Handle unexpected errors while reconnecting

[blaxter]

When we reconnect we are doing an explicit disconnect, this can fail and if we don't handle possible exceptions we won't reconnect (even when it's possible to do so)

A way to reproduce this easily is killing the connection with ss -K (linux only)

A standalone script that I used to reproduce this:

import asyncio
import signal
import time

from gmqtt import Client as MQTTClient

import uvloop
asyncio.set_event_loop_policy(uvloop.EventLoopPolicy())

STOP = asyncio.Event()

def on_connect(client, flags, rc, properties):
    print('Connected')
    client.subscribe('TEST/#', qos=0)

def on_disconnect(client, packet, exc=None):
    print('Disconnected')

def on_subscribe(client, mid, qos, properties):
    print('SUBSCRIBED')

    client.publish('TEST/TIME', str(time.time()), qos=1)

def on_message(client, topic, payload, qos, properties):
    print('RECV MSG:', payload)

def ask_exit(*args):
    STOP.set()

async def main(broker_host):
    client = MQTTClient("foobar")
    client.set_config({'reconnect_retries': -1, 'reconnect_delay': 0})

    client.on_connect = on_connect
    client.on_message = on_message
    client.on_disconnect = on_disconnect
    client.on_subscribe = on_subscribe

    await client.connect(broker_host)

    await STOP.wait()
    await client.disconnect()

if __name__ == '__main__':
    loop = asyncio.get_event_loop()

    host = 'test.mosquitto.org'

    loop.add_signal_handler(signal.SIGINT, ask_exit)
    loop.add_signal_handler(signal.SIGTERM, ask_exit)

    loop.run_until_complete(main(host))

Execution without this patch:

$ python gmqtt_disconnect_error.py 
Connected
SUBSCRIBED
RECV MSG: b'1605609671.003748'
# To force a network error, I execute in a different shell: sudo ss -K dst `sudo netstat -putan | grep 1883 | grep python | awk '{print $5}'`
[EXC: CONN LOST]
ConnectionAbortedError: [Errno 103] Software caused connection abort
Disconnected
[TRYING WRITE TO CLOSED SOCKET]
[EXC OCCURED] in reconnect future [Errno 103] Software caused connection abort

Execution with this patch:

$ python gmqtt_disconnect_error.py 
Connected
SUBSCRIBED
RECV MSG: b'1605609903.1251647'
# Forced network error
[EXC: CONN LOST]
ConnectionAbortedError: [Errno 103] Software caused connection abort
Disconnected
[TRYING WRITE TO CLOSED SOCKET]
Connected
SUBSCRIBED
RECV MSG: b'1605609905.9536421'

Notice we have successfully reconnected.

[Mixser]

Thanks for PR. We have updated the lib with your fix (v0.6.9).