fix(async): synchronize connect() promise with connection_made callback

[Yuvrajup]

Closes #3019

[janiversen]

This is overly complicated and not needed, current solution uses the standard asyncio methods.

client,connect returns the value comming from asyncio, which according to the documentation is true/false depending on whether a connection was established.

client.connected tests if the connection is stil open by referring to the transport object. Remark connection_made/ connection_lost changes the transport object.

The issue you refer to, is not actually an issue in pymodbus (see the discussion) but a device problem.

[janiversen]

If you want this merged, you need to make a test case that shows that the current solution is wrong and yours work.

[Yuvrajup]

Challenge accepted, @janiversen! I completely understand wanting to keep the library lean and relying on standard asyncio methods.

You are right that create_connection returns the underlying connection. However, the issue is that there is a microscopic event-loop gap between create_connection resolving and the protocol's connection_made() callback actually firing to set the .transport object inside the client.

I just pushed a new test case (test_async_connect_race_condition) that artificially delays the connection_made callback by a few milliseconds to deterministically simulate a slow event loop or hardware latency.

• Without this PR's synchronization, client.connect() returns True, but client.connected evaluates to False (crashing subsequent requests).
• With this PR, client.connect() safely awaits the callback, ensuring the transport is fully hydrated before returning control to the caller.

Let me know what you think of the test case!

[janiversen]

Forget about that race, pymodbus do not have the transport object until connection_made is called.

Apart from that in my experience, when debugging, connection_made was always called before the connect returned.

Just checked your test case, the delay is inside connection_made() and thus in pymodbus code, so your test case does not show if connection_made is called before connect returns.