feat: HA Discovery protocol handler for auto-registering devices

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/mqtt_home/discovery.py

@@ -0,0 +1,84 @@
+import json
+import logging
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from mqtt_home.models import Device
+from mqtt_home.mqtt_client import MqttClient
+from mqtt_home.device_registry import create_device, handle_state_update
+
+logger = logging.getLogger(__name__)
+
+DISCOVERY_TOPIC_PREFIX = "homeassistant/"
+
+
+def parse_discovery_topic(topic: str) -> dict[str, str] | None:
+    """Parse HA Discovery topic, returns component and node_id"""
+    parts = topic.split("/")
+    if len(parts) < 4 or parts[0] != DISCOVERY_TOPIC_PREFIX.strip("/"):
+        return None
+    if parts[-1] != "config":
+        return None
+    return {
+        "component": parts[1],
+        "node_id": "/".join(parts[2:-1]),
+    }
+
+
+async def handle_discovery_message(
+    topic: str, payload: str, db: AsyncSession, mqtt_client: MqttClient
+) -> Device | None:
+    """Handle HA Discovery config message, auto-register device and subscribe to state topic"""
+    parsed = parse_discovery_topic(topic)
+    if not parsed:
+        return None
+
+    try:
+        config = json.loads(payload)
+    except json.JSONDecodeError:
+        logger.warning("Invalid JSON in discovery payload for %s", topic)
+        return None
+
+    state_topic = config.get("state_topic")
+    command_topic = config.get("command_topic")
+    device_name = config.get("name", config.get("device", {}).get("name", parsed["node_id"]))
+    device_class = config.get("device_class", "")
+
+    if not state_topic:
+        logger.warning("Discovery config for %s has no state_topic", topic)
+        return None
+
+    # Check if already exists (deduplicate by discovery_topic)
+    from sqlalchemy import select
+    result = await db.execute(
+        select(Device).where(Device.discovery_topic == topic)
+    )
+    existing = result.scalar_one_or_none()
+    if existing:
+        logger.debug("Device already registered: %s", topic)
+        return existing
+
+    from mqtt_home.schemas import DeviceCreate
+    device = await create_device(db, DeviceCreate(
+        name=device_name,
+        type=parsed["component"],
+        protocol="ha_discovery",
+        mqtt_topic=state_topic,
+        command_topic=command_topic,
+    ))
+
+    # Update discovery-related fields
+    device.discovery_topic = topic
+    device.discovery_payload = payload
+    device.attributes = json.dumps({
+        "device_class": device_class,
+        "unit_of_measurement": config.get("unit_of_measurement"),
+        "icon": config.get("icon"),
+    })
+    await db.commit()
+    await db.refresh(device)
+
+    # Subscribe to state topic
+    await mqtt_client.subscribe(state_topic, qos=1)
+    logger.info("HA Discovery device registered: %s -> %s", device.name, state_topic)
+
+    return device

tests/test_discovery.py

@@ -0,0 +1,78 @@
+import json
+import pytest
+from unittest.mock import AsyncMock
+
+from mqtt_home.discovery import parse_discovery_topic, handle_discovery_message
+from mqtt_home.config import Settings
+from mqtt_home.mqtt_client import MqttClient
+
+
+@pytest.fixture
+def settings():
+    return Settings(
+        mqtt_host="localhost",
+        emqx_api_url="http://localhost:18083/api/v5",
+        emqx_api_key="test-key",
+        emqx_api_secret="test-secret",
+        database_url="sqlite+aiosqlite:///:memory:",
+    )
+
+
+def test_parse_discovery_topic_valid():
+    result = parse_discovery_topic("homeassistant/light/abc123/config")
+    assert result is not None
+    assert result["component"] == "light"
+    assert result["node_id"] == "abc123"
+
+
+def test_parse_discovery_topic_nested_node():
+    result = parse_discovery_topic("homeassistant/sensor/room/temperature/config")
+    assert result is not None
+    assert result["component"] == "sensor"
+    assert result["node_id"] == "room/temperature"
+
+
+def test_parse_discovery_topic_invalid():
+    assert parse_discovery_topic("other/topic/config") is None
+    assert parse_discovery_topic("homeassistant/light/abc") is None
+    assert parse_discovery_topic("homeassistant/light/abc/status") is None
+
+
+async def test_handle_discovery_creates_device(db_session, settings):
+    mqtt_client = MqttClient(settings)
+    mqtt_client.subscribe = AsyncMock()
+
+    payload = json.dumps({
+        "name": "客厅灯",
+        "state_topic": "home/living/light/status",
+        "command_topic": "home/living/light/set",
+        "device_class": "light",
+    })
+
+    device = await handle_discovery_message(
+        "homeassistant/light/living_room/config",
+        payload,
+        db_session,
+        mqtt_client,
+    )
+    assert device is not None
+    assert device.name == "客厅灯"
+    assert device.protocol == "ha_discovery"
+    assert device.mqtt_topic == "home/living/light/status"
+    mqtt_client.subscribe.assert_called_once_with("home/living/light/status", qos=1)
+
+
+async def test_handle_discovery_duplicate(db_session, settings):
+    mqtt_client = MqttClient(settings)
+    mqtt_client.subscribe = AsyncMock()
+
+    payload = json.dumps({
+        "name": "灯",
+        "state_topic": "home/light",
+    })
+
+    await handle_discovery_message("homeassistant/light/test/config", payload, db_session, mqtt_client)
+    device2 = await handle_discovery_message("homeassistant/light/test/config", payload, db_session, mqtt_client)
+    # Same discovery_topic should not create duplicate
+    assert device2 is not None
+    mqtt_client.subscribe.assert_called_once()  # Only called once