From 3a67b9965cd78a405bc97743c2f91e4f6870f3cf Mon Sep 17 00:00:00 2001
From: Paolo Invernizzi <paolo.invernizzi@suse.com>
Date: Tue, 23 Jul 2024 18:05:26 +0200
Subject: [PATCH] Add ARP packets parsing and socket support

---
 protocols/arp.go      | 69 +++++++++++++++++++++++++++++++++++++++++++
 protocols/eth.go      |  1 +
 sockets/raw_socket.go | 15 ++++++++--
 3 files changed, 83 insertions(+), 2 deletions(-)
 create mode 100644 protocols/arp.go

diff --git a/protocols/arp.go b/protocols/arp.go
new file mode 100644
index 0000000..2bbf8be
--- /dev/null
+++ b/protocols/arp.go
@@ -0,0 +1,69 @@
+package protocols
+
+import (
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"net"
+)
+
+var HardwareTypeValues = map[uint16]string{
+	1:  "Ethernet",
+	6:  "IEE 802 (Token Ring)",
+	11: "ATM",
+	12: "HDLC",
+}
+
+type ARPPacket struct {
+	EthFrame        EthernetFrame
+	HardwareType    uint16
+	ProtocolType    uint16
+	HardwareAddrLen uint8
+	ProtocolAddrLen uint8
+	Operation       uint16
+	SenderHWAddr    net.HardwareAddr
+	SenderProtoAddr net.IP // only IPv4 - IPv6 should rely on NDP
+	TargetHWAddr    net.HardwareAddr
+	TargetProtoAddr net.IP // only IPv4 - IPv6 should rely on NDP
+}
+
+var errInvalidARPPacket = errors.New("ARP packet must be 28 bytes")
+
+// ARPPacketFromBytes parses an array of bytes to the corresponding ARP packet and returns a pointer to it.
+// Returns an error if the number of bytes is less than 28
+func ARPPacketFromBytes(raw []byte) (*ARPPacket, error) {
+	frame, err := EthFrameFromBytes(raw)
+	if err != nil {
+		return nil, err
+	}
+
+	if len(frame.Payload) < 28 {
+		return nil, errInvalidARPPacket
+	}
+	payload := frame.Payload
+
+	return &ARPPacket{
+		EthFrame:        *frame,
+		HardwareType:    binary.BigEndian.Uint16(payload[0:2]),
+		ProtocolType:    binary.BigEndian.Uint16(payload[2:4]),
+		HardwareAddrLen: payload[4],
+		ProtocolAddrLen: payload[5],
+		Operation:       binary.BigEndian.Uint16(payload[6:8]),
+		SenderHWAddr:    payload[8:14],
+		SenderProtoAddr: payload[14:18],
+		TargetHWAddr:    payload[18:24],
+		TargetProtoAddr: payload[24:28],
+	}, nil
+}
+
+func (p ARPPacket) Destination() string {
+	return fmt.Sprintf("%s|%s", p.TargetHWAddr.String(), p.TargetProtoAddr.String())
+}
+
+func (p ARPPacket) Source() string {
+	return fmt.Sprintf("%s|%s", p.SenderHWAddr.String(), p.SenderProtoAddr.String())
+}
+
+func (p ARPPacket) Info() string {
+	return fmt.Sprintf("%s ARP packet from %s to %s", HardwareTypeValues[p.HardwareType], p.Source(), p.Destination())
+}
diff --git a/protocols/eth.go b/protocols/eth.go
index a21db81..5e121b5 100644
--- a/protocols/eth.go
+++ b/protocols/eth.go
@@ -12,6 +12,7 @@ var EtherTypesValues = map[uint16]string{
 	0x0800: "IPv4",
 	0x0806: "ARP",
 	0x0842: "Wake-on-LAN",
+	0x8535: "RARP",
 	0x86DD: "IPv6",
 	0x8808: "Ethernet flow control",
 }
diff --git a/sockets/raw_socket.go b/sockets/raw_socket.go
index 99ce225..388e117 100644
--- a/sockets/raw_socket.go
+++ b/sockets/raw_socket.go
@@ -89,12 +89,12 @@ func (rs *RawSocket) ReadToChan(dataChan chan<- NetworkPacket, errChan chan<- er
 
 			switch ethFrame.Type() {
 			case "ARP":
-				// TODO: ARP parsing
+				handleARPPacket(buf[:n], dataChan, errChan)
 			case "IPv4", "IPv6":
 				handleIPPacket(buf[:n], rs.layer4Filter, dataChan, errChan)
 			}
 		case syscall.ETH_P_ARP:
-			// TODO: ARP parsing
+			handleARPPacket(buf[:n], dataChan, errChan)
 		case syscall.ETH_P_IP, syscall.ETH_P_IPV6:
 			handleIPPacket(buf[:n], rs.layer4Filter, dataChan, errChan)
 		}
@@ -106,6 +106,17 @@ func (rs *RawSocket) Close() error {
 	return syscall.Close(rs.fd)
 }
 
+// handleARPPacket parses the provided bytes to an ARP packet's data and sends its representation, or
+// an error, to the provided channels.
+func handleARPPacket(raw []byte, dataChan chan<- NetworkPacket, errChan chan<- error) {
+	packet, err := protocols.ARPPacketFromBytes(raw)
+	if err != nil {
+		errChan <- err
+		return
+	}
+	dataChan <- packet
+}
+
 // handleIPPacket parses the provided bytes to an Ipv4 or Ipv6 packet's data and sends its representation, or
 // an error, to the provided channels. It is possible to apply a layer 4 filter to the packets.
 func handleIPPacket(raw []byte, filter string, dataChan chan<- NetworkPacket, errChan chan<- error) {