fix: advertise LAN IP instead of mDNS hostname when --host 0.0.0.0

socket.getfqdn() returns *.localdomain names that other machines on
the same LAN (especially cross-OS) cannot resolve via DNS. When the
node is bound to 0.0.0.0 and --advertise-host is not given, probe the
outbound IP by connecting a UDP socket toward the tracker — this picks
the correct interface IP without sending any data.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/node/meshnet_node/startup.py

@@ -40,28 +40,58 @@ def _start_heartbeat(
     register_payload: dict,
     interval: float = 20.0,
 ) -> threading.Thread:
-    """Daemon thread: sends heartbeats; re-registers automatically on 404 (tracker restart)."""
+    """Daemon thread: sends heartbeats and re-registers automatically after tracker restarts."""
+    def _reregister() -> bool:
+        nonlocal node_id
+        try:
+            resp = _post_json(f"{tracker_url}/v1/nodes/register", register_payload)
+            node_id = resp.get("node_id", node_id)
+            return True
+        except Exception:
+            return False
+
     def _loop() -> None:
         nonlocal node_id
         hb_url = f"{tracker_url}/v1/nodes/{node_id}/heartbeat"
+        outage_streak = 0  # consecutive intervals where tracker was unreachable
+
         while True:
             time.sleep(interval)
+
+            if outage_streak > 0:
+                # Tracker was down — attempt re-registration first (it may have restarted
+                # with a clean slate and won't know this node).
+                if _reregister():
+                    hb_url = f"{tracker_url}/v1/nodes/{node_id}/heartbeat"
+                    print(f"  [node] re-registered after outage — node ID: {node_id}", flush=True)
+                    outage_streak = 0
+                else:
+                    outage_streak += 1
+                    if outage_streak <= 3 or outage_streak % 10 == 0:
+                        print(
+                            f"  [node] WARNING: tracker still unreachable "
+                            f"({outage_streak * interval:.0f}s)",
+                            flush=True,
+                        )
+                continue
+
             try:
                 _post_json(hb_url, {})
             except urllib.error.HTTPError as exc:
                 if exc.code == 404:
+                    # Node was purged (e.g. long gap before restart noticed) — re-register now.
                     print("  [node] tracker lost registration — re-registering...", flush=True)
-                    try:
-                        resp = _post_json(f"{tracker_url}/v1/nodes/register", register_payload)
-                        node_id = resp.get("node_id", node_id)
+                    if _reregister():
                         hb_url = f"{tracker_url}/v1/nodes/{node_id}/heartbeat"
                         print(f"  [node] re-registered — node ID: {node_id}", flush=True)
-                    except Exception as re_exc:
-                        print(f"  [node] WARNING: re-registration failed: {re_exc}", flush=True)
+                    else:
+                        print("  [node] WARNING: re-registration failed", flush=True)
+                        outage_streak = 1
                 else:
-                    print(f"  [node] WARNING: heartbeat failed: {exc}", flush=True)
+                    print(f"  [node] WARNING: heartbeat failed ({exc.code}): {exc}", flush=True)
             except Exception as exc:
-                print(f"  [node] WARNING: heartbeat failed: {exc}", flush=True)
+                outage_streak = 1
+                print(f"  [node] WARNING: tracker unreachable: {exc}", flush=True)
 
     t = threading.Thread(target=_loop, daemon=True, name="heartbeat")
     t.start()
@@ -98,6 +128,19 @@ def run_startup(
     tracker_url = tracker_url.rstrip("/")
 
     # 1. Hardware detection
+    if advertise_host is None and host == "0.0.0.0":
+        # socket.getfqdn() returns an mDNS name (.local / .localdomain) that remote
+        # machines on a different OS or subnet often can't resolve. Instead, probe the
+        # outbound IP by opening a UDP socket toward the tracker — no data is sent.
+        try:
+            _tracker_host = urllib.parse.urlparse(tracker_url).hostname or "8.8.8.8"
+            _s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+            _s.connect((_tracker_host, 80))
+            advertise_host = _s.getsockname()[0]
+            _s.close()
+        except Exception:
+            advertise_host = socket.getfqdn()
+
     print("Detecting hardware...", flush=True)
     hw = detect_hardware()
     device: str = hw["device"]