Method SetPeerByIPPacketFunc

wgengine/userspace.go:742–756

SetPeerByIPPacketFunc installs a callback used by wireguard-go to look up which peer should handle an outbound packet by destination IP. fn is an optional fast path for exact node-address matches (e.g. dst is a Tailscale IP). On miss (or if fn is nil), the engine's own BART table ([userspaceEngine.

(fn func(netip.Addr) (_ key.NodePublic, ok bool))

// so callers that don't call SetPeerByIPPacketFunc (e.g. those not running
// a LocalBackend) still get working outbound packet routing.
func (e *userspaceEngine) SetPeerByIPPacketFunc(fn func(netip.Addr) (_ key.NodePublic, ok bool)) {
	e.wgdev.SetPeerByIPPacketFunc(func(_, dst netip.Addr, _ []byte) (device.NoisePublicKey, bool) {
		if fn != nil {
			if pk, ok := fn(dst); ok {
				return pk.Raw32(), true
			}
		}
		if rt := e.peerByIPRoute.Load(); rt != nil {
			if pk, ok := rt.Lookup(dst); ok {
				return pk.Raw32(), true
			}
		}
		return device.NoisePublicKey{}, false
	})
}

// hasOverlap checks if there is a IPPrefix which is common amongst the two
// provided slices.