func DecodeUDPPacket(user *protocol.User, payload *buf.Buffer) (*protocol.RequestHeader, *buf.Buffer, error) {
rawAccount, err := user.GetTypedAccount()
if err != nil {
return nil, nil, errors.Base(err).Message("Shadowsocks|UDP: Failed to parse account.")
}
account := rawAccount.(*ShadowsocksAccount)
ivLen := account.Cipher.IVSize()
iv := payload.BytesTo(ivLen)
payload.SliceFrom(ivLen)
stream, err := account.Cipher.NewDecodingStream(account.Key, iv)
if err != nil {
return nil, nil, errors.Base(err).Message("Shadowsocks|UDP: Failed to initialize decoding stream.")
}
stream.XORKeyStream(payload.Bytes(), payload.Bytes())
authenticator := NewAuthenticator(HeaderKeyGenerator(account.Key, iv))
request := &protocol.RequestHeader{
Version: Version,
User: user,
Command: protocol.RequestCommandUDP,
}
addrType := (payload.Byte(0) & 0x0F)
if (payload.Byte(0) & 0x10) == 0x10 {
request.Option |= RequestOptionOneTimeAuth
}
if request.Option.Has(RequestOptionOneTimeAuth) && account.OneTimeAuth == Account_Disabled {
return nil, nil, errors.New("Shadowsocks|UDP: Rejecting packet with OTA enabled, while server disables OTA.")
}
if !request.Option.Has(RequestOptionOneTimeAuth) && account.OneTimeAuth == Account_Enabled {
return nil, nil, errors.New("Shadowsocks|UDP: Rejecting packet with OTA disabled, while server enables OTA.")
}
if request.Option.Has(RequestOptionOneTimeAuth) {
payloadLen := payload.Len() - AuthSize
authBytes := payload.BytesFrom(payloadLen)
actualAuth := make([]byte, AuthSize)
authenticator.Authenticate(payload.BytesTo(payloadLen))(actualAuth)
if !bytes.Equal(actualAuth, authBytes) {
return nil, nil, errors.New("Shadowsocks|UDP: Invalid OTA.")
}
payload.Slice(0, payloadLen)
}
payload.SliceFrom(1)
switch addrType {
case AddrTypeIPv4:
request.Address = v2net.IPAddress(payload.BytesTo(4))
payload.SliceFrom(4)
case AddrTypeIPv6:
request.Address = v2net.IPAddress(payload.BytesTo(16))
payload.SliceFrom(16)
case AddrTypeDomain:
domainLength := int(payload.Byte(0))
request.Address = v2net.DomainAddress(string(payload.BytesRange(1, 1+domainLength)))
payload.SliceFrom(1 + domainLength)
default:
return nil, nil, errors.New("Shadowsocks|UDP: Unknown address type: ", addrType)
}
request.Port = v2net.PortFromBytes(payload.BytesTo(2))
payload.SliceFrom(2)
return request, payload, nil
}