net: if: Add helper to return the first IPv4 address for iface

This is helper is only needed in socket multicast interface selection
where we need to get one address from the interface so that it will
tell (when getsockopt() is used), the interface IPv4 address where
multicast packets will be sent. This is private function which is not
needed in public headers so place the prototype to net_private.h file.

Signed-off-by: Jukka Rissanen <[email protected]>

Author: jukkar

subsys/net/ip/net_if.c

@@ -3728,6 +3728,40 @@ const struct in_addr *net_if_ipv4_select_src_addr(struct net_if *dst_iface,
 	return src;
 }
 
+/* Internal function to get the first IPv4 address of the interface */
+struct net_if_addr *net_if_ipv4_addr_get_first_by_index(int ifindex)
+{
+	struct net_if *iface = net_if_get_by_index(ifindex);
+	struct net_if_addr *ifaddr = NULL;
+	struct net_if_ipv4 *ipv4;
+
+	if (!iface) {
+		return NULL;
+	}
+
+	net_if_lock(iface);
+
+	ipv4 = iface->config.ip.ipv4;
+	if (!ipv4) {
+		goto out;
+	}
+
+	ARRAY_FOR_EACH(ipv4->unicast, i) {
+		if (!ipv4->unicast[i].ipv4.is_used ||
+		    ipv4->unicast[i].ipv4.address.family != AF_INET) {
+			continue;
+		}
+
+		ifaddr = &ipv4->unicast[i].ipv4;
+		break;
+	}
+
+out:
+	net_if_unlock(iface);
+
+	return ifaddr;
+}
+
 struct net_if_addr *net_if_ipv4_addr_lookup(const struct in_addr *addr,
 					    struct net_if **ret)
 {

subsys/net/ip/net_private.h

@@ -62,6 +62,8 @@ extern void net_if_stats_reset_all(void);
 extern void net_process_rx_packet(struct net_pkt *pkt);
 extern void net_process_tx_packet(struct net_pkt *pkt);
 
+extern struct net_if_addr *net_if_ipv4_addr_get_first_by_index(int ifindex);
+
 extern int net_icmp_call_ipv4_handlers(struct net_pkt *pkt,
 				       struct net_ipv4_hdr *ipv4_hdr,
 				       struct net_icmp_hdr *icmp_hdr);