Fix blocking IO calls in mqtt client setup (#119647)

homeassistant/components/mqtt/async_client.py

@@ -44,7 +44,7 @@ class AsyncMQTTClient(MQTTClient):
     that is not needed since we are running in an async event loop.
     """
 
-    def async_setup(self) -> None:
+    def setup(self) -> None:
         """Set up the client.
 
         All the threading locks are replaced with NullLock

homeassistant/components/mqtt/client.py

@@ -277,9 +277,22 @@ class Subscription:
 class MqttClientSetup:
     """Helper class to setup the paho mqtt client from config."""
 
-    def __init__(self, config: ConfigType) -> None:
-        """Initialize the MQTT client setup helper."""
+    _client: AsyncMQTTClient
 
+    def __init__(self, config: ConfigType) -> None:
+        """Initialize the MQTT client setup helper.
+
+        self.setup must be run in an executor job.
+        """
+
+        self._config = config
+
+    def setup(self) -> None:
+        """Set up the MQTT client.
+
+        The setup of the MQTT client should be run in an executor job,
+        because it accesses files, so it does IO.
+        """
         # We don't import on the top because some integrations
         # should be able to optionally rely on MQTT.
         import paho.mqtt.client as mqtt  # pylint: disable=import-outside-toplevel
@@ -287,6 +300,7 @@ class MqttClientSetup:
         # pylint: disable-next=import-outside-toplevel
         from .async_client import AsyncMQTTClient
 
+        config = self._config
         if (protocol := config.get(CONF_PROTOCOL, DEFAULT_PROTOCOL)) == PROTOCOL_31:
             proto = mqtt.MQTTv31
         elif protocol == PROTOCOL_5:
@@ -298,11 +312,14 @@ class MqttClientSetup:
             # PAHO MQTT relies on the MQTT server to generate random client IDs.
             # However, that feature is not mandatory so we generate our own.
             client_id = mqtt.base62(uuid.uuid4().int, padding=22)
-        transport = config.get(CONF_TRANSPORT, DEFAULT_TRANSPORT)
+        transport: str = config.get(CONF_TRANSPORT, DEFAULT_TRANSPORT)
         self._client = AsyncMQTTClient(
-            client_id, protocol=proto, transport=transport, reconnect_on_failure=False
+            client_id,
+            protocol=proto,
+            transport=transport,
+            reconnect_on_failure=False,
         )
-        self._client.async_setup()
+        self._client.setup()
 
         # Enable logging
         self._client.enable_logger()
@@ -544,7 +561,9 @@ class MQTT:
                 self.hass, "homeassistant.components.mqtt.async_client"
             )
 
-        mqttc = MqttClientSetup(self.conf).client
+        mqttc_setup = MqttClientSetup(self.conf)
+        await self.hass.async_add_executor_job(mqttc_setup.setup)
+        mqttc = mqttc_setup.client
         # on_socket_unregister_write and _async_on_socket_close
         # are only ever called in the event loop
         mqttc.on_socket_close = self._async_on_socket_close

homeassistant/components/mqtt/config_flow.py

@@ -834,7 +834,9 @@ def try_connection(
     # should be able to optionally rely on MQTT.
     import paho.mqtt.client as mqtt  # pylint: disable=import-outside-toplevel
 
-    client = MqttClientSetup(user_input).client
+    mqtt_client_setup = MqttClientSetup(user_input)
+    mqtt_client_setup.setup()
+    client = mqtt_client_setup.client
 
     result: queue.Queue[bool] = queue.Queue(maxsize=1)