matter-server: add nixos service module

New module to run the python-matter-server executable as a sandboxed
system service.

nixos/doc/manual/release-notes/rl-2405.section.md

@@ -62,6 +62,10 @@ In addition to numerous new and upgraded packages, this release has the followin
 
 - [hebbot](https://github.com/haecker-felix/hebbot), a Matrix bot to generate "This Week in X" like blog posts. Available as [services.hebbot](#opt-services.hebbot.enable).
 
+- [Python Matter Server](https://github.com/home-assistant-libs/python-matter-server), a
+  Matter Controller Server exposing websocket connections for use with other services, notably Home Assistant.
+  Available as [services.matter-server](#opt-services.matter-server.enable)
+
 - [Anki Sync Server](https://docs.ankiweb.net/sync-server.html), the official sync server built into recent versions of Anki. Available as [services.anki-sync-server](#opt-services.anki-sync-server.enable).
 The pre-existing [services.ankisyncd](#opt-services.ankisyncd.enable) has been marked deprecated and will be dropped after 24.05 due to lack of maintenance of the anki-sync-server softwares.
 

nixos/modules/module-list.nix

@@ -580,6 +580,7 @@
   ./services/home-automation/govee2mqtt.nix
   ./services/home-automation/home-assistant.nix
   ./services/home-automation/homeassistant-satellite.nix
+  ./services/home-automation/matter-server.nix
   ./services/home-automation/zigbee2mqtt.nix
   ./services/home-automation/zwave-js.nix
   ./services/logging/SystemdJournal2Gelf.nix

nixos/modules/services/home-automation/matter-server.nix

@@ -0,0 +1,125 @@
+{ lib
+, pkgs
+, config
+, ...
+}:
+
+with lib;
+
+let
+  cfg = config.services.matter-server;
+  storageDir = "matter-server";
+  storagePath = "/var/lib/${storageDir}";
+  vendorId = "4939"; # home-assistant vendor ID
+in
+
+{
+  meta.maintainers = with lib.maintainers; [ leonm1 ];
+
+  options.services.matter-server = with types; {
+    enable = mkEnableOption (lib.mdDoc "Matter-server");
+
+    package = mkPackageOptionMD pkgs "python-matter-server" { };
+
+    port = mkOption {
+      type = types.port;
+      default = 5580;
+      description = "Port to expose the matter-server service on.";
+    };
+
+    logLevel = mkOption {
+      type = types.enum [ "critical" "error" "warning" "info" "debug" ];
+      default = "info";
+      description = "Verbosity of logs from the matter-server";
+    };
+
+    extraArgs = mkOption {
+      type = listOf str;
+      default = [];
+      description = ''
+        Extra arguments to pass to the matter-server executable.
+        See https://github.com/home-assistant-libs/python-matter-server?tab=readme-ov-file#running-the-development-server for options.
+      '';
+    };
+  };
+
+  config = mkIf cfg.enable {
+    systemd.services.matter-server = {
+      after = [ "network-online.target" ];
+      before = [ "home-assistant.service" ];
+      wants = [ "network-online.target" ];
+      wantedBy = [ "multi-user.target" ];
+      description = "Matter Server";
+      environment.HOME = storagePath;
+      serviceConfig = {
+        ExecStart = (concatStringsSep " " [
+          "${cfg.package}/bin/matter-server"
+          "--port" (toString cfg.port)
+          "--vendorid" vendorId
+          "--storage-path" storagePath
+          "--log-level" "${cfg.logLevel}"
+          "${escapeShellArgs cfg.extraArgs}"
+        ]);
+        # Start with a clean root filesystem, and allowlist what the container
+        # is permitted to access.
+        TemporaryFileSystem = "/";
+        # Allowlist /nix/store (to allow the binary to find its dependencies)
+        # and dbus.
+        ReadOnlyPaths = "/nix/store /run/dbus";
+        # Let systemd manage `/var/lib/matter-server` for us inside the
+        # ephemeral TemporaryFileSystem.
+        StateDirectory = storageDir;
+        # `python-matter-server` writes to /data even when a storage-path is
+        # specified. This bind-mount points /data at the systemd-managed
+        # /var/lib/matter-server, so all files get dropped into the state
+        # directory.
+        BindPaths = "${storagePath}:/data";
+
+        # Hardening bits
+        AmbientCapabilities = "";
+        CapabilityBoundingSet = "";
+        DevicePolicy = "closed";
+        DynamicUser = true;
+        LockPersonality = true;
+        MemoryDenyWriteExecute = true;
+        NoNewPrivileges = true;
+        PrivateDevices = true;
+        PrivateTmp = true;
+        PrivateUsers = true;
+        ProcSubset = "pid";
+        ProtectClock = true;
+        ProtectControlGroups = true;
+        ProtectHome = true;
+        ProtectHostname = true;
+        ProtectKernelLogs = true;
+        ProtectKernelModules = true;
+        ProtectKernelTunables = true;
+        ProtectProc = "invisible";
+        RestrictAddressFamilies = [
+          "AF_INET"
+          "AF_INET6"
+          "AF_NETLINK"
+        ];
+        RestrictNamespaces = true;
+        RestrictRealtime = true;
+        RestrictSUIDSGID = true;
+        SystemCallFilter = concatStringsSep " " [
+          "~" # Blocklist
+          "@clock"
+          "@cpu-emulation"
+          "@debug"
+          "@module"
+          "@mount"
+          "@obsolete"
+          "@privileged"
+          "@raw-io"
+          "@reboot"
+          "@resources"
+          "@swap"
+        ];
+        UMask = "0077";
+      };
+    };
+  };
+}
+

nixos/tests/all-tests.nix

@@ -510,6 +510,7 @@ in {
   mastodon = discoverTests (import ./web-apps/mastodon { inherit handleTestOn; });
   pixelfed = discoverTests (import ./web-apps/pixelfed { inherit handleTestOn; });
   mate = handleTest ./mate.nix {};
+  matter-server = handleTest ./matter-server.nix {};
   matomo = handleTest ./matomo.nix {};
   matrix-appservice-irc = handleTest ./matrix/appservice-irc.nix {};
   matrix-conduit = handleTest ./matrix/conduit.nix {};

nixos/tests/matter-server.nix

@@ -0,0 +1,45 @@
+import ./make-test-python.nix ({ pkgs, lib, ...} :
+
+let
+  chipVersion = pkgs.python311Packages.home-assistant-chip-core.version;
+in
+
+{
+  name = "matter-server";
+  meta.maintainers = with lib.maintainers; [ leonm1 ];
+
+  nodes = {
+    machine = { config, ... }: {
+      services.matter-server = {
+        enable = true;
+        port = 1234;
+      };
+    };
+  };
+
+  testScript = /* python */ ''
+    start_all()
+
+    machine.wait_for_unit("matter-server.service")
+    machine.wait_for_open_port(1234)
+
+    with subtest("Check websocket server initialized"):
+        output = machine.succeed("echo \"\" | ${pkgs.websocat}/bin/websocat ws://localhost:1234/ws")
+        machine.log(output)
+
+    assert '"sdk_version": "${chipVersion}"' in output, (
+      'CHIP version \"${chipVersion}\" not present in websocket message'
+    )
+
+    assert '"fabric_id": 1' in output, (
+      "fabric_id not propagated to server"
+    )
+
+    with subtest("Check storage directory is created"):
+        machine.succeed("ls /var/lib/matter-server/chip.json")
+
+    with subtest("Check systemd hardening"):
+        _, output = machine.execute("systemd-analyze security matter-server.service | grep -v '✓'")
+        machine.log(output)
+  '';
+})