Handle IPv6-only results even in GETHOSTBYNAME

[andir]

Previously IPv6-only results would return an empty successful result
message. This doesn't seem to be a valid response from the perspective
of Glibc. In my case it caused Firefox to crash.

[flokli]

Previously IPv6-only results would return an empty successful result
message.

Not sure I follow. The previous code did return an error if addresses was not Ok, and you changed it to become an empty list of addresses.

We did filter out all addresses that are not IPv4 from the getaddrinfo call, so I would have assumed this to be an empty list in that case?

[grahamc]

I can confirm that switching to nsncd causes firefox to crash in scenarios like this.

This PR appears to fix it. I applied it via:

  inputs.nsncd = {
    url = "github:andir/nsncd/fix-ipv6";
    flake = false;
  };

  outputs = { self, nixpkgs, nsncd, ... }: {
    nixosConfigurations.hermes-conrad = nixpkgs.lib.nixosSystem {
      system = "x86_64-linux";
      modules = [
        ({
          nixpkgs.overlays = [
            (self: super: {
              nsncd = super.nsncd.overrideAttrs (_: {
                src = nsncd;
              });
            })
          ];
        })
        ...
      

[grahamc]

Not sure I follow. The previous code did return an error if addresses was not Ok, and you changed it to become an empty list of addresses.

We did filter out all addresses that are not IPv4 from the getaddrinfo call, so I would have assumed this to be an empty list in that case?

It looks to me like the change is making it return Ok(None) if there are no IPv4 addresses, and that returning an Ok(Some(...)) with an empty list is causing firefox to crash. It may be that Vec1 would be a better return type: https://crates.io/crates/vec1/1.0.0

[andir]

Not sure I follow. The previous code did return an error if addresses was not Ok, and you changed it to become an empty list of addresses.
We did filter out all addresses that are not IPv4 from the getaddrinfo call, so I would have assumed this to be an empty list in that case?

It looks to me like the change is making it return Ok(None) if there are no IPv4 addresses, and that returning an Ok(Some(...)) with an empty list is causing firefox to crash. It may be that Vec1 would be a better return type: https://crates.io/crates/vec1/1.0.0

I fixed that in andir@16bee69 which is in another branch with tons of refactorings. Instead of requiring a Vec1 I made it so that the code is safe to use with an empty list.

[flokli]

@andir can you cherry-pick the fixes into this PR here, and maybe improve some of the commit messages, if things are still unclear?

Happy to also merge the refactoring a, but that should probably be a separate PR :-)

[flokli]

Alright, I'm gonna merge this and cherry-pick some of the fixes too. Thanks for the PR!