implement net::lookup_host

[japaric]

it was missing from #85

cc @aleksander

[tbu-]

This is hard. :) We need to implement our own resolver for that, or find some library that does it.

[aleksander]

I'll try to implement. I use musl libc implementation as reference.

[briansmith]

Implementing a resolver is a major project that IMO should be in its own crate that can be shared with other projects. There are already multiple projects implementing DNS in Rust and it would be great to work together with them.

[aleksander]

host lookup implementations I found:

• trust-dns
• rotor-dns
• domain

Can we use such big crates as trust-dns or rotor-dns?

[tbu-]

It will be hard to use those libraries directly right now: They use a lot of the standard library that we haven't implemented yet. Other than that, I'd not be opposed to using a big existing library, we can always find a smaller one later.

[japaric]

We can directly use no_std crates that don't depend on libc. Everything else we would have to vendor here and hope that we won't have to modify it too much.

So, if we have to pick one of those three, I'd vote for the one that needs less modifications. Code size is not much of a problem but the more we have to modify the crate, the greater the work required to upgrade the dependency.