Devices: connector tests follow ssh to the IPv4 address that answered

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

tests/test_link.py

@@ -123,6 +123,9 @@ class Connecting(unittest.TestCase):
         fd.known_hosts(device_id).write_text(f"frame-control-{device_id} ssh-ed25519 AAAA\n")
 
     def hosts(self, mapping):
+        # An IPv4 answer is what ssh is pointed at, so localhost arrives as 127.0.0.1.
+        if "localhost" in mapping:
+            mapping = dict({"127.0.0.1": mapping["localhost"]}, **mapping)
         os.environ["FAKESSH_HOSTS"] = json.dumps(mapping)
 
     def calls(self):
@@ -136,8 +139,15 @@ class Connecting(unittest.TestCase):
 
     def test_falls_through_to_the_address_that_is_really_the_headset(self):
         # Tried in this order: a name that doesn't resolve, a different device, the headset.
-        d = self.device("nothing.invalid", "127.0.0.1", "localhost")
-        self.hosts({"127.0.0.1": "wrong", "localhost": "ok"})
+        try:  # the "different device": the same port on IPv6 loopback
+            six = socket.socket(socket.AF_INET6)
+            self.addCleanup(six.close)
+            six.bind(("::1", self.port))
+            six.listen(4)
+        except OSError:
+            self.skipTest("no IPv6 loopback")
+        d = self.device("nothing.invalid", "::1", "localhost")
+        self.hosts({"::1": "wrong", "localhost": "ok"})
         self.link.connect(["start"])
         s = self.link.snapshot()
         self.assertEqual(s["phase"], "connected", s["error"])
@@ -145,12 +155,13 @@ class Connecting(unittest.TestCase):
         self.assertEqual([st["state"] for st in s["stages"]], ["done"] * 5)
         rows = {p["host"]: p for p in s["probes"]}
         self.assertEqual(rows["nothing.invalid"]["state"], "unresolved")
-        self.assertEqual(rows["127.0.0.1"]["state"], "sshfailed")
-        self.assertIn("different headset", rows["127.0.0.1"]["detail"])
+        self.assertEqual(rows["::1"]["state"], "sshfailed")
+        self.assertIn("different headset", rows["::1"]["detail"])
         # Every ssh command was pointed at the winner, with the host key pinned per device.
         alias, opts = self.routes[-1]
         self.assertEqual(alias, "frame-t")
-        self.assertIn(f"HostName=localhost", opts)
+        ip = rows["localhost"]["ip"]  # an IPv4 answer is used as is; an IPv6 one keeps the name
+        self.assertIn("HostName=" + (ip if "." in ip else "localhost"), opts)
         self.assertIn(f"HostKeyAlias=frame-control-{d['id']}", opts)
         self.assertIn(f"Port={self.port}", opts)
         master = [c for c in self.calls() if "ControlMaster=yes" in c][-1]
@@ -159,7 +170,7 @@ class Connecting(unittest.TestCase):
         # It learned: localhost works on this network.
         learned = {a["host"]: a for a in self.reg.get(d["id"])["addresses"]}
         self.assertEqual(learned["localhost"]["networks"], ["n-test"])
-        self.assertEqual(learned["127.0.0.1"]["networks"], [])
+        self.assertEqual(learned["::1"]["networks"], [])
         self.assertTrue(self.link.alive())
         self.link.close_master()
         self.assertFalse(any(p.name.startswith("master-") for p in self.dir.iterdir()))
@@ -210,6 +221,14 @@ class Connecting(unittest.TestCase):
         master = [c for c in self.calls() if "ControlMaster=yes" in c][-1]
         self.assertIn("StrictHostKeyChecking=yes", master)
 
+    def test_ssh_goes_to_the_ipv4_address_that_answered(self):
+        self.device("localhost")
+        self.hosts({"localhost": "ok"})
+        self.link.connect(["start"])
+        s = self.link.snapshot()
+        self.assertEqual((s["phase"], s["via"]["host"], s["via"]["ip"]), ("connected", "localhost", "127.0.0.1"))
+        self.assertIn("HostName=127.0.0.1", self.routes[-1][1])
+
     def test_a_bare_alias_lets_ssh_config_decide(self):
         self.link.override = "frame-bare"
         self.hosts({"frame-bare": "ok"})  # the stand-in ssh has no config: the alias is the host
@@ -356,7 +375,7 @@ class ServerConnection(unittest.TestCase):
                                         "  User steamos\nHost *\n# <<< steam-frame (frame) <<<\n")
         env = {**os.environ, "PYTHONDONTWRITEBYTECODE": "1", "FRAME_CONTROL_SSH_DIR": str(ssh_dir),
                "FRAME_CONTROL_DATA_DIR": str(cls.dir / "data"), "FAKESSH_LOG": str(cls.dir / "calls.jsonl"),
-               "FAKESSH_DIR": str(cls.dir), "FAKESSH_HOSTS": json.dumps({"localhost": "ok"}),
+               "FAKESSH_DIR": str(cls.dir), "FAKESSH_HOSTS": json.dumps({"localhost": "ok", "127.0.0.1": "ok"}),
                "PATH": f"{FAKESSH}{os.pathsep}{os.environ['PATH']}"}
         env.pop("FRAME_ALIAS", None)
         cls.log = tempfile.TemporaryFile()