377 lines
11 KiB
Go
377 lines
11 KiB
Go
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
|
|
|
|
// Raw IP packets remain bounded by the IPv4/IPv6 packet-length model.
|
|
VPNMaxPacket = 65535
|
|
|
|
// DragonTCP transfer objects/records are independent of IP packet size.
|
|
// Multiple IP packets may be batched into one transfer object.
|
|
VPNMaxFragment = 1024 * 1024
|
|
VPNMaxBatch = 1024 * 1024
|
|
|
|
VPNBatchVersion byte = 1
|
|
)
|
|
|
|
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 > VPNMaxPacket {
|
|
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 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
|
|
}
|
|
|
|
// OPENED v2 response: cmd(1) maxChunk(4).
|
|
// ParseVPNOpened also accepts the old 3-byte/uint16 response for compatibility.
|
|
func BuildVPNOpened(maxChunk int) []byte {
|
|
if maxChunk > VPNMaxFragment {
|
|
maxChunk = VPNMaxFragment
|
|
}
|
|
if maxChunk < 1 {
|
|
maxChunk = 1
|
|
}
|
|
out := make([]byte, 5)
|
|
out[0] = VPNRespOpened
|
|
binary.BigEndian.PutUint32(out[1:5], uint32(maxChunk))
|
|
return out
|
|
}
|
|
|
|
func ParseVPNOpened(payload []byte) (int, error) {
|
|
if err := ParseVPNError(payload); err != nil {
|
|
return 0, err
|
|
}
|
|
if len(payload) == 5 && payload[0] == VPNRespOpened {
|
|
v := int(binary.BigEndian.Uint32(payload[1:5]))
|
|
if v < 1 || v > VPNMaxFragment {
|
|
return 0, errors.New("bad VPN OPENED max chunk")
|
|
}
|
|
return v, nil
|
|
}
|
|
if len(payload) == 3 && payload[0] == VPNRespOpened {
|
|
return int(binary.BigEndian.Uint16(payload[1:3])), nil
|
|
}
|
|
return 0, errors.New("bad VPN OPENED response")
|
|
}
|
|
|
|
// PUSH v2 request: cmd(1) sid(16) seq(4) offset(4) total(4) data(N)
|
|
func BuildVPNPush(sid VPNSessionID, seq uint32, offset, total int, data []byte) ([]byte, error) {
|
|
if total < 1 || total > VPNMaxBatch || 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, 29+len(data))
|
|
out[0] = VPNCmdPush
|
|
copy(out[1:17], sid[:])
|
|
binary.BigEndian.PutUint32(out[17:21], seq)
|
|
binary.BigEndian.PutUint32(out[21:25], uint32(offset))
|
|
binary.BigEndian.PutUint32(out[25:29], uint32(total))
|
|
copy(out[29:], data)
|
|
return out, nil
|
|
}
|
|
|
|
func ParseVPNPush(payload []byte) (sid VPNSessionID, seq uint32, offset, total int, data []byte, err error) {
|
|
if len(payload) < 30 || 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.Uint32(payload[21:25]))
|
|
total = int(binary.BigEndian.Uint32(payload[25:29]))
|
|
data = payload[29:]
|
|
if total < 1 || total > VPNMaxBatch || offset < 0 || offset > total || len(data) < 1 || len(data) > VPNMaxFragment || offset+len(data) > total {
|
|
err = errors.New("bad VPN PUSH fragment bounds")
|
|
}
|
|
return
|
|
}
|
|
|
|
func BuildVPNAck(seq uint32, accepted int) []byte {
|
|
out := make([]byte, 9)
|
|
out[0] = VPNRespAck
|
|
binary.BigEndian.PutUint32(out[1:5], seq)
|
|
binary.BigEndian.PutUint32(out[5:9], uint32(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) != 9 || payload[0] != VPNRespAck {
|
|
err = errors.New("bad VPN ACK")
|
|
return
|
|
}
|
|
seq = binary.BigEndian.Uint32(payload[1:5])
|
|
accepted = int(binary.BigEndian.Uint32(payload[5:9]))
|
|
return
|
|
}
|
|
|
|
// PULL v2 request: cmd(1) sid(16) ack(4) want(4) offset(4) limit(4)
|
|
func BuildVPNPull(sid VPNSessionID, ack, want uint32, offset, limit int) ([]byte, error) {
|
|
if offset < 0 || offset > VPNMaxBatch || limit < 1 || limit > VPNMaxFragment {
|
|
return nil, errors.New("invalid VPN PULL")
|
|
}
|
|
out := make([]byte, 33)
|
|
out[0] = VPNCmdPull
|
|
copy(out[1:17], sid[:])
|
|
binary.BigEndian.PutUint32(out[17:21], ack)
|
|
binary.BigEndian.PutUint32(out[21:25], want)
|
|
binary.BigEndian.PutUint32(out[25:29], uint32(offset))
|
|
binary.BigEndian.PutUint32(out[29:33], uint32(limit))
|
|
return out, nil
|
|
}
|
|
|
|
func ParseVPNPull(payload []byte) (sid VPNSessionID, ack, want uint32, offset, limit int, err error) {
|
|
if len(payload) != 33 || 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.Uint32(payload[25:29]))
|
|
limit = int(binary.BigEndian.Uint32(payload[29:33]))
|
|
if offset < 0 || offset > VPNMaxBatch || limit < 1 || limit > VPNMaxFragment {
|
|
err = errors.New("bad VPN PULL bounds")
|
|
}
|
|
return
|
|
}
|
|
|
|
// DATA v2 response: cmd(1) seq(4) offset(4) total(4) data(N)
|
|
func BuildVPNData(seq uint32, offset, total int, data []byte) []byte {
|
|
out := make([]byte, 13+len(data))
|
|
out[0] = VPNRespData
|
|
binary.BigEndian.PutUint32(out[1:5], seq)
|
|
binary.BigEndian.PutUint32(out[5:9], uint32(offset))
|
|
binary.BigEndian.PutUint32(out[9:13], uint32(total))
|
|
copy(out[13:], 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) < 14 || payload[0] != VPNRespData {
|
|
err = fmt.Errorf("bad VPN DATA response type/length")
|
|
return
|
|
}
|
|
seq = binary.BigEndian.Uint32(payload[1:5])
|
|
offset = int(binary.BigEndian.Uint32(payload[5:9]))
|
|
total = int(binary.BigEndian.Uint32(payload[9:13]))
|
|
data = payload[13:]
|
|
if total < 1 || total > VPNMaxBatch || offset < 0 || offset+len(data) > total || len(data) < 1 || len(data) > VPNMaxFragment {
|
|
err = errors.New("bad VPN DATA bounds")
|
|
}
|
|
return
|
|
}
|
|
|
|
// A transfer object is a batch of raw IP packets:
|
|
// version(1), then repeated packetLen(2) + packet bytes.
|
|
func BuildVPNBatch(packets [][]byte) ([]byte, error) {
|
|
if len(packets) == 0 {
|
|
return nil, errors.New("empty VPN batch")
|
|
}
|
|
total := 1
|
|
for _, packet := range packets {
|
|
if len(packet) < 1 || len(packet) > VPNMaxPacket {
|
|
return nil, errors.New("invalid IP packet length in VPN batch")
|
|
}
|
|
total += 2 + len(packet)
|
|
if total > VPNMaxBatch {
|
|
return nil, errors.New("VPN batch exceeds maximum")
|
|
}
|
|
}
|
|
out := make([]byte, total)
|
|
out[0] = VPNBatchVersion
|
|
pos := 1
|
|
for _, packet := range packets {
|
|
binary.BigEndian.PutUint16(out[pos:pos+2], uint16(len(packet)))
|
|
pos += 2
|
|
copy(out[pos:pos+len(packet)], packet)
|
|
pos += len(packet)
|
|
}
|
|
return out, nil
|
|
}
|
|
|
|
func ParseVPNBatch(batch []byte) ([][]byte, error) {
|
|
if len(batch) < 4 || len(batch) > VPNMaxBatch || batch[0] != VPNBatchVersion {
|
|
return nil, errors.New("bad VPN batch")
|
|
}
|
|
packets := make([][]byte, 0, 8)
|
|
pos := 1
|
|
for pos < len(batch) {
|
|
if pos+2 > len(batch) {
|
|
return nil, errors.New("truncated VPN batch packet length")
|
|
}
|
|
n := int(binary.BigEndian.Uint16(batch[pos : pos+2]))
|
|
pos += 2
|
|
if n < 1 || n > VPNMaxPacket || pos+n > len(batch) {
|
|
return nil, errors.New("invalid VPN batch packet")
|
|
}
|
|
packet := make([]byte, n)
|
|
copy(packet, batch[pos:pos+n])
|
|
packets = append(packets, packet)
|
|
pos += n
|
|
}
|
|
if len(packets) == 0 {
|
|
return nil, errors.New("VPN batch contains no packets")
|
|
}
|
|
return packets, nil
|
|
}
|
|
|
|
// PacketAddresses returns the source and destination addresses from a raw
|
|
// IPv4/IPv6 packet. The packet may contain trailing bytes; the IP header's own
|
|
// length field is validated against the supplied buffer.
|
|
func PacketAddresses(packet []byte) (src, dst netip.Addr, err error) {
|
|
if len(packet) < 1 {
|
|
return src, dst, errors.New("empty IP packet")
|
|
}
|
|
switch packet[0] >> 4 {
|
|
case 4:
|
|
if len(packet) < 20 {
|
|
return src, dst, errors.New("short IPv4 packet")
|
|
}
|
|
total := int(packet[2])<<8 | int(packet[3])
|
|
if total < 20 || total > len(packet) {
|
|
return src, dst, errors.New("invalid IPv4 total length")
|
|
}
|
|
var a, b [4]byte
|
|
copy(a[:], packet[12:16])
|
|
copy(b[:], packet[16:20])
|
|
return netip.AddrFrom4(a), netip.AddrFrom4(b), nil
|
|
case 6:
|
|
if len(packet) < 40 {
|
|
return src, dst, errors.New("short IPv6 packet")
|
|
}
|
|
total := 40 + (int(packet[4])<<8 | int(packet[5]))
|
|
if total > len(packet) {
|
|
return src, dst, errors.New("invalid IPv6 payload length")
|
|
}
|
|
var a, b [16]byte
|
|
copy(a[:], packet[8:24])
|
|
copy(b[:], packet[24:40])
|
|
return netip.AddrFrom16(a), netip.AddrFrom16(b), nil
|
|
default:
|
|
return src, dst, errors.New("unsupported IP version")
|
|
}
|
|
}
|
|
|
|
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
|
|
}
|