refactor: convert script to automtu package with CI workflow

https://chatgpt.com/share/697112b2-0410-800f-93ff-9372b603d43f

tests/unit/test_core.py

@@ -0,0 +1,94 @@
+import io
+import unittest
+from contextlib import redirect_stdout
+from types import SimpleNamespace
+from unittest.mock import patch
+
+from automtu.core import run_automtu
+
+
+class TestCore(unittest.TestCase):
+    def test_run_automtu_happy_path_all_mocked(self) -> None:
+        args = SimpleNamespace(
+            dry_run=True,
+            egress_if=None,
+            prefer_wg_egress=False,
+            force_egress_mtu=None,
+            pmtu_target=["1.1.1.1,8.8.8.8"],
+            auto_pmtu_from_wg=False,
+            pmtu_min_payload=1200,
+            pmtu_max_payload=1472,
+            pmtu_timeout=1.0,
+            pmtu_policy="min",
+            apply_egress_mtu=True,
+            apply_wg_mtu=True,
+            wg_if="wg0",
+            wg_overhead=80,
+            wg_min=1280,
+            set_wg_mtu=None,
+        )
+
+        # PMTU probes: 1452 and 1500 -> min policy => 1452, effective=min(base(1500),1452)=1452
+        # wg_mtu = 1452-80 = 1372
+        with (
+            patch("automtu.core.require_root", return_value=None),
+            patch("automtu.core.detect_egress_iface", return_value="eth0"),
+            patch("automtu.core.iface_exists", return_value=True),
+            patch("automtu.core.read_iface_mtu", return_value=1500),
+            patch("automtu.core.probe_pmtu", side_effect=[1452, 1500]),
+            patch("automtu.core.set_iface_mtu") as mock_set,
+            patch("automtu.core.wg_is_active", return_value=False),
+            patch("automtu.core.wg_peer_endpoints", return_value=[]),
+            patch("automtu.core.default_route_uses_iface", return_value=False),
+        ):
+            buf = io.StringIO()
+            with redirect_stdout(buf):
+                rc = run_automtu(args)
+
+        self.assertEqual(rc, 0)
+        s = buf.getvalue()
+        self.assertIn("Detected egress interface: eth0", s)
+        self.assertIn("Egress base MTU: 1500", s)
+        self.assertIn("Selected Path MTU (policy=min): 1452", s)
+        self.assertIn("Computed wg0 MTU: 1372", s)
+
+        # apply egress and wg are both true -> two calls in order
+        mock_set.assert_any_call("eth0", 1452, True)
+        mock_set.assert_any_call("wg0", 1372, True)
+
+    def test_run_automtu_does_not_apply_wg_without_flag(self) -> None:
+        args = SimpleNamespace(
+            dry_run=True,
+            egress_if="eth0",
+            prefer_wg_egress=False,
+            force_egress_mtu=None,
+            pmtu_target=None,
+            auto_pmtu_from_wg=False,
+            pmtu_min_payload=1200,
+            pmtu_max_payload=1472,
+            pmtu_timeout=1.0,
+            pmtu_policy="min",
+            apply_egress_mtu=False,
+            apply_wg_mtu=False,
+            wg_if="wg0",
+            wg_overhead=80,
+            wg_min=1280,
+            set_wg_mtu=None,
+        )
+
+        with (
+            patch("automtu.core.require_root", return_value=None),
+            patch("automtu.core.iface_exists", return_value=True),
+            patch("automtu.core.read_iface_mtu", return_value=1500),
+            patch("automtu.core.set_iface_mtu") as mock_set,
+        ):
+            buf = io.StringIO()
+            with redirect_stdout(buf):
+                rc = run_automtu(args)
+
+        self.assertEqual(rc, 0)
+        mock_set.assert_not_called()
+
+
+if __name__ == "__main__":
+    unittest.main(verbosity=2)