Added filter for MAC/IP [Close #8]

proxy/main.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"bytes"
 	"encoding/binary"
 	"flag"
 	"fmt"
@@ -11,7 +12,6 @@ import (
 	"net"
 	"proxy/cmd"
 	"proxy/util"
-	"strconv"
 	"time"
 )
 
@@ -72,29 +72,19 @@ func pipeForward(reader io.Reader, writer io.Writer, prefix string, passthrough
 
 		// Handle Ethernet frame
 		frame := packet.Layer(layers.LayerTypeEthernet).(*layers.Ethernet)
-		if prefix == cmd.In {
+		log.Debug("Start packet")
-			log.Debug(prefix, "Incoming MAC rewritten ", frame.DstMAC, OldMac)
+		filterMAC(prefix, &frame.DstMAC, &frame.SrcMAC, frame.LayerType())
-			frame.DstMAC = OldMac
-		} else if prefix == cmd.Out {
-			log.Debug(prefix, "Outgoing MAC rewritten ", frame.SrcMAC, NewMac)
-			frame.SrcMAC = NewMac
-		}
 
 		// Handle IPv6 packet
 		if ipv4layer := packet.Layer(layers.LayerTypeIPv4); ipv4layer != nil {
 			ipv4Packet, _ := ipv4layer.(*layers.IPv4)
-			if prefix == cmd.In {
+			log.Debug("IP Protocol", ipv4Packet.Protocol)
-				log.Debug(prefix, "Incoming IP rewritten ", ipv4Packet.DstIP, OldIP)
+			filterIP(prefix, &ipv4Packet.DstIP, &ipv4Packet.SrcIP, ipv4Packet.LayerType())
-				ipv4Packet.DstIP = OldIP
-			} else if prefix == cmd.Out {
-				log.Debug(prefix, "Outgoing IP rewritten ", ipv4Packet.SrcIP, NewIP)
-				ipv4Packet.SrcIP = NewIP
-			}
 
 			// Handle ICMP packet (based on IPv4)
 			if icmpLayer := packet.Layer(layers.LayerTypeICMPv4); icmpLayer != nil {
 				icmpPacket, _ := icmpLayer.(*layers.ICMPv4)
-				log.Debugf("%s ICMP packet\nType/Code:\t%s\n", prefix, icmpPacket.TypeCode.String())
+				log.Debug(prefix, "ICMP Type ", icmpPacket.TypeCode)
 			}
 
 			// Handle DHCP packet (based on IPv4) - drop for now
@@ -122,47 +112,13 @@ func pipeForward(reader io.Reader, writer io.Writer, prefix string, passthrough
 		// Handle ARP packet
 		if frame.EthernetType == layers.EthernetTypeARP {
 			arpPacket := packet.Layer(layers.LayerTypeARP).(*layers.ARP)
-			log.Debugf(
+			log.Debug(prefix, "ARP Type ", arpPacket.Operation)
-				"%sARP before modification\nAddrType:\t%s\nProtocol:\t%s\nOperation:\t%s\n"+
+			filterIPb(prefix, &arpPacket.DstProtAddress, &arpPacket.SourceProtAddress, arpPacket.LayerType())
-					"SrcHwAddress:\t%s\nSrcProtAddress:\t%s\nDstHwAddress:\t%s\nDstProtAddress:\t%s\n",
+			filterMACb(prefix, &arpPacket.DstHwAddress, &arpPacket.SourceHwAddress, arpPacket.LayerType())
-				prefix,
-				arpPacket.AddrType,
-				arpPacket.Protocol,
-				strconv.Itoa(int(arpPacket.Operation)),
-				net.HardwareAddr(arpPacket.SourceHwAddress),
-				net.IP(arpPacket.SourceProtAddress),
-				net.HardwareAddr(arpPacket.DstHwAddress),
-				net.IP(arpPacket.DstProtAddress),
-			)
-
-			if prefix == cmd.In {
-				arpPacket.DstProtAddress = OldIP
-				log.Debugf(
-					"%sARP after modification\nDstProtAddress:\t%s\n",
-					prefix,
-					net.IP(arpPacket.DstProtAddress),
-				)
-				if arpPacket.Operation == layers.ARPReply {
-					isInteresting = true
-					arpPacket.DstHwAddress = OldMac
-					log.Debugf(
-						"%sDstHwAddress:\t%s\n",
-						prefix,
-						net.HardwareAddr(arpPacket.DstHwAddress),
-					)
-				}
-			} else if prefix == cmd.Out {
-				arpPacket.SourceHwAddress = NewMac
-				arpPacket.SourceProtAddress = NewIP
-				log.Debugf(
-					"%sARP after modification\nSrcHwAddress:\t%s\nSrcProtAddress:\t%s\n",
-					prefix,
-					net.HardwareAddr(arpPacket.SourceHwAddress),
-					net.IP(arpPacket.SourceProtAddress),
-				)
-			}
 		}
 
+		log.Debug("End packet")
+
 		// Forward original frame to other plug
 		if passthrough {
 			writer.Write(frameLength)
@@ -193,3 +149,95 @@ func pipeForward(reader io.Reader, writer io.Writer, prefix string, passthrough
 		writer.Write(newFrameBytes)
 	}
 }
+
+// filterIP checks whether an IP target in net.IP format equals a given value. If yes, it is changed
+func filterIP(prefix string, dst *net.IP, src *net.IP, context gopacket.LayerType) {
+	var target *net.IP
+	var condVal net.IP
+	var newVal net.IP
+	var which string
+	if prefix == cmd.In {
+		target = dst
+		which = "dst"
+		condVal = NewIP
+		newVal = OldIP
+	} else if prefix == cmd.Out {
+		target = src
+		which = "src"
+		condVal = OldIP
+		newVal = NewIP
+	}
+	if bytes.Equal(*target, condVal) {
+		*target = newVal
+		log.Debugf("%s%s %s IP %s changed to %s", prefix, context, which, condVal, newVal)
+	}
+}
+
+// filterIPb checks whether an IP target in []byte format equals a given value. If yes, it is changed
+func filterIPb(prefix string, dst *[]byte, src *[]byte, context gopacket.LayerType) {
+	var target *[]byte
+	var condVal net.IP
+	var newVal net.IP
+	var which string
+	if prefix == cmd.In {
+		target = dst
+		which = "dst"
+		condVal = NewIP
+		newVal = OldIP
+	} else if prefix == cmd.Out {
+		target = src
+		which = "src"
+		condVal = OldIP
+		newVal = NewIP
+	}
+	if bytes.Equal(*target, condVal) {
+		*target = newVal
+		log.Debugf("%s%s %s IP %s changed to %s", prefix, context, which, condVal, newVal)
+	}
+}
+
+// filterMAC checks whether a MAC target in net.HardwareAddr format equals a given value. If yes, it is changed
+func filterMAC(prefix string, dst *net.HardwareAddr, src *net.HardwareAddr, context gopacket.LayerType) {
+	var target *net.HardwareAddr
+	var condVal net.HardwareAddr
+	var newVal net.HardwareAddr
+	var which string
+	if prefix == cmd.In {
+		target = dst
+		which = "dst"
+		condVal = NewMac
+		newVal = OldMac
+	} else if prefix == cmd.Out {
+		target = src
+		which = "src"
+		condVal = OldMac
+		newVal = NewMac
+	}
+	if bytes.Equal(*target, condVal) {
+		*target = newVal
+		log.Debugf("%s%s %s MAC %s changed to %s", prefix, context, which, condVal, newVal)
+	}
+}
+
+// filterMACb checks whether a MAC target in []byte format equals a given value. If yes, it is changed
+func filterMACb(prefix string, dst *[]byte, src *[]byte, context gopacket.LayerType) {
+	var target *[]byte
+	var condVal net.HardwareAddr
+	var newVal net.HardwareAddr
+	var which string
+	if prefix == cmd.In {
+		target = dst
+		which = "dst"
+		condVal = NewMac
+		newVal = OldMac
+	} else if prefix == cmd.Out {
+		target = src
+		which = "src"
+		condVal = OldMac
+		newVal = NewMac
+	}
+	if bytes.Equal(*target, condVal) {
+		*target = newVal
+		log.Debugf("%s%s %s MAC %s changed to %s", prefix, context, which, condVal, newVal)
+	}
+}

proxy/util/util.go

@@ -9,6 +9,7 @@ import (
 	"os"
 )
 
+// WritePcap writes the provided data to a given pcap file
 func WritePcap(file string, data []byte, ci gopacket.CaptureInfo) {
 	f, err := os.Create(file)
 	if err != nil {
@@ -25,6 +26,7 @@ func WritePcap(file string, data []byte, ci gopacket.CaptureInfo) {
 	err = r.WritePacket(ci, data)
 }
 
+// WriteBinary writes the provided data to a given binary file
 func WriteBinary(file string, data []byte) {
 	if err := ioutil.WriteFile(file, data, 0644); err != nil {
 		log.Errorf("Error writing binary file %s", file)