Fix client_id not generated when connecting to the MQTT broker (#140264)

Fix client_id not generated when connecting to the MQTT broker

homeassistant/components/mqtt/client.py

@@ -15,6 +15,7 @@ import socket
 import ssl
 import time
 from typing import TYPE_CHECKING, Any
+from uuid import uuid4
 
 import certifi
 
@@ -292,7 +293,7 @@ class MqttClientSetup:
         """
         # 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
+        from paho.mqtt import client as mqtt  # pylint: disable=import-outside-toplevel
 
         # pylint: disable-next=import-outside-toplevel
         from .async_client import AsyncMQTTClient
@@ -309,9 +310,10 @@ class MqttClientSetup:
             clean_session = True
 
         if (client_id := config.get(CONF_CLIENT_ID)) is None:
-            # 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 = None
+            # PAHO MQTT relies on the MQTT server to generate random client ID
+            # for protocol version 3.1, however, that feature is not mandatory
+            # so we generate our own.
+            client_id = mqtt._base62(uuid4().int, padding=22)  # noqa: SLF001
         transport: str = config.get(CONF_TRANSPORT, DEFAULT_TRANSPORT)
         self._client = AsyncMQTTClient(
             callback_api_version=mqtt.CallbackAPIVersion.VERSION2,

tests/components/mqtt/test_client.py

@@ -1556,6 +1556,42 @@ async def test_setup_uses_certificate_on_certificate_set_to_auto_and_insecure(
     assert insecure_check["insecure"] == insecure_param
 
 
+@pytest.mark.parametrize(
+    ("mqtt_config_entry_data", "client_id"),
+    [
+        (
+            {
+                mqtt.CONF_BROKER: "mock-broker",
+                "client_id": "random01234random0124",
+            },
+            "random01234random0124",
+        ),
+        (
+            {
+                mqtt.CONF_BROKER: "mock-broker",
+            },
+            None,
+        ),
+    ],
+)
+async def test_client_id_is_set(
+    hass: HomeAssistant,
+    mqtt_mock_entry: MqttMockHAClientGenerator,
+    client_id: str | None,
+) -> None:
+    """Test setup defaults for tls."""
+    with patch(
+        "homeassistant.components.mqtt.async_client.AsyncMQTTClient"
+    ) as async_client_mock:
+        await mqtt_mock_entry()
+        await hass.async_block_till_done()
+    assert async_client_mock.call_count == 1
+    call_params: dict[str, Any] = async_client_mock.call_args[1]
+    assert "client_id" in call_params
+    assert client_id is None or client_id == call_params["client_id"]
+    assert call_params["client_id"] is not None
+
+
 @pytest.mark.parametrize(
     "mqtt_config_entry_data",
     [