained_messages = dict()
            self.transitions.shutdown()
        except (MachineError, ValueError) as exc:
            # Backwards compat: MachineError is raised by transitions < 0.5.0.
            self.logger.debug("Invalid method call at this moment: %s" % exc)
            raise BrokerException("Broker instance can't be stopped: %s" % exc)

        # Fire broker_shutdown event to plugins
        yield from self.plugins_manager.fire_event(EVENT_BROKER_PRE_SHUTDOWN)

        # Stop broadcast loop
        if self._broadcast_task:
            self._broadcast_task.cancel()
        if self._broadcast_queue.qsize() > 0:
            self.logger.warning("%d messages not broadcasted" % self._broadcast_queue.qsize())

        for listener_name in self._servers:
            server = self._servers[listener_name]
            yield from server.close_instance()
        self.logger.debug("Broker closing")
        self.logger.info("Broker closed")
        yield from self.plugins_manager.fire_event(EVENT_BROKER_POST_SHUTDOWN)
        self.transitions.stopping_success()

    @asyncio.coroutine
    def internal_message_broadcast(self, topic, data, qos=None):
        return (yield from self._broadcast_message(None, topic, data))

    @asyncio.coroutine
    def ws_connected(self, websocket, uri, listener_name):
        yield from self.client_connected(listener_name, WebSocketsReader(websocket), WebSocketsWriter(websocket))

    @asyncio.coroutine
    def stream_connected(self, reader, writer, listener_name):
        yield from self.client_connected(listener_name, StreamReaderAdapter(reader), StreamWriterAdapter(writer))

    @asyncio.coroutine
    def client_connected(self, listener_name, reader: ReaderAdapter, writer: WriterAdapter):
        # Wait for connection available on listener
        server = self._servers.get(listener_name, None)
        if not server:
            raise BrokerException("Invalid listener name '%s'" % listener_name)
        yield from server.acquire_connection()

        remote_address, remote_port = writer.get_peer_info()
        self.logger.info("Connection from %s:%d on listener '%s'" % (remote_address, remote_port, listener_name))

        # Wait for first packet and expect a CONNECT
        try:
            handler, client_session = yield from BrokerProtocolHandler.init_from_connect(reader, writer, self.plugins_manager, loop=self._loop)
        except HBMQTTException as exc:
            self.logger.warning("[MQTT-3.1.0-1] %s: Can't read first packet an CONNECT: %s" %
                                (format_client_message(address=remote_address, port=remote_port), exc))
            #yield from writer.close()
            self.logger.debug("Connection closed")
            return
        except MQTTException as me:
            self.logger.error('Invalid connection from %s : %s' %
                              (format_client_message(address=remote_address, port=remote_port), me))
            yield from writer.close()
            self.logger.debug("Connection closed")
            return

        if client_session.clean_session:
            # Delete existing session and create a new one
            if client_session.client_id is not None and client_session.client_id != "":
                self.delete_session(client_session.client_id)
            else:
                client_session.client_id = gen_client_id()
            client_session.parent = 0
        else:
            # Get session from cache
            if client_session.client_id in self._sessions:
                self.logger.debug("Found old session %s" % repr(self._sessions[client_session.client_id]))
                (client_session, h) = self._sessions[client_session.client_id]
                client_session.parent = 1
            else:
                client_session.parent = 0
        if client_session.keep_alive > 0:
            client_session.keep_alive += self.config['timeout-disconnect-delay']
        self.logger.debug("Keep-alive timeout=%d" % client_session.keep_alive)

        handler.attach(client_session, reader, writer)
        self._sessions[client_session.client_id] = (client_session, handler)

        authenticated = yield from self.authenticate(client_session, self.listeners_config[listener_name])
        if not authenticated:
            yield from writer.close()
            server.release_connection()  # Delete client from connections list
            return

        while True:
            try:
                client_session.transitions.connect()
                break
            except (MachineError, ValueError):
                # Backwards compat: MachineError is raised by transitions < 0.5.0.
                self.logger.warning("Client %s is reconnecting too quickly, make it wait" % client_session.client_id)
                # Wait a bit may be client is reconnecting too fast
                yield from asyncio.sleep(1, loop=self._loop)
        yield from handler.mqtt_connack_authorize(authenticated)

        yield from self.plugins_manager.fire_event(EVENT_BROKER_CLIENT_CONNECTED, client_id=client_session.client_id)

        self.logger.debug("%s Start messages handling" % client_session.client_id)
        yield from handler.start()
        self.logger.debug("Retained messages queue size: %d" % client_session.retained_messages.qsize())
        yield from self.publish_session_retained_messages(client_session)

        # Init and start loop for handling client messages (publish, subscribe/unsubscribe, disconnect)
        disconnect_waiter = asyncio.ensure_future(handler.wait_disconnect(), loop=self._loop)
        subscribe_waiter = asyncio.ensure_future(handler.get_next_pending_subscription(), loop=self._loop)
        unsubscribe_waiter = asyncio.ensure_future(handler.get_next_pending_unsubscription(), loop=self._loop)
        wait_deliver = asyncio.ensure_future(handler.mqtt_deliver_next_message(), loop=self._loop)
        connected = True
        while connected:
            try:
                done, pending = yield from asyncio.wait(
                    [disconnect_waiter, subscribe_waiter, unsubscribe_waiter, wait_deliver],
                    return_when=asyncio.FIRST_COMPLETED, loop=self._loop)
                if disconnect_waiter in done:
                    result = disconnect_waiter.result()
                    self.logger.debug("%s Result from wait_diconnect: %s" % (client_session.client_id, result))
                    if result is None:
                        self.logger.debug("Will flag: %s" % client_session.will_flag)
                        # Connection closed anormally, send will message
                        if client_session.will_flag:
                            self.logger.debug("Client %s disconnected abnormally, sending will message" %
                                              format_client_message(client_session))
                            yield from self._broadcast_message(
                                client_session,
                                client_session.will_topic,
                                client_session.will_message,
                                client_session.will_qos)
                            if client_session.will_retain:
                                self.retain_message(client_session,
                                                    client_session.will_topic,
                                                    client_session.will_message,
                                                    client_session.will_qos)
                    self.logger.debug("%s Disconnecting session" % client_session.client_id)
                    yield from self._stop_handler(handler)
                    client_session.transitions.disconnect()
                    yield from self.plugins_manager.fire_event(EVENT_BROKER_CLIENT_DISCONNECTED, client_id=client_session.client_id)
                    connected = False
                if unsubscribe_waiter in done:
                    self.logger.debug("%s handling unsubscription" % client_session.client_id)
                    unsubscription = unsubscribe_waiter.result()
                    for topic in unsubscription['topics']:
                        self._del_subscription(topic, client_session)
                        yield from self.plugins_manager.fire_event(
                            EVENT_BROKER_CLIENT_UNSUBSCRIBED,
                            client_id=client_session.client_id,
                            topic=topic)
                    yield from handler.mqtt_acknowledge_unsubscription(unsubscription['packet_id'])
                    unsubscribe_waiter = asyncio.Task(handler.get_next_pending_unsubscription(), loop=self._loop)
                if subscribe_waiter in done:
                    self.logger.debug("%s handling subscription" % client_session.client_id)
                    subscriptions = subscribe_waiter.result()
                    return_codes = []
                    for subscription in subscriptions['topics']:
                        result = yield from self.add_subscription(subscription, client_session)
                        return_codes.append(result)
                    yield from handler.mqtt_acknowledge_subscription(subscriptions['packet_id'], return_codes)
                    for index, subscription in enumerate(subscriptions['topics']):
                        if return_codes[index] != 0x80:
                            yield from self.plugins_manager.fire_event(
                                EVENT_BROKER_CLIENT_SUBSCRIBED,
                                client_id=client_session.client_id,
                                topic=subscription[0],
                                qos=subscription[1])
                            yield from self.publish_retained_messages_for_subscription(subscription, client_session)
                    subscribe_waiter = asyncio.Task(handler.get_next_pending_subscription(), loop=self._loop)
                    self.logger.debug(repr(self._subscriptions))
                if wait_deliver in done:
                    if self.logger.isEnabledFor(logging.DEBUG):
                        self.logger.debug("%s handling message delivery" % client_session.client_id)
                    app_message = wait_deliver.result()
                    if not app_message.topic:
                        self.logger.warning("[MQTT-4.7.3-1] - %s invalid TOPIC sent in PUBLISH message, closing connection" % client_session.client_id)
                        break
                    if "#" in app_message.topic or "+" in app_message.topic:
                        self.logger.warning("[MQTT-3.3.2-2] - %s invalid TOPIC sent in PUBLISH message, closing connection" % client_session.client_id)
                        break
                    yield from self.plugins_manager.fire_event(EVENT_BROKER_MESSAGE_RECEIVED,
                                                               client_id=client_session.client_id,
                                                               message=app_message)
                    yield from self._broadcast_message_acl(client_session, app_message.topic, app_message.data)
                    if app_message.publish_packet.retain_flag:
                        self.retain_message(client_session, app_message.topic, app_message.data, app_message.qos)
                    wait_deliver = asyncio.Task(handler.mqtt_deliver_next_message(), loop=self._loop)
            except asyncio.CancelledError:
                self.logger.debug("Client loop cancelled")
                break
        disconnect_waiter.cancel()
        subscribe_waiter.cancel()
        unsubscribe_waiter.cancel()
        wait_deliver.cancel()

        self.logger.debug("%s Client disconnected" % client_session.client_id)
        server.release_connection()

    def _init_handler(self, session, reader, writer):
        """
        Create a BrokerProtocolHandler and attach to a session
        :return:
        """
        handler = BrokerProtocolHandler(self.plugins_manager, self._loop)
        handler.attach(session, reader, writer)
        return handler

    @asyncio.coroutine
    def _stop_handler(self, handler):
        """
        Stop a running handler and detach if from the session
        :param handler:
        :return:
        """
        try:
            yield from handler.stop()
        except Exception as e:
            self.logger.error(e)

    @asyncio.coroutine
    def authenticate(self, session: Session, listener):
        """
        This method call the authenticate method on registered plugins to test user authentication.
        User is considered authenticated if all plugins called returns True.
        Plugins authenticate() method are supposed to return :
         - True if user is authentication succeed
         - False if user authentication fails
         - None if authentication can't be achieved (then plugin result is then ignored)
        :param session:
        :param listener:
        :return:
        """
        auth_plugins = None
        auth_config = self.config.get('auth', None)
        if auth_config:
            auth_plugins = auth_config.get('plugins', None)
        returns = yield from self.plugins_manager.map_plugin_coro(
            "authenticate",
            session=session,
            filter_plugins=auth_plugins)
        auth_result = True
        if returns:
            for plugin in returns:
                res = returns[plugin]
                if res is False:
                    auth_result = False
                    self.logger.debug("Authentication failed due to '%s' plugin result: %s" % (plugin.name, res))
                else:
                    self.logger.debug("'%s' plugin result: %s" % (plugin.name, res))
        # If all plugins returned True, authentication is success
        return auth_result

    @asyncio.coroutine
    def topic_filtering(self, session: Session, topic):
        """
        This method call the topic_filtering method on registered plugins to check that the subscription is allowed.
        User is considered allowed if all plugins called return True.
        Plugins topic_filtering() method are supposed to return :
         - True if MQTT client can be subscribed to the topic
         - False if MQTT client is not allowed to subscribe to the topic
         - None if topic filtering can't be achieved (then plugin result is then ignored)
        :param session:
        :param listener:
        :param topic: Topic in which the client wants to subscribe
        :return:
        """
        topic_plugins = None
        topic_config = self.config.get('topic-check', None)
        if topic_config and topic_config.get('enabled', False):
            topic_plugins = topic_config.get('plugins', None)
        returns = yield from self.plugins_manager.map_plugin_coro(
            "topic_filtering",
            session=session,
            topic=topic,
            filter_plugins=topic_plugins)
        topic_result = True
        if returns:
            for plugin in returns:
                res = returns[plugin]
                if res is False:
                    topic_result = False
                    self.logger.debug("Topic filtering failed due to '%s' plugin result: %s" % (plugin.name, res))
                else:
                    self.logger.debug("'%s' plugin result: %s" % (plugin.name, res))
        # If all plugins returned True, authentication is success
        return topic_result

    def retain_message(self, source_session, topic_name, data, qos=None):
        if data is not None and data != b'':
            # If retained flag set, store the message for further subscriptions
            self.logger.debug("Retaining message on topic %s" % topic_name)
            retained_message = RetainedApplicationMessage(source_session, topic_name, data, qos)
            self._retained_messages[topic_name] = retained_message
        else:
            # [MQTT-3.3.1-10]
            if topic_name in self._retained_messages:
                self.logger.debug("Clear retained messages for topic '%s'" % topic_name)
                del self._retained_messages[topic_name]

    @asyncio.coroutine
    def add_subscription(self, subscription, session):
        try:
            a_filter = subscription[0]
            if '#' in a_filter and not a_filter.endswith('#'):
                # [MQTT-4.7.1-2] Wildcard character '#' is only allowed as last character in filter
                return 0x80
            if a_filter != "+":
                if '+' in a_filter:
                    if "/+" not in a_filter and "+/" not in a_filter:
                        # [MQTT-4.7.1-3] + wildcard character must occupy entire level
                        return 0x80
            # Check if the client is authorised to connect to the topic
            permitted = yield from self.topic_filtering(session, topic=a_filter)
            if not permitted:
                return 0x80
            qos = subscription[1]
            if 'max-qos' in self.config and qos > self.config['max-qos']:
                qos = self.config['max-qos']
            if a_filter not in self._subscriptions:
                self._subscriptions[a_filter] = []
            already_subscribed = next(
                (s for (s, qos) in self._subscriptions[a_filter] if s.client_id == session.client_id), None)
            if not already_subscribed:
                self._subscriptions[a_filter].append((session, qos))
            else:
                self.logger.debug("Client %s has already subscribed to %s" % (format_client_message(session=session), a_filter))
            return qos
        except KeyError:
            return 0x80

    def _del_subscription(self, a_filter, session):
        """
        Delete a session subscription on a given topic
        :param a_filter:
        :param session:
        :return:
        """
        deleted = 0
        try:
            subscriptions = self._subscriptions[a_filter]
            for index, (sub_session, qos) in enumerate(subscriptions):
                if sub_session.client_id == session.client_id:
                    self.logger.debug("Removing subscription on topic '%s' for client %s" %
                                      (a_filter, format_client_message(session=session)))
                    subscriptions.pop(index)
                    deleted += 1
                    break
        except KeyError:
            # Unsubscribe topic not found in current subscribed topics
            pass
        finally:
            return deleted

    def _del_all_subscriptions(self, session):
        """
        Delete all topic subscriptions for a given session
        :param session:
        :return:
        """
        filter_queue = deque()
        for topic in self._subscriptions:
            if self._del_subscription(topic, session):
                filter_queue.append(topic)
        for topic in filter_queue:
            if not self._subscriptions[topic]:
                del self._subscriptions[topic]

    def matches(self, topic, a_filter):
        if "#" not in a_filter and "+" not in a_filter:
            # if filter doesn't contain wildcard, return exact match
            return a_filter == topic
        else:
            # else use regex
            match_pattern = re.compile(a_filter.replace('#', '.*').replace('$', '\$').replace('+', '[/\$\s\w\d]+'))
            return match_pattern.match(topic)

    @asyncio.coroutine
    def _broadcast_loop(self):
        running_tasks = deque()
        try:
            while True:
                while running_tasks and running_tasks[0].done():
                    running_tasks.popleft()
                broadcast = yield from self._broadcast_queue.get()
                if self.logger.isEnabledFor(logging.DEBUG):
                    self.logger.debug("broadcasting %r" % broadcast)
                for k_filter in self._subscriptions:
                    if broadcast['topic'].startswith("$") and (k_filter.startswith("+") or k_filter.startswith("#")):
                        self.logger.debug("[MQTT-4.7.2-1] - ignoring brodcasting $ topic to subscriptions starting with + or #")
                    elif self.matches(broadcast['topic'], k_filter):
                        subscriptions = self._subscriptions[k_filter]
                        for (target_session, qos) in subscriptions:
                            if 'qos' in broadcast:
                                qos = broadcast['qos']
                            if target_session.transitions.state == 'connected':
                                self.logger.debug("broadcasting application message from %s on topic '%s' to %s" %
                                                  (format_client_message(session=broadcast['session']),
                                                   broadcast['topic'], format_client_message(session=target_session)))
                                handler = self._get_handler(target_session)
                                task = asyncio.ensure_future(
                                    handler.mqtt_publish(broadcast['topic'], broadcast['data'], qos, retain=False),
                                    loop=self._loop)
                                running_tasks.append(task)
                            else:
                                self.logger.debug("retaining application message from %s on topic '%s' to client '%s'" %
                                                  (format_client_message(session=broadcast['session']),
                                                   broadcast['topic'], format_client_message(session=target_session)))
                                retained_message = RetainedApplicationMessage(
                                    broadcast['session'], broadcast['topic'], broadcast['data'], qos)
                                yield from target_session.retained_messages.put(retained_message)
        except CancelledError:
            # Wait until current broadcasting tasks end
            if running_tasks:
                yield from asyncio.wait(running_tasks, loop=self._loop)

    @asyncio.coroutine
    def _broadcast_message_acl(self, session, topic, data, force_qos=None):
        permitted = yield from self.topic_filtering(session, topic=topic)

        if permitted:
            yield from self._broadcast_message(session, topic, data, force_qos)

    @asyncio.coroutine
    def _broadcast_message(self, session, topic, data, force_qos=None):
        broadcast = {
            'session': session,
            'topic': topic,
            'data': data
        }
        if force_qos:
            broadcast['qos'] = force_qos
        yield from self._broadcast_queue.put(broadcast)

    @asyncio.coroutine
    def publish_session_retained_messages(self, session):
        self.logger.debug("Publishing %d messages retained for session %s" %
                          (session.retained_messages.qsize(), format_client_message(session=session))
                          )
        publish_tasks = []
        handler = self._get_handler(session)
        while not session.retained_messages.empty():
            retained = yield from session.retained_messages.get()
            publish_tasks.append(asyncio.ensure_future(
                handler.mqtt_publish(
                    retained.topic, retained.data, retained.qos, True), loop=self._loop))
        if publish_tasks:
            yield from asyncio.wait(publish_tasks, loop=self._loop)

    @asyncio.coroutine
    def publish_retained_messages_for_subscription(self, subscription, session):
        self.logger.debug("Begin broadcasting messages retained due to subscription on '%s' from %s" %
                          (subscription[0], format_client_message(session=session)))
        publish_tasks = []
        handler = self._get_handler(session)
        for d_topic in self._retained_messages:
            self.logger.debug("matching : %s %s" % (d_topic, subscription[0]))
            if self.matches(d_topic, subscription[0]):
                self.logger.debug("%s and %s match" % (d_topic, subscription[0]))
                retained = self._retained_messages[d_topic]
                publish_tasks.append(asyncio.Task(
                    handler.mqtt_publish(
                        retained.topic, retained.data, subscription[1], True), loop=self._loop))
        if publish_tasks:
            yield from asyncio.wait(publish_tasks, loop=self._loop)
        self.logger.debug("End broadcasting messages retained due to subscription on '%s' from %s" %
                          (subscription[0], format_client_message(session=session)))

    def delete_session(self, client_id):
        """
        Delete an existing session data, for example due to clean session set in CONNECT
        :param client_id:
        :return:
        """
        try:
            session = self._sessions[client_id][0]
        except KeyError:
            session = None
        if session is None:
            self.logger.debug("Delete session : session %s doesn't exist" % client_id)
            return

        # Delete subscriptions
        self.logger.debug("deleting session %s subscriptions" % repr(session))
        self._del_all_subscriptions(session)

        self.logger.debug("deleting existing session %s" % repr(self._sessions[client_id]))
        del self._sessions[client_id]

    def _get_handler(self, session):
        client_id = session.client_id
        if client_id:
            try:
                return self._sessions[client_id][1]
            except KeyError:
                pass
        return None