Improved the MQTT event broker

* Connection success, failure and disconnection events are now logged
* The client parameter is now optional

2 files changed, 21 insertions, 3 deletions

diff --git a/docs/versionhistory.rst b/docs/versionhistory.rst
index 4c91c58..7f997f1 100644
--- a/docs/versionhistory.rst
+++ b/docs/versionhistory.rst
@@ -12,6 +12,7 @@ APScheduler, see the :doc:`migration section <migration>`.
 - Replaced ``from_asyncpg_pool()`` with ``from_dsn()`` in the asyncpg event broker
 - Changed ``from_async_sqla_engine()`` in asyncpg event broker to only copy the
   connection options instead of directly using the engine
+- Simplified the MQTT event broker by providing a default ``client`` instance if omitted
 
 **4.0.0a1**
 
diff --git a/src/apscheduler/eventbrokers/mqtt.py b/src/apscheduler/eventbrokers/mqtt.py
index ab5dc88..10ac605 100644
--- a/src/apscheduler/eventbrokers/mqtt.py
+++ b/src/apscheduler/eventbrokers/mqtt.py
@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import sys
 from concurrent.futures import Future
 from typing import Any
 
@@ -33,7 +34,7 @@ class MQTTEventBroker(LocalEventBroker, DistributedEventBrokerMixin):
     :param publish_qos: MQTT QoS to use for publishing messages
     """
 
-    client: Client
+    client: Client = attrs.field(factory=Client)
     serializer: Serializer = attrs.field(factory=JSONSerializer)
     host: str = attrs.field(kw_only=True, default="localhost")
     port: int = attrs.field(kw_only=True, default=1883)
@@ -45,8 +46,9 @@ class MQTTEventBroker(LocalEventBroker, DistributedEventBrokerMixin):
     def start(self) -> None:
         super().start()
         self._ready_future = Future()
-        self.client.enable_logger(self._logger)
         self.client.on_connect = self._on_connect
+        self.client.on_connect_fail = self._on_connect_fail
+        self.client.on_disconnect = self._on_disconnect
         self.client.on_message = self._on_message
         self.client.on_subscribe = self._on_subscribe
         self.client.connect(self.host, self.port)
@@ -66,15 +68,30 @@ class MQTTEventBroker(LocalEventBroker, DistributedEventBrokerMixin):
         rc: ReasonCodes | int,
         properties: Properties | None = None,
     ) -> None:
+        self._logger.info(f"{self.__class__.__name__}: Connected")
         try:
             client.subscribe(self.topic, qos=self.subscribe_qos)
         except Exception as exc:
             self._ready_future.set_exception(exc)
             raise
 
+    def _on_connect_fail(self, client: Client, userdata: Any) -> None:
+        exc = sys.exc_info()[1]
+        self._logger.error(f"{self.__class__.__name__}: Connection failed ({exc})")
+
+    def _on_disconnect(
+        self,
+        client: Client,
+        userdata: Any,
+        rc: ReasonCodes | int,
+        properties: Properties | None = None,
+    ) -> None:
+        self._logger.error(f"{self.__class__.__name__}: Disconnected (code: {rc})")
+
     def _on_subscribe(
-        self, client: Client, userdata: Any, mid, granted_qos: list[int]
+        self, client: Client, userdata: Any, mid: int, granted_qos: list[int]
     ) -> None:
+        self._logger.info(f"{self.__class__.__name__}: Subscribed")
         self._ready_future.set_result(None)
 
     def _on_message(self, client: Client, userdata: Any, msg: MQTTMessage) -> None: