net: ip: route: Add support to search mcast route by interface

subsys/net/ip/route.c

@@ -957,6 +957,30 @@ net_route_mcast_lookup(struct in6_addr *group)
 
 	return NULL;
 }
+
+struct net_route_entry_mcast *
+net_route_mcast_lookup_by_iface(struct in6_addr *group, struct net_if *iface)
+{
+	ARRAY_FOR_EACH_PTR(route_mcast_entries, route) {
+		if (!route->is_used) {
+			continue;
+		}
+
+		ARRAY_FOR_EACH(route->ifaces, i) {
+			if (route->ifaces[i] == NULL || route->ifaces[i] != iface) {
+				continue;
+			}
+
+			if (net_ipv6_is_prefix(group->s6_addr,
+						route->group.s6_addr,
+						route->prefix_len)) {
+				return route;
+			}
+		}
+	}
+
+	return NULL;
+}
 #endif /* CONFIG_NET_ROUTE_MCAST */
 
 bool net_route_get_info(struct net_if *iface,

subsys/net/ip/route.h

@@ -272,6 +272,17 @@ bool net_route_mcast_del(struct net_route_entry_mcast *route);
 struct net_route_entry_mcast *
 net_route_mcast_lookup(struct in6_addr *group);
 
+/**
+ * @brief Lookup a multicast routing entry on a given interface.
+ *
+ * @param group IPv6 multicast group address
+ * @param iface Network interface to check
+ *
+ * @return Routing entry corresponding to this multicast group and interface.
+ */
+struct net_route_entry_mcast *
+net_route_mcast_lookup_by_iface(struct in6_addr *group, struct net_if *iface);
+
 /**
  * @brief Add an interface to multicast routing entry.
  *

tests/net/route_mcast/src/main.c

@@ -417,6 +417,23 @@ static void test_route_mcast_lookup(void)
 	zassert_equal_ptr(test_mcast_routes[3], route,
 						  "mcast lookup failed");
 }
+
+static void test_route_mcast_lookup_by_iface(void)
+{
+	struct net_route_entry_mcast *route =
+			net_route_mcast_lookup_by_iface(&mcast_prefix_admin, iface_1);
+
+	zassert_not_null(route, "mcast lookup by iface failed");
+
+	route = net_route_mcast_lookup_by_iface(&mcast_prefix_site_local, iface_2);
+
+	zassert_not_null(route, "mcast lookup by iface failed");
+
+	route = net_route_mcast_lookup_by_iface(&mcast_prefix_site_local, iface_1);
+
+	zassert_is_null(route, "mcast lookup by iface should not find a route on this interface");
+}
+
 static void test_route_mcast_route_del(void)
 {
 	struct net_route_entry_mcast *route;
@@ -752,6 +769,7 @@ ZTEST(route_mcast_test_suite, test_route_mcast)
 	test_route_mcast_scenario3();
 	test_route_mcast_multiple_route_ifaces();
 	test_route_mcast_lookup();
+	test_route_mcast_lookup_by_iface();
 	test_route_mcast_route_del();
 }
 ZTEST_SUITE(route_mcast_test_suite, NULL, NULL, NULL, NULL, NULL);