From 9d77e4f49dd02404009d762d165b61377a0a6434 Mon Sep 17 00:00:00 2001
From: "jiasheng.yu" <jiasheng.yu@ucloud.cn>
Date: Mon, 13 Jan 2025 15:26:59 +0800
Subject: [PATCH] fix: Fix the ARP packet parsing code to adapt to the scenario
 where the switch adds extra padding bytes to ARP packets to meet the 64-byte
 minimum frame size.

Signed-off-by: jiasheng.yu <jiasheng.yu@ucloud.cn>
---
 protocol/arp.go      | 10 ++++++++++
 protocol/arp_test.go | 18 ++++++++++++++++++
 2 files changed, 28 insertions(+)
 create mode 100644 protocol/arp_test.go

diff --git a/protocol/arp.go b/protocol/arp.go
index 59f1d61..a4e1374 100755
--- a/protocol/arp.go
+++ b/protocol/arp.go
@@ -21,6 +21,9 @@ type ARP struct {
 	IPSrc       net.IP
 	HWDst       net.HardwareAddr
 	IPDst       net.IP
+	// The actual test shows that ARP reply packets sent by the H3C switch include an additional 14 bytes.
+	// This is done by the switch to meet the minimum frame length requirement of 64 bytes.
+	Padding []byte
 }
 
 func NewARP(opt int) (*ARP, error) {
@@ -43,6 +46,8 @@ func NewARP(opt int) (*ARP, error) {
 func (a *ARP) Len() (n uint16) {
 	n = 8
 	n += uint16(a.HWLength*2 + a.ProtoLength*2)
+	// Including the padding bytes, an inaccurate length can cause a panic in PacketIn2PropPacket.UnmarshalBinary.
+	n += uint16(len(a.Padding))
 	return
 }
 
@@ -91,5 +96,10 @@ func (a *ARP) UnmarshalBinary(data []byte) error {
 	n += int(a.HWLength)
 	a.IPDst = make([]byte, a.ProtoLength)
 	copy(a.IPDst, data[n:n+int(a.ProtoLength)])
+	n += int(a.ProtoLength)
+	if len(data[n:]) > 0 {
+		a.Padding = make([]byte, len(data[n:]))
+		copy(a.Padding, data[n:])
+	}
 	return nil
 }
diff --git a/protocol/arp_test.go b/protocol/arp_test.go
new file mode 100644
index 0000000..924fb20
--- /dev/null
+++ b/protocol/arp_test.go
@@ -0,0 +1,18 @@
+package protocol
+
+import (
+	"encoding/hex"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_ARPUnmarshalBinary(t *testing.T) {
+	data, err := hex.DecodeString("00010800060400027057bf301a03c0a8ac01525400ec4b98c0a8accc0000000000000000000000000000")
+	assert.Nil(t, err)
+	arp := new(ARP)
+	err = arp.UnmarshalBinary(data)
+	assert.Nil(t, err)
+	assert.Equal(t, []byte{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, arp.Padding)
+	assert.Equal(t, 42, arp.Len())
+}