When a peer reconnects with the same ID, other peers were not reliably
notified that the old connection went offline. This caused "connection
already exists" errors when attempting to establish new connections to the
reconnected peer.
The issue occurred because the old peer's cleanup notification raced with
the new peer's online notification. If reconnection happened before
cleanup, the offline notification was silently dropped.
The fix sends an offline notification synchronously during reconnection
(when AddPeer returns true), ensuring all subscribed peers receive events
in the correct order (offline → online).
Added TestBindReconnectRace to validate the fix with 1000 reconnection
iterations.
- Move `util/grpc` and `util/net` to `client` so `internal` packages can be accessed
- Add methods to return the next best interface after the NetBird interface.
- Use `IP_UNICAST_IF` sock opt to force the outgoing interface for the NetBird `net.Dialer` and `net.ListenerConfig` to avoid routing loops. The interface is picked by the new route lookup method.
- Some refactoring to avoid import cycles
- Old behavior is available through `NB_USE_LEGACY_ROUTING=true` env var
