[PATCH] module-rtp-recv: Only try adding the group membership for multicast addresses

[lnicola@xxxxxxx (Laurentiu Nicola)]

Currently, module-rtp-recv always tries to add a multicast group membership, even if the configured listening address is unicast. The setsockopt call fails, so the module cannot be used in an unicast configuration, which might be desired.
This patch adds a check for the address type.

---
 src/modules/rtp/module-rtp-recv.c | 25 +++++++++++++++++--------
 1 file changed, 17 insertions(+), 8 deletions(-)

diff --git a/src/modules/rtp/module-rtp-recv.c b/src/modules/rtp/module-rtp-recv.c
index 41b18ab..adc642d 100644
--- a/src/modules/rtp/module-rtp-recv.c
+++ b/src/modules/rtp/module-rtp-recv.c
@@ -450,17 +450,26 @@ static int mcast_socket(const struct sockaddr* sa, socklen_t salen) {
         goto fail;
     }
 
+    r = 0;
     if (af == AF_INET) {
-        struct ip_mreq mr4;
-        memset(&mr4, 0, sizeof(mr4));
-        mr4.imr_multiaddr = ((const struct sockaddr_in*) sa)->sin_addr;
-        r = setsockopt(fd, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mr4, sizeof(mr4));
+        // IPv4 multicast addresses are in the 224.0.0.0-239.255.255.255 range
+        static const unsigned int ipv4_mcast_mask = 0xe0000000;
+
+        if ((ntohl(((const struct sockaddr_in*) sa)->sin_addr.s_addr) & ipv4_mcast_mask) == ipv4_mcast_mask) {
+            struct ip_mreq mr4;
+            memset(&mr4, 0, sizeof(mr4));
+            mr4.imr_multiaddr = ((const struct sockaddr_in*) sa)->sin_addr;
+            r = setsockopt(fd, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mr4, sizeof(mr4));
+        }
 #ifdef HAVE_IPV6
     } else if (af == AF_INET6) {
-        struct ipv6_mreq mr6;
-        memset(&mr6, 0, sizeof(mr6));
-        mr6.ipv6mr_multiaddr = ((const struct sockaddr_in6*) sa)->sin6_addr;
-        r = setsockopt(fd, IPPROTO_IPV6, IPV6_JOIN_GROUP, &mr6, sizeof(mr6));
+        // IPv6 multicase addresses have 255 as the most significant byte
+        if (((const struct sockaddr_in6*) sa)->sin6_addr.s6_addr[0] == 0xff) {
+            struct ipv6_mreq mr6;
+            memset(&mr6, 0, sizeof(mr6));
+            mr6.ipv6mr_multiaddr = ((const struct sockaddr_in6*) sa)->sin6_addr;
+            r = setsockopt(fd, IPPROTO_IPV6, IPV6_JOIN_GROUP, &mr6, sizeof(mr6));
+        }
 #endif
     } else
         pa_assert_not_reached();
-- 
1.8.5.2