nixos/getaddrinfo: init

This commit introduces a new NixOS module `networking.getaddrinfo` to allow
declarative configuration of `/etc/gai.conf`, which controls address
selection behavior for `getaddrinfo(3)` as defined in RFC 3484 and
RFC 6724.

nixos/modules/config/getaddrinfo.nix

@@ -0,0 +1,120 @@
+{
+  pkgs,
+  lib,
+  config,
+  ...
+}:
+let
+  cfg = config.networking.getaddrinfo;
+
+  formatTableEntries =
+    tableName: table:
+    if table == null then
+      [ ]
+    else
+      lib.mapAttrsToList (cidr: val: "${tableName} ${cidr} ${toString val}") table;
+
+  gaiConfText = lib.concatStringsSep "\n" (
+    [
+      "# Generated by NixOS module networking.getaddrinfo"
+      "# Do not edit manually!"
+      "reload ${if cfg.reload then "yes" else "no"}"
+    ]
+    ++ formatTableEntries "label" cfg.label
+    ++ formatTableEntries "precedence" cfg.precedence
+    ++ formatTableEntries "scopev4" cfg.scopev4
+  );
+in
+{
+  options.networking.getaddrinfo = {
+    enable = lib.mkOption {
+      type = lib.types.bool;
+      default = pkgs.stdenv.hostPlatform.libc == "glibc";
+      defaultText = lib.literalExpression ''
+        pkgs.stdenv.hostPlatform.libc == "glibc"
+      '';
+      description = ''
+        Enables custom address sorting configuration for {manpage}`getaddrinfo(3)` according to RFC 3484.
+
+        This option generates a {file}`/etc/gai.conf` file to override the default address sorting tables,
+        as described in {manpage}`gai.conf(5)`.
+
+        This setting is only applicable when using the GNU C Library (glibc).
+        It has no effect with other libc implementations.
+      '';
+    };
+
+    reload = lib.mkOption {
+      type = lib.types.bool;
+      default = false;
+      description = ''
+        Determines whether a process should detect changes to the configuration file since it was last read.
+
+        If enabled, the file is re-read automatically. This may cause issues in multithreaded applications
+        and is generally discouraged.
+      '';
+    };
+
+    label = lib.mkOption {
+      type = lib.types.nullOr (lib.types.attrsOf lib.types.int);
+      default = null;
+      description = ''
+        Adds entries to the label table, as described in section 2.1 of RFC 3484.
+
+        If any label entries are provided, the glibc’s default label table is ignored.
+      '';
+      example = {
+        "::/0" = 1;
+        "2002::/16" = 2;
+        "::/96" = 3;
+        "::ffff:0:0/96" = 4;
+        "fec0::/10" = 5;
+        "fc00::/7" = 6;
+        "2001:0::/32" = 7;
+      };
+    };
+
+    precedence = lib.mkOption {
+      type = lib.types.nullOr (lib.types.attrsOf lib.types.int);
+      default = null;
+      description = ''
+        Similar to {option}`networking.getaddrinfo.label`, but this option
+        defines entries for the precedence table instead.
+
+        See sections 2.1 and 10.3 of RFC 3484 for details.
+
+        Providing any value will disable the glibc's default precedence table.
+      '';
+      example = {
+        "::1/128" = 50;
+        "::/0" = 40;
+        "2002::/16" = 30;
+        "::/96" = 20;
+        "::ffff:0:0/96" = 10;
+      };
+    };
+
+    scopev4 = lib.mkOption {
+      type = lib.types.nullOr (lib.types.attrsOf lib.types.int);
+      default = null;
+      description = ''
+        Adds custom rules to the IPv4 scope table.
+
+        By default, the scope IDs described in section 3.2 of RFC 6724 are used.
+
+        Modifying these values is rarely necessary.
+      '';
+      example = {
+        "::ffff:169.254.0.0/112" = 2;
+        "::ffff:127.0.0.0/104" = 2;
+        "::ffff:0.0.0.0/96" = 14;
+      };
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    environment.etc."gai.conf".text = gaiConfText;
+  };
+
+  meta.maintainers = with lib.maintainers; [ moraxyc ];
+}

nixos/modules/module-list.nix

@@ -8,6 +8,7 @@
   ./config/fonts/fontdir.nix
   ./config/fonts/ghostscript.nix
   ./config/fonts/packages.nix
+  ./config/getaddrinfo.nix
   ./config/gtk/gtk-icon-cache.nix
   ./config/i18n.nix
   ./config/iproute2.nix