With UDP

2026-08-16 02:33:07 -03:00
parent 14beee38b0
commit 6dac260155
33 changed files with 2065 additions and 2301 deletions
@@ -0,0 +1,267 @@
+package protocol
+
+import (
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"net/netip"
+)
+
+const (
+	VPNCmdOpen  byte = 0x30
+	VPNCmdPush  byte = 0x31
+	VPNCmdPull  byte = 0x32
+	VPNCmdClose byte = 0x33
+
+	VPNRespOpened byte = 0x40
+	VPNRespAck    byte = 0x41
+	VPNRespData   byte = 0x42
+	VPNRespWait   byte = 0x43
+	VPNRespClosed byte = 0x44
+	VPNRespError  byte = 0x7f
+
+	VPNNoAck       uint32 = 0xffffffff
+	VPNMaxFragment        = 65535
+)
+
+type VPNSessionID [16]byte
+
+func VPNError(message string) []byte {
+	b := []byte(message)
+	if len(b) > 4096 {
+		b = b[:4096]
+	}
+	out := make([]byte, 1+len(b))
+	out[0] = VPNRespError
+	copy(out[1:], b)
+	return out
+}
+
+func ParseVPNError(payload []byte) error {
+	if len(payload) == 0 {
+		return errors.New("empty DragonTCP VPN response")
+	}
+	if payload[0] == VPNRespError {
+		return errors.New(string(payload[1:]))
+	}
+	return nil
+}
+
+// OPEN request:
+// cmd(1) sid(16) tokenLen(2) token(N) ipv4(4) ipv6(16) mtu(2)
+func BuildVPNOpen(sid VPNSessionID, token string, ipv4, ipv6 netip.Addr, mtu int) ([]byte, error) {
+	if len(token) > 4096 {
+		return nil, errors.New("token too long")
+	}
+	if !ipv4.Is4() || !ipv6.Is6() {
+		return nil, errors.New("invalid VPN client addresses")
+	}
+	if mtu < 576 || mtu > 65535 {
+		return nil, errors.New("invalid VPN MTU")
+	}
+	out := make([]byte, 1+16+2+len(token)+4+16+2)
+	out[0] = VPNCmdOpen
+	copy(out[1:17], sid[:])
+	binary.BigEndian.PutUint16(out[17:19], uint16(len(token)))
+	pos := 19
+	copy(out[pos:pos+len(token)], token)
+	pos += len(token)
+	v4 := ipv4.As4()
+	copy(out[pos:pos+4], v4[:])
+	pos += 4
+	v6 := ipv6.As16()
+	copy(out[pos:pos+16], v6[:])
+	pos += 16
+	binary.BigEndian.PutUint16(out[pos:pos+2], uint16(mtu))
+	return out, nil
+}
+
+func ParseVPNOpen(payload []byte) (sid VPNSessionID, token string, ipv4, ipv6 netip.Addr, mtu int, err error) {
+	if len(payload) < 1+16+2+4+16+2 || payload[0] != VPNCmdOpen {
+		err = errors.New("bad VPN OPEN")
+		return
+	}
+	copy(sid[:], payload[1:17])
+	tokenLen := int(binary.BigEndian.Uint16(payload[17:19]))
+	need := 1 + 16 + 2 + tokenLen + 4 + 16 + 2
+	if tokenLen < 0 || len(payload) != need {
+		err = errors.New("bad VPN OPEN length")
+		return
+	}
+	pos := 19
+	token = string(payload[pos : pos+tokenLen])
+	pos += tokenLen
+	var a4 [4]byte
+	copy(a4[:], payload[pos:pos+4])
+	ipv4 = netip.AddrFrom4(a4)
+	pos += 4
+	var a6 [16]byte
+	copy(a6[:], payload[pos:pos+16])
+	ipv6 = netip.AddrFrom16(a6)
+	pos += 16
+	mtu = int(binary.BigEndian.Uint16(payload[pos : pos+2]))
+	return
+}
+
+func BuildVPNOpened(maxChunk int) []byte {
+	if maxChunk > VPNMaxFragment {
+		maxChunk = VPNMaxFragment
+	}
+	if maxChunk < 1 {
+		maxChunk = 1
+	}
+	out := make([]byte, 3)
+	out[0] = VPNRespOpened
+	binary.BigEndian.PutUint16(out[1:3], uint16(maxChunk))
+	return out
+}
+
+func ParseVPNOpened(payload []byte) (int, error) {
+	if err := ParseVPNError(payload); err != nil {
+		return 0, err
+	}
+	if len(payload) != 3 || payload[0] != VPNRespOpened {
+		return 0, errors.New("bad VPN OPENED response")
+	}
+	return int(binary.BigEndian.Uint16(payload[1:3])), nil
+}
+
+// PUSH request: cmd(1) sid(16) seq(4) offset(2) total(2) data(N)
+func BuildVPNPush(sid VPNSessionID, seq uint32, offset, total int, data []byte) ([]byte, error) {
+	if total < 1 || total > 65535 || offset < 0 || offset > total || len(data) < 1 || offset+len(data) > total || len(data) > VPNMaxFragment {
+		return nil, errors.New("invalid VPN PUSH fragment")
+	}
+	out := make([]byte, 25+len(data))
+	out[0] = VPNCmdPush
+	copy(out[1:17], sid[:])
+	binary.BigEndian.PutUint32(out[17:21], seq)
+	binary.BigEndian.PutUint16(out[21:23], uint16(offset))
+	binary.BigEndian.PutUint16(out[23:25], uint16(total))
+	copy(out[25:], data)
+	return out, nil
+}
+
+func ParseVPNPush(payload []byte) (sid VPNSessionID, seq uint32, offset, total int, data []byte, err error) {
+	if len(payload) < 26 || payload[0] != VPNCmdPush {
+		err = errors.New("bad VPN PUSH")
+		return
+	}
+	copy(sid[:], payload[1:17])
+	seq = binary.BigEndian.Uint32(payload[17:21])
+	offset = int(binary.BigEndian.Uint16(payload[21:23]))
+	total = int(binary.BigEndian.Uint16(payload[23:25]))
+	data = payload[25:]
+	if total < 1 || offset < 0 || offset > total || len(data) < 1 || offset+len(data) > total {
+		err = errors.New("bad VPN PUSH fragment bounds")
+	}
+	return
+}
+
+func BuildVPNAck(seq uint32, accepted int) []byte {
+	out := make([]byte, 7)
+	out[0] = VPNRespAck
+	binary.BigEndian.PutUint32(out[1:5], seq)
+	binary.BigEndian.PutUint16(out[5:7], uint16(accepted))
+	return out
+}
+
+func ParseVPNAck(payload []byte) (seq uint32, accepted int, err error) {
+	if e := ParseVPNError(payload); e != nil {
+		err = e
+		return
+	}
+	if len(payload) != 7 || payload[0] != VPNRespAck {
+		err = errors.New("bad VPN ACK")
+		return
+	}
+	seq = binary.BigEndian.Uint32(payload[1:5])
+	accepted = int(binary.BigEndian.Uint16(payload[5:7]))
+	return
+}
+
+// PULL request: cmd(1) sid(16) ack(4) want(4) offset(2) limit(2)
+func BuildVPNPull(sid VPNSessionID, ack, want uint32, offset, limit int) ([]byte, error) {
+	if offset < 0 || offset > 65535 || limit < 1 || limit > VPNMaxFragment {
+		return nil, errors.New("invalid VPN PULL")
+	}
+	out := make([]byte, 29)
+	out[0] = VPNCmdPull
+	copy(out[1:17], sid[:])
+	binary.BigEndian.PutUint32(out[17:21], ack)
+	binary.BigEndian.PutUint32(out[21:25], want)
+	binary.BigEndian.PutUint16(out[25:27], uint16(offset))
+	binary.BigEndian.PutUint16(out[27:29], uint16(limit))
+	return out, nil
+}
+
+func ParseVPNPull(payload []byte) (sid VPNSessionID, ack, want uint32, offset, limit int, err error) {
+	if len(payload) != 29 || payload[0] != VPNCmdPull {
+		err = errors.New("bad VPN PULL")
+		return
+	}
+	copy(sid[:], payload[1:17])
+	ack = binary.BigEndian.Uint32(payload[17:21])
+	want = binary.BigEndian.Uint32(payload[21:25])
+	offset = int(binary.BigEndian.Uint16(payload[25:27]))
+	limit = int(binary.BigEndian.Uint16(payload[27:29]))
+	if limit < 1 {
+		err = errors.New("bad VPN PULL limit")
+	}
+	return
+}
+
+// DATA response: cmd(1) seq(4) offset(2) total(2) data(N)
+func BuildVPNData(seq uint32, offset, total int, data []byte) []byte {
+	out := make([]byte, 9+len(data))
+	out[0] = VPNRespData
+	binary.BigEndian.PutUint32(out[1:5], seq)
+	binary.BigEndian.PutUint16(out[5:7], uint16(offset))
+	binary.BigEndian.PutUint16(out[7:9], uint16(total))
+	copy(out[9:], data)
+	return out
+}
+
+func ParseVPNData(payload []byte) (seq uint32, offset, total int, data []byte, wait bool, err error) {
+	if e := ParseVPNError(payload); e != nil {
+		err = e
+		return
+	}
+	if len(payload) == 1 && payload[0] == VPNRespWait {
+		wait = true
+		return
+	}
+	if len(payload) < 10 || payload[0] != VPNRespData {
+		err = fmt.Errorf("bad VPN DATA response type/length")
+		return
+	}
+	seq = binary.BigEndian.Uint32(payload[1:5])
+	offset = int(binary.BigEndian.Uint16(payload[5:7]))
+	total = int(binary.BigEndian.Uint16(payload[7:9]))
+	data = payload[9:]
+	if total < 1 || offset < 0 || offset+len(data) > total || len(data) < 1 {
+		err = errors.New("bad VPN DATA bounds")
+	}
+	return
+}
+
+func BuildVPNClose(sid VPNSessionID) []byte {
+	out := make([]byte, 17)
+	out[0] = VPNCmdClose
+	copy(out[1:17], sid[:])
+	return out
+}
+
+func ParseVPNClose(payload []byte) (sid VPNSessionID, err error) {
+	if len(payload) != 17 || payload[0] != VPNCmdClose {
+		return sid, errors.New("bad VPN CLOSE")
+	}
+	copy(sid[:], payload[1:17])
+	return sid, nil
+}
+
+func IsVPNCommand(payload []byte) bool {
+	if len(payload) == 0 {
+		return false
+	}
+	return payload[0] >= VPNCmdOpen && payload[0] <= VPNCmdClose
+}