Fix serial integration connection stability (#33067)

* Fix serial integration connection stability

Retry to connect if serial device is not available on start, or connection is lost.
Added some more log entries upon connection or when errors are encountered.

* Updated code based on review

* Fixed exception indentation

* Handle SerialException

* Sort imports

* Update homeassistant/components/serial/sensor.py

Co-Authored-By: Martin Hjelmare <marhje52@gmail.com>

* Update homeassistant/components/serial/sensor.py

Co-Authored-By: Martin Hjelmare <marhje52@gmail.com>

* More clean up

* Format and delint

* Extract error handler

* Clean up stop handler

Co-authored-by: Martin Hjelmare <marhje52@gmail.com>

homeassistant/components/serial/sensor.py

@@ -1,12 +1,15 @@
 """Support for reading data from a serial port."""
+import asyncio
 import json
 import logging
 
+from serial import SerialException
 import serial_asyncio
 import voluptuous as vol
 
 from homeassistant.components.sensor import PLATFORM_SCHEMA
 from homeassistant.const import CONF_NAME, CONF_VALUE_TEMPLATE, EVENT_HOMEASSISTANT_STOP
+from homeassistant.core import callback
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
 
@@ -40,7 +43,7 @@ async def async_setup_platform(hass, config, async_add_entities, discovery_info=
 
     sensor = SerialSensor(name, port, baudrate, value_template)
 
-    hass.bus.async_listen_once(EVENT_HOMEASSISTANT_STOP, sensor.stop_serial_read())
+    hass.bus.async_listen_once(EVENT_HOMEASSISTANT_STOP, sensor.stop_serial_read)
     async_add_entities([sensor], True)
 
 
@@ -55,7 +58,7 @@ class SerialSensor(Entity):
         self._baudrate = baudrate
         self._serial_loop_task = None
         self._template = value_template
-        self._attributes = []
+        self._attributes = None
 
     async def async_added_to_hass(self):
         """Handle when an entity is about to be added to Home Assistant."""
@@ -65,28 +68,61 @@ class SerialSensor(Entity):
 
     async def serial_read(self, device, rate, **kwargs):
         """Read the data from the port."""
+        logged_error = False
+        while True:
+            try:
                 reader, _ = await serial_asyncio.open_serial_connection(
                     url=device, baudrate=rate, **kwargs
                 )
+            except SerialException as exc:
+                if not logged_error:
+                    _LOGGER.exception(
+                        "Unable to connect to the serial device %s: %s. Will retry",
+                        device,
+                        exc,
+                    )
+                    logged_error = True
+                await self._handle_error()
+            else:
+                _LOGGER.info("Serial device %s connected", device)
                 while True:
+                    try:
                         line = await reader.readline()
+                    except SerialException as exc:
+                        _LOGGER.exception(
+                            "Error while reading serial device %s: %s", device, exc
+                        )
+                        await self._handle_error()
+                        break
+                    else:
                         line = line.decode("utf-8").strip()
 
                         try:
                             data = json.loads(line)
-                if isinstance(data, dict):
-                    self._attributes = data
                         except ValueError:
                             pass
+                        else:
+                            if isinstance(data, dict):
+                                self._attributes = data
 
                         if self._template is not None:
-                line = self._template.async_render_with_possible_json_value(line)
+                            line = self._template.async_render_with_possible_json_value(
+                                line
+                            )
 
                         _LOGGER.debug("Received: %s", line)
                         self._state = line
                         self.async_write_ha_state()
 
-    async def stop_serial_read(self):
+    async def _handle_error(self):
+        """Handle error for serial connection."""
+        self._state = None
+        self._attributes = None
+        self.async_write_ha_state()
+        await asyncio.sleep(5)
+
+    @callback
+    def stop_serial_read(self, event):
         """Close resources."""
         if self._serial_loop_task:
             self._serial_loop_task.cancel()