Replace ddclient with shell script

hosts/dyndns.nix

@@ -1,9 +1,6 @@
 { config, pkgs, lib, ... }:
 let
-    definedInPersonalDotNix = lib.mkDefault (throw "Configuration option missing from personal.nix");
-    getipv6 = pkgs.writeText "getipv6.sh" ''
-      ${pkgs.nettools}/bin/ifconfig enp3s0 | sed -n -E 's/^\ *inet6 (2001(:[0-9a-f]+)+)\ .*$/\1/p'
-    '';
+    interface = "enp3s0";
 in
 {
     networking.tempAddresses = "disabled";
@@ -15,7 +12,7 @@ in
             slaac hwaddr
             noipv4ll
 
-            interface enp3s0
+            interface ${interface}
                 static ip_address=192.168.178.43/24	
                 static routers=192.168.178.1
                 static domain_name_servers=192.168.178.1 8.8.8.8
@@ -24,19 +21,9 @@ in
         '';
     };
 
-    services.ddclient = {
+    services.dyndns = {
         enable = true;
-        verbose = true;
-        use = "cmd, cmd='${pkgs.bash}/bin/bash ${getipv6}'";
-        domains = [
-            ((lib.toLower config.networking.hostName) + ".gvfr.de")
-        ];
-        ipv6 = true;
-        server = definedInPersonalDotNix;
-        username = definedInPersonalDotNix;
-        passwordFile = "/secrets/dyndns_password_${config.services.ddclient.username}.txt";
-        extraConfig = ''
-            wildcard=no
-        '';
+        interface = interface;
+        passwordFile = "/secrets/dyndns_password_${config.services.dyndns.username}.txt";
     };
 }

options/default.nix

@@ -6,5 +6,6 @@
         ./auto-upgrade.nix
         ./status-email.nix
         ./btrfs-scrub.nix
+        ./dyndns.nix
     ];
 }

options/dyndns.nix

@@ -0,0 +1,95 @@
+{ pkgs, lib, config, ... }:
+let
+    cfg = config.services.dyndns;
+in
+{
+    options.services.dyndns = {
+        enable = lib.mkEnableOption "Update DNS AAAA records via dyndns";
+
+        interface = lib.mkOption {
+            type = lib.types.str;
+            description = "Identifier of the network interface to use";
+        };
+
+        domain = lib.mkOption {
+            type = lib.types.str;
+            description = "Domain name to update";
+        };
+
+        server = lib.mkOption {
+            type = lib.types.str;
+            description = "DynDNS server name";
+        };
+
+        username = lib.mkOption {
+            type = lib.types.str;
+            description = "Username for DynDNS updates";
+        };
+
+        passwordFile = lib.mkOption {
+            type = lib.types.str;
+            description = "File containing the DynDNS password";
+        };
+    };
+
+    config = lib.mkIf cfg.enable {
+        systemd.services.dyndns = {
+            enable = true;
+            after = [ "network.target" ];
+            unitConfig = {
+                Description = "Update AAAA records for ${cfg.domain} via DynDNS";
+            };
+            serviceConfig = {
+                DynamicUser = true;
+                PrivateTmp = true;
+                PrivateDevices = true;
+                ProtectSystem = true;
+                ProtectHome = true;
+                NoNewPrivileges = true;
+            };
+            script = ''
+                #!${pkgs.bash}/bin/bash
+
+                set -eu
+
+                host="${cfg.domain}"
+                interface="${cfg.interface}"
+                dyndns_server="${cfg.server}"
+                dyndns_user="${cfg.username}"
+                dyndns_password="$(cat "${cfg.passwordFile}")"
+
+                new_ip=$(${pkgs.iproute}/bin/ip -6 a show scope global -temporary dev "$interface" | ${pkgs.gnused}/bin/sed -n -E 's/^\ *inet6\ (2001(:[0-9a-f]+)+).*$/\1/p' | head -1)
+
+                if [ -z "$new_ip" ] ; then
+                    echo "Could not determine IP address."
+                    exit 1
+                fi
+
+                current_ip=$(${pkgs.dig}/bin/dig aaaa +short "$host")
+
+                if [ -z "$current_ip" ] ; then
+                    echo "Could not determine current AAAA record."
+                    exit 1
+                fi
+
+                if [ "$current_ip" = "$new_ip" ] ; then
+                    echo "Current AAAA record is already $current_ip, no update needed."
+                    exit 0
+                fi
+
+                echo "Updating IP to $new_ip."
+                ${pkgs.curl}/bin/curl "https://$dyndns_user:$dyndns_password@$dyndns_server/?hostname=$host&myip=$new_ip"
+            '';
+        };
+
+        systemd.timers.dyndns = {
+            description = "Timer for triggering DynDNS updates";
+            wantedBy = [ "timers.target" ];
+            timerConfig = {
+                OnBootSec = "2min";
+                OnUnitActiveSec = "20min";
+                Unit = "dyndns.service";
+            };
+        };
+    };
+}