From b93f6b3e8f6dc7271d1b5100176c79193bb38fbe Mon Sep 17 00:00:00 2001
From: Simon Moser <mosers@tf.uni-freiburg.de>
Date: Tue, 12 Oct 2021 23:29:02 +0200
Subject: [PATCH] Display ARP nad DHCP packets

---
 README.md     |  4 ++--
 proxy/main.go | 21 ++++++++++++++-------
 2 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/README.md b/README.md
index 450ab6e..4af1951 100644
--- a/README.md
+++ b/README.md
@@ -66,8 +66,8 @@ Keep in mind:
 
 ### Go:
 
-* Internet layer packet modification: https://github.com/google/gopacket / https://pkg.go.dev/github.com/google/gopacket
-* Link layer frame modification: https://github.com/mdlayher/ethernet / https://pkg.go.dev/github.com/mdlayher/ethernet (not recently updated, alternative?)
+* gopacket (~libpcap): https://github.com/google/gopacket / https://pkg.go.dev/github.com/google/gopacket
+* (Link layer frame modification: https://github.com/mdlayher/ethernet / https://pkg.go.dev/github.com/mdlayher/ethernet)
 
 ### Rust:
 
diff --git a/proxy/main.go b/proxy/main.go
index e0e208a..1b7e717 100644
--- a/proxy/main.go
+++ b/proxy/main.go
@@ -7,7 +7,6 @@ import (
 	"github.com/google/gopacket/layers"
 	_ "github.com/google/gopacket/layers"
 	"io"
-	"os"
 	"proxy/cmd"
 )
 
@@ -25,7 +24,7 @@ func main() {
 
 // Reads from an input and writes to and output,
 // do things to the content in between.
-// For now only output the frames information
+// For now only output the packet's information
 // Is meant to be run concurrently with "go pipeForward(...)"
 func pipeForward(reader io.Reader, writer io.Writer, prefix string) {
 	for {
@@ -36,7 +35,7 @@ func pipeForward(reader io.Reader, writer io.Writer, prefix string) {
 			break
 		}
 		frameLengthInt := int(binary.BigEndian.Uint16(frameLength))
-		os.Stdout.WriteString(fmt.Sprintf("%s Frame length: %d\n", prefix, frameLengthInt))
+		fmt.Printf("%s Frame length: %d\n", prefix, frameLengthInt)
 
 		// Read actual frame
 		frameBytes := make([]byte, frameLengthInt)
@@ -45,15 +44,23 @@ func pipeForward(reader io.Reader, writer io.Writer, prefix string) {
 			break
 		}
 
+		// Convert frame to full stack packet
 		packet := gopacket.NewPacket(frameBytes, layers.LayerTypeEthernet, gopacket.Default)
-		frame := packet.Layer(layers.LayerTypeEthernet).(*layers.Ethernet)
 
+		// Handle Ethernet frame
+		frame := packet.Layer(layers.LayerTypeEthernet).(*layers.Ethernet)
 		fmt.Printf("src: %s\ndst: %s\ntyp: %s\n", frame.SrcMAC, frame.DstMAC, frame.EthernetType)
 
-		switch frame.EthernetType {
-		case layers.EthernetTypeARP:
+		// Handle ARP packet
+		if frame.EthernetType == layers.EthernetTypeARP {
 			arpPacket := packet.Layer(layers.LayerTypeARP).(*layers.ARP)
-			fmt.Printf("%#v", arpPacket)
+			fmt.Printf("%sARP Packet:\n%#v\n", prefix, arpPacket)
+		}
+
+		// Handle DHCP packet
+		if dhcpLayer := packet.Layer(layers.LayerTypeDHCPv4); dhcpLayer != nil {
+			dhcpPacket, _ := dhcpLayer.(*layers.DHCPv4)
+			fmt.Printf("%sDHCP Packet:\n%#v\n", prefix, dhcpPacket)
 		}
 
 		// Forward original frame to other plug