i2p: add nixos service

nixos/modules/misc/ids.nix

@@ -215,6 +215,7 @@
       mediatomb = 187;
       rdnssd = 188;
       ihaskell = 189;
+      i2p = 190;
 
       # When adding a uid, make sure it doesn't match an existing gid. And don't use uids above 399!
 
@@ -407,6 +408,7 @@
       mediatomb = 187;
       #rdnssd = 188; # unused
       ihaskell = 189;
+      i2p = 190;
 
       # When adding a gid, make sure it doesn't match an existing
       # uid. Users and groups with the same name should have equal

nixos/modules/services/networking/i2p.nix

@@ -0,0 +1,42 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.services.i2p;
+  homeDir = "/var/lib/i2p";
+in {
+  ###### interface
+  options.services.i2p = {
+      enable = mkOption {
+        type = types.bool;
+        default = false;
+        description = ''
+          Enables i2p as a running service upon activation.
+        '';
+      };
+  };
+
+  ###### implementation
+  config = mkIf cfg.enable {
+    users.extraUsers.i2p = {
+      group = "i2p";
+      description = "i2p User";
+      home = homeDir;
+      createHome = true;
+      uid = config.ids.uids.i2p;
+    };
+    users.extraGroups.i2p.gid = config.ids.gids.i2p;
+    systemd.services.i2p = {
+      description = "I2P router with administration interface for hidden services";
+      after = [ "network.target" ];
+      wantedBy = [ "multi-user.target" ];
+      serviceConfig = {
+        User = "i2p";
+        WorkingDirectory = homeDir;
+        Restart = "on-abort";
+        ExecStart = "${pkgs.i2p}/bin/i2prouter-plain";
+      };
+    };
+  };
+}