Add Fake DNS support (#309)

Co-authored-by: Xiaokang Wang <xiaokangwang@outlook.com>
Co-authored-by: loyalsoldier <10487845+Loyalsoldier@users.noreply.github.com>
Co-authored-by: kslr <kslrwang@gmail.com>

app/dns/config.proto

@@ -68,4 +68,6 @@ message Config {
 
   // Tag is the inbound tag of DNS client.
   string tag = 6;
+
+  reserved 7;
 }

app/dns/dnscommon.go

@@ -2,6 +2,7 @@ package dns
 
 import (
 	"encoding/binary"
+	"strings"
 	"time"
 
 	"github.com/xtls/xray-core/common"
@@ -13,7 +14,7 @@ import (
 
 // Fqdn normalize domain make sure it ends with '.'
 func Fqdn(domain string) string {
-	if len(domain) > 0 && domain[len(domain)-1] == '.' {
+	if len(domain) > 0 && strings.HasSuffix(domain, ".") {
 		return domain
 	}
 	return domain + "."
@@ -112,7 +113,7 @@ func genEDNS0Options(clientIP net.IP) *dnsmessage.Resource {
 	return opt
 }
 
-func buildReqMsgs(domain string, option IPOption, reqIDGen func() uint16, reqOpts *dnsmessage.Resource) []*dnsRequest {
+func buildReqMsgs(domain string, option dns_feature.IPOption, reqIDGen func() uint16, reqOpts *dnsmessage.Resource) []*dnsRequest {
 	qA := dnsmessage.Question{
 		Name:  dnsmessage.MustNewName(domain),
 		Type:  dnsmessage.TypeA,

app/dns/dnscommon_test.go

@@ -9,6 +9,7 @@ import (
 	"github.com/miekg/dns"
 	"github.com/xtls/xray-core/common"
 	"github.com/xtls/xray-core/common/net"
+	dns_feature "github.com/xtls/xray-core/features/dns"
 	"golang.org/x/net/dns/dnsmessage"
 )
 
@@ -92,7 +93,7 @@ func Test_buildReqMsgs(t *testing.T) {
 	}
 	type args struct {
 		domain  string
-		option  IPOption
+		option  dns_feature.IPOption
 		reqOpts *dnsmessage.Resource
 	}
 	tests := []struct {
@@ -100,10 +101,26 @@ func Test_buildReqMsgs(t *testing.T) {
 		args args
 		want int
 	}{
-		{"dual stack", args{"test.com", IPOption{true, true}, nil}, 2},
-		{"ipv4 only", args{"test.com", IPOption{true, false}, nil}, 1},
-		{"ipv6 only", args{"test.com", IPOption{false, true}, nil}, 1},
-		{"none/error", args{"test.com", IPOption{false, false}, nil}, 0},
+		{"dual stack", args{"test.com", dns_feature.IPOption{
+			IPv4Enable: true,
+			IPv6Enable: true,
+			FakeEnable: false,
+		}, nil}, 2},
+		{"ipv4 only", args{"test.com", dns_feature.IPOption{
+			IPv4Enable: true,
+			IPv6Enable: false,
+			FakeEnable: false,
+		}, nil}, 1},
+		{"ipv6 only", args{"test.com", dns_feature.IPOption{
+			IPv4Enable: false,
+			IPv6Enable: true,
+			FakeEnable: false,
+		}, nil}, 1},
+		{"none/error", args{"test.com", dns_feature.IPOption{
+			IPv4Enable: false,
+			IPv6Enable: false,
+			FakeEnable: false,
+		}, nil}, 0},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {

app/dns/dohdns.go

@@ -234,7 +234,7 @@ func (s *DoHNameServer) newReqID() uint16 {
 	return uint16(atomic.AddUint32(&s.reqID, 1))
 }
 
-func (s *DoHNameServer) sendQuery(ctx context.Context, domain string, option IPOption) {
+func (s *DoHNameServer) sendQuery(ctx context.Context, domain string, option dns_feature.IPOption) {
 	newError(s.name, " querying: ", domain).AtInfo().WriteToLog(session.ExportIDToError(ctx))
 
 	if s.name+"." == "DOH//"+domain {
@@ -320,7 +320,7 @@ func (s *DoHNameServer) dohHTTPSContext(ctx context.Context, b []byte) ([]byte,
 	return ioutil.ReadAll(resp.Body)
 }
 
-func (s *DoHNameServer) findIPsForDomain(domain string, option IPOption) ([]net.IP, error) {
+func (s *DoHNameServer) findIPsForDomain(domain string, option dns_feature.IPOption) ([]net.IP, error) {
 	s.RLock()
 	record, found := s.ips[domain]
 	s.RUnlock()
@@ -363,7 +363,7 @@ func (s *DoHNameServer) findIPsForDomain(domain string, option IPOption) ([]net.
 }
 
 // QueryIP is called from dns.Server->queryIPTimeout
-func (s *DoHNameServer) QueryIP(ctx context.Context, domain string, option IPOption) ([]net.IP, error) {
+func (s *DoHNameServer) QueryIP(ctx context.Context, domain string, option dns_feature.IPOption) ([]net.IP, error) { // nolint: dupl
 	fqdn := Fqdn(domain)
 
 	ips, err := s.findIPsForDomain(fqdn, option)

app/dns/fakedns/errors.generated.go

@@ -0,0 +1,9 @@
+package fakedns
+
+import "github.com/xtls/xray-core/common/errors"
+
+type errPathObjHolder struct{}
+
+func newError(values ...interface{}) *errors.Error {
+	return errors.New(values...).WithPathObj(errPathObjHolder{})
+}

app/dns/fakedns/fake.go

@@ -0,0 +1,136 @@
+// +build !confonly
+
+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
+	}))
+}

app/dns/fakedns/fakedns.go

@@ -0,0 +1,5 @@
+// +build !confonly
+
+package fakedns
+
+//go:generate go run github.com/xtls/xray-core/common/errors/errorgen

app/dns/fakedns/fakedns.pb.go

@@ -0,0 +1,164 @@
+// Code generated by protoc-gen-go. DO NOT EDIT.
+// versions:
+// 	protoc-gen-go v1.25.0
+// 	protoc        v3.13.0
+// source: app/dns/fakedns/fakedns.proto
+
+package fakedns
+
+import (
+	proto "github.com/golang/protobuf/proto"
+	protoreflect "google.golang.org/protobuf/reflect/protoreflect"
+	protoimpl "google.golang.org/protobuf/runtime/protoimpl"
+	reflect "reflect"
+	sync "sync"
+)
+
+const (
+	// Verify that this generated code is sufficiently up-to-date.
+	_ = protoimpl.EnforceVersion(20 - protoimpl.MinVersion)
+	// Verify that runtime/protoimpl is sufficiently up-to-date.
+	_ = protoimpl.EnforceVersion(protoimpl.MaxVersion - 20)
+)
+
+// This is a compile-time assertion that a sufficiently up-to-date version
+// of the legacy proto package is being used.
+const _ = proto.ProtoPackageIsVersion4
+
+type FakeDnsPool struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	IpPool  string `protobuf:"bytes,1,opt,name=ip_pool,json=ipPool,proto3" json:"ip_pool,omitempty"` //CIDR of IP pool used as fake DNS IP
+	LruSize int64  `protobuf:"varint,2,opt,name=lruSize,proto3" json:"lruSize,omitempty"`            //Size of Pool for remembering relationship between domain name and IP address
+}
+
+func (x *FakeDnsPool) Reset() {
+	*x = FakeDnsPool{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_app_dns_fakedns_fakedns_proto_msgTypes[0]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *FakeDnsPool) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*FakeDnsPool) ProtoMessage() {}
+
+func (x *FakeDnsPool) ProtoReflect() protoreflect.Message {
+	mi := &file_app_dns_fakedns_fakedns_proto_msgTypes[0]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use FakeDnsPool.ProtoReflect.Descriptor instead.
+func (*FakeDnsPool) Descriptor() ([]byte, []int) {
+	return file_app_dns_fakedns_fakedns_proto_rawDescGZIP(), []int{0}
+}
+
+func (x *FakeDnsPool) GetIpPool() string {
+	if x != nil {
+		return x.IpPool
+	}
+	return ""
+}
+
+func (x *FakeDnsPool) GetLruSize() int64 {
+	if x != nil {
+		return x.LruSize
+	}
+	return 0
+}
+
+var File_app_dns_fakedns_fakedns_proto protoreflect.FileDescriptor
+
+var file_app_dns_fakedns_fakedns_proto_rawDesc = []byte{
+	0x0a, 0x1d, 0x61, 0x70, 0x70, 0x2f, 0x64, 0x6e, 0x73, 0x2f, 0x66, 0x61, 0x6b, 0x65, 0x64, 0x6e,
+	0x73, 0x2f, 0x66, 0x61, 0x6b, 0x65, 0x64, 0x6e, 0x73, 0x2e, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x12,
+	0x1a, 0x76, 0x32, 0x72, 0x61, 0x79, 0x2e, 0x63, 0x6f, 0x72, 0x65, 0x2e, 0x61, 0x70, 0x70, 0x2e,
+	0x64, 0x6e, 0x73, 0x2e, 0x66, 0x61, 0x6b, 0x65, 0x64, 0x6e, 0x73, 0x22, 0x40, 0x0a, 0x0b, 0x46,
+	0x61, 0x6b, 0x65, 0x44, 0x6e, 0x73, 0x50, 0x6f, 0x6f, 0x6c, 0x12, 0x17, 0x0a, 0x07, 0x69, 0x70,
+	0x5f, 0x70, 0x6f, 0x6f, 0x6c, 0x18, 0x01, 0x20, 0x01, 0x28, 0x09, 0x52, 0x06, 0x69, 0x70, 0x50,
+	0x6f, 0x6f, 0x6c, 0x12, 0x18, 0x0a, 0x07, 0x6c, 0x72, 0x75, 0x53, 0x69, 0x7a, 0x65, 0x18, 0x02,
+	0x20, 0x01, 0x28, 0x03, 0x52, 0x07, 0x6c, 0x72, 0x75, 0x53, 0x69, 0x7a, 0x65, 0x42, 0x5f, 0x0a,
+	0x1e, 0x63, 0x6f, 0x6d, 0x2e, 0x76, 0x32, 0x72, 0x61, 0x79, 0x2e, 0x63, 0x6f, 0x72, 0x65, 0x2e,
+	0x61, 0x70, 0x70, 0x2e, 0x64, 0x6e, 0x73, 0x2e, 0x66, 0x61, 0x6b, 0x65, 0x64, 0x6e, 0x73, 0x50,
+	0x01, 0x5a, 0x1e, 0x76, 0x32, 0x72, 0x61, 0x79, 0x2e, 0x63, 0x6f, 0x6d, 0x2f, 0x63, 0x6f, 0x72,
+	0x65, 0x2f, 0x61, 0x70, 0x70, 0x2f, 0x64, 0x6e, 0x73, 0x2f, 0x66, 0x61, 0x6b, 0x65, 0x64, 0x6e,
+	0x73, 0xaa, 0x02, 0x1a, 0x56, 0x32, 0x52, 0x61, 0x79, 0x2e, 0x43, 0x6f, 0x72, 0x65, 0x2e, 0x41,
+	0x70, 0x70, 0x2e, 0x44, 0x6e, 0x73, 0x2e, 0x46, 0x61, 0x6b, 0x65, 0x64, 0x6e, 0x73, 0x62, 0x06,
+	0x70, 0x72, 0x6f, 0x74, 0x6f, 0x33,
+}
+
+var (
+	file_app_dns_fakedns_fakedns_proto_rawDescOnce sync.Once
+	file_app_dns_fakedns_fakedns_proto_rawDescData = file_app_dns_fakedns_fakedns_proto_rawDesc
+)
+
+func file_app_dns_fakedns_fakedns_proto_rawDescGZIP() []byte {
+	file_app_dns_fakedns_fakedns_proto_rawDescOnce.Do(func() {
+		file_app_dns_fakedns_fakedns_proto_rawDescData = protoimpl.X.CompressGZIP(file_app_dns_fakedns_fakedns_proto_rawDescData)
+	})
+	return file_app_dns_fakedns_fakedns_proto_rawDescData
+}
+
+var file_app_dns_fakedns_fakedns_proto_msgTypes = make([]protoimpl.MessageInfo, 1)
+var file_app_dns_fakedns_fakedns_proto_goTypes = []interface{}{
+	(*FakeDnsPool)(nil), // 0: xray.app.dns.fakedns.FakeDnsPool
+}
+var file_app_dns_fakedns_fakedns_proto_depIdxs = []int32{
+	0, // [0:0] is the sub-list for method output_type
+	0, // [0:0] is the sub-list for method input_type
+	0, // [0:0] is the sub-list for extension type_name
+	0, // [0:0] is the sub-list for extension extendee
+	0, // [0:0] is the sub-list for field type_name
+}
+
+func init() { file_app_dns_fakedns_fakedns_proto_init() }
+func file_app_dns_fakedns_fakedns_proto_init() {
+	if File_app_dns_fakedns_fakedns_proto != nil {
+		return
+	}
+	if !protoimpl.UnsafeEnabled {
+		file_app_dns_fakedns_fakedns_proto_msgTypes[0].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*FakeDnsPool); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+	}
+	type x struct{}
+	out := protoimpl.TypeBuilder{
+		File: protoimpl.DescBuilder{
+			GoPackagePath: reflect.TypeOf(x{}).PkgPath(),
+			RawDescriptor: file_app_dns_fakedns_fakedns_proto_rawDesc,
+			NumEnums:      0,
+			NumMessages:   1,
+			NumExtensions: 0,
+			NumServices:   0,
+		},
+		GoTypes:           file_app_dns_fakedns_fakedns_proto_goTypes,
+		DependencyIndexes: file_app_dns_fakedns_fakedns_proto_depIdxs,
+		MessageInfos:      file_app_dns_fakedns_fakedns_proto_msgTypes,
+	}.Build()
+	File_app_dns_fakedns_fakedns_proto = out.File
+	file_app_dns_fakedns_fakedns_proto_rawDesc = nil
+	file_app_dns_fakedns_fakedns_proto_goTypes = nil
+	file_app_dns_fakedns_fakedns_proto_depIdxs = nil
+}

app/dns/fakedns/fakedns.proto

@@ -0,0 +1,12 @@
+syntax = "proto3";
+
+package xray.app.dns.fakedns;
+option csharp_namespace = "Xray.App.Dns.Fakedns";
+option go_package = "github.com/xtls/xray-core/app/dns/fakedns";
+option java_package = "com.xray.app.dns.fakedns";
+option java_multiple_files = true;
+
+message FakeDnsPool{
+  string ip_pool = 1; //CIDR of IP pool used as fake DNS IP
+  int64  lruSize = 2; //Size of Pool for remembering relationship between domain name and IP address
+}

app/dns/fakedns/fakedns_test.go

@@ -0,0 +1,99 @@
+package fakedns
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/xtls/xray-core/common"
+	"github.com/xtls/xray-core/common/net"
+	"github.com/xtls/xray-core/common/uuid"
+)
+
+func TestNewFakeDnsHolder(_ *testing.T) {
+	_, err := NewFakeDNSHolder()
+	common.Must(err)
+}
+
+func TestFakeDnsHolderCreateMapping(t *testing.T) {
+	fkdns, err := NewFakeDNSHolder()
+	common.Must(err)
+
+	addr := fkdns.GetFakeIPForDomain("fakednstest.v2fly.org")
+	assert.Equal(t, "240.", addr[0].IP().String()[0:4])
+}
+
+func TestFakeDnsHolderCreateMappingMany(t *testing.T) {
+	fkdns, err := NewFakeDNSHolder()
+	common.Must(err)
+
+	addr := fkdns.GetFakeIPForDomain("fakednstest.v2fly.org")
+	assert.Equal(t, "240.", addr[0].IP().String()[0:4])
+
+	addr2 := fkdns.GetFakeIPForDomain("fakednstest2.v2fly.org")
+	assert.Equal(t, "240.", addr2[0].IP().String()[0:4])
+	assert.NotEqual(t, addr[0].IP().String(), addr2[0].IP().String())
+}
+
+func TestFakeDnsHolderCreateMappingManyAndResolve(t *testing.T) {
+	fkdns, err := NewFakeDNSHolder()
+	common.Must(err)
+
+	addr := fkdns.GetFakeIPForDomain("fakednstest.v2fly.org")
+	addr2 := fkdns.GetFakeIPForDomain("fakednstest2.v2fly.org")
+
+	{
+		result := fkdns.GetDomainFromFakeDNS(addr[0])
+		assert.Equal(t, "fakednstest.v2fly.org", result)
+	}
+
+	{
+		result := fkdns.GetDomainFromFakeDNS(addr2[0])
+		assert.Equal(t, "fakednstest2.v2fly.org", result)
+	}
+}
+
+func TestFakeDnsHolderCreateMappingManySingleDomain(t *testing.T) {
+	fkdns, err := NewFakeDNSHolder()
+	common.Must(err)
+
+	addr := fkdns.GetFakeIPForDomain("fakednstest.v2fly.org")
+	addr2 := fkdns.GetFakeIPForDomain("fakednstest.v2fly.org")
+	assert.Equal(t, addr[0].IP().String(), addr2[0].IP().String())
+}
+
+func TestFakeDnsHolderCreateMappingAndRollOver(t *testing.T) {
+	fkdns, err := NewFakeDNSHolderConfigOnly(&FakeDnsPool{
+		IpPool:  "240.0.0.0/12",
+		LruSize: 256,
+	})
+	common.Must(err)
+
+	err = fkdns.Start()
+
+	common.Must(err)
+
+	addr := fkdns.GetFakeIPForDomain("fakednstest.v2fly.org")
+	addr2 := fkdns.GetFakeIPForDomain("fakednstest2.v2fly.org")
+
+	for i := 0; i <= 8192; i++ {
+		{
+			result := fkdns.GetDomainFromFakeDNS(addr[0])
+			assert.Equal(t, "fakednstest.v2fly.org", result)
+		}
+
+		{
+			result := fkdns.GetDomainFromFakeDNS(addr2[0])
+			assert.Equal(t, "fakednstest2.v2fly.org", result)
+		}
+
+		{
+			uuid := uuid.New()
+			domain := uuid.String() + ".fakednstest.v2fly.org"
+			tempAddr := fkdns.GetFakeIPForDomain(domain)
+			rsaddr := tempAddr[0].IP().String()
+
+			result := fkdns.GetDomainFromFakeDNS(net.ParseAddress(rsaddr))
+			assert.Equal(t, domain, result)
+		}
+	}
+}

app/dns/hosts.go

@@ -5,6 +5,7 @@ import (
 	"github.com/xtls/xray-core/common/net"
 	"github.com/xtls/xray-core/common/strmatcher"
 	"github.com/xtls/xray-core/features"
+	"github.com/xtls/xray-core/features/dns"
 )
 
 // StaticHosts represents static domain-ip mapping in DNS server.
@@ -92,7 +93,7 @@ func NewStaticHosts(hosts []*Config_HostMapping, legacy map[string]*net.IPOrDoma
 	return sh, nil
 }
 
-func filterIP(ips []net.Address, option IPOption) []net.Address {
+func filterIP(ips []net.Address, option dns.IPOption) []net.Address {
 	filtered := make([]net.Address, 0, len(ips))
 	for _, ip := range ips {
 		if (ip.Family().IsIPv4() && option.IPv4Enable) || (ip.Family().IsIPv6() && option.IPv6Enable) {
@@ -106,7 +107,7 @@ func filterIP(ips []net.Address, option IPOption) []net.Address {
 }
 
 // LookupIP returns IP address for the given domain, if exists in this StaticHosts.
-func (h *StaticHosts) LookupIP(domain string, option IPOption) []net.Address {
+func (h *StaticHosts) LookupIP(domain string, option dns.IPOption) []net.Address {
 	indices := h.matchers.Match(domain)
 	if len(indices) == 0 {
 		return nil

app/dns/hosts_test.go

@@ -8,6 +8,7 @@ import (
 	. "github.com/xtls/xray-core/app/dns"
 	"github.com/xtls/xray-core/common"
 	"github.com/xtls/xray-core/common/net"
+	"github.com/xtls/xray-core/features/dns"
 )
 
 func TestStaticHosts(t *testing.T) {
@@ -39,7 +40,7 @@ func TestStaticHosts(t *testing.T) {
 	common.Must(err)
 
 	{
-		ips := hosts.LookupIP("example.com", IPOption{
+		ips := hosts.LookupIP("example.com", dns.IPOption{
 			IPv4Enable: true,
 			IPv6Enable: true,
 		})
@@ -52,7 +53,7 @@ func TestStaticHosts(t *testing.T) {
 	}
 
 	{
-		ips := hosts.LookupIP("www.example.cn", IPOption{
+		ips := hosts.LookupIP("www.example.cn", dns.IPOption{
 			IPv4Enable: true,
 			IPv6Enable: true,
 		})
@@ -65,7 +66,7 @@ func TestStaticHosts(t *testing.T) {
 	}
 
 	{
-		ips := hosts.LookupIP("baidu.com", IPOption{
+		ips := hosts.LookupIP("baidu.com", dns.IPOption{
 			IPv4Enable: false,
 			IPv6Enable: true,
 		})

app/dns/nameserver.go

@@ -4,39 +4,26 @@ import (
 	"context"
 
 	"github.com/xtls/xray-core/common/net"
+	"github.com/xtls/xray-core/features/dns"
 	"github.com/xtls/xray-core/features/dns/localdns"
 )
 
-// IPOption is an object for IP query options.
-type IPOption struct {
-	IPv4Enable bool
-	IPv6Enable bool
-}
-
 // Client is the interface for DNS client.
 type Client interface {
 	// Name of the Client.
 	Name() string
 
 	// QueryIP sends IP queries to its configured server.
-	QueryIP(ctx context.Context, domain string, option IPOption) ([]net.IP, error)
+	QueryIP(ctx context.Context, domain string, option dns.IPOption) ([]net.IP, error)
 }
 
 type LocalNameServer struct {
 	client *localdns.Client
 }
 
-func (s *LocalNameServer) QueryIP(ctx context.Context, domain string, option IPOption) ([]net.IP, error) {
-	if option.IPv4Enable && option.IPv6Enable {
-		return s.client.LookupIP(domain)
-	}
-
-	if option.IPv4Enable {
-		return s.client.LookupIPv4(domain)
-	}
-
-	if option.IPv6Enable {
-		return s.client.LookupIPv6(domain)
+func (s *LocalNameServer) QueryIP(_ context.Context, domain string, option dns.IPOption) ([]net.IP, error) {
+	if option.IPv4Enable || option.IPv6Enable {
+		return s.client.LookupIP(domain, option)
 	}
 
 	return nil, newError("neither IPv4 nor IPv6 is enabled")

app/dns/nameserver_fakedns.go

@@ -0,0 +1,43 @@
+// +build !confonly
+
+package dns
+
+import (
+	"context"
+
+	"github.com/xtls/xray-core/core"
+	"github.com/xtls/xray-core/common/net"
+	"github.com/xtls/xray-core/features/dns"
+)
+
+type FakeDNSServer struct {
+	fakeDNSEngine dns.FakeDNSEngine
+}
+
+func NewFakeDNSServer() *FakeDNSServer {
+	return &FakeDNSServer{}
+}
+
+func (FakeDNSServer) Name() string {
+	return "FakeDNS"
+}
+
+func (f *FakeDNSServer) QueryIP(ctx context.Context, domain string, _ dns.IPOption) ([]net.IP, error) {
+	if f.fakeDNSEngine == nil {
+		if err := core.RequireFeatures(ctx, func(fd dns.FakeDNSEngine) {
+			f.fakeDNSEngine = fd
+		}); err != nil {
+			return nil, newError("Unable to locate a fake DNS Engine").Base(err).AtError()
+		}
+	}
+	ips := f.fakeDNSEngine.GetFakeIPForDomain(domain)
+
+	netIP := toNetIP(ips)
+	if netIP == nil {
+		return nil, newError("Unable to convert IP to net ip").AtError()
+	}
+
+	newError(f.Name(), " got answer: ", domain, " -> ", ips).AtInfo().WriteToLog()
+
+	return netIP, nil
+}

app/dns/nameserver_test.go

@@ -7,14 +7,16 @@ import (
 
 	. "github.com/xtls/xray-core/app/dns"
 	"github.com/xtls/xray-core/common"
+	dns_feature "github.com/xtls/xray-core/features/dns"
 )
 
 func TestLocalNameServer(t *testing.T) {
 	s := NewLocalNameServer()
 	ctx, cancel := context.WithTimeout(context.Background(), time.Second*2)
-	ips, err := s.QueryIP(ctx, "google.com", IPOption{
+	ips, err := s.QueryIP(ctx, "google.com", dns_feature.IPOption{
 		IPv4Enable: true,
 		IPv6Enable: true,
+		FakeEnable: false,
 	})
 	cancel()
 	common.Must(err)

app/dns/server.go

@@ -31,6 +31,7 @@ type Server struct {
 	hosts         *StaticHosts
 	clientIP      net.IP
 	clients       []Client             // clientIdx -> Client
+	ctx           context.Context
 	ipIndexMap    []*MultiGeoIPMatcher // clientIdx -> *MultiGeoIPMatcher
 	domainRules   [][]string           // clientIdx -> domainRuleIdx -> DomainRule
 	domainMatcher strmatcher.IndexMatcher
@@ -75,6 +76,7 @@ func generateRandomTag() string {
 func New(ctx context.Context, config *Config) (*Server, error) {
 	server := &Server{
 		clients: make([]Client, 0, len(config.NameServers)+len(config.NameServer)),
+		ctx:     ctx,
 		tag:     config.Tag,
 	}
 	if server.tag == "" {
@@ -144,6 +146,9 @@ func New(ctx context.Context, config *Config) (*Server, error) {
 				server.clients[idx] = c
 			}))
 
+		case address.Family().IsDomain() && address.Domain() == "fakedns":
+			server.clients = append(server.clients, NewFakeDNSServer())
+
 		default:
 			// UDP classic DNS mode
 			dest := endpoint.AsDestination()
@@ -295,8 +300,8 @@ func (s *Server) Match(idx int, client Client, domain string, ips []net.IP) ([]n
 	return newIps, nil
 }
 
-func (s *Server) queryIPTimeout(idx int, client Client, domain string, option IPOption) ([]net.IP, error) {
-	ctx, cancel := context.WithTimeout(context.Background(), time.Second*4)
+func (s *Server) queryIPTimeout(idx int, client Client, domain string, option dns.IPOption) ([]net.IP, error) {
+	ctx, cancel := context.WithTimeout(s.ctx, time.Second*4)
 	if len(s.tag) > 0 {
 		ctx = session.ContextWithInbound(ctx, &session.Inbound{
 			Tag: s.tag,
@@ -314,31 +319,7 @@ func (s *Server) queryIPTimeout(idx int, client Client, domain string, option IP
 	return ips, err
 }
 
-// LookupIP implements dns.Client.
-func (s *Server) LookupIP(domain string) ([]net.IP, error) {
-	return s.lookupIPInternal(domain, IPOption{
-		IPv4Enable: true,
-		IPv6Enable: true,
-	})
-}
-
-// LookupIPv4 implements dns.IPv4Lookup.
-func (s *Server) LookupIPv4(domain string) ([]net.IP, error) {
-	return s.lookupIPInternal(domain, IPOption{
-		IPv4Enable: true,
-		IPv6Enable: false,
-	})
-}
-
-// LookupIPv6 implements dns.IPv6Lookup.
-func (s *Server) LookupIPv6(domain string) ([]net.IP, error) {
-	return s.lookupIPInternal(domain, IPOption{
-		IPv4Enable: false,
-		IPv6Enable: true,
-	})
-}
-
-func (s *Server) lookupStatic(domain string, option IPOption, depth int32) []net.Address {
+func (s *Server) lookupStatic(domain string, option dns.IPOption, depth int32) []net.Address {
 	ips := s.hosts.LookupIP(domain, option)
 	if ips == nil {
 		return nil
@@ -362,14 +343,15 @@ func toNetIP(ips []net.Address) []net.IP {
 	return netips
 }
 
-func (s *Server) lookupIPInternal(domain string, option IPOption) ([]net.IP, error) {
+// LookupIP implements dns.Client.
+func (s *Server) LookupIP(domain string, option dns.IPOption) ([]net.IP, error) {
 	if domain == "" {
 		return nil, newError("empty domain name")
 	}
 	domain = strings.ToLower(domain)
 
 	// normalize the FQDN form query
-	if domain[len(domain)-1] == '.' {
+	if strings.HasSuffix(domain, ".") {
 		domain = domain[:len(domain)-1]
 	}
 
@@ -406,6 +388,10 @@ func (s *Server) lookupIPInternal(domain string, option IPOption) ([]net.IP, err
 		for _, idx := range indices {
 			clientIdx := int(s.matcherInfos[idx].clientIdx)
 			matchedClient = s.clients[clientIdx]
+			if !option.FakeEnable && strings.EqualFold(matchedClient.Name(), "FakeDNS") {
+				newError("skip DNS resolution for domain ", domain, " at server ", matchedClient.Name()).AtDebug().WriteToLog()
+				continue
+			}
 			ips, err := s.queryIPTimeout(clientIdx, matchedClient, domain, option)
 			if len(ips) > 0 {
 				return ips, nil
@@ -425,7 +411,10 @@ func (s *Server) lookupIPInternal(domain string, option IPOption) ([]net.IP, err
 			newError("domain ", domain, " at server ", client.Name(), " idx:", idx, " already lookup failed, just ignore").AtDebug().WriteToLog()
 			continue
 		}
-
+		if !option.FakeEnable && strings.EqualFold(client.Name(), "FakeDNS") {
+			newError("skip DNS resolution for domain ", domain, " at server ", client.Name()).AtDebug().WriteToLog()
+			continue
+		}
 		ips, err := s.queryIPTimeout(idx, client, domain, option)
 		if len(ips) > 0 {
 			return ips, nil

app/dns/server_test.go

@@ -154,7 +154,11 @@ func TestUDPServerSubnet(t *testing.T) {
 
 	client := v.GetFeature(feature_dns.ClientType()).(feature_dns.Client)
 
-	ips, err := client.LookupIP("google.com")
+	ips, err := client.LookupIP("google.com", feature_dns.IPOption{
+		IPv4Enable: true,
+		IPv6Enable: true,
+		FakeEnable: false,
+	})
 	if err != nil {
 		t.Fatal("unexpected error: ", err)
 	}
@@ -209,7 +213,11 @@ func TestUDPServer(t *testing.T) {
 	client := v.GetFeature(feature_dns.ClientType()).(feature_dns.Client)
 
 	{
-		ips, err := client.LookupIP("google.com")
+		ips, err := client.LookupIP("google.com", feature_dns.IPOption{
+			IPv4Enable: true,
+			IPv6Enable: true,
+			FakeEnable: false,
+		})
 		if err != nil {
 			t.Fatal("unexpected error: ", err)
 		}
@@ -220,7 +228,11 @@ func TestUDPServer(t *testing.T) {
 	}
 
 	{
-		ips, err := client.LookupIP("facebook.com")
+		ips, err := client.LookupIP("facebook.com", feature_dns.IPOption{
+			IPv4Enable: true,
+			IPv6Enable: true,
+			FakeEnable: false,
+		})
 		if err != nil {
 			t.Fatal("unexpected error: ", err)
 		}
@@ -231,7 +243,11 @@ func TestUDPServer(t *testing.T) {
 	}
 
 	{
-		_, err := client.LookupIP("notexist.google.com")
+		_, err := client.LookupIP("notexist.google.com", feature_dns.IPOption{
+			IPv4Enable: true,
+			IPv6Enable: true,
+			FakeEnable: false,
+		})
 		if err == nil {
 			t.Fatal("nil error")
 		}
@@ -241,8 +257,11 @@ func TestUDPServer(t *testing.T) {
 	}
 
 	{
-		clientv6 := client.(feature_dns.IPv6Lookup)
-		ips, err := clientv6.LookupIPv6("ipv4only.google.com")
+		ips, err := client.LookupIP("ipv4only.google.com", feature_dns.IPOption{
+			IPv4Enable: false,
+			IPv6Enable: true,
+			FakeEnable: false,
+		})
 		if err != feature_dns.ErrEmptyResponse {
 			t.Fatal("error: ", err)
 		}
@@ -254,7 +273,11 @@ func TestUDPServer(t *testing.T) {
 	dnsServer.Shutdown()
 
 	{
-		ips, err := client.LookupIP("google.com")
+		ips, err := client.LookupIP("google.com", feature_dns.IPOption{
+			IPv4Enable: true,
+			IPv6Enable: true,
+			FakeEnable: false,
+		})
 		if err != nil {
 			t.Fatal("unexpected error: ", err)
 		}
@@ -331,7 +354,11 @@ func TestPrioritizedDomain(t *testing.T) {
 	startTime := time.Now()
 
 	{
-		ips, err := client.LookupIP("google.com")
+		ips, err := client.LookupIP("google.com", feature_dns.IPOption{
+			IPv4Enable: true,
+			IPv6Enable: true,
+			FakeEnable: false,
+		})
 		if err != nil {
 			t.Fatal("unexpected error: ", err)
 		}
@@ -390,10 +417,12 @@ func TestUDPServerIPv6(t *testing.T) {
 	common.Must(err)
 
 	client := v.GetFeature(feature_dns.ClientType()).(feature_dns.Client)
-	client6 := client.(feature_dns.IPv6Lookup)
-
 	{
-		ips, err := client6.LookupIPv6("ipv6.google.com")
+		ips, err := client.LookupIP("ipv6.google.com", feature_dns.IPOption{
+			IPv4Enable: false,
+			IPv6Enable: true,
+			FakeEnable: false,
+		})
 		if err != nil {
 			t.Fatal("unexpected error: ", err)
 		}
@@ -456,7 +485,11 @@ func TestStaticHostDomain(t *testing.T) {
 	client := v.GetFeature(feature_dns.ClientType()).(feature_dns.Client)
 
 	{
-		ips, err := client.LookupIP("example.com")
+		ips, err := client.LookupIP("example.com", feature_dns.IPOption{
+			IPv4Enable: true,
+			IPv6Enable: true,
+			FakeEnable: false,
+		})
 		if err != nil {
 			t.Fatal("unexpected error: ", err)
 		}
@@ -563,7 +596,11 @@ func TestIPMatch(t *testing.T) {
 	startTime := time.Now()
 
 	{
-		ips, err := client.LookupIP("google.com")
+		ips, err := client.LookupIP("google.com", feature_dns.IPOption{
+			IPv4Enable: true,
+			IPv6Enable: true,
+			FakeEnable: false,
+		})
 		if err != nil {
 			t.Fatal("unexpected error: ", err)
 		}
@@ -682,7 +719,11 @@ func TestLocalDomain(t *testing.T) {
 	startTime := time.Now()
 
 	{ // Will match dotless:
-		ips, err := client.LookupIP("hostname")
+		ips, err := client.LookupIP("hostname", feature_dns.IPOption{
+			IPv4Enable: true,
+			IPv6Enable: true,
+			FakeEnable: false,
+		})
 		if err != nil {
 			t.Fatal("unexpected error: ", err)
 		}
@@ -693,7 +734,11 @@ func TestLocalDomain(t *testing.T) {
 	}
 
 	{ // Will match domain:local
-		ips, err := client.LookupIP("hostname.local")
+		ips, err := client.LookupIP("hostname.local", feature_dns.IPOption{
+			IPv4Enable: true,
+			IPv6Enable: true,
+			FakeEnable: false,
+		})
 		if err != nil {
 			t.Fatal("unexpected error: ", err)
 		}
@@ -704,7 +749,11 @@ func TestLocalDomain(t *testing.T) {
 	}
 
 	{ // Will match static ip
-		ips, err := client.LookupIP("hostnamestatic")
+		ips, err := client.LookupIP("hostnamestatic", feature_dns.IPOption{
+			IPv4Enable: true,
+			IPv6Enable: true,
+			FakeEnable: false,
+		})
 		if err != nil {
 			t.Fatal("unexpected error: ", err)
 		}
@@ -715,7 +764,11 @@ func TestLocalDomain(t *testing.T) {
 	}
 
 	{ // Will match domain replacing
-		ips, err := client.LookupIP("hostnamealias")
+		ips, err := client.LookupIP("hostnamealias", feature_dns.IPOption{
+			IPv4Enable: true,
+			IPv6Enable: true,
+			FakeEnable: false,
+		})
 		if err != nil {
 			t.Fatal("unexpected error: ", err)
 		}
@@ -726,7 +779,11 @@ func TestLocalDomain(t *testing.T) {
 	}
 
 	{ // Will match dotless:localhost, but not expectIPs: 127.0.0.2, 127.0.0.3, then matches at dotless:
-		ips, err := client.LookupIP("localhost")
+		ips, err := client.LookupIP("localhost", feature_dns.IPOption{
+			IPv4Enable: true,
+			IPv6Enable: true,
+			FakeEnable: false,
+		})
 		if err != nil {
 			t.Fatal("unexpected error: ", err)
 		}
@@ -737,7 +794,11 @@ func TestLocalDomain(t *testing.T) {
 	}
 
 	{ // Will match dotless:localhost, and expectIPs: 127.0.0.2, 127.0.0.3
-		ips, err := client.LookupIP("localhost-a")
+		ips, err := client.LookupIP("localhost-a", feature_dns.IPOption{
+			IPv4Enable: true,
+			IPv6Enable: true,
+			FakeEnable: false,
+		})
 		if err != nil {
 			t.Fatal("unexpected error: ", err)
 		}
@@ -748,7 +809,11 @@ func TestLocalDomain(t *testing.T) {
 	}
 
 	{ // Will match dotless:localhost, and expectIPs: 127.0.0.2, 127.0.0.3
-		ips, err := client.LookupIP("localhost-b")
+		ips, err := client.LookupIP("localhost-b", feature_dns.IPOption{
+			IPv4Enable: true,
+			IPv6Enable: true,
+			FakeEnable: false,
+		})
 		if err != nil {
 			t.Fatal("unexpected error: ", err)
 		}
@@ -759,7 +824,11 @@ func TestLocalDomain(t *testing.T) {
 	}
 
 	{ // Will match dotless:
-		ips, err := client.LookupIP("Mijia Cloud")
+		ips, err := client.LookupIP("Mijia Cloud", feature_dns.IPOption{
+			IPv4Enable: true,
+			IPv6Enable: true,
+			FakeEnable: false,
+		})
 		if err != nil {
 			t.Fatal("unexpected error: ", err)
 		}
@@ -921,7 +990,11 @@ func TestMultiMatchPrioritizedDomain(t *testing.T) {
 	startTime := time.Now()
 
 	{ // Will match server 1,2 and server 1 returns expected ip
-		ips, err := client.LookupIP("google.com")
+		ips, err := client.LookupIP("google.com", feature_dns.IPOption{
+			IPv4Enable: true,
+			IPv6Enable: true,
+			FakeEnable: false,
+		})
 		if err != nil {
 			t.Fatal("unexpected error: ", err)
 		}
@@ -932,8 +1005,11 @@ func TestMultiMatchPrioritizedDomain(t *testing.T) {
 	}
 
 	{ // Will match server 1,2 and server 1 returns unexpected ip, then server 2 returns expected one
-		clientv4 := client.(feature_dns.IPv4Lookup)
-		ips, err := clientv4.LookupIPv4("ipv6.google.com")
+		ips, err := client.LookupIP("ipv6.google.com", feature_dns.IPOption{
+			IPv4Enable: true,
+			IPv6Enable: false,
+			FakeEnable: false,
+		})
 		if err != nil {
 			t.Fatal("unexpected error: ", err)
 		}
@@ -944,7 +1020,11 @@ func TestMultiMatchPrioritizedDomain(t *testing.T) {
 	}
 
 	{ // Will match server 3,1,2 and server 3 returns expected one
-		ips, err := client.LookupIP("api.google.com")
+		ips, err := client.LookupIP("api.google.com", feature_dns.IPOption{
+			IPv4Enable: true,
+			IPv6Enable: true,
+			FakeEnable: false,
+		})
 		if err != nil {
 			t.Fatal("unexpected error: ", err)
 		}
@@ -955,7 +1035,11 @@ func TestMultiMatchPrioritizedDomain(t *testing.T) {
 	}
 
 	{ // Will match server 4,3,1,2 and server 4 returns expected one
-		ips, err := client.LookupIP("v2.api.google.com")
+		ips, err := client.LookupIP("v2.api.google.com", feature_dns.IPOption{
+			IPv4Enable: true,
+			IPv6Enable: true,
+			FakeEnable: false,
+		})
 		if err != nil {
 			t.Fatal("unexpected error: ", err)
 		}

app/dns/udpns.go

@@ -54,7 +54,7 @@ func NewClassicNameServer(address net.Destination, dispatcher routing.Dispatcher
 		Execute:  s.Cleanup,
 	}
 	s.udpServer = udp.NewDispatcher(dispatcher, s.HandleResponse)
-	newError("DNS: created udp client inited for ", address.NetAddr()).AtInfo().WriteToLog()
+	newError("DNS: created UDP client initialized for ", address.NetAddr()).AtInfo().WriteToLog()
 	return s
 }
 
@@ -180,7 +180,7 @@ func (s *ClassicNameServer) addPendingRequest(req *dnsRequest) {
 	s.requests[id] = *req
 }
 
-func (s *ClassicNameServer) sendQuery(ctx context.Context, domain string, option IPOption) {
+func (s *ClassicNameServer) sendQuery(ctx context.Context, domain string, option dns_feature.IPOption) {
 	newError(s.name, " querying DNS for: ", domain).AtDebug().WriteToLog(session.ExportIDToError(ctx))
 
 	reqs := buildReqMsgs(domain, option, s.newReqID, genEDNS0Options(s.clientIP))
@@ -206,7 +206,7 @@ func (s *ClassicNameServer) sendQuery(ctx context.Context, domain string, option
 	}
 }
 
-func (s *ClassicNameServer) findIPsForDomain(domain string, option IPOption) ([]net.IP, error) {
+func (s *ClassicNameServer) findIPsForDomain(domain string, option dns_feature.IPOption) ([]net.IP, error) {
 	s.RLock()
 	record, found := s.ips[domain]
 	s.RUnlock()
@@ -244,7 +244,8 @@ func (s *ClassicNameServer) findIPsForDomain(domain string, option IPOption) ([]
 	return nil, dns_feature.ErrEmptyResponse
 }
 
-func (s *ClassicNameServer) QueryIP(ctx context.Context, domain string, option IPOption) ([]net.IP, error) {
+// QueryIP implements Server.
+func (s *ClassicNameServer) QueryIP(ctx context.Context, domain string, option dns_feature.IPOption) ([]net.IP, error) {
 	fqdn := Fqdn(domain)
 
 	ips, err := s.findIPsForDomain(fqdn, option)