Add wg-mtu-auto initial implementation, documentation, and unit tests

- Added main.py: automatic WireGuard MTU calculation and PMTU probing - Added test.py: unittests covering base, PMTU, and fallback scenarios - Added Makefile: includes test target and install guidance - Added README.md: usage, pkgmgr installation, and MIT license Reference: https://chatgpt.com/share/68efc179-1a10-800f-9656-1e8731b40546
2025-10-15 19:56:43 +02:00
commit 10522d591a
6 changed files with 429 additions and 0 deletions
--- a/test.py
+++ b/test.py
@@ -0,0 +1,134 @@
+import io
+import sys
+import unittest
+from unittest.mock import patch, call
+from contextlib import redirect_stdout
+
+# Import the script as a module
+import main as automtu
+
+
+class TestWgMtuAuto(unittest.TestCase):
+
+    @patch("main.set_mtu")
+    @patch("main.read_mtu", return_value=1500)
+    @patch("main.exists_iface", return_value=True)
+    @patch("main.get_default_ifaces", return_value=["eth0"])
+    @patch("main.require_root", return_value=None)
+    def test_no_pmtu_uses_egress_minus_overhead(
+        self, _req_root, _get_def, _exists, _read_mtu, mock_set_mtu
+    ):
+        """
+        Without PMTU probing, wg MTU should be base_mtu - overhead (clamped by min).
+        With base=1500, overhead=80 ⇒ wg_mtu=1420.
+        """
+        argv = ["main.py", "--dry-run"]
+        with patch.object(sys, "argv", argv):
+            buf = io.StringIO()
+            with redirect_stdout(buf):
+                automtu.main()
+
+        out = buf.getvalue()
+        self.assertIn("Detected egress interface: eth0", out)
+        self.assertIn("Egress base MTU: 1500", out)
+        self.assertIn("Computed wg0 MTU: 1420", out)
+
+        # dry-run still calls set_mtu (but prints DRY-RUN); ensure it targeted wg0 with 1420
+        mock_set_mtu.assert_any_call("wg0", 1420, True)
+
+    @patch("main.set_mtu")
+    @patch("main.exists_iface", return_value=True)
+    @patch("main.get_default_ifaces", return_value=["eth0"])
+    @patch("main.require_root", return_value=None)
+    def test_force_egress_mtu_and_pmtu_multiple_targets_min_policy(
+        self, _req_root, _get_def, _exists, mock_set_mtu
+    ):
+        """
+        base_mtu forced=1452; PMTU results: 1452, 1420 -> policy=min => 1420 chosen.
+        effective=min(1452,1420)=1420; wg_mtu=1420-80=1340
+        """
+        with patch("main.read_mtu", return_value=9999):  # should be ignored because we force
+            with patch("main.probe_pmtu", side_effect=[1452, 1420]):
+                argv = [
+                    "main.py",
+                    "--dry-run",
+                    "--force-egress-mtu", "1452",
+                    "--pmtu-target", "t1",
+                    "--pmtu-target", "t2",
+                    "--pmtu-policy", "min",
+                ]
+                with patch.object(sys, "argv", argv):
+                    buf = io.StringIO()
+                    with redirect_stdout(buf):
+                        automtu.main()
+
+        out = buf.getvalue()
+        self.assertIn("Forcing egress MTU 1452 on eth0", out)
+        self.assertIn("Probing Path MTU for: t1, t2 (policy=min)", out)
+        self.assertIn("Selected Path MTU (policy=min): 1420", out)
+        self.assertIn("Computed wg0 MTU: 1340", out)
+        mock_set_mtu.assert_any_call("wg0", 1340, True)
+
+    @patch("main.set_mtu")
+    @patch("main.read_mtu", return_value=1500)
+    @patch("main.exists_iface", return_value=True)
+    @patch("main.get_default_ifaces", return_value=["eth0"])
+    @patch("main.require_root", return_value=None)
+    def test_pmtu_policy_median(
+        self, _req_root, _get_def, _exists, _read_mtu, mock_set_mtu
+    ):
+        """
+        base=1500; PMTUs: 1500, 1452, 1472 -> median=1472.
+        effective=min(1500,1472)=1472; wg_mtu=1472-80=1392
+        """
+        with patch("main.probe_pmtu", side_effect=[1500, 1452, 1472]):
+            argv = [
+                "main.py",
+                "--dry-run",
+                "--pmtu-target", "a",
+                "--pmtu-target", "b",
+                "--pmtu-target", "c",
+                "--pmtu-policy", "median",
+            ]
+            with patch.object(sys, "argv", argv):
+                buf = io.StringIO()
+                with redirect_stdout(buf):
+                    automtu.main()
+
+        out = buf.getvalue()
+        self.assertIn("Probing Path MTU for: a, b, c (policy=median)", out)
+        self.assertIn("Selected Path MTU (policy=median): 1472", out)
+        self.assertIn("Computed wg0 MTU: 1392", out)
+        mock_set_mtu.assert_any_call("wg0", 1392, True)
+
+    @patch("main.set_mtu")
+    @patch("main.read_mtu", return_value=1500)
+    @patch("main.exists_iface", return_value=True)
+    @patch("main.get_default_ifaces", return_value=["eth0"])
+    @patch("main.require_root", return_value=None)
+    def test_pmtu_all_fail_falls_back_to_base(
+        self, _req_root, _get_def, _exists, _read_mtu, mock_set_mtu
+    ):
+        """
+        If all PMTU probes fail, fall back to base MTU (1500) => wg_mtu=1420.
+        """
+        with patch("main.probe_pmtu", side_effect=[None, None]):
+            argv = [
+                "main.py",
+                "--dry-run",
+                "--pmtu-target", "bad1",
+                "--pmtu-target", "bad2",
+            ]
+            with patch.object(sys, "argv", argv):
+                buf = io.StringIO()
+                with redirect_stdout(buf):
+                    automtu.main()
+
+        out = buf.getvalue()
+        self.assertIn("WARNING: All PMTU probes failed. Falling back to egress MTU.", out)
+        self.assertIn("Computed wg0 MTU: 1420", out)
+        mock_set_mtu.assert_any_call("wg0", 1420, True)
+
+
+if __name__ == "__main__":
+    unittest.main(verbosity=2)