feat(output): add machine-readable MTU output modes (single number + JSON)

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

tests/unit/test_cli.py

@@ -37,6 +37,8 @@ class TestCli(unittest.TestCase):
                 "--force-egress-mtu",
                 "1452",
                 "--dry-run",
+                "--print-mtu",
+                "wg",
             ]
         )
 
@@ -56,6 +58,8 @@ class TestCli(unittest.TestCase):
         self.assertEqual(args.set_wg_mtu, 1372)
         self.assertEqual(args.force_egress_mtu, 1452)
         self.assertTrue(args.dry_run)
+        self.assertEqual(args.print_mtu, "wg")
+        self.assertFalse(args.print_json)
 
 
 if __name__ == "__main__":

tests/unit/test_output.py

@@ -0,0 +1,87 @@
+import io
+import json
+import unittest
+from contextlib import redirect_stdout, redirect_stderr
+
+from automtu.output import OutputMode, emit_json, emit_single_number, Logger
+
+
+class TestOutput(unittest.TestCase):
+    def test_output_mode_validate_mutual_exclusive(self) -> None:
+        mode = OutputMode(print_mtu="effective", print_json=True)
+        self.assertIsNotNone(mode.validate())
+
+        mode_ok = OutputMode(print_mtu=None, print_json=True)
+        self.assertIsNone(mode_ok.validate())
+
+    def test_logger_routes_to_stderr_in_machine_mode(self) -> None:
+        log = Logger(machine_mode=True).log
+
+        out = io.StringIO()
+        err = io.StringIO()
+        with redirect_stdout(out), redirect_stderr(err):
+            log("[automtu] hello")
+
+        self.assertEqual(out.getvalue(), "")
+        self.assertIn("hello", err.getvalue())
+
+    def test_emit_single_number_effective(self) -> None:
+        mode = OutputMode(print_mtu="effective", print_json=False)
+
+        out = io.StringIO()
+        with redirect_stdout(out):
+            emitted = emit_single_number(
+                mode, base_mtu=1500, effective_mtu=1452, wg_mtu=1372
+            )
+
+        self.assertTrue(emitted)
+        self.assertEqual(out.getvalue().strip(), "1452")
+
+    def test_emit_json_is_valid_and_contains_expected_fields(self) -> None:
+        mode = OutputMode(print_mtu=None, print_json=True)
+
+        out = io.StringIO()
+        with redirect_stdout(out):
+            emitted = emit_json(
+                mode,
+                egress_iface="eth0",
+                base_mtu=1500,
+                effective_mtu=1452,
+                egress_forced_mtu=None,
+                egress_applied=False,
+                pmtu_targets=["1.1.1.1", "8.8.8.8"],
+                pmtu_auto_targets_added=[],
+                pmtu_policy="min",
+                pmtu_chosen=1452,
+                pmtu_results={"1.1.1.1": 1452, "8.8.8.8": None},
+                wg_iface="wg0",
+                wg_mtu=1372,
+                wg_overhead=80,
+                wg_min=1280,
+                wg_set_mtu=None,
+                wg_clamped=False,
+                wg_present=True,
+                wg_active=False,
+                wg_applied=False,
+                dry_run=True,
+            )
+
+        self.assertTrue(emitted)
+
+        payload = json.loads(out.getvalue())
+        self.assertEqual(payload["egress"]["iface"], "eth0")
+        self.assertEqual(payload["egress"]["base_mtu"], 1500)
+        self.assertEqual(payload["egress"]["effective_mtu"], 1452)
+
+        self.assertEqual(payload["pmtu"]["policy"], "min")
+        self.assertEqual(payload["pmtu"]["chosen"], 1452)
+        self.assertEqual(payload["pmtu"]["results"]["1.1.1.1"], 1452)
+        self.assertIsNone(payload["pmtu"]["results"]["8.8.8.8"])
+
+        self.assertEqual(payload["wg"]["iface"], "wg0")
+        self.assertEqual(payload["wg"]["mtu"], 1372)
+        self.assertTrue(payload["dry_run"])
+
+
+if __name__ == "__main__":
+    unittest.main(verbosity=2)