refactor: Deprecate connect and disconnect methods

[empicano]

As previously discussed in #216, this deprecates calls to connect and disconnect in favor of __aenter__ and __aexit__.

Hopefully, this will also simplify the internal state in the future. On that matter, Frederik, could you elaborate on what you meant by "Have all internal state inside a tagged union (sum type) in rust-style, concurrency-safe semantics."?

[codecov]

Codecov Report

Patch coverage: 96.2% and project coverage change: -0.4% ⚠️

Comparison is base (aedaf14) 84.7% compared to head (d83de6e) 84.4%.

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #247     +/-   ##
=======================================
- Coverage   84.7%   84.4%   -0.4%     
=======================================
  Files          4       4             
  Lines        473     483     +10     
  Branches      88      90      +2     
=======================================
+ Hits         401     408      +7     
- Misses        45      47      +2     
- Partials      27      28      +1     

Files Changed	Coverage Δ
aiomqtt/client.py	83.1% <96.2%> (-0.4%)	⬇️

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[empicano]

Ready for review now, I pulled in the functionality from connect and disconnect so that we can simply delete them in the next major version, but thus had to duplicate the tests for the _disconnect future handling.

Let me know what you think! 🙂

[vvanglro]

If it times out here, the lock will not be released, so my suggestion is to change the release lock to be executed anyway in aexit.

[empicano]

Thanks for checking the changes, and good point! 😊 If we release the lock, we can then call __aenter__ while the client is (potentially) still connected. I'm not sure what's best here.

I aimed for having equal logic to before in this PR. I hope that we can simplify the internal state when we remove connect and disconnect, so that such things are clearer. Right now it's slightly confusing having _connected, _disconnected, and _lock and what these three should specify.

[skewty]

Once connected and and async for message in client.messages is underway and some unrelated code has a critical error and I want the MQTT connection to shut down and do a graceful exit, what is the best method to accomplish this?

Assuming no new messages are coming in that for loop isn't going to be useful in this situation.

Is there a special / sentinel message I can somehow stuff onto the queue to get the desired result? If not, is this something the team would consider?

[empicano]

I did not test this now, but I'd expect the client to do a graceful shutdown when you cancel the surrounding task.

So something like:

async def test():
    with aiomqtt.Client("test.mosquitto.org") as client:
        # Subscribe to topics here
        async for message in client.messages:
            # Process message

async def main():
    task = asyncio.create_task(test())
    # Do something else
    await asyncio.sleep(1)
    # Oh no, error!
    task.cancel()
    try:
        await task
    except asyncio.CancelledError:
        pass

Hope that helps!