Fix future exception on disconnect

[MartinHjelmare]

I'm testing this library to use with Home Assistant. I've written a client based on the advanced example in the readme.

It seems we're setting an exception on the self._disconnected asyncio.Future used in _on_disconnect, even though the future is never awaited if there's an exception in the connect flow.

Without this fix, when the connection is refused, I'm seeing:

2020-11-27 01:20:49,138 INFO (MainThread) [openzwavemqtt] Starting client.
2020-11-27 01:20:49,138 DEBUG (MainThread) [asyncio] Using selector: EpollSelector
2020-11-27 01:20:49,147 DEBUG (ThreadPoolExecutor-0_0) [paho.mqtt.client] Sending CONNECT (u0, p0, wr0, wq0, wf0, c1, k60) client_id=b'6SHLIyeUtZENAYM3p4xxFi'
2020-11-27 01:20:49,150 DEBUG (MainThread) [paho.mqtt.client] Received CONNACK (0, 5)
2020-11-27 01:20:49,150 ERROR (MainThread) [openzwavemqtt] MQTT error: [code:5] Connection refused: Not authorised. Reconnecting in 2 seconds
2020-11-27 01:20:51,153 ERROR (MainThread) [asyncio] Future exception was never retrieved
future: <Future finished exception=MqttCodeError('Unexpected disconnect')>
asyncio_mqtt.error.MqttCodeError: [code:5] Unexpected disconnect
2020-11-27 01:20:51,159 DEBUG (ThreadPoolExecutor-0_0) [paho.mqtt.client] Sending CONNECT (u0, p0, wr0, wq0, wf0, c1, k60) client_id=b'6SHLIyeUtZENAYM3p4xxFi'
2020-11-27 01:20:51,161 DEBUG (MainThread) [paho.mqtt.client] Received CONNACK (0, 5)
2020-11-27 01:20:51,162 ERROR (MainThread) [openzwavemqtt] MQTT error: [code:5] Connection refused: Not authorised. Reconnecting in 4 seconds
2020-11-27 01:20:55,296 DEBUG (ThreadPoolExecutor-0_0) [paho.mqtt.client] Sending CONNECT (u0, p0, wr0, wq0, wf0, c1, k60) client_id=b'6SHLIyeUtZENAYM3p4xxFi'
2020-11-27 01:20:55,301 DEBUG (MainThread) [paho.mqtt.client] Received CONNACK (0, 5)
2020-11-27 01:20:55,302 ERROR (MainThread) [openzwavemqtt] MQTT error: [code:5] Connection refused: Not authorised. Reconnecting in 8 seconds
^C2020-11-27 01:20:55,976 INFO (MainThread) [openzwavemqtt] Exiting client.
2020-11-27 01:20:55,982 ERROR (MainThread) [asyncio] Future exception was never retrieved
future: <Future finished exception=MqttCodeError('Unexpected disconnect')>
asyncio_mqtt.error.MqttCodeError: [code:5] Unexpected disconnect
2020-11-27 01:20:55,983 ERROR (MainThread) [asyncio] Future exception was never retrieved
future: <Future finished exception=MqttCodeError('Unexpected disconnect')>
asyncio_mqtt.error.MqttCodeError: [code:5] Unexpected disconnect

With this fix:

2020-11-27 01:20:30,700 INFO (MainThread) [openzwavemqtt] Starting client.
2020-11-27 01:20:30,700 DEBUG (MainThread) [asyncio] Using selector: EpollSelector
2020-11-27 01:20:30,709 DEBUG (ThreadPoolExecutor-0_0) [paho.mqtt.client] Sending CONNECT (u0, p0, wr0, wq0, wf0, c1, k60) client_id=b'1c0Jnihm0DyAfyK4ETcfXp'
2020-11-27 01:20:30,712 DEBUG (MainThread) [paho.mqtt.client] Received CONNACK (0, 5)
2020-11-27 01:20:30,713 ERROR (MainThread) [openzwavemqtt] MQTT error: [code:5] Connection refused: Not authorised. Reconnecting in 2 seconds
2020-11-27 01:20:32,722 DEBUG (ThreadPoolExecutor-0_0) [paho.mqtt.client] Sending CONNECT (u0, p0, wr0, wq0, wf0, c1, k60) client_id=b'1c0Jnihm0DyAfyK4ETcfXp'
2020-11-27 01:20:32,725 DEBUG (MainThread) [paho.mqtt.client] Received CONNACK (0, 5)
2020-11-27 01:20:32,725 ERROR (MainThread) [openzwavemqtt] MQTT error: [code:5] Connection refused: Not authorised. Reconnecting in 4 seconds
2020-11-27 01:20:36,731 DEBUG (ThreadPoolExecutor-0_0) [paho.mqtt.client] Sending CONNECT (u0, p0, wr0, wq0, wf0, c1, k60) client_id=b'1c0Jnihm0DyAfyK4ETcfXp'
2020-11-27 01:20:36,734 DEBUG (MainThread) [paho.mqtt.client] Received CONNACK (0, 5)
2020-11-27 01:20:36,735 ERROR (MainThread) [openzwavemqtt] MQTT error: [code:5] Connection refused: Not authorised. Reconnecting in 8 seconds
^C2020-11-27 01:20:37,383 INFO (MainThread) [openzwavemqtt] Exiting client.

[MartinHjelmare]

This change isn't required to resolve the issue, but it seems like a typo so I included it. Let me know if you want that as a separate PR/discussion.

[frederikaalund]

Hi Martin. Thanks for the pull request. Let me have a look. :)

Great catch! Both of them, that is. :)) I thought I got rid of all those annoying "Future exception was never retrieved" messages. Guess I was wrong.

Looks good to me. 👍

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I'm testing this library to use with Home Assistant. I've written a client based on the advanced example in the readme.

Glad to hear that people use asyncio-mqtt in practice. Let me know if you run into other bugs in the implementation or quirks in the API design itself. I'm planning a 1.0.0 release at the end of the year.