From f618fe125cdf5e544382752e9e85a1fa8eed6a39 Mon Sep 17 00:00:00 2001
From: "Sergio R. Caprile" <scaprile@cesanta.com>
Date: Tue, 29 Apr 2025 19:24:17 -0300
Subject: [PATCH] Fix lwIP builds

fixes #3119

lwIP does not export ip_mreq by default, it requires enabling support for IGMP by setting LWIP_IGMP, with the associated extra stuff. Mongoose will print an error if mg_multicast_add() is called with no multicast support in lwIP.
---
 mongoose.c | 4 ++++
 src/sock.c | 4 ++++
 2 files changed, 8 insertions(+)

diff --git a/mongoose.c b/mongoose.c
index b94797fb..a3142326 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -8394,11 +8394,15 @@ void mg_multicast_add(struct mg_connection *c, char *ip) {
   // TODO(): prvAllowIPPacketIPv4()
 #else
   // lwIP, Unix, Windows, Zephyr(, AzureRTOS ?)
+#if MG_ENABLE_LWIP && !LWIP_IGMP
+  MG_ERROR(("LWIP_IGMP not defined, no multicast support"));
+#else
   struct ip_mreq mreq;
   mreq.imr_multiaddr.s_addr = inet_addr(ip);
   mreq.imr_interface.s_addr = mg_htonl(INADDR_ANY);
   setsockopt(FD(c), IPPROTO_IP, IP_ADD_MEMBERSHIP, (char *) &mreq, sizeof(mreq));
 #endif
+#endif
 }
 
 bool mg_open_listener(struct mg_connection *c, const char *url) {
diff --git a/src/sock.c b/src/sock.c
index 46e2ad2a..64147555 100644
--- a/src/sock.c
+++ b/src/sock.c
@@ -184,11 +184,15 @@ void mg_multicast_add(struct mg_connection *c, char *ip) {
   // TODO(): prvAllowIPPacketIPv4()
 #else
   // lwIP, Unix, Windows, Zephyr(, AzureRTOS ?)
+#if MG_ENABLE_LWIP && !LWIP_IGMP
+  MG_ERROR(("LWIP_IGMP not defined, no multicast support"));
+#else
   struct ip_mreq mreq;
   mreq.imr_multiaddr.s_addr = inet_addr(ip);
   mreq.imr_interface.s_addr = mg_htonl(INADDR_ANY);
   setsockopt(FD(c), IPPROTO_IP, IP_ADD_MEMBERSHIP, (char *) &mreq, sizeof(mreq));
 #endif
+#endif
 }
 
 bool mg_open_listener(struct mg_connection *c, const char *url) {