An empty IP can be represented using an empty slice or nil, so check for both.

This code is inspired from commit 3720584 where isEmptyIP is fixed to handle both nil and "" IP

An incorrectly performed IP-emptiness check may lead to zedrouter trying to stop metadata server which has not been yet started, resulting in panic triggered from log.Fatal.

Signed-off-by: Pramodh Pallapothu <[email protected]>

Author: Pramodh Pallapothu

pkg/pillar/cmd/zedrouter/dnsmasq.go

@@ -573,7 +573,7 @@ func checkAndPublishDhcpLeases(ctx *zedrouterContext) {
 }
 
 func isEmptyIP(ip net.IP) bool {
-	return ip.Equal(net.IP{})
+	return ip == nil || ip.Equal(net.IP{})
 }
 
 func ipListEqual(one []net.IP, two []string) bool {

pkg/pillar/cmd/zedrouter/networkinstance.go

@@ -1083,7 +1083,7 @@ func handleMetaDataServerChange(ctx *zedrouterContext, dnstatus *types.DeviceNet
 		if addr.String() == status.MetaDataServerIP {
 			continue
 		}
-		if (err != nil || (addr.String() == "" && status.MetaDataServerIP != "")) &&
+		if (err != nil || (isEmptyIP(addr) && status.MetaDataServerIP != "")) &&
 			status.Server4Running == true {
 			// Bridge had a valid IP and it is gone now
 			deleteServer4(ctx, status.MetaDataServerIP, status.BridgeName)
@@ -1102,7 +1102,7 @@ func handleMetaDataServerChange(ctx *zedrouterContext, dnstatus *types.DeviceNet
 				status.MetaDataServerIP, status.BridgeName)
 			status.Server4Running = false
 		}
-		if addr.String() != "" {
+		if !isEmptyIP(addr) {
 			// Start new meta-data server
 			status.MetaDataServerIP = addr.String()
 			err := createServer4(ctx, status.MetaDataServerIP, status.BridgeName)