* Track MAC addresses in the client cache (when we can find them); so if we have an expired cache entry, but the MAC hasn't changed, we can assume the original ID is still valid.

getifaddr.c

@@ -127,3 +127,38 @@ getifhwaddr(const char * ifname, char * buf, int len)
 	}
 	return 0;
 }
+
+int
+get_remote_mac(struct in_addr ip_addr, unsigned char * mac)
+{
+	struct in_addr arp_ent;
+	FILE * arp;
+	char remote_ip[16];
+	int matches, hwtype, flags;
+	memset(mac, 0xFF, 6);
+
+ 	arp = fopen("/proc/net/arp", "r");
+	if( !arp )
+		return 1;
+	while( !feof(arp) )
+	{
+	        matches = fscanf(arp, "%s 0x%X 0x%X %hhx:%hhx:%hhx:%hhx:%hhx:%hhx",
+		                      remote_ip, &hwtype, &flags,
+		                      &mac[0], &mac[1], &mac[2], &mac[3], &mac[4], &mac[5]);
+		if( matches != 9 )
+			continue;
+		inet_pton(AF_INET, remote_ip, &arp_ent);
+		if( ip_addr.s_addr == arp_ent.s_addr )
+			break;
+		mac[0] = 0xFF;
+	}
+	fclose(arp);
+
+	if( mac[0] == 0xFF )
+	{
+		memset(mac, 0xFF, 6);
+		return 1;
+	}
+
+	return 0;
+}