Add system stack

internal/clashtcpip/ip.go

@@ -0,0 +1,209 @@
+package clashtcpip
+
+import (
+	"encoding/binary"
+	"errors"
+	"net/netip"
+)
+
+type IPProtocol = byte
+
+type IP interface {
+	Payload() []byte
+	SourceIP() netip.Addr
+	DestinationIP() netip.Addr
+	SetSourceIP(ip netip.Addr)
+	SetDestinationIP(ip netip.Addr)
+	Protocol() IPProtocol
+	DecTimeToLive()
+	ResetChecksum()
+	PseudoSum() uint32
+}
+
+// IPProtocol type
+const (
+	ICMP   IPProtocol = 0x01
+	TCP    IPProtocol = 0x06
+	UDP    IPProtocol = 0x11
+	ICMPv6 IPProtocol = 0x3a
+)
+
+const (
+	FlagDontFragment = 1 << 1
+	FlagMoreFragment = 1 << 2
+)
+
+const (
+	IPv4HeaderSize = 20
+
+	IPv4Version = 4
+
+	IPv4OptionsOffset   = 20
+	IPv4PacketMinLength = IPv4OptionsOffset
+)
+
+var (
+	ErrInvalidLength    = errors.New("invalid packet length")
+	ErrInvalidIPVersion = errors.New("invalid ip version")
+	ErrInvalidChecksum  = errors.New("invalid checksum")
+)
+
+type IPv4Packet []byte
+
+func (p IPv4Packet) TotalLen() uint16 {
+	return binary.BigEndian.Uint16(p[2:])
+}
+
+func (p IPv4Packet) SetTotalLength(length uint16) {
+	binary.BigEndian.PutUint16(p[2:], length)
+}
+
+func (p IPv4Packet) HeaderLen() uint16 {
+	return uint16(p[0]&0xf) * 4
+}
+
+func (p IPv4Packet) SetHeaderLen(length uint16) {
+	p[0] &= 0xF0
+	p[0] |= byte(length / 4)
+}
+
+func (p IPv4Packet) TypeOfService() byte {
+	return p[1]
+}
+
+func (p IPv4Packet) SetTypeOfService(tos byte) {
+	p[1] = tos
+}
+
+func (p IPv4Packet) Identification() uint16 {
+	return binary.BigEndian.Uint16(p[4:])
+}
+
+func (p IPv4Packet) SetIdentification(id uint16) {
+	binary.BigEndian.PutUint16(p[4:], id)
+}
+
+func (p IPv4Packet) FragmentOffset() uint16 {
+	return binary.BigEndian.Uint16([]byte{p[6] & 0x7, p[7]}) * 8
+}
+
+func (p IPv4Packet) SetFragmentOffset(offset uint32) {
+	flags := p.Flags()
+	binary.BigEndian.PutUint16(p[6:], uint16(offset/8))
+	p.SetFlags(flags)
+}
+
+func (p IPv4Packet) DataLen() uint16 {
+	return p.TotalLen() - p.HeaderLen()
+}
+
+func (p IPv4Packet) Payload() []byte {
+	return p[p.HeaderLen():p.TotalLen()]
+}
+
+func (p IPv4Packet) Protocol() IPProtocol {
+	return p[9]
+}
+
+func (p IPv4Packet) SetProtocol(protocol IPProtocol) {
+	p[9] = protocol
+}
+
+func (p IPv4Packet) Flags() byte {
+	return p[6] >> 5
+}
+
+func (p IPv4Packet) SetFlags(flags byte) {
+	p[6] &= 0x1F
+	p[6] |= flags << 5
+}
+
+func (p IPv4Packet) SourceIP() netip.Addr {
+	return netip.AddrFrom4([4]byte{p[12], p[13], p[14], p[15]})
+}
+
+func (p IPv4Packet) SetSourceIP(ip netip.Addr) {
+	if ip.Is4() {
+		copy(p[12:16], ip.AsSlice())
+	}
+}
+
+func (p IPv4Packet) DestinationIP() netip.Addr {
+	return netip.AddrFrom4([4]byte{p[16], p[17], p[18], p[19]})
+}
+
+func (p IPv4Packet) SetDestinationIP(ip netip.Addr) {
+	if ip.Is4() {
+		copy(p[16:20], ip.AsSlice())
+	}
+}
+
+func (p IPv4Packet) Checksum() uint16 {
+	return binary.BigEndian.Uint16(p[10:])
+}
+
+func (p IPv4Packet) SetChecksum(sum [2]byte) {
+	p[10] = sum[0]
+	p[11] = sum[1]
+}
+
+func (p IPv4Packet) TimeToLive() uint8 {
+	return p[8]
+}
+
+func (p IPv4Packet) SetTimeToLive(ttl uint8) {
+	p[8] = ttl
+}
+
+func (p IPv4Packet) DecTimeToLive() {
+	p[8] = p[8] - uint8(1)
+}
+
+func (p IPv4Packet) ResetChecksum() {
+	p.SetChecksum(zeroChecksum)
+	p.SetChecksum(Checksum(0, p[:p.HeaderLen()]))
+}
+
+// PseudoSum for tcp checksum
+func (p IPv4Packet) PseudoSum() uint32 {
+	sum := Sum(p[12:20])
+	sum += uint32(p.Protocol())
+	sum += uint32(p.DataLen())
+	return sum
+}
+
+func (p IPv4Packet) Valid() bool {
+	return len(p) >= IPv4HeaderSize && uint16(len(p)) >= p.TotalLen()
+}
+
+func (p IPv4Packet) Verify() error {
+	if len(p) < IPv4PacketMinLength {
+		return ErrInvalidLength
+	}
+
+	checksum := []byte{p[10], p[11]}
+	headerLength := uint16(p[0]&0xF) * 4
+	packetLength := binary.BigEndian.Uint16(p[2:])
+
+	if p[0]>>4 != 4 {
+		return ErrInvalidIPVersion
+	}
+
+	if uint16(len(p)) < packetLength || packetLength < headerLength {
+		return ErrInvalidLength
+	}
+
+	p[10] = 0
+	p[11] = 0
+	defer copy(p[10:12], checksum)
+
+	answer := Checksum(0, p[:headerLength])
+
+	if answer[0] != checksum[0] || answer[1] != checksum[1] {
+		return ErrInvalidChecksum
+	}
+
+	return nil
+}
+
+var _ IP = (*IPv4Packet)(nil)