nixos/whois: init module

Add a NixOS module for the whois client.

This module installs the package and generates /etc/whois.conf from
programs.whois.settings.

nixos/doc/manual/release-notes/rl-2605.section.md

@@ -110,6 +110,8 @@
 
 - [Tdarr](https://tdarr.io), Audio/Video Library Analytics & Transcode/Remux Automation. Available as [services.tdarr](#opt-services.tdarr.enable)
 
+- [whois](https://packages.qa.debian.org/w/whois.html), an intelligent WHOIS client. Available as `programs.whois`.
+
 ## Backward Incompatibilities {#sec-release-26.05-incompatibilities}
 
 <!-- To avoid merge conflicts, consider adding your item at an arbitrary place in the list instead. -->

nixos/modules/module-list.nix

@@ -357,6 +357,7 @@
   ./programs/wayland/wayfire.nix
   ./programs/wayland/wayvnc.nix
   ./programs/weylus.nix
+  ./programs/whois.nix
   ./programs/winbox.nix
   ./programs/wireshark.nix
   ./programs/wshowkeys.nix

nixos/modules/programs/whois.nix

@@ -0,0 +1,89 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+
+let
+  cfg = config.programs.whois;
+
+  configText =
+    lib.concatStringsSep "\n" (
+      [
+        "# Generated by NixOS."
+        "# See whois.conf(5) for the file format."
+      ]
+      ++ map (entry: "${entry.pattern} ${entry.server}") cfg.settings
+    )
+    + "\n";
+in
+
+{
+  options.programs.whois = {
+    enable = lib.mkEnableOption "whois, an intelligent WHOIS client";
+
+    package = lib.mkPackageOption pkgs "whois" { };
+
+    settings = lib.mkOption {
+      type = lib.types.listOf (
+        lib.types.submodule {
+          options = {
+            pattern = lib.mkOption {
+              type = lib.types.str;
+              example = "\\.dn42$";
+              description = ''
+                Case-insensitive extended regular expression used to match the
+                WHOIS object identifier.
+              '';
+            };
+
+            server = lib.mkOption {
+              type = lib.types.str;
+              example = "whois.dn42";
+              description = ''
+                WHOIS server to use when {option}`pattern` matches.
+              '';
+            };
+          };
+        }
+      );
+      default = [ ];
+      example = lib.literalExpression ''
+        [
+          {
+            pattern = "\\.dn42$";
+            server = "whois.dn42";
+          }
+          {
+            pattern = "\\-DN42$";
+            server = "whois.dn42";
+          }
+          {
+            pattern = "^as424242[0-9]{4}$";
+            server = "whois.dn42";
+          }
+          {
+            pattern = "^172\\.2[0-3]\\.[0-9]{1,3}\\.[0-9]{1,3}(/(1[56789]|2[0-9]|3[012]))?$";
+            server = "whois.dn42";
+          }
+        ]
+      '';
+      description = ''
+        WHOIS configuration entries written to {file}`/etc/whois.conf`.
+
+        Entries are written in the declared order, which matters when multiple
+        patterns may match the same query.
+      '';
+    };
+
+  };
+
+  config = lib.mkIf cfg.enable {
+    environment.systemPackages = [ cfg.package ];
+
+    environment.etc."whois.conf".text = configText;
+  };
+
+  meta.maintainers = with lib.maintainers; [ Cryolitia ];
+}