package fakedns import ( "context" "math" "math/big" gonet "net" "time" "github.com/xtls/xray-core/common" "github.com/xtls/xray-core/common/cache" "github.com/xtls/xray-core/common/net" "github.com/xtls/xray-core/features/dns" ) type Holder struct { domainToIP cache.Lru ipRange *gonet.IPNet config *FakeDnsPool } func (*Holder) Type() interface{} { return (*dns.FakeDNSEngine)(nil) } func (fkdns *Holder) Start() error { return fkdns.initializeFromConfig() } func (fkdns *Holder) Close() error { fkdns.domainToIP = nil fkdns.ipRange = nil return nil } func NewFakeDNSHolder() (*Holder, error) { var fkdns *Holder var err error if fkdns, err = NewFakeDNSHolderConfigOnly(nil); err != nil { return nil, newError("Unable to create Fake Dns Engine").Base(err).AtError() } err = fkdns.initialize("240.0.0.0/8", 65535) if err != nil { return nil, err } return fkdns, nil } func NewFakeDNSHolderConfigOnly(conf *FakeDnsPool) (*Holder, error) { return &Holder{nil, nil, conf}, nil } func (fkdns *Holder) initializeFromConfig() error { return fkdns.initialize(fkdns.config.IpPool, int(fkdns.config.LruSize)) } func (fkdns *Holder) initialize(ipPoolCidr string, lruSize int) error { var ipRange *gonet.IPNet var err error if _, ipRange, err = gonet.ParseCIDR(ipPoolCidr); err != nil { return newError("Unable to parse CIDR for Fake DNS IP assignment").Base(err).AtError() } ones, bits := ipRange.Mask.Size() rooms := bits - ones if math.Log2(float64(lruSize)) >= float64(rooms) { return newError("LRU size is bigger than subnet size").AtError() } fkdns.domainToIP = cache.NewLru(lruSize) fkdns.ipRange = ipRange return nil } // GetFakeIPForDomain check and generate a fake IP for a domain name func (fkdns *Holder) GetFakeIPForDomain(domain string) []net.Address { if v, ok := fkdns.domainToIP.Get(domain); ok { return []net.Address{v.(net.Address)} } var currentTimeMillis = uint64(time.Now().UnixNano() / 1e6) ones, bits := fkdns.ipRange.Mask.Size() rooms := bits - ones if rooms < 64 { currentTimeMillis %= (uint64(1) << rooms) } var bigIntIP = big.NewInt(0).SetBytes(fkdns.ipRange.IP) bigIntIP = bigIntIP.Add(bigIntIP, new(big.Int).SetUint64(currentTimeMillis)) var ip net.Address for { ip = net.IPAddress(bigIntIP.Bytes()) // if we run for a long time, we may go back to beginning and start seeing the IP in use if _, ok := fkdns.domainToIP.PeekKeyFromValue(ip); !ok { break } bigIntIP = bigIntIP.Add(bigIntIP, big.NewInt(1)) if !fkdns.ipRange.Contains(bigIntIP.Bytes()) { bigIntIP = big.NewInt(0).SetBytes(fkdns.ipRange.IP) } } fkdns.domainToIP.Put(domain, ip) return []net.Address{ip} } // GetDomainFromFakeDNS check if an IP is a fake IP and have corresponding domain name func (fkdns *Holder) GetDomainFromFakeDNS(ip net.Address) string { if !ip.Family().IsIP() || !fkdns.ipRange.Contains(ip.IP()) { return "" } if k, ok := fkdns.domainToIP.GetKeyFromValue(ip); ok { return k.(string) } newError("A fake ip request to ", ip, ", however there is no matching domain name in fake DNS").AtInfo().WriteToLog() return "" } // GetFakeIPRange return fake IP range from configuration func (fkdns *Holder) GetFakeIPRange() *gonet.IPNet { return fkdns.ipRange } func init() { common.Must(common.RegisterConfig((*FakeDnsPool)(nil), func(ctx context.Context, config interface{}) (interface{}, error) { var f *Holder var err error if f, err = NewFakeDNSHolderConfigOnly(config.(*FakeDnsPool)); err != nil { return nil, err } return f, nil })) }