How to bind all interfaces dual-stack?

I wish to write a server application that binds to all interfaces in a dual-stack IPv4/IPv6 environment.

I thought the example server would be doing that, as it appears to bind to ‘::0’. In other applications, like CherryPy, binding to that address makes the server available on all interfaces, IPv4 and IPv6, but in aiosmtpd, the server is only reachable on IPv6. As a result, when the application moves to an environment that only supports IPv4 (looking at you, Docker), the application is unreachable.

Reading up on the docs for create_server, I see that passing a None value for the host should bind to all interfaces on both stacks, and indeed, that’s the behavior I see.

But aiosmtpd doesn’t allow passing None due to the the localhost default behavior.

I did find one interface that worked, but I’m not happy with it:

	cont = controller.Controller(proxy, port=8025)
	# no really, I want all interfaces
	cont.hostname = None
	cont.start()

[Mortal]

I think we can label this issue “rubber ducking” 😃

Thanks for the PR and for figuring this out!

[jaraco]

I’ve presented a PR, and that approach feels minimally invasive to address the concern.