libip: prefer v4 over v6 for myipaddr()

myipaddr() is used in legacy applications that assume a
single ip address per host. so prefer to retun a v4
address over a v6 one.

1 files changed, 22 insertions, 12 deletions

diff --git a/sys/src/libip/myipaddr.c b/sys/src/libip/myipaddr.c
index 31f5573ce..e744cb179 100644
--- a/sys/src/libip/myipaddr.c
+++ b/sys/src/libip/myipaddr.c
@@ -21,8 +21,8 @@ static uchar loopback6[IPaddrlen] = {
 	0, 0, 0, 1
 };
 
-// find first ip addr that isn't the friggin loopback address
-// unless there are no others
+// find first ip that isn't a friggin loopback or
+// link-local address. prefer v4 over v6.
 int
 myipaddr(uchar *ip, char *net)
 {
@@ -31,29 +31,39 @@ myipaddr(uchar *ip, char *net)
 	static Ipifc *ifc;
 	uchar mynet[IPaddrlen];
 
+	ipmove(ip, IPnoaddr);
 	ifc = readipifc(net, ifc, -1);
-	for(nifc = ifc; nifc; nifc = nifc->next)
-		for(lifc = nifc->lifc; lifc; lifc = lifc->next){
+	for(nifc = ifc; nifc != nil; nifc = nifc->next){
+		for(lifc = nifc->lifc; lifc != nil; lifc = lifc->next){
 			/* unspecified */
 			if(ipcmp(lifc->ip, IPnoaddr) == 0)
 				continue;
 
+			if(isv4(lifc->ip)){
+				/* ipv4 loopback */
+				maskip(lifc->ip, loopbackmask, mynet);
+				if(ipcmp(mynet, loopbacknet) == 0)
+					continue;
+	
+				ipmove(ip, lifc->ip);
+				return 0;
+			}
+
+			/* already got a v6 address? */
+			if(ipcmp(ip, IPnoaddr) != 0)
+				continue;
+
 			/* ipv6 loopback */
 			if(ipcmp(lifc->ip, loopback6) == 0)
 				continue;
 
-			/* ipv4 loopback */
-			maskip(lifc->ip, loopbackmask, mynet);
-			if(ipcmp(mynet, loopbacknet) == 0)
-				continue;
-	
 			/* ipv6 linklocal */
 			if(ISIPV6LINKLOCAL(lifc->ip))
 				continue;
 
+			/* save first v6 address */
 			ipmove(ip, lifc->ip);
-			return 0;
 		}
-	ipmove(ip, IPnoaddr);
-	return -1;
+	}
+	return ipcmp(ip, IPnoaddr) != 0 ? 0 : -1;
 }