Implement networks routed through wesher

This adds an option for specifying a routed network. Every node route
that belongs to that routed network will be announced to the cluster and
every other node will direct traffic to that node for said route.

wg/wireguard.go

@@ -94,7 +94,7 @@ func (s *State) DownInterface() error {
 }
 
 // SetUpInterface creates and sets up the associated network interface
-func (s *State) SetUpInterface(nodes []common.Node) error {
+func (s *State) SetUpInterface(nodes []common.Node, routedNet *net.IPNet) error {
 	if err := netlink.LinkAdd(&wireguard{LinkAttrs: netlink.LinkAttrs{Name: s.iface}}); err != nil && !os.IsExist(err) {
 		return errors.Wrapf(err, "could not create interface %s", s.iface)
 	}
@@ -128,12 +128,45 @@ func (s *State) SetUpInterface(nodes []common.Node) error {
 	if err := netlink.LinkSetUp(link); err != nil {
 		return errors.Wrapf(err, "could not enable interface %s", s.iface)
 	}
-	for _, node := range nodes {
-		netlink.RouteAdd(&netlink.Route{
+
+	// first compute routes
+	currentRoutes, err := netlink.RouteList(link, netlink.FAMILY_ALL)
+	if err != nil {
+		return errors.Wrapf(err, "could not update the routing table for %s", s.iface)
+	}
+	routes := make([]netlink.Route, 0)
+	for index, node := range nodes {
+		// dev route
+		routes = append(routes, netlink.Route{
 			LinkIndex: link.Attrs().Index,
-			Dst:       &node.OverlayAddr,
+			Dst:       &nodes[index].OverlayAddr,
 			Scope:     netlink.SCOPE_LINK,
 		})
+		// via routes
+		for _, route := range node.Routes {
+			routes = append(routes, netlink.Route{
+				LinkIndex: link.Attrs().Index,
+				Dst:       &route,
+				Gw:        node.OverlayAddr.IP,
+				Scope:     netlink.SCOPE_SITE,
+			})
+		}
+	}
+	// then actually update the routing table
+	for _, route := range routes {
+		match := matchRoute(currentRoutes, route)
+		if match == nil {
+			netlink.RouteAdd(&route)
+		} else if match.Gw.String() != route.Gw.String() {
+			netlink.RouteReplace(&route)
+		}
+	}
+	for _, route := range routes {
+		// only delete a reoute if it is a site scope route that belongs to the routed net, mainly to
+		// avoid deleting otherwise manually set routes
+		if matchRoute(currentRoutes, route) == nil && route.Scope == netlink.SCOPE_LINK && routedNet.Contains(route.Dst.IP) {
+			netlink.RouteDel(&route)
+		}
 	}
 
 	return nil
@@ -153,10 +186,20 @@ func (s *State) nodesToPeerConfigs(nodes []common.Node) ([]wgtypes.PeerConfig, e
 				IP:   node.Addr,
 				Port: s.Port,
 			},
-			AllowedIPs: []net.IPNet{
-				node.OverlayAddr,
-			},
+			AllowedIPs: append([]net.IPNet{node.OverlayAddr}, node.Routes...),
 		}
 	}
 	return peerCfgs, nil
 }
+
+func matchRoute(set []netlink.Route, needle netlink.Route) *netlink.Route {
+	// routes are considered equal if they overlap and have the same prefix length
+	prefixn, _ := needle.Dst.Mask.Size()
+	for _, route := range set {
+		prefixr, _ := route.Dst.Mask.Size()
+		if prefixn == prefixr && route.Dst.Contains(needle.Dst.IP) {
+			return &route
+		}
+	}
+	return nil
+}