feature: Cancellable connection establish event

[kezz]

Don't know if it makes more sense to do something else that isn't blocking on this event firing - couldn't really think of a better way to handle it. Potential for this to be expanded in the future to distinguish between ping vs. connection.

[Dominik48N]

Good pull request. A feature that you need, in my opinion.

[Gerrygames]

The event should include the intention of the connection.
Also instead of blocking you should disabled auto-reading while the event is being fired (like here for example).

[kezz]

In other event classes, the method arguments are not declared final. In order to ensure a uniform code style, I would remove the final here.

I'm just going to leave this one, it's a better code style that is less error prone. Other event classes, for example, do not have nullness annotations, we shouldn't follow that just because they use that style.

The event should include the intention of the connection. Also instead of blocking you should disabled auto-reading while the event is being fired (like here for example).

Thanks, edited this and it should be good now.