appc: add RouteInfo struct and persist it to StateStore

Lays the groundwork for the ability to persist app connectors discovered
routes, which will allow us to stop advertising routes for a domain if
the app connector no longer monitors that domain.

Updates #11008
Signed-off-by: Fran Bull <fran@tailscale.com>

ipn/ipnlocal/local.go

@@ -6210,6 +6210,43 @@ func (b *LocalBackend) UnadvertiseRoute(toRemove ...netip.Prefix) error {
 	return err
 }
 
+// namespace a key with the profile manager's current profile key, if any
+func namespaceKeyForCurrentProfile(pm *profileManager, key ipn.StateKey) ipn.StateKey {
+	return pm.CurrentProfile().Key + "||" + key
+}
+
+const routeInfoStateStoreKey ipn.StateKey = "_routeInfo"
+
+func (b *LocalBackend) storeRouteInfo(ri *appc.RouteInfo) error {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	if b.pm.CurrentProfile().ID == "" {
+		return nil
+	}
+	key := namespaceKeyForCurrentProfile(b.pm, routeInfoStateStoreKey)
+	bs, err := json.Marshal(ri)
+	if err != nil {
+		return err
+	}
+	return b.pm.WriteState(key, bs)
+}
+
+func (b *LocalBackend) readRouteInfoLocked() (*appc.RouteInfo, error) {
+	if b.pm.CurrentProfile().ID == "" {
+		return &appc.RouteInfo{}, nil
+	}
+	key := namespaceKeyForCurrentProfile(b.pm, routeInfoStateStoreKey)
+	bs, err := b.pm.Store().ReadState(key)
+	ri := &appc.RouteInfo{}
+	if err != nil {
+		return nil, err
+	}
+	if err := json.Unmarshal(bs, ri); err != nil {
+		return nil, err
+	}
+	return ri, nil
+}
+
 // seamlessRenewalEnabled reports whether seamless key renewals are enabled
 // (i.e. we saw our self node with the SeamlessKeyRenewal attr in a netmap).
 // This enables beta functionality of renewing node keys without breaking