refactor: inline

This eliminates the unnecessary indirection via interface names,
instead identifying the interface by its index.

net/if.go

@@ -52,15 +52,25 @@ func EnsureInterfaceAndMcastRoute(ifaceName string) (*net.Interface, error) {
 		return nil, err
 	}
 	dest := net.IPv4(224, 0, 0, 0)
-	// check for currently-existing route after subscribing, to avoid race
-	if CheckRouteExists(ifaceName, dest) {
-		return iface, err
+	check := func(route netlink.Route) bool {
+		return route.LinkIndex == iface.Index && route.Dst.IP.Equal(dest)
 	}
-	for update := range ch {
-		if update.Route.LinkIndex == iface.Index && update.Route.Dst.IP.Equal(dest) {
-			break
+	// check for currently-existing route after subscribing, to avoid race
+	routes, err := netlink.RouteList(nil, netlink.FAMILY_V4)
+	if err != nil {
+		return nil, err
+	}
+	for _, route := range routes {
+		if check(route) {
+			return iface, nil
 		}
 	}
+	for update := range ch {
+		if check(update.Route) {
+			return iface, nil
+		}
+	}
+	// should never get here
 	return iface, nil
 }
 

net/route.go

@@ -54,14 +54,3 @@ func forEachRoute(ignoreIfaceNames map[string]struct{}, check func(name string,
 	}
 	return nil
 }
-
-func CheckRouteExists(ifaceName string, dest net.IP) bool {
-	found := false
-	forEachRoute(map[string]struct{}{}, func(name string, route netlink.Route) error {
-		if name == ifaceName && route.Dst.IP.Equal(dest) {
-			found = true
-		}
-		return nil
-	})
-	return found
-}