feat(persist): add systemd persistence backend with uninstall

https://chatgpt.com/share/69733e45-96ec-800f-9aad-0cac7306dedd

.gitignore

@@ -1,4 +1,5 @@
 *.pyc
 __pycache__
 dist/
+build/*
 *.egg-info

Makefile

@@ -10,3 +10,6 @@ help:
 
 test:
 	@PYTHONPATH="$(CURDIR)/src" "$(PYTHON)" -m unittest discover -s tests/unit -p "test_*.py" -v
+
+install:
+	sudo pip install -e . --upgrade --break-system-packages

src/automtu/__init__.py

@@ -1,2 +0,0 @@
-__all__ = ["__version__"]
-__version__ = "0.1.0"

src/automtu/cli.py

@@ -91,6 +91,18 @@ def build_parser() -> argparse.ArgumentParser:
         "--dry-run", action="store_true", help="Show actions without applying changes."
     )
 
+    # --- Persistence ---
+    ap.add_argument(
+        "--persist",
+        choices=["systemd"],
+        help="Persist MTU configuration across reboots (currently supported: systemd).",
+    )
+    ap.add_argument(
+        "--uninstall",
+        action="store_true",
+        help="Uninstall persistence backend (requires --persist).",
+    )
+
     # --- Machine-readable output modes ---
     ap.add_argument(
         "--print-mtu",

src/automtu/core.py

@@ -57,14 +57,31 @@ def run_automtu(args) -> int:
 
     log = Logger(mode.machine).log
 
-    # Root is only needed if we actually change something (without --dry-run).
     needs_root = bool(
-        args.apply_egress_mtu
-        or args.apply_wg_mtu
-        or (args.force_egress_mtu is not None)
+        getattr(args, "apply_egress_mtu", False)
+        or getattr(args, "apply_wg_mtu", False)
+        or (getattr(args, "force_egress_mtu", None) is not None)
+        or (getattr(args, "persist", None) is not None)
     )
     require_root(dry=args.dry_run, needs_root=needs_root)
 
+    # Persistence mode: install/uninstall persistence mechanism and exit.
+    if getattr(args, "persist", None):
+        if args.persist == "systemd":
+            from .persist import persist_systemd, uninstall_systemd
+
+            if getattr(args, "uninstall", False):
+                uninstall_systemd(dry=args.dry_run)
+                return 0
+
+            persist_systemd(sys.argv, dry=args.dry_run)
+            return 0
+
+        print(
+            f"[automtu][ERROR] Unknown persist backend: {args.persist}", file=sys.stderr
+        )
+        return 4
+
     egress = args.egress_if or detect_egress_iface(ignore_vpn=not args.prefer_wg_egress)
     if not egress:
         print(

src/automtu/persist.py

@@ -0,0 +1,119 @@
+from __future__ import annotations
+
+import shlex
+import shutil
+import subprocess
+from pathlib import Path
+from typing import List
+
+
+_SYSTEMD_UNIT_PATH = Path("/etc/systemd/system/automtu.service")
+
+
+def _strip_persist_args(argv: List[str]) -> List[str]:
+    """
+    Remove persistence-only arguments from argv:
+    - --persist systemd
+    - --persist=systemd
+    - --uninstall
+    Keeps all other args as-is.
+    """
+    out: list[str] = []
+    i = 0
+    while i < len(argv):
+        a = argv[i]
+        if a == "--persist":
+            i += 1
+            if i < len(argv) and not argv[i].startswith("-"):
+                i += 1
+            continue
+        if a.startswith("--persist="):
+            i += 1
+            continue
+        if a == "--uninstall":
+            i += 1
+            continue
+        out.append(a)
+        i += 1
+    return out
+
+
+def _resolve_exec(argv0: str) -> str:
+    """
+    Resolve the executable path for systemd ExecStart.
+
+    Prefer an absolute path (from PATH lookup). Fall back to argv0.
+    """
+    resolved = shutil.which(argv0)
+    if resolved:
+        return resolved
+    return argv0
+
+
+def persist_systemd(argv: List[str], *, dry: bool) -> None:
+    """
+    Install a systemd oneshot service that re-runs automtu with the same arguments.
+    This provides a distro-agnostic persistence mechanism.
+    """
+    if not argv:
+        raise ValueError("argv must not be empty")
+
+    filtered = _strip_persist_args(argv[:])
+    if not filtered:
+        raise ValueError("argv filtered to empty; cannot persist")
+
+    exe = _resolve_exec(filtered[0])
+    args = [exe, *filtered[1:]]
+
+    execstart = shlex.join(args)
+
+    unit = f"""\
+[Unit]
+Description=Auto MTU via automtu
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=oneshot
+ExecStart={execstart}
+
+[Install]
+WantedBy=multi-user.target
+"""
+
+    if dry:
+        print(f"[automtu] DRY-RUN: would write systemd unit to {_SYSTEMD_UNIT_PATH}")
+        print(unit.rstrip())
+        print("[automtu] DRY-RUN: would run: systemctl daemon-reload")
+        print("[automtu] DRY-RUN: would run: systemctl enable automtu.service")
+        return
+
+    _SYSTEMD_UNIT_PATH.write_text(unit)
+
+    subprocess.run(["systemctl", "daemon-reload"], check=True)
+    subprocess.run(["systemctl", "enable", "automtu.service"], check=True)
+
+    print("[automtu] Installed and enabled systemd service: automtu.service")
+    print("[automtu] Tip: run 'systemctl start automtu.service' to apply immediately.")
+
+
+def uninstall_systemd(*, dry: bool) -> None:
+    """
+    Uninstall the systemd persistence backend:
+    - disable automtu.service
+    - remove unit file (if present)
+    - daemon-reload
+    """
+    if dry:
+        print("[automtu] DRY-RUN: would run: systemctl disable automtu.service")
+        print(f"[automtu] DRY-RUN: would remove: {_SYSTEMD_UNIT_PATH} (if exists)")
+        print("[automtu] DRY-RUN: would run: systemctl daemon-reload")
+        return
+
+    subprocess.run(["systemctl", "disable", "automtu.service"], check=True)
+
+    if _SYSTEMD_UNIT_PATH.exists():
+        _SYSTEMD_UNIT_PATH.unlink()
+
+    subprocess.run(["systemctl", "daemon-reload"], check=True)
+    print("[automtu] Uninstalled systemd service: automtu.service")

tests/unit/test___init__.py

@@ -1,14 +0,0 @@
-import unittest
-
-import automtu
-
-
-class TestInit(unittest.TestCase):
-    def test_version_is_exposed(self) -> None:
-        self.assertTrue(hasattr(automtu, "__version__"))
-        self.assertIsInstance(automtu.__version__, str)
-        self.assertRegex(automtu.__version__, r"^\d+\.\d+\.\d+$")
-
-
-if __name__ == "__main__":
-    unittest.main(verbosity=2)

tests/unit/test_persist.py

@@ -0,0 +1,114 @@
+import io
+import unittest
+from contextlib import redirect_stdout
+from pathlib import Path
+from unittest.mock import patch
+
+import automtu.persist as persist
+
+
+class TestPersist(unittest.TestCase):
+    def test_strip_persist_args_removes_flag_and_value(self) -> None:
+        argv = ["automtu", "--apply-wg-mtu", "--persist", "systemd"]
+        self.assertEqual(
+            persist._strip_persist_args(argv),
+            ["automtu", "--apply-wg-mtu"],
+        )
+
+    def test_strip_persist_args_removes_equals_form(self) -> None:
+        argv = ["automtu", "--apply-wg-mtu", "--persist=systemd"]
+        self.assertEqual(
+            persist._strip_persist_args(argv),
+            ["automtu", "--apply-wg-mtu"],
+        )
+
+    def test_strip_persist_args_removes_uninstall(self) -> None:
+        argv = ["automtu", "--persist", "systemd", "--uninstall", "--apply-wg-mtu"]
+        self.assertEqual(
+            persist._strip_persist_args(argv),
+            ["automtu", "--apply-wg-mtu"],
+        )
+
+    def test_persist_systemd_dry_run_prints_unit(self) -> None:
+        argv = [
+            "automtu",
+            "--auto-pmtu-from-wg",
+            "--apply-wg-mtu",
+            "--persist",
+            "systemd",
+        ]
+
+        with (
+            patch("automtu.persist.shutil.which", return_value="/usr/bin/automtu"),
+            patch("automtu.persist._SYSTEMD_UNIT_PATH", Path("/tmp/automtu.service")),
+        ):
+            out = io.StringIO()
+            with redirect_stdout(out):
+                persist.persist_systemd(argv, dry=True)
+
+        s = out.getvalue()
+        self.assertIn("DRY-RUN", s)
+        self.assertIn(
+            "ExecStart=/usr/bin/automtu --auto-pmtu-from-wg --apply-wg-mtu", s
+        )
+
+    def test_uninstall_systemd_dry_run_prints_actions(self) -> None:
+        with patch("automtu.persist._SYSTEMD_UNIT_PATH", Path("/tmp/automtu.service")):
+            out = io.StringIO()
+            with redirect_stdout(out):
+                persist.uninstall_systemd(dry=True)
+
+        s = out.getvalue()
+        self.assertIn("DRY-RUN", s)
+        self.assertIn("systemctl disable", s)
+
+    def test_uninstall_systemd_runs_disable_and_removes_unit_when_present(self) -> None:
+        fake_path = Path("/tmp/automtu.service")
+
+        calls = []
+
+        def fake_run(cmd, check=False):  # type: ignore[no-untyped-def]
+            calls.append((tuple(cmd), bool(check)))
+
+        with (
+            patch("automtu.persist._SYSTEMD_UNIT_PATH", fake_path),
+            patch("automtu.persist.subprocess.run", side_effect=fake_run),
+            patch.object(Path, "exists", return_value=True),
+            patch.object(Path, "unlink", return_value=None),
+        ):
+            persist.uninstall_systemd(dry=False)
+
+        # Must disable unit and reload daemon
+        self.assertIn((("systemctl", "disable", "automtu.service"), True), calls)
+        self.assertIn((("systemctl", "daemon-reload"), True), calls)
+
+    def test_persist_systemd_writes_unit_and_enables(self) -> None:
+        argv = ["automtu", "--apply-wg-mtu", "--persist", "systemd"]
+
+        writes = {"text": None}
+        calls = []
+
+        def fake_write_text(self, txt, *args, **kwargs):  # type: ignore[no-untyped-def]
+            writes["text"] = txt
+            return len(txt)
+
+        def fake_run(cmd, check=False):  # type: ignore[no-untyped-def]
+            calls.append((tuple(cmd), bool(check)))
+
+        with (
+            patch("automtu.persist.shutil.which", return_value="/usr/bin/automtu"),
+            patch("automtu.persist._SYSTEMD_UNIT_PATH", Path("/tmp/automtu.service")),
+            patch.object(Path, "write_text", new=fake_write_text),
+            patch("automtu.persist.subprocess.run", side_effect=fake_run),
+        ):
+            persist.persist_systemd(argv, dry=False)
+
+        self.assertIsNotNone(writes["text"])
+        self.assertIn("ExecStart=/usr/bin/automtu --apply-wg-mtu", writes["text"] or "")
+
+        self.assertIn((("systemctl", "daemon-reload"), True), calls)
+        self.assertIn((("systemctl", "enable", "automtu.service"), True), calls)
+
+
+if __name__ == "__main__":
+    unittest.main(verbosity=2)