Add system stack

internal/clashtcpip/udp.go

@@ -0,0 +1,55 @@
+package clashtcpip
+
+import (
+	"encoding/binary"
+)
+
+const UDPHeaderSize = 8
+
+type UDPPacket []byte
+
+func (p UDPPacket) Length() uint16 {
+	return binary.BigEndian.Uint16(p[4:])
+}
+
+func (p UDPPacket) SetLength(length uint16) {
+	binary.BigEndian.PutUint16(p[4:], length)
+}
+
+func (p UDPPacket) SourcePort() uint16 {
+	return binary.BigEndian.Uint16(p)
+}
+
+func (p UDPPacket) SetSourcePort(port uint16) {
+	binary.BigEndian.PutUint16(p, port)
+}
+
+func (p UDPPacket) DestinationPort() uint16 {
+	return binary.BigEndian.Uint16(p[2:])
+}
+
+func (p UDPPacket) SetDestinationPort(port uint16) {
+	binary.BigEndian.PutUint16(p[2:], port)
+}
+
+func (p UDPPacket) Payload() []byte {
+	return p[UDPHeaderSize:p.Length()]
+}
+
+func (p UDPPacket) Checksum() uint16 {
+	return binary.BigEndian.Uint16(p[6:])
+}
+
+func (p UDPPacket) SetChecksum(sum [2]byte) {
+	p[6] = sum[0]
+	p[7] = sum[1]
+}
+
+func (p UDPPacket) ResetChecksum(psum uint32) {
+	p.SetChecksum(zeroChecksum)
+	p.SetChecksum(Checksum(psum, p))
+}
+
+func (p UDPPacket) Valid() bool {
+	return len(p) >= UDPHeaderSize && uint16(len(p)) >= p.Length()
+}