configuration.nix

{ lib, config, pkgs, ... }:

{
        services = {
                toxvpn.enable = true;
                toxvpn.localip = "192.168.123.10";
        };
        imports = [ <nixpkgs/nixos/modules/profiles/all-hardware.nix> "/etc/nixos/toxvpn_module.nix" ];
}

toxvpn.nix

#{ stdenv, fetchFromGitHub, libtoxcore, cmake, jsoncpp, lib, ... }:
with import <nixpkgs> {};

with lib;

let libtoxcoreLocked = stdenv.lib.overrideDerivation libtoxcore (oldAttrs: {
        name = "libtoxcore-20150424";
        src = fetchFromGitHub {
                owner = "irungentoo";
                repo = "toxcore";
                rev = "964233b0bf8240e70bb8bfddce17262756171231";
                sha256 = "1vcx9qjbnnjvqmc3xwjvisc31wrs4hpcy27qd6icbdl6npls1vgd";
        };
});
stdenv2 = stdenvAdapters.keepDebugInfo stdenv;
in

stdenv2.mkDerivation {
        name = "toxvpn-20150614";
        buildInputs = [ cmake libtoxcoreLocked jsoncpp ];
        src = fetchFromGitHub {
                owner = "cleverca22";
                repo = "toxvpn";
                rev = "90bd373c1ac4594be7e78bf9668801985da6cea6";
                sha256 = "0l6r9k4hq65g76s071q1rv64w3125ir3v4l47qdgn5p9hjb8d2hy";
        };
        meta = {
                description = "a tox based vpn program";
                license = stdenv.lib.licenses.gpl3;
                platforms = stdenv.lib.platforms.linux;
        };
}

toxvpn_module.nix

{ config, stdenv, pkgs, lib, ... }:
#with import <nixpkgs> {};

with lib;

{
        options = {
                services.toxvpn = {
                        enable = mkOption {
                                type = types.bool;
                                default = false;
                                description = "enable toxvpn running on startup";
                        };
                        localip = mkOption {
                                type = types.string;
                                default = "10.123.123.1";
                                description = "your ip on the vpn";
                        };
                };
        };

        config = mkIf config.services.toxvpn.enable {
                nixpkgs.config = {
                        packageOverrides = pkgs: {
                                toxvpn = (import "/etc/nixos/toxvpn.nix");
                        };
                };
                #environment.systemPackages = [ pkgs.toxvpn ];
                systemd = let
                        service = {
                                description = "toxvpn daemon";
                                #path = [ config.programs.toxvpn.package ];
                                serviceConfig = {
                                        ExecStart = "${pkgs.toxvpn}/bin/toxvpn -si ${config.services.toxvpn.localip}";
                                        #ExecStart = "/root/toxvpn/toxvpn -si ${config.services.toxvpn.localip}";
                                        KillMode = "process";
                                        Restart = "on-success";
                                        StandardInput = "socket";
                                        StandardOutput = "journal";
                                };
                        };
                        socket = {
                                socketConfig = {
                                        ListenStream = "/run/toxvpn";
                                };
                        };
                in {
                        services.toxvpn = service;
                        sockets.toxvpn = socket;
                };
        };
}