New minecraft-server module

modules/default.nix

@@ -6,6 +6,7 @@
     ./anycast_healthchecker
     ./gitea
     ./gre-tunnel
+    ./minecraft-server
     ./nginx-port-forward
   ];
 }

modules/minecraft-server/default.nix

@@ -0,0 +1,84 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.clerie.minecraft-server;
+
+  # We don't allow eula=false anyways
+  eulaFile = builtins.toFile "eula.txt" ''
+    # eula.txt managed by NixOS Configuration
+    eula=true
+  '';
+
+  generateServerUnit = name: server: (
+    nameValuePair "minecraft-server-${name}" (mkIf server.enable {
+
+      description   = "Minecraft Server ${name}";
+      wantedBy      = [ "multi-user.target" ];
+      after         = [ "network.target" ];
+
+      serviceConfig = {
+        ExecStart = "${server.package}/bin/minecraft-server ${server.jvmOpts}";
+        Restart = "always";
+        WorkingDirectory = if server.dataDir != null then server.dataDir else "/var/lib/minecraft-server-${name}";
+        StateDirectory = "minecraft-server-${name}";
+        DynamicUser = true;
+      };
+
+      preStart = ''
+        ln -sf ${eulaFile} eula.txt
+      '';
+    })
+  );
+
+  serverOpts = { config, ... }@moduleAttrs: {
+    options = {
+
+      enable = mkEnableOption "A shared minecraft hosting service.";
+
+      dataDir = mkOption {
+        type = with types; nullOr path;
+        default = null;
+        description = ''
+          Directory to store Minecraft database and other state/data files.
+          When null defaulting to /var/lib/minecraft-server-${name}
+        '';
+      };
+
+      package = mkOption {
+        type = types.package;
+        default = pkgs.papermc;
+        defaultText = "pkgs.papermc";
+        example = literalExample "pkgs.minecraft-server_1_12_2";
+        description = "Version of minecraft-server to run.";
+      };
+
+      jvmOpts = mkOption {
+        type = types.separatedString " ";
+        default = "-Xmx2G -Xms1G";
+        # Example options from https://minecraft.gamepedia.com/Tutorials/Server_startup_script
+        example = "-Xmx2048M -Xms4092M -XX:+UseG1GC -XX:+CMSIncrementalPacing "
+          + "-XX:+CMSClassUnloadingEnabled -XX:ParallelGCThreads=2 "
+          + "-XX:MinHeapFreeRatio=5 -XX:MaxHeapFreeRatio=10";
+        description = "JVM options for the Minecraft server.";
+      };
+    };
+  };
+
+in {
+  options = {
+    clerie.minecraft-server = {
+
+      servers = mkOption {
+        type = with types; attrsOf (submodule serverOpts);
+        default = {};
+      };
+
+    };
+  };
+
+  config = {
+    systemd.services = (mapAttrs' generateServerUnit cfg.servers);
+  };
+}