Merge pull request #246 from sparks-baird/hivemq

add more useful error message for hivemq fail

src/public_mqtt_sdl_demo/main.py

@@ -290,7 +290,13 @@ def callback(topic, msg, retain=None, dup=None):
         print(get_traceback(e))
         print("Retrying client.connect() in 2 seconds...")
         sleep(2.0)
-        client.connect()
+        try:
+            client.connect()
+        except OSError as e:
+            print(get_traceback(e))
+            print(
+                "Failed to connect on second attempt. Ensure you have the correct 'hivemq-com-chain.der' file *specific* to your HiveMQ Cloud broker instance (now required as of June 2024). The default file works for the self-driving-lab-demo, but for your own instance, generate and upload the correct CA file to your microcontroller. Your certificate can be generated via https://colab.research.google.com/github/sparks-baird/self-driving-lab-demo/blob/main/notebooks/7.2.1-hivemq-openssl-certificate.ipynb. See also https://github.com/sparks-baird/self-driving-lab-demo/issues/245"
+            )  # noqa: E501
 
     client.set_callback(callback)
     client.subscribe(prefix + "GPIO/#")