core/homeassistant/components/mqtt/__init__.py

"""
Support for MQTT message handling.

For more details about this component, please refer to the documentation at
https://home-assistant.io/components/mqtt/
"""
import asyncio
from itertools import groupby
import logging
from operator import attrgetter
import os
import socket
import ssl
import time
from typing import Any, Callable, List, Optional, Union, cast  # noqa: F401

import attr
import requests.certs
import voluptuous as vol

from homeassistant import config_entries
from homeassistant.const import (
    CONF_PASSWORD, CONF_PAYLOAD, CONF_PORT, CONF_PROTOCOL, CONF_USERNAME,
    CONF_VALUE_TEMPLATE, EVENT_HOMEASSISTANT_STOP)
from homeassistant.core import Event, ServiceCall, callback
from homeassistant.exceptions import HomeAssistantError
from homeassistant.helpers import config_validation as cv
from homeassistant.helpers import template
from homeassistant.helpers.entity import Entity
from homeassistant.helpers.typing import (
    ConfigType, HomeAssistantType, ServiceDataType)
from homeassistant.loader import bind_hass
from homeassistant.setup import async_prepare_setup_platform
from homeassistant.util.async_ import (
    run_callback_threadsafe, run_coroutine_threadsafe)

# Loading the config flow file will register the flow
from . import config_flow  # noqa  # pylint: disable=unused-import
from .const import CONF_BROKER, CONF_DISCOVERY, DEFAULT_DISCOVERY
from .server import HBMQTT_CONFIG_SCHEMA

REQUIREMENTS = ['paho-mqtt==1.4.0']

_LOGGER = logging.getLogger(__name__)

DOMAIN = 'mqtt'

DATA_MQTT = 'mqtt'
DATA_MQTT_CONFIG = 'mqtt_config'
DATA_MQTT_HASS_CONFIG = 'mqtt_hass_config'

SERVICE_PUBLISH = 'publish'

CONF_EMBEDDED = 'embedded'

CONF_CLIENT_ID = 'client_id'
CONF_DISCOVERY_PREFIX = 'discovery_prefix'
CONF_KEEPALIVE = 'keepalive'
CONF_CERTIFICATE = 'certificate'
CONF_CLIENT_KEY = 'client_key'
CONF_CLIENT_CERT = 'client_cert'
CONF_TLS_INSECURE = 'tls_insecure'
CONF_TLS_VERSION = 'tls_version'

CONF_BIRTH_MESSAGE = 'birth_message'
CONF_WILL_MESSAGE = 'will_message'

CONF_STATE_TOPIC = 'state_topic'
CONF_COMMAND_TOPIC = 'command_topic'
CONF_AVAILABILITY_TOPIC = 'availability_topic'
CONF_PAYLOAD_AVAILABLE = 'payload_available'
CONF_PAYLOAD_NOT_AVAILABLE = 'payload_not_available'
CONF_QOS = 'qos'
CONF_RETAIN = 'retain'

PROTOCOL_31 = '3.1'
PROTOCOL_311 = '3.1.1'

DEFAULT_PORT = 1883
DEFAULT_KEEPALIVE = 60
DEFAULT_QOS = 0
DEFAULT_RETAIN = False
DEFAULT_PROTOCOL = PROTOCOL_311
DEFAULT_DISCOVERY_PREFIX = 'homeassistant'
DEFAULT_TLS_PROTOCOL = 'auto'
DEFAULT_PAYLOAD_AVAILABLE = 'online'
DEFAULT_PAYLOAD_NOT_AVAILABLE = 'offline'

ATTR_TOPIC = 'topic'
ATTR_PAYLOAD = 'payload'
ATTR_PAYLOAD_TEMPLATE = 'payload_template'
ATTR_QOS = CONF_QOS
ATTR_RETAIN = CONF_RETAIN
ATTR_DISCOVERY_HASH = 'discovery_hash'

MAX_RECONNECT_WAIT = 300  # seconds


def valid_topic(value: Any) -> str:
    """Validate that this is a valid topic name/filter."""
    value = cv.string(value)
    try:
        raw_value = value.encode('utf-8')
    except UnicodeError:
        raise vol.Invalid("MQTT topic name/filter must be valid UTF-8 string.")
    if not raw_value:
        raise vol.Invalid("MQTT topic name/filter must not be empty.")
    if len(raw_value) > 65535:
        raise vol.Invalid("MQTT topic name/filter must not be longer than "
                          "65535 encoded bytes.")
    if '\0' in value:
        raise vol.Invalid("MQTT topic name/filter must not contain null "
                          "character.")
    return value


def valid_subscribe_topic(value: Any) -> str:
    """Validate that we can subscribe using this MQTT topic."""
    value = valid_topic(value)
    for i in (i for i, c in enumerate(value) if c == '+'):
        if (i > 0 and value[i - 1] != '/') or \
                (i < len(value) - 1 and value[i + 1] != '/'):
            raise vol.Invalid("Single-level wildcard must occupy an entire "
                              "level of the filter")

    index = value.find('#')
    if index != -1:
        if index != len(value) - 1:
            # If there are multiple wildcards, this will also trigger
            raise vol.Invalid("Multi-level wildcard must be the last "
                              "character in the topic filter.")
        if len(value) > 1 and value[index - 1] != '/':
            raise vol.Invalid("Multi-level wildcard must be after a topic "
                              "level separator.")

    return value


def valid_publish_topic(value: Any) -> str:
    """Validate that we can publish using this MQTT topic."""
    value = valid_topic(value)
    if '+' in value or '#' in value:
        raise vol.Invalid("Wildcards can not be used in topic names")
    return value


_VALID_QOS_SCHEMA = vol.All(vol.Coerce(int), vol.In([0, 1, 2]))

CLIENT_KEY_AUTH_MSG = 'client_key and client_cert must both be present in ' \
                      'the MQTT broker configuration'

MQTT_WILL_BIRTH_SCHEMA = vol.Schema({
    vol.Required(ATTR_TOPIC): valid_publish_topic,
    vol.Required(ATTR_PAYLOAD, CONF_PAYLOAD): cv.string,
    vol.Optional(ATTR_QOS, default=DEFAULT_QOS): _VALID_QOS_SCHEMA,
    vol.Optional(ATTR_RETAIN, default=DEFAULT_RETAIN): cv.boolean,
}, required=True)

CONFIG_SCHEMA = vol.Schema({
    DOMAIN: vol.Schema({
        vol.Optional(CONF_CLIENT_ID): cv.string,
        vol.Optional(CONF_KEEPALIVE, default=DEFAULT_KEEPALIVE):
            vol.All(vol.Coerce(int), vol.Range(min=15)),
        vol.Optional(CONF_BROKER): cv.string,
        vol.Optional(CONF_PORT, default=DEFAULT_PORT): cv.port,
        vol.Optional(CONF_USERNAME): cv.string,
        vol.Optional(CONF_PASSWORD): cv.string,
        vol.Optional(CONF_CERTIFICATE): vol.Any('auto', cv.isfile),
        vol.Inclusive(CONF_CLIENT_KEY, 'client_key_auth',
                      msg=CLIENT_KEY_AUTH_MSG): cv.isfile,
        vol.Inclusive(CONF_CLIENT_CERT, 'client_key_auth',
                      msg=CLIENT_KEY_AUTH_MSG): cv.isfile,
        vol.Optional(CONF_TLS_INSECURE): cv.boolean,
        vol.Optional(CONF_TLS_VERSION, default=DEFAULT_TLS_PROTOCOL):
            vol.Any('auto', '1.0', '1.1', '1.2'),
        vol.Optional(CONF_PROTOCOL, default=DEFAULT_PROTOCOL):
            vol.All(cv.string, vol.In([PROTOCOL_31, PROTOCOL_311])),
        vol.Optional(CONF_EMBEDDED): HBMQTT_CONFIG_SCHEMA,
        vol.Optional(CONF_WILL_MESSAGE): MQTT_WILL_BIRTH_SCHEMA,
        vol.Optional(CONF_BIRTH_MESSAGE): MQTT_WILL_BIRTH_SCHEMA,
        vol.Optional(CONF_DISCOVERY, default=DEFAULT_DISCOVERY): cv.boolean,
        # discovery_prefix must be a valid publish topic because if no
        # state topic is specified, it will be created with the given prefix.
        vol.Optional(CONF_DISCOVERY_PREFIX,
                     default=DEFAULT_DISCOVERY_PREFIX): valid_publish_topic,
    }),
}, extra=vol.ALLOW_EXTRA)

SCHEMA_BASE = {
    vol.Optional(CONF_QOS, default=DEFAULT_QOS): _VALID_QOS_SCHEMA,
}

MQTT_AVAILABILITY_SCHEMA = vol.Schema({
    vol.Optional(CONF_AVAILABILITY_TOPIC): valid_subscribe_topic,
    vol.Optional(CONF_PAYLOAD_AVAILABLE,
                 default=DEFAULT_PAYLOAD_AVAILABLE): cv.string,
    vol.Optional(CONF_PAYLOAD_NOT_AVAILABLE,
                 default=DEFAULT_PAYLOAD_NOT_AVAILABLE): cv.string,
})

MQTT_BASE_PLATFORM_SCHEMA = cv.PLATFORM_SCHEMA.extend(SCHEMA_BASE)

# Sensor type platforms subscribe to MQTT events
MQTT_RO_PLATFORM_SCHEMA = MQTT_BASE_PLATFORM_SCHEMA.extend({
    vol.Required(CONF_STATE_TOPIC): valid_subscribe_topic,
    vol.Optional(CONF_VALUE_TEMPLATE): cv.template,
})

# Switch type platforms publish to MQTT and may subscribe
MQTT_RW_PLATFORM_SCHEMA = MQTT_BASE_PLATFORM_SCHEMA.extend({
    vol.Required(CONF_COMMAND_TOPIC): valid_publish_topic,
    vol.Optional(CONF_RETAIN, default=DEFAULT_RETAIN): cv.boolean,
    vol.Optional(CONF_STATE_TOPIC): valid_subscribe_topic,
    vol.Optional(CONF_VALUE_TEMPLATE): cv.template,
})

# Service call validation schema
MQTT_PUBLISH_SCHEMA = vol.Schema({
    vol.Required(ATTR_TOPIC): valid_publish_topic,
    vol.Exclusive(ATTR_PAYLOAD, CONF_PAYLOAD): object,
    vol.Exclusive(ATTR_PAYLOAD_TEMPLATE, CONF_PAYLOAD): cv.string,
    vol.Optional(ATTR_QOS, default=DEFAULT_QOS): _VALID_QOS_SCHEMA,
    vol.Optional(ATTR_RETAIN, default=DEFAULT_RETAIN): cv.boolean,
}, required=True)


# pylint: disable=invalid-name
PublishPayloadType = Union[str, bytes, int, float, None]
SubscribePayloadType = Union[str, bytes]  # Only bytes if encoding is None
MessageCallbackType = Callable[[str, SubscribePayloadType, int], None]


def _build_publish_data(topic: Any, qos: int, retain: bool) -> ServiceDataType:
    """Build the arguments for the publish service without the payload."""
    data = {ATTR_TOPIC: topic}
    if qos is not None:
        data[ATTR_QOS] = qos
    if retain is not None:
        data[ATTR_RETAIN] = retain
    return data


@bind_hass
def publish(hass: HomeAssistantType, topic, payload, qos=None,
            retain=None) -> None:
    """Publish message to an MQTT topic."""
    hass.add_job(async_publish, hass, topic, payload, qos, retain)


@callback
@bind_hass
def async_publish(hass: HomeAssistantType, topic: Any, payload, qos=None,
                  retain=None) -> None:
    """Publish message to an MQTT topic."""
    data = _build_publish_data(topic, qos, retain)
    data[ATTR_PAYLOAD] = payload
    hass.async_add_job(hass.services.async_call(DOMAIN, SERVICE_PUBLISH, data))


@bind_hass
def publish_template(hass: HomeAssistantType, topic, payload_template,
                     qos=None, retain=None) -> None:
    """Publish message to an MQTT topic using a template payload."""
    data = _build_publish_data(topic, qos, retain)
    data[ATTR_PAYLOAD_TEMPLATE] = payload_template
    hass.services.call(DOMAIN, SERVICE_PUBLISH, data)


@bind_hass
async def async_subscribe(hass: HomeAssistantType, topic: str,
                          msg_callback: MessageCallbackType,
                          qos: int = DEFAULT_QOS,
                          encoding: str = 'utf-8'):
    """Subscribe to an MQTT topic.

    Call the return value to unsubscribe.
    """
    async_remove = await hass.data[DATA_MQTT].async_subscribe(
        topic, msg_callback, qos, encoding)
    return async_remove


@bind_hass
def subscribe(hass: HomeAssistantType, topic: str,
              msg_callback: MessageCallbackType, qos: int = DEFAULT_QOS,
              encoding: str = 'utf-8') -> Callable[[], None]:
    """Subscribe to an MQTT topic."""
    async_remove = run_coroutine_threadsafe(
        async_subscribe(hass, topic, msg_callback, qos, encoding), hass.loop
    ).result()

    def remove():
        """Remove listener convert."""
        run_callback_threadsafe(hass.loop, async_remove).result()

    return remove


async def _async_setup_server(hass: HomeAssistantType, config: ConfigType):
    """Try to start embedded MQTT broker.

    This method is a coroutine.
    """
    conf = config.get(DOMAIN, {})  # type: ConfigType

    server = await async_prepare_setup_platform(
        hass, config, DOMAIN, 'server')

    if server is None:
        _LOGGER.error("Unable to load embedded server")
        return None

    success, broker_config = \
        await server.async_start(
            hass, conf.get(CONF_PASSWORD), conf.get(CONF_EMBEDDED))

    if not success:
        return None

    return broker_config


async def _async_setup_discovery(hass: HomeAssistantType, conf: ConfigType,
                                 hass_config: ConfigType,
                                 config_entry) -> bool:
    """Try to start the discovery of MQTT devices.

    This method is a coroutine.
    """
    discovery = await async_prepare_setup_platform(
        hass, hass_config, DOMAIN, 'discovery')

    if discovery is None:
        _LOGGER.error("Unable to load MQTT discovery")
        return False

    success = await discovery.async_start(
        hass, conf[CONF_DISCOVERY_PREFIX], hass_config,
        config_entry)  # type: bool

    return success


async def async_setup(hass: HomeAssistantType, config: ConfigType) -> bool:
    """Start the MQTT protocol service."""
    conf = config.get(DOMAIN)  # type: Optional[ConfigType]

    # We need this because discovery can cause components to be set up and
    # otherwise it will not load the users config.
    # This needs a better solution.
    hass.data[DATA_MQTT_HASS_CONFIG] = config

    if conf is None:
        # If we have a config entry, setup is done by that config entry.
        # If there is no config entry, this should fail.
        return bool(hass.config_entries.async_entries(DOMAIN))

    conf = dict(conf)

    if CONF_EMBEDDED in conf or CONF_BROKER not in conf:
        if (conf.get(CONF_PASSWORD) is None and
                config.get('http', {}).get('api_password') is not None):
            _LOGGER.error(
                "Starting from release 0.76, the embedded MQTT broker does not"
                " use api_password as default password anymore. Please set"
                " password configuration. See https://home-assistant.io/docs/"
                "mqtt/broker#embedded-broker for details")
            return False

        broker_config = await _async_setup_server(hass, config)

        if broker_config is None:
            _LOGGER.error("Unable to start embedded MQTT broker")
            return False

        conf.update({
            CONF_BROKER: broker_config[0],
            CONF_PORT: broker_config[1],
            CONF_USERNAME: broker_config[2],
            CONF_PASSWORD: broker_config[3],
            CONF_CERTIFICATE: broker_config[4],
            CONF_PROTOCOL: broker_config[5],
            CONF_CLIENT_KEY: None,
            CONF_CLIENT_CERT: None,
            CONF_TLS_INSECURE: None,
        })

    hass.data[DATA_MQTT_CONFIG] = conf

    # Only import if we haven't before.
    if not hass.config_entries.async_entries(DOMAIN):
        hass.async_create_task(hass.config_entries.flow.async_init(
            DOMAIN, context={'source': config_entries.SOURCE_IMPORT},
            data={}
        ))

    return True


async def async_setup_entry(hass, entry):
    """Load a config entry."""
    conf = hass.data.get(DATA_MQTT_CONFIG)

    # Config entry was created because user had configuration.yaml entry
    # They removed that, so remove entry.
    if conf is None and entry.source == config_entries.SOURCE_IMPORT:
        hass.async_create_task(
            hass.config_entries.async_remove(entry.entry_id))
        return False

    # If user didn't have configuration.yaml config, generate defaults
    if conf is None:
        conf = CONFIG_SCHEMA({
            DOMAIN: entry.data
        })[DOMAIN]
    elif any(key in conf for key in entry.data):
        _LOGGER.warning(
            "Data in your config entry is going to override your "
            "configuration.yaml: %s", entry.data)

    conf.update(entry.data)

    broker = conf[CONF_BROKER]
    port = conf[CONF_PORT]
    client_id = conf.get(CONF_CLIENT_ID)
    keepalive = conf[CONF_KEEPALIVE]
    username = conf.get(CONF_USERNAME)
    password = conf.get(CONF_PASSWORD)
    client_key = conf.get(CONF_CLIENT_KEY)
    client_cert = conf.get(CONF_CLIENT_CERT)
    tls_insecure = conf.get(CONF_TLS_INSECURE)
    protocol = conf[CONF_PROTOCOL]

    # For cloudmqtt.com, secured connection, auto fill in certificate
    if (conf.get(CONF_CERTIFICATE) is None and
            19999 < conf[CONF_PORT] < 30000 and
            conf[CONF_BROKER].endswith('.cloudmqtt.com')):
        certificate = os.path.join(
            os.path.dirname(__file__), 'addtrustexternalcaroot.crt')

    # When the certificate is set to auto, use bundled certs from requests
    elif conf.get(CONF_CERTIFICATE) == 'auto':
        certificate = requests.certs.where()

    else:
        certificate = None

    if CONF_WILL_MESSAGE in conf:
        will_message = Message(**conf[CONF_WILL_MESSAGE])
    else:
        will_message = None

    if CONF_BIRTH_MESSAGE in conf:
        birth_message = Message(**conf[CONF_BIRTH_MESSAGE])
    else:
        birth_message = None

    # Be able to override versions other than TLSv1.0 under Python3.6
    conf_tls_version = conf.get(CONF_TLS_VERSION)  # type: str
    if conf_tls_version == '1.2':
        tls_version = ssl.PROTOCOL_TLSv1_2
    elif conf_tls_version == '1.1':
        tls_version = ssl.PROTOCOL_TLSv1_1
    elif conf_tls_version == '1.0':
        tls_version = ssl.PROTOCOL_TLSv1
    else:
        import sys
        # Python3.6 supports automatic negotiation of highest TLS version
        if sys.hexversion >= 0x03060000:
            tls_version = ssl.PROTOCOL_TLS  # pylint: disable=no-member
        else:
            tls_version = ssl.PROTOCOL_TLSv1

    hass.data[DATA_MQTT] = MQTT(
        hass,
        broker=broker,
        port=port,
        client_id=client_id,
        keepalive=keepalive,
        username=username,
        password=password,
        certificate=certificate,
        client_key=client_key,
        client_cert=client_cert,
        tls_insecure=tls_insecure,
        protocol=protocol,
        will_message=will_message,
        birth_message=birth_message,
        tls_version=tls_version,
    )

    success = await hass.data[DATA_MQTT].async_connect()  # type: bool

    if not success:
        return False

    async def async_stop_mqtt(event: Event):
        """Stop MQTT component."""
        await hass.data[DATA_MQTT].async_disconnect()

    hass.bus.async_listen_once(EVENT_HOMEASSISTANT_STOP, async_stop_mqtt)

    async def async_publish_service(call: ServiceCall):
        """Handle MQTT publish service calls."""
        msg_topic = call.data[ATTR_TOPIC]  # type: str
        payload = call.data.get(ATTR_PAYLOAD)
        payload_template = call.data.get(ATTR_PAYLOAD_TEMPLATE)
        qos = call.data[ATTR_QOS]  # type: int
        retain = call.data[ATTR_RETAIN]  # type: bool
        if payload_template is not None:
            try:
                payload = \
                    template.Template(payload_template, hass).async_render()
            except template.jinja2.TemplateError as exc:
                _LOGGER.error(
                    "Unable to publish to %s: rendering payload template of "
                    "%s failed because %s",
                    msg_topic, payload_template, exc)
                return

        await hass.data[DATA_MQTT].async_publish(
            msg_topic, payload, qos, retain)

    hass.services.async_register(
        DOMAIN, SERVICE_PUBLISH, async_publish_service,
        schema=MQTT_PUBLISH_SCHEMA)

    if conf.get(CONF_DISCOVERY):
        await _async_setup_discovery(
            hass, conf, hass.data[DATA_MQTT_HASS_CONFIG], entry)

    return True


@attr.s(slots=True, frozen=True)
class Subscription:
    """Class to hold data about an active subscription."""

    topic = attr.ib(type=str)
    callback = attr.ib(type=MessageCallbackType)
    qos = attr.ib(type=int, default=0)
    encoding = attr.ib(type=str, default='utf-8')


@attr.s(slots=True, frozen=True)
class Message:
    """MQTT Message."""

    topic = attr.ib(type=str)
    payload = attr.ib(type=PublishPayloadType)
    qos = attr.ib(type=int, default=0)
    retain = attr.ib(type=bool, default=False)


class MQTT:
    """Home Assistant MQTT client."""

    def __init__(self, hass: HomeAssistantType, broker: str, port: int,
                 client_id: Optional[str], keepalive: Optional[int],
                 username: Optional[str], password: Optional[str],
                 certificate: Optional[str], client_key: Optional[str],
                 client_cert: Optional[str], tls_insecure: Optional[bool],
                 protocol: Optional[str], will_message: Optional[Message],
                 birth_message: Optional[Message],
                 tls_version: Optional[int]) -> None:
        """Initialize Home Assistant MQTT client."""
        import paho.mqtt.client as mqtt

        self.hass = hass
        self.broker = broker
        self.port = port
        self.keepalive = keepalive
        self.subscriptions = []  # type: List[Subscription]
        self.birth_message = birth_message
        self._mqttc = None  # type: mqtt.Client
        self._paho_lock = asyncio.Lock(loop=hass.loop)

        if protocol == PROTOCOL_31:
            proto = mqtt.MQTTv31  # type: int
        else:
            proto = mqtt.MQTTv311

        if client_id is None:
            self._mqttc = mqtt.Client(protocol=proto)
        else:
            self._mqttc = mqtt.Client(client_id, protocol=proto)

        if username is not None:
            self._mqttc.username_pw_set(username, password)

        if certificate is not None:
            self._mqttc.tls_set(
                certificate, certfile=client_cert,
                keyfile=client_key, tls_version=tls_version)

            if tls_insecure is not None:
                self._mqttc.tls_insecure_set(tls_insecure)

        self._mqttc.on_connect = self._mqtt_on_connect
        self._mqttc.on_disconnect = self._mqtt_on_disconnect
        self._mqttc.on_message = self._mqtt_on_message

        if will_message is not None:
            self._mqttc.will_set(*attr.astuple(will_message))

    async def async_publish(self, topic: str, payload: PublishPayloadType,
                            qos: int, retain: bool) -> None:
        """Publish a MQTT message.

        This method must be run in the event loop and returns a coroutine.
        """
        async with self._paho_lock:
            _LOGGER.debug("Transmitting message on %s: %s", topic, payload)
            await self.hass.async_add_job(
                self._mqttc.publish, topic, payload, qos, retain)

    async def async_connect(self) -> bool:
        """Connect to the host. Does process messages yet.

        This method is a coroutine.
        """
        result = None  # type: int
        try:
            result = await self.hass.async_add_job(
                self._mqttc.connect, self.broker, self.port, self.keepalive)
        except OSError as err:
            _LOGGER.error("Failed to connect due to exception: %s", err)
            return False

        if result != 0:
            import paho.mqtt.client as mqtt
            _LOGGER.error("Failed to connect: %s", mqtt.error_string(result))
            return False

        self._mqttc.loop_start()
        return True

    @callback
    def async_disconnect(self):
        """Stop the MQTT client.

        This method must be run in the event loop and returns a coroutine.
        """
        def stop():
            """Stop the MQTT client."""
            self._mqttc.disconnect()
            self._mqttc.loop_stop()

        return self.hass.async_add_job(stop)

    async def async_subscribe(self, topic: str,
                              msg_callback: MessageCallbackType,
                              qos: int, encoding: str) -> Callable[[], None]:
        """Set up a subscription to a topic with the provided qos.

        This method is a coroutine.
        """
        if not isinstance(topic, str):
            raise HomeAssistantError("Topic needs to be a string!")

        subscription = Subscription(topic, msg_callback, qos, encoding)
        self.subscriptions.append(subscription)

        await self._async_perform_subscription(topic, qos)

        @callback
        def async_remove() -> None:
            """Remove subscription."""
            if subscription not in self.subscriptions:
                raise HomeAssistantError("Can't remove subscription twice")
            self.subscriptions.remove(subscription)

            if any(other.topic == topic for other in self.subscriptions):
                # Other subscriptions on topic remaining - don't unsubscribe.
                return
            self.hass.async_add_job(self._async_unsubscribe(topic))

        return async_remove

    async def _async_unsubscribe(self, topic: str) -> None:
        """Unsubscribe from a topic.

        This method is a coroutine.
        """
        async with self._paho_lock:
            result = None  # type: int
            result, _ = await self.hass.async_add_job(
                self._mqttc.unsubscribe, topic)
            _raise_on_error(result)

    async def _async_perform_subscription(self, topic: str, qos: int) -> None:
        """Perform a paho-mqtt subscription."""
        _LOGGER.debug("Subscribing to %s", topic)

        async with self._paho_lock:
            result = None  # type: int
            result, _ = await self.hass.async_add_job(
                self._mqttc.subscribe, topic, qos)
            _raise_on_error(result)

    def _mqtt_on_connect(
            self, _mqttc, _userdata, _flags, result_code: int) -> None:
        """On connect callback.

        Resubscribe to all topics we were subscribed to and publish birth
        message.
        """
        import paho.mqtt.client as mqtt

        if result_code != mqtt.CONNACK_ACCEPTED:
            _LOGGER.error("Unable to connect to the MQTT broker: %s",
                          mqtt.connack_string(result_code))
            self._mqttc.disconnect()
            return

        # Group subscriptions to only re-subscribe once for each topic.
        keyfunc = attrgetter('topic')
        for topic, subs in groupby(sorted(self.subscriptions, key=keyfunc),
                                   keyfunc):
            # Re-subscribe with the highest requested qos
            max_qos = max(subscription.qos for subscription in subs)
            self.hass.add_job(self._async_perform_subscription, topic, max_qos)

        if self.birth_message:
            self.hass.add_job(
                self.async_publish(*attr.astuple(self.birth_message)))

    def _mqtt_on_message(self, _mqttc, _userdata, msg) -> None:
        """Message received callback."""
        self.hass.add_job(self._mqtt_handle_message, msg)

    @callback
    def _mqtt_handle_message(self, msg) -> None:
        _LOGGER.debug("Received message on %s: %s", msg.topic, msg.payload)

        for subscription in self.subscriptions:
            if not _match_topic(subscription.topic, msg.topic):
                continue

            payload = msg.payload  # type: SubscribePayloadType
            if subscription.encoding is not None:
                try:
                    payload = msg.payload.decode(subscription.encoding)
                except (AttributeError, UnicodeDecodeError):
                    _LOGGER.warning(
                        "Can't decode payload %s on %s with encoding %s",
                        msg.payload, msg.topic, subscription.encoding)
                    continue

            self.hass.async_run_job(
                subscription.callback, msg.topic, payload, msg.qos)

    def _mqtt_on_disconnect(self, _mqttc, _userdata, result_code: int) -> None:
        """Disconnected callback."""
        # When disconnected because of calling disconnect()
        if result_code == 0:
            return

        tries = 0

        while True:
            try:
                if self._mqttc.reconnect() == 0:
                    _LOGGER.info("Successfully reconnected to the MQTT server")
                    break
            except socket.error:
                pass

            wait_time = min(2**tries, MAX_RECONNECT_WAIT)
            _LOGGER.warning(
                "Disconnected from MQTT (%s). Trying to reconnect in %s s",
                result_code, wait_time)
            # It is ok to sleep here as we are in the MQTT thread.
            time.sleep(wait_time)
            tries += 1


def _raise_on_error(result_code: int) -> None:
    """Raise error if error result."""
    if result_code != 0:
        import paho.mqtt.client as mqtt

        raise HomeAssistantError(
            'Error talking to MQTT: {}'.format(mqtt.error_string(result_code)))


def _match_topic(subscription: str, topic: str) -> bool:
    """Test if topic matches subscription."""
    from paho.mqtt.matcher import MQTTMatcher
    matcher = MQTTMatcher()
    matcher[subscription] = True
    try:
        next(matcher.iter_match(topic))
        return True
    except StopIteration:
        return False


class MqttAvailability(Entity):
    """Mixin used for platforms that report availability."""

    def __init__(self, availability_topic: Optional[str], qos: Optional[int],
                 payload_available: Optional[str],
                 payload_not_available: Optional[str]) -> None:
        """Initialize the availability mixin."""
        self._availability_topic = availability_topic
        self._availability_qos = qos
        self._available = availability_topic is None  # type: bool
        self._payload_available = payload_available
        self._payload_not_available = payload_not_available

    async def async_added_to_hass(self) -> None:
        """Subscribe MQTT events.

        This method must be run in the event loop and returns a coroutine.
        """
        @callback
        def availability_message_received(topic: str,
                                          payload: SubscribePayloadType,
                                          qos: int) -> None:
            """Handle a new received MQTT availability message."""
            if payload == self._payload_available:
                self._available = True
            elif payload == self._payload_not_available:
                self._available = False

            self.async_schedule_update_ha_state()

        if self._availability_topic is not None:
            await async_subscribe(
                self.hass, self._availability_topic,
                availability_message_received, self._availability_qos)

    @property
    def available(self) -> bool:
        """Return if the device is available."""
        return self._available


class MqttDiscoveryUpdate(Entity):
    """Mixin used to handle updated discovery message."""

    def __init__(self, discovery_hash) -> None:
        """Initialize the discovery update mixin."""
        self._discovery_hash = discovery_hash
        self._remove_signal = None

    async def async_added_to_hass(self) -> None:
        """Subscribe to discovery updates."""
        from homeassistant.helpers.dispatcher import async_dispatcher_connect
        from homeassistant.components.mqtt.discovery import (
            ALREADY_DISCOVERED, MQTT_DISCOVERY_UPDATED)

        @callback
        def discovery_callback(payload):
            """Handle discovery update."""
            _LOGGER.info("Got update for entity with hash: %s '%s'",
                         self._discovery_hash, payload)
            if not payload:
                # Empty payload: Remove component
                _LOGGER.info("Removing component: %s", self.entity_id)
                self.hass.async_create_task(self.async_remove())
                del self.hass.data[ALREADY_DISCOVERED][self._discovery_hash]
                self._remove_signal()

        if self._discovery_hash:
            self._remove_signal = async_dispatcher_connect(
                self.hass,
                MQTT_DISCOVERY_UPDATED.format(self._discovery_hash),
                discovery_callback)