From 06ddb3e0a7265a8a054b9b225a2d9fb994535cde Mon Sep 17 00:00:00 2001
From: wwqgtxx <wwqgtxx@gmail.com>
Date: Mon, 25 Aug 2025 10:18:22 +0800
Subject: [PATCH] ping: Add comments

---
 internal/gtcpip/header/ipv4.go | 8 ++++----
 ping/cmsg_windows.go           | 7 ++++---
 ping/ping.go                   | 3 +++
 3 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/internal/gtcpip/header/ipv4.go b/internal/gtcpip/header/ipv4.go
index 624166c..8253936 100644
--- a/internal/gtcpip/header/ipv4.go
+++ b/internal/gtcpip/header/ipv4.go
@@ -335,7 +335,7 @@ func (b IPv4) FragmentOffset() uint16 {
 }
 
 func (b IPv4) FragmentOffsetDarwinRaw() uint16 {
-	return binary.NativeEndian.Uint16(b[flagsFO:]) << 3
+	return common.NativeEndian.Uint16(b[flagsFO:]) << 3
 }
 
 // TotalLength returns the "total length" field of the IPv4 header.
@@ -344,7 +344,7 @@ func (b IPv4) TotalLength() uint16 {
 }
 
 func (b IPv4) TotalLengthDarwinRaw() uint16 {
-	return binary.NativeEndian.Uint16(b[IPv4TotalLenOffset:]) + uint16(b.HeaderLength())
+	return common.NativeEndian.Uint16(b[IPv4TotalLenOffset:]) + uint16(b.HeaderLength())
 }
 
 // Checksum returns the checksum field of the IPv4 header.
@@ -441,7 +441,7 @@ func (b IPv4) SetTotalLength(totalLength uint16) {
 }
 
 func (b IPv4) SetTotalLengthDarwinRaw(totalLength uint16) {
-	binary.NativeEndian.PutUint16(b[IPv4TotalLenOffset:], totalLength)
+	common.NativeEndian.PutUint16(b[IPv4TotalLenOffset:], totalLength)
 }
 
 // SetChecksum sets the checksum field of the IPv4 header.
@@ -458,7 +458,7 @@ func (b IPv4) SetFlagsFragmentOffset(flags uint8, offset uint16) {
 
 func (b IPv4) SetFlagsFragmentOffsetDarwinRaw(flags uint8, offset uint16) {
 	v := (uint16(flags) << 13) | (offset >> 3)
-	binary.NativeEndian.PutUint16(b[flagsFO:], v)
+	common.NativeEndian.PutUint16(b[flagsFO:], v)
 }
 
 // SetID sets the identification field.
diff --git a/ping/cmsg_windows.go b/ping/cmsg_windows.go
index be5be9b..07c322c 100644
--- a/ping/cmsg_windows.go
+++ b/ping/cmsg_windows.go
@@ -1,10 +1,11 @@
 package ping
 
 import (
-	"encoding/binary"
 	"fmt"
 	"unsafe"
 
+	"github.com/sagernet/sing/common"
+
 	"golang.org/x/net/ipv6"
 	"golang.org/x/sys/windows"
 )
@@ -36,9 +37,9 @@ func parseIPv6ControlMessage(cmsg []byte) (*ipv6.ControlMessage, error) {
 		}
 		switch cmsghdr.Type {
 		case IPV6_TCLASS:
-			controlMessage.TrafficClass = int(binary.NativeEndian.Uint32(cmsg[alignedSizeofCmsghdr : alignedSizeofCmsghdr+4]))
+			controlMessage.TrafficClass = int(common.NativeEndian.Uint32(cmsg[alignedSizeofCmsghdr : alignedSizeofCmsghdr+4]))
 		case IPV6_HOPLIMIT:
-			controlMessage.HopLimit = int(binary.NativeEndian.Uint32(cmsg[alignedSizeofCmsghdr : alignedSizeofCmsghdr+4]))
+			controlMessage.HopLimit = int(common.NativeEndian.Uint32(cmsg[alignedSizeofCmsghdr : alignedSizeofCmsghdr+4]))
 		}
 		cmsg = cmsg[msgSize:]
 	}
diff --git a/ping/ping.go b/ping/ping.go
index f3f661c..e8b6ef5 100644
--- a/ping/ping.go
+++ b/ping/ping.go
@@ -160,6 +160,9 @@ func (c *Conn) ReadIP(buffer *buf.Buffer) error {
 		if !c.destination.Is6() {
 			ipHdr := header.IPv4(buffer.Bytes())
 			if runtime.GOOS == "darwin" || runtime.GOOS == "ios" {
+				// MacOS have different TotalLen and FragOff in ipv4 header from socket api:
+				// https://stackoverflow.com/questions/13829712/mac-changes-ip-total-length-field/15881825#15881825
+				// but in the tun api still same data format as other system
 				ipHdr.SetTotalLength(ipHdr.TotalLengthDarwinRaw())
 				ipHdr.SetFlagsFragmentOffset(ipHdr.FlagsDarwinRaw(), ipHdr.FragmentOffsetDarwinRaw())
 			}