nixos service: add ipv6 support. Better control of port sharing.

 use-case: ipv6 addr can be used in multi-instances mode so that instances
 on same machine can be included each other topology's, while still
 sharing ipv4 port.

nix/nixos/cardano-node-service.nix

@@ -56,12 +56,13 @@ let
           "--config ${realNodeConfigFile}"
           "--database-path ${instanceDbPath}"
           "--topology ${topology}"
-        ] ++ (lib.optionals (!cfg.systemdSocketActivation) [
+        ] ++ (lib.optionals (!cfg.systemdSocketActivation) ([
           "--host-addr ${cfg.hostAddr}"
-          "--port ${toString cfg.port}"
+          "--port ${toString (cfg.port + i)}"
           "--socket-path ${cfg.socketPath}"
-        ])
-          ++ consensusParams.${cfg.nodeConfig.Protocol} ++ cfg.extraArgs ++ cfg.rtsArgs;
+        ] ++ lib.optional (cfg.ipv6HostAddr != null)
+          "--host-ipv6-addr ${cfg.ipv6HostAddr}"
+        )) ++ consensusParams.${cfg.nodeConfig.Protocol} ++ cfg.extraArgs ++ cfg.rtsArgs;
     in ''
         choice() { i=$1; shift; eval "echo \''${$((i + 1))}"; }
         echo "Starting ${exec}: ${concatStringsSep "\"\n   echo \"" cmd}"
@@ -258,6 +259,14 @@ in {
         '';
       };
 
+      ipv6HostAddr = mkOption {
+        type = types.nullOr types.str;
+        default = "::1";
+        description = ''
+          The ipv6 host address to bind to. Set to null to disable.
+        '';
+      };
+
       stateDir = mkOption {
         type = types.str;
         default = "/var/lib/cardano-node";
@@ -333,6 +342,27 @@ in {
         '';
       };
 
+      shareIpv4port = mkOption {
+        type = types.bool;
+        default = cfg.systemdSocketActivation;
+        description = ''
+          Should instances on same machine share ipv4 port.
+          Default: true if systemd activated socket. Otherwise always false.
+          If false use port increments starting from `port`.
+        '';
+      };
+
+      shareIpv6port = mkOption {
+        type = types.bool;
+        default = false;
+        description = ''
+          Should instances on same machine share ipv6 port.
+          Only works with systemd socket.
+          Default: false.
+          If false use port increments starting from `port`.
+        '';
+      };
+
       nodeId = mkOption {
         type = types.int;
         default = 0;
@@ -356,7 +386,7 @@ in {
         # type = types.functionTo (types.listOf types.attrs);
         default = _: [];
         description = ''
-          Static routes to peers, specific to a given instance (when multiple instances are used)
+          Static routes to peers, specific to a given instance (when multiple instances are used).
         '';
       };
 
@@ -481,7 +511,8 @@ in {
         wantedBy = [ "sockets.target" ];
         partOf = [ "${n}.service" ];
         socketConfig = {
-          ListenStream = [ "${cfg.hostAddr}:${toString cfg.port}" ]
+          ListenStream = [ "${cfg.hostAddr}:${toString (if cfg.shareIpv4port then cfg.port else cfg.port + i)}" ]
+            ++ optional (cfg.ipv6HostAddr != null) "[${cfg.ipv6HostAddr}]:${toString (if cfg.shareIpv6port then cfg.port else cfg.port + i)}"
             ++ [(if (i == 0) then cfg.socketPath else "${runtimeDir}-${toString i}/node.socket")];
           ReusePort = "yes";
           SocketMode = "0660";