From 6511baabaf8eafa6bc4ae265bf390f638a3960bc Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Gustaf=20Alh=C3=A4ll?= <gustaf@hanicef.me>
Date: Wed, 22 Nov 2023 19:41:35 +0100
Subject: [PATCH] Fix LAN discovery for SRB2 servers

---
 src/i_tcp.c | 97 ++++++++++++++++++++++++-----------------------------
 1 file changed, 43 insertions(+), 54 deletions(-)

diff --git a/src/i_tcp.c b/src/i_tcp.c
index d7b5b0993..c86c1146a 100644
--- a/src/i_tcp.c
+++ b/src/i_tcp.c
@@ -165,7 +165,9 @@ typedef union
 	#define ERRSOCKET (-1)
 #endif
 
-// define socklen_t in Windows if it is not already defined
+#define IPV6_MULTICAST_ADDRESS "ff15::57e1:1a12"
+
+// define socklen_t in DOS/Windows if it is not already defined
 #ifdef USE_WINSOCK1
 	typedef int socklen_t;
 #endif
@@ -717,6 +719,7 @@ static inline ssize_t SOCK_SendToAddr(SOCKET_TYPE socket, mysockaddr_t *sockaddr
 	socklen_t d6 = (socklen_t)sizeof(struct sockaddr_in6);
 #endif
 	socklen_t d, da = (socklen_t)sizeof(mysockaddr_t);
+	ssize_t status;
 
 	switch (sockaddr->any.sa_family)
 	{
@@ -727,7 +730,12 @@ static inline ssize_t SOCK_SendToAddr(SOCKET_TYPE socket, mysockaddr_t *sockaddr
 		default:       d = da; break;
 	}
 
-	return sendto(socket, (char *)&doomcom->data, doomcom->datalength, 0, &sockaddr->any, d);
+	status = sendto(socket, (char *)&doomcom->data, doomcom->datalength, 0, &sockaddr->any, d);
+	if (status == -1)
+	{
+		CONS_Alert(CONS_WARNING, "Unable to send packet to %s: %s\n", SOCK_AddrToStr(sockaddr), strerror(errno));
+	}
+	return status;
 }
 
 #define ALLOWEDERROR(x) ((x) == ECONNREFUSED || (x) == EWOULDBLOCK || (x) == EHOSTUNREACH || (x) == ENETUNREACH)
@@ -880,6 +888,24 @@ static SOCKET_TYPE UDP_Bind(int family, struct sockaddr *addr, socklen_t addrlen
 		return (SOCKET_TYPE)ERRSOCKET;
 	}
 
+#ifdef HAVE_IPV6
+	if (family == AF_INET6)
+	{
+		// we need to set all of this *after* binding to an address!
+		if (memcmp(&straddr.ip6.sin6_addr, &in6addr_any, sizeof(in6addr_any)) == 0) //IN6_ARE_ADDR_EQUAL
+		{
+			struct ipv6_mreq maddr;
+
+			inet_pton(AF_INET6, IPV6_MULTICAST_ADDRESS, &maddr.ipv6mr_multiaddr);
+			maddr.ipv6mr_interface = 0;
+			if (setsockopt(s, IPPROTO_IPV6, IPV6_JOIN_GROUP, &maddr, sizeof(maddr)) != 0)
+			{
+				CONS_Alert(CONS_WARNING, M_GetText("Could not register multicast address\n"));
+			}
+		}
+	}
+#endif
+
 #ifdef FIONBIO
 	// make it non blocking
 	opt = true;
@@ -1053,65 +1079,28 @@ static boolean UDP_Socket(void)
 	// ip + udp
 	packetheaderlength = 20 + 8; // for stats
 
-	hints.ai_family = AF_INET;
-	gaie = I_getaddrinfo("127.0.0.1", "0", &hints, &ai);
-	if (gaie == 0)
-	{
-		runp = ai;
-		while (runp != NULL && s < MAXNETNODES+1)
-		{
-			memcpy(&clientaddress[s], runp->ai_addr, runp->ai_addrlen);
-			s++;
-			runp = runp->ai_next;
-		}
-		I_freeaddrinfo(ai);
-	}
-	else
-	{
-		clientaddress[s].any.sa_family = AF_INET;
-		clientaddress[s].ip4.sin_port = htons(0);
-		clientaddress[s].ip4.sin_addr.s_addr = htonl(INADDR_LOOPBACK); //GetLocalAddress(); // my own ip
-		s++;
-	}
+	clientaddress[s].any.sa_family = AF_INET;
+	clientaddress[s].ip4.sin_port = htons(0);
+	clientaddress[s].ip4.sin_addr.s_addr = htonl(INADDR_LOOPBACK); //GetLocalAddress(); // my own ip
+	s++;
 
 	s = 0;
 
 	// setup broadcast adress to BROADCASTADDR entry
-	gaie = I_getaddrinfo("255.255.255.255", "0", &hints, &ai);
-	if (gaie == 0)
-	{
-		runp = ai;
-		while (runp != NULL && s < MAXNETNODES+1)
-		{
-			memcpy(&broadcastaddress[s], runp->ai_addr, runp->ai_addrlen);
-			s++;
-			runp = runp->ai_next;
-		}
-		I_freeaddrinfo(ai);
-	}
-	else
-	{
-		broadcastaddress[s].any.sa_family = AF_INET;
-		broadcastaddress[s].ip4.sin_port = htons(0);
-		broadcastaddress[s].ip4.sin_addr.s_addr = htonl(INADDR_BROADCAST);
-		s++;
-	}
+	broadcastaddress[s].any.sa_family = AF_INET;
+	broadcastaddress[s].ip4.sin_port = htons(atoi(DEFAULTPORT));
+	broadcastaddress[s].ip4.sin_addr.s_addr = htonl(INADDR_BROADCAST);
+	s++;
+
 #ifdef HAVE_IPV6
 	if (b_ipv6)
 	{
-		hints.ai_family = AF_INET6;
-		gaie = I_getaddrinfo("ff02::1", "0", &hints, &ai);
-		if (gaie == 0)
-		{
-			runp = ai;
-			while (runp != NULL && s < MAXNETNODES+1)
-			{
-				memcpy(&broadcastaddress[s], runp->ai_addr, runp->ai_addrlen);
-				s++;
-				runp = runp->ai_next;
-			}
-			I_freeaddrinfo(ai);
-		}
+		broadcastaddress[s].any.sa_family = AF_INET6;
+		broadcastaddress[s].ip6.sin6_port = htons(atoi(DEFAULTPORT));
+		broadcastaddress[s].ip6.sin6_flowinfo = 0;
+		inet_pton(AF_INET6, IPV6_MULTICAST_ADDRESS, &broadcastaddress[s].ip6.sin6_addr);
+		broadcastaddress[s].ip6.sin6_scope_id = 0;
+		s++;
 	}
 #endif