net: socket: Add support for setting hop limit options

Add IP_RECVTTL or IPV6_RECVHOPLIMIT BSD socket options
that can be used to extract ttl/hop limit from ancillary data
in recvmsg() call.

Signed-off-by: Cristian Bulacu <[email protected]>

Author: Cristib05

include/zephyr/net/socket.h

@@ -9,6 +9,7 @@
  * Copyright (c) 2017-2018 Linaro Limited
  * Copyright (c) 2021 Nordic Semiconductor
  * Copyright (c) 2025 Aerlync Labs Inc.
+ * Copyright 2025 NXP
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -991,6 +992,11 @@ struct in_pktinfo {
 	struct in_addr ipi_addr;     /**< Header Destination address */
 };
 
+/** Pass an IP_RECVTTL ancillary message that contains information
+ *  about the time to live of the incoming packet.
+ */
+#define IP_RECVTTL 12
+
 /** Retrieve the current known path MTU of the current socket. Returns an
  *  integer. IP_MTU is valid only for getsockopt and can be employed only when
  *  the socket has been connected.
@@ -1086,6 +1092,14 @@ struct ipv6_mreq {
  */
 #define IPV6_RECVPKTINFO 49
 
+/** Pass an IPV6_RECVHOPLIMIT ancillary message that contains information
+ *  about the hop limit of the incoming packet. See RFC 3542.
+ */
+#define IPV6_RECVHOPLIMIT 51
+
+/** Set or receive the hoplimit value for an outgoing packet. */
+#define IPV6_HOPLIMIT 52
+
 /** RFC5014: Source address selection. */
 #define IPV6_ADDR_PREFERENCES   72
 

subsys/net/lib/sockets/sockets_inet.c

@@ -3,6 +3,7 @@
  * Copyright (c) 2021 Nordic Semiconductor
  * Copyright (c) 2023 Arm Limited (or its affiliates). All rights reserved.
  * Copyright (c) 2025 Aerlync Labs Inc.
+ * Copyright 2025 NXP
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -1061,6 +1062,35 @@ static int add_pktinfo(struct net_context *ctx,
 	return ret;
 }
 
+static int add_hoplimit(struct net_context *ctx,
+			struct net_pkt *pkt,
+			struct msghdr *msg)
+{
+	int ret = -ENOTSUP;
+
+	if (IS_ENABLED(CONFIG_NET_IPV4) && net_pkt_family(pkt) == AF_INET) {
+		int ttl = net_pkt_ipv4_ttl(pkt);
+
+		ret = insert_pktinfo(msg, IPPROTO_IP, IP_TTL,
+				     &ttl, sizeof(ttl));
+
+		goto out;
+	}
+
+	if (IS_ENABLED(CONFIG_NET_IPV6) && net_pkt_family(pkt) == AF_INET6) {
+		int hop_limit = net_pkt_ipv6_hop_limit(pkt);
+
+		ret = insert_pktinfo(msg, IPPROTO_IPV6, IPV6_HOPLIMIT,
+				     &hop_limit, sizeof(hop_limit));
+
+		goto out;
+	}
+
+out:
+
+	return ret;
+}
+
 static int update_msg_controllen(struct msghdr *msg)
 {
 	struct cmsghdr *cmsg;
@@ -1231,6 +1261,13 @@ static ssize_t zsock_recv_dgram(struct net_context *ctx,
 					}
 				}
 
+				if (IS_ENABLED(CONFIG_NET_CONTEXT_RECV_HOPLIMIT) &&
+				    net_context_is_recv_hoplimit_set(ctx)) {
+					if (add_hoplimit(ctx, pkt, msg) < 0) {
+						msg->msg_flags |= ZSOCK_MSG_CTRUNC;
+					}
+				}
+
 				/* msg_controllen must be updated to reflect the total length of all
 				 * control messages in the buffer. If there are no control data,
 				 * msg_controllen will be cleared as expected It will also take into
@@ -2584,6 +2621,23 @@ int zsock_setsockopt_ctx(struct net_context *ctx, int level, int optname,
 
 			break;
 
+		case IP_RECVTTL:
+			if (IS_ENABLED(CONFIG_NET_IPV4) &&
+			    IS_ENABLED(CONFIG_NET_CONTEXT_RECV_HOPLIMIT)) {
+				ret = net_context_set_option(ctx,
+							     NET_OPT_RECV_HOPLIMIT,
+							     optval,
+							     optlen);
+				if (ret < 0) {
+					errno = -ret;
+					return -1;
+				}
+
+				return 0;
+			}
+
+			break;
+
 		case IP_MULTICAST_IF:
 			if (IS_ENABLED(CONFIG_NET_IPV4)) {
 				return ipv4_multicast_if(ctx, optval, optlen, false);
@@ -2704,6 +2758,23 @@ int zsock_setsockopt_ctx(struct net_context *ctx, int level, int optname,
 
 			break;
 
+		case IPV6_RECVHOPLIMIT:
+			if (IS_ENABLED(CONFIG_NET_IPV6) &&
+			    IS_ENABLED(CONFIG_NET_CONTEXT_RECV_HOPLIMIT)) {
+				ret = net_context_set_option(ctx,
+							     NET_OPT_RECV_HOPLIMIT,
+							     optval,
+							     optlen);
+				if (ret < 0) {
+					errno  = -ret;
+					return -1;
+				}
+
+				return 0;
+			}
+
+			break;
+
 		case IPV6_ADDR_PREFERENCES:
 			if (IS_ENABLED(CONFIG_NET_IPV6)) {
 				ret = net_context_set_option(ctx,