Resolve canonical_name to support "localhost" on windows

[Faaux]

Hi Mireo Team,

on Windows async_mqtt5 fails to resolve localhost. Changing to a canonical resolver fixes this.

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[ksimicevic]

Hello and thank you very much for submitting this PR!
We are currently undergoing a Boost review until the end of this week. We will look at this PR next week.
Sorry for the inconvenience.

[Faaux]

First of all congrats on passing with condition :)

I just found another case in Docker + WSL2 where localhost (with the fix applied) couldn't be resolved. So something is still amiss but I am out of my ASIO depth here.

[ksimicevic]

Sorry for taking so long to get back to you.

I tried to replicate the issue you described on Windows 11 by installing a mosquito broker and running it locally. I compiled my client code with MSVC 14.37.

I could not connect to my local broker. However, I did not find any issues with the resolver. It resolved localhost successfully and returned 2 endpoints (IPv6 and IPv4). In my case, the issue was in connect_op.hpp:112 where we call async_connect with the first endpoint in the list (which was the IPv6 endpoint here and my broker was listening on IPv4). I fixed the issue by changing the perform function to use the free function boost::asio::async_connect that will iteratively try to connect to every endpoint in the list until it successfully establishes a connection:

void perform(
	const epoints& eps, authority_path ap
) {
	auto& stream = lowest_layer(_stream);
	asio::async_connect(
		stream, eps,
		asio::append(
			asio::prepend(std::move(*this), on_connect {}),
			std::move(ap)
		)
	);
}

Additionally, I tried running both the broker and the client code on WSL2 (Debian 12 distro) and encountered no issues.

Therefore, I think I need more information about your situation to figure out what is going on:

1. When you said that your client failed to resolve to localhost on Windows and Docker+WSL2, does that mean you have received an error_code in resolve_op in endpoints.hpp:109? If yes, what was the resolve_ec and timer_ec?
2. Could you precisely specify the client and broker setups where you encountered the issue (the Windows version, WSL2 distribution, and compilers used to compile your client code)?

Thanks!