add MQTT handler example

Author: vladak

examples/logging_mqtt_handler.py

@@ -0,0 +1,43 @@
+"""
+Demonstrate how to use a single logger to emit log records to
+both console and MQTT broker, in this case Adafruit IO.
+"""
+
+import json
+import socket
+import ssl
+
+import adafruit_logging as logging
+import adafruit_minimqtt.adafruit_minimqtt as MQTT
+
+from mqtt_handler import MQTTHandler
+
+logger = logging.getLogger(__name__)
+
+broker = "io.adafruit.com"
+port = 8883
+username = "Adafruit_IO_username"
+password = "Adafruit_IO_key"
+feedname = "Adafruit_feed_name"
+mqtt_topic = f"{username}/feeds/{feedname}"
+mqtt_client = MQTT.MQTT(
+    broker=broker,
+    port=port,
+    username=username,
+    password=password,
+    socket_pool=socket,
+    ssl_context=ssl.create_default_context(),
+)
+mqtt_client.connect()
+mqtt_handler = MQTTHandler(mqtt_client, mqtt_topic)
+print("adding MQTT handler")
+logger.addHandler(mqtt_handler)
+
+stream_handler = logging.StreamHandler()
+print("adding Stream handler")
+logger.addHandler(stream_handler)
+
+data = "foo bar"
+print("logging begins !")
+# This should emit both to the console as well as to the MQTT broker.
+logger.warning(json.dumps(data))

examples/mqtt_handler.py

@@ -0,0 +1,38 @@
+"""
+MQTT logging handler - log records will be published as MQTT messages
+"""
+
+import adafruit_minimqtt.adafruit_minimqtt as MQTT
+# adafruit_logging defines log levels dynamically.
+# pylint: disable=no-name-in-module
+from adafruit_logging import NOTSET, Handler, LogRecord
+
+
+class MQTTHandler(Handler):
+    """
+    Log handler that emits log records as MQTT PUBLISH messages.
+    """
+    def __init__(self, mqtt_client: MQTT.MQTT, topic: str) -> None:
+        """
+        Assumes that the MQTT client object is already connected.
+        """
+        super().__init__()
+
+        self._mqtt_client = mqtt_client
+        self._topic = topic
+
+        # To make it work also in CPython.
+        self.level = NOTSET
+
+    def emit(self, record: LogRecord) -> None:
+        """
+        Publish message from the LogRecord to the MQTT broker.
+        """
+        self._mqtt_client.publish(self._topic, record.msg)
+
+    # To make this work also in CPython's logging.
+    def handle(self, record: LogRecord) -> None:
+        """
+        Handle the log record. Here, it means just emit.
+        """
+        self.emit(record)