Gethostbyname: use proper glibc function

[picnoir]

We internally used getai to restpond to the gethostbyname operations. Sadly, it did not behave as expected and broke some tools (like hostname --fqdn, see #4.

We FFI the right Glibc gethostbyname_2r (now deprecated) function and use it to back the GETHOSTBYNAME and GETHOSTBYNAME6 Nscd interfaces.

Fixes #4

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[picnoir]

Adressed Flokli's nits. Seems to work. I'll use that on my systems the whole day to see if it breaks more stuff.

[picnoir]

I tested that for the day. 2 issues with this:

1. there's something wrong with gethostbyname (both v4 and v6). Most of the function calls are failing with "HOST_NOT_FOUND".
2. there's also something wrong with the error number we're getting back from the glibc functions. This is a h_errno, not a errno.

Here's the h_errno definition:

#define HOST_NOT_FOUND 1
#define TRY_AGAIN      2
#define NO_RECOVERY    3
#define NO_DATA        4
#define NO_ADDRESS     NO_DATA

[picnoir]

Turns out, a lot of things were wrong. I ended up rewriting this PR from scratch twice since last commit…

I think I finally found the right abstraction for hostent... ...and the right defaults wrt. error management. More information in the commit message.

According to sockburp, we're bit-to-bit identical to Nscd for these two new operations now.

[Edit]: hmm, seems like the CI setup has more aliases than my NixOS desktop for localhost. This is annoying, trying to find a more "stable" test case across different hosts.

[picnoir]

I've been using this PR for the last 12h. Sockburp is happy, it seems to behave correctly.

[flokli]

This fails to build on aarch64-linux:

error[E0308]: mismatched types
   --> src/ffi.rs:209:17
    |
204 |             glibcffi::gethostbyaddr_r(
    |             ------------------------- arguments to this function are incorrect
...
209 |                 buf.as_mut_ptr() as *mut i8,
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `*mut u8`, found `*mut i8`
    |
    = note: expected raw pointer `*mut u8`
               found raw pointer `*mut i8`
note: function defined here
   --> src/ffi.rs:65:16
    |
65  |         pub fn gethostbyaddr_r (
    |                ^^^^^^^^^^^^^^^

error[E0308]: mismatched types
   --> src/ffi.rs:253:17
    |
249 |             glibcffi::gethostbyname2_r(
    |             -------------------------- arguments to this function are incorrect
...
253 |                 buf.as_mut_ptr() as *mut i8,
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `*mut u8`, found `*mut i8`
    |
    = note: expected raw pointer `*mut u8`
               found raw pointer `*mut i8`
note: function defined here
   --> src/ffi.rs:55:16
    |
55  |         pub fn gethostbyname2_r (
    |                ^^^^^^^^^^^^^^^^

For more information about this error, try `rustc --explain E0308`.
error: could not compile `nsncd` (bin "nsncd") due to 2 previous errors

[picnoir]

~/code-root/github.com/nix-community/nsncd (hande*) » cargo build                                          101 ↵ ninjatrappeur@framework
   Compiling nsncd v1.4.1 (/home/ninjatrappeur/code-root/github.com/nix-community/nsncd)
error[E0308]: mismatched types
   --> src/ffi.rs:209:17
    |
204 |             glibcffi::gethostbyaddr_r(
    |             ------------------------- arguments to this function are incorrect
...
209 |                 buf.as_mut_ptr() as *mut u8,
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `*mut i8`, found `*mut u8`
    |
    = note: expected raw pointer `*mut i8`
               found raw pointer `*mut u8`
note: function defined here
   --> src/ffi.rs:65:16
    |
65  |         pub fn gethostbyaddr_r (

^ on x86_64.

What the hell.

EDIT: got it. c_char is u8 on arm64, i8 on x86. Fixing that.

[picnoir]

@flokli: PTAL on aarch64

[flokli]

Yes, now builds and works on aarch64-linux!

[flokli]

We both tested this for an extended period of time, and also validated with sockburp comparing responses from nsncd with glibc-nscd. Other than DNS servers returning responses sometimes in different order, there seems to be no differences for host-related lookups. Let's get this in!