Fix #178: Server IP parameter now accepts IPv6 addresses

ethr.go

@@ -157,7 +157,12 @@ func main() {
 	}
 
 	if *ip != "" {
-		gLocalIP = *ip
+		ipToParse := *ip
+		// Strip brackets from IPv6 addresses if present (e.g., "[2001:db8::1]")
+		if strings.HasPrefix(ipToParse, "[") && strings.HasSuffix(ipToParse, "]") {
+			ipToParse = ipToParse[1 : len(ipToParse)-1]
+		}
+		gLocalIP = ipToParse
 		ipAddr := net.ParseIP(gLocalIP)
 		if ipAddr == nil {
 			printUsageError(fmt.Sprintf("Invalid IP address: <%s> specified.", *ip))

server.go

@@ -204,7 +204,7 @@ func trySyncStartWithClient(test *ethrTest, conn net.Conn) (isControl bool, err
 }
 
 func srvrRunTCPServer() error {
-	l, err := net.Listen(Tcp(), gLocalIP+":"+gEthrPortStr)
+	l, err := net.Listen(Tcp(), formatListenAddress(gLocalIP, gEthrPortStr))
 	if err != nil {
 		return err
 	}
@@ -378,7 +378,7 @@ func srvrRunTCPLatencyTest(test *ethrTest, clientParam EthrClientParam, conn net
 }
 
 func srvrRunUDPServer() error {
-	udpAddr, err := net.ResolveUDPAddr(Udp(), gLocalIP+":"+gEthrPortStr)
+	udpAddr, err := net.ResolveUDPAddr(Udp(), formatListenAddress(gLocalIP, gEthrPortStr))
 	if err != nil {
 		ui.printDbg("Unable to resolve UDP address: %v", err)
 		return err

utils.go

@@ -35,6 +35,30 @@ const (
 // gPrecision controls decimal places for rate display (1 or 2)
 var gPrecision int = 1
 
+// formatListenAddress formats a local IP and port into a proper listen address.
+// For IPv4, it returns "ip:port".
+// For IPv6, it returns "[ip]:port".
+// Empty IP returns ":port" (listen on all interfaces).
+func formatListenAddress(ip string, port string) string {
+	if ip == "" {
+		return ":" + port
+	}
+
+	parsedIP := net.ParseIP(ip)
+	if parsedIP == nil {
+		// Not a valid IP, return as-is
+		return ip + ":" + port
+	}
+
+	if parsedIP.To4() == nil {
+		// IPv6 address - wrap in brackets
+		return "[" + ip + "]:" + port
+	}
+
+	// IPv4 address
+	return ip + ":" + port
+}
+
 func numberToUnit(num uint64) string {
 	unit := ""
 	value := float64(num)