umqtt (MQTT) simple 'OSError: -1' and Mosquitto Broker - Duplicate MQTT Client Names

[DS256]

I encounter the following Micropython error on a previously working PICO W that publishes weather readings to a Mosquitto 2.0.11 MQTT Broker. I am using 'simple 1.3.4'

Traceback (most recent call last):
  File "main_enviro.py", line 227, in main_enviro
  File "umqtt/simple.py", line 144, in publish
  File "umqtt/simple.py", line 184, in wait_msg
OSError: -1

Google searches return all sorts of approaches to solve the 'OSError: -1' problem with simple, normally socket related. I was plagued by the idea nothing had change in the programming.

Running a 'mosquitto_sub' revealed sensor readings that were not associated with the PICO BME280 sensor but registered to 'weth-2'. The PICO is client 'weth-2'.

2023-06-15T18:18:27-0400 reading {"pressure": "980.74", "temp": "26.31", "seq": "8", "sensor": "BME280", "datetime": "2023-06-15 18:18:22", "host": "weth-2", "humidity": "31.84"}
2023-06-15T18:18:32-0400 reading {"host": "weth-2", "datetime": "2023-06-15 18:18:32", "sensor": "DHT22", "seq": "28", "temp": "23.4", "humidity": "47.1", "pressure": "0"}
2023-06-15T18:18:33-0400 reading {"host": "weth-2", "datetime": "2023-06-15 18:18:33", "sensor": "DB18B20", "seq": "28", "temp": "22.25", "humidity": "0", "pressure": "0"}

I then checked the Mosquitto log file and found the same 'weth-2' client connecting from two different IP addresses. Mosquitto was dropping one when the other connection request came in closing the socket I presume.

2023-06-15T18:16:12: New connection from 192.168.0.145:54518 on port 1883.
2023-06-15T18:16:12: Client weth-2 already connected, closing old connection.
2023-06-15T18:16:12: New client connected from 192.168.0.145:54518 as weth-2 (p2, c1, k3600).

2023-06-15T18:16:13: New connection from 192.168.0.146:34523 on port 1883.
2023-06-15T18:16:13: Client weth-2 already connected, closing old connection.
2023-06-15T18:16:13: New client connected from 192.168.0.146:34523 as weth-2 (p2, c1, k60).

192.168.0.145 is the PICO and registers as 'weth-2' . 192.168.0.146 is a PI 3 B+ and is normally 'weth-1'. I had been modifying the program on 'weth-1' and inadvertently changed it's name from 'weth-1' to 'weth-2'. Both the PICO and PI 3 were running at the same time with the same client name.

Correcting the naming from 'weth-2' back to 'weth-1' stopped the 'OSError: -1' error from occurring on the PICO W.

Interestingly enough, the Python program running on the PI 3 never reported an error. I am using the 'PAHO MQTT Client' there. It was too big to use with Micropython on the PICO W so I used 'simple'

I'm posting this in case someone else has the same problem since it is not the same as the other 'OSERR: -1' issues related to sockets. Check that you are not using duplicate MQTT Client names.

[peterhinch]

The behaviour of Mosquitto seems reasonable. A broker on the internet may have clients with dynamic IP's. If a client connects with a new IP, it makes sense to drop the original connection and to accept the new one. In any event, this does not seem to be a problem with the MicroPython client.

[DS256]

Oh, I agree that this is not a Mosquitto problem or even a MQTT implementation issue @peterhinch. My point is that the error reported by ‘simple’ is a symptom and not an issue. Especially when looking at other issues the error points to.