feat(services): add syncthing service

hosts/laptop/configuration.nix

@@ -93,6 +93,7 @@ in {
       polkit.enable = true;
       gnome-keyring.enable = true;
       wallpaper.enable = true;
+      syncthing.enable = true;
       ssh = {
         enable = true;
         server = {

hosts/pc/configuration.nix

@@ -132,6 +132,7 @@ in {
       gnome-keyring.enable = true;
       wallpaper.enable = true;
       ssh.enable = true;
+      syncthing.enable = true;
     };
     dev = {
       tools.enable = true;

modules/services/syncthing.nix

@@ -0,0 +1,63 @@
+{
+  config,
+  lib,
+  username,
+  ...
+}:
+with lib;
+with lib.my; let
+  cfg = config.modules.services.syncthing;
+  hmConfig = config.home-manager.users.${username};
+  homeDirectory = hmConfig.home.homeDirectory;
+  configDirectory = hmConfig.xdg.configHome;
+in {
+  options.modules.services.syncthing = {
+    enable = mkEnableOption "syncthing synchronization service";
+  };
+
+  config = mkIf (cfg.enable) {
+    # Syncthing ports: 8384 for remote access to GUI
+    # 22000 TCP and/or UDP for sync traffic
+    # 21027/UDP for discovery
+    # source: https://docs.syncthing.net/users/firewall.html
+    networking.firewall.allowedTCPPorts = [22000];
+    networking.firewall.allowedUDPPorts = [22000 21027];
+
+    # https://github.com/quic-go/quic-go/wiki/UDP-Buffer-Sizes
+    boot.kernel.sysctl = {
+      "net.core.rmem_max" = 7500000;
+      "net.core.wmem_max" = 7500000;
+    };
+
+    services.syncthing = {
+      enable = true;
+      systemService = true;
+      user = username;
+      configDir = "${configDirectory}/syncthing";
+      overrideDevices = true;
+      overrideFolders = true;
+      settings = {
+        options = {
+          urAccepted = -1;
+          globalAnnounceEnabled = false;
+          localAnnounceEnabled = true;
+          relaysEnabled = false;
+          startBrowser = false;
+        };
+
+        devices = {
+          nixos.id = "3EL5IKS-DVGUYLS-3JYXXGI-IEK2VEQ-C2ZUZ5X-PC3CAWN-GAV4OYI-PN6B2AH";
+          laptop.id = "5LUIWNJ-U6567EN-LDFDEZX-65F5MA5-DIBJZDA-LH5N2E5-VVD5CLE-UTWFSAT";
+        };
+
+        folders = {
+          "Development" = {
+            id = "hVYpBP-yrTzAX-PxYRGw-UHvw";
+            path = "${homeDirectory}/dev";
+            devices = ["nixos" "laptop"];
+          };
+        };
+      };
+    };
+  };
+}