Get MAC/IP from traffic [Close #12]

proxy/main.go

@@ -24,9 +24,9 @@ var NewIP net.IP
 func main() {
 	// Get command line arguments
 	logLvl := flag.Int("log", 4, "allowed: 5 (debug), 4 (info), 3 (warning), 2 (error), 1 (fatal)")
-	oldip := flag.String("oldip", "10.0.0.11", "IP before change")
+	oldip := flag.String("oldip", "", "IP before change")
 	newip := flag.String("newip", "10.0.0.15", "IP after change")
-	oldmac := flag.String("oldmac", "52:54:00:12:34:56", "MAC before change")
+	oldmac := flag.String("oldmac", "", "MAC before change")
 	newmac := flag.String("newmac", "52:54:00:12:34:aa", "MAC after change")
 	passthrough := flag.Bool("passthrough", false, "Whether to pass every traffic through")
 	proxy := flag.String("proxy", "1", "Number of the proxy switch")
@@ -169,6 +169,22 @@ func filterIP(prefix string, dst interface{}, src interface{}, context gopacket.
 	}
 	ip, isIp := target.(*net.IP)
 	bs, isBs := target.(*[]byte)
+
+	// If no OldIP is set yet, get it from outgoing src field
+	if OldIP == nil {
+		if prefix == cmd.In {
+			return
+		} else if prefix == cmd.Out {
+			if isIp {
+				OldIP = *ip
+			} else if isBs {
+				OldIP = *bs
+			}
+			log.Info("OldIP set to ", OldIP)
+			condVal = OldIP
+		}
+	}
+
 	if isIp && bytes.Equal(*ip, condVal) {
 		*ip = newVal
 		log.Debugf("%s%s %s IP %s changed to %s", prefix, context, which, condVal, newVal)
@@ -181,6 +197,17 @@ func filterIP(prefix string, dst interface{}, src interface{}, context gopacket.
 
 // filterMAC checks whether a MAC target selected from src and dst equals a given value. If yes, it is changed
 func filterMAC(prefix string, dst interface{}, src interface{}, context gopacket.LayerType) {
+	// If no OldMac is set yet, get it from outgoing src field
+	// Has to be HardwareAddr because this is used for ethernet frames which call this method first
+	if OldMac == nil {
+		if prefix == cmd.In {
+			return
+		} else if prefix == cmd.Out {
+			OldMac = *src.(*net.HardwareAddr)
+			log.Info("OldMac set to ", OldMac)
+		}
+	}
+
 	var target interface{}
 	var condVal net.HardwareAddr
 	var newVal net.HardwareAddr