[Fix] RMQ event handlers not removed (#4044)

[ravriel]

Fixes #4044 by removing channel event handlers in each event handler.

[CLAassistant]

All committers have signed the CLA.

[iancooper]

Issues with the Fix

The handlers are removed inside OnPublishSucceeded / OnPublishFailed — before the pending confirmation is processed for the current delivery tag. But more importantly, unsubscribing in the event handler creates a window in which a subsequent SendWithDelayAsync call has already re-registered handlers, and the first event's handler then removes those new registrations. With concurrent sends on the same producer, this can cause missed confirmations.

The root cause is that handlers are registered per-send when they should be registered once per channel. The handlers already use _pendingConfirmations (a ConcurrentDictionary) to correlate delivery tags, so they work correctly for multiple in-flight messages. The fix should be:

• Subscribe to BasicAcksAsync/BasicNacksAsync once when the channel is created (in EnsureBrokerAsync or after it returns), not on every send.
• Unsubscribe when the channel is disposed/reset (in ResetConnectionToBrokerAsync or Dispose).

This eliminates the add/remove churn entirely and is safe for concurrent sends.

// In EnsureBrokerAsync (or right after it returns), subscribe once:
if (Channel != null)
{
Channel.BasicAcksAsync += OnPublishSucceeded;
Channel.BasicNacksAsync += OnPublishFailed;
}

// Remove the per-send subscription entirely from SendWithDelayAsync
// Unsubscribe in ResetConnectionToBrokerAsync before creating a new channel

This is simpler, correct for concurrent use, and doesn't require the RegisterChannelEvents method at all.

The PR has no tests verifying the fix. A test that sends N messages and asserts the handler is invoked exactly N times (once per message, not N×(N+1)/2 times) would prevent regression.

[iancooper]

@ravriel Your idea is right, but it needs adjusting so that it doesn't do this every time

[iancooper]

@ravriel Just nudging in case you missed the feedback

[lillo42]

Split it into two methods, register and unregister

[iancooper]

We need to do it in a different place, as we don't want to register/unregister per publish

[iancooper]

Thanks for adding the test, I think we should link at cleaning up in the Dispose as well, then we are done

[iancooper]

We should unsubscribe in Dispose, if not already disposed, since if we exit without an error, we want to remove any subscriptions.

[codescene-delta-analysis]

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Quality Gate Profile: Clean Code Collective
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[iancooper]

Thanks for the contribution @ravriel I am going to get a release out soon