dns: unify the Lua API for local and configured DNS

Expose localdns.Client in xray.dns.Servers with the ID "localhost",
so Lua scripts can use the same server API for both clients.

app/dispatcher/default.go

@@ -470,6 +470,9 @@ func (d *DefaultDispatcher) routedDispatch(ctx context.Context, link *transport.
 				return // DO NOT CHANGE: the traffic shouldn't be processed by default outbound if the specified outbound tag doesn't exist (yet), e.g., VLESS Reverse Proxy
 			}
 		} else {
+			if err != common.ErrNoClue {
+				errors.LogErrorInner(ctx, err, "failed to pick route for ", destination)
+			}
 			errors.LogInfo(ctx, "default route for ", destination)
 		}
 	}

app/dns/config.pb.go

@@ -93,6 +93,7 @@ type NameServer struct {
 	UnexpectedIp    []*geodata.IPRule      `protobuf:"bytes,13,rep,name=unexpected_ip,json=unexpectedIp,proto3" json:"unexpected_ip,omitempty"`
 	ActUnprior      bool                   `protobuf:"varint,14,opt,name=actUnprior,proto3" json:"actUnprior,omitempty"`
 	PolicyID        uint32                 `protobuf:"varint,17,opt,name=policyID,proto3" json:"policyID,omitempty"`
+	Id              string                 `protobuf:"bytes,18,opt,name=id,proto3" json:"id,omitempty"`
 	unknownFields   protoimpl.UnknownFields
 	sizeCache       protoimpl.SizeCache
 }
@@ -239,6 +240,13 @@ func (x *NameServer) GetPolicyID() uint32 {
 	return 0
 }
 
+func (x *NameServer) GetId() string {
+	if x != nil {
+		return x.Id
+	}
+	return ""
+}
+
 type Config struct {
 	state protoimpl.MessageState `protogen:"open.v1"`
 	// NameServer list used by this DNS client.
@@ -258,8 +266,10 @@ type Config struct {
 	DisableFallback        bool          `protobuf:"varint,10,opt,name=disableFallback,proto3" json:"disableFallback,omitempty"`
 	DisableFallbackIfMatch bool          `protobuf:"varint,11,opt,name=disableFallbackIfMatch,proto3" json:"disableFallbackIfMatch,omitempty"`
 	EnableParallelQuery    bool          `protobuf:"varint,14,opt,name=enableParallelQuery,proto3" json:"enableParallelQuery,omitempty"`
-	unknownFields          protoimpl.UnknownFields
-	sizeCache              protoimpl.SizeCache
+	// Absolute path to the Lua DNS query script.
+	Script        string `protobuf:"bytes,15,opt,name=script,proto3" json:"script,omitempty"`
+	unknownFields protoimpl.UnknownFields
+	sizeCache     protoimpl.SizeCache
 }
 
 func (x *Config) Reset() {
@@ -369,6 +379,13 @@ func (x *Config) GetEnableParallelQuery() bool {
 	return false
 }
 
+func (x *Config) GetScript() string {
+	if x != nil {
+		return x.Script
+	}
+	return ""
+}
+
 type Config_HostMapping struct {
 	state  protoimpl.MessageState `protogen:"open.v1"`
 	Domain *geodata.DomainRule    `protobuf:"bytes,2,opt,name=domain,proto3" json:"domain,omitempty"`
@@ -435,7 +452,7 @@ var File_app_dns_config_proto protoreflect.FileDescriptor
 
 const file_app_dns_config_proto_rawDesc = "" +
 	"\n" +
-	"\x14app/dns/config.proto\x12\fxray.app.dns\x1a\x1ccommon/net/destination.proto\x1a\x1bcommon/geodata/geodat.proto\"\xde\x05\n" +
+	"\x14app/dns/config.proto\x12\fxray.app.dns\x1a\x1ccommon/net/destination.proto\x1a\x1bcommon/geodata/geodat.proto\"\xee\x05\n" +
 	"\n" +
 	"NameServer\x123\n" +
 	"\aaddress\x18\x01 \x01(\v2\x19.xray.common.net.EndpointR\aaddress\x12\x1b\n" +
@@ -461,10 +478,11 @@ const file_app_dns_config_proto_rawDesc = "" +
 	"\n" +
 	"actUnprior\x18\x0e \x01(\bR\n" +
 	"actUnprior\x12\x1a\n" +
-	"\bpolicyID\x18\x11 \x01(\rR\bpolicyIDB\x0f\n" +
+	"\bpolicyID\x18\x11 \x01(\rR\bpolicyID\x12\x0e\n" +
+	"\x02id\x18\x12 \x01(\tR\x02idB\x0f\n" +
 	"\r_disableCacheB\r\n" +
 	"\v_serveStaleB\x12\n" +
-	"\x10_serveExpiredTTLJ\x04\b\x04\x10\x05\"\x82\x05\n" +
+	"\x10_serveExpiredTTLJ\x04\b\x04\x10\x05\"\x9a\x05\n" +
 	"\x06Config\x129\n" +
 	"\vname_server\x18\x05 \x03(\v2\x18.xray.app.dns.NameServerR\n" +
 	"nameServer\x12\x1b\n" +
@@ -480,7 +498,8 @@ const file_app_dns_config_proto_rawDesc = "" +
 	"\x0fdisableFallback\x18\n" +
 	" \x01(\bR\x0fdisableFallback\x126\n" +
 	"\x16disableFallbackIfMatch\x18\v \x01(\bR\x16disableFallbackIfMatch\x120\n" +
-	"\x13enableParallelQuery\x18\x0e \x01(\bR\x13enableParallelQuery\x1a}\n" +
+	"\x13enableParallelQuery\x18\x0e \x01(\bR\x13enableParallelQuery\x12\x16\n" +
+	"\x06script\x18\x0f \x01(\tR\x06script\x1a}\n" +
 	"\vHostMapping\x127\n" +
 	"\x06domain\x18\x02 \x01(\v2\x1f.xray.common.geodata.DomainRuleR\x06domain\x12\x0e\n" +
 	"\x02ip\x18\x03 \x03(\fR\x02ip\x12%\n" +

app/dns/config.proto

@@ -27,6 +27,7 @@ message NameServer {
   repeated xray.common.geodata.IPRule unexpected_ip = 13;
   bool actUnprior = 14;
   uint32 policyID = 17;
+  string id = 18;
 }
 
 enum QueryStrategy {
@@ -73,4 +74,7 @@ message Config {
   bool disableFallbackIfMatch = 11;
 
   bool enableParallelQuery = 14;
+
+  // Absolute path to the Lua DNS query script.
+  string script = 15;
 }

app/dns/dns.go

@@ -31,6 +31,8 @@ type DNS struct {
 	domainMatcher          geodata.DomainMatcher
 	matcherInfos           []*DomainMatcherInfo
 	checkSystem            bool
+	script                 *scriptEngine
+	scriptPath             string
 }
 
 // DomainMatcherInfo contains information attached to index returned by Server.domainMatcher.
@@ -180,6 +182,7 @@ func New(ctx context.Context, config *Config) (*DNS, error) {
 		disableFallbackIfMatch: config.DisableFallbackIfMatch,
 		enableParallelQuery:    config.EnableParallelQuery,
 		checkSystem:            checkSystem,
+		scriptPath:             config.Script,
 	}, nil
 }
 
@@ -190,11 +193,21 @@ func (*DNS) Type() interface{} {
 
 // Start implements common.Runnable.
 func (s *DNS) Start() error {
+	if s.scriptPath != "" {
+		engine, err := newScriptEngine(s.scriptPath, s)
+		if err != nil {
+			return errors.New("failed to initialize DNS script").Base(err)
+		}
+		s.script = engine
+	}
 	return nil
 }
 
 // Close implements common.Closable.
 func (s *DNS) Close() error {
+	if s.script != nil {
+		s.script.close()
+	}
 	return nil
 }
 
@@ -257,6 +270,9 @@ func (s *DNS) LookupIP(domain string, option dns.IPOption) ([]net.IP, uint32, er
 	}
 
 	// Name servers lookup
+	if s.script != nil {
+		return s.script.query(domain, option)
+	}
 	if s.enableParallelQuery {
 		return s.parallelQuery(domain, option)
 	} else {

app/dns/lua.go

@@ -0,0 +1,201 @@
+package dns
+
+import (
+	"context"
+	"math"
+	"strings"
+
+	"github.com/xtls/xray-core/common/errors"
+	"github.com/xtls/xray-core/common/net"
+	featureDNS "github.com/xtls/xray-core/features/dns"
+	"github.com/xtls/xray-core/features/dns/localdns"
+	lua "github.com/yuin/gopher-lua"
+)
+
+// luaDNSServer adapts configured and local DNS to the same Lua API.
+type luaDNSServer struct {
+	id    string
+	name  string
+	query func(context.Context, string, featureDNS.IPOption) ([]net.IP, uint32, error)
+}
+
+// RegisterLua makes xray.dns available to scripts backed by client.
+func RegisterLua(L *lua.LState, client featureDNS.Client) {
+	var servers []luaDNSServer
+	switch client := client.(type) {
+	case *DNS:
+		servers = luaServers(client)
+	case *localdns.Client:
+		servers = []luaDNSServer{{
+			id:   "localhost",
+			name: "localhost",
+			query: func(_ context.Context, domain string, option featureDNS.IPOption) ([]net.IP, uint32, error) {
+				return client.LookupIP(domain, option)
+			},
+		}}
+	}
+	registerLua(L, servers, client)
+}
+
+// RegisterLua makes xray.dns available to DNS scripts.
+func (s *DNS) RegisterLua(L *lua.LState) {
+	registerLua(L, luaServers(s), nil)
+}
+
+func luaServers(s *DNS) []luaDNSServer {
+	servers := make([]luaDNSServer, len(s.clients))
+	for i, client := range s.clients {
+		servers[i] = luaDNSServer{id: client.id, name: client.Name(), query: client.QueryIP}
+	}
+	return servers
+}
+
+func registerLua(L *lua.LState, servers []luaDNSServer, client featureDNS.Client) {
+	L.PreloadModule("xray.dns", func(L *lua.LState) int {
+		serverList := L.NewTable()
+		for i, client := range servers {
+			server := L.NewTable()
+
+			server.RawSetString("ID", lua.LString(client.id))
+
+			server.RawSetString("Query", L.NewFunction(func(L *lua.LState) int {
+				domain, ok := L.Get(2).(lua.LString)
+				if !ok {
+					L.RaiseError("server:Query requires a domain")
+					return 0
+				}
+				option := featureDNS.IPOption{
+					IPv4Enable: L.CheckBool(3),
+					IPv6Enable: L.CheckBool(4),
+					FakeEnable: L.CheckBool(5),
+				}
+				ctx := L.Context()
+				if ctx == nil {
+					L.RaiseError("server:Query requires an active DNS query")
+					return 0
+				}
+				var ips []net.IP
+				var ttl uint32
+				var err error
+				if !option.FakeEnable && strings.EqualFold(client.name, "FakeDNS") {
+					err = featureDNS.ErrEmptyResponse
+				} else {
+					ips, ttl, err = client.query(ctx, string(domain), option)
+				}
+				addresses := L.NewUserData()
+				addresses.Value = ips
+				L.Push(addresses)
+				L.Push(lua.LNumber(ttl))
+				if err != nil {
+					ud := L.NewUserData()
+					ud.Value = err
+					L.Push(ud)
+				} else {
+					L.Push(lua.LNil)
+				}
+				return 3
+			}))
+			serverList.RawSetInt(i+1, server)
+		}
+
+		module := L.NewTable()
+		if servers != nil {
+			module.RawSetString("Servers", serverList)
+		}
+		if client != nil {
+			module.RawSetString("Query", newLuaClientQuery(L, client))
+		}
+		L.Push(module)
+		return 1
+	})
+}
+
+func newLuaClientQuery(L *lua.LState, client featureDNS.Client) *lua.LFunction {
+	return L.NewFunction(func(L *lua.LState) int {
+		domain, ok := L.Get(1).(lua.LString)
+		if !ok {
+			L.RaiseError("dns.Query requires a domain")
+			return 0
+		}
+		option := featureDNS.IPOption{
+			IPv4Enable: L.CheckBool(2),
+			IPv6Enable: L.CheckBool(3),
+			FakeEnable: L.CheckBool(4),
+		}
+		if L.Context() == nil {
+			L.RaiseError("dns.Query requires an active DNS query")
+			return 0
+		}
+		ips, ttl, err := client.LookupIP(string(domain), option)
+		addresses := L.NewUserData()
+		addresses.Value = ips
+		L.Push(addresses)
+		L.Push(lua.LNumber(ttl))
+		if err != nil {
+			ud := L.NewUserData()
+			ud.Value = err
+			L.Push(ud)
+		} else {
+			L.Push(lua.LNil)
+		}
+		return 3
+	})
+}
+
+// CallLuaHook invokes HandleDNSQuery in the supplied state.
+// Returned slices and IP bytes may share storage with DNS caches or matcher inputs.
+func (s *DNS) CallLuaHook(L *lua.LState, ctx context.Context, domain string, option featureDNS.IPOption) ([]net.IP, uint32, error) {
+	previous, top := L.Context(), L.GetTop()
+	L.SetContext(ctx)
+	defer func() {
+		L.SetTop(top)
+		if previous == nil {
+			L.RemoveContext()
+		} else {
+			L.SetContext(previous)
+		}
+	}()
+	fn := L.GetGlobal("HandleDNSQuery")
+	if fn.Type() != lua.LTFunction {
+		return nil, 0, errors.New("DNS script must define HandleDNSQuery(domain, ipv4, ipv6, fake)")
+	}
+	if err := L.CallByParam(lua.P{Fn: fn, NRet: 3, Protect: true},
+		lua.LString(strings.ToLower(domain)), lua.LBool(option.IPv4Enable),
+		lua.LBool(option.IPv6Enable), lua.LBool(option.FakeEnable)); err != nil {
+		return nil, 0, err
+	}
+	return readLuaDNSResult(L.Get(-3), L.Get(-2), L.Get(-1))
+}
+
+func readLuaDNSResult(addresses, ttlValue, errorValue lua.LValue) ([]net.IP, uint32, error) {
+	if errorValue != lua.LNil {
+		if ud, ok := errorValue.(*lua.LUserData); ok {
+			if err, ok := ud.Value.(error); ok {
+				return nil, 0, err
+			}
+		}
+		if s, ok := errorValue.(lua.LString); ok {
+			return nil, 0, errors.New(string(s))
+		}
+		return nil, 0, errors.New("DNS script error must be an error or string")
+	}
+	ttl, ok := ttlValue.(lua.LNumber)
+	if !ok || ttl < 0 || ttl > math.MaxUint32 || math.Trunc(float64(ttl)) != float64(ttl) {
+		return nil, 0, errors.New("DNS script returned invalid TTL")
+	}
+	if addresses == lua.LNil {
+		return nil, 0, featureDNS.ErrEmptyResponse
+	}
+	ud, ok := addresses.(*lua.LUserData)
+	if !ok {
+		return nil, 0, errors.New("DNS script IPs must be native IP slice userdata")
+	}
+	ips, ok := ud.Value.([]net.IP)
+	if !ok {
+		return nil, 0, errors.New("DNS script IPs must be native IP slice userdata")
+	}
+	if len(ips) == 0 {
+		return nil, 0, featureDNS.ErrEmptyResponse
+	}
+	return ips, uint32(ttl), nil
+}

app/dns/lua_test.go

@@ -0,0 +1,296 @@
+package dns
+
+import (
+	"context"
+	go_errors "errors"
+	"math"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/xtls/xray-core/common/geodata"
+	"github.com/xtls/xray-core/common/net"
+	featureDNS "github.com/xtls/xray-core/features/dns"
+	"github.com/xtls/xray-core/features/dns/localdns"
+	lua "github.com/yuin/gopher-lua"
+)
+
+func TestReadLuaDNSResult(t *testing.T) {
+	L := lua.NewState()
+	defer L.Close()
+	want := []net.IP{net.ParseIP("8.8.8.8"), {127, 0, 0, 1}, net.ParseIP("::1")}
+	addresses := L.NewUserData()
+	addresses.Value = want
+	ips, ttl, err := readLuaDNSResult(addresses, lua.LNumber(45), lua.LNil)
+	if err != nil || ttl != 45 || len(ips) != len(want) {
+		t.Fatalf("readLuaDNSResult() = %v, TTL %d, %v", ips, ttl, err)
+	}
+	for i := range want {
+		if !ips[i].Equal(want[i]) {
+			t.Fatalf("IP %d = %v, want %v", i, ips[i], want[i])
+		}
+	}
+}
+
+func TestReadLuaDNSResultValidation(t *testing.T) {
+	L := lua.NewState()
+	defer L.Close()
+
+	for _, tc := range []struct {
+		name   string
+		change func(*[3]lua.LValue)
+		want   string
+	}{
+		{"fractional TTL", func(v *[3]lua.LValue) { v[1] = lua.LNumber(1.5) }, "invalid TTL"},
+		{"oversized TTL", func(v *[3]lua.LValue) { v[1] = lua.LNumber(4294967296) }, "invalid TTL"},
+		{"negative TTL", func(v *[3]lua.LValue) { v[1] = lua.LNumber(-1) }, "invalid TTL"},
+		{"NaN TTL", func(v *[3]lua.LValue) { v[1] = lua.LNumber(math.NaN()) }, "invalid TTL"},
+		{"missing TTL", func(v *[3]lua.LValue) { v[1] = lua.LNil }, "invalid TTL"},
+		{"string IPs", func(v *[3]lua.LValue) { v[0] = lua.LString("127.0.0.1") }, "native IP slice"},
+		{"wrong userdata", func(v *[3]lua.LValue) { v[0].(*lua.LUserData).Value = net.ParseIP("127.0.0.1") }, "native IP slice"},
+		{"script error", func(v *[3]lua.LValue) { v[2] = lua.LString("blocked by script") }, "blocked by script"},
+		{"invalid error", func(v *[3]lua.LValue) { v[2] = lua.LTrue }, "error or string"},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			addresses := L.NewUserData()
+			addresses.Value = []net.IP{net.ParseIP("127.0.0.1")}
+			values := [3]lua.LValue{addresses, lua.LNumber(60), lua.LNil}
+			tc.change(&values)
+			_, _, err := readLuaDNSResult(values[0], values[1], values[2])
+			if err == nil || !strings.Contains(err.Error(), tc.want) {
+				t.Fatalf("readLuaDNSResult error = %v, want %q", err, tc.want)
+			}
+		})
+	}
+
+	addresses := L.NewUserData()
+	addresses.Value = []net.IP(nil)
+	for _, empty := range []lua.LValue{addresses, lua.LNil} {
+		if _, _, err := readLuaDNSResult(empty, lua.LNumber(0), lua.LNil); !go_errors.Is(err, featureDNS.ErrEmptyResponse) {
+			t.Fatalf("empty result error = %v, want ErrEmptyResponse", err)
+		}
+	}
+	wantErr := go_errors.New("upstream failed")
+	errorValue := L.NewUserData()
+	errorValue.Value = wantErr
+	if _, _, err := readLuaDNSResult(lua.LNil, lua.LNil, errorValue); err != wantErr {
+		t.Fatalf("upstream error = %v, want original error %v", err, wantErr)
+	}
+}
+
+func TestCallLuaHookCancellation(t *testing.T) {
+	L := lua.NewState()
+	defer L.Close()
+	if err := L.DoString(`function HandleDNSQuery(domain, ipv4, ipv6, fake) while true do end end`); err != nil {
+		t.Fatal(err)
+	}
+	ctx, cancel := context.WithTimeout(context.Background(), 50*time.Millisecond)
+	defer cancel()
+	_, _, err := (&DNS{}).CallLuaHook(L, ctx, "example.com", featureDNS.IPOption{IPv4Enable: true})
+	if err == nil {
+		t.Fatal("CallLuaHook did not stop after context cancellation")
+	}
+	if L.Context() != nil {
+		t.Fatal("CallLuaHook left the canceled context on the Lua state")
+	}
+}
+
+func TestCallLuaHookNormalizesDomain(t *testing.T) {
+	L := lua.NewState()
+	defer L.Close()
+	addresses := L.NewUserData()
+	addresses.Value = []net.IP{net.ParseIP("127.0.0.1")}
+	L.SetGlobal("ips", addresses)
+	if err := L.DoString(`
+		function HandleDNSQuery(domain, ipv4, ipv6, fake)
+			assert(domain == "example.com")
+			assert(ipv4 and not ipv6 and not fake)
+			return ips, 60, nil
+		end
+	`); err != nil {
+		t.Fatal(err)
+	}
+	s := &DNS{}
+	if _, _, err := s.CallLuaHook(L, context.Background(), "ExAmPlE.CoM", featureDNS.IPOption{IPv4Enable: true}); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestCallLuaHookRestoresState(t *testing.T) {
+	for _, tc := range []struct {
+		name    string
+		body    string
+		wantErr bool
+	}{
+		{"success", `return ips, 60`, false},
+		{"error", `error("failed")`, true},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			L := lua.NewState()
+			defer L.Close()
+			addresses := L.NewUserData()
+			addresses.Value = []net.IP{net.ParseIP("127.0.0.1")}
+			L.SetGlobal("ips", addresses)
+			if err := L.DoString("function HandleDNSQuery() " + tc.body + " end"); err != nil {
+				t.Fatal(err)
+			}
+			previous, cancel := context.WithCancel(context.Background())
+			defer cancel()
+			L.SetContext(previous)
+			L.Push(lua.LTrue)
+			_, _, err := (&DNS{}).CallLuaHook(L, context.Background(), "example.com", featureDNS.IPOption{IPv4Enable: true})
+			if (err != nil) != tc.wantErr {
+				t.Fatalf("hook error = %v, want error %t", err, tc.wantErr)
+			}
+			if L.Context() != previous || L.GetTop() != 1 || L.Get(1) != lua.LTrue {
+				t.Fatal("hook did not restore the previous context and stack")
+			}
+		})
+	}
+}
+
+func TestLuaDNSServerQuery(t *testing.T) {
+	L := lua.NewState()
+	defer L.Close()
+	geodata.RegisterLua(L)
+	option := featureDNS.IPOption{IPv4Enable: true}
+	ips := []net.IP{net.ParseIP("127.0.0.1"), net.ParseIP("8.8.8.8")}
+	server := &DNS{clients: []*Client{{server: &benchmarkLuaNameServer{ips: ips}, ipOption: &option, timeoutMs: time.Second}}}
+	server.RegisterLua(L)
+	if err := L.DoString(`
+local server = require("xray.dns").Servers[1]
+local matcher = require("xray.geodata").BuildIPMatcher("127.0.0.0/8")
+function HandleDNSQuery(domain, ipv4, ipv6, fake)
+    local ips, ttl, err = server:Query(domain, ipv4, ipv6, fake)
+    assert(type(ips) == "userdata" and not err)
+    assert(matcher:AnyMatch(ips))
+    local matched = matcher:FilterIPs(ips)
+    return matched, ttl, err
+end
+`); err != nil {
+		t.Fatal(err)
+	}
+	got, ttl, err := server.CallLuaHook(L, context.Background(), "example.com", option)
+	if err != nil || ttl != 60 || len(got) != 1 || !got[0].Equal(ips[0]) {
+		t.Fatalf("server query = %v, TTL %d, %v", got, ttl, err)
+	}
+}
+
+type luaDNSClient struct {
+	featureDNS.Client
+	lookup func(string, featureDNS.IPOption) ([]net.IP, uint32, error)
+}
+
+func (c *luaDNSClient) LookupIP(domain string, option featureDNS.IPOption) ([]net.IP, uint32, error) {
+	return c.lookup(domain, option)
+}
+
+func TestLuaDNSClientQuery(t *testing.T) {
+	L := lua.NewState()
+	defer L.Close()
+	L.SetContext(context.Background())
+	defer L.RemoveContext()
+	geodata.RegisterLua(L)
+	want := []net.IP{{127, 0, 0, 1}}
+	client := &luaDNSClient{lookup: func(domain string, option featureDNS.IPOption) ([]net.IP, uint32, error) {
+		if domain != "MiXeD.Example." || !option.IPv4Enable || option.IPv6Enable || !option.FakeEnable {
+			t.Fatalf("dns.Query arguments = %q, %+v", domain, option)
+		}
+		return want, 42, nil
+	}}
+	RegisterLua(L, client)
+	if err := L.DoString(`
+local dns = require("xray.dns")
+local matcher = require("xray.geodata").BuildIPMatcher("127.0.0.1")
+assert(dns.Servers == nil)
+ips, ttl, err = dns.Query("MiXeD.Example.", true, false, true)
+assert(not err and ttl == 42 and matcher:AnyMatch(ips))
+`); err != nil {
+		t.Fatal(err)
+	}
+	got := L.GetGlobal("ips").(*lua.LUserData).Value.([]net.IP)
+	if &got[0] != &want[0] {
+		t.Fatal("dns.Query copied the IP slice")
+	}
+}
+
+func TestLuaDNSLocalClient(t *testing.T) {
+	L := lua.NewState()
+	defer L.Close()
+	L.SetContext(context.Background())
+	defer L.RemoveContext()
+	RegisterLua(L, localdns.New())
+	if err := L.DoString(`
+local dns = require("xray.dns")
+assert(dns.Servers[1].ID == "localhost")
+serverIPs, _, serverErr = dns.Servers[1]:Query("127.0.0.1", true, false, false)
+clientIPs, _, clientErr = dns.Query("127.0.0.1", true, false, false)
+assert(not serverErr and not clientErr)
+`); err != nil {
+		t.Fatal(err)
+	}
+	for _, name := range []string{"serverIPs", "clientIPs"} {
+		ips := L.GetGlobal(name).(*lua.LUserData).Value.([]net.IP)
+		if len(ips) != 1 || !ips[0].Equal(net.ParseIP("127.0.0.1")) {
+			t.Fatalf("%s = %v", name, ips)
+		}
+	}
+}
+
+type benchmarkLuaNameServer struct {
+	ips []net.IP
+}
+
+func (*benchmarkLuaNameServer) Name() string         { return "benchmark" }
+func (*benchmarkLuaNameServer) IsDisableCache() bool { return true }
+func (s *benchmarkLuaNameServer) QueryIP(context.Context, string, featureDNS.IPOption) ([]net.IP, uint32, error) {
+	return s.ips, 60, nil
+}
+
+// BenchmarkLuaDNSHookCall isolates a preloaded Lua hook and its server:Query bridge.
+// The direct case measures the same DNS client without Lua.
+func BenchmarkLuaDNSHookCall(b *testing.B) {
+	option := featureDNS.IPOption{IPv4Enable: true}
+	ip := net.ParseIP("127.0.0.1")
+	upstream := &benchmarkLuaNameServer{ips: []net.IP{ip}}
+	client := &Client{server: upstream, ipOption: &option, timeoutMs: time.Second}
+	server := &DNS{clients: []*Client{client}}
+	L := lua.NewState()
+	defer L.Close()
+	server.RegisterLua(L)
+	if err := L.DoString(`
+local server = require("xray.dns").Servers[1]
+function HandleDNSQuery(domain, ipv4, ipv6, fake)
+    return server:Query(domain, ipv4, ipv6, fake)
+end
+`); err != nil {
+		b.Fatal(err)
+	}
+
+	ctx := context.Background()
+	for _, bench := range []struct {
+		name  string
+		query func() ([]net.IP, uint32, error)
+	}{
+		{"direct", func() ([]net.IP, uint32, error) { return client.QueryIP(ctx, "example.com", option) }},
+		{"lua_hook", func() ([]net.IP, uint32, error) { return server.CallLuaHook(L, ctx, "example.com", option) }},
+	} {
+		b.Run(bench.name, func(b *testing.B) {
+			b.ReportAllocs()
+			b.ResetTimer()
+			var ips []net.IP
+			var ttl uint32
+			var err error
+			for i := 0; i < b.N; i++ {
+				ips, ttl, err = bench.query()
+				if err != nil {
+					b.Fatal(err)
+				}
+			}
+			b.StopTimer()
+			if ttl != 60 || len(ips) != 1 || !ips[0].Equal(ip) {
+				b.Fatalf("query() = %v, TTL %d; want %v, TTL 60", ips, ttl, ip)
+			}
+		})
+	}
+}

app/dns/nameserver.go

@@ -29,6 +29,7 @@ type Server interface {
 
 // Client is the interface for DNS client.
 type Client struct {
+	id            string
 	server        Server
 	skipFallback  bool
 	expectedIPs   geodata.IPMatcher
@@ -97,7 +98,7 @@ func NewClient(
 	ipOption dns.IPOption,
 	updateRules func(bool),
 ) (*Client, error) {
-	client := &Client{}
+	client := &Client{id: ns.Id}
 	err := core.RequireFeatures(ctx, func(dispatcher routing.Dispatcher) error {
 		// Create a new server for each client for now
 		server, err := NewServer(ctx, ns.Address.AsDestination(), dispatcher, disableCache, serveStale, serveExpiredTTL, clientIP)

app/dns/nameserver_local.go

@@ -49,5 +49,5 @@ func NewLocalNameServer() *LocalNameServer {
 
 // NewLocalDNSClient creates localdns client object for directly lookup in system DNS.
 func NewLocalDNSClient(ipOption dns.IPOption) *Client {
-	return &Client{server: NewLocalNameServer(), ipOption: &ipOption}
+	return &Client{id: "localhost", server: NewLocalNameServer(), ipOption: &ipOption}
 }

app/dns/script.go

@@ -0,0 +1,73 @@
+package dns
+
+import (
+	"context"
+	"time"
+
+	"github.com/xtls/xray-core/common/errors"
+	"github.com/xtls/xray-core/common/geodata"
+	"github.com/xtls/xray-core/common/log"
+	luamgr "github.com/xtls/xray-core/common/lua"
+	"github.com/xtls/xray-core/common/net"
+	"github.com/xtls/xray-core/features/dns"
+	lua "github.com/yuin/gopher-lua"
+)
+
+const scriptExecutionTimeout = 10 * time.Second
+
+type scriptEngine struct {
+	dns  *DNS
+	pool *luamgr.Pool
+}
+
+func newScriptEngine(path string, server *DNS) (*scriptEngine, error) {
+	program, err := luamgr.CompileFile(path)
+	if err != nil {
+		return nil, err
+	}
+	e := &scriptEngine{dns: server}
+	e.pool, err = luamgr.NewPool(server.ctx, func(poolCtx context.Context) (*lua.LState, error) {
+		initCtx, cancel := context.WithTimeout(poolCtx, scriptExecutionTimeout)
+		defer cancel()
+		L, err := program.NewState(initCtx, func(L *lua.LState) {
+			geodata.RegisterLua(L)
+			log.RegisterLua(L)
+			server.RegisterLua(L)
+		})
+		if err != nil {
+			return nil, err
+		}
+		if L.GetGlobal("HandleDNSQuery").Type() != lua.LTFunction {
+			L.Close()
+			return nil, errors.New("DNS script must define HandleDNSQuery(domain, ipv4, ipv6, fake)")
+		}
+		return L, nil
+	})
+	if err != nil {
+		return nil, err
+	}
+	errors.LogInfo(server.ctx, "DNS script initialized from ", path)
+	return e, nil
+}
+
+func (e *scriptEngine) close() {
+	e.pool.Close()
+}
+
+func (e *scriptEngine) query(domain string, option dns.IPOption) ([]net.IP, uint32, error) {
+	L, err := e.pool.Acquire()
+	if err != nil {
+		return nil, 0, err
+	}
+	reusable := false
+	defer func() {
+		e.pool.Release(L, reusable)
+	}()
+	queryCtx, cancel := context.WithTimeout(e.pool.Context(), scriptExecutionTimeout)
+	defer cancel()
+	ips, ttl, err := e.dns.CallLuaHook(L, queryCtx, domain, option)
+	if err == nil {
+		reusable = true
+	}
+	return ips, ttl, err
+}

app/dns/script_test.go

@@ -0,0 +1,197 @@
+package dns
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/xtls/xray-core/common/net"
+	featureDNS "github.com/xtls/xray-core/features/dns"
+)
+
+type geoIPScriptNameServer struct {
+	name    string
+	answers map[string]net.IP
+	ttl     uint32
+	calls   int
+}
+
+func (s *geoIPScriptNameServer) Name() string         { return s.name }
+func (s *geoIPScriptNameServer) IsDisableCache() bool { return true }
+
+func (s *geoIPScriptNameServer) QueryIP(ctx context.Context, domain string, _ featureDNS.IPOption) ([]net.IP, uint32, error) {
+	if err := ctx.Err(); err != nil {
+		return nil, 0, err
+	}
+	s.calls++
+	ip, ok := s.answers[domain]
+	if !ok {
+		return nil, 0, featureDNS.ErrEmptyResponse
+	}
+	return []net.IP{ip}, s.ttl, nil
+}
+
+func TestDNSScriptGeoIPFallback(t *testing.T) {
+	t.Setenv("xray.location.asset", filepath.Join("..", "..", "resources"))
+	script := `
+local servers = require("xray.dns").Servers
+local us_ips = require("xray.geodata").BuildIPMatcher("geoip:us")
+
+local by_id = {}
+for _, server in ipairs(servers) do
+    by_id[server.ID] = server
+end
+assert(by_id.primary and by_id.fallback, "primary and fallback DNS servers are required")
+
+function HandleDNSQuery(domain, ipv4, ipv6, fake)
+    local ips, ttl, err = by_id.primary:Query(domain, ipv4, ipv6, fake)
+    if not err and us_ips:AnyMatch(ips) then
+        return ips, ttl, nil
+    end
+    return by_id.fallback:Query(domain, ipv4, ipv6, fake)
+end
+`
+	scriptPath := filepath.Join(t.TempDir(), "geoip_fallback.lua")
+	if err := os.WriteFile(scriptPath, []byte(script), 0o600); err != nil {
+		t.Fatal(err)
+	}
+
+	primary := &geoIPScriptNameServer{
+		name: "primary",
+		answers: map[string]net.IP{
+			"us.example":    net.ParseIP("2001:4860:4860::8888"),
+			"other.example": net.ParseIP("127.0.0.1"),
+		},
+		ttl: 30,
+	}
+	fallback := &geoIPScriptNameServer{
+		name:    "fallback",
+		answers: map[string]net.IP{"other.example": net.ParseIP("9.9.9.9")},
+		ttl:     60,
+	}
+	option := featureDNS.IPOption{IPv4Enable: true, IPv6Enable: true}
+	hosts, err := NewStaticHosts(nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	server := &DNS{
+		ctx:        context.Background(),
+		hosts:      hosts,
+		ipOption:   &option,
+		scriptPath: scriptPath,
+		clients: []*Client{
+			{id: "primary", server: primary, ipOption: &option, timeoutMs: 2 * time.Second},
+			{id: "fallback", server: fallback, ipOption: &option, timeoutMs: 2 * time.Second},
+		},
+	}
+	if err := server.Start(); err != nil {
+		t.Fatal(err)
+	}
+	defer server.Close()
+
+	for _, tc := range []struct {
+		domain string
+		ip     net.IP
+		ttl    uint32
+	}{
+		{"Us.Example.", net.ParseIP("2001:4860:4860::8888"), 30},
+		{"other.example", net.ParseIP("9.9.9.9"), 60},
+	} {
+		ips, ttl, err := server.LookupIP(tc.domain, option)
+		if err != nil {
+			t.Fatalf("LookupIP(%q): %v", tc.domain, err)
+		}
+		if ttl != tc.ttl || len(ips) != 1 || !ips[0].Equal(tc.ip) {
+			t.Fatalf("LookupIP(%q) = %v, TTL %d; want %v, TTL %d", tc.domain, ips, ttl, tc.ip, tc.ttl)
+		}
+	}
+	if primary.calls != 2 || fallback.calls != 1 {
+		t.Fatalf("upstream calls: primary %d, fallback %d; want 2 and 1", primary.calls, fallback.calls)
+	}
+}
+
+func TestDNSScriptRejectsInvalidStartup(t *testing.T) {
+	for _, tc := range []struct {
+		name   string
+		script string
+	}{
+		{"syntax", "function HandleDNSQuery("},
+		{"missing hook", "value = 1"},
+		{"top-level error", `error("setup failed")`},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			path := filepath.Join(t.TempDir(), "script.lua")
+			if err := os.WriteFile(path, []byte(tc.script), 0o600); err != nil {
+				t.Fatal(err)
+			}
+			server := &DNS{ctx: context.Background(), scriptPath: path}
+			if err := server.Start(); err == nil {
+				t.Fatal("Start accepted an invalid DNS script")
+			}
+			if server.script != nil {
+				t.Fatal("Start retained a script engine after failure")
+			}
+		})
+	}
+}
+
+func TestDNSScriptHookErrorAndFakeDNSOption(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "script.lua")
+	script := `
+local server = require("xray.dns").Servers[1]
+local log = require("xray.log")
+log.Info("DNS script loaded")
+function HandleDNSQuery(domain, ipv4, ipv6, fake)
+    log.Debug("DNS query: ", domain)
+    if domain == "bad.example" then error("script failure") end
+    local ips, ttl, err = server:Query(domain, ipv4, ipv6, fake)
+    if err then log.Error("DNS failed: ", err) end
+    return ips, ttl, err
+end
+`
+	if err := os.WriteFile(path, []byte(script), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	option := featureDNS.IPOption{IPv4Enable: true}
+	hosts, err := NewStaticHosts(nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	upstream := &geoIPScriptNameServer{
+		name:    "FakeDNS",
+		answers: map[string]net.IP{"good.example": net.ParseIP("198.18.0.1")},
+		ttl:     30,
+	}
+	server := &DNS{
+		ctx:        context.Background(),
+		hosts:      hosts,
+		ipOption:   &option,
+		scriptPath: path,
+		clients:    []*Client{{id: "fake", server: upstream, ipOption: &option, timeoutMs: time.Second}},
+	}
+	if err := server.Start(); err != nil {
+		t.Fatal(err)
+	}
+	defer server.Close()
+
+	if _, _, err := server.LookupIP("bad.example", option); err == nil || !strings.Contains(err.Error(), "script failure") {
+		t.Fatalf("hook failure = %v, want script failure", err)
+	}
+	if _, _, err := server.LookupIP("good.example", option); err != featureDNS.ErrEmptyResponse {
+		t.Fatalf("FakeDNS without FakeEnable = %v, want ErrEmptyResponse", err)
+	}
+	if upstream.calls != 0 {
+		t.Fatalf("FakeDNS was queried without FakeEnable: %d calls", upstream.calls)
+	}
+	withFake := featureDNS.IPOption{IPv4Enable: true, FakeEnable: true}
+	ips, ttl, err := server.LookupIP("good.example", withFake)
+	if err != nil || ttl != 30 || len(ips) != 1 || !ips[0].Equal(net.ParseIP("198.18.0.1")) {
+		t.Fatalf("FakeDNS with FakeEnable = %v, TTL %d, %v", ips, ttl, err)
+	}
+	if upstream.calls != 1 {
+		t.Fatalf("FakeDNS query count = %d, want 1", upstream.calls)
+	}
+}

app/router/config.pb.go

@@ -587,8 +587,10 @@ type Config struct {
 	DomainStrategy Config_DomainStrategy  `protobuf:"varint,1,opt,name=domain_strategy,json=domainStrategy,proto3,enum=xray.app.router.Config_DomainStrategy" json:"domain_strategy,omitempty"`
 	Rule           []*RoutingRule         `protobuf:"bytes,2,rep,name=rule,proto3" json:"rule,omitempty"`
 	BalancingRule  []*BalancingRule       `protobuf:"bytes,3,rep,name=balancing_rule,json=balancingRule,proto3" json:"balancing_rule,omitempty"`
-	unknownFields  protoimpl.UnknownFields
-	sizeCache      protoimpl.SizeCache
+	// Absolute path to the Lua routing script.
+	Script        string `protobuf:"bytes,4,opt,name=script,proto3" json:"script,omitempty"`
+	unknownFields protoimpl.UnknownFields
+	sizeCache     protoimpl.SizeCache
 }
 
 func (x *Config) Reset() {
@@ -642,6 +644,13 @@ func (x *Config) GetBalancingRule() []*BalancingRule {
 	return nil
 }
 
+func (x *Config) GetScript() string {
+	if x != nil {
+		return x.Script
+	}
+	return ""
+}
+
 var File_app_router_config_proto protoreflect.FileDescriptor
 
 const file_app_router_config_proto_rawDesc = "" +
@@ -699,11 +708,12 @@ const file_app_router_config_proto_rawDesc = "" +
 	"\tbaselines\x18\x03 \x03(\x03R\tbaselines\x12\x1a\n" +
 	"\bexpected\x18\x04 \x01(\x05R\bexpected\x12\x16\n" +
 	"\x06maxRTT\x18\x05 \x01(\x03R\x06maxRTT\x12\x1c\n" +
-	"\ttolerance\x18\x06 \x01(\x02R\ttolerance\"\x96\x02\n" +
+	"\ttolerance\x18\x06 \x01(\x02R\ttolerance\"\xae\x02\n" +
 	"\x06Config\x12O\n" +
 	"\x0fdomain_strategy\x18\x01 \x01(\x0e2&.xray.app.router.Config.DomainStrategyR\x0edomainStrategy\x120\n" +
 	"\x04rule\x18\x02 \x03(\v2\x1c.xray.app.router.RoutingRuleR\x04rule\x12E\n" +
-	"\x0ebalancing_rule\x18\x03 \x03(\v2\x1e.xray.app.router.BalancingRuleR\rbalancingRule\"B\n" +
+	"\x0ebalancing_rule\x18\x03 \x03(\v2\x1e.xray.app.router.BalancingRuleR\rbalancingRule\x12\x16\n" +
+	"\x06script\x18\x04 \x01(\tR\x06script\"B\n" +
 	"\x0eDomainStrategy\x12\b\n" +
 	"\x04AsIs\x10\x00\x12\x10\n" +
 	"\fIpIfNonMatch\x10\x02\x12\x0e\n" +

app/router/config.proto

@@ -110,4 +110,6 @@ message Config {
   DomainStrategy domain_strategy = 1;
   repeated RoutingRule rule = 2;
   repeated BalancingRule balancing_rule = 3;
+  // Absolute path to the Lua routing script.
+  string script = 4;
 }

app/router/lua.go

@@ -0,0 +1,206 @@
+package router
+
+import (
+	"context"
+	"runtime"
+
+	"github.com/xtls/xray-core/common/errors"
+	"github.com/xtls/xray-core/common/net"
+	"github.com/xtls/xray-core/features/routing"
+	lua "github.com/yuin/gopher-lua"
+)
+
+const (
+	luaContextType    = "xray.router.Context"
+	luaAttributesType = "xray.router.Attributes"
+)
+
+// RegisterLua makes xray.router available to routing scripts.
+func (r *Router) RegisterLua(L *lua.LState) {
+	registerLuaContext(L)
+
+	L.PreloadModule("xray.router", func(L *lua.LState) int {
+		module := L.NewTable()
+
+		module.RawSetString("NetworkUnknown", lua.LNumber(net.Network_Unknown))
+		module.RawSetString("NetworkTCP", lua.LNumber(net.Network_TCP))
+		module.RawSetString("NetworkUDP", lua.LNumber(net.Network_UDP))
+		module.RawSetString("NetworkUNIX", lua.LNumber(net.Network_UNIX))
+		module.RawSetString("LocalOS", lua.LString(runtime.GOOS))
+
+		module.RawSetString("PickOutbound", L.NewFunction(func(L *lua.LState) int {
+			tag, ok := L.Get(2).(lua.LString)
+			if !ok {
+				L.ArgError(2, "balancer tag must be a string")
+				return 0
+			}
+			balancer, found := (*r.balancers.Load())[string(tag)]
+			if !found {
+				L.Push(lua.LNil)
+				pushLuaError(L, errors.New("balancer ", tag, " not found"))
+				return 2
+			}
+			outboundTag, err := balancer.PickOutbound()
+			L.Push(lua.LString(outboundTag))
+			pushLuaError(L, err)
+			return 2
+		}))
+
+		module.RawSetString("FindProcess", L.NewFunction(func(L *lua.LState) int {
+			pid, name, path, err := findProcess(checkLuaContext(L), net.FindProcess)
+			L.Push(lua.LNumber(pid))
+			L.Push(lua.LString(name))
+			L.Push(lua.LString(path))
+			pushLuaError(L, err)
+			return 4
+		}))
+
+		L.Push(module)
+		return 1
+	})
+}
+
+func registerLuaContext(L *lua.LState) {
+	attributes := L.NewTypeMetatable(luaAttributesType)
+	L.SetField(attributes, "__index", L.NewFunction(func(L *lua.LState) int {
+		values := L.CheckUserData(1).Value.(map[string]string)
+		key := L.CheckString(2)
+		if value, found := values[key]; found {
+			L.Push(lua.LString(value))
+		} else {
+			L.Push(lua.LNil)
+		}
+		return 1
+	}))
+	methods := L.NewTable()
+	L.SetFuncs(methods, map[string]lua.LGFunction{
+		"GetSourceIPs": func(L *lua.LState) int {
+			return pushLuaIPs(L, checkLuaContext(L).GetSourceIPs())
+		},
+		"GetTargetIPs": func(L *lua.LState) int {
+			return pushLuaIPs(L, checkLuaContext(L).GetTargetIPs())
+		},
+		"GetLocalIPs": func(L *lua.LState) int {
+			return pushLuaIPs(L, checkLuaContext(L).GetLocalIPs())
+		},
+		"GetAttributes": func(L *lua.LState) int {
+			values := L.NewUserData()
+			values.Value = checkLuaContext(L).GetAttributes()
+			L.SetMetatable(values, attributes)
+			L.Push(values)
+			return 1
+		},
+	})
+	L.SetField(L.NewTypeMetatable(luaContextType), "__index", methods)
+}
+
+func checkLuaContext(L *lua.LState) routing.Context {
+	ctx, ok := L.CheckUserData(1).Value.(routing.Context)
+	if !ok {
+		L.ArgError(1, "routing context expected")
+	}
+	return ctx
+}
+
+func pushLuaIPs(L *lua.LState, ips []net.IP) int {
+	addresses := L.NewUserData()
+	addresses.Value = ips
+	L.Push(addresses)
+	return 1
+}
+
+func pushLuaError(L *lua.LState, err error) {
+	if err == nil {
+		L.Push(lua.LNil)
+		return
+	}
+	value := L.NewUserData()
+	value.Value = err
+	L.Push(value)
+}
+
+// CallLuaHook invokes HandleRoute in the supplied state.
+func (r *Router) CallLuaHook(L *lua.LState, ctx context.Context, routeCtx routing.Context) (string, string, error) {
+	previous, top := L.Context(), L.GetTop()
+	L.SetContext(ctx)
+	defer func() {
+		L.SetTop(top)
+		if previous == nil {
+			L.RemoveContext()
+		} else {
+			L.SetContext(previous)
+		}
+	}()
+	fn := L.GetGlobal("HandleRoute")
+	if fn.Type() != lua.LTFunction {
+		return "", "", errors.New("routing script must define HandleRoute(...)")
+	}
+	value := L.NewUserData()
+	value.Value = routeCtx
+	L.SetMetatable(value, L.GetTypeMetatable(luaContextType))
+	if err := L.CallByParam(lua.P{Fn: fn, NRet: 3, Protect: true},
+		value, lua.LString(routeCtx.GetInboundTag()), lua.LNumber(routeCtx.GetSourcePort()),
+		lua.LNumber(routeCtx.GetTargetPort()), lua.LNumber(routeCtx.GetLocalPort()),
+		lua.LString(routeCtx.GetTargetDomain()), lua.LNumber(routeCtx.GetNetwork()),
+		lua.LString(routeCtx.GetProtocol()), lua.LString(routeCtx.GetUser()),
+		lua.LNumber(routeCtx.GetVlessRoute()), lua.LBool(routeCtx.GetSkipDNSResolve())); err != nil {
+		return "", "", err
+	}
+	return readLuaRouteResult(L.Get(-3), L.Get(-2), L.Get(-1))
+}
+
+func readLuaRouteResult(tagValue, ruleValue, errorValue lua.LValue) (string, string, error) {
+	if errorValue != lua.LNil {
+		if value, ok := errorValue.(*lua.LUserData); ok {
+			if err, ok := value.Value.(error); ok {
+				return "", "", err
+			}
+		}
+		if value, ok := errorValue.(lua.LString); ok {
+			return "", "", errors.New(string(value))
+		}
+		return "", "", errors.New("routing script error must be an error or string")
+	}
+	if tagValue == lua.LNil {
+		return "", "", nil
+	}
+	tag, ok := tagValue.(lua.LString)
+	if !ok {
+		return "", "", errors.New("routing script outboundTag must be a string or nil")
+	}
+	if tag == "" {
+		return "", "", nil
+	}
+	var ruleTag string
+	if ruleValue != lua.LNil {
+		value, ok := ruleValue.(lua.LString)
+		if !ok {
+			return "", "", errors.New("routing script ruleTag must be a string")
+		}
+		ruleTag = string(value)
+	}
+	return string(tag), ruleTag, nil
+}
+
+type processFinder func(string, string, uint16, string, uint16) (int, string, string, error)
+
+func findProcess(ctx routing.Context, finder processFinder) (int, string, string, error) {
+	sources := ctx.GetSourceIPs()
+	if len(sources) == 0 {
+		return 0, "", "", errors.New("process lookup requires a source IP")
+	}
+	var network string
+	switch ctx.GetNetwork() {
+	case net.Network_TCP:
+		network = "tcp"
+	case net.Network_UDP:
+		network = "udp"
+	default:
+		return 0, "", "", errors.New("process lookup requires TCP or UDP")
+	}
+	targetIP, targetPort := "", uint16(0)
+	if targets := ctx.GetTargetIPs(); len(targets) > 0 {
+		targetIP, targetPort = targets[0].String(), uint16(ctx.GetTargetPort())
+	}
+	return finder(network, sources[0].String(), uint16(ctx.GetSourcePort()), targetIP, targetPort)
+}

app/router/lua_test.go

@@ -0,0 +1,292 @@
+package router
+
+import (
+	"context"
+	go_errors "errors"
+	"runtime"
+	"strings"
+	"testing"
+
+	"github.com/xtls/xray-core/common/geodata"
+	"github.com/xtls/xray-core/common/net"
+	"github.com/xtls/xray-core/common/protocol"
+	"github.com/xtls/xray-core/common/session"
+	"github.com/xtls/xray-core/features/routing"
+	routing_session "github.com/xtls/xray-core/features/routing/session"
+	lua "github.com/yuin/gopher-lua"
+)
+
+type luaRouteTestContext struct {
+	*routing_session.Context
+	sourceIPs, targetIPs, localIPs []net.IP
+}
+
+func (c *luaRouteTestContext) GetSourceIPs() []net.IP { return c.sourceIPs }
+func (c *luaRouteTestContext) GetTargetIPs() []net.IP { return c.targetIPs }
+func (c *luaRouteTestContext) GetLocalIPs() []net.IP  { return c.localIPs }
+
+func newLuaRouteTestContext() *luaRouteTestContext {
+	return &luaRouteTestContext{
+		Context: &routing_session.Context{
+			Inbound: &session.Inbound{
+				Tag: "in", VlessRoute: 4321,
+				Source: net.TCPDestination(net.LocalHostIP, 1234),
+				Local:  net.TCPDestination(net.LocalHostIP, 5678),
+				User:   &protocol.MemoryUser{Email: "user@example.com"},
+			},
+			Outbound: &session.Outbound{
+				Target:      net.TCPDestination(net.LocalHostIP, 443),
+				RouteTarget: net.TCPDestination(net.DomainAddress("MiXeD.Example."), 443),
+			},
+			Content: &session.Content{
+				Protocol: "tls", Attributes: map[string]string{"key": "value"}, SkipDNSResolve: true,
+			},
+		},
+		sourceIPs: []net.IP{{127, 0, 0, 2}},
+		targetIPs: []net.IP{{127, 0, 0, 3}},
+		localIPs:  []net.IP{{127, 0, 0, 1}},
+	}
+}
+
+func newLuaRouterState(t *testing.T, script string) (*Router, *lua.LState) {
+	t.Helper()
+	r := new(Router)
+	if err := r.Init(context.Background(), &Config{}, nil, nil, nil); err != nil {
+		t.Fatal(err)
+	}
+	L := lua.NewState()
+	t.Cleanup(L.Close)
+	r.RegisterLua(L)
+	geodata.RegisterLua(L)
+	if err := L.DoString(script); err != nil {
+		t.Fatal(err)
+	}
+	return r, L
+}
+
+func TestLuaRouteBinding(t *testing.T) {
+	r, L := newLuaRouterState(t, `
+local router = require("xray.router")
+local matcher = require("xray.geodata").BuildIPMatcher("127.0.0.0/8")
+assert(router.NetworkUnknown == 0 and router.NetworkTCP == 2)
+assert(router.NetworkUDP == 3 and router.NetworkUNIX == 4)
+assert(router.BuildIPMatcher == nil and router.BuildDomainMatcher == nil)
+function HandleRoute(ctx, inboundTag, sourcePort, targetPort, localPort,
+    targetDomain, network, protocol, user, vlessRoute, skipDNSResolve, ...)
+    assert(select("#", ...) == 0)
+    assert(inboundTag == "in" and sourcePort == 1234 and targetPort == 443 and localPort == 5678)
+    assert(targetDomain == "MiXeD.Example." and network == router.NetworkTCP)
+    assert(protocol == "tls" and user == "user@example.com" and vlessRoute == 4321 and skipDNSResolve)
+    assert(ctx.GetNetwork == nil and ctx.Context == nil)
+    savedContext = ctx
+    sourceIPs, targetIPs, localIPs = ctx:GetSourceIPs(), ctx:GetTargetIPs(), ctx:GetLocalIPs()
+    attributes = ctx:GetAttributes()
+    assert(matcher:AnyMatch(sourceIPs) and matcher:AnyMatch(targetIPs) and matcher:AnyMatch(localIPs))
+    assert(attributes.key == "value" and attributes.missing == nil)
+    assert(not pcall(function() attributes.key = "changed" end))
+    return "out", "rule"
+end`)
+
+	ctx := newLuaRouteTestContext()
+	tag, rule, err := r.CallLuaHook(L, context.Background(), ctx)
+	if err != nil || tag != "out" || rule != "rule" {
+		t.Fatalf("hook = %q, %q, %v", tag, rule, err)
+	}
+	if L.GetGlobal("savedContext").(*lua.LUserData).Value != ctx {
+		t.Fatal("routing context was copied")
+	}
+	for _, tc := range []struct {
+		name string
+		want []net.IP
+	}{
+		{"sourceIPs", ctx.sourceIPs},
+		{"targetIPs", ctx.targetIPs},
+		{"localIPs", ctx.localIPs},
+	} {
+		got := L.GetGlobal(tc.name).(*lua.LUserData).Value.([]net.IP)
+		if &got[0] != &tc.want[0] {
+			t.Fatalf("%s storage was copied", tc.name)
+		}
+	}
+	ctx.Content.Attributes["key"] = "updated"
+	L.SetGlobal("expectedOS", lua.LString(runtime.GOOS))
+	if err := L.DoString(`
+assert(attributes.key == "updated")
+assert(require("xray.router").LocalOS == expectedOS)`); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestLuaRouteResult(t *testing.T) {
+	nativeErr := go_errors.New("native failure")
+	for _, tc := range []struct {
+		name, body, tag, rule, wantErr string
+		native                         bool
+	}{
+		{name: "route", body: `return "out", "rule"`, tag: "out", rule: "rule"},
+		{name: "no match", body: `return nil`},
+		{name: "empty tag", body: `return ""`},
+		{name: "invalid tag", body: `return 1`, wantErr: "outboundTag"},
+		{name: "invalid rule", body: `return "out", false`, wantErr: "ruleTag"},
+		{name: "string error", body: `return nil, nil, "script failure"`, wantErr: "script failure"},
+		{name: "native error", body: `return nil, nil, nativeError`, native: true},
+		{name: "runtime error", body: `error("runtime failure")`, wantErr: "runtime failure"},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			r, L := newLuaRouterState(t, "function HandleRoute() "+tc.body+" end")
+			value := L.NewUserData()
+			value.Value = nativeErr
+			L.SetGlobal("nativeError", value)
+			previous := context.WithValue(context.Background(), struct{}{}, true)
+			L.SetContext(previous)
+			L.Push(lua.LTrue)
+
+			tag, rule, err := r.CallLuaHook(L, context.Background(), &routing_session.Context{})
+			if tag != tc.tag || rule != tc.rule {
+				t.Fatalf("result = %q, %q, %v", tag, rule, err)
+			}
+			switch {
+			case tc.native:
+				if err != nativeErr {
+					t.Fatalf("error = %v, want original error", err)
+				}
+			case tc.wantErr != "":
+				if err == nil || !strings.Contains(err.Error(), tc.wantErr) {
+					t.Fatalf("error = %v, want %q", err, tc.wantErr)
+				}
+			case err != nil:
+				t.Fatal(err)
+			}
+			if L.Context() != previous || L.GetTop() != 1 || L.Get(1) != lua.LTrue {
+				t.Fatal("hook did not restore the previous context and stack")
+			}
+		})
+	}
+}
+
+func TestLuaRouteCancellation(t *testing.T) {
+	r, L := newLuaRouterState(t, `function HandleRoute() while true do end end`)
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+	if _, _, err := r.CallLuaHook(L, ctx, &routing_session.Context{}); err == nil {
+		t.Fatal("CallLuaHook did not stop after context cancellation")
+	}
+	if L.Context() != nil || L.GetTop() != 0 {
+		t.Fatal("CallLuaHook did not restore the Lua state")
+	}
+}
+
+func TestFindProcess(t *testing.T) {
+	for _, tc := range []struct {
+		name, network, target string
+		targetPort            uint16
+		modify                func(*luaRouteTestContext)
+		wantErr               bool
+	}{
+		{name: "TCP", network: "tcp", target: "127.0.0.3", targetPort: 443},
+		{name: "UDP", network: "udp", target: "127.0.0.3", targetPort: 443, modify: func(c *luaRouteTestContext) {
+			c.Outbound.Target.Network = net.Network_UDP
+		}},
+		{name: "domain target", network: "tcp", modify: func(c *luaRouteTestContext) { c.targetIPs = nil }},
+		{name: "missing source", modify: func(c *luaRouteTestContext) { c.sourceIPs = nil }, wantErr: true},
+		{name: "unsupported network", modify: func(c *luaRouteTestContext) {
+			c.Outbound.Target.Network = net.Network_UNIX
+		}, wantErr: true},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			ctx := newLuaRouteTestContext()
+			if tc.modify != nil {
+				tc.modify(ctx)
+			}
+			called := false
+			pid, name, path, err := findProcess(ctx, func(network, source string, sourcePort uint16, target string, targetPort uint16) (int, string, string, error) {
+				called = true
+				if network != tc.network || source != "127.0.0.2" || sourcePort != 1234 || target != tc.target || targetPort != tc.targetPort {
+					t.Fatalf("endpoints = %s %s:%d -> %s:%d", network, source, sourcePort, target, targetPort)
+				}
+				return 42, "process", "/path/process", nil
+			})
+			if tc.wantErr {
+				if err == nil || called {
+					t.Fatalf("findProcess = %d, %q, %q, %v", pid, name, path, err)
+				}
+				return
+			}
+			if err != nil || !called || pid != 42 || name != "process" || path != "/path/process" {
+				t.Fatalf("findProcess = %d, %q, %q, %v", pid, name, path, err)
+			}
+		})
+	}
+}
+
+// BenchmarkLuaRouteHookCall isolates a preloaded Lua hook and its routing context bridge.
+// The direct case runs an equivalent native routing rule.
+func BenchmarkLuaRouteHookCall(b *testing.B) {
+	r := new(Router)
+	if err := r.Init(context.Background(), &Config{Rule: []*RoutingRule{{
+		TargetTag:  &RoutingRule_Tag{Tag: "out"},
+		RuleTag:    "rule",
+		InboundTag: []string{"in"},
+		Networks:   []net.Network{net.Network_TCP},
+		Ip: []*geodata.IPRule{{
+			Value: &geodata.IPRule_Custom{Custom: &geodata.CIDRRule{
+				Cidr: &geodata.CIDR{Ip: []byte{127, 0, 0, 0}, Prefix: 8},
+			}},
+		}},
+	}}}, nil, nil, nil); err != nil {
+		b.Fatal(err)
+	}
+	L := lua.NewState()
+	defer L.Close()
+	r.RegisterLua(L)
+	geodata.RegisterLua(L)
+	if err := L.DoString(`
+local router = require("xray.router")
+local matcher = require("xray.geodata").BuildIPMatcher("127.0.0.0/8")
+function HandleRoute(ctx, inboundTag, sourcePort, targetPort, localPort,
+    targetDomain, network, protocol, user, vlessRoute, skipDNSResolve)
+    if inboundTag == "in" and network == router.NetworkTCP and matcher:AnyMatch(ctx:GetTargetIPs()) then
+        return "out", "rule"
+    end
+end
+`); err != nil {
+		b.Fatal(err)
+	}
+
+	ctx := context.Background()
+	routeCtx := newLuaRouteTestContext()
+	for _, benchmark := range []struct {
+		name  string
+		route func() (string, string, error)
+	}{
+		{"direct", func() (string, string, error) {
+			route, err := r.PickRoute(routeCtx)
+			if err != nil {
+				return "", "", err
+			}
+			return route.GetOutboundTag(), route.GetRuleTag(), nil
+		}},
+		{"lua_hook", func() (string, string, error) {
+			return r.CallLuaHook(L, ctx, routeCtx)
+		}},
+	} {
+		b.Run(benchmark.name, func(b *testing.B) {
+			b.ReportAllocs()
+			b.ResetTimer()
+			var tag, rule string
+			var err error
+			for i := 0; i < b.N; i++ {
+				tag, rule, err = benchmark.route()
+				if err != nil {
+					b.Fatal(err)
+				}
+			}
+			b.StopTimer()
+			if tag != "out" || rule != "rule" {
+				b.Fatalf("route() = %q, %q; want out, rule", tag, rule)
+			}
+		})
+	}
+}
+
+var _ routing.Context = (*luaRouteTestContext)(nil)

app/router/router.go

@@ -20,6 +20,8 @@ import (
 type Router struct {
 	domainStrategy Config_DomainStrategy
 	rules          atomic.Pointer[[]*Rule]
+	scriptPath     string
+	script         *scriptEngine
 	balancers      atomic.Pointer[map[string]*Balancer]
 	dns            dns.Client
 
@@ -40,6 +42,7 @@ type Route struct {
 // Init initializes the Router.
 func (r *Router) Init(ctx context.Context, config *Config, d dns.Client, ohm outbound.Manager, dispatcher routing.Dispatcher) error {
 	r.domainStrategy = config.DomainStrategy
+	r.scriptPath = config.Script
 	r.dns = d
 	r.ctx = ctx
 	r.ohm = ohm
@@ -52,6 +55,10 @@ func (r *Router) Init(ctx context.Context, config *Config, d dns.Client, ohm out
 
 // PickRoute implements routing.Router.
 func (r *Router) PickRoute(ctx routing.Context) (routing.Route, error) {
+	if r.script != nil {
+		return r.script.pickRoute(ctx)
+	}
+
 	originalCtx := ctx
 	rule, ctx, err := r.pickRouteInternal(ctx)
 	if err != nil {
@@ -221,6 +228,13 @@ func (r *Router) pickRouteInternal(ctx routing.Context) (*Rule, routing.Context,
 
 // Start implements common.Runnable.
 func (r *Router) Start() error {
+	if r.scriptPath != "" {
+		engine, err := newScriptEngine(r.scriptPath, r)
+		if err != nil {
+			return errors.New("failed to initialize routing script").Base(err)
+		}
+		r.script = engine
+	}
 	return nil
 }
 
@@ -235,6 +249,9 @@ func closeWebhooks(rules []*Rule) {
 
 // Close implements common.Closable.
 func (r *Router) Close() error {
+	if r.script != nil {
+		r.script.close()
+	}
 	r.mu.Lock()
 	defer r.mu.Unlock()
 	closeWebhooks(*r.rules.Load())

app/router/script.go

@@ -0,0 +1,79 @@
+package router
+
+import (
+	"context"
+	"time"
+
+	"github.com/xtls/xray-core/app/dns"
+	"github.com/xtls/xray-core/common"
+	"github.com/xtls/xray-core/common/errors"
+	"github.com/xtls/xray-core/common/geodata"
+	"github.com/xtls/xray-core/common/log"
+	luamgr "github.com/xtls/xray-core/common/lua"
+	"github.com/xtls/xray-core/features/routing"
+	lua "github.com/yuin/gopher-lua"
+)
+
+const scriptExecutionTimeout = 10 * time.Second
+
+type scriptEngine struct {
+	router *Router
+	pool   *luamgr.Pool
+}
+
+func newScriptEngine(path string, router *Router) (*scriptEngine, error) {
+	program, err := luamgr.CompileFile(path)
+	if err != nil {
+		return nil, err
+	}
+	e := &scriptEngine{router: router}
+	e.pool, err = luamgr.NewPool(router.ctx, func(poolCtx context.Context) (*lua.LState, error) {
+		initCtx, cancel := context.WithTimeout(poolCtx, scriptExecutionTimeout)
+		defer cancel()
+		L, err := program.NewState(initCtx, func(L *lua.LState) {
+			geodata.RegisterLua(L)
+			log.RegisterLua(L)
+			router.RegisterLua(L)
+			dns.RegisterLua(L, router.dns)
+		})
+		if err != nil {
+			return nil, err
+		}
+		if L.GetGlobal("HandleRoute").Type() != lua.LTFunction {
+			L.Close()
+			return nil, errors.New("routing script must define HandleRoute(...)")
+		}
+		return L, nil
+	})
+	if err != nil {
+		return nil, err
+	}
+	errors.LogInfo(router.ctx, "routing script initialized from ", path)
+	return e, nil
+}
+
+func (e *scriptEngine) close() {
+	e.pool.Close()
+}
+
+func (e *scriptEngine) pickRoute(ctx routing.Context) (routing.Route, error) {
+	L, err := e.pool.Acquire()
+	if err != nil {
+		return nil, err
+	}
+	reusable := false
+	defer func() {
+		e.pool.Release(L, reusable)
+	}()
+	callCtx, cancel := context.WithTimeout(e.pool.Context(), scriptExecutionTimeout)
+	defer cancel()
+	tag, ruleTag, err := e.router.CallLuaHook(L, callCtx, ctx)
+	if err != nil {
+		return nil, err
+	}
+	reusable = true
+	if tag == "" {
+		return nil, common.ErrNoClue
+	}
+	return &Route{Context: ctx, outboundTag: tag, ruleTag: ruleTag}, nil
+}

app/router/script_test.go

@@ -0,0 +1,372 @@
+package router
+
+import (
+	"context"
+	stdnet "net"
+	"os"
+	"path/filepath"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	wireDNS "github.com/miekg/dns"
+	"github.com/xtls/xray-core/app/dispatcher"
+	appdns "github.com/xtls/xray-core/app/dns"
+	"github.com/xtls/xray-core/app/proxyman"
+	_ "github.com/xtls/xray-core/app/proxyman/outbound"
+	"github.com/xtls/xray-core/common"
+	"github.com/xtls/xray-core/common/net"
+	"github.com/xtls/xray-core/common/serial"
+	"github.com/xtls/xray-core/core"
+	featureDNS "github.com/xtls/xray-core/features/dns"
+	"github.com/xtls/xray-core/features/outbound"
+	"github.com/xtls/xray-core/features/routing"
+	routing_session "github.com/xtls/xray-core/features/routing/session"
+	"github.com/xtls/xray-core/proxy/blackhole"
+	"github.com/xtls/xray-core/proxy/freedom"
+)
+
+type luaRouteDNSClient struct {
+	featureDNS.Client
+	lookup func(string, featureDNS.IPOption) ([]net.IP, uint32, error)
+}
+
+func (d *luaRouteDNSClient) LookupIP(domain string, option featureDNS.IPOption) ([]net.IP, uint32, error) {
+	return d.lookup(domain, option)
+}
+
+type luaRouteOutboundManager struct{ outbound.Manager }
+
+func (*luaRouteOutboundManager) Select(selectors []string) []string { return selectors }
+
+func writeRouteScript(t *testing.T, script string) string {
+	t.Helper()
+	path := filepath.Join(t.TempDir(), "route.lua")
+	if err := os.WriteFile(path, []byte(script), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	return path
+}
+
+func startLuaRouter(t *testing.T, script string, d featureDNS.Client, config *Config) *Router {
+	t.Helper()
+	if config == nil {
+		config = &Config{}
+	}
+	config.Script = writeRouteScript(t, script)
+	r := new(Router)
+	if err := r.Init(context.Background(), config, d, &luaRouteOutboundManager{}, nil); err != nil {
+		t.Fatal(err)
+	}
+	if err := r.Start(); err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() {
+		if err := r.Close(); err != nil {
+			t.Error(err)
+		}
+	})
+	return r
+}
+
+func TestRouterScriptStartup(t *testing.T) {
+	for _, tc := range []struct{ name, script string }{
+		{"syntax error", "function HandleRoute("},
+		{"missing hook", "value = 1"},
+		{"initialization error", `error("setup failed")`},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			r := new(Router)
+			if err := r.Init(context.Background(), &Config{Script: writeRouteScript(t, tc.script)}, nil, nil, nil); err != nil {
+				t.Fatal(err)
+			}
+			defer r.Close()
+			if err := r.Start(); err == nil {
+				t.Fatal("Start accepted an invalid routing script")
+			}
+		})
+	}
+}
+
+func TestRouterScriptRouting(t *testing.T) {
+	var dnsCalls atomic.Int32
+	d := &luaRouteDNSClient{lookup: func(string, featureDNS.IPOption) ([]net.IP, uint32, error) {
+		dnsCalls.Add(1)
+		return []net.IP{{1, 2, 3, 4}}, 60, nil
+	}}
+	r := startLuaRouter(t, `
+function HandleRoute(ctx, inbound)
+    if inbound == "miss" then return nil end
+    return "lua-out", "lua-rule"
+end`, d, &Config{
+		DomainStrategy: Config_IpOnDemand,
+		Rule: []*RoutingRule{{
+			TargetTag: &RoutingRule_Tag{Tag: "json-out"},
+			Networks:  []net.Network{net.Network_TCP},
+		}},
+	})
+	ctx := newLuaRouteTestContext()
+	ctx.Content.SkipDNSResolve = false
+	route, err := r.PickRoute(ctx)
+	if err != nil || route.GetOutboundTag() != "lua-out" || route.GetRuleTag() != "lua-rule" || route.(*Route).Context != ctx {
+		t.Fatalf("route = %v, %v", route, err)
+	}
+	ctx.Inbound.Tag = "miss"
+	if route, err := r.PickRoute(ctx); route != nil || err != common.ErrNoClue {
+		t.Fatalf("miss = %v, %v", route, err)
+	}
+	if dnsCalls.Load() != 0 {
+		t.Fatal("script routing implicitly resolved DNS")
+	}
+}
+
+func TestRouterScriptModules(t *testing.T) {
+	ips := []net.IP{{127, 0, 0, 7}}
+	calls := 0
+	d := &luaRouteDNSClient{lookup: func(domain string, option featureDNS.IPOption) ([]net.IP, uint32, error) {
+		calls++
+		if domain != "MiXeD.Example." || !option.IPv4Enable || option.IPv6Enable || !option.FakeEnable {
+			t.Fatalf("dns.Query arguments = %q, %+v", domain, option)
+		}
+		return ips, 17, nil
+	}}
+	r := startLuaRouter(t, `
+local dns = require("xray.dns")
+local matcher = require("xray.geodata").BuildIPMatcher("127.0.0.0/8")
+assert(dns.Servers == nil and type(dns.Query) == "function")
+assert(type(require("xray.log").Info) == "function")
+function HandleRoute(ctx, inbound, sourcePort, targetPort, localPort, domain)
+    local ips, ttl, err = dns.Query(domain, true, false, true)
+    assert(not err and ttl == 17)
+    assert(matcher:AnyMatch(ips) and matcher:AnyMatch(ctx:GetTargetIPs()))
+    return "out"
+end`, d, nil)
+	if _, err := r.PickRoute(newLuaRouteTestContext()); err != nil {
+		t.Fatal(err)
+	}
+	if calls != 1 {
+		t.Fatalf("DNS calls = %d, want 1", calls)
+	}
+}
+
+func TestRouterScriptBalancerReload(t *testing.T) {
+	config := func(tag string) *Config {
+		return &Config{BalancingRule: []*BalancingRule{{
+			Tag: "balance", Strategy: "roundrobin", OutboundSelector: []string{tag},
+		}}}
+	}
+	r := startLuaRouter(t, `
+local router = require("xray.router")
+function HandleRoute()
+    local tag, err = router:PickOutbound("balance")
+    return tag, "balanced", err
+end`, nil, config("old"))
+	pick := func(want string) {
+		t.Helper()
+		route, err := r.PickRoute(&routing_session.Context{})
+		if err != nil || route.GetOutboundTag() != want || route.GetRuleTag() != "balanced" {
+			t.Fatalf("route = %v, %v, want %q", route, err, want)
+		}
+	}
+
+	pick("old")
+	if err := r.SetOverrideTarget("balance", "override"); err != nil {
+		t.Fatal(err)
+	}
+	pick("override")
+	if err := r.SetOverrideTarget("balance", ""); err != nil {
+		t.Fatal(err)
+	}
+	if err := r.ReloadRules(config("new"), false); err != nil {
+		t.Fatal(err)
+	}
+	pick("new")
+}
+
+func TestRouterScriptConcurrentBalancerReload(t *testing.T) {
+	config := func(tag string) *Config {
+		return &Config{BalancingRule: []*BalancingRule{{
+			Tag: "balance", Strategy: "roundrobin", OutboundSelector: []string{tag},
+		}}}
+	}
+	r := startLuaRouter(t, `
+local router = require("xray.router")
+function HandleRoute()
+    local tag, err = router:PickOutbound("balance")
+    return tag, nil, err
+end`, nil, config("a"))
+
+	var wg sync.WaitGroup
+	for range 4 {
+		wg.Go(func() {
+			for range 20 {
+				route, err := r.PickRoute(&routing_session.Context{})
+				if err != nil {
+					t.Errorf("PickRoute: %v", err)
+					return
+				}
+				if tag := route.GetOutboundTag(); tag != "a" && tag != "b" {
+					t.Errorf("unexpected tag %q", tag)
+				}
+			}
+		})
+	}
+	wg.Go(func() {
+		for range 20 {
+			for _, tag := range []string{"a", "b"} {
+				if err := r.ReloadRules(config(tag), false); err != nil {
+					t.Error(err)
+					return
+				}
+			}
+		}
+	})
+	wg.Wait()
+}
+
+func TestRouterScriptStateReuse(t *testing.T) {
+	r := startLuaRouter(t, `
+local calls = 0
+function HandleRoute(ctx, inbound)
+    calls = calls + 1
+    if inbound == "miss" then return nil end
+    if inbound == "fail" then error("failed") end
+    return tostring(calls)
+end`, nil, nil)
+	ctx := newLuaRouteTestContext()
+	pick := func(want string) {
+		t.Helper()
+		route, err := r.PickRoute(ctx)
+		if err != nil || route.GetOutboundTag() != want {
+			t.Fatalf("route = %v, %v, want %q", route, err, want)
+		}
+	}
+
+	pick("1")
+	ctx.Inbound.Tag = "miss"
+	if _, err := r.PickRoute(ctx); err != common.ErrNoClue {
+		t.Fatalf("miss = %v", err)
+	}
+	ctx.Inbound.Tag = "in"
+	pick("3")
+	ctx.Inbound.Tag = "fail"
+	if _, err := r.PickRoute(ctx); err == nil {
+		t.Fatal("script error was ignored")
+	}
+	ctx.Inbound.Tag = "in"
+	pick("1")
+}
+
+func TestRouterScriptDNSDispatcherReentry(t *testing.T) {
+	conn, err := stdnet.ListenPacket("udp4", "127.0.0.1:0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	port := conn.LocalAddr().(*stdnet.UDPAddr).Port
+	ready, stopped := make(chan struct{}), make(chan error, 1)
+	var queries atomic.Int32
+	server := &wireDNS.Server{
+		PacketConn: conn,
+		NotifyStartedFunc: func() {
+			close(ready)
+		},
+		Handler: wireDNS.HandlerFunc(func(w wireDNS.ResponseWriter, query *wireDNS.Msg) {
+			queries.Add(1)
+			response := new(wireDNS.Msg).SetReply(query)
+			for _, question := range query.Question {
+				if question.Name == "nested.example." && question.Qtype == wireDNS.TypeA {
+					response.Answer = append(response.Answer, &wireDNS.A{
+						Hdr: wireDNS.RR_Header{Name: question.Name, Rrtype: wireDNS.TypeA, Class: wireDNS.ClassINET, Ttl: 60},
+						A:   stdnet.IP{127, 0, 0, 7},
+					})
+				}
+			}
+			if err := w.WriteMsg(response); err != nil {
+				t.Error(err)
+			}
+		}),
+	}
+	go func() { stopped <- server.ActivateAndServe() }()
+	defer func() {
+		server.Shutdown()
+		select {
+		case err := <-stopped:
+			if err != nil {
+				t.Error(err)
+			}
+		case <-time.After(3 * time.Second):
+			t.Error("DNS server did not stop")
+		}
+	}()
+	select {
+	case <-ready:
+	case err := <-stopped:
+		t.Fatalf("DNS server startup: %v", err)
+	case <-time.After(3 * time.Second):
+		t.Fatal("DNS server did not start")
+	}
+
+	dnsScript := writeRouteScript(t, `
+local server = require("xray.dns").Servers[1]
+function HandleDNSQuery(domain, ipv4, ipv6, fake)
+    return server:Query(domain, ipv4, ipv6, fake)
+end`)
+	routerScript := writeRouteScript(t, `
+local router = require("xray.router")
+local dns = require("xray.dns")
+local matcher = require("xray.geodata").BuildIPMatcher("127.0.0.7")
+local active = false
+function HandleRoute(ctx, inbound, sourcePort, targetPort, localPort, domain, network,
+    protocol, user, vlessRoute, skipDNSResolve)
+    assert(not active, "borrowed Router VM reentered")
+    if inbound == "dns" then
+        assert(network == router.NetworkUDP and skipDNSResolve == false)
+        return "direct", "dns-route"
+    end
+    active = true
+    local ips, ttl, err = dns.Query("nested.example", true, false, false)
+    assert(not err and matcher:AnyMatch(ips) and active)
+    active = false
+    return "direct", "outer-route"
+end`)
+	instance, err := core.New(&core.Config{
+		App: []*serial.TypedMessage{
+			serial.ToTypedMessage(&appdns.Config{
+				Tag: "dns", Script: dnsScript, DisableCache: true,
+				NameServer: []*appdns.NameServer{{
+					Id: "upstream", TimeoutMs: 1000,
+					Address: &net.Endpoint{
+						Network: net.Network_UDP,
+						Address: &net.IPOrDomain{Address: &net.IPOrDomain_Ip{Ip: []byte{127, 0, 0, 1}}},
+						Port:    uint32(port),
+					},
+				}},
+			}),
+			serial.ToTypedMessage(&Config{Script: routerScript}),
+			serial.ToTypedMessage(&dispatcher.Config{}),
+			serial.ToTypedMessage(&proxyman.OutboundConfig{}),
+		},
+		Outbound: []*core.OutboundHandlerConfig{
+			{Tag: "default", ProxySettings: serial.ToTypedMessage(&blackhole.Config{})},
+			{Tag: "direct", ProxySettings: serial.ToTypedMessage(&freedom.Config{
+				FinalRules: []*freedom.FinalRuleConfig{{Action: freedom.RuleAction_Allow}},
+			})},
+		},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer instance.Close()
+	if err := instance.Start(); err != nil {
+		t.Fatal(err)
+	}
+	r := instance.GetFeature(routing.RouterType()).(*Router)
+	route, err := r.PickRoute(newLuaRouteTestContext())
+	if err != nil || route.GetOutboundTag() != "direct" || route.GetRuleTag() != "outer-route" {
+		t.Fatalf("nested DNS routing = %v, %v", route, err)
+	}
+	if queries.Load() == 0 {
+		t.Fatal("DNS query did not pass through the dispatcher")
+	}
+}

common/geodata/lua.go

@@ -0,0 +1,58 @@
+package geodata
+
+import (
+	lua "github.com/yuin/gopher-lua"
+	luar "layeh.com/gopher-luar"
+)
+
+// RegisterLua makes xray.geodata available to require in an LState.
+func RegisterLua(L *lua.LState) {
+	L.PreloadModule("xray.geodata", func(L *lua.LState) int {
+		module := L.NewTable()
+
+		module.RawSetString("BuildDomainMatcher", L.NewFunction(func(L *lua.LState) int {
+			parsed, err := ParseDomainRules(luaRules(L), Domain_Domain)
+			if err != nil {
+				L.RaiseError("%v", err)
+				return 0
+			}
+			matcher, err := DomainReg.BuildDomainMatcher(parsed)
+			if err != nil {
+				L.RaiseError("%v", err)
+				return 0
+			}
+			L.Push(luar.New(L, matcher))
+			return 1
+		}))
+
+		module.RawSetString("BuildIPMatcher", L.NewFunction(func(L *lua.LState) int {
+			parsed, err := ParseIPRules(luaRules(L))
+			if err != nil {
+				L.RaiseError("%v", err)
+				return 0
+			}
+			matcher, err := IPReg.BuildIPMatcher(parsed)
+			if err != nil {
+				L.RaiseError("%v", err)
+				return 0
+			}
+			L.Push(luar.New(L, matcher))
+			return 1
+		}))
+		L.Push(module)
+		return 1
+	})
+}
+
+func luaRules(L *lua.LState) []string {
+	rules := make([]string, L.GetTop())
+	for i := range rules {
+		value, ok := L.Get(i + 1).(lua.LString)
+		if !ok {
+			L.RaiseError("geodata rules must be strings")
+			return nil
+		}
+		rules[i] = string(value)
+	}
+	return rules
+}

common/geodata/lua_test.go

@@ -0,0 +1,66 @@
+package geodata
+
+import (
+	"testing"
+
+	"github.com/xtls/xray-core/common/net"
+	lua "github.com/yuin/gopher-lua"
+)
+
+func TestLuaIPMatcher(t *testing.T) {
+	L := lua.NewState()
+	defer L.Close()
+	RegisterLua(L)
+	ip := L.NewUserData()
+	ip.Value = net.ParseIP("127.0.0.1")
+	L.SetGlobal("ip", ip)
+	ips := L.NewUserData()
+	ips.Value = []net.IP{ip.Value.(net.IP), net.ParseIP("8.8.8.8")}
+	L.SetGlobal("ips", ips)
+	if err := L.DoString(`
+		local matcher = require("xray.geodata").BuildIPMatcher("127.0.0.0/8", "::1")
+		assert(matcher:Match(ip))
+		assert(matcher:AnyMatch(ips))
+		assert(not matcher:Matches(ips))
+		local matched, unmatched = matcher:FilterIPs(ips)
+		assert(type(matched) == "userdata" and type(unmatched) == "userdata")
+		assert(#matched == 1 and #unmatched == 1)
+	`); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestLuaDomainMatcher(t *testing.T) {
+	L := lua.NewState()
+	defer L.Close()
+	RegisterLua(L)
+	if err := L.DoString(`
+		local matcher = require("xray.geodata").BuildDomainMatcher("example.com", "full:other.com")
+		assert(matcher:MatchAny("example.com"))
+		assert(matcher:MatchAny("www.example.com"))
+		assert(matcher:MatchAny("other.com"))
+		assert(not matcher:MatchAny("www.other.com"))
+		assert(#(matcher:Match("www.example.com")) == 1)
+	`); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestLuaMatchersRejectInvalidRules(t *testing.T) {
+	for _, tc := range []struct {
+		name   string
+		script string
+	}{
+		{"IP rule", `require("xray.geodata").BuildIPMatcher("not-an-ip")`},
+		{"non-string domain rule", `require("xray.geodata").BuildDomainMatcher("example.com", true)`},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			L := lua.NewState()
+			defer L.Close()
+			RegisterLua(L)
+			if err := L.DoString(tc.script); err == nil {
+				t.Fatal("invalid geodata rule was accepted")
+			}
+		})
+	}
+}

common/log/lua.go

@@ -0,0 +1,50 @@
+package log
+
+import (
+	"path/filepath"
+	"strings"
+
+	lua "github.com/yuin/gopher-lua"
+)
+
+// RegisterLua makes xray.log available to require in an LState.
+func RegisterLua(L *lua.LState) {
+	L.PreloadModule("xray.log", func(L *lua.LState) int {
+		module := L.NewTable()
+		for name, severity := range map[string]Severity{
+			"Debug":   Severity_Debug,
+			"Info":    Severity_Info,
+			"Warning": Severity_Warning,
+			"Error":   Severity_Error,
+		} {
+			module.RawSetString(name, L.NewFunction(func(L *lua.LState) int {
+				var content strings.Builder
+				// Prefix with the calling script's filename.
+				if caller, ok := L.GetStack(1); ok {
+					if _, err := L.GetInfo("S", caller, lua.LNil); err == nil && caller.Source != "" {
+						content.WriteString(filepath.Base(strings.TrimPrefix(caller.Source, "@")))
+						content.WriteString(": ")
+					}
+				}
+				for i := 1; i <= L.GetTop(); i++ {
+					value := L.Get(i)
+					// Use Error() for Go errors in userdata.
+					if ud, ok := value.(*lua.LUserData); ok {
+						if err, ok := ud.Value.(error); ok {
+							content.WriteString(err.Error())
+							continue
+						}
+					}
+					content.WriteString(L.ToStringMeta(value).String())
+				}
+				Record(&GeneralMessage{
+					Severity: severity,
+					Content:  content.String(),
+				})
+				return 0
+			}))
+		}
+		L.Push(module)
+		return 1
+	})
+}

common/log/lua_test.go

@@ -0,0 +1,92 @@
+package log
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"testing"
+
+	lua "github.com/yuin/gopher-lua"
+)
+
+type luaLogHandler struct {
+	messages []Message
+}
+
+func (h *luaLogHandler) Handle(msg Message) {
+	h.messages = append(h.messages, msg)
+}
+
+func TestLuaLog(t *testing.T) {
+	logHandler.RLock()
+	previous := logHandler.Handler
+	logHandler.RUnlock()
+	t.Cleanup(func() { RegisterHandler(previous) })
+	handler := &luaLogHandler{}
+	RegisterHandler(handler)
+
+	L := lua.NewState()
+	defer L.Close()
+	RegisterLua(L)
+	nativeError := L.NewUserData()
+	nativeError.Value = fmt.Errorf("lookup failed: %w", errors.New("upstream timeout"))
+	L.SetGlobal("nativeError", nativeError)
+	path := filepath.Join(t.TempDir(), "logging.lua")
+	if err := os.WriteFile(path, []byte(`
+		local log = require("xray.log")
+		assert(log == require("xray.log"))
+		log.Debug("query: ", "example.com")
+		log.Info("count=", 42, ", enabled=", true, ", value=", nil)
+		log.Warning(setmetatable({}, {
+			__tostring = function() return "fallback" end
+		}))
+		assert(select("#", log.Error("failed")) == 0)
+		log.Error("DNS failed: ", nativeError)
+		log.Warning(nativeError)
+		local ok, err = pcall(function() error("Lua failure", 0) end)
+		assert(not ok)
+		log.Error(err)
+		function logHook()
+			log.Info("hook")
+		end
+	`), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	if err := L.DoFile(path); err != nil {
+		t.Fatal(err)
+	}
+	if err := L.DoString(`
+		logHook()
+		require("xray.log").Info("anonymous")
+	`); err != nil {
+		t.Fatal(err)
+	}
+
+	want := []struct {
+		severity Severity
+		message  string
+	}{
+		{Severity_Debug, "[Debug] logging.lua: query: example.com"},
+		{Severity_Info, "[Info] logging.lua: count=42, enabled=true, value=nil"},
+		{Severity_Warning, "[Warning] logging.lua: fallback"},
+		{Severity_Error, "[Error] logging.lua: failed"},
+		{Severity_Error, "[Error] logging.lua: DNS failed: lookup failed: upstream timeout"},
+		{Severity_Warning, "[Warning] logging.lua: lookup failed: upstream timeout"},
+		{Severity_Error, "[Error] logging.lua: Lua failure"},
+		{Severity_Info, "[Info] logging.lua: hook"},
+		{Severity_Info, "[Info] <string>: anonymous"},
+	}
+	if len(handler.messages) != len(want) {
+		t.Fatalf("logged %d messages, want %d", len(handler.messages), len(want))
+	}
+	for i, expected := range want {
+		msg, ok := handler.messages[i].(*GeneralMessage)
+		if !ok {
+			t.Fatalf("message %d has type %T, want *GeneralMessage", i, handler.messages[i])
+		}
+		if msg.Severity != expected.severity || msg.String() != expected.message {
+			t.Errorf("message %d = %q with severity %v, want %q with severity %v", i, msg.String(), msg.Severity, expected.message, expected.severity)
+		}
+	}
+}

common/lua/pool.go

@@ -0,0 +1,138 @@
+package lua
+
+import (
+	"context"
+	"errors"
+	"sync"
+
+	glua "github.com/yuin/gopher-lua"
+)
+
+const maxIdleStates = 16
+
+// LStateFactory must initialize a state fully and observe ctx while doing so.
+// The pool owns any non-nil state it returns, even when it also returns an error.
+type LStateFactory func(ctx context.Context) (*glua.LState, error)
+
+// Pool lends each state to one caller at a time. It grows on contention and
+// keeps up to maxIdleStates idle states until Close. Callers decide whether a
+// state is reusable.
+type Pool struct {
+	ctx    context.Context
+	cancel context.CancelFunc
+
+	factory LStateFactory
+	idle    []*glua.LState
+
+	mu     sync.Mutex
+	active sync.WaitGroup
+	closed bool
+}
+
+// NewPool initializes one state before returning, so top-level errors surface at startup.
+func NewPool(ctx context.Context, factory LStateFactory) (*Pool, error) {
+	poolCtx, cancel := context.WithCancel(ctx)
+
+	// Create one state now to catch factory errors at startup.
+	state, err := factory(poolCtx)
+	if err != nil {
+		cancel()
+		if state != nil {
+			state.Close()
+		}
+		return nil, err
+	}
+	if state == nil {
+		cancel()
+		return nil, errors.New("Lua state factory returned nil")
+	}
+	if err := poolCtx.Err(); err != nil {
+		state.Close()
+		cancel()
+		return nil, err
+	}
+
+	return &Pool{ctx: poolCtx, cancel: cancel, factory: factory, idle: []*glua.LState{state}}, nil
+}
+
+// Context is cancelled by Close. Query contexts should derive from it.
+func (p *Pool) Context() context.Context {
+	return p.ctx
+}
+
+// Acquire returns an initialized exclusive state, growing the pool if necessary.
+func (p *Pool) Acquire() (*glua.LState, error) {
+	p.mu.Lock()
+	if p.closed || p.ctx.Err() != nil {
+		p.mu.Unlock()
+		return nil, p.ctx.Err()
+	}
+
+	p.active.Add(1)
+
+	n := len(p.idle)
+	if n != 0 {
+		state := p.idle[n-1]
+		p.idle = p.idle[:n-1]
+		p.mu.Unlock()
+		return state, nil
+	}
+	p.mu.Unlock()
+
+	// TODO: Limit the total number of states. When the limit is reached, wait
+	// for a Release instead of creating another state; allow the wait to be
+	// cancelled by the caller or by Close.
+	state, err := p.factory(p.ctx)
+	if err == nil && state == nil {
+		err = errors.New("Lua state factory returned nil")
+	}
+	if err != nil {
+		if state != nil {
+			state.Close()
+		}
+		p.active.Done()
+		return nil, err
+	}
+	if err := p.ctx.Err(); err != nil {
+		state.Close()
+		p.active.Done()
+		return nil, err
+	}
+
+	return state, nil
+}
+
+// Release returns a healthy state to the pool and closes a failed or cancelled one.
+func (p *Pool) Release(state *glua.LState, reusable bool) {
+	if reusable {
+		p.mu.Lock()
+		if !p.closed && p.ctx.Err() == nil && len(p.idle) < maxIdleStates {
+			p.idle = append(p.idle, state)
+		} else {
+			reusable = false
+		}
+		p.mu.Unlock()
+	}
+
+	if !reusable {
+		state.Close()
+	}
+
+	p.active.Done()
+}
+
+// Close cancels active work, closes idle states, and waits for borrowed states.
+func (p *Pool) Close() {
+	p.mu.Lock()
+	if !p.closed {
+		p.closed = true
+		p.cancel()
+		for _, state := range p.idle {
+			state.Close()
+		}
+		p.idle = nil
+	}
+	p.mu.Unlock()
+
+	p.active.Wait()
+}

common/lua/pool_test.go

@@ -0,0 +1,197 @@
+package lua
+
+import (
+	"context"
+	"errors"
+	"testing"
+	"time"
+
+	glua "github.com/yuin/gopher-lua"
+)
+
+func TestPoolFactoryFailureClosesReturnedState(t *testing.T) {
+	failure := errors.New("factory failed")
+	state := glua.NewState()
+	_, err := NewPool(context.Background(), func(context.Context) (*glua.LState, error) {
+		return state, failure
+	})
+	if !errors.Is(err, failure) || !state.IsClosed() {
+		t.Fatalf("NewPool error = %v, state closed = %t", err, state.IsClosed())
+	}
+
+	var failedState *glua.LState
+	calls := 0
+	pool, err := NewPool(context.Background(), func(context.Context) (*glua.LState, error) {
+		calls++
+		if calls == 1 {
+			return glua.NewState(), nil
+		}
+		failedState = glua.NewState()
+		return failedState, failure
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer pool.Close()
+	borrowed, err := pool.Acquire()
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer pool.Release(borrowed, true)
+	_, err = pool.Acquire()
+	if !errors.Is(err, failure) || !failedState.IsClosed() {
+		t.Fatalf("Acquire error = %v, state closed = %t", err, failedState.IsClosed())
+	}
+}
+
+func TestPoolReusesStatesAndLimitsIdle(t *testing.T) {
+	created := 0
+	pool, err := NewPool(context.Background(), func(context.Context) (*glua.LState, error) {
+		created++
+		return glua.NewState(), nil
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer pool.Close()
+
+	states := make([]*glua.LState, maxIdleStates+3)
+	for i := range states {
+		states[i], err = pool.Acquire()
+		if err != nil {
+			t.Fatal(err)
+		}
+	}
+	for _, state := range states {
+		pool.Release(state, true)
+	}
+	for i, state := range states {
+		if got, want := state.IsClosed(), i >= maxIdleStates; got != want {
+			t.Fatalf("state %d closed = %t, want %t", i, got, want)
+		}
+	}
+	borrowed, err := pool.Acquire()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if created != len(states) {
+		t.Fatalf("Acquire created %d states, want %d", created, len(states))
+	}
+	pool.Release(borrowed, true)
+}
+
+func TestPoolCloseCancelsAndWaitsForBorrowedState(t *testing.T) {
+	pool, err := NewPool(context.Background(), func(context.Context) (*glua.LState, error) {
+		return glua.NewState(), nil
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	state, err := pool.Acquire()
+	if err != nil {
+		t.Fatal(err)
+	}
+	done := make(chan struct{})
+	go func() {
+		pool.Close()
+		close(done)
+	}()
+	select {
+	case <-pool.Context().Done():
+	case <-time.After(time.Second):
+		pool.Release(state, false)
+		t.Fatal("Close did not cancel the pool context")
+	}
+	select {
+	case <-done:
+		pool.Release(state, false)
+		t.Fatal("Close returned while a state was borrowed")
+	default:
+	}
+	pool.Release(state, true)
+	select {
+	case <-done:
+	case <-time.After(time.Second):
+		t.Fatal("Close did not finish after Release")
+	}
+	if !state.IsClosed() {
+		t.Fatal("borrowed state was not closed")
+	}
+	if _, err := pool.Acquire(); !errors.Is(err, context.Canceled) {
+		t.Fatalf("Acquire after Close = %v, want context.Canceled", err)
+	}
+	pool.Close()
+}
+
+func TestPoolCloseCancelsStateCreation(t *testing.T) {
+	started := make(chan struct{})
+	first := true
+	pool, err := NewPool(context.Background(), func(ctx context.Context) (*glua.LState, error) {
+		if first {
+			first = false
+			return glua.NewState(), nil
+		}
+		close(started)
+		<-ctx.Done()
+		return nil, ctx.Err()
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	borrowed, err := pool.Acquire()
+	if err != nil {
+		t.Fatal(err)
+	}
+	acquireDone := make(chan error, 1)
+	go func() {
+		_, err := pool.Acquire()
+		acquireDone <- err
+	}()
+	<-started
+	closeDone := make(chan struct{})
+	go func() {
+		pool.Close()
+		close(closeDone)
+	}()
+	select {
+	case err := <-acquireDone:
+		if !errors.Is(err, context.Canceled) {
+			t.Fatalf("Acquire during Close = %v, want context.Canceled", err)
+		}
+	case <-time.After(time.Second):
+		t.Fatal("state creation did not stop after Close")
+	}
+	select {
+	case <-closeDone:
+		pool.Release(borrowed, false)
+		t.Fatal("Close returned while the initial state was borrowed")
+	default:
+	}
+	pool.Release(borrowed, true)
+	select {
+	case <-closeDone:
+	case <-time.After(time.Second):
+		t.Fatal("Close did not finish after Release")
+	}
+}
+
+func BenchmarkPoolAcquireRelease(b *testing.B) {
+	pool, err := NewPool(context.Background(), func(context.Context) (*glua.LState, error) {
+		return glua.NewState(), nil
+	})
+	if err != nil {
+		b.Fatal(err)
+	}
+	defer pool.Close()
+
+	b.ReportAllocs()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		state, err := pool.Acquire()
+		if err != nil {
+			b.Fatal(err)
+		}
+		pool.Release(state, true)
+	}
+	b.StopTimer()
+}

common/lua/program.go

@@ -0,0 +1,56 @@
+// Package lua provides shared GopherLua programs and state management for Xray scripts.
+package lua
+
+import (
+	"bufio"
+	"context"
+	"os"
+
+	glua "github.com/yuin/gopher-lua"
+	"github.com/yuin/gopher-lua/parse"
+)
+
+// Program holds immutable bytecode that can be run by independent LStates.
+type Program struct {
+	proto *glua.FunctionProto
+}
+
+// CompileFile reads and compiles a Lua file once.
+func CompileFile(path string) (*Program, error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+	chunk, err := parse.Parse(bufio.NewReader(f), path)
+	if err != nil {
+		return nil, err
+	}
+	proto, err := glua.Compile(chunk, path)
+	if err != nil {
+		return nil, err
+	}
+	return &Program{proto: proto}, nil
+}
+
+// NewState creates a VM, makes modules available, and executes the file top level.
+// Module loaders run only when Lua calls require. Each state gets its own globals.
+// The caller owns the returned state.
+func (p *Program) NewState(ctx context.Context, register func(*glua.LState)) (*glua.LState, error) {
+	L := glua.NewState()
+	if register != nil {
+		register(L)
+	}
+	L.SetContext(ctx)
+	L.Push(L.NewFunctionFromProto(p.proto))
+	err := L.PCall(0, 0, nil)
+	L.RemoveContext()
+	if err == nil {
+		err = ctx.Err()
+	}
+	if err != nil {
+		L.Close()
+		return nil, err
+	}
+	return L, nil
+}

common/lua/program_test.go

@@ -0,0 +1,55 @@
+package lua
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"testing"
+
+	glua "github.com/yuin/gopher-lua"
+)
+
+func TestProgramStatesAreIndependent(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "state.lua")
+	if err := os.WriteFile(path, []byte("value = (value or 0) + 1"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	program, err := CompileFile(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	first, err := program.NewState(context.Background(), nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer first.Close()
+	first.SetGlobal("value", glua.LNumber(42))
+	second, err := program.NewState(context.Background(), nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer second.Close()
+	if got := second.GetGlobal("value"); got != glua.LNumber(1) {
+		t.Fatalf("second state value = %v, want 1", got)
+	}
+}
+
+func TestProgramInitializationObservesCancellation(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "loop.lua")
+	if err := os.WriteFile(path, []byte("while true do end"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	program, err := CompileFile(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+	state, err := program.NewState(ctx, nil)
+	if err == nil || state != nil {
+		if state != nil {
+			state.Close()
+		}
+		t.Fatalf("NewState with canceled context = %v, %v; want nil state and error", state, err)
+	}
+}

common/platform/platform.go

@@ -1,6 +1,8 @@
 package platform // import "github.com/xtls/xray-core/common/platform"
 
 import (
+	"errors"
+	"fmt"
 	"os"
 	"path/filepath"
 	"strconv"
@@ -90,3 +92,49 @@ func GetConfDirPath() string {
 	configPath := NewEnvFlag(ConfdirLocation).GetValue(func() string { return "" })
 	return configPath
 }
+
+// ResolveLuaFile finds a local Lua script and returns its absolute path.
+// Relative paths: XRAY_LOCATION_CONFDIR > XRAY_LOCATION_CONFIG > working dir > executable dir.
+func ResolveLuaFile(path string) (string, error) {
+	if path == "" {
+		return "", errors.New("Lua file path is empty")
+	}
+	paths := []string{path}
+	if !filepath.IsAbs(path) {
+		paths = nil
+		for _, dir := range []string{
+			GetConfDirPath(),
+			NewEnvFlag(ConfigLocation).GetValue(func() string { return "" }),
+			".",
+			getExecutableDir(),
+		} {
+			if dir != "" {
+				paths = append(paths, filepath.Join(dir, path))
+			}
+		}
+	}
+	return resolveFile(paths)
+}
+
+func resolveFile(paths []string) (string, error) {
+	var tried []string
+	for _, path := range paths {
+		path, err := filepath.Abs(path)
+		if err != nil {
+			return "", fmt.Errorf("failed to resolve file path: %w", err)
+		}
+		tried = append(tried, path)
+		info, err := os.Stat(path)
+		if errors.Is(err, os.ErrNotExist) {
+			continue
+		}
+		if err != nil {
+			return "", fmt.Errorf("failed to inspect file %q: %w", path, err)
+		}
+		if !info.Mode().IsRegular() {
+			return "", fmt.Errorf("file is not a regular file: %s", path)
+		}
+		return path, nil
+	}
+	return "", fmt.Errorf("file not found; tried %q: %w", tried, os.ErrNotExist)
+}

common/platform/platform_test.go

@@ -1,6 +1,7 @@
 package platform_test
 
 import (
+	"errors"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -64,3 +65,53 @@ func TestGetAssetLocation(t *testing.T) {
 		}
 	}
 }
+
+func TestResolveLuaFile(t *testing.T) {
+	workingDir := t.TempDir()
+	t.Chdir(workingDir)
+	executable, err := os.Executable()
+	common.Must(err)
+	file, err := os.CreateTemp(filepath.Dir(executable), "lua-*.lua")
+	common.Must(err)
+	common.Must(file.Close())
+	defer os.Remove(file.Name())
+
+	name := filepath.Base(file.Name())
+	paths := []string{
+		filepath.Join(t.TempDir(), name),
+		filepath.Join(t.TempDir(), name),
+		filepath.Join(workingDir, name),
+		file.Name(),
+	}
+	t.Setenv(ConfdirLocation, filepath.Dir(paths[0]))
+	t.Setenv(ConfigLocation, filepath.Dir(paths[1]))
+	for _, path := range paths[:3] {
+		common.Must(os.WriteFile(path, nil, 0o600))
+	}
+	if got, err := ResolveLuaFile(paths[2]); err != nil || got != paths[2] {
+		t.Fatalf("absolute path = %q, %v; want %q", got, err, paths[2])
+	}
+	for i, want := range paths {
+		if i == 2 {
+			t.Setenv(ConfdirLocation, "")
+			t.Setenv(ConfigLocation, "")
+		}
+		if got, err := ResolveLuaFile(name); err != nil || got != want {
+			t.Fatalf("resolved path = %q, %v; want %q", got, err, want)
+		}
+		common.Must(os.Remove(want))
+	}
+	if _, err := ResolveLuaFile(name); !errors.Is(err, os.ErrNotExist) {
+		t.Fatalf("missing file error = %v", err)
+	}
+
+	t.Setenv(ConfdirLocation, filepath.Dir(paths[0]))
+	t.Setenv(ConfigLocation, filepath.Dir(paths[1]))
+	common.Must(os.Mkdir(paths[0], 0o700))
+	common.Must(os.WriteFile(paths[1], nil, 0o600))
+	for _, path := range []string{"", name, filepath.Join(t.TempDir(), name)} {
+		if _, err := ResolveLuaFile(path); err == nil {
+			t.Fatalf("accepted invalid path %q", path)
+		}
+	}
+}

go.mod

@@ -23,6 +23,7 @@ require (
 	github.com/stretchr/testify v1.12.1
 	github.com/vishvananda/netlink v1.3.1
 	github.com/xtls/reality v0.0.0-20260908062103-8cdf7bf9c7f0
+	github.com/yuin/gopher-lua v1.1.2
 	go4.org/netipx v0.0.0-20231129151722-fdeea329fbba
 	golang.org/x/crypto v0.57.0
 	golang.org/x/exp v0.0.0-20240506185415-9bf2ced13842
@@ -31,11 +32,12 @@ require (
 	golang.org/x/sys v0.48.0
 	golang.zx2c4.com/wintun v0.0.0-20230126152724-0fa3db229ce2
 	golang.zx2c4.com/wireguard v0.0.0-20250521234502-f333402bd9cb
-	golang.zx2c4.com/wireguard/windows v1.0.1
-	google.golang.org/grpc v1.83.2
+	golang.zx2c4.com/wireguard/windows v1.1.1
+	google.golang.org/grpc v1.84.0
 	google.golang.org/protobuf v1.36.12
 	gvisor.dev/gvisor v0.0.0-20260122175437-89a5d21be8f0
 	h12.io/socks v1.0.3
+	layeh.com/gopher-luar v1.0.11
 	lukechampine.com/blake3 v1.4.1
 	mvdan.cc/gofumpt v0.12.0
 )
@@ -60,6 +62,6 @@ require (
 	golang.org/x/text v0.42.0 // indirect
 	golang.org/x/time v0.14.0 // indirect
 	golang.org/x/tools v0.49.0 // indirect
-	google.golang.org/genproto/googleapis/rpc v0.0.0-20260526163538-3dc84a4a5aaa // indirect
+	google.golang.org/genproto/googleapis/rpc v0.0.0-20260706201446-f0a921348800 // indirect
 	gopkg.in/yaml.v2 v2.4.0 // indirect
 )

go.sum

@@ -2,16 +2,13 @@ github.com/andybalholm/brotli v1.0.6 h1:Yf9fFpf49Zrxb9NlQaluyE92/+X7UVHlhMNJN2sx
 github.com/andybalholm/brotli v1.0.6/go.mod h1:fO7iG3H7G2nSZ7m0zPUDn85XEX2GTukHGRSepvi9Eig=
 github.com/apernet/quic-go v0.61.1-0.20260806010916-184d081eef3e h1:5mgtR5gwIgBKMiGI1QdXldZZ+SNor06Nbu1wCBulQBg=
 github.com/apernet/quic-go v0.61.1-0.20260806010916-184d081eef3e/go.mod h1:x7qxEvX6MCVtDuBKHj3E+88+BtrbEMuAL5qGUKItjW8=
-github.com/cespare/xxhash/v2 v2.3.0 h1:UL815xU9SqsFlibzuggzjXhog7bL6oX9BbNZnL2UFvs=
-github.com/cespare/xxhash/v2 v2.3.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
+github.com/chzyer/logex v1.1.10/go.mod h1:+Ywpsq7O8HXn0nuIou7OrIPyXbp3wmkHB+jjWRnGsAI=
+github.com/chzyer/readline v0.0.0-20180603132655-2972be24d48e/go.mod h1:nSuG5e5PlCu98SY8svDHJxuZscDgtXS6KTTbou5AhLI=
+github.com/chzyer/test v0.0.0-20180213035817-a1ea475d72b1/go.mod h1:Q3SI9o4m/ZMnBNeIyt5eFwwo7qiLfzFZmjNmxjkiQlU=
 github.com/cloudflare/circl v1.6.5 h1:O64F26HEqNhznd/hrC5KZXVKYuKM2rx4deZDTc4ihQA=
 github.com/cloudflare/circl v1.6.5/go.mod h1:h5LNyxAc5nTue9DS5jT+48en2PSDYt3zdGnz5OstK6c=
 github.com/ghodss/yaml v1.0.1-0.20220118164431-d8423dcdf344 h1:Arcl6UOIS/kgO2nW3A65HN+7CMjSDP/gofXL4CZt1V4=
 github.com/ghodss/yaml v1.0.1-0.20220118164431-d8423dcdf344/go.mod h1:GIjDIg/heH5DOkXY3YJ/wNhfHsQHoXGjl8G8amsYQ1I=
-github.com/go-logr/logr v1.4.3 h1:CjnDlHq8ikf6E492q6eKboGOC0T8CDaOvkHCIg8idEI=
-github.com/go-logr/logr v1.4.3/go.mod h1:9T104GzyrTigFIr8wt5mBrctHMim0Nb2HLGrmQ40KvY=
-github.com/go-logr/stdr v1.2.2 h1:hSWxHoqTgW2S2qGc0LTAI563KZ5YKYRhT3MFKZMbjag=
-github.com/go-logr/stdr v1.2.2/go.mod h1:mMo/vtBO5dYbehREoey6XUKy/eSumjCCveDpRre4VKE=
 github.com/go-quicktest/qt v1.102.0 h1:HSQxCeh5YZH3EL3W39ixjtyaEhcWSXQHtHnMBzSs474=
 github.com/go-quicktest/qt v1.102.0/go.mod h1:p4lGIVX+8Wa6ZPNDvqcxq36XpUDLh42FLetFU7odllI=
 github.com/golang/mock v1.7.0-rc.1 h1:YojYx61/OLFsiv6Rw1Z96LpldJIy31o+UHmwAUMJ6/U=
@@ -91,18 +88,9 @@ github.com/wlynxg/anet v0.0.5/go.mod h1:eay5PRQr7fIVAMbTbchTnO9gG65Hg/uYGdc7mguH
 github.com/xtls/reality v0.0.0-20260908062103-8cdf7bf9c7f0 h1:rb+fKQFhz+5I2PPuQsNYxI5mUU840XWYtRF0ZBjvkws=
 github.com/xtls/reality v0.0.0-20260908062103-8cdf7bf9c7f0/go.mod h1:DsJblcWDGt76+FVqBVwbwRhxyyNJsGV48gJLch0OOWI=
 github.com/yuin/goldmark v1.4.1/go.mod h1:mwnBkeHKe2W/ZEtQ+71ViKU8L12m81fl3OWwC1Zlc8k=
-go.opentelemetry.io/auto/sdk v1.2.1 h1:jXsnJ4Lmnqd11kwkBV2LgLoFMZKizbCi5fNZ/ipaZ64=
-go.opentelemetry.io/auto/sdk v1.2.1/go.mod h1:KRTj+aOaElaLi+wW1kO/DZRXwkF4C5xPbEe3ZiIhN7Y=
-go.opentelemetry.io/otel v1.44.0 h1:JjwHmHpA4iZ3wBxluu2fbbE7j4kqlE8jXyAyPXH7HqU=
-go.opentelemetry.io/otel v1.44.0/go.mod h1:BMgjTHL9WPRlRjL2oZCBTL4whCGtXch2H4BhOPIAyYc=
-go.opentelemetry.io/otel/metric v1.44.0 h1:1w0gILTcHdr3YI+ixLyjemwrVnsMURbTZFrSYCdDdmc=
-go.opentelemetry.io/otel/metric v1.44.0/go.mod h1:8O7hanEPBNgEMmybD3s2VBKcgWOCsA6tzHBPODAiquo=
-go.opentelemetry.io/otel/sdk v1.44.0 h1:nHYwb9lK+fJPU/dnT6s7W7Z8itMWyqrnVfbheVYrZ58=
-go.opentelemetry.io/otel/sdk v1.44.0/go.mod h1:Osuydd3Se74nqjAKxid74N5eC+jfEqfTegHRnq58oK0=
-go.opentelemetry.io/otel/sdk/metric v1.44.0 h1:3LlKgI+VjbVsjNRFZJZAJ30WjXC5VkNRks6si09iEfI=
-go.opentelemetry.io/otel/sdk/metric v1.44.0/go.mod h1:5B5pMARnXxKhltooO4xUuCBorl65a4EpnTalObqOigA=
-go.opentelemetry.io/otel/trace v1.44.0 h1:jxF5CsGYCe74MCRx2X4g7WsY/VBKRqqpNvXlX/6gtIk=
-go.opentelemetry.io/otel/trace v1.44.0/go.mod h1:oLl1jrMQAVo6v3GAggN+1VH9VIz9iUSvW53sW1Q8PIE=
+github.com/yuin/gopher-lua v0.0.0-20190206043414-8bfc7677f583/go.mod h1:gqRgreBUhTSL0GeU64rtZ3Uq3wtjOa/TB2YfrtkCbVQ=
+github.com/yuin/gopher-lua v1.1.2 h1:yF/FjE3hD65tBbt0VXLE13HWS9h34fdzJmrWRXwobGA=
+github.com/yuin/gopher-lua v1.1.2/go.mod h1:7aRmXIWl37SqRf0koeyylBEzJ+aPt8A+mmkQ4f1ntR8=
 go.uber.org/mock v0.5.2 h1:LbtPTcP8A5k9WPXj54PPPbjcI4Y6lhyOZXn+VS7wNko=
 go.uber.org/mock v0.5.2/go.mod h1:wLlUxC2vVTPTaE3UD51E0BGOAElKrILxhVSDYQLld5o=
 go.yaml.in/yaml/v3 v3.0.5 h1:N6y/pJk8buWs9NY5ERU2HSMfm+IuD/OtfdAnq6kESPw=
@@ -127,6 +115,7 @@ golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJ
 golang.org/x/sync v0.0.0-20210220032951-036812b2e83c/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.23.0 h1:KameEIfc1IkluZyXWLn39Wd4tURc6GbCiISGiZm2bQk=
 golang.org/x/sync v0.23.0/go.mod h1:sUUOizhqBxiL6pEWpqNLUiaJn1ShEbZ6BBqskPbjZm0=
+golang.org/x/sys v0.0.0-20190204203706-41f3e6584952/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
@@ -157,14 +146,14 @@ golang.zx2c4.com/wintun v0.0.0-20230126152724-0fa3db229ce2 h1:B82qJJgjvYKsXS9jeu
 golang.zx2c4.com/wintun v0.0.0-20230126152724-0fa3db229ce2/go.mod h1:deeaetjYA+DHMHg+sMSMI58GrEteJUUzzw7en6TJQcI=
 golang.zx2c4.com/wireguard v0.0.0-20250521234502-f333402bd9cb h1:whnFRlWMcXI9d+ZbWg+4sHnLp52d5yiIPUxMBSt4X9A=
 golang.zx2c4.com/wireguard v0.0.0-20250521234502-f333402bd9cb/go.mod h1:rpwXGsirqLqN2L0JDJQlwOboGHmptD5ZD6T2VmcqhTw=
-golang.zx2c4.com/wireguard/windows v1.0.1 h1:eOxiDVbywPC+ZQqvdCK7x+ZwWXKbYv50TtH8ysFIbw8=
-golang.zx2c4.com/wireguard/windows v1.0.1/go.mod h1:+fbT3FFdX4zzYDLwJh5+HPEcNN/3HyNdzhNSVsQM+zs=
+golang.zx2c4.com/wireguard/windows v1.1.1 h1:8/H97U1v1PNDNcBsMZgU3KFuND9MQdTsU2NOwmCXArE=
+golang.zx2c4.com/wireguard/windows v1.1.1/go.mod h1:+fbT3FFdX4zzYDLwJh5+HPEcNN/3HyNdzhNSVsQM+zs=
 gonum.org/v1/gonum v0.17.0 h1:VbpOemQlsSMrYmn7T2OUvQ4dqxQXU+ouZFQsZOx50z4=
 gonum.org/v1/gonum v0.17.0/go.mod h1:El3tOrEuMpv2UdMrbNlKEh9vd86bmQ6vqIcDwxEOc1E=
-google.golang.org/genproto/googleapis/rpc v0.0.0-20260526163538-3dc84a4a5aaa h1:mZHHdPZl0dbGHCflZgAq/Q468DWVFcU2whhB2KAo8fk=
-google.golang.org/genproto/googleapis/rpc v0.0.0-20260526163538-3dc84a4a5aaa/go.mod h1:4Hqkh8ycfw05ld/3BWL7rJOSfebL2Q+DVDeRgYgxUU8=
-google.golang.org/grpc v1.83.2 h1:EManeRomTObA0BU7I8vXgg/78uE5MJ9M8B39EX2WscU=
-google.golang.org/grpc v1.83.2/go.mod h1:YPI1hK3kDked6iHvgX3tR0y+nX/qpMFKhPgFsokw1S8=
+google.golang.org/genproto/googleapis/rpc v0.0.0-20260706201446-f0a921348800 h1:qEHAMpSaUhtD0p3NbEEI83HwNGFxEwaSJ1G9PLnCBZE=
+google.golang.org/genproto/googleapis/rpc v0.0.0-20260706201446-f0a921348800/go.mod h1:4Hqkh8ycfw05ld/3BWL7rJOSfebL2Q+DVDeRgYgxUU8=
+google.golang.org/grpc v1.84.0 h1:soMyaPJ8pAak5PIQ0DGBUir0XRo2fRoMqhNWMLlLxO0=
+google.golang.org/grpc v1.84.0/go.mod h1:ljCht0DrxQrXBDRTZp52Qxh3Ffk8CdYm2sj4O2QN2C0=
 google.golang.org/protobuf v1.36.12 h1:pJOKDDOyeXErUroCihFAd5LQuwXBSpVnKGrj5o/fwxc=
 google.golang.org/protobuf v1.36.12/go.mod h1:HTf+CrKn2C3g5S8VImy6tdcUvCska2kB7j23XfzDpco=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
@@ -177,6 +166,8 @@ gvisor.dev/gvisor v0.0.0-20260122175437-89a5d21be8f0 h1:Lk6hARj5UPY47dBep70OD/TI
 gvisor.dev/gvisor v0.0.0-20260122175437-89a5d21be8f0/go.mod h1:QkHjoMIBaYtpVufgwv3keYAbln78mBoCuShZrPrer1Q=
 h12.io/socks v1.0.3 h1:Ka3qaQewws4j4/eDQnOdpr4wXsC//dXtWvftlIcCQUo=
 h12.io/socks v1.0.3/go.mod h1:AIhxy1jOId/XCz9BO+EIgNL2rQiPTBNnOfnVnQ+3Eck=
+layeh.com/gopher-luar v1.0.11 h1:8zJudpKI6HWkoh9eyyNFaTM79PY6CAPcIr6X/KTiliw=
+layeh.com/gopher-luar v1.0.11/go.mod h1:TPnIVCZ2RJBndm7ohXyaqfhzjlZ+OA2SZR/YwL8tECk=
 lukechampine.com/blake3 v1.4.1 h1:I3Smz7gso8w4/TunLKec6K2fn+kyKtDxr/xcQEN84Wg=
 lukechampine.com/blake3 v1.4.1/go.mod h1:QFosUxmjB8mnrWFSNwKmvxHpfY72bmD2tQ0kBMM3kwo=
 mvdan.cc/gofumpt v0.12.0 h1:1Lbudkz2kpM9Cjz2pL4M19u7q+GaEhCTNf7N9mfpcho=

infra/conf/dns.go

@@ -14,9 +14,11 @@ import (
 	"github.com/xtls/xray-core/common/errors"
 	"github.com/xtls/xray-core/common/geodata"
 	"github.com/xtls/xray-core/common/net"
+	"github.com/xtls/xray-core/common/platform"
 )
 
 type NameServerConfig struct {
+	ID              string     `json:"id"`
 	Address         *Address   `json:"address"`
 	ClientIP        *Address   `json:"clientIp"`
 	Port            uint16     `json:"port"`
@@ -43,6 +45,7 @@ func (c *NameServerConfig) UnmarshalJSON(data []byte) error {
 	}
 
 	var advanced struct {
+		ID              string     `json:"id"`
 		Address         *Address   `json:"address"`
 		ClientIP        *Address   `json:"clientIp"`
 		Port            uint16     `json:"port"`
@@ -60,6 +63,7 @@ func (c *NameServerConfig) UnmarshalJSON(data []byte) error {
 		UnexpectedIPs   StringList `json:"unexpectedIPs"`
 	}
 	if err := json.Unmarshal(data, &advanced); err == nil {
+		c.ID = advanced.ID
 		c.Address = advanced.Address
 		c.ClientIP = advanced.ClientIP
 		c.Port = advanced.Port
@@ -134,6 +138,7 @@ func (c *NameServerConfig) Build() (*dns.NameServer, error) {
 	}
 
 	return &dns.NameServer{
+		Id: c.ID,
 		Address: &net.Endpoint{
 			Network: net.Network_UDP,
 			Address: c.Address.Build(),
@@ -159,6 +164,7 @@ func (c *NameServerConfig) Build() (*dns.NameServer, error) {
 // DNSConfig is a JSON serializable object for dns.Config
 type DNSConfig struct {
 	Servers                []*NameServerConfig `json:"servers"`
+	Script                 string              `json:"script"`
 	Hosts                  *HostsWrapper       `json:"hosts"`
 	ClientIP               *Address            `json:"clientIp"`
 	Tag                    string              `json:"tag"`
@@ -278,6 +284,14 @@ func (c *DNSConfig) Build() (*dns.Config, error) {
 		QueryStrategy:          resolveQueryStrategy(c.QueryStrategy),
 	}
 
+	if c.Script != "" {
+		path, err := platform.ResolveLuaFile(c.Script)
+		if err != nil {
+			return nil, errors.New("failed to resolve DNS script: ", c.Script).Base(err)
+		}
+		config.Script = path
+	}
+
 	if c.ClientIP != nil {
 		if !c.ClientIP.Family().IsIP() {
 			return nil, errors.New("not an IP address:", c.ClientIP.String())

infra/conf/dns_test.go

@@ -2,6 +2,8 @@ package conf_test
 
 import (
 	"encoding/json"
+	"os"
+	"path/filepath"
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
@@ -122,3 +124,51 @@ func TestDNSConfigParsing(t *testing.T) {
 		}
 	}
 }
+
+func TestDNSScriptConfig(t *testing.T) {
+	dir := t.TempDir()
+	t.Setenv("xray.location.confdir", dir)
+	path := filepath.Join(dir, "lookup.lua")
+	if err := os.WriteFile(path, []byte("function HandleDNSQuery(domain, ipv4, ipv6, fake) end"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+
+	for _, tc := range []struct {
+		name      string
+		script    string
+		wantError bool
+	}{
+		{"relative", "lookup.lua", false},
+		{"absolute", path, false},
+		{"missing", "missing.lua", true},
+		{"directory", dir, true},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			built, err := (&DNSConfig{Script: tc.script}).Build()
+			if tc.wantError {
+				if err == nil {
+					t.Fatal("Build accepted an invalid script path")
+				}
+				return
+			}
+			if err != nil {
+				t.Fatal(err)
+			}
+			if built.Script != path {
+				t.Fatalf("script path = %q, want %q", built.Script, path)
+			}
+		})
+	}
+
+	var parsed DNSConfig
+	if err := json.Unmarshal([]byte(`{"servers":[{"id":"primary","address":"1.1.1.1"}]}`), &parsed); err != nil {
+		t.Fatal(err)
+	}
+	built, err := parsed.Build()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(built.NameServer) != 1 || built.NameServer[0].Id != "primary" {
+		t.Fatalf("nameserver IDs = %v, want primary", built.NameServer)
+	}
+}

infra/conf/masque.go

@@ -0,0 +1,37 @@
+package conf
+
+import (
+	"net/netip"
+
+	"github.com/xtls/xray-core/common/errors"
+	"github.com/xtls/xray-core/common/protocol"
+	"github.com/xtls/xray-core/proxy/masque"
+	"google.golang.org/protobuf/proto"
+)
+
+type MasqueClientConfig struct {
+	Address   *Address `json:"address"`
+	Port      uint16   `json:"port"`
+	RemoteDNS []string `json:"remoteDNS"`
+}
+
+func (c *MasqueClientConfig) Build() (proto.Message, error) {
+	if c.Address == nil {
+		return nil, errors.New(`MASQUE: "address" is not set`)
+	}
+	if c.Port == 0 {
+		return nil, errors.New(`MASQUE: "port" is not set`)
+	}
+	for _, s := range c.RemoteDNS {
+		if _, err := netip.ParseAddr(s); err != nil {
+			return nil, errors.New(`MASQUE: invalid "remoteDNS" `, s).Base(err)
+		}
+	}
+	return &masque.ClientConfig{
+		Server: &protocol.ServerEndpoint{
+			Address: c.Address.Build(),
+			Port:    uint32(c.Port),
+		},
+		RemoteDns: c.RemoteDNS,
+	}, nil
+}

infra/conf/masque_test.go

@@ -0,0 +1,85 @@
+package conf_test
+
+import (
+	"encoding/json"
+	"testing"
+
+	. "github.com/xtls/xray-core/infra/conf"
+	"github.com/xtls/xray-core/transport/internet/masque"
+)
+
+func TestMasqueConfig(t *testing.T) {
+	creator := func() Buildable {
+		return new(MasqueConfig)
+	}
+
+	runMultiTestCase(t, []TestCase{
+		{
+			Input:  `{}`,
+			Parser: loadJSON(creator),
+			Output: &masque.Config{Path: "/.well-known/masque/ip/*/*/"},
+		},
+		{
+			Input: `{
+				"host": "example.com:8443",
+				"path": "/.well-known/masque/ip/{target}/{ipproto}/",
+				"headers": {"Authorization": "Basic dTpw"}
+			}`,
+			Parser: loadJSON(creator),
+			Output: &masque.Config{
+				Host:    "example.com:8443",
+				Path:    "/.well-known/masque/ip/*/*/",
+				Headers: map[string]string{"Authorization": "Basic dTpw"},
+			},
+		},
+		{
+			Input:  `{"path": "/masque/ip{?target,ipproto}"}`,
+			Parser: loadJSON(creator),
+			Output: &masque.Config{Path: "/masque/ip?target=*&ipproto=*"},
+		},
+	})
+
+	for _, input := range []string{
+		`{"path": "/masque/{target}/{ipproto}/{dns}"}`,
+		`{"path": "masque"}`,
+		`{"host": "example.com/path"}`,
+		`{"headers": {"host": "example.com"}}`,
+		`{"headers": {"Capsule-Protocol": "?0"}}`,
+		`{"headers": {"X Token": "a"}}`,
+		`{"headers": {"X-Token": "a\r\nb"}}`,
+	} {
+		if _, err := loadJSON(creator)(input); err == nil {
+			t.Errorf("expected an error for %s", input)
+		}
+	}
+}
+
+func TestMasqueOutboundConfig(t *testing.T) {
+	build := func(s string) error {
+		c := new(OutboundDetourConfig)
+		if err := json.Unmarshal([]byte(s), c); err != nil {
+			return err
+		}
+		_, err := c.Build()
+		return err
+	}
+
+	if err := build(`{
+		"protocol": "masque",
+		"settings": {"address": "example.com", "port": 443},
+		"streamSettings": {"network": "masque", "security": "tls"},
+		"mux": {"enabled": false, "concurrency": -1}
+	}`); err != nil {
+		t.Error(err)
+	}
+	for _, input := range []string{
+		`{"protocol": "masque", "settings": {"address": "example.com"}, "streamSettings": {"network": "masque", "security": "tls"}}`,
+		`{"protocol": "masque", "settings": {"address": "example.com", "port": 443}, "streamSettings": {"network": "masque", "security": "tls"}, "mux": {"enabled": true}}`,
+		`{"protocol": "masque", "settings": {"address": "example.com", "port": 443}, "streamSettings": {"network": "masque", "security": "tls"}, "mux": {"enabled": true, "concurrency": -1}}`,
+		`{"protocol": "freedom", "streamSettings": {"network": "masque", "security": "tls"}}`,
+	} {
+		if err := build(input); err == nil {
+			t.Errorf("expected an error for %s", input)
+		}
+	}
+}

infra/conf/router.go

@@ -7,6 +7,7 @@ import (
 	"github.com/xtls/xray-core/app/router"
 	"github.com/xtls/xray-core/common/errors"
 	"github.com/xtls/xray-core/common/geodata"
+	"github.com/xtls/xray-core/common/platform"
 	"github.com/xtls/xray-core/common/serial"
 
 	"google.golang.org/protobuf/proto"
@@ -72,6 +73,7 @@ type RouterConfig struct {
 	RuleList       []json.RawMessage `json:"rules"`
 	DomainStrategy *string           `json:"domainStrategy"`
 	Balancers      []*BalancingRule  `json:"balancers"`
+	Script         string            `json:"script"`
 }
 
 func (c *RouterConfig) getDomainStrategy() router.Config_DomainStrategy {
@@ -92,6 +94,15 @@ func (c *RouterConfig) getDomainStrategy() router.Config_DomainStrategy {
 
 func (c *RouterConfig) Build() (*router.Config, error) {
 	config := new(router.Config)
+
+	if c.Script != "" {
+		path, err := platform.ResolveLuaFile(c.Script)
+		if err != nil {
+			return nil, errors.New("failed to resolve routing script").Base(err)
+		}
+		config.Script = path
+	}
+
 	config.DomainStrategy = c.getDomainStrategy()
 
 	var rawRuleList []json.RawMessage

infra/conf/router_test.go

@@ -2,6 +2,8 @@ package conf_test
 
 import (
 	"encoding/json"
+	"os"
+	"path/filepath"
 	"testing"
 	"time"
 	_ "unsafe"
@@ -236,3 +238,39 @@ func TestRouterConfig(t *testing.T) {
 		},
 	})
 }
+
+func TestRouterScriptConfig(t *testing.T) {
+	dir := t.TempDir()
+	t.Setenv("xray.location.confdir", dir)
+	path := filepath.Join(dir, "route.lua")
+	if err := os.WriteFile(path, []byte("function HandleRoute() end"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+
+	for _, tc := range []struct {
+		name      string
+		script    string
+		wantError bool
+	}{
+		{"relative", "route.lua", false},
+		{"absolute", path, false},
+		{"missing", "missing.lua", true},
+		{"directory", dir, true},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			built, err := (&RouterConfig{Script: tc.script}).Build()
+			if tc.wantError {
+				if err == nil {
+					t.Fatal("Build accepted invalid script path")
+				}
+				return
+			}
+			if err != nil {
+				t.Fatal(err)
+			}
+			if built.Script != path {
+				t.Fatalf("script path = %q, want %q", built.Script, path)
+			}
+		})
+	}
+}

infra/conf/transport_internet.go

@@ -36,6 +36,8 @@ func (p TransportProtocol) Build() (string, error) {
 		return "", errors.PrintRemovedFeatureError("QUIC transport (without web service, etc.)", "XHTTP stream-one H3")
 	case "hysteria":
 		return "hysteria", nil
+	case "masque":
+		return "masque", nil
 	case "xdrive":
 		return "xdrive", nil
 	default:
@@ -61,6 +63,7 @@ type StreamConfig struct {
 	WSSettings          *WebSocketConfig   `json:"wsSettings"`
 	HTTPUPGRADESettings *HttpUpgradeConfig `json:"httpupgradeSettings"`
 	HysteriaSettings    *HysteriaConfig    `json:"hysteriaSettings"`
+	MASQUESettings      *MasqueConfig      `json:"masqueSettings"`
 	XDRIVESettings      *XDriveConfig      `json:"xdriveSettings"`
 	SocketSettings      *SocketConfig      `json:"sockopt"`
 }
@@ -195,6 +198,16 @@ func (c *StreamConfig) Build() (*internet.StreamConfig, error) {
 			Settings:     serial.ToTypedMessage(hs),
 		})
 	}
+	if c.MASQUESettings != nil {
+		ms, err := c.MASQUESettings.Build()
+		if err != nil {
+			return nil, errors.New("Failed to build MASQUE config.").Base(err)
+		}
+		config.TransportSettings = append(config.TransportSettings, &internet.TransportConfig{
+			ProtocolName: "masque",
+			Settings:     serial.ToTypedMessage(ms),
+		})
+	}
 	if c.XDRIVESettings != nil {
 		xs, err := c.XDRIVESettings.Build()
 		if err != nil {

infra/conf/transport_method.go

@@ -20,10 +20,12 @@ import (
 	"github.com/xtls/xray-core/transport/internet/httpupgrade"
 	"github.com/xtls/xray-core/transport/internet/hysteria"
 	"github.com/xtls/xray-core/transport/internet/kcp"
+	"github.com/xtls/xray-core/transport/internet/masque"
 	"github.com/xtls/xray-core/transport/internet/splithttp"
 	"github.com/xtls/xray-core/transport/internet/tcp"
 	"github.com/xtls/xray-core/transport/internet/websocket"
 	"github.com/xtls/xray-core/transport/internet/xdrive"
+	"golang.org/x/net/http/httpguts"
 	"google.golang.org/protobuf/proto"
 )
 
@@ -786,6 +788,46 @@ func (c *HysteriaConfig) Build() (proto.Message, error) {
 	return config, nil
 }
 
+type MasqueConfig struct {
+	Host    string            `json:"host"`
+	Path    string            `json:"path"`
+	Headers map[string]string `json:"headers"`
+}
+
+func (c *MasqueConfig) Build() (proto.Message, error) {
+	path := c.Path
+	if path == "" {
+		path = masque.DefaultPath
+	}
+	path = strings.NewReplacer(
+		"{target}", "*", "{ipproto}", "*",
+		"{?target,ipproto}", "?target=*&ipproto=*", "{?ipproto,target}", "?ipproto=*&target=*",
+		"{&target,ipproto}", "&target=*&ipproto=*", "{&ipproto,target}", "&ipproto=*&target=*",
+	).Replace(path)
+	if !strings.HasPrefix(path, "/") || strings.ContainsAny(path, "{}") {
+		return nil, errors.New(`invalid "path": `, path, `, only the variables {target} and {ipproto} are supported`)
+	}
+	if c.Host != "" {
+		if u, err := url.Parse("https://" + c.Host); err != nil || u.Host != c.Host {
+			return nil, errors.New(`invalid "host": `, c.Host)
+		}
+	}
+	for k, v := range c.Headers {
+		if !httpguts.ValidHeaderFieldName(k) || !httpguts.ValidHeaderFieldValue(v) {
+			return nil, errors.New(`invalid header in "headers": `, strconv.Quote(k))
+		}
+		switch strings.ToLower(k) {
+		case "host", "capsule-protocol":
+			return nil, errors.New(`"headers" can't contain "`, k, `"`)
+		}
+	}
+	return &masque.Config{
+		Host:    c.Host,
+		Path:    path,
+		Headers: c.Headers,
+	}, nil
+}
+
 func readFileOrString(f string, s []string) ([]byte, error) {
 	if len(f) > 0 {
 		return filesystem.ReadCert(f)

infra/conf/xray.go

@@ -16,6 +16,7 @@ import (
 	"github.com/xtls/xray-core/common/serial"
 	core "github.com/xtls/xray-core/core"
 	"github.com/xtls/xray-core/proxy/freedom"
+	"github.com/xtls/xray-core/proxy/masque"
 	"github.com/xtls/xray-core/transport/internet"
 )
 
@@ -48,6 +49,7 @@ var (
 		"vmess":       func() interface{} { return new(VMessOutboundConfig) },
 		"trojan":      func() interface{} { return new(TrojanClientConfig) },
 		"hysteria":    func() interface{} { return new(HysteriaClientConfig) },
+		"masque":      func() interface{} { return new(MasqueClientConfig) },
 		"dns":         func() interface{} { return new(DNSOutboundConfig) },
 		"wireguard":   func() interface{} { return &WireGuardConfig{IsClient: true} },
 	}, "protocol", "settings")
@@ -338,6 +340,14 @@ func (c *OutboundDetourConfig) Build() (*core.OutboundHandlerConfig, error) {
 		return nil, err
 	}
 
+	if _, ok := ts.(*masque.ClientConfig); ok {
+		if ms := senderSettings.MultiplexSettings; ms != nil && ms.Enabled {
+			return nil, errors.New(`masque outbound does not support "mux"`)
+		}
+	} else if senderSettings.StreamSettings != nil && senderSettings.StreamSettings.ProtocolName == "masque" {
+		return nil, errors.New("the masque transport can only be used by the masque outbound")
+	}
+
 	if fc, ok := ts.(*freedom.Config); ok {
 		if senderSettings.StreamSettings != nil &&
 			senderSettings.StreamSettings.SocketSettings != nil &&

main/distro/all/all.go

@@ -41,6 +41,7 @@ import (
 	_ "github.com/xtls/xray-core/proxy/freedom"
 	_ "github.com/xtls/xray-core/proxy/http"
 	_ "github.com/xtls/xray-core/proxy/loopback"
+	_ "github.com/xtls/xray-core/proxy/masque"
 	_ "github.com/xtls/xray-core/proxy/shadowsocks"
 	_ "github.com/xtls/xray-core/proxy/socks"
 	_ "github.com/xtls/xray-core/proxy/trojan"
@@ -54,6 +55,7 @@ import (
 	_ "github.com/xtls/xray-core/transport/internet/grpc"
 	_ "github.com/xtls/xray-core/transport/internet/httpupgrade"
 	_ "github.com/xtls/xray-core/transport/internet/kcp"
+	_ "github.com/xtls/xray-core/transport/internet/masque"
 	_ "github.com/xtls/xray-core/transport/internet/reality"
 	_ "github.com/xtls/xray-core/transport/internet/splithttp"
 	_ "github.com/xtls/xray-core/transport/internet/tcp"

proxy/masque/client.go

@@ -0,0 +1,328 @@
+package masque
+
+import (
+	"context"
+	go_errors "errors"
+	"io"
+	"net/netip"
+	"slices"
+	"sync"
+	"sync/atomic"
+	"time"
+
+	"golang.zx2c4.com/wireguard/tun"
+
+	"github.com/xtls/xray-core/common"
+	"github.com/xtls/xray-core/common/buf"
+	"github.com/xtls/xray-core/common/errors"
+	"github.com/xtls/xray-core/common/net"
+	"github.com/xtls/xray-core/common/protocol"
+	"github.com/xtls/xray-core/common/session"
+	"github.com/xtls/xray-core/common/signal"
+	"github.com/xtls/xray-core/common/task"
+	"github.com/xtls/xray-core/core"
+	"github.com/xtls/xray-core/features/policy"
+	"github.com/xtls/xray-core/proxy/wireguard"
+	"github.com/xtls/xray-core/transport"
+	"github.com/xtls/xray-core/transport/internet"
+	"github.com/xtls/xray-core/transport/internet/masque"
+	"github.com/xtls/xray-core/transport/internet/stat"
+	"github.com/xtls/xray-core/transport/internet/tls"
+)
+
+const (
+	establishTimeout = 10 * time.Second
+	retryInterval    = time.Second
+)
+
+type Client struct {
+	server        *protocol.ServerSpec
+	policyManager policy.Manager
+	remoteDNS     []netip.Addr
+
+	ctx    context.Context
+	cancel context.CancelFunc
+
+	tunnel atomic.Pointer[tunnel]
+
+	mu        sync.Mutex
+	lastErr   error
+	lastErrAt time.Time
+}
+
+func NewClient(ctx context.Context, config *ClientConfig) (*Client, error) {
+	v := core.MustFromContext(ctx)
+	p := v.GetFeature(policy.ManagerType()).(policy.Manager)
+
+	streamSettings := session.StreamSettingsFromContext(ctx).(*internet.MemoryStreamConfig)
+	if _, ok := streamSettings.ProtocolSettings.(*masque.Config); !ok {
+		return nil, errors.New("not masque transport")
+	}
+	if tls.ConfigFromStreamSettings(streamSettings) == nil {
+		return nil, errors.New(`MASQUE requires "security": "tls"`)
+	}
+	if config.Server == nil {
+		return nil, errors.New(`no target server found`)
+	}
+	server, err := protocol.NewServerSpecFromPB(config.Server)
+	if err != nil {
+		return nil, errors.New("failed to get server spec").Base(err)
+	}
+
+	dns := config.RemoteDns
+	if len(dns) == 0 {
+		dns = []string{"1.1.1.1", "1.0.0.1", "2606:4700:4700::1111", "2606:4700:4700::1001"}
+	}
+	remoteDNS := make([]netip.Addr, 0, len(dns))
+	for _, s := range dns {
+		addr, err := netip.ParseAddr(s)
+		if err != nil {
+			return nil, errors.New("invalid remote DNS server ", s).Base(err)
+		}
+		remoteDNS = append(remoteDNS, addr)
+	}
+
+	c := &Client{
+		server:        server,
+		policyManager: p,
+		remoteDNS:     remoteDNS,
+	}
+	c.ctx, c.cancel = context.WithCancel(context.Background())
+	return c, nil
+}
+
+func (c *Client) Process(ctx context.Context, link *transport.Link, dialer internet.Dialer) error {
+	outbounds := session.OutboundsFromContext(ctx)
+	ob := outbounds[len(outbounds)-1]
+	if !ob.Target.IsValid() {
+		return errors.New("target not specified")
+	}
+	ob.Name = "masque"
+	ob.CanSpliceCopy = 3
+
+	t, err := c.getTunnel(ctx, dialer)
+	if err != nil {
+		return errors.New("failed to establish CONNECT-IP tunnel").Base(err)
+	}
+
+	var newCtx context.Context
+	var newCancel context.CancelFunc
+	if session.TimeoutOnlyFromContext(ctx) {
+		newCtx, newCancel = context.WithCancel(context.Background())
+	}
+
+	sessionPolicy := c.policyManager.ForLevel(0)
+	ctx, cancel := context.WithCancel(ctx)
+	timer := signal.CancelAfterInactivity(ctx, func() {
+		cancel()
+		if newCancel != nil {
+			newCancel()
+		}
+	}, sessionPolicy.Timeouts.ConnectionIdle)
+
+	if newCtx != nil {
+		ctx = newCtx
+	}
+
+	var reader buf.Reader
+	var writer buf.Writer
+
+	switch ob.Target.Network {
+	case net.Network_TCP:
+		var conn net.Conn
+		var err error
+		if sessionPolicy.Timeouts.Handshake != 0 {
+			timeoutCtx, timeoutCancel := context.WithTimeout(ctx, sessionPolicy.Timeouts.Handshake)
+			conn, err = t.tnet.DialContext(timeoutCtx, "tcp", ob.Target.NetAddr())
+			timeoutCancel()
+		} else {
+			conn, err = t.tnet.Dial("tcp", ob.Target.NetAddr())
+		}
+		if err != nil {
+			return errors.New("failed to create TCP connection").Base(err)
+		}
+		defer conn.Close()
+		reader = buf.NewReader(conn)
+		writer = buf.NewWriter(conn)
+	case net.Network_UDP:
+		conn, err := t.tnet.Dial("udp", ob.Target.NetAddr())
+		if err != nil {
+			return errors.New("failed to create UDP connection").Base(err)
+		}
+		defer conn.Close()
+		uc := &wireguard.UDPConnClient{
+			PacketConn: conn.(*internet.PacketConnWrapper).PacketConn,
+			Dest:       conn.RemoteAddr().(*net.UDPAddr),
+		}
+		reader = uc
+		writer = uc
+	default:
+		panic(ob.Target.Network)
+	}
+
+	requestFunc := func() error {
+		defer timer.SetTimeout(sessionPolicy.Timeouts.DownlinkOnly)
+		return buf.Copy(link.Reader, writer, buf.UpdateActivity(timer))
+	}
+
+	responseFunc := func() error {
+		defer timer.SetTimeout(sessionPolicy.Timeouts.UplinkOnly)
+		return buf.Copy(reader, link.Writer, buf.UpdateActivity(timer))
+	}
+
+	responseDonePost := task.OnSuccess(responseFunc, task.Close(link.Writer))
+	if err := task.Run(ctx, requestFunc, responseDonePost); err != nil {
+		common.Interrupt(link.Reader)
+		common.Interrupt(link.Writer)
+		return errors.New("connection ends").Base(err)
+	}
+
+	return nil
+}
+
+func (c *Client) getTunnel(ctx context.Context, dialer internet.Dialer) (*tunnel, error) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if c.ctx.Err() != nil {
+		return nil, errors.New("closed")
+	}
+	if t := c.tunnel.Load(); t != nil {
+		select {
+		case <-t.done:
+		default:
+			return t, nil
+		}
+	}
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	if c.lastErr != nil && time.Since(c.lastErrAt) < retryInterval {
+		return nil, c.lastErr
+	}
+
+	t, err := c.establish(ctx, dialer)
+	if err != nil {
+		c.lastErr, c.lastErrAt = err, time.Now()
+		return nil, err
+	}
+	c.lastErr = nil
+	c.tunnel.Store(t)
+	if c.ctx.Err() != nil {
+		if c.tunnel.CompareAndSwap(t, nil) {
+			t.close()
+		}
+		return nil, errors.New("closed")
+	}
+	return t, nil
+}
+
+func (c *Client) establish(ctx context.Context, dialer internet.Dialer) (*tunnel, error) {
+	ctx, cancel := context.WithTimeout(context.WithoutCancel(ctx), establishTimeout)
+	defer cancel()
+	defer context.AfterFunc(c.ctx, cancel)()
+	conn, err := dialer.Dial(ctx, c.server.Destination)
+	if err != nil {
+		return nil, err
+	}
+	mconn, ok := stat.TryUnwrapStatsConn(conn).(*masque.Conn)
+	if !ok {
+		conn.Close()
+		return nil, errors.New("not a CONNECT-IP connection")
+	}
+	t, err := newTunnel(conn, mconn.LocalAddrs(), c.remoteDNS)
+	if err != nil {
+		conn.Close()
+		return nil, err
+	}
+	errors.LogInfo(ctx, "MASQUE: tunnel established from ", mconn.LocalAddrs())
+	return t, nil
+}
+
+func (c *Client) Close() error {
+	c.cancel()
+	if t := c.tunnel.Swap(nil); t != nil {
+		t.close()
+	}
+	return nil
+}
+
+type tunnel struct {
+	conn      stat.Connection
+	dev       tun.Device
+	tnet      *wireguard.Net
+	done      chan struct{}
+	closeOnce sync.Once
+}
+
+func newTunnel(conn stat.Connection, local []netip.Addr, remoteDNS []netip.Addr) (*tunnel, error) {
+	var dns []netip.Addr
+	for _, addr := range remoteDNS {
+		if slices.ContainsFunc(local, func(l netip.Addr) bool { return l.Is4() == addr.Is4() }) {
+			dns = append(dns, addr)
+		}
+	}
+	if len(dns) == 0 {
+		errors.LogWarning(context.Background(), "MASQUE: no remote DNS server is reachable from the assigned addresses ", local, ", domain names will fail to resolve")
+		dns = remoteDNS
+	}
+
+	dev, tnet, _, err := wireguard.CreateNetTUN(local, dns, masque.MinPacketSize, true)
+	if err != nil {
+		return nil, err
+	}
+	t := &tunnel{
+		conn: conn,
+		dev:  dev,
+		tnet: tnet,
+		done: make(chan struct{}),
+	}
+	go t.readFromTunnel()
+	go t.writeToTunnel()
+	return t, nil
+}
+
+func (t *tunnel) readFromTunnel() {
+	defer t.close()
+	b := make([]byte, buf.Size)
+	for {
+		n, err := t.conn.Read(b)
+		if err != nil {
+			if go_errors.Is(err, io.ErrShortBuffer) {
+				continue
+			}
+			errors.LogInfoInner(context.Background(), err, "MASQUE: tunnel closed")
+			return
+		}
+		t.dev.Write([][]byte{b[:n]}, 0)
+	}
+}
+
+func (t *tunnel) writeToTunnel() {
+	bufs := [][]byte{make([]byte, masque.MinPacketSize)}
+	sizes := []int{0}
+	for {
+		if _, err := t.dev.Read(bufs, sizes, 0); err != nil {
+			return
+		}
+		if _, err := t.conn.Write(bufs[0][:sizes[0]]); err != nil {
+			var ptb *masque.PacketTooBigError
+			if go_errors.As(err, &ptb) {
+				go t.dev.Write([][]byte{ptb.ICMP}, 0)
+			}
+		}
+	}
+}
+
+func (t *tunnel) close() {
+	t.closeOnce.Do(func() {
+		close(t.done)
+		t.conn.Close()
+		t.dev.Close()
+	})
+}
+
+func init() {
+	common.Must(common.RegisterConfig((*ClientConfig)(nil), func(ctx context.Context, config interface{}) (interface{}, error) {
+		return NewClient(ctx, config.(*ClientConfig))
+	}))
+}

proxy/masque/config.pb.go

@@ -0,0 +1,136 @@
+// Code generated by protoc-gen-go. DO NOT EDIT.
+// versions:
+// 	protoc-gen-go v1.36.11
+// 	protoc        v6.33.5
+// source: proxy/masque/config.proto
+
+package masque
+
+import (
+	protocol "github.com/xtls/xray-core/common/protocol"
+	protoreflect "google.golang.org/protobuf/reflect/protoreflect"
+	protoimpl "google.golang.org/protobuf/runtime/protoimpl"
+	reflect "reflect"
+	sync "sync"
+	unsafe "unsafe"
+)
+
+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)
+)
+
+type ClientConfig struct {
+	state         protoimpl.MessageState   `protogen:"open.v1"`
+	Server        *protocol.ServerEndpoint `protobuf:"bytes,1,opt,name=server,proto3" json:"server,omitempty"`
+	RemoteDns     []string                 `protobuf:"bytes,2,rep,name=remote_dns,json=remoteDns,proto3" json:"remote_dns,omitempty"`
+	unknownFields protoimpl.UnknownFields
+	sizeCache     protoimpl.SizeCache
+}
+
+func (x *ClientConfig) Reset() {
+	*x = ClientConfig{}
+	mi := &file_proxy_masque_config_proto_msgTypes[0]
+	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+	ms.StoreMessageInfo(mi)
+}
+
+func (x *ClientConfig) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*ClientConfig) ProtoMessage() {}
+
+func (x *ClientConfig) ProtoReflect() protoreflect.Message {
+	mi := &file_proxy_masque_config_proto_msgTypes[0]
+	if x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use ClientConfig.ProtoReflect.Descriptor instead.
+func (*ClientConfig) Descriptor() ([]byte, []int) {
+	return file_proxy_masque_config_proto_rawDescGZIP(), []int{0}
+}
+
+func (x *ClientConfig) GetServer() *protocol.ServerEndpoint {
+	if x != nil {
+		return x.Server
+	}
+	return nil
+}
+
+func (x *ClientConfig) GetRemoteDns() []string {
+	if x != nil {
+		return x.RemoteDns
+	}
+	return nil
+}
+
+var File_proxy_masque_config_proto protoreflect.FileDescriptor
+
+const file_proxy_masque_config_proto_rawDesc = "" +
+	"\n" +
+	"\x19proxy/masque/config.proto\x12\x11xray.proxy.masque\x1a!common/protocol/server_spec.proto\"k\n" +
+	"\fClientConfig\x12<\n" +
+	"\x06server\x18\x01 \x01(\v2$.xray.common.protocol.ServerEndpointR\x06server\x12\x1d\n" +
+	"\n" +
+	"remote_dns\x18\x02 \x03(\tR\tremoteDnsBU\n" +
+	"\x15com.xray.proxy.masqueP\x01Z&github.com/xtls/xray-core/proxy/masque\xaa\x02\x11Xray.Proxy.Masqueb\x06proto3"
+
+var (
+	file_proxy_masque_config_proto_rawDescOnce sync.Once
+	file_proxy_masque_config_proto_rawDescData []byte
+)
+
+func file_proxy_masque_config_proto_rawDescGZIP() []byte {
+	file_proxy_masque_config_proto_rawDescOnce.Do(func() {
+		file_proxy_masque_config_proto_rawDescData = protoimpl.X.CompressGZIP(unsafe.Slice(unsafe.StringData(file_proxy_masque_config_proto_rawDesc), len(file_proxy_masque_config_proto_rawDesc)))
+	})
+	return file_proxy_masque_config_proto_rawDescData
+}
+
+var file_proxy_masque_config_proto_msgTypes = make([]protoimpl.MessageInfo, 1)
+var file_proxy_masque_config_proto_goTypes = []any{
+	(*ClientConfig)(nil),            // 0: xray.proxy.masque.ClientConfig
+	(*protocol.ServerEndpoint)(nil), // 1: xray.common.protocol.ServerEndpoint
+}
+var file_proxy_masque_config_proto_depIdxs = []int32{
+	1, // 0: xray.proxy.masque.ClientConfig.server:type_name -> xray.common.protocol.ServerEndpoint
+	1, // [1:1] is the sub-list for method output_type
+	1, // [1:1] is the sub-list for method input_type
+	1, // [1:1] is the sub-list for extension type_name
+	1, // [1:1] is the sub-list for extension extendee
+	0, // [0:1] is the sub-list for field type_name
+}
+
+func init() { file_proxy_masque_config_proto_init() }
+func file_proxy_masque_config_proto_init() {
+	if File_proxy_masque_config_proto != nil {
+		return
+	}
+	type x struct{}
+	out := protoimpl.TypeBuilder{
+		File: protoimpl.DescBuilder{
+			GoPackagePath: reflect.TypeOf(x{}).PkgPath(),
+			RawDescriptor: unsafe.Slice(unsafe.StringData(file_proxy_masque_config_proto_rawDesc), len(file_proxy_masque_config_proto_rawDesc)),
+			NumEnums:      0,
+			NumMessages:   1,
+			NumExtensions: 0,
+			NumServices:   0,
+		},
+		GoTypes:           file_proxy_masque_config_proto_goTypes,
+		DependencyIndexes: file_proxy_masque_config_proto_depIdxs,
+		MessageInfos:      file_proxy_masque_config_proto_msgTypes,
+	}.Build()
+	File_proxy_masque_config_proto = out.File
+	file_proxy_masque_config_proto_goTypes = nil
+	file_proxy_masque_config_proto_depIdxs = nil
+}

proxy/masque/config.proto

@@ -0,0 +1,14 @@
+syntax = "proto3";
+
+package xray.proxy.masque;
+option csharp_namespace = "Xray.Proxy.Masque";
+option go_package = "github.com/xtls/xray-core/proxy/masque";
+option java_package = "com.xray.proxy.masque";
+option java_multiple_files = true;
+
+import "common/protocol/server_spec.proto";
+
+message ClientConfig {
+  xray.common.protocol.ServerEndpoint server = 1;
+  repeated string remote_dns = 2;
+}

proxy/wireguard/client.go

@@ -199,9 +199,9 @@ func (h *Handler) Process(ctx context.Context, link *transport.Link, dialer inte
 			return errors.New("failed to create UDP connection").Base(err)
 		}
 		defer conn.Close()
-		c := &udpConnClient{
+		c := &UDPConnClient{
 			PacketConn: conn.(*internet.PacketConnWrapper).PacketConn,
-			dest:       conn.RemoteAddr().(*net.UDPAddr),
+			Dest:       conn.RemoteAddr().(*net.UDPAddr),
 		}
 		reader = c
 		writer = c
@@ -336,6 +336,9 @@ func (h *Handler) init(ctx context.Context) error {
 }
 
 func (h *Handler) resolveLocal(host string) (net.IP, error) {
+	if ip := net.ParseIP(host); ip != nil {
+		return ip, nil
+	}
 	ips, _, err := h.dns.LookupIP(host, dns.IPOption{IPv4Enable: true, IPv6Enable: true})
 	if err != nil {
 		return nil, err
@@ -375,12 +378,12 @@ func (h *Handler) resolveLocal(host string) (net.IP, error) {
 	return got[dice.Roll(len(got))], nil
 }
 
-type udpConnClient struct {
+type UDPConnClient struct {
 	net.PacketConn
-	dest *net.UDPAddr
+	Dest *net.UDPAddr
 }
 
-func (c *udpConnClient) ReadMultiBuffer() (buf.MultiBuffer, error) {
+func (c *UDPConnClient) ReadMultiBuffer() (buf.MultiBuffer, error) {
 	b := buf.New()
 	b.Resize(0, buf.Size)
 	n, addr, err := c.PacketConn.ReadFrom(b.Bytes())
@@ -399,9 +402,9 @@ func (c *udpConnClient) ReadMultiBuffer() (buf.MultiBuffer, error) {
 	return buf.MultiBuffer{b}, nil
 }
 
-func (c *udpConnClient) WriteMultiBuffer(mb buf.MultiBuffer) error {
+func (c *UDPConnClient) WriteMultiBuffer(mb buf.MultiBuffer) error {
 	for i, b := range mb {
-		dst := c.dest
+		dst := c.Dest
 		if b.UDP != nil {
 			if b.UDP.Address.Family().IsDomain() {
 				if b.UDP.Port != net.Port(dst.Port) {
@@ -459,20 +462,27 @@ func (c *cache) run() {
 		return
 	}
 	c.running = true
-	c.m = make(map[string]entry)
+	if c.m == nil {
+		c.m = make(map[string]entry)
+	}
 	go c.gc()
 }
 
 func (c *cache) gc() {
 	ticker := time.NewTicker(time.Minute)
-	for {
-		now := <-ticker.C
+	defer ticker.Stop()
+	for now := range ticker.C {
 		c.mu.Lock()
 		for key, entry := range c.m {
 			if now.After(entry.deadline) {
 				delete(c.m, key)
 			}
 		}
+		if len(c.m) == 0 {
+			c.running = false
+			c.mu.Unlock()
+			return
+		}
 		c.mu.Unlock()
 	}
 }

proxy/wireguard/netstack.go

@@ -136,6 +136,7 @@ func (tun *netTun) Read(buf [][]byte, sizes []int, offset int) (int, error) {
 	}
 
 	n, err := view.Read(buf[0][offset:])
+	view.Release()
 	if err != nil {
 		return 0, err
 	}
@@ -175,6 +176,7 @@ func (tun *netTun) WriteNotify() {
 	select {
 	case tun.incomingPacket <- view:
 	case <-tun.closed:
+		view.Release()
 	}
 }
 

testing/scenarios/masque_test.go

@@ -0,0 +1,275 @@
+package scenarios
+
+import (
+	"context"
+	gotls "crypto/tls"
+	"crypto/x509"
+	go_errors "errors"
+	"io"
+	"net/http"
+	"net/netip"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/apernet/quic-go"
+	"github.com/apernet/quic-go/http3"
+	"golang.org/x/sync/errgroup"
+	"gvisor.dev/gvisor/pkg/tcpip"
+	"gvisor.dev/gvisor/pkg/tcpip/adapters/gonet"
+	"gvisor.dev/gvisor/pkg/tcpip/network/ipv4"
+	"gvisor.dev/gvisor/pkg/tcpip/network/ipv6"
+
+	"github.com/xtls/xray-core/app/log"
+	"github.com/xtls/xray-core/app/proxyman"
+	"github.com/xtls/xray-core/common"
+	clog "github.com/xtls/xray-core/common/log"
+	"github.com/xtls/xray-core/common/net"
+	"github.com/xtls/xray-core/common/protocol"
+	"github.com/xtls/xray-core/common/protocol/tls/cert"
+	"github.com/xtls/xray-core/common/serial"
+	core "github.com/xtls/xray-core/core"
+	"github.com/xtls/xray-core/proxy/dokodemo"
+	"github.com/xtls/xray-core/proxy/masque"
+	"github.com/xtls/xray-core/proxy/wireguard"
+	"github.com/xtls/xray-core/testing/servers/tcp"
+	"github.com/xtls/xray-core/testing/servers/udp"
+	"github.com/xtls/xray-core/transport/internet"
+	transmasque "github.com/xtls/xray-core/transport/internet/masque"
+	"github.com/xtls/xray-core/transport/internet/masque/connectip"
+	"github.com/xtls/xray-core/transport/internet/tls"
+)
+
+var (
+	masqueServerV4 = netip.MustParseAddr("10.13.0.1")
+	masqueServerV6 = netip.MustParseAddr("fd13::1")
+	masqueClientV4 = netip.MustParsePrefix("10.13.0.2/32")
+	masqueClientV6 = netip.MustParsePrefix("fd13::2/128")
+)
+
+const (
+	masqueEchoPort      = 7
+	masqueAuthorization = "Basic dTpw"
+)
+
+func startMasqueServer(t *testing.T) (net.Port, [32]byte) {
+	dev, _, gstack, err := wireguard.CreateNetTUN([]netip.Addr{masqueServerV4, masqueServerV6}, nil, transmasque.MinPacketSize, false)
+	common.Must(err)
+	t.Cleanup(func() { dev.Close() })
+
+	for _, addr := range []netip.Addr{masqueServerV4, masqueServerV6} {
+		proto := ipv4.ProtocolNumber
+		if addr.Is6() {
+			proto = ipv6.ProtocolNumber
+		}
+		local := tcpip.FullAddress{NIC: 1, Addr: tcpip.AddrFromSlice(addr.AsSlice()), Port: masqueEchoPort}
+		l, err := gonet.ListenTCP(gstack, local, proto)
+		common.Must(err)
+		go func() {
+			for {
+				c, err := l.Accept()
+				if err != nil {
+					return
+				}
+				go func() {
+					defer c.Close()
+					b := make([]byte, 2048)
+					for {
+						n, err := c.Read(b)
+						if err != nil {
+							return
+						}
+						if _, err := c.Write(xor(b[:n])); err != nil {
+							return
+						}
+					}
+				}()
+			}
+		}()
+		u, err := gonet.DialUDP(gstack, &local, nil, proto)
+		common.Must(err)
+		go func() {
+			b := make([]byte, 2048)
+			for {
+				n, addr, err := u.ReadFrom(b)
+				if err != nil {
+					return
+				}
+				u.WriteTo(xor(b[:n]), addr)
+			}
+		}()
+	}
+
+	var current atomic.Pointer[connectip.Conn]
+	go func() {
+		bufs := [][]byte{make([]byte, transmasque.MinPacketSize)}
+		sizes := []int{0}
+		for {
+			if _, err := dev.Read(bufs, sizes, 0); err != nil {
+				return
+			}
+			if conn := current.Load(); conn != nil {
+				if icmp, _ := conn.WritePacket(bufs[0][:sizes[0]]); len(icmp) > 0 {
+					go dev.Write([][]byte{icmp}, 0)
+				}
+			}
+		}
+	}()
+
+	handler := func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path != transmasque.DefaultPath {
+			w.WriteHeader(http.StatusNotFound)
+			return
+		}
+		if r.Header.Get("Authorization") != masqueAuthorization {
+			w.WriteHeader(http.StatusUnauthorized)
+			return
+		}
+		req, err := connectip.ParseProxyRequest(r)
+		if err != nil {
+			var perr *connectip.ProxyRequestParseError
+			if go_errors.As(err, &perr) {
+				w.WriteHeader(perr.HTTPStatus)
+			}
+			return
+		}
+		conn, err := (&connectip.Proxy{}).Proxy(w, req)
+		if err != nil {
+			return
+		}
+		defer conn.Close()
+		common.Must(conn.AssignAddresses([]netip.Prefix{masqueClientV4, masqueClientV6}))
+		common.Must(conn.AdvertiseRoute([]connectip.IPRoute{
+			{StartIP: netip.IPv4Unspecified(), EndIP: netip.AddrFrom4([4]byte{255, 255, 255, 255})},
+			{StartIP: netip.IPv6Unspecified(), EndIP: netip.AddrFrom16([16]byte{0: 0xff, 1: 0xff, 2: 0xff, 3: 0xff, 4: 0xff, 5: 0xff, 6: 0xff, 7: 0xff, 8: 0xff, 9: 0xff, 10: 0xff, 11: 0xff, 12: 0xff, 13: 0xff, 14: 0xff, 15: 0xff})},
+		}))
+		go func() {
+			for {
+				ar, err := conn.ReceiveAddressRequest(context.Background())
+				if err != nil {
+					return
+				}
+				assigned := make([]netip.Prefix, len(ar.Prefixes))
+				for i, p := range ar.Prefixes {
+					if p.Addr().Is4() {
+						assigned[i] = masqueClientV4
+					} else {
+						assigned[i] = masqueClientV6
+					}
+				}
+				ar.Respond(assigned, nil)
+			}
+		}()
+		current.Store(conn)
+		b := make([]byte, 2048)
+		for {
+			n, err := conn.ReadPacket(b)
+			if err != nil {
+				if go_errors.Is(err, io.ErrShortBuffer) {
+					continue
+				}
+				return
+			}
+			dev.Write([][]byte{b[:n]}, 0)
+		}
+	}
+
+	certificate, certHash := cert.MustGenerate(nil, cert.CommonName("localhost"))
+	key := common.Must2(x509.ParsePKCS8PrivateKey(certificate.PrivateKey))
+	tlsConfig := &gotls.Config{
+		Certificates: []gotls.Certificate{{Certificate: [][]byte{certificate.Certificate}, PrivateKey: key}},
+		NextProtos:   []string{http3.NextProtoH3},
+	}
+	pktConn := common.Must2(net.ListenUDP("udp", &net.UDPAddr{IP: net.LocalHostIP.IP()}))
+	tr := &quic.Transport{Conn: pktConn}
+	ln := common.Must2(tr.ListenEarly(tlsConfig, &quic.Config{EnableDatagrams: true, InitialPacketSize: 1350}))
+	server := &http3.Server{Handler: http.HandlerFunc(handler), EnableDatagrams: true}
+	go server.ServeListener(ln)
+	t.Cleanup(func() {
+		server.Close()
+		ln.Close()
+		tr.Close()
+		pktConn.Close()
+	})
+
+	return net.Port(pktConn.LocalAddr().(*net.UDPAddr).Port), certHash
+}
+
+func TestMasque(t *testing.T) {
+	serverPort, certHash := startMasqueServer(t)
+
+	tcpPort := tcp.PickPort()
+	tcp6Port := tcp.PickPort()
+	udpPort := udp.PickPort()
+	dokodemoTo := func(port net.Port, addr netip.Addr, network net.Network) *core.InboundHandlerConfig {
+		return &core.InboundHandlerConfig{
+			ReceiverSettings: serial.ToTypedMessage(&proxyman.ReceiverConfig{
+				PortList: &net.PortList{Range: []*net.PortRange{net.SinglePortRange(port)}},
+				Listen:   net.NewIPOrDomain(net.LocalHostIP),
+			}),
+			ProxySettings: serial.ToTypedMessage(&dokodemo.Config{
+				RewriteAddress:  net.NewIPOrDomain(net.IPAddress(addr.AsSlice())),
+				RewritePort:     masqueEchoPort,
+				AllowedNetworks: []net.Network{network},
+			}),
+		}
+	}
+	clientConfig := &core.Config{
+		App: []*serial.TypedMessage{
+			serial.ToTypedMessage(&log.Config{
+				ErrorLogLevel: clog.Severity_Debug,
+				ErrorLogType:  log.LogType_Console,
+			}),
+		},
+		Inbound: []*core.InboundHandlerConfig{
+			dokodemoTo(tcpPort, masqueServerV4, net.Network_TCP),
+			dokodemoTo(tcp6Port, masqueServerV6, net.Network_TCP),
+			dokodemoTo(udpPort, masqueServerV4, net.Network_UDP),
+		},
+		Outbound: []*core.OutboundHandlerConfig{
+			{
+				ProxySettings: serial.ToTypedMessage(&masque.ClientConfig{
+					Server: &protocol.ServerEndpoint{
+						Address: net.NewIPOrDomain(net.LocalHostIP),
+						Port:    uint32(serverPort),
+					},
+				}),
+				SenderSettings: serial.ToTypedMessage(&proxyman.SenderConfig{
+					StreamSettings: &internet.StreamConfig{
+						ProtocolName: "masque",
+						TransportSettings: []*internet.TransportConfig{
+							{
+								ProtocolName: "masque",
+								Settings: serial.ToTypedMessage(&transmasque.Config{
+									Path:    transmasque.DefaultPath,
+									Headers: map[string]string{"Authorization": masqueAuthorization},
+								}),
+							},
+						},
+						SecurityType: serial.GetMessageType(&tls.Config{}),
+						SecuritySettings: []*serial.TypedMessage{
+							serial.ToTypedMessage(&tls.Config{
+								ServerName:           "localhost",
+								PinnedPeerCertSha256: [][]byte{certHash[:]},
+							}),
+						},
+					},
+				}),
+			},
+		},
+	}
+
+	servers, err := InitializeServerConfigs(clientConfig)
+	common.Must(err)
+	defer CloseAllServers(servers)
+
+	var errg errgroup.Group
+	for range 3 {
+		errg.Go(testTCPConn(tcpPort, 1024*1024, time.Second*20))
+	}
+	errg.Go(testTCPConn(tcp6Port, 1024*1024, time.Second*20))
+	errg.Go(testUDPConn(udpPort, 1024, time.Second*5))
+	if err := errg.Wait(); err != nil {
+		t.Error(err)
+	}
+}

transport/internet/masque/config.go

@@ -0,0 +1,18 @@
+package masque
+
+import (
+	"github.com/xtls/xray-core/common"
+	"github.com/xtls/xray-core/transport/internet"
+)
+
+const protocolName = "masque"
+
+const DefaultPath = "/.well-known/masque/ip/*/*/"
+
+func init() {
+	common.Must(internet.RegisterProtocolConfigCreator(protocolName, func() interface{} {
+		return &Config{
+			Path: DefaultPath,
+		}
+	}))
+}

transport/internet/masque/config.pb.go

@@ -0,0 +1,146 @@
+// Code generated by protoc-gen-go. DO NOT EDIT.
+// versions:
+// 	protoc-gen-go v1.36.11
+// 	protoc        v6.33.5
+// source: transport/internet/masque/config.proto
+
+package masque
+
+import (
+	protoreflect "google.golang.org/protobuf/reflect/protoreflect"
+	protoimpl "google.golang.org/protobuf/runtime/protoimpl"
+	reflect "reflect"
+	sync "sync"
+	unsafe "unsafe"
+)
+
+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)
+)
+
+type Config struct {
+	state         protoimpl.MessageState `protogen:"open.v1"`
+	Host          string                 `protobuf:"bytes,1,opt,name=host,proto3" json:"host,omitempty"`
+	Path          string                 `protobuf:"bytes,2,opt,name=path,proto3" json:"path,omitempty"`
+	Headers       map[string]string      `protobuf:"bytes,3,rep,name=headers,proto3" json:"headers,omitempty" protobuf_key:"bytes,1,opt,name=key" protobuf_val:"bytes,2,opt,name=value"`
+	unknownFields protoimpl.UnknownFields
+	sizeCache     protoimpl.SizeCache
+}
+
+func (x *Config) Reset() {
+	*x = Config{}
+	mi := &file_transport_internet_masque_config_proto_msgTypes[0]
+	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+	ms.StoreMessageInfo(mi)
+}
+
+func (x *Config) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*Config) ProtoMessage() {}
+
+func (x *Config) ProtoReflect() protoreflect.Message {
+	mi := &file_transport_internet_masque_config_proto_msgTypes[0]
+	if x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use Config.ProtoReflect.Descriptor instead.
+func (*Config) Descriptor() ([]byte, []int) {
+	return file_transport_internet_masque_config_proto_rawDescGZIP(), []int{0}
+}
+
+func (x *Config) GetHost() string {
+	if x != nil {
+		return x.Host
+	}
+	return ""
+}
+
+func (x *Config) GetPath() string {
+	if x != nil {
+		return x.Path
+	}
+	return ""
+}
+
+func (x *Config) GetHeaders() map[string]string {
+	if x != nil {
+		return x.Headers
+	}
+	return nil
+}
+
+var File_transport_internet_masque_config_proto protoreflect.FileDescriptor
+
+const file_transport_internet_masque_config_proto_rawDesc = "" +
+	"\n" +
+	"&transport/internet/masque/config.proto\x12\x1exray.transport.internet.masque\"\xbb\x01\n" +
+	"\x06Config\x12\x12\n" +
+	"\x04host\x18\x01 \x01(\tR\x04host\x12\x12\n" +
+	"\x04path\x18\x02 \x01(\tR\x04path\x12M\n" +
+	"\aheaders\x18\x03 \x03(\v23.xray.transport.internet.masque.Config.HeadersEntryR\aheaders\x1a:\n" +
+	"\fHeadersEntry\x12\x10\n" +
+	"\x03key\x18\x01 \x01(\tR\x03key\x12\x14\n" +
+	"\x05value\x18\x02 \x01(\tR\x05value:\x028\x01B|\n" +
+	"\"com.xray.transport.internet.masqueP\x01Z3github.com/xtls/xray-core/transport/internet/masque\xaa\x02\x1eXray.Transport.Internet.Masqueb\x06proto3"
+
+var (
+	file_transport_internet_masque_config_proto_rawDescOnce sync.Once
+	file_transport_internet_masque_config_proto_rawDescData []byte
+)
+
+func file_transport_internet_masque_config_proto_rawDescGZIP() []byte {
+	file_transport_internet_masque_config_proto_rawDescOnce.Do(func() {
+		file_transport_internet_masque_config_proto_rawDescData = protoimpl.X.CompressGZIP(unsafe.Slice(unsafe.StringData(file_transport_internet_masque_config_proto_rawDesc), len(file_transport_internet_masque_config_proto_rawDesc)))
+	})
+	return file_transport_internet_masque_config_proto_rawDescData
+}
+
+var file_transport_internet_masque_config_proto_msgTypes = make([]protoimpl.MessageInfo, 2)
+var file_transport_internet_masque_config_proto_goTypes = []any{
+	(*Config)(nil), // 0: xray.transport.internet.masque.Config
+	nil,            // 1: xray.transport.internet.masque.Config.HeadersEntry
+}
+var file_transport_internet_masque_config_proto_depIdxs = []int32{
+	1, // 0: xray.transport.internet.masque.Config.headers:type_name -> xray.transport.internet.masque.Config.HeadersEntry
+	1, // [1:1] is the sub-list for method output_type
+	1, // [1:1] is the sub-list for method input_type
+	1, // [1:1] is the sub-list for extension type_name
+	1, // [1:1] is the sub-list for extension extendee
+	0, // [0:1] is the sub-list for field type_name
+}
+
+func init() { file_transport_internet_masque_config_proto_init() }
+func file_transport_internet_masque_config_proto_init() {
+	if File_transport_internet_masque_config_proto != nil {
+		return
+	}
+	type x struct{}
+	out := protoimpl.TypeBuilder{
+		File: protoimpl.DescBuilder{
+			GoPackagePath: reflect.TypeOf(x{}).PkgPath(),
+			RawDescriptor: unsafe.Slice(unsafe.StringData(file_transport_internet_masque_config_proto_rawDesc), len(file_transport_internet_masque_config_proto_rawDesc)),
+			NumEnums:      0,
+			NumMessages:   2,
+			NumExtensions: 0,
+			NumServices:   0,
+		},
+		GoTypes:           file_transport_internet_masque_config_proto_goTypes,
+		DependencyIndexes: file_transport_internet_masque_config_proto_depIdxs,
+		MessageInfos:      file_transport_internet_masque_config_proto_msgTypes,
+	}.Build()
+	File_transport_internet_masque_config_proto = out.File
+	file_transport_internet_masque_config_proto_goTypes = nil
+	file_transport_internet_masque_config_proto_depIdxs = nil
+}

transport/internet/masque/config.proto

@@ -0,0 +1,13 @@
+syntax = "proto3";
+
+package xray.transport.internet.masque;
+option csharp_namespace = "Xray.Transport.Internet.Masque";
+option go_package = "github.com/xtls/xray-core/transport/internet/masque";
+option java_package = "com.xray.transport.internet.masque";
+option java_multiple_files = true;
+
+message Config {
+  string host = 1;
+  string path = 2;
+  map<string, string> headers = 3;
+}

transport/internet/masque/conn.go

@@ -0,0 +1,115 @@
+package masque
+
+import (
+	"context"
+	go_errors "errors"
+	"net/netip"
+	"slices"
+	"sync"
+	"time"
+
+	"github.com/apernet/quic-go"
+	"github.com/apernet/quic-go/http3"
+	"github.com/xtls/xray-core/common/errors"
+	"github.com/xtls/xray-core/common/net"
+	"github.com/xtls/xray-core/transport/internet/masque/connectip"
+)
+
+type PacketTooBigError struct {
+	ICMP []byte
+}
+
+func (e *PacketTooBigError) Error() string {
+	return "packet too big for the tunnel"
+}
+
+type Conn struct {
+	ipConn    *connectip.Conn
+	quicConn  *quic.Conn
+	local     []netip.Addr
+	closeOnce sync.Once
+}
+
+func (c *Conn) LocalAddrs() []netip.Addr {
+	return c.local
+}
+
+func (c *Conn) Read(b []byte) (int, error) {
+	return c.ipConn.ReadPacket(b)
+}
+
+func (c *Conn) Write(b []byte) (int, error) {
+	icmp, err := c.ipConn.WritePacket(b)
+	if err != nil {
+		if go_errors.Is(err, connectip.ErrMTUTooSmall) {
+			errors.LogWarning(context.Background(), "MASQUE: closing the tunnel as it cannot carry ", MinPacketSize, "-byte packets")
+		} else {
+			errors.LogInfoInner(context.Background(), err, "MASQUE: closing the tunnel as sending failed")
+		}
+		c.Close()
+		return 0, err
+	}
+	if len(icmp) > 0 {
+		return 0, &PacketTooBigError{ICMP: icmp}
+	}
+	return len(b), nil
+}
+
+func (c *Conn) Close() error {
+	c.closeOnce.Do(func() {
+		c.ipConn.Close()
+		c.quicConn.CloseWithError(quic.ApplicationErrorCode(http3.ErrCodeNoError), "")
+	})
+	return nil
+}
+
+func (c *Conn) LocalAddr() net.Addr {
+	return c.quicConn.LocalAddr()
+}
+
+func (c *Conn) RemoteAddr() net.Addr {
+	return c.quicConn.RemoteAddr()
+}
+
+func (c *Conn) SetDeadline(time.Time) error {
+	return nil
+}
+
+func (c *Conn) SetReadDeadline(time.Time) error {
+	return nil
+}
+
+func (c *Conn) SetWriteDeadline(time.Time) error {
+	return nil
+}
+
+func (c *Conn) serveAddressAssignments() {
+	for {
+		assigned, err := c.ipConn.ReceiveAddressAssignment(context.Background())
+		if err != nil {
+			return
+		}
+		for _, addr := range c.local {
+			if !slices.ContainsFunc(assigned, func(a connectip.AssignedAddress) bool { return !a.Rejected() && a.IPPrefix.Contains(addr) }) {
+				errors.LogInfo(context.Background(), "MASQUE: closing the tunnel as the proxy withdrew ", addr)
+				c.Close()
+				return
+			}
+		}
+		if len(localAddrs(assigned)) > len(c.local) {
+			errors.LogInfo(context.Background(), "MASQUE: the proxy assigned another IP family, which is used once the tunnel is set up again")
+		}
+	}
+}
+
+func (c *Conn) serveAddressRequests() {
+	for {
+		req, err := c.ipConn.ReceiveAddressRequest(context.Background())
+		if err != nil {
+			return
+		}
+		if err := req.Respond(make([]netip.Prefix, len(req.Prefixes)), nil); err != nil {
+			return
+		}
+	}
+}

transport/internet/masque/connectip/LICENSE

@@ -0,0 +1,7 @@
+Copyright 2024 Marten Seemann
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

transport/internet/masque/connectip/address.go

@@ -0,0 +1,86 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright 2024 Marten Seemann
+ * Adapted from github.com/quic-go/connect-ip-go (commit a0c35fa).
+ */
+
+package connectip
+
+import (
+	"errors"
+	"fmt"
+	"net/netip"
+	"slices"
+	"sync/atomic"
+)
+
+var (
+	rejectedIPv4Prefix = netip.PrefixFrom(netip.IPv4Unspecified(), 32)
+	rejectedIPv6Prefix = netip.PrefixFrom(netip.IPv6Unspecified(), 128)
+)
+
+type AddressRequestID uint64
+
+type AddressRequest struct {
+	Prefixes []netip.Prefix
+
+	conn      *Conn
+	requested *addressRequestCapsule
+	responded *atomic.Bool
+}
+
+func newAddressRequest(conn *Conn, requested *addressRequestCapsule) *AddressRequest {
+	return &AddressRequest{
+		Prefixes:  slices.Clone(requested.Prefixes),
+		conn:      conn,
+		requested: requested,
+		responded: &atomic.Bool{},
+	}
+}
+
+func (r *AddressRequest) Respond(assignments, additional []netip.Prefix) error {
+	if r.conn == nil {
+		return errors.New("connect-ip: invalid address request")
+	}
+	if len(assignments) != len(r.requested.RequestIDs) {
+		return fmt.Errorf(
+			"connect-ip: expected %d address assignments, got %d",
+			len(r.requested.RequestIDs),
+			len(assignments),
+		)
+	}
+	capsule := &addressAssignCapsule{
+		AssignedAddresses: make([]AssignedAddress, 0, len(assignments)+len(additional)),
+	}
+	var zeroPrefix netip.Prefix
+	for i, p := range assignments {
+		if p == zeroPrefix {
+			if r.requested.Prefixes[i].Addr().Is4() {
+				p = rejectedIPv4Prefix
+			} else {
+				p = rejectedIPv6Prefix
+			}
+		} else if !p.IsValid() || p != p.Masked() {
+			return fmt.Errorf("connect-ip: invalid assigned prefix %d: %s", i, p)
+		}
+		capsule.AssignedAddresses = append(
+			capsule.AssignedAddresses,
+			AssignedAddress{RequestID: r.requested.RequestIDs[i], IPPrefix: p},
+		)
+	}
+	for i, p := range additional {
+		if !p.IsValid() || p != p.Masked() {
+			return fmt.Errorf("connect-ip: invalid additional prefix %d: %s", i, p)
+		}
+		capsule.AssignedAddresses = append(capsule.AssignedAddresses, AssignedAddress{IPPrefix: p})
+	}
+	if !r.responded.CompareAndSwap(false, true) {
+		return errors.New("connect-ip: address request already answered")
+	}
+	restrictPeer := slices.ContainsFunc(capsule.AssignedAddresses, func(a AssignedAddress) bool { return !a.Rejected() })
+	if err := r.conn.sendAddressAssignment(capsule, restrictPeer); err != nil {
+		r.responded.Store(false)
+		return err
+	}
+	return nil
+}

transport/internet/masque/connectip/address_test.go

@@ -0,0 +1,85 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright 2024 Marten Seemann
+ * Adapted from github.com/quic-go/connect-ip-go (commit a0c35fa).
+ */
+
+package connectip
+
+import (
+	"context"
+	"net/netip"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestAddressRequests(t *testing.T) {
+	client, server := setupConns(t)
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second)
+	defer cancel()
+	prefixes := []netip.Prefix{
+		netip.MustParsePrefix("0.0.0.0/32"),
+		netip.MustParsePrefix("0.0.0.0/32"),
+		netip.MustParsePrefix("::/64"),
+	}
+	ids, err := client.RequestAddresses(prefixes)
+	require.NoError(t, err)
+	require.Equal(t, []AddressRequestID{1, 2, 3}, ids)
+	req, err := server.ReceiveAddressRequest(ctx)
+	require.NoError(t, err)
+	require.Equal(t, prefixes, req.Prefixes)
+
+	assignments := []netip.Prefix{netip.MustParsePrefix("192.0.2.1/32"), {}, {}}
+	additional := []netip.Prefix{netip.MustParsePrefix("2001:db8::/64")}
+	require.NoError(t, req.Respond(assignments, additional))
+	received, err := client.ReceiveAddressAssignment(ctx)
+	require.NoError(t, err)
+	require.Len(t, received, 4)
+	require.Equal(t, AssignedAddress{RequestID: ids[0], IPPrefix: assignments[0]}, received[0])
+	require.Equal(t, ids[1], received[1].RequestID)
+	require.True(t, received[1].Rejected())
+	require.Equal(t, ids[2], received[2].RequestID)
+	require.True(t, received[2].Rejected())
+	require.Equal(t, AssignedAddress{IPPrefix: additional[0]}, received[3])
+
+	ids, err = client.RequestAddresses(prefixes[:1])
+	require.NoError(t, err)
+	require.Equal(t, []AddressRequestID{4}, ids)
+}
+
+func TestAddressRequestValidation(t *testing.T) {
+	conn := newProxiedConn(&mockStream{})
+	defer conn.Close()
+
+	for _, prefixes := range [][]netip.Prefix{
+		nil,
+		{{}},
+		{netip.MustParsePrefix("192.0.2.1/24")},
+		{netip.MustParsePrefix("2001:db8::1/64")},
+	} {
+		ids, err := conn.RequestAddresses(prefixes)
+		require.Error(t, err)
+		require.Nil(t, ids)
+	}
+}
+
+func TestAddressResponseValidation(t *testing.T) {
+	conn := newProxiedConn(&mockStream{})
+	defer conn.Close()
+
+	prefixes := []netip.Prefix{netip.MustParsePrefix("192.0.2.1/32")}
+	req := newAddressRequest(conn, &addressRequestCapsule{RequestIDs: []AddressRequestID{1}, Prefixes: prefixes})
+	require.ErrorContains(t, (&AddressRequest{}).Respond(nil, nil), "invalid address request")
+	require.ErrorContains(t, req.Respond(nil, nil), "expected 1 address assignments")
+	require.ErrorContains(t, req.Respond(prefixes, []netip.Prefix{{}}), "invalid additional prefix")
+	require.ErrorContains(t,
+		req.Respond([]netip.Prefix{netip.MustParsePrefix("192.0.2.1/24")}, nil),
+		"invalid assigned prefix",
+	)
+
+	copied := *req
+	require.NoError(t, req.Respond(prefixes, nil))
+	require.ErrorContains(t, copied.Respond(prefixes, nil), "already answered")
+}

transport/internet/masque/connectip/capsule.go

@@ -0,0 +1,308 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright 2024 Marten Seemann
+ * Adapted from github.com/quic-go/connect-ip-go (commit a0c35fa).
+ */
+
+package connectip
+
+import (
+	"cmp"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"io"
+	"net/netip"
+
+	"github.com/apernet/quic-go/http3"
+	"github.com/apernet/quic-go/quicvarint"
+)
+
+const (
+	capsuleTypeDatagram           http3.CapsuleType = 0
+	capsuleTypeAddressAssign      http3.CapsuleType = 1
+	capsuleTypeAddressRequest     http3.CapsuleType = 2
+	capsuleTypeRouteAdvertisement http3.CapsuleType = 3
+)
+
+const (
+	maxAddressesPerCapsule = 8192
+	maxRoutesPerCapsule    = 8192
+)
+
+type addressAssignCapsule struct {
+	AssignedAddresses []AssignedAddress
+}
+
+type AssignedAddress struct {
+	RequestID AddressRequestID
+	IPPrefix  netip.Prefix
+}
+
+func (a AssignedAddress) Rejected() bool {
+	return a.IPPrefix == rejectedIPv4Prefix || a.IPPrefix == rejectedIPv6Prefix
+}
+
+func (a AssignedAddress) len() int {
+	return quicvarint.Len(uint64(a.RequestID)) + 1 + a.IPPrefix.Addr().BitLen()/8 + 1
+}
+
+type addressRequestCapsule struct {
+	RequestIDs []AddressRequestID
+	Prefixes   []netip.Prefix
+}
+
+func parseAddressAssignCapsule(r http3.CapsuleReader) (*addressAssignCapsule, error) {
+	var assignedAddresses []AssignedAddress
+	for r.Remaining() > 0 {
+		if len(assignedAddresses) >= maxAddressesPerCapsule {
+			return nil, fmt.Errorf("%w: ADDRESS_ASSIGN capsule contains too many addresses (maximum %d)", errCapsuleLimit, maxAddressesPerCapsule)
+		}
+		requestID, prefix, err := parseAddress(r)
+		if err != nil {
+			return nil, err
+		}
+		assignedAddresses = append(assignedAddresses, AssignedAddress{RequestID: AddressRequestID(requestID), IPPrefix: prefix})
+	}
+	return &addressAssignCapsule{AssignedAddresses: assignedAddresses}, nil
+}
+
+func (c *addressAssignCapsule) append(b []byte) []byte {
+	totalLen := 0
+	for _, addr := range c.AssignedAddresses {
+		totalLen += addr.len()
+	}
+
+	b = quicvarint.Append(b, uint64(capsuleTypeAddressAssign))
+	b = quicvarint.Append(b, uint64(totalLen))
+
+	for _, addr := range c.AssignedAddresses {
+		b = quicvarint.Append(b, uint64(addr.RequestID))
+		if addr.IPPrefix.Addr().Is4() {
+			b = append(b, 4)
+		} else {
+			b = append(b, 6)
+		}
+		b = append(b, addr.IPPrefix.Addr().AsSlice()...)
+		b = append(b, byte(addr.IPPrefix.Bits()))
+	}
+	return b
+}
+
+func parseAddressRequestCapsule(r http3.CapsuleReader) (*addressRequestCapsule, error) {
+	if r.Remaining() == 0 {
+		return nil, errors.New("ADDRESS_REQUEST capsule contains no addresses")
+	}
+	capsule := &addressRequestCapsule{}
+	for r.Remaining() > 0 {
+		if len(capsule.Prefixes) >= maxAddressesPerCapsule {
+			return nil, fmt.Errorf("%w: ADDRESS_REQUEST capsule contains too many addresses (maximum %d)", errCapsuleLimit, maxAddressesPerCapsule)
+		}
+		requestID, prefix, err := parseAddress(r)
+		if err != nil {
+			return nil, err
+		}
+		if requestID == 0 {
+			return nil, errors.New("ADDRESS_REQUEST capsule contains a zero request ID")
+		}
+		capsule.RequestIDs = append(capsule.RequestIDs, AddressRequestID(requestID))
+		capsule.Prefixes = append(capsule.Prefixes, prefix)
+	}
+	return capsule, nil
+}
+
+func (c *addressRequestCapsule) append(b []byte) []byte {
+	var totalLen int
+	for i, p := range c.Prefixes {
+		totalLen += quicvarint.Len(uint64(c.RequestIDs[i])) + 1 + p.Addr().BitLen()/8 + 1
+	}
+
+	b = quicvarint.Append(b, uint64(capsuleTypeAddressRequest))
+	b = quicvarint.Append(b, uint64(totalLen))
+
+	for i, p := range c.Prefixes {
+		b = quicvarint.Append(b, uint64(c.RequestIDs[i]))
+		if p.Addr().Is4() {
+			b = append(b, 4)
+		} else {
+			b = append(b, 6)
+		}
+		b = append(b, p.Addr().AsSlice()...)
+		b = append(b, byte(p.Bits()))
+	}
+	return b
+}
+
+func parseAddress(r io.Reader) (requestID uint64, prefix netip.Prefix, _ error) {
+	vr := quicvarint.NewReader(r)
+	requestID, err := quicvarint.Read(vr)
+	if err != nil {
+		return 0, netip.Prefix{}, err
+	}
+	ipVersion, err := vr.ReadByte()
+	if err != nil {
+		return 0, netip.Prefix{}, err
+	}
+	var ip netip.Addr
+	switch ipVersion {
+	case 4:
+		var ipv4 [4]byte
+		if _, err := io.ReadFull(r, ipv4[:]); err != nil {
+			return 0, netip.Prefix{}, err
+		}
+		ip = netip.AddrFrom4(ipv4)
+	case 6:
+		var ipv6 [16]byte
+		if _, err := io.ReadFull(r, ipv6[:]); err != nil {
+			return 0, netip.Prefix{}, err
+		}
+		ip = netip.AddrFrom16(ipv6)
+	default:
+		return 0, netip.Prefix{}, fmt.Errorf("invalid IP version: %d", ipVersion)
+	}
+	prefixLen, err := vr.ReadByte()
+	if err != nil {
+		return 0, netip.Prefix{}, err
+	}
+	if int(prefixLen) > ip.BitLen() {
+		return 0, netip.Prefix{}, fmt.Errorf("prefix length %d exceeds IP address length (%d)", prefixLen, ip.BitLen())
+	}
+	prefix = netip.PrefixFrom(ip, int(prefixLen))
+	if prefix != prefix.Masked() {
+		return 0, netip.Prefix{}, errors.New("lower bits not covered by prefix length are not all zero")
+	}
+	return requestID, prefix, nil
+}
+
+type routeAdvertisementCapsule struct {
+	IPAddressRanges []IPRoute
+}
+
+type IPRoute struct {
+	StartIP    netip.Addr
+	EndIP      netip.Addr
+	IPProtocol uint8
+}
+
+func (r IPRoute) len() int { return 1 + r.StartIP.BitLen()/8 + r.EndIP.BitLen()/8 + 1 }
+
+func (r IPRoute) Prefixes() []netip.Prefix { return rangeToPrefixes(r.StartIP, r.EndIP) }
+
+func parseRouteAdvertisementCapsule(r http3.CapsuleReader) (*routeAdvertisementCapsule, error) {
+	var ranges []IPRoute
+	for r.Remaining() > 0 {
+		if len(ranges) >= maxRoutesPerCapsule {
+			return nil, fmt.Errorf("%w: ROUTE_ADVERTISEMENT capsule contains too many routes (maximum %d)", errCapsuleLimit, maxRoutesPerCapsule)
+		}
+		ipRange, err := parseIPAddressRange(r)
+		if err != nil {
+			return nil, err
+		}
+		if len(ranges) > 0 {
+			if err := checkRouteOrder(ranges[len(ranges)-1], ipRange); err != nil {
+				return nil, err
+			}
+		}
+		ranges = append(ranges, ipRange)
+	}
+	return &routeAdvertisementCapsule{IPAddressRanges: ranges}, nil
+}
+
+func (r IPRoute) validate() error {
+	if !r.StartIP.IsValid() || !r.EndIP.IsValid() || r.StartIP.Zone() != "" || r.EndIP.Zone() != "" {
+		return fmt.Errorf("invalid IP address range %s-%s", r.StartIP, r.EndIP)
+	}
+	if r.StartIP.Is4() != r.EndIP.Is4() {
+		return fmt.Errorf("IP address range %s-%s mixes IP versions", r.StartIP, r.EndIP)
+	}
+	if r.StartIP.Compare(r.EndIP) > 0 {
+		return fmt.Errorf("start IP %s is greater than end IP %s", r.StartIP, r.EndIP)
+	}
+	return nil
+}
+
+func checkRouteOrder(a, b IPRoute) error {
+	switch cmp.Or(
+		cmp.Compare(a.StartIP.BitLen(), b.StartIP.BitLen()),
+		cmp.Compare(a.IPProtocol, b.IPProtocol),
+	) {
+	case 1:
+		return fmt.Errorf("routes are not ordered by IP version and IP protocol: %s-%s (protocol %d) precedes %s-%s (protocol %d)",
+			a.StartIP, a.EndIP, a.IPProtocol, b.StartIP, b.EndIP, b.IPProtocol)
+	case 0:
+		if a.EndIP.Compare(b.StartIP) >= 0 {
+			return fmt.Errorf("IP address ranges %s-%s and %s-%s (protocol %d) overlap or are not in ascending order",
+				a.StartIP, a.EndIP, b.StartIP, b.EndIP, b.IPProtocol)
+		}
+	}
+	return nil
+}
+
+func (c *routeAdvertisementCapsule) append(b []byte) []byte {
+	var totalLen int
+	for _, ipRange := range c.IPAddressRanges {
+		totalLen += ipRange.len()
+	}
+
+	b = quicvarint.Append(b, uint64(capsuleTypeRouteAdvertisement))
+	b = quicvarint.Append(b, uint64(totalLen))
+
+	for _, ipRange := range c.IPAddressRanges {
+		if ipRange.StartIP.Is4() {
+			b = append(b, 4)
+		} else {
+			b = append(b, 6)
+		}
+		b = append(b, ipRange.StartIP.AsSlice()...)
+		b = append(b, ipRange.EndIP.AsSlice()...)
+		b = append(b, ipRange.IPProtocol)
+	}
+	return b
+}
+
+func parseIPAddressRange(r io.Reader) (IPRoute, error) {
+	var ipVersion uint8
+	if err := binary.Read(r, binary.LittleEndian, &ipVersion); err != nil {
+		return IPRoute{}, err
+	}
+
+	var startIP, endIP netip.Addr
+	switch ipVersion {
+	case 4:
+		var start, end [4]byte
+		if _, err := io.ReadFull(r, start[:]); err != nil {
+			return IPRoute{}, err
+		}
+		if _, err := io.ReadFull(r, end[:]); err != nil {
+			return IPRoute{}, err
+		}
+		startIP = netip.AddrFrom4(start)
+		endIP = netip.AddrFrom4(end)
+	case 6:
+		var start, end [16]byte
+		if _, err := io.ReadFull(r, start[:]); err != nil {
+			return IPRoute{}, err
+		}
+		if _, err := io.ReadFull(r, end[:]); err != nil {
+			return IPRoute{}, err
+		}
+		startIP = netip.AddrFrom16(start)
+		endIP = netip.AddrFrom16(end)
+	default:
+		return IPRoute{}, fmt.Errorf("invalid IP version: %d", ipVersion)
+	}
+
+	if startIP.Compare(endIP) > 0 {
+		return IPRoute{}, errors.New("start IP is greater than end IP")
+	}
+
+	var ipProtocol uint8
+	if err := binary.Read(r, binary.LittleEndian, &ipProtocol); err != nil {
+		return IPRoute{}, err
+	}
+	return IPRoute{
+		StartIP:    startIP,
+		EndIP:      endIP,
+		IPProtocol: ipProtocol,
+	}, nil
+}

transport/internet/masque/connectip/capsule_test.go

@@ -0,0 +1,449 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright 2024 Marten Seemann
+ * Adapted from github.com/quic-go/connect-ip-go (commit a0c35fa).
+ */
+
+package connectip
+
+import (
+	"bytes"
+	"context"
+	"io"
+	"net"
+	"net/netip"
+	"testing"
+	"time"
+
+	"github.com/apernet/quic-go/http3"
+	"github.com/apernet/quic-go/quicvarint"
+	"github.com/stretchr/testify/require"
+)
+
+func newCapsuleReader(t *testing.T, typ http3.CapsuleType, payload []byte) http3.CapsuleReader {
+	t.Helper()
+
+	data := quicvarint.Append(nil, uint64(typ))
+	data = quicvarint.Append(data, uint64(len(payload)))
+	data = append(data, payload...)
+	parsedType, cr, err := http3.NewCapsuleParser(bytes.NewReader(data)).Next()
+	require.NoError(t, err)
+	require.Equal(t, typ, parsedType)
+	return cr
+}
+
+func testIncompleteCapsule(t *testing.T, data []byte, parse func(http3.CapsuleReader) error) {
+	t.Helper()
+
+	r := bytes.NewReader(data)
+	_, cr, err := http3.NewCapsuleParser(r).Next()
+	require.NoError(t, err)
+	require.NoError(t, parse(cr))
+	require.Zero(t, r.Len())
+	for i := range data {
+		_, cr, err := http3.NewCapsuleParser(bytes.NewReader(data[:i])).Next()
+		if err != nil {
+			if i == 0 {
+				require.ErrorIs(t, err, io.EOF)
+			} else {
+				require.ErrorIs(t, err, io.ErrUnexpectedEOF)
+			}
+			continue
+		}
+		require.ErrorIs(t, parse(cr), io.ErrUnexpectedEOF)
+	}
+}
+
+func testCapsuleEntryLimit[T any](t *testing.T, typ http3.CapsuleType, limit int, entry func(i int) []byte, parse func(http3.CapsuleReader) (*T, error)) {
+	t.Helper()
+	var payload []byte
+	for i := range limit {
+		payload = append(payload, entry(i)...)
+	}
+	r := newCapsuleReader(t, typ, payload)
+	_, err := parse(r)
+	require.NoError(t, err)
+	require.Zero(t, r.Remaining())
+
+	data := quicvarint.Append(nil, uint64(typ))
+	data = quicvarint.Append(data, uint64(len(payload)+1))
+	_, r, err = http3.NewCapsuleParser(bytes.NewReader(append(data, payload...))).Next()
+	require.NoError(t, err)
+	_, err = parse(r)
+	require.ErrorContains(t, err, "too many")
+	require.Equal(t, int64(1), r.Remaining())
+}
+
+func TestParseAddressAssignCapsule(t *testing.T) {
+	addr1 := quicvarint.Append(nil, 1337)
+	addr1 = append(addr1, 4)
+	addr1 = append(addr1, netip.AddrFrom4([4]byte{1, 2, 3, 0}).AsSlice()...)
+	addr1 = append(addr1, 24)
+	addr2 := quicvarint.Append(nil, 1338)
+	addr2 = append(addr2, 6)
+	addr2 = append(addr2, netip.MustParseAddr("2001:db8::1").AsSlice()...)
+	addr2 = append(addr2, 128)
+
+	data := quicvarint.Append(nil, uint64(capsuleTypeAddressAssign))
+	data = quicvarint.Append(data, uint64(len(addr1)+len(addr2)))
+	data = append(data, addr1...)
+	data = append(data, addr2...)
+
+	r := bytes.NewReader(data)
+	typ, cr, err := http3.NewCapsuleParser(r).Next()
+	require.NoError(t, err)
+	require.Equal(t, capsuleTypeAddressAssign, typ)
+	capsule, err := parseAddressAssignCapsule(cr)
+	require.NoError(t, err)
+	require.Equal(t,
+		[]AssignedAddress{
+			{RequestID: 1337, IPPrefix: netip.MustParsePrefix("1.2.3.0/24")},
+			{RequestID: 1338, IPPrefix: netip.MustParsePrefix("2001:db8::1/128")},
+		},
+		capsule.AssignedAddresses,
+	)
+	require.Zero(t, r.Len())
+}
+
+func TestParseAddressAssignCapsuleLimit(t *testing.T) {
+	entry := []byte{1, 4, 192, 0, 2, 1, 32}
+	testCapsuleEntryLimit(t, capsuleTypeAddressAssign, maxAddressesPerCapsule, func(int) []byte { return entry }, parseAddressAssignCapsule)
+}
+
+func TestAssignedAddressRejected(t *testing.T) {
+	for _, prefix := range []string{"0.0.0.0/32", "::/128"} {
+		require.True(t, (AssignedAddress{RequestID: 1, IPPrefix: netip.MustParsePrefix(prefix)}).Rejected())
+	}
+	for _, prefix := range []string{"0.0.0.0/0", "0.0.0.0/31", "::/0", "::/127", "192.0.2.1/32", "2001:db8::1/128"} {
+		require.False(t, (AssignedAddress{RequestID: 1, IPPrefix: netip.MustParsePrefix(prefix)}).Rejected())
+	}
+	require.False(t, (AssignedAddress{}).Rejected())
+}
+
+func TestWriteAddressAssignCapsule(t *testing.T) {
+	c := &addressAssignCapsule{
+		AssignedAddresses: []AssignedAddress{
+			{RequestID: 1337, IPPrefix: netip.MustParsePrefix("1.2.3.0/24")},
+			{RequestID: 1338, IPPrefix: netip.MustParsePrefix("2001:db8::1/128")},
+		},
+	}
+	data := c.append(nil)
+	r := bytes.NewReader(data)
+	typ, cr, err := http3.NewCapsuleParser(r).Next()
+	require.NoError(t, err)
+	require.Equal(t, capsuleTypeAddressAssign, typ)
+	parsed, err := parseAddressAssignCapsule(cr)
+	require.NoError(t, err)
+	require.Equal(t, c, parsed)
+	require.Zero(t, r.Len())
+}
+
+func TestParseAddressAssignCapsuleInvalid(t *testing.T) {
+	testParseAddressCapsuleInvalid(t, capsuleTypeAddressAssign, func(r http3.CapsuleReader) error {
+		_, err := parseAddressAssignCapsule(r)
+		return err
+	})
+}
+
+func testParseAddressCapsuleInvalid(t *testing.T, typ http3.CapsuleType, f func(r http3.CapsuleReader) error) {
+	t.Run("invalid IP version", func(t *testing.T) {
+		addr1 := quicvarint.Append(nil, 1337)
+		addr1 = append(addr1, 5)
+		addr1 = append(addr1, netip.AddrFrom4([4]byte{1, 2, 3, 4}).AsSlice()...)
+		addr1 = append(addr1, 32)
+		require.ErrorContains(t, f(newCapsuleReader(t, typ, addr1)), "invalid IP version: 5")
+	})
+
+	t.Run("invalid prefix length", func(t *testing.T) {
+		addr1 := quicvarint.Append(nil, 1337)
+		addr1 = append(addr1, 4)
+		addr1 = append(addr1, netip.AddrFrom4([4]byte{1, 2, 3, 4}).AsSlice()...)
+		addr1 = append(addr1, 33)
+		require.ErrorContains(t, f(newCapsuleReader(t, typ, addr1)), "prefix length 33 exceeds IP address length (32)")
+	})
+
+	t.Run("lower bits not covered by prefix length are not all zero", func(t *testing.T) {
+		addr1 := quicvarint.Append(nil, 1337)
+		addr1 = append(addr1, 4)
+		addr1 = append(addr1, netip.AddrFrom4([4]byte{1, 2, 3, 4}).AsSlice()...)
+		addr1 = append(addr1, 28)
+		require.ErrorContains(t, f(newCapsuleReader(t, typ, addr1)), "lower bits not covered by prefix length are not all zero")
+	})
+
+	t.Run("incomplete capsule", func(t *testing.T) {
+		var data []byte
+		switch typ {
+		case capsuleTypeAddressAssign:
+			data = (&addressAssignCapsule{
+				AssignedAddresses: []AssignedAddress{
+					{RequestID: 1337, IPPrefix: netip.MustParsePrefix("1.2.3.4/32")},
+					{RequestID: 1338, IPPrefix: netip.MustParsePrefix("2001:db8::1/128")},
+				},
+			}).append(nil)
+		case capsuleTypeAddressRequest:
+			data = (&addressRequestCapsule{
+				RequestIDs: []AddressRequestID{1337, 1338},
+				Prefixes:   []netip.Prefix{netip.MustParsePrefix("1.2.3.4/32"), netip.MustParsePrefix("2001:db8::1/128")},
+			}).append(nil)
+		default:
+			t.Fatalf("unexpected capsule type: %d", typ)
+		}
+
+		testIncompleteCapsule(t, data, f)
+	})
+}
+
+func TestParseAddressRequestCapsule(t *testing.T) {
+	addr1 := quicvarint.Append(nil, 1337)
+	addr1 = append(addr1, 4)
+	addr1 = append(addr1, netip.AddrFrom4([4]byte{1, 2, 3, 0}).AsSlice()...)
+	addr1 = append(addr1, 24)
+	addr2 := quicvarint.Append(nil, 1338)
+	addr2 = append(addr2, 6)
+	addr2 = append(addr2, netip.MustParseAddr("2001:db8::1").AsSlice()...)
+	addr2 = append(addr2, 128)
+	data := quicvarint.Append(nil, uint64(capsuleTypeAddressRequest))
+	data = quicvarint.Append(data, uint64(len(addr1)+len(addr2)))
+	data = append(data, addr1...)
+	data = append(data, addr2...)
+
+	r := bytes.NewReader(data)
+	typ, cr, err := http3.NewCapsuleParser(r).Next()
+	require.NoError(t, err)
+	require.Equal(t, capsuleTypeAddressRequest, typ)
+	capsule, err := parseAddressRequestCapsule(cr)
+	require.NoError(t, err)
+	require.Equal(t, []AddressRequestID{1337, 1338}, capsule.RequestIDs)
+	require.Equal(t, []netip.Prefix{netip.MustParsePrefix("1.2.3.0/24"), netip.MustParsePrefix("2001:db8::1/128")}, capsule.Prefixes)
+	require.Zero(t, r.Len())
+}
+
+func TestParseAddressRequestCapsuleLimit(t *testing.T) {
+	entry := []byte{1, 4, 192, 0, 2, 1, 32}
+	testCapsuleEntryLimit(t, capsuleTypeAddressRequest, maxAddressesPerCapsule, func(int) []byte { return entry }, parseAddressRequestCapsule)
+}
+
+func TestWriteAddressRequestCapsule(t *testing.T) {
+	c := &addressRequestCapsule{
+		RequestIDs: []AddressRequestID{1337, 1338},
+		Prefixes:   []netip.Prefix{netip.MustParsePrefix("1.2.3.0/24"), netip.MustParsePrefix("2001:db8::1/128")},
+	}
+	data := c.append(nil)
+	r := bytes.NewReader(data)
+	typ, cr, err := http3.NewCapsuleParser(r).Next()
+	require.NoError(t, err)
+	require.Equal(t, capsuleTypeAddressRequest, typ)
+	parsed, err := parseAddressRequestCapsule(cr)
+	require.NoError(t, err)
+	require.Equal(t, c, parsed)
+	require.Zero(t, r.Len())
+}
+
+func TestParseAddressRequestCapsuleInvalid(t *testing.T) {
+	t.Run("empty", func(t *testing.T) {
+		_, err := parseAddressRequestCapsule(newCapsuleReader(t, capsuleTypeAddressRequest, nil))
+		require.ErrorContains(t, err, "contains no addresses")
+	})
+	t.Run("zero request ID", func(t *testing.T) {
+		_, err := parseAddressRequestCapsule(newCapsuleReader(t, capsuleTypeAddressRequest, []byte{0, 4, 192, 0, 2, 1, 32}))
+		require.ErrorContains(t, err, "zero request ID")
+	})
+	testParseAddressCapsuleInvalid(t, capsuleTypeAddressRequest, func(r http3.CapsuleReader) error {
+		_, err := parseAddressRequestCapsule(r)
+		return err
+	})
+}
+
+func TestParseRouteAdvertisementCapsule(t *testing.T) {
+	iprange1 := []byte{4}
+	iprange1 = append(iprange1, netip.AddrFrom4([4]byte{1, 1, 1, 1}).AsSlice()...)
+	iprange1 = append(iprange1, netip.AddrFrom4([4]byte{1, 2, 3, 4}).AsSlice()...)
+	iprange1 = append(iprange1, 13)
+	iprange2 := []byte{6}
+	iprange2 = append(iprange2, netip.MustParseAddr("2001:db8::1").AsSlice()...)
+	iprange2 = append(iprange2, netip.MustParseAddr("2001:db8::100").AsSlice()...)
+	iprange2 = append(iprange2, 37)
+
+	data := quicvarint.Append(nil, uint64(capsuleTypeRouteAdvertisement))
+	data = quicvarint.Append(data, uint64(len(iprange1)+len(iprange2)))
+	data = append(data, iprange1...)
+	data = append(data, iprange2...)
+
+	r := bytes.NewReader(data)
+	typ, cr, err := http3.NewCapsuleParser(r).Next()
+	require.NoError(t, err)
+	require.Equal(t, capsuleTypeRouteAdvertisement, typ)
+	capsule, err := parseRouteAdvertisementCapsule(cr)
+	require.NoError(t, err)
+	require.Equal(t,
+		[]IPRoute{
+			{StartIP: netip.MustParseAddr("1.1.1.1"), EndIP: netip.MustParseAddr("1.2.3.4"), IPProtocol: 13},
+			{StartIP: netip.MustParseAddr("2001:db8::1"), EndIP: netip.MustParseAddr("2001:db8::100"), IPProtocol: 37},
+		},
+		capsule.IPAddressRanges,
+	)
+	require.Equal(t,
+		rangeToPrefixes(netip.MustParseAddr("1.1.1.1"), netip.MustParseAddr("1.2.3.4")),
+		capsule.IPAddressRanges[0].Prefixes(),
+	)
+	require.Equal(t,
+		rangeToPrefixes(netip.MustParseAddr("2001:db8::1"), netip.MustParseAddr("2001:db8::100")),
+		capsule.IPAddressRanges[1].Prefixes(),
+	)
+	require.Zero(t, r.Len())
+}
+
+func TestParseRouteAdvertisementCapsuleLimit(t *testing.T) {
+	entry := func(i int) []byte { return []byte{4, 10, 0, byte(i >> 8), byte(i), 10, 0, byte(i >> 8), byte(i), 0} }
+	testCapsuleEntryLimit(t, capsuleTypeRouteAdvertisement, maxRoutesPerCapsule, entry, parseRouteAdvertisementCapsule)
+}
+
+func TestWriteRouteAdvertisementCapsule(t *testing.T) {
+	c := &routeAdvertisementCapsule{
+		IPAddressRanges: []IPRoute{
+			{StartIP: netip.MustParseAddr("1.1.1.1"), EndIP: netip.MustParseAddr("1.2.3.4"), IPProtocol: 13},
+			{StartIP: netip.MustParseAddr("2001:db8::1"), EndIP: netip.MustParseAddr("2001:db8::100"), IPProtocol: 37},
+		},
+	}
+	data := c.append(nil)
+	r := bytes.NewReader(data)
+	typ, cr, err := http3.NewCapsuleParser(r).Next()
+	require.NoError(t, err)
+	require.Equal(t, capsuleTypeRouteAdvertisement, typ)
+	parsed, err := parseRouteAdvertisementCapsule(cr)
+	require.NoError(t, err)
+	require.Equal(t, c, parsed)
+	require.Zero(t, r.Len())
+}
+
+func TestParseRouteAdvertisementCapsuleInvalid(t *testing.T) {
+	t.Run("invalid IP version", func(t *testing.T) {
+		iprange1 := []byte{5}
+		iprange1 = append(iprange1, netip.AddrFrom4([4]byte{1, 1, 1, 1}).AsSlice()...)
+		iprange1 = append(iprange1, netip.AddrFrom4([4]byte{1, 1, 1, 2}).AsSlice()...)
+		iprange1 = append(iprange1, 13)
+		_, err := parseRouteAdvertisementCapsule(newCapsuleReader(t, capsuleTypeRouteAdvertisement, iprange1))
+		require.ErrorContains(t, err, "invalid IP version: 5")
+	})
+
+	t.Run("start IP is greater than end IP", func(t *testing.T) {
+		iprange1 := []byte{4}
+		iprange1 = append(iprange1, netip.AddrFrom4([4]byte{1, 2, 3, 4}).AsSlice()...)
+		iprange1 = append(iprange1, netip.AddrFrom4([4]byte{1, 1, 1, 1}).AsSlice()...)
+		iprange1 = append(iprange1, 13)
+		_, err := parseRouteAdvertisementCapsule(newCapsuleReader(t, capsuleTypeRouteAdvertisement, iprange1))
+		require.ErrorContains(t, err, "start IP is greater than end IP")
+	})
+
+	t.Run("incomplete capsule", func(t *testing.T) {
+		data := (&routeAdvertisementCapsule{
+			IPAddressRanges: []IPRoute{
+				{StartIP: netip.MustParseAddr("1.1.1.1"), EndIP: netip.MustParseAddr("2.2.2.2"), IPProtocol: 13},
+				{StartIP: netip.MustParseAddr("2001:db8::1"), EndIP: netip.MustParseAddr("2001:db8::100"), IPProtocol: 37},
+			},
+		}).append(nil)
+
+		testIncompleteCapsule(t, data, func(r http3.CapsuleReader) error {
+			_, err := parseRouteAdvertisementCapsule(r)
+			return err
+		})
+	})
+}
+
+var (
+	route4a  = IPRoute{StartIP: netip.MustParseAddr("10.0.0.0"), EndIP: netip.MustParseAddr("10.0.0.9")}
+	route4b  = IPRoute{StartIP: netip.MustParseAddr("10.0.0.10"), EndIP: netip.MustParseAddr("10.0.0.20")}
+	route4ab = IPRoute{StartIP: netip.MustParseAddr("10.0.0.9"), EndIP: netip.MustParseAddr("10.0.0.20")}
+	route6   = IPRoute{StartIP: netip.MustParseAddr("2001:db8::"), EndIP: netip.MustParseAddr("2001:db8::ffff")}
+)
+
+func withProtocol(r IPRoute, proto uint8) IPRoute {
+	r.IPProtocol = proto
+	return r
+}
+
+var routeOrderTests = []struct {
+	name   string
+	routes []IPRoute
+	err    string
+}{
+	{name: "empty"},
+	{name: "adjacent ranges", routes: []IPRoute{route4a, route4b}},
+	{name: "IPv4 before IPv6 with a lower IP protocol", routes: []IPRoute{withProtocol(route4a, 17), route6}},
+	{name: "same range for different IP protocols", routes: []IPRoute{withProtocol(route4a, 6), withProtocol(route4a, 17)}},
+	{name: "IP protocol order before address order", routes: []IPRoute{withProtocol(route4b, 6), withProtocol(route4a, 17)}},
+	{name: "IPv6 before IPv4", routes: []IPRoute{route6, route4a}, err: "not ordered by IP version and IP protocol"},
+	{name: "descending IP protocols", routes: []IPRoute{withProtocol(route4a, 17), withProtocol(route4b, 6)}, err: "not ordered by IP version and IP protocol"},
+	{name: "descending ranges", routes: []IPRoute{route4b, route4a}, err: "overlap or are not in ascending order"},
+	{name: "overlapping ranges", routes: []IPRoute{route4a, route4ab}, err: "overlap or are not in ascending order"},
+	{name: "duplicate range", routes: []IPRoute{route6, route6}, err: "overlap or are not in ascending order"},
+}
+
+func TestParseRouteAdvertisementCapsuleOrder(t *testing.T) {
+	for _, tc := range routeOrderTests {
+		t.Run(tc.name, func(t *testing.T) {
+			data := (&routeAdvertisementCapsule{IPAddressRanges: tc.routes}).append(nil)
+			_, cr, err := http3.NewCapsuleParser(bytes.NewReader(data)).Next()
+			require.NoError(t, err)
+			capsule, err := parseRouteAdvertisementCapsule(cr)
+			if tc.err != "" {
+				require.ErrorContains(t, err, tc.err)
+				return
+			}
+			require.NoError(t, err)
+			require.Equal(t, tc.routes, capsule.IPAddressRanges)
+		})
+	}
+}
+
+func TestAdvertiseRouteValidation(t *testing.T) {
+	tests := []struct {
+		name   string
+		routes []IPRoute
+		err    string
+	}{
+		{name: "invalid start IP", routes: []IPRoute{{EndIP: route4a.EndIP}}, err: "invalid IP address range"},
+		{name: "invalid end IP", routes: []IPRoute{{StartIP: route4a.StartIP}}, err: "invalid IP address range"},
+		{
+			name:   "IPv6 zone",
+			routes: []IPRoute{{StartIP: netip.MustParseAddr("fe80::1%eth0"), EndIP: netip.MustParseAddr("fe80::2%eth0")}},
+			err:    "invalid IP address range",
+		},
+		{name: "mixed IP versions", routes: []IPRoute{{StartIP: route4a.StartIP, EndIP: route6.EndIP}}, err: "mixes IP versions"},
+		{
+			name:   "IPv4 and IPv4-mapped IPv6",
+			routes: []IPRoute{{StartIP: netip.MustParseAddr("10.0.0.1"), EndIP: netip.MustParseAddr("::ffff:10.0.0.2")}},
+			err:    "mixes IP versions",
+		},
+		{name: "start after end", routes: []IPRoute{route4a, {StartIP: route4b.EndIP, EndIP: route4b.StartIP}}, err: "invalid route 1: start IP 10.0.0.20 is greater than end IP 10.0.0.10"},
+	}
+	tests = append(tests, routeOrderTests...)
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			conn := newProxiedConn(&mockStream{})
+			t.Cleanup(func() { conn.Close() })
+			err := conn.AdvertiseRoute(tc.routes)
+			if tc.err != "" {
+				require.ErrorContains(t, err, tc.err)
+				conn.mu.Lock()
+				defer conn.mu.Unlock()
+				require.Empty(t, conn.queuedWrites)
+				require.Nil(t, conn.localRoutes)
+				return
+			}
+			require.NoError(t, err)
+		})
+	}
+}
+
+func TestReceiveMisorderedRouteAdvertisement(t *testing.T) {
+	toRead := make(chan []byte, 1)
+	conn := newProxiedConn(&mockStream{toRead: toRead})
+	t.Cleanup(func() { conn.Close() })
+
+	toRead <- (&routeAdvertisementCapsule{IPAddressRanges: []IPRoute{route6, route4a}}).append(nil)
+	ctx, cancel := context.WithTimeout(t.Context(), time.Second)
+	defer cancel()
+	_, err := conn.Routes(ctx)
+	require.ErrorIs(t, err, net.ErrClosed)
+}

transport/internet/masque/connectip/cert_test.go

@@ -0,0 +1,95 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright 2024 Marten Seemann
+ * Adapted from github.com/quic-go/connect-ip-go (commit a0c35fa).
+ */
+
+package connectip
+
+import (
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/tls"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"log"
+	"math/big"
+	"time"
+
+	"github.com/apernet/quic-go/http3"
+)
+
+var (
+	tlsConf  *tls.Config
+	certPool *x509.CertPool
+)
+
+func generateCA() (*x509.Certificate, *rsa.PrivateKey, error) {
+	certTempl := &x509.Certificate{
+		SerialNumber:          big.NewInt(2019),
+		Subject:               pkix.Name{},
+		NotBefore:             time.Now(),
+		NotAfter:              time.Now().Add(24 * time.Hour),
+		IsCA:                  true,
+		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageClientAuth, x509.ExtKeyUsageServerAuth},
+		KeyUsage:              x509.KeyUsageDigitalSignature | x509.KeyUsageCertSign,
+		BasicConstraintsValid: true,
+	}
+	caPrivateKey, err := rsa.GenerateKey(rand.Reader, 2048)
+	if err != nil {
+		return nil, nil, err
+	}
+	caBytes, err := x509.CreateCertificate(rand.Reader, certTempl, certTempl, &caPrivateKey.PublicKey, caPrivateKey)
+	if err != nil {
+		return nil, nil, err
+	}
+	ca, err := x509.ParseCertificate(caBytes)
+	if err != nil {
+		return nil, nil, err
+	}
+	return ca, caPrivateKey, nil
+}
+
+func generateLeafCert(ca *x509.Certificate, caPrivateKey *rsa.PrivateKey) (*x509.Certificate, *rsa.PrivateKey, error) {
+	certTempl := &x509.Certificate{
+		SerialNumber: big.NewInt(1),
+		DNSNames:     []string{"localhost", "127.0.0.1"},
+		NotBefore:    time.Now(),
+		NotAfter:     time.Now().Add(24 * time.Hour),
+		ExtKeyUsage:  []x509.ExtKeyUsage{x509.ExtKeyUsageClientAuth, x509.ExtKeyUsageServerAuth},
+		KeyUsage:     x509.KeyUsageDigitalSignature,
+	}
+	privKey, err := rsa.GenerateKey(rand.Reader, 2048)
+	if err != nil {
+		return nil, nil, err
+	}
+	certBytes, err := x509.CreateCertificate(rand.Reader, certTempl, ca, &privKey.PublicKey, caPrivateKey)
+	if err != nil {
+		return nil, nil, err
+	}
+	cert, err := x509.ParseCertificate(certBytes)
+	if err != nil {
+		return nil, nil, err
+	}
+	return cert, privKey, nil
+}
+
+func init() {
+	ca, caPrivateKey, err := generateCA()
+	if err != nil {
+		log.Fatal("failed to generate CA certificate:", err)
+	}
+	leafCert, leafPrivateKey, err := generateLeafCert(ca, caPrivateKey)
+	if err != nil {
+		log.Fatal("failed to generate leaf certificate:", err)
+	}
+	certPool = x509.NewCertPool()
+	certPool.AddCert(ca)
+	tlsConf = &tls.Config{
+		Certificates: []tls.Certificate{{
+			Certificate: [][]byte{leafCert.Raw},
+			PrivateKey:  leafPrivateKey,
+		}},
+		NextProtos: []string{http3.NextProtoH3},
+	}
+}

transport/internet/masque/connectip/checksum.go

@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright 2024 Marten Seemann
+ * Adapted from github.com/quic-go/connect-ip-go (commit a0c35fa).
+ */
+
+package connectip
+
+import "encoding/binary"
+
+func calculateIPv4Checksum(header []byte) uint16 {
+	var sum uint32
+	for i := 0; i < len(header); i += 2 {
+		if i == 10 {
+			continue
+		}
+		sum += uint32(binary.BigEndian.Uint16(header[i : i+2]))
+	}
+	for (sum >> 16) > 0 {
+		sum = (sum & 0xffff) + (sum >> 16)
+	}
+	return ^uint16(sum)
+}

transport/internet/masque/connectip/checksum_test.go

@@ -0,0 +1,27 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright 2024 Marten Seemann
+ * Adapted from github.com/quic-go/connect-ip-go (commit a0c35fa).
+ */
+
+package connectip
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestIPv4ChecksumTestVector(t *testing.T) {
+	data := []byte{0x45, 0x00, 0x00, 0x73, 0x00, 0x00, 0x40, 0x00, 0x40, 0x11, 0xb8, 0x61, 0xc0, 0xa8, 0x00, 0x01, 0xc0, 0xa8, 0x00, 0xc7}
+	checksum := calculateIPv4Checksum(data)
+	require.Equal(t, uint16(0xb861), checksum)
+}
+
+func TestIPv4ChecksumWithOptions(t *testing.T) {
+	data := []byte{0x46, 0x00, 0x00, 0x77, 0x00, 0x00, 0x40, 0x00, 0x40, 0x11, 0x00, 0x00, 0xc0, 0xa8, 0x00, 0x01, 0xc0, 0xa8, 0x00, 0xc7, 0x94, 0x04, 0x00, 0x00}
+	checksum := calculateIPv4Checksum(data)
+	data[10], data[11] = byte(checksum>>8), byte(checksum)
+	require.True(t, ipv4ChecksumValid(data))
+	require.NotEqual(t, checksum, calculateIPv4Checksum(data[:20]), "the options must be covered")
+}

transport/internet/masque/connectip/client.go

@@ -0,0 +1,75 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright 2024 Marten Seemann
+ * Adapted from github.com/quic-go/connect-ip-go (commit a0c35fa).
+ */
+
+package connectip
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net/http"
+
+	"github.com/apernet/quic-go"
+	"github.com/apernet/quic-go/http3"
+)
+
+type ClientConn struct {
+	clientConn *http3.ClientConn
+}
+
+func NewClientConn(conn *http3.ClientConn) *ClientConn {
+	return &ClientConn{clientConn: conn}
+}
+
+func (c *ClientConn) Dial(req *Request) (*Conn, *http.Response, error) {
+	httpReq := req.httpRequest()
+	if httpReq.URL == nil {
+		return nil, nil, errors.New("connect-ip: request URL is nil")
+	}
+	if httpReq.Host == "" && httpReq.URL.Host == "" {
+		return nil, nil, errors.New("connect-ip: request needs a host")
+	}
+
+	select {
+	case <-httpReq.Context().Done():
+		return nil, nil, context.Cause(httpReq.Context())
+	case <-c.clientConn.Context().Done():
+		return nil, nil, context.Cause(c.clientConn.Context())
+	case <-c.clientConn.ReceivedSettings():
+	}
+
+	settings := c.clientConn.Settings()
+	if !settings.EnableExtendedConnect {
+		return nil, nil, errors.New("connect-ip: server didn't enable Extended CONNECT")
+	}
+	if !settings.EnableDatagrams {
+		return nil, nil, errors.New("connect-ip: server didn't enable datagrams")
+	}
+
+	rstr, err := c.clientConn.OpenRequestStream(httpReq.Context())
+	if err != nil {
+		return nil, nil, fmt.Errorf("connect-ip: failed to open request stream: %w", err)
+	}
+	var keepStream bool
+	defer func() {
+		if !keepStream {
+			rstr.CancelRead(quic.StreamErrorCode(http3.ErrCodeNoError))
+			rstr.CancelWrite(quic.StreamErrorCode(http3.ErrCodeNoError))
+		}
+	}()
+	if err := rstr.SendRequestHeader(httpReq); err != nil {
+		return nil, nil, fmt.Errorf("connect-ip: failed to send request: %w", err)
+	}
+	rsp, err := rstr.ReadResponse()
+	if err != nil {
+		return nil, nil, fmt.Errorf("connect-ip: failed to read response: %w", err)
+	}
+	if rsp.StatusCode < 200 || rsp.StatusCode > 299 {
+		return nil, rsp, fmt.Errorf("connect-ip: server responded with %d", rsp.StatusCode)
+	}
+	keepStream = true
+	return newProxiedConn(rstr), rsp, nil
+}

transport/internet/masque/connectip/client_test.go

@@ -0,0 +1,101 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright 2024 Marten Seemann
+ * Adapted from github.com/quic-go/connect-ip-go (commit a0c35fa).
+ */
+
+package connectip
+
+import (
+	"context"
+	"net"
+	"net/http"
+	"testing"
+	"time"
+
+	"github.com/apernet/quic-go"
+	"github.com/apernet/quic-go/http3"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestClientWaitForSettings(t *testing.T) {
+	conn, err := net.ListenUDP("udp", &net.UDPAddr{IP: net.IPv4(127, 0, 0, 1), Port: 0})
+	require.NoError(t, err)
+	ln, err := quic.Listen(conn, tlsConf, &quic.Config{EnableDatagrams: true})
+	require.NoError(t, err)
+	defer ln.Close()
+
+	h3conn := dialHTTP3(t, conn.LocalAddr().String())
+	ctx, cancel := context.WithTimeout(t.Context(), 100*time.Millisecond)
+	defer cancel()
+	req, err := NewRequest(ctx, "https://example.org/.well-known/masque/ip/")
+	require.NoError(t, err)
+	_, _, err = NewClientConn(h3conn).Dial(req)
+	require.ErrorIs(t, err, context.DeadlineExceeded)
+}
+
+func TestClientDatagramCheck(t *testing.T) {
+	s := http3.Server{
+		TLSConfig:       tlsConf,
+		QUICConfig:      &quic.Config{EnableDatagrams: true},
+		EnableDatagrams: false,
+	}
+	ln, err := net.ListenUDP("udp", &net.UDPAddr{IP: net.IPv4(127, 0, 0, 1), Port: 0})
+	require.NoError(t, err)
+	go func() { s.Serve(ln) }()
+	defer s.Close()
+
+	h3conn := dialHTTP3(t, ln.LocalAddr().String())
+	ctx, cancel := context.WithTimeout(t.Context(), 5*time.Second)
+	defer cancel()
+	req, err := NewRequest(ctx, "https://example.org/.well-known/masque/ip/")
+	require.NoError(t, err)
+	_, _, err = NewClientConn(h3conn).Dial(req)
+	require.ErrorContains(t, err, "connect-ip: server didn't enable datagrams")
+}
+
+func TestNewClientConnSharesHTTP3Connection(t *testing.T) {
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	ln, err := net.ListenUDP("udp4", &net.UDPAddr{IP: net.IPv4(127, 0, 0, 1)})
+	require.NoError(t, err)
+	defer ln.Close()
+	url := "https://" + ln.LocalAddr().String()
+
+	mux := http.NewServeMux()
+	mux.HandleFunc("/connect-ip", func(w http.ResponseWriter, r *http.Request) {
+		req, err := ParseProxyRequest(r)
+		if !assert.NoError(t, err) {
+			w.WriteHeader(http.StatusBadRequest)
+			return
+		}
+		_, err = (&Proxy{}).Proxy(w, req)
+		assert.NoError(t, err)
+	})
+	mux.HandleFunc("GET /hello", func(http.ResponseWriter, *http.Request) {})
+	s := http3.Server{Handler: mux, TLSConfig: tlsConf, EnableDatagrams: true}
+	go func() { s.Serve(ln) }()
+	defer s.Close()
+
+	h3conn := dialHTTP3(t, ln.LocalAddr().String())
+	httpClient := &http.Client{Transport: h3conn, Timeout: time.Second}
+	checkHTTP := func() {
+		t.Helper()
+		rsp, err := httpClient.Get(url + "/hello")
+		require.NoError(t, err)
+		rsp.Body.Close()
+		require.Equal(t, http.StatusOK, rsp.StatusCode)
+	}
+
+	checkHTTP()
+	req, err := NewRequest(ctx, url+"/connect-ip")
+	require.NoError(t, err)
+	tunnel, rsp, err := NewClientConn(h3conn).Dial(req)
+	require.NoError(t, err)
+	require.Equal(t, http.StatusOK, rsp.StatusCode)
+	checkHTTP()
+	require.NoError(t, tunnel.Close())
+	checkHTTP()
+}

transport/internet/masque/connectip/conn.go

@@ -0,0 +1,620 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright 2024 Marten Seemann
+ * Adapted from github.com/quic-go/connect-ip-go (commit a0c35fa).
+ */
+
+package connectip
+
+import (
+	"context"
+	"encoding/binary"
+	goerrors "errors"
+	"fmt"
+	"io"
+	"net"
+	"net/netip"
+	"slices"
+	"sync"
+	"time"
+
+	"github.com/apernet/quic-go"
+	"github.com/apernet/quic-go/http3"
+	"github.com/apernet/quic-go/quicvarint"
+	"github.com/xtls/xray-core/common/errors"
+	"golang.org/x/net/ipv4"
+	"golang.org/x/net/ipv6"
+)
+
+type CloseError struct {
+	Remote bool
+}
+
+func (e *CloseError) Error() string        { return net.ErrClosed.Error() }
+func (e *CloseError) Is(target error) bool { return target == net.ErrClosed }
+
+const (
+	ipProtoICMP   = 1
+	ipProtoICMPv6 = 58
+)
+
+type http3Stream interface {
+	io.ReadWriteCloser
+	StreamID() quic.StreamID
+	ReceiveDatagram(context.Context) ([]byte, error)
+	SendDatagram([]byte) error
+	CancelRead(quic.StreamErrorCode)
+	CancelWrite(quic.StreamErrorCode)
+	SetWriteDeadline(time.Time) error
+}
+
+var (
+	_ http3Stream = &http3.Stream{}
+	_ http3Stream = &http3.RequestStream{}
+)
+
+const maxQueuedCapsules = 128
+
+var errCapsuleLimit = goerrors.New("connect-ip: capsule limit exceeded")
+
+type streamWrite struct {
+	Data []byte
+	Fin  bool
+}
+
+type Conn struct {
+	str         http3Stream
+	writeNotify chan struct{}
+	writeDone   chan error
+
+	assignedAddressUpdates chan []AssignedAddress
+	addressRequests        chan *addressRequestCapsule
+	availableRouteUpdates  chan []IPRoute
+
+	mu                   sync.Mutex
+	queuedWrites         []streamWrite
+	peerAddresses        []netip.Prefix
+	localRoutes          []IPRoute
+	assignedAddresses    []netip.Prefix
+	lastAddressRequestID AddressRequestID
+
+	closeChan chan struct{}
+	closeErr  error
+
+	closeOnce   sync.Once
+	closeResult error
+
+	datagramCapsuleOnce sync.Once
+}
+
+func newProxiedConn(str http3Stream) *Conn {
+	c := &Conn{
+		str:                    str,
+		writeNotify:            make(chan struct{}, 1),
+		writeDone:              make(chan error, 1),
+		assignedAddressUpdates: make(chan []AssignedAddress, maxQueuedCapsules),
+		addressRequests:        make(chan *addressRequestCapsule, maxQueuedCapsules),
+		availableRouteUpdates:  make(chan []IPRoute, 1),
+		closeChan:              make(chan struct{}),
+	}
+	go func() {
+		err := c.readFromStream()
+		c.mu.Lock()
+		closing := c.closeErr != nil
+		if !closing {
+			c.closeErr = &CloseError{Remote: true}
+			close(c.closeChan)
+			if err != nil {
+				code := http3.ErrCodeMessageError
+				var streamErr *quic.StreamError
+				var h3Err *http3.Error
+				switch {
+				case goerrors.Is(err, errCapsuleLimit):
+					code = http3.ErrCodeExcessiveLoad
+				case goerrors.As(err, &streamErr) && streamErr.Remote, goerrors.As(err, &h3Err) && h3Err.Remote:
+					code = http3.ErrCodeRequestCanceled
+				}
+				c.str.CancelRead(quic.StreamErrorCode(code))
+				c.str.CancelWrite(quic.StreamErrorCode(code))
+				close(c.writeNotify)
+			} else {
+				c.queueFin()
+			}
+		}
+		c.mu.Unlock()
+		if err != nil && !closing {
+			errors.LogInfoInner(context.Background(), err, "reading capsules failed")
+		}
+	}()
+	go func() {
+		err := c.writeToStream()
+		if err != nil {
+			c.mu.Lock()
+			closing := c.closeErr != nil
+			if !closing {
+				c.closeErr = &CloseError{Remote: true}
+				close(c.closeChan)
+				c.str.CancelRead(quic.StreamErrorCode(http3.ErrCodeExcessiveLoad))
+				c.str.CancelWrite(quic.StreamErrorCode(http3.ErrCodeExcessiveLoad))
+			} else {
+				c.str.CancelWrite(quic.StreamErrorCode(http3.ErrCodeNoError))
+			}
+			c.mu.Unlock()
+			if !closing {
+				errors.LogInfoInner(context.Background(), err, "writing capsules failed")
+			}
+		}
+		c.writeDone <- err
+		close(c.writeDone)
+	}()
+	return c
+}
+
+func (c *Conn) AdvertiseRoute(routes []IPRoute) error {
+	for i, route := range routes {
+		err := route.validate()
+		if err == nil && i > 0 {
+			err = checkRouteOrder(routes[i-1], route)
+		}
+		if err != nil {
+			return fmt.Errorf("connect-ip: invalid route %d: %w", i, err)
+		}
+	}
+
+	c.mu.Lock()
+	if c.closeErr != nil {
+		err := c.closeErr
+		c.mu.Unlock()
+		return err
+	}
+	routes = slices.Clone(routes)
+	err := c.queueWrite(streamWrite{Data: (&routeAdvertisementCapsule{IPAddressRanges: routes}).append(nil)})
+	if err == nil {
+		c.localRoutes = routes
+	}
+	c.mu.Unlock()
+	if err != nil {
+		c.Close()
+		return err
+	}
+	return nil
+}
+
+func (c *Conn) RequestAddresses(prefixes []netip.Prefix) ([]AddressRequestID, error) {
+	if len(prefixes) == 0 {
+		return nil, goerrors.New("connect-ip: address request must contain at least one prefix")
+	}
+	for i, p := range prefixes {
+		if !p.IsValid() || p != p.Masked() {
+			return nil, fmt.Errorf("connect-ip: invalid requested prefix %d: %s", i, p)
+		}
+	}
+
+	c.mu.Lock()
+	if c.closeErr != nil {
+		err := c.closeErr
+		c.mu.Unlock()
+		return nil, err
+	}
+	ids := make([]AddressRequestID, len(prefixes))
+	for i := range ids {
+		ids[i] = c.lastAddressRequestID + AddressRequestID(i) + 1
+	}
+	capsule := &addressRequestCapsule{RequestIDs: ids, Prefixes: prefixes}
+	err := c.queueWrite(streamWrite{Data: capsule.append(nil)})
+	if err == nil {
+		c.lastAddressRequestID = ids[len(ids)-1]
+	}
+	c.mu.Unlock()
+	if err != nil {
+		c.Close()
+		return nil, err
+	}
+	return ids, nil
+}
+
+func (c *Conn) ReceiveAddressAssignment(ctx context.Context) ([]AssignedAddress, error) {
+	select {
+	case <-ctx.Done():
+		return nil, ctx.Err()
+	case assignment := <-c.assignedAddressUpdates:
+		return assignment, nil
+	case <-c.closeChan:
+		select {
+		case assignment := <-c.assignedAddressUpdates:
+			return assignment, nil
+		default:
+			return nil, c.closeErr
+		}
+	}
+}
+
+func (c *Conn) ReceiveAddressRequest(ctx context.Context) (*AddressRequest, error) {
+	var requested *addressRequestCapsule
+	select {
+	case <-ctx.Done():
+		return nil, ctx.Err()
+	case requested = <-c.addressRequests:
+	case <-c.closeChan:
+		select {
+		case requested = <-c.addressRequests:
+		default:
+			return nil, c.closeErr
+		}
+	}
+	return newAddressRequest(c, requested), nil
+}
+
+func (c *Conn) AssignAddresses(prefixes []netip.Prefix) error {
+	capsule := &addressAssignCapsule{}
+	if prefixes != nil {
+		capsule.AssignedAddresses = make([]AssignedAddress, len(prefixes))
+		for i, p := range prefixes {
+			capsule.AssignedAddresses[i] = AssignedAddress{IPPrefix: p}
+		}
+	}
+	return c.sendAddressAssignment(capsule, true)
+}
+
+func (c *Conn) sendAddressAssignment(capsule *addressAssignCapsule, restrictPeer bool) error {
+	c.mu.Lock()
+	if c.closeErr != nil {
+		err := c.closeErr
+		c.mu.Unlock()
+		return err
+	}
+	if err := c.queueWrite(streamWrite{Data: capsule.append(nil)}); err != nil {
+		c.mu.Unlock()
+		c.Close()
+		return err
+	}
+
+	if !restrictPeer && c.peerAddresses == nil {
+		c.mu.Unlock()
+		return nil
+	}
+	var prefixes []netip.Prefix
+	if capsule.AssignedAddresses != nil {
+		prefixes = make([]netip.Prefix, 0, len(capsule.AssignedAddresses))
+	}
+	for _, assigned := range capsule.AssignedAddresses {
+		if !assigned.Rejected() {
+			prefixes = append(prefixes, assigned.IPPrefix)
+		}
+	}
+	c.peerAddresses = prefixes
+	c.mu.Unlock()
+	return nil
+}
+
+func (c *Conn) queueWrite(w streamWrite) error {
+	if len(c.queuedWrites) >= maxQueuedCapsules {
+		c.closeErr = &CloseError{Remote: false}
+		close(c.closeChan)
+		c.str.CancelRead(quic.StreamErrorCode(http3.ErrCodeExcessiveLoad))
+		c.str.CancelWrite(quic.StreamErrorCode(http3.ErrCodeExcessiveLoad))
+		close(c.writeNotify)
+		return goerrors.New("connect-ip: capsule queue full")
+	}
+	c.queuedWrites = append(c.queuedWrites, w)
+	c.notifyWriter()
+	return nil
+}
+
+func (c *Conn) queueFin() {
+	c.str.SetWriteDeadline(time.Now())
+	c.queuedWrites = append(c.queuedWrites, streamWrite{Fin: true})
+	c.notifyWriter()
+}
+
+func (c *Conn) notifyWriter() {
+	select {
+	case c.writeNotify <- struct{}{}:
+	default:
+	}
+}
+
+func queueLatest[T any](ch chan T, value T) {
+	for {
+		select {
+		case ch <- value:
+			return
+		case <-ch:
+		}
+	}
+}
+
+func (c *Conn) Routes(ctx context.Context) ([]IPRoute, error) {
+	select {
+	case <-ctx.Done():
+		return nil, ctx.Err()
+	case <-c.closeChan:
+		return nil, c.closeErr
+	case routes := <-c.availableRouteUpdates:
+		return routes, nil
+	}
+}
+
+func (c *Conn) readFromStream() error {
+	p := http3.NewCapsuleParser(c.str)
+	for {
+		t, cr, err := p.Next()
+		if goerrors.Is(err, io.EOF) {
+			return nil
+		}
+		if err != nil {
+			return err
+		}
+		switch t {
+		case capsuleTypeAddressAssign:
+			capsule, err := parseAddressAssignCapsule(cr)
+			if err != nil {
+				return err
+			}
+			prefixes := make([]netip.Prefix, 0, len(capsule.AssignedAddresses))
+			for _, assigned := range capsule.AssignedAddresses {
+				if !assigned.Rejected() {
+					prefixes = append(prefixes, assigned.IPPrefix)
+				}
+			}
+			c.mu.Lock()
+			c.assignedAddresses = prefixes
+			c.mu.Unlock()
+			select {
+			case c.assignedAddressUpdates <- capsule.AssignedAddresses:
+			default:
+				return fmt.Errorf("%w: address assignment queue full", errCapsuleLimit)
+			}
+		case capsuleTypeAddressRequest:
+			capsule, err := parseAddressRequestCapsule(cr)
+			if err != nil {
+				return err
+			}
+			select {
+			case c.addressRequests <- capsule:
+			default:
+				return fmt.Errorf("%w: address request queue full", errCapsuleLimit)
+			}
+		case capsuleTypeRouteAdvertisement:
+			capsule, err := parseRouteAdvertisementCapsule(cr)
+			if err != nil {
+				return err
+			}
+			queueLatest(c.availableRouteUpdates, capsule.IPAddressRanges)
+		case capsuleTypeDatagram:
+			c.datagramCapsuleOnce.Do(func() {
+				errors.LogWarning(context.Background(), "connect-ip: dropping IP packets sent in DATAGRAM capsules, only QUIC DATAGRAM frames are supported")
+			})
+			if err := cr.Discard(); err != nil {
+				return err
+			}
+		default:
+			if err := cr.Discard(); err != nil {
+				return err
+			}
+		}
+	}
+}
+
+func (c *Conn) writeToStream() error {
+	for range c.writeNotify {
+		for {
+			c.mu.Lock()
+			if len(c.queuedWrites) == 0 {
+				c.mu.Unlock()
+				break
+			}
+			w := c.queuedWrites[0]
+			c.queuedWrites[0] = streamWrite{}
+			c.queuedWrites = c.queuedWrites[1:]
+			c.mu.Unlock()
+
+			if w.Fin {
+				return c.str.Close()
+			}
+			if _, err := c.str.Write(w.Data); err != nil {
+				return err
+			}
+		}
+	}
+	return c.closeErr
+}
+
+func (c *Conn) ReadPacket(b []byte) (int, error) {
+	for {
+		select {
+		case <-c.closeChan:
+			return 0, c.closeErr
+		default:
+		}
+		data, err := c.str.ReceiveDatagram(context.Background())
+		if err != nil {
+			select {
+			case <-c.closeChan:
+				return 0, c.closeErr
+			default:
+				return 0, err
+			}
+		}
+		contextID, n, err := quicvarint.Parse(data)
+		if err != nil {
+			errors.LogDebugInner(context.Background(), err, "dropping malformed datagram")
+			continue
+		}
+		if contextID != 0 {
+			continue
+		}
+		packet := data[n:]
+		if err := c.handleIncomingProxiedPacket(packet); err != nil {
+			errors.LogDebugInner(context.Background(), err, "dropping proxied packet")
+			continue
+		}
+		if len(packet) > len(b) {
+			return 0, io.ErrShortBuffer
+		}
+		return copy(b, packet), nil
+	}
+}
+
+func (c *Conn) handleIncomingProxiedPacket(data []byte) error {
+	if len(data) == 0 {
+		return goerrors.New("connect-ip: empty packet")
+	}
+	var src, dst netip.Addr
+	var ipProto uint8
+	switch v := ipVersion(data); v {
+	default:
+		return fmt.Errorf("connect-ip: unknown IP versions: %d", v)
+	case 4:
+		if len(data) < ipv4.HeaderLen {
+			return fmt.Errorf("connect-ip: malformed datagram: too short")
+		}
+		src = netip.AddrFrom4([4]byte(data[12:16]))
+		dst = netip.AddrFrom4([4]byte(data[16:20]))
+		ipProto = data[9]
+	case 6:
+		if len(data) < ipv6.HeaderLen {
+			return fmt.Errorf("connect-ip: malformed datagram: too short")
+		}
+		src = netip.AddrFrom16([16]byte(data[8:24]))
+		dst = netip.AddrFrom16([16]byte(data[24:40]))
+		ipProto = data[6]
+	}
+
+	c.mu.Lock()
+	assignedAddresses := c.assignedAddresses
+	localRoutes := c.localRoutes
+	peerAddresses := c.peerAddresses
+	c.mu.Unlock()
+
+	if peerAddresses != nil {
+		if !slices.ContainsFunc(peerAddresses, func(p netip.Prefix) bool { return p.Contains(src) }) {
+			return fmt.Errorf("connect-ip: datagram source address not allowed: %s", src)
+		}
+	}
+
+	var isAllowedDst bool
+	if len(assignedAddresses) > 0 {
+		isAllowedDst = slices.ContainsFunc(assignedAddresses, func(p netip.Prefix) bool { return p.Contains(dst) })
+	}
+	if !isAllowedDst {
+		isAllowedDst = slices.ContainsFunc(localRoutes, func(r IPRoute) bool {
+			if r.StartIP.Compare(dst) > 0 || dst.Compare(r.EndIP) > 0 {
+				return false
+			}
+			if (ipVersion(data) == 4 && ipProto == ipProtoICMP) || (ipVersion(data) == 6 && ipProto == ipProtoICMPv6) {
+				return true
+			}
+			return r.IPProtocol == 0 || r.IPProtocol == ipProto
+		})
+	}
+	if !isAllowedDst {
+		return fmt.Errorf("connect-ip: datagram destination address / protocol not allowed: %s (protocol: %d)", dst, ipProto)
+	}
+	return nil
+}
+
+func (c *Conn) WritePacket(b []byte) (icmp []byte, err error) {
+	select {
+	case <-c.closeChan:
+		return nil, c.closeErr
+	default:
+	}
+	data, err := c.composeDatagram(b)
+	if err != nil {
+		errors.LogDebugInner(context.Background(), err, "dropping proxied packet (", len(b), " bytes) that can't be proxied")
+		return nil, nil
+	}
+	if err := c.str.SendDatagram(data); err != nil {
+		if tooLarge, ok := goerrors.AsType[*quic.DatagramTooLargeError](err); ok {
+			icmpPacket, err := composeICMPTooLargePacket(b, int(tooLarge.MaxDatagramPayloadSize)-c.datagramOverhead())
+			if err != nil {
+				if goerrors.Is(err, ErrMTUTooSmall) {
+					return nil, err
+				}
+				errors.LogDebugInner(context.Background(), err, "failed to compose ICMP Packet Too Big")
+			}
+			return icmpPacket, nil
+		}
+		select {
+		case <-c.closeChan:
+			return nil, c.closeErr
+		default:
+			return nil, err
+		}
+	}
+	return nil, nil
+}
+
+func (c *Conn) composeDatagram(b []byte) ([]byte, error) {
+	if len(b) == 0 {
+		return nil, goerrors.New("connect-ip: empty packet")
+	}
+	switch v := ipVersion(b); v {
+	default:
+		return nil, fmt.Errorf("connect-ip: unknown IP versions: %d", v)
+	case 4:
+		if len(b) < ipv4.HeaderLen {
+			return nil, fmt.Errorf("connect-ip: IPv4 packet too short")
+		}
+		hdrLen := int(b[0]&0x0f) << 2
+		totalLen := int(binary.BigEndian.Uint16(b[2:4]))
+		if hdrLen < ipv4.HeaderLen || hdrLen > totalLen || totalLen > len(b) {
+			return nil, fmt.Errorf("connect-ip: malformed IPv4 header: header length %d, total length %d, packet length %d", hdrLen, totalLen, len(b))
+		}
+		ttl := b[8]
+		if ttl <= 1 {
+			return nil, fmt.Errorf("connect-ip: datagram TTL too small: %d", ttl)
+		}
+		b[8]--
+		binary.BigEndian.PutUint16(b[10:12], calculateIPv4Checksum(b[:hdrLen]))
+	case 6:
+		if len(b) < ipv6.HeaderLen {
+			return nil, fmt.Errorf("connect-ip: IPv6 packet too short")
+		}
+		hopLimit := b[7]
+		if hopLimit <= 1 {
+			return nil, fmt.Errorf("connect-ip: datagram Hop Limit too small: %d", hopLimit)
+		}
+		b[7]--
+	}
+	data := make([]byte, 0, len(contextIDZero)+len(b))
+	data = append(data, contextIDZero...)
+	data = append(data, b...)
+	return data, nil
+}
+
+func (c *Conn) datagramOverhead() int {
+	return quicvarint.Len(uint64(c.str.StreamID()/4)) + len(contextIDZero)
+}
+
+func (c *Conn) MaxPacketSize() int {
+	select {
+	case <-c.closeChan:
+		return 0
+	default:
+	}
+	err := c.str.SendDatagram(make([]byte, 1<<16))
+	tooLarge, ok := goerrors.AsType[*quic.DatagramTooLargeError](err)
+	if !ok {
+		return 0
+	}
+	return max(0, int(tooLarge.MaxDatagramPayloadSize)-c.datagramOverhead())
+}
+
+func (c *Conn) Close() error {
+	c.closeOnce.Do(func() {
+		c.mu.Lock()
+		if c.closeErr == nil {
+			c.closeErr = &CloseError{Remote: false}
+			close(c.closeChan)
+			c.queueFin()
+		}
+		c.mu.Unlock()
+		c.closeResult = <-c.writeDone
+		c.str.CancelRead(quic.StreamErrorCode(http3.ErrCodeNoError))
+	})
+	return c.closeResult
+}
+
+func ipVersion(b []byte) uint8 { return b[0] >> 4 }

transport/internet/masque/connectip/conn_test.go

@@ -0,0 +1,706 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright 2024 Marten Seemann
+ * Adapted from github.com/quic-go/connect-ip-go (commit a0c35fa).
+ */
+
+package connectip
+
+import (
+	"bytes"
+	"context"
+	"encoding/binary"
+	"errors"
+	"io"
+	"net"
+	"net/netip"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/apernet/quic-go"
+	"github.com/apernet/quic-go/http3"
+	"github.com/apernet/quic-go/quicvarint"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"golang.org/x/net/icmp"
+	"golang.org/x/net/ipv4"
+	"golang.org/x/net/ipv6"
+)
+
+var ipv6Header = []byte{
+	0x60, 0x00, 0x00, 0x00,
+	0x00, 0x20, 59, 64,
+	0x20, 0x01, 0x0d, 0xb8, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01,
+	0x20, 0x01, 0x0d, 0xb8, 0x85, 0xa3, 0x08, 0xd3, 0x13, 0x19, 0x8a, 0x2e, 0x03, 0x70, 0x73, 0x48,
+}
+
+var (
+	testSrc4 = netip.MustParseAddr("192.0.2.1")
+	testDst4 = netip.MustParseAddr("198.51.100.1")
+	testSrc6 = netip.MustParseAddr("2001:db8::1")
+	testDst6 = netip.MustParseAddr("2001:db8:1::1")
+)
+
+func ipv4Packet(ttl, proto uint8, src, dst netip.Addr, options, payload []byte) []byte {
+	hdrLen := ipv4.HeaderLen + len(options)
+	b := make([]byte, hdrLen, hdrLen+len(payload))
+	b[0] = 4<<4 | byte(hdrLen>>2)
+	binary.BigEndian.PutUint16(b[2:4], uint16(hdrLen+len(payload)))
+	b[8] = ttl
+	b[9] = proto
+	copy(b[12:16], src.AsSlice())
+	copy(b[16:20], dst.AsSlice())
+	copy(b[ipv4.HeaderLen:], options)
+	return append(b, payload...)
+}
+
+func ipv6Packet(hopLimit, nextHeader uint8, src, dst netip.Addr, payload []byte) []byte {
+	b := make([]byte, ipv6.HeaderLen, ipv6.HeaderLen+len(payload))
+	b[0] = 6 << 4
+	binary.BigEndian.PutUint16(b[4:6], uint16(len(payload)))
+	b[6] = nextHeader
+	b[7] = hopLimit
+	copy(b[8:24], src.AsSlice())
+	copy(b[24:40], dst.AsSlice())
+	return append(b, payload...)
+}
+
+func ipv4ChecksumValid(header []byte) bool {
+	var sum uint32
+	for i := 0; i+1 < len(header); i += 2 {
+		sum += uint32(binary.BigEndian.Uint16(header[i:]))
+	}
+	for sum > 0xffff {
+		sum = sum&0xffff + sum>>16
+	}
+	return sum == 0xffff
+}
+
+type mockStream struct {
+	streamID               quic.StreamID
+	reading                []byte
+	toRead                 <-chan []byte
+	datagrams              <-chan []byte
+	maxDatagramPayloadSize int
+	sendDatagramErr        error
+	sent                   [][]byte
+	writeStarted           chan struct{}
+	written                chan<- []byte
+	readErr                error
+
+	mu               sync.Mutex
+	cancelWriteCodes []quic.StreamErrorCode
+}
+
+func (m *mockStream) cancelWriteCode() (quic.StreamErrorCode, bool) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	if len(m.cancelWriteCodes) == 0 {
+		return 0, false
+	}
+	return m.cancelWriteCodes[0], true
+}
+
+var _ http3Stream = &mockStream{}
+
+func (m *mockStream) StreamID() quic.StreamID { return m.streamID }
+func (m *mockStream) Read(p []byte) (int, error) {
+	if len(m.reading) == 0 && m.readErr != nil {
+		return 0, m.readErr
+	}
+	if len(m.reading) == 0 {
+		m.reading = <-m.toRead
+	}
+	n := copy(p, m.reading)
+	m.reading = m.reading[n:]
+	return n, nil
+}
+func (m *mockStream) CancelRead(quic.StreamErrorCode) {}
+func (m *mockStream) Write(p []byte) (int, error) {
+	if m.writeStarted != nil {
+		close(m.writeStarted)
+		m.writeStarted = nil
+	}
+	if m.written != nil {
+		m.written <- bytes.Clone(p)
+	}
+	return len(p), nil
+}
+func (m *mockStream) Close() error { return nil }
+func (m *mockStream) CancelWrite(code quic.StreamErrorCode) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	m.cancelWriteCodes = append(m.cancelWriteCodes, code)
+}
+func (m *mockStream) SetWriteDeadline(time.Time) error { return nil }
+func (m *mockStream) SendDatagram(data []byte) error {
+	if m.sendDatagramErr != nil {
+		return m.sendDatagramErr
+	}
+	if size := quicvarint.Len(uint64(m.streamID/4)) + len(data); m.maxDatagramPayloadSize > 0 && size > m.maxDatagramPayloadSize {
+		return &quic.DatagramTooLargeError{MaxDatagramPayloadSize: int64(m.maxDatagramPayloadSize)}
+	}
+	m.sent = append(m.sent, bytes.Clone(data))
+	return nil
+}
+
+func (m *mockStream) ReceiveDatagram(ctx context.Context) ([]byte, error) {
+	select {
+	case <-ctx.Done():
+		return nil, ctx.Err()
+	case data, ok := <-m.datagrams:
+		if !ok {
+			return nil, io.EOF
+		}
+		return data, nil
+	}
+}
+
+func TestCapsuleWriteQueueLimit(t *testing.T) {
+	writes := make(chan []byte)
+	writeStarted := make(chan struct{})
+	conn := newProxiedConn(&mockStream{
+		writeStarted: writeStarted,
+		written:      writes,
+	})
+	t.Cleanup(func() { conn.Close() })
+
+	require.NoError(t, conn.AssignAddresses(nil))
+	select {
+	case <-writeStarted:
+	case <-time.After(time.Second):
+		t.Fatal("capsule write did not start")
+	}
+
+	for range maxQueuedCapsules {
+		require.NoError(t, conn.AssignAddresses(nil))
+	}
+	go func() {
+		conn.Routes(context.Background())
+		for range maxQueuedCapsules + 1 {
+			<-writes
+		}
+	}()
+	require.ErrorContains(t, conn.AssignAddresses(nil), "capsule queue full")
+	require.ErrorIs(t, conn.AssignAddresses(nil), net.ErrClosed)
+}
+
+func TestCapsuleReceiveQueueLimit(t *testing.T) {
+	for _, name := range []string{"assignments", "requests"} {
+		t.Run(name, func(t *testing.T) {
+			var data []byte
+			for i := range maxQueuedCapsules + 1 {
+				if name == "assignments" {
+					data = (&addressAssignCapsule{}).append(data)
+				} else {
+					data = (&addressRequestCapsule{
+						RequestIDs: []AddressRequestID{AddressRequestID(i + 1)},
+						Prefixes:   []netip.Prefix{netip.MustParsePrefix("192.0.2.1/32")},
+					}).append(data)
+				}
+			}
+			conn := newProxiedConn(&mockStream{reading: data})
+			t.Cleanup(func() { conn.Close() })
+			ctx, cancel := context.WithTimeout(context.Background(), time.Second)
+			defer cancel()
+			_, err := conn.Routes(ctx)
+			require.ErrorIs(t, err, net.ErrClosed)
+		})
+	}
+}
+
+func TestAbortErrorCode(t *testing.T) {
+	var overflow []byte
+	for range maxQueuedCapsules + 1 {
+		overflow = (&addressAssignCapsule{}).append(overflow)
+	}
+	misordered := (&routeAdvertisementCapsule{IPAddressRanges: []IPRoute{
+		{StartIP: netip.MustParseAddr("192.0.2.2"), EndIP: netip.MustParseAddr("192.0.2.1")},
+	}}).append(nil)
+	for _, c := range []struct {
+		name string
+		str  *mockStream
+		code http3.ErrCode
+	}{
+		{"malformed capsule", &mockStream{reading: misordered}, http3.ErrCodeMessageError},
+		{"queue limit", &mockStream{reading: overflow}, http3.ErrCodeExcessiveLoad},
+		{"reset by peer", &mockStream{readErr: &quic.StreamError{ErrorCode: quic.StreamErrorCode(http3.ErrCodeNoError), Remote: true}}, http3.ErrCodeRequestCanceled},
+		{"reset by peer on a request stream", &mockStream{readErr: &http3.Error{ErrorCode: http3.ErrCodeNoError, Remote: true}}, http3.ErrCodeRequestCanceled},
+	} {
+		t.Run(c.name, func(t *testing.T) {
+			conn := newProxiedConn(c.str)
+			t.Cleanup(func() { conn.Close() })
+			require.Eventually(t, func() bool {
+				_, ok := c.str.cancelWriteCode()
+				return ok
+			}, time.Second, time.Millisecond)
+			code, _ := c.str.cancelWriteCode()
+			require.Equal(t, quic.StreamErrorCode(c.code), code)
+		})
+	}
+}
+
+func TestIncomingDatagrams(t *testing.T) {
+	t.Run("empty packets", func(t *testing.T) {
+		conn := newProxiedConn(&mockStream{})
+		require.ErrorContains(t,
+			conn.handleIncomingProxiedPacket([]byte{}),
+			"connect-ip: empty packet",
+		)
+	})
+
+	t.Run("invalid IP version", func(t *testing.T) {
+		conn := newProxiedConn(&mockStream{})
+		data := make([]byte, 20)
+		data[0] = 5 << 4
+		require.ErrorContains(t,
+			conn.handleIncomingProxiedPacket(data),
+			"connect-ip: unknown IP versions: 5",
+		)
+	})
+
+	t.Run("IPv4 packet too short", func(t *testing.T) {
+		conn := newProxiedConn(&mockStream{})
+		data, err := (&ipv4.Header{
+			Src:      net.IPv4(1, 2, 3, 4),
+			Dst:      net.IPv4(159, 70, 42, 98),
+			Len:      20,
+			Checksum: 89,
+		}).Marshal()
+		require.NoError(t, err)
+		require.ErrorContains(t,
+			conn.handleIncomingProxiedPacket(data[:ipv4.HeaderLen-1]),
+			"connect-ip: malformed datagram: too short",
+		)
+	})
+
+	t.Run("IPv6 packet too short", func(t *testing.T) {
+		conn := newProxiedConn(&mockStream{})
+		require.ErrorContains(t,
+			conn.handleIncomingProxiedPacket(ipv6Header[:ipv6.HeaderLen-1]),
+			"connect-ip: malformed datagram: too short",
+		)
+	})
+
+	t.Run("invalid source address", func(t *testing.T) {
+		conn := newProxiedConn(&mockStream{})
+		require.NoError(t, conn.AssignAddresses([]netip.Prefix{netip.MustParsePrefix("192.168.0.10/32")}))
+		hdr := &ipv4.Header{
+			Src:      net.IPv4(192, 168, 0, 11),
+			Dst:      net.IPv4(159, 70, 42, 98),
+			Len:      20,
+			Checksum: 89,
+		}
+		data, err := hdr.Marshal()
+		require.NoError(t, err)
+		require.ErrorContains(t,
+			conn.handleIncomingProxiedPacket(data),
+			"connect-ip: datagram source address not allowed: 192.168.0.11",
+		)
+	})
+
+	t.Run("invalid destination address", func(t *testing.T) {
+		conn := newProxiedConn(&mockStream{})
+		require.NoError(t, conn.AssignAddresses([]netip.Prefix{netip.MustParsePrefix("192.168.0.10/32")}))
+		require.NoError(t, conn.AdvertiseRoute([]IPRoute{
+			{StartIP: netip.MustParseAddr("10.0.0.0"), EndIP: netip.MustParseAddr("10.1.2.3")},
+		}))
+		hdr := &ipv4.Header{
+			Src:      net.IPv4(192, 168, 0, 10),
+			Dst:      net.IPv4(10, 1, 2, 3),
+			Len:      20,
+			Checksum: 89,
+		}
+		data, err := hdr.Marshal()
+		require.NoError(t, err)
+		require.NoError(t, conn.handleIncomingProxiedPacket(data))
+
+		hdr.Dst = net.IPv4(10, 1, 2, 4)
+		data, err = hdr.Marshal()
+		require.NoError(t, err)
+		require.ErrorContains(t,
+			conn.handleIncomingProxiedPacket(data),
+			"connect-ip: datagram destination address / protocol not allowed: 10.1.2.4 (protocol: 0)",
+		)
+	})
+
+	t.Run("invalid IP protocol", func(t *testing.T) {
+		conn := newProxiedConn(&mockStream{})
+		require.NoError(t, conn.AssignAddresses([]netip.Prefix{netip.MustParsePrefix("192.168.0.10/32")}))
+		require.NoError(t, conn.AdvertiseRoute([]IPRoute{
+			{StartIP: netip.MustParseAddr("10.0.0.0"), EndIP: netip.MustParseAddr("10.1.2.3"), IPProtocol: 42},
+		}))
+		hdr := &ipv4.Header{
+			Src:      net.IPv4(192, 168, 0, 10),
+			Dst:      net.IPv4(10, 1, 2, 3),
+			Len:      20,
+			Checksum: 89,
+			Protocol: 42,
+		}
+		data, err := hdr.Marshal()
+		require.NoError(t, err)
+		require.NoError(t, conn.handleIncomingProxiedPacket(data))
+
+		hdr.Protocol = 41
+		data, err = hdr.Marshal()
+		require.NoError(t, err)
+		require.ErrorContains(t,
+			conn.handleIncomingProxiedPacket(data),
+			"connect-ip: datagram destination address / protocol not allowed: 10.1.2.3 (protocol: 41)",
+		)
+
+		hdr.Protocol = ipProtoICMP
+		data, err = hdr.Marshal()
+		require.NoError(t, err)
+		require.NoError(t, conn.handleIncomingProxiedPacket(data))
+	})
+
+	t.Run("packet from assigned address", func(t *testing.T) {
+		readChan := make(chan []byte, 1)
+		conn := newProxiedConn(&mockStream{toRead: readChan})
+
+		hdr := &ipv4.Header{
+			Src:      net.IPv4(159, 70, 42, 98),
+			Dst:      net.IPv4(192, 168, 0, 10),
+			Len:      20,
+			Checksum: 89,
+		}
+		data, err := hdr.Marshal()
+		require.NoError(t, err)
+		require.Error(t, conn.handleIncomingProxiedPacket(data), "connect-ip: datagram destination address")
+
+		readChan <- (&addressAssignCapsule{
+			AssignedAddresses: []AssignedAddress{{IPPrefix: netip.MustParsePrefix("192.168.0.10/32")}},
+		}).append(nil)
+
+		ctx, cancel := context.WithTimeout(context.Background(), time.Second)
+		defer cancel()
+		_, err = conn.ReceiveAddressAssignment(ctx)
+		require.NoError(t, err)
+		require.NoError(t, conn.handleIncomingProxiedPacket(data))
+	})
+}
+
+func TestSkipUnknownCapsule(t *testing.T) {
+	for _, typ := range []http3.CapsuleType{42, capsuleTypeDatagram} {
+		readChan := make(chan []byte, 1)
+		conn := newProxiedConn(&mockStream{toRead: readChan})
+
+		data := quicvarint.Append(nil, uint64(typ))
+		data = quicvarint.Append(data, 3)
+		data = append(data, "foo"...)
+		data = (&addressAssignCapsule{
+			AssignedAddresses: []AssignedAddress{{IPPrefix: netip.MustParsePrefix("192.168.0.10/32")}},
+		}).append(data)
+		readChan <- data
+
+		ctx, cancel := context.WithTimeout(context.Background(), time.Second)
+		assigned, err := conn.ReceiveAddressAssignment(ctx)
+		cancel()
+		require.NoError(t, err, "capsule type %d", typ)
+		require.Equal(t, []AssignedAddress{{IPPrefix: netip.MustParsePrefix("192.168.0.10/32")}}, assigned)
+		conn.Close()
+	}
+}
+
+func FuzzIncomingDatagram(f *testing.F) {
+	conn := newProxiedConn(&mockStream{})
+	require.NoError(f, conn.AssignAddresses([]netip.Prefix{
+		netip.MustParsePrefix("192.168.0.0/16"),
+		netip.MustParsePrefix("2001:db8::0/64"),
+	}))
+	require.NoError(f, conn.AdvertiseRoute([]IPRoute{
+		{StartIP: netip.MustParseAddr("10.0.0.0"), EndIP: netip.MustParseAddr("10.1.2.3"), IPProtocol: 42},
+		{StartIP: netip.MustParseAddr("2001:db8:1::"), EndIP: netip.MustParseAddr("2001:db8:1::ffff"), IPProtocol: 42},
+	}))
+
+	ipv4Header, err := (&ipv4.Header{
+		Src:      net.IPv4(1, 2, 3, 4),
+		Dst:      net.IPv4(159, 70, 42, 98),
+		Len:      20,
+		Checksum: 89,
+	}).Marshal()
+	require.NoError(f, err)
+
+	f.Add(ipv4Header)
+	f.Add(ipv6Header)
+
+	f.Fuzz(func(t *testing.T, data []byte) {
+		conn.handleIncomingProxiedPacket(data)
+	})
+}
+
+func TestSendingDatagrams(t *testing.T) {
+	t.Run("invalid IP version", func(t *testing.T) {
+		conn := newProxiedConn(&mockStream{})
+		data := make([]byte, 20)
+		data[0] = 5 << 4
+		_, err := conn.composeDatagram(data)
+		require.ErrorContains(t, err, "connect-ip: unknown IP versions: 5")
+	})
+
+	t.Run("IPv4 packet too short", func(t *testing.T) {
+		conn := newProxiedConn(&mockStream{})
+		data, err := (&ipv4.Header{
+			Src:      net.IPv4(1, 2, 3, 4),
+			Dst:      net.IPv4(159, 70, 42, 98),
+			Len:      20,
+			Checksum: 89,
+		}).Marshal()
+		require.NoError(t, err)
+		_, err = conn.composeDatagram(data[:ipv4.HeaderLen-1])
+		require.ErrorContains(t, err, "connect-ip: IPv4 packet too short")
+	})
+
+	t.Run("IPv6 packet too short", func(t *testing.T) {
+		conn := newProxiedConn(&mockStream{})
+		_, err := conn.composeDatagram(ipv6Header[:ipv6.HeaderLen-1])
+		require.ErrorContains(t, err, "connect-ip: IPv6 packet too short")
+	})
+}
+
+func TestWritePacketDropsWithoutSending(t *testing.T) {
+	setIHL := func(b []byte, ihl byte) []byte { b[0] = 4<<4 | ihl; return b }
+	setTotalLen := func(b []byte, l uint16) []byte { binary.BigEndian.PutUint16(b[2:4], l); return b }
+	payload := make([]byte, 20)
+
+	for _, tc := range []struct {
+		name   string
+		packet []byte
+	}{
+		{"nil", nil},
+		{"empty", []byte{}},
+		{"IPv4 TTL 1", ipv4Packet(1, 17, testSrc4, testDst4, nil, payload)},
+		{"IPv4 TTL 0", ipv4Packet(0, 17, testSrc4, testDst4, nil, payload)},
+		{"IPv6 Hop Limit 1", ipv6Packet(1, 17, testSrc6, testDst6, payload)},
+		{"IPv6 Hop Limit 0", ipv6Packet(0, 17, testSrc6, testDst6, payload)},
+		{"IPv4 IHL below 5", setIHL(ipv4Packet(64, 17, testSrc4, testDst4, nil, payload), 4)},
+		{"IPv4 IHL beyond total length", setIHL(ipv4Packet(64, 17, testSrc4, testDst4, nil, payload[:8]), 8)},
+		{"IPv4 IHL beyond packet", setTotalLen(setIHL(ipv4Packet(64, 17, testSrc4, testDst4, nil, payload), 15), 60)},
+		{"IPv4 total length beyond packet", setTotalLen(ipv4Packet(64, 17, testSrc4, testDst4, nil, payload), 41)},
+		{"IPv4 total length below header", setTotalLen(ipv4Packet(64, 17, testSrc4, testDst4, nil, payload), 19)},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			str := &mockStream{}
+			conn := newProxiedConn(str)
+			t.Cleanup(func() { conn.Close() })
+
+			orig := bytes.Clone(tc.packet)
+			icmpPacket, err := conn.WritePacket(tc.packet)
+			require.NoError(t, err)
+			require.Nil(t, icmpPacket)
+			require.Empty(t, str.sent)
+			require.Equal(t, orig, tc.packet, "dropped packets must not be modified")
+		})
+	}
+}
+
+func TestWritePacketIPv4Checksum(t *testing.T) {
+	for _, tc := range []struct {
+		name    string
+		options []byte
+	}{
+		{"no options", nil},
+		{"Router Alert option", []byte{0x94, 0x04, 0x00, 0x00}},
+		{"maximum header length", bytes.Repeat([]byte{0x01}, 40)},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			str := &mockStream{}
+			conn := newProxiedConn(str)
+			t.Cleanup(func() { conn.Close() })
+
+			packet := ipv4Packet(64, 17, testSrc4, testDst4, tc.options, []byte("foobar"))
+			icmpPacket, err := conn.WritePacket(packet)
+			require.NoError(t, err)
+			require.Nil(t, icmpPacket)
+			require.Len(t, str.sent, 1)
+			require.Equal(t, contextIDZero, str.sent[0][:len(contextIDZero)])
+			sent := str.sent[0][len(contextIDZero):]
+			require.Len(t, sent, len(packet))
+			require.Equal(t, uint8(63), sent[8])
+			require.True(t, ipv4ChecksumValid(sent[:ipv4.HeaderLen+len(tc.options)]))
+		})
+	}
+}
+
+func TestWritePacketTooLarge(t *testing.T) {
+	for _, tc := range []struct {
+		name            string
+		streamID        quic.StreamID
+		maxPayloadSize  int
+		ipv6            bool
+		wantMTU         int
+		wantMTUTooSmall bool
+	}{
+		{name: "IPv4", maxPayloadSize: 1200, wantMTU: 1198},
+		{name: "IPv4, 2-byte Quarter Stream ID", streamID: 4 * 64, maxPayloadSize: 1200, wantMTU: 1197},
+		{name: "IPv4 minimum MTU", maxPayloadSize: 70, wantMTU: 68},
+		{name: "IPv4 below minimum MTU", maxPayloadSize: 69, wantMTU: 67, wantMTUTooSmall: true},
+		{name: "IPv6", maxPayloadSize: 1400, ipv6: true, wantMTU: 1398},
+		{name: "IPv6, 4-byte Quarter Stream ID", streamID: 4 * 20000, maxPayloadSize: 1400, ipv6: true, wantMTU: 1395},
+		{name: "IPv6 minimum MTU", maxPayloadSize: 1282, ipv6: true, wantMTU: 1280},
+		{name: "IPv6 below minimum MTU", maxPayloadSize: 1281, ipv6: true, wantMTU: 1279, wantMTUTooSmall: true},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			str := &mockStream{streamID: tc.streamID, maxDatagramPayloadSize: tc.maxPayloadSize}
+			conn := newProxiedConn(str)
+			t.Cleanup(func() { conn.Close() })
+
+			packetOfSize := func(size int) []byte {
+				if tc.ipv6 {
+					return ipv6Packet(64, 17, testSrc6, testDst6, make([]byte, size-ipv6.HeaderLen))
+				}
+				return ipv4Packet(64, 17, testSrc4, testDst4, nil, make([]byte, size-ipv4.HeaderLen))
+			}
+			require.Equal(t, tc.wantMTU, conn.MaxPacketSize())
+
+			icmpPacket, err := conn.WritePacket(packetOfSize(tc.wantMTU))
+			require.NoError(t, err)
+			require.Nil(t, icmpPacket)
+			require.Len(t, str.sent, 1)
+
+			icmpPacket, err = conn.WritePacket(packetOfSize(tc.wantMTU + 1))
+			if tc.wantMTUTooSmall {
+				require.ErrorIs(t, err, ErrMTUTooSmall)
+				require.Nil(t, icmpPacket)
+				return
+			}
+			require.NoError(t, err)
+			if tc.ipv6 {
+				msg, err := icmp.ParseMessage(ipProtoICMPv6, icmpPacket[ipv6.HeaderLen:])
+				require.NoError(t, err)
+				require.Equal(t, ipv6.ICMPTypePacketTooBig, msg.Type)
+				require.Equal(t, tc.wantMTU, msg.Body.(*icmp.PacketTooBig).MTU)
+			} else {
+				msg := icmpPacket[ipv4.HeaderLen:]
+				require.Equal(t, []byte{3, 4}, msg[:2])
+				require.Equal(t, uint16(tc.wantMTU), binary.BigEndian.Uint16(msg[6:8]))
+			}
+		})
+	}
+}
+
+func TestMaxPacketSize(t *testing.T) {
+	t.Run("sends nothing", func(t *testing.T) {
+		str := &mockStream{streamID: 8, maxDatagramPayloadSize: 1350}
+		conn := newProxiedConn(str)
+		t.Cleanup(func() { conn.Close() })
+		require.Equal(t, 1348, conn.MaxPacketSize())
+		require.Empty(t, str.sent)
+	})
+
+	t.Run("datagrams unsupported", func(t *testing.T) {
+		conn := newProxiedConn(&mockStream{sendDatagramErr: errors.New("datagram support disabled")})
+		t.Cleanup(func() { conn.Close() })
+		require.Zero(t, conn.MaxPacketSize())
+	})
+
+	t.Run("closed", func(t *testing.T) {
+		conn := newProxiedConn(&mockStream{maxDatagramPayloadSize: 1350})
+		require.NoError(t, conn.Close())
+		require.Zero(t, conn.MaxPacketSize())
+	})
+}
+
+func TestReadPacketDropsMalformedDatagrams(t *testing.T) {
+	packet := ipv4Packet(64, 17, testSrc4, testDst4, nil, []byte("foobar"))
+	for _, tc := range []struct {
+		name     string
+		datagram []byte
+	}{
+		{"empty", []byte{}},
+		{"truncated Context ID", []byte{0x40}},
+		{"unknown Context ID", append([]byte{0x02}, packet...)},
+		{"empty IP packet", []byte{0x00}},
+		{"invalid IP packet", []byte{0x00, 0x50}},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			datagrams := make(chan []byte, 2)
+			conn := newProxiedConn(&mockStream{datagrams: datagrams})
+			t.Cleanup(func() { conn.Close() })
+			require.NoError(t, conn.AdvertiseRoute([]IPRoute{
+				{StartIP: netip.IPv4Unspecified(), EndIP: netip.MustParseAddr("255.255.255.255")},
+			}))
+
+			datagrams <- tc.datagram
+			datagrams <- append(bytes.Clone(contextIDZero), packet...)
+			b := make([]byte, 1500)
+			n, err := conn.ReadPacket(b)
+			require.NoError(t, err)
+			require.Equal(t, packet, b[:n])
+		})
+	}
+}
+
+func TestReadPacketShortBuffer(t *testing.T) {
+	datagrams := make(chan []byte, 3)
+	conn := newProxiedConn(&mockStream{datagrams: datagrams})
+	t.Cleanup(func() { conn.Close() })
+	require.NoError(t, conn.AdvertiseRoute([]IPRoute{
+		{StartIP: netip.IPv4Unspecified(), EndIP: netip.MustParseAddr("255.255.255.255")},
+	}))
+
+	packet := ipv4Packet(64, 17, testSrc4, testDst4, nil, []byte("foobar"))
+	for range 3 {
+		datagrams <- append(bytes.Clone(contextIDZero), packet...)
+	}
+	n, err := conn.ReadPacket(make([]byte, len(packet)-1))
+	require.ErrorIs(t, err, io.ErrShortBuffer)
+	require.Zero(t, n)
+
+	b := make([]byte, len(packet))
+	n, err = conn.ReadPacket(b)
+	require.NoError(t, err)
+	require.Equal(t, packet, b[:n])
+	n, err = conn.ReadPacket(make([]byte, 1500))
+	require.NoError(t, err)
+	require.Equal(t, len(packet), n)
+}
+
+func TestCloseConcurrently(t *testing.T) {
+	for _, side := range []string{"client", "proxy"} {
+		t.Run(side, func(t *testing.T) {
+			client, server := setupConns(t)
+			conn := client
+			if side == "proxy" {
+				conn = server
+			}
+
+			readErr := make(chan error, 1)
+			go func() {
+				b := make([]byte, 1500)
+				for {
+					if _, err := conn.ReadPacket(b); err != nil {
+						readErr <- err
+						return
+					}
+				}
+			}()
+			writeErr := make(chan error, 1)
+			go func() {
+				for {
+					if _, err := conn.WritePacket(ipv4Packet(64, 17, testSrc4, testDst4, nil, nil)); err != nil {
+						writeErr <- err
+						return
+					}
+				}
+			}()
+
+			var wg sync.WaitGroup
+			for range 4 {
+				wg.Go(func() { assert.NoError(t, conn.Close()) })
+			}
+			wg.Wait()
+			for _, errChan := range []chan error{readErr, writeErr} {
+				select {
+				case err := <-errChan:
+					require.ErrorIs(t, err, net.ErrClosed)
+				case <-time.After(5 * time.Second):
+					t.Fatal("timeout")
+				}
+			}
+			require.NoError(t, conn.Close())
+		})
+	}
+}

transport/internet/masque/connectip/icmp.go

@@ -0,0 +1,94 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright 2024 Marten Seemann
+ * Adapted from github.com/quic-go/connect-ip-go (commit a0c35fa).
+ */
+
+package connectip
+
+import (
+	"encoding/binary"
+	"errors"
+	"fmt"
+
+	"golang.org/x/net/icmp"
+	"golang.org/x/net/ipv4"
+	"golang.org/x/net/ipv6"
+)
+
+const (
+	ipv4MinMTU = 68
+	ipv6MinMTU = 1280
+)
+
+var ErrMTUTooSmall = errors.New("connect-ip: tunnel MTU below the minimum link MTU")
+
+func composeICMPTooLargePacket(b []byte, mtu int) ([]byte, error) {
+	if len(b) == 0 {
+		return nil, errors.New("connect-ip: empty packet")
+	}
+
+	var icmpMessage *icmp.Message
+	var psh []byte
+	switch v := ipVersion(b); v {
+	case 4:
+		if len(b) < ipv4.HeaderLen {
+			return nil, errors.New("connect-ip: IPv4 packet too short")
+		}
+		if mtu < ipv4MinMTU {
+			return nil, fmt.Errorf("%w: %d bytes", ErrMTUTooSmall, mtu)
+		}
+		icmpMessage = &icmp.Message{
+			Type: ipv4.ICMPTypeDestinationUnreachable,
+			Code: 4,
+			Body: &icmp.PacketTooBig{
+				MTU:  mtu,
+				Data: b[:min(len(b), max(ipv4.HeaderLen, int(b[0]&0x0f)<<2)+8)],
+			},
+		}
+	case 6:
+		if len(b) < ipv6.HeaderLen {
+			return nil, errors.New("connect-ip: IPv6 packet too short")
+		}
+		if mtu < ipv6MinMTU {
+			return nil, fmt.Errorf("%w: %d bytes", ErrMTUTooSmall, mtu)
+		}
+		icmpMessage = &icmp.Message{
+			Type: ipv6.ICMPTypePacketTooBig,
+			Body: &icmp.PacketTooBig{
+				MTU:  mtu,
+				Data: b[:min(len(b), 1232)],
+			},
+		}
+		psh = icmp.IPv6PseudoHeader(b[24:40], b[8:24])
+	default:
+		return nil, fmt.Errorf("connect-ip: unknown IP version: %d", v)
+	}
+
+	icmp, err := icmpMessage.Marshal(psh)
+	if err != nil {
+		return nil, fmt.Errorf("connect-ip: failed to marshal ICMP message: %w", err)
+	}
+
+	if ipVersion(b) == 4 {
+		var header [ipv4.HeaderLen]byte
+		header[0] = 4<<4 | ipv4.HeaderLen>>2
+		ipLen := ipv4.HeaderLen + len(icmp)
+		binary.BigEndian.PutUint16(header[2:4], uint16(ipLen))
+		header[8] = 64
+		header[9] = 1
+		copy(header[12:16], b[16:20])
+		copy(header[16:20], b[12:16])
+		binary.BigEndian.PutUint16(header[10:12], calculateIPv4Checksum(header[:]))
+		return append(header[:], icmp...), nil
+	}
+
+	var header [ipv6.HeaderLen]byte
+	header[0] = 6 << 4
+	binary.BigEndian.PutUint16(header[4:6], uint16(len(icmp)))
+	header[6] = 58
+	header[7] = 64
+	copy(header[8:24], b[24:40])
+	copy(header[24:40], b[8:24])
+	return append(header[:], icmp...), nil
+}

transport/internet/masque/connectip/icmp_test.go

@@ -0,0 +1,158 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright 2024 Marten Seemann
+ * Adapted from github.com/quic-go/connect-ip-go (commit a0c35fa).
+ */
+
+package connectip
+
+import (
+	"encoding/binary"
+	"net"
+	"net/netip"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	"golang.org/x/net/icmp"
+	"golang.org/x/net/ipv4"
+	"golang.org/x/net/ipv6"
+)
+
+func TestICMPTooLargeIPv4(t *testing.T) {
+	src := netip.MustParseAddr("192.168.1.1")
+	dst := netip.MustParseAddr("8.8.8.8")
+	origHdr := &ipv4.Header{
+		Version:  4,
+		Len:      ipv4.HeaderLen,
+		TotalLen: 60,
+		TTL:      64,
+		Protocol: 6,
+		Src:      src.AsSlice(),
+		Dst:      dst.AsSlice(),
+	}
+	origBytes, err := origHdr.Marshal()
+	require.NoError(t, err)
+	data, err := composeICMPTooLargePacket(origBytes, 1200)
+	require.NoError(t, err)
+
+	hdr, err := ipv4.ParseHeader(data)
+	require.NoError(t, err)
+	require.Equal(t, 4, hdr.Version)
+	require.Equal(t, ipProtoICMP, hdr.Protocol)
+	require.Equal(t, dst.String(), hdr.Src.String())
+	require.Equal(t, src.String(), hdr.Dst.String())
+	require.Equal(t, uint16(hdr.Checksum), calculateIPv4Checksum(data[:ipv4.HeaderLen]))
+	icmpMsg, err := icmp.ParseMessage(ipProtoICMP, data[ipv4.HeaderLen:])
+	require.NoError(t, err)
+	require.Equal(t, ipv4.ICMPTypeDestinationUnreachable, icmpMsg.Type)
+	require.Equal(t, 4, icmpMsg.Code)
+	require.Equal(t, uint16(1200), binary.BigEndian.Uint16(data[ipv4.HeaderLen+6:]))
+	require.Equal(t, origBytes, data[ipv4.HeaderLen+8:])
+}
+
+func TestICMPTooLargeIPv4Options(t *testing.T) {
+	options := []byte{0x94, 0x04, 0x00, 0x00}
+	orig := ipv4Packet(64, 6, netip.MustParseAddr("192.168.1.1"), netip.MustParseAddr("8.8.8.8"), options, make([]byte, 20))
+	data, err := composeICMPTooLargePacket(orig, 1200)
+	require.NoError(t, err)
+	require.Equal(t, orig[:ipv4.HeaderLen+len(options)+8], data[ipv4.HeaderLen+8:])
+}
+
+func TestICMPTooLargeIPv6(t *testing.T) {
+	const mtu = 1337
+	src := netip.MustParseAddr("2001:db8::1")
+	dst := netip.MustParseAddr("1:2:3:4::5")
+	orig := []byte{
+		0x60, 0x00, 0x00, 0x00,
+		0x00, 0x00,
+		0x00, 0x2a,
+	}
+	orig = append(orig, src.AsSlice()...)
+	orig = append(orig, dst.AsSlice()...)
+	orig = append(orig, []byte("foobar")...)
+	data, err := composeICMPTooLargePacket(orig, mtu)
+	require.NoError(t, err)
+
+	hdr, err := ipv6.ParseHeader(data)
+	require.NoError(t, err)
+	require.Equal(t, 6, hdr.Version)
+	require.Equal(t, ipProtoICMPv6, hdr.NextHeader)
+	require.Equal(t, dst.String(), hdr.Src.String())
+	require.Equal(t, src.String(), hdr.Dst.String())
+	icmpMsg, err := icmp.ParseMessage(ipProtoICMPv6, data[ipv6.HeaderLen:])
+	require.NoError(t, err)
+	require.Equal(t, ipv6.ICMPTypePacketTooBig, icmpMsg.Type)
+	icmpBody, ok := icmpMsg.Body.(*icmp.PacketTooBig)
+	require.True(t, ok)
+	require.Equal(t, mtu, icmpBody.MTU)
+	require.Equal(t, orig, icmpBody.Data)
+}
+
+func TestICMPTooLargeMinimumMTU(t *testing.T) {
+	ipv4Orig := ipv4Packet(64, 6, testSrc4, testDst4, nil, make([]byte, 100))
+	ipv6Orig := ipv6Packet(64, 6, testSrc6, testDst6, make([]byte, 1300))
+	for _, tc := range []struct {
+		name     string
+		packet   []byte
+		mtu      int
+		tooSmall bool
+	}{
+		{"IPv4 minimum", ipv4Orig, 68, false},
+		{"IPv4 below minimum", ipv4Orig, 67, true},
+		{"IPv4 negative", ipv4Orig, -1, true},
+		{"IPv6 minimum", ipv6Orig, 1280, false},
+		{"IPv6 below minimum", ipv6Orig, 1279, true},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			data, err := composeICMPTooLargePacket(tc.packet, tc.mtu)
+			if tc.tooSmall {
+				require.ErrorIs(t, err, ErrMTUTooSmall)
+				require.Nil(t, data)
+				return
+			}
+			require.NoError(t, err)
+			require.NotEmpty(t, data)
+		})
+	}
+}
+
+func TestICMPFailures(t *testing.T) {
+	t.Run("empty packet", func(t *testing.T) {
+		_, err := composeICMPTooLargePacket([]byte{}, 1)
+		require.EqualError(t, err, "connect-ip: empty packet")
+	})
+
+	t.Run("too short IPv4 header", func(t *testing.T) {
+		origHdr := &ipv4.Header{
+			Version:  4,
+			Len:      ipv4.HeaderLen,
+			TotalLen: 60,
+			Src:      net.IPv4(1, 2, 3, 4),
+			Dst:      net.IPv4(5, 6, 7, 8),
+		}
+		data, err := origHdr.Marshal()
+		require.NoError(t, err)
+		_, err = composeICMPTooLargePacket(data[:ipv4.HeaderLen-1], 1)
+		require.EqualError(t, err, "connect-ip: IPv4 packet too short")
+	})
+
+	t.Run("too short IPv6 header", func(t *testing.T) {
+		data := []byte{
+			0x60, 0x00, 0x00, 0x00,
+			0x00, 0x00,
+			0x00, 0x40,
+		}
+		data = append(data, net.ParseIP("2001:db8::1").To16()...)
+		data = append(data, net.ParseIP("2001:db8::2").To16()...)
+		_, err := composeICMPTooLargePacket(data[:ipv6.HeaderLen-1], 1)
+		require.EqualError(t, err, "connect-ip: IPv6 packet too short")
+	})
+
+	t.Run("unknown IP version", func(t *testing.T) {
+		data := []byte{
+			0x30, 0x00, 0x00, 0x00,
+		}
+		_, err := composeICMPTooLargePacket(data, 1)
+		require.EqualError(t, err, "connect-ip: unknown IP version: 3")
+	})
+}

transport/internet/masque/connectip/iprange.go

@@ -0,0 +1,73 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright 2024 Marten Seemann
+ * Adapted from github.com/quic-go/connect-ip-go (commit a0c35fa).
+ */
+
+package connectip
+
+import "net/netip"
+
+func rangeToPrefixes(start, end netip.Addr) []netip.Prefix {
+	var prefixes []netip.Prefix
+	for current := start; current.Compare(end) <= 0; {
+		prefix := findLargestPrefix(current, end)
+		prefixes = append(prefixes, prefix)
+
+		lastIP := lastIPInPrefix(prefix)
+		if lastIP.Compare(end) >= 0 {
+			break
+		}
+		current = lastIP.Next()
+	}
+	return prefixes
+}
+
+func findLargestPrefix(start, end netip.Addr) netip.Prefix {
+	if start == end {
+		return netip.PrefixFrom(start, start.BitLen())
+	}
+
+	var prefixLen int
+	for prefixLen = start.BitLen(); prefixLen > 0; prefixLen-- {
+		prefix := netip.PrefixFrom(start, prefixLen-1)
+		if lastIPInPrefix(prefix).Compare(end) > 0 || !isAligned(start, prefixLen-1) {
+			break
+		}
+	}
+	return netip.PrefixFrom(start, prefixLen)
+}
+
+func lastIPInPrefix(prefix netip.Prefix) netip.Addr {
+	addr := prefix.Addr()
+	bits := addr.As16()
+
+	hostBits := addr.BitLen() - prefix.Bits()
+
+	for i := len(bits) - 1; i >= 0 && hostBits > 0; i-- {
+		bitsInThisByte := min(8, hostBits)
+		mask := byte((1 << bitsInThisByte) - 1)
+		bits[i] |= mask
+		hostBits -= bitsInThisByte
+	}
+
+	if addr.Is4() {
+		return netip.AddrFrom4([4]byte(bits[12:16]))
+	}
+	return netip.AddrFrom16(bits)
+}
+
+func isAligned(addr netip.Addr, prefixLen int) bool {
+	bits := addr.As16()
+
+	hostBits := addr.BitLen() - prefixLen
+	for i := len(bits) - 1; i >= 0 && hostBits > 0; i-- {
+		bitsInThisByte := min(8, hostBits)
+		mask := byte((1 << bitsInThisByte) - 1)
+		if bits[i]&mask != 0 {
+			return false
+		}
+		hostBits -= bitsInThisByte
+	}
+	return true
+}

transport/internet/masque/connectip/iprange_test.go

@@ -0,0 +1,78 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright 2024 Marten Seemann
+ * Adapted from github.com/quic-go/connect-ip-go (commit a0c35fa).
+ */
+
+package connectip
+
+import (
+	"fmt"
+	"net/netip"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestIPRanges(t *testing.T) {
+	tests := []struct {
+		start, end netip.Addr
+		want       []netip.Prefix
+	}{
+		{
+			start: netip.MustParseAddr("192.168.1.1"),
+			end:   netip.MustParseAddr("192.168.1.1"),
+			want:  []netip.Prefix{netip.MustParsePrefix("192.168.1.1/32")},
+		},
+		{
+			start: netip.MustParseAddr("192.168.1.0"),
+			end:   netip.MustParseAddr("192.168.1.1"),
+			want:  []netip.Prefix{netip.MustParsePrefix("192.168.1.0/31")},
+		},
+		{
+			start: netip.MustParseAddr("192.168.1.1"),
+			end:   netip.MustParseAddr("192.168.1.2"),
+			want:  []netip.Prefix{netip.MustParsePrefix("192.168.1.1/32"), netip.MustParsePrefix("192.168.1.2/32")},
+		},
+		{
+			start: netip.MustParseAddr("192.168.1.0"),
+			end:   netip.MustParseAddr("192.168.1.255"),
+			want:  []netip.Prefix{netip.MustParsePrefix("192.168.1.0/24")},
+		},
+		{
+			start: netip.MustParseAddr("10.0.0.0"),
+			end:   netip.MustParseAddr("10.1.0.255"),
+			want:  []netip.Prefix{netip.MustParsePrefix("10.0.0.0/16"), netip.MustParsePrefix("10.1.0.0/24")},
+		},
+		{
+			start: netip.MustParseAddr("2001:0db8:85a3::8a2e:0370:7334"),
+			end:   netip.MustParseAddr("2001:0db8:85a3::8a2e:0370:7334"),
+			want:  []netip.Prefix{netip.MustParsePrefix("2001:0db8:85a3::8a2e:0370:7334/128")},
+		},
+		{
+			start: netip.MustParseAddr("2001:db8::0"),
+			end:   netip.MustParseAddr("2001:db8::ffff:ffff:ffff:ffff"),
+			want:  []netip.Prefix{netip.MustParsePrefix("2001:db8::/64")},
+		},
+		{
+			start: netip.MustParseAddr("2001:db8::1"),
+			end:   netip.MustParseAddr("2001:db8::2"),
+			want:  []netip.Prefix{netip.MustParsePrefix("2001:db8::1/128"), netip.MustParsePrefix("2001:db8::2/128")},
+		},
+		{
+			start: netip.MustParseAddr("2001:db8:1234:5678::"),
+			end:   netip.MustParseAddr("2001:db8:1234:5679::"),
+			want: []netip.Prefix{
+				netip.MustParsePrefix("2001:db8:1234:5678::/64"),
+				netip.MustParsePrefix("2001:db8:1234:5679::/128"),
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(fmt.Sprintf("%s-%s", test.start, test.end), func(t *testing.T) {
+			prefixes := rangeToPrefixes(test.start, test.end)
+			require.Equal(t, test.want, prefixes)
+		})
+	}
+}

transport/internet/masque/connectip/proxy.go

@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright 2024 Marten Seemann
+ * Adapted from github.com/quic-go/connect-ip-go (commit a0c35fa).
+ */
+
+package connectip
+
+import (
+	"errors"
+	"net/http"
+
+	"github.com/apernet/quic-go/http3"
+	"github.com/apernet/quic-go/quicvarint"
+)
+
+var contextIDZero = quicvarint.Append([]byte{}, 0)
+
+type Proxy struct{}
+
+func (s *Proxy) Proxy(w http.ResponseWriter, _ *ProxyRequest) (*Conn, error) {
+	streamer, ok := w.(http3.HTTPStreamer)
+	if !ok {
+		return nil, errors.New("connect-ip: response writer is not an HTTP/3 stream")
+	}
+	w.Header().Set(http3.CapsuleProtocolHeader, capsuleProtocolHeaderValue)
+	w.WriteHeader(http.StatusOK)
+
+	return newProxiedConn(streamer.HTTPStream()), nil
+}

transport/internet/masque/connectip/proxy_test.go

@@ -0,0 +1,413 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright 2024 Marten Seemann
+ * Adapted from github.com/quic-go/connect-ip-go (commit a0c35fa).
+ */
+
+package connectip
+
+import (
+	"context"
+	"crypto/tls"
+	"encoding/binary"
+	"fmt"
+	"net"
+	"net/http"
+	"net/netip"
+	"slices"
+	"testing"
+	"time"
+
+	"github.com/apernet/quic-go"
+	"github.com/apernet/quic-go/http3"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"golang.org/x/net/ipv4"
+	"golang.org/x/net/ipv6"
+)
+
+func dialHTTP3(t *testing.T, addr string) *http3.ClientConn {
+	t.Helper()
+
+	ctx, cancel := context.WithTimeout(t.Context(), 5*time.Second)
+	defer cancel()
+	qconn, err := quic.DialAddr(
+		ctx,
+		addr,
+		&tls.Config{ServerName: "localhost", RootCAs: certPool, NextProtos: []string{http3.NextProtoH3}},
+		&quic.Config{EnableDatagrams: true, InitialPacketSize: 1350, DisablePathMTUDiscovery: true},
+	)
+	require.NoError(t, err)
+	t.Cleanup(func() { qconn.CloseWithError(0, "") })
+	return (&http3.Transport{EnableDatagrams: true}).NewClientConn(qconn)
+}
+
+func setupConns(t *testing.T) (client, server *Conn) {
+	t.Helper()
+
+	p := &Proxy{}
+	conn, err := net.ListenUDP("udp4", &net.UDPAddr{IP: net.IPv4(127, 0, 0, 1), Port: 0})
+	require.NoError(t, err)
+	t.Cleanup(func() { conn.Close() })
+
+	proxyURL := fmt.Sprintf("https://%s/connect-ip", conn.LocalAddr())
+	connChan := make(chan *Conn, 1)
+	mux := http.NewServeMux()
+	mux.HandleFunc("/connect-ip", func(w http.ResponseWriter, r *http.Request) {
+		assert.Equal(t, "Bearer token", r.Header.Get("Authorization"))
+		mreq, err := ParseProxyRequest(r)
+		if !assert.NoError(t, err) {
+			w.WriteHeader(http.StatusBadRequest)
+			return
+		}
+
+		conn, err := p.Proxy(w, mreq)
+		if assert.NoError(t, err) {
+			connChan <- conn
+		}
+	})
+	s := http3.Server{
+		Handler:         mux,
+		Addr:            ":0",
+		EnableDatagrams: true,
+		TLSConfig:       tlsConf,
+	}
+	go func() { s.Serve(conn) }()
+	t.Cleanup(func() { s.Close() })
+
+	ctx, cancel := context.WithTimeout(t.Context(), 5*time.Second)
+	defer cancel()
+	req, err := NewRequest(ctx, proxyURL)
+	require.NoError(t, err)
+	req.Header().Set("Authorization", "Bearer token")
+	client, rsp, err := NewClientConn(dialHTTP3(t, conn.LocalAddr().String())).Dial(req)
+	require.NoError(t, err)
+	t.Cleanup(func() { client.Close() })
+	require.Equal(t, http.StatusOK, rsp.StatusCode)
+
+	select {
+	case <-time.After(5 * time.Second):
+		t.Fatal("timed out")
+	case server = <-connChan:
+	}
+	t.Cleanup(func() { server.Close() })
+	return client, server
+}
+
+func TestAddressAssignment(t *testing.T) {
+	client, server := setupConns(t)
+
+	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Millisecond)
+	defer cancel()
+	_, err := server.ReceiveAddressAssignment(ctx)
+	require.ErrorIs(t, err, context.DeadlineExceeded)
+
+	ctx, cancel = context.WithTimeout(context.Background(), time.Second)
+	defer cancel()
+	pref1 := netip.MustParsePrefix("1.1.1.0/24")
+	pref2 := netip.MustParsePrefix("2001:db8::/64")
+	require.NoError(t, client.AssignAddresses([]netip.Prefix{pref1, pref2}))
+	assigned, err := server.ReceiveAddressAssignment(ctx)
+	require.NoError(t, err)
+	require.Equal(t, []AssignedAddress{{IPPrefix: pref1}, {IPPrefix: pref2}}, assigned)
+
+	require.NoError(t, client.AssignAddresses([]netip.Prefix{}))
+	assigned, err = server.ReceiveAddressAssignment(ctx)
+	require.NoError(t, err)
+	require.Empty(t, assigned)
+}
+
+func TestRejectingAddressRequestKeepsPeerUnrestricted(t *testing.T) {
+	client, server := setupConns(t)
+	ctx, cancel := context.WithTimeout(t.Context(), 5*time.Second)
+	defer cancel()
+
+	clientAddr := netip.MustParsePrefix("192.0.2.2/32")
+	require.NoError(t, server.AssignAddresses([]netip.Prefix{clientAddr}))
+	_, err := client.ReceiveAddressAssignment(ctx)
+	require.NoError(t, err)
+
+	_, err = server.RequestAddresses([]netip.Prefix{netip.MustParsePrefix("0.0.0.0/32")})
+	require.NoError(t, err)
+	req, err := client.ReceiveAddressRequest(ctx)
+	require.NoError(t, err)
+	require.NoError(t, req.Respond([]netip.Prefix{{}}, nil))
+	assigned, err := server.ReceiveAddressAssignment(ctx)
+	require.NoError(t, err)
+	require.Len(t, assigned, 1)
+	require.True(t, assigned[0].Rejected())
+
+	packet := ipv4Packet(64, 17, netip.MustParseAddr("203.0.113.9"), clientAddr.Addr(), nil, []byte("foobar"))
+	_, err = server.WritePacket(slices.Clone(packet))
+	require.NoError(t, err)
+	received := make(chan []byte, 1)
+	go func() {
+		b := make([]byte, 1500)
+		if n, err := client.ReadPacket(b); err == nil {
+			received <- b[:n]
+		}
+	}()
+	select {
+	case b := <-received:
+		require.Equal(t, packet[20:], b[20:])
+	case <-ctx.Done():
+		t.Fatal("packet was not received")
+	}
+}
+
+func TestRejectingAddressRequestWithdrawsAssignment(t *testing.T) {
+	client, server := setupConns(t)
+	ctx, cancel := context.WithTimeout(t.Context(), 5*time.Second)
+	defer cancel()
+
+	clientAddr := netip.MustParsePrefix("192.0.2.2/32")
+	dst := netip.MustParseAddr("198.51.100.1")
+	require.NoError(t, server.AssignAddresses([]netip.Prefix{clientAddr}))
+	require.NoError(t, server.AdvertiseRoute([]IPRoute{{StartIP: dst, EndIP: dst}}))
+	_, err := client.ReceiveAddressAssignment(ctx)
+	require.NoError(t, err)
+
+	received := make(chan []byte, 4)
+	go func() {
+		b := make([]byte, 1500)
+		for {
+			n, err := server.ReadPacket(b)
+			if err != nil {
+				return
+			}
+			received <- slices.Clone(b[20:n])
+		}
+	}()
+	send := func(payload string) {
+		_, err := client.WritePacket(ipv4Packet(64, 17, clientAddr.Addr(), dst, nil, []byte(payload)))
+		require.NoError(t, err)
+	}
+
+	send("assigned")
+	select {
+	case b := <-received:
+		require.Equal(t, "assigned", string(b))
+	case <-ctx.Done():
+		t.Fatal("packet from the assigned address was not received")
+	}
+
+	_, err = client.RequestAddresses([]netip.Prefix{netip.MustParsePrefix("0.0.0.0/32")})
+	require.NoError(t, err)
+	req, err := server.ReceiveAddressRequest(ctx)
+	require.NoError(t, err)
+	require.NoError(t, req.Respond([]netip.Prefix{{}}, nil))
+	assigned, err := client.ReceiveAddressAssignment(ctx)
+	require.NoError(t, err)
+	require.Len(t, assigned, 1)
+	require.True(t, assigned[0].Rejected())
+
+	send("withdrawn")
+	select {
+	case b := <-received:
+		t.Fatalf("packet from a withdrawn address was received: %q", b)
+	case <-time.After(200 * time.Millisecond):
+	}
+}
+
+func TestRouteAdvertisement(t *testing.T) {
+	client, server := setupConns(t)
+
+	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Millisecond)
+	defer cancel()
+	_, err := server.Routes(ctx)
+	require.ErrorIs(t, err, context.DeadlineExceeded)
+
+	ctx, cancel = context.WithTimeout(context.Background(), time.Second)
+	defer cancel()
+
+	require.ErrorContains(t,
+		client.AdvertiseRoute([]IPRoute{
+			{StartIP: netip.MustParseAddr("1.1.1.2"), EndIP: netip.MustParseAddr("1.1.1.1"), IPProtocol: 42},
+		}),
+		"connect-ip: invalid route 0: start IP 1.1.1.2 is greater than end IP 1.1.1.1",
+	)
+
+	require.NoError(t, client.AdvertiseRoute([]IPRoute{
+		{StartIP: netip.MustParseAddr("1.1.1.1"), EndIP: netip.MustParseAddr("2.2.2.2"), IPProtocol: 42},
+		{StartIP: netip.MustParseAddr("2001:db8::1"), EndIP: netip.MustParseAddr("2001:db8::100"), IPProtocol: 24},
+	}))
+	routes, err := server.Routes(ctx)
+	require.NoError(t, err)
+	require.Equal(t, []IPRoute{
+		{StartIP: netip.MustParseAddr("1.1.1.1"), EndIP: netip.MustParseAddr("2.2.2.2"), IPProtocol: 42},
+		{StartIP: netip.MustParseAddr("2001:db8::1"), EndIP: netip.MustParseAddr("2001:db8::100"), IPProtocol: 24},
+	}, routes)
+
+	require.NoError(t, client.AdvertiseRoute([]IPRoute{}))
+	routes, err = server.Routes(ctx)
+	require.NoError(t, err)
+	require.Empty(t, routes)
+}
+
+func TestTTLs(t *testing.T) {
+	t.Run("IPv4", func(t *testing.T) {
+		client, server := setupConns(t)
+		require.NoError(t, server.AssignAddresses([]netip.Prefix{netip.MustParsePrefix("192.168.1.1/32")}))
+		require.NoError(t, server.AdvertiseRoute([]IPRoute{
+			{StartIP: netip.MustParseAddr("0.0.0.0"), EndIP: netip.MustParseAddr("255.255.255.255")},
+		}))
+
+		src, dst := netip.MustParseAddr("192.168.1.1"), netip.MustParseAddr("8.8.8.8")
+		icmp, err := client.WritePacket(ipv4Packet(1, 0, src, dst, nil, nil))
+		require.NoError(t, err)
+		require.Empty(t, icmp)
+
+		icmp, err = client.WritePacket(ipv4Packet(42, 0, src, dst, nil, nil))
+		require.NoError(t, err)
+		require.Empty(t, icmp)
+
+		receivedPacket := make([]byte, 1500)
+		n, err := server.ReadPacket(receivedPacket)
+		require.NoError(t, err)
+		receivedPacket = receivedPacket[:n]
+
+		receivedHdr, err := ipv4.ParseHeader(receivedPacket)
+		require.NoError(t, err)
+		require.Equal(t, uint16(receivedHdr.Checksum), calculateIPv4Checksum(receivedPacket[:ipv4.HeaderLen]))
+		require.Equal(t, 41, receivedHdr.TTL)
+	})
+
+	t.Run("IPv6", func(t *testing.T) {
+		client, server := setupConns(t)
+		require.NoError(t, server.AssignAddresses([]netip.Prefix{netip.MustParsePrefix("2001:db8::1/128")}))
+		require.NoError(t, server.AdvertiseRoute([]IPRoute{
+			{StartIP: netip.MustParseAddr("::"), EndIP: netip.MustParseAddr("ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff")},
+		}))
+
+		packetHopLimit1 := []byte{
+			0x60, 0x00, 0x00, 0x00,
+			0x00, 0x00,
+			0x00, 0x01,
+			0x20, 0x01, 0x0d, 0xb8, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01,
+			0x20, 0x01, 0x48, 0x60, 0x48, 0x60, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x88, 0x88,
+		}
+		icmp, err := client.WritePacket(packetHopLimit1)
+		require.NoError(t, err)
+		require.Empty(t, icmp)
+
+		packet := []byte{
+			0x60, 0x00, 0x00, 0x00,
+			0x00, 0x00,
+			0x00, 0x2A,
+			0x20, 0x01, 0x0d, 0xb8, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01,
+			0x20, 0x01, 0x48, 0x60, 0x48, 0x60, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x88, 0x88,
+		}
+		icmp, err = client.WritePacket(packet)
+		require.NoError(t, err)
+		require.Empty(t, icmp)
+
+		receivedPacket := make([]byte, 1500)
+		n, err := server.ReadPacket(receivedPacket)
+		require.NoError(t, err)
+		receivedPacket = receivedPacket[:n]
+
+		receivedHdr, err := ipv6.ParseHeader(receivedPacket)
+		require.NoError(t, err)
+		require.Equal(t, 41, receivedHdr.HopLimit)
+	})
+}
+
+func TestMaxPacketSizeOverQUIC(t *testing.T) {
+	client, server := setupConns(t)
+	require.NoError(t, server.AdvertiseRoute([]IPRoute{
+		{StartIP: netip.MustParseAddr("0.0.0.0"), EndIP: netip.MustParseAddr("255.255.255.255")},
+	}))
+
+	size := client.MaxPacketSize()
+	require.Greater(t, size, 1200)
+	require.Less(t, size, 1350)
+
+	icmp, err := client.WritePacket(ipv4Packet(64, 17, testSrc4, testDst4, nil, make([]byte, size-ipv4.HeaderLen)))
+	require.NoError(t, err)
+	require.Nil(t, icmp)
+	type readResult struct {
+		n   int
+		err error
+	}
+	received := make(chan readResult, 1)
+	go func() {
+		n, err := server.ReadPacket(make([]byte, 1500))
+		received <- readResult{n, err}
+	}()
+	select {
+	case r := <-received:
+		require.NoError(t, r.err)
+		require.Equal(t, size, r.n)
+	case <-time.After(5 * time.Second):
+		t.Fatal("timeout")
+	}
+
+	icmp, err = client.WritePacket(ipv4Packet(64, 17, testSrc4, testDst4, nil, make([]byte, size+1-ipv4.HeaderLen)))
+	require.NoError(t, err)
+	require.NotNil(t, icmp)
+	require.Equal(t, uint16(size), binary.BigEndian.Uint16(icmp[ipv4.HeaderLen+6:]))
+}
+
+func TestClosing(t *testing.T) {
+	ipv6Packet := []byte{
+		0x60, 0x00, 0x00, 0x00,
+		0x00, 0x00,
+		0x00, 0x2A,
+		0x20, 0x01, 0x0d, 0xb8, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01,
+		0x20, 0x01, 0x48, 0x60, 0x48, 0x60, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x88, 0x88,
+	}
+
+	client, server := setupConns(t)
+	routeErrChan := make(chan error, 1)
+	prefixErrChan := make(chan error, 1)
+	go func() {
+		_, err := server.Routes(context.Background())
+		routeErrChan <- err
+	}()
+	go func() {
+		_, err := server.ReceiveAddressAssignment(context.Background())
+		prefixErrChan <- err
+	}()
+
+	require.NoError(t, client.Close())
+	_, err := client.ReceiveAddressAssignment(context.Background())
+	require.ErrorIs(t, err, net.ErrClosed)
+	var closeErr *CloseError
+	require.ErrorAs(t, err, &closeErr)
+	require.False(t, closeErr.Remote)
+	_, err = client.Routes(context.Background())
+	require.ErrorIs(t, err, net.ErrClosed)
+	require.ErrorIs(t,
+		client.AssignAddresses([]netip.Prefix{netip.MustParsePrefix("1.1.1.0/24")}),
+		net.ErrClosed,
+	)
+	require.ErrorIs(t,
+		client.AdvertiseRoute([]IPRoute{
+			{StartIP: netip.MustParseAddr("1.1.1.0"), EndIP: netip.MustParseAddr("1.1.1.1"), IPProtocol: 42},
+		}),
+		net.ErrClosed,
+	)
+	_, err = client.ReadPacket([]byte{0})
+	require.ErrorIs(t, err, net.ErrClosed)
+	_, err = client.WritePacket(ipv6Packet)
+	require.ErrorIs(t, err, net.ErrClosed)
+
+	select {
+	case err := <-routeErrChan:
+		require.ErrorIs(t, err, net.ErrClosed)
+	case <-time.After(time.Second):
+		t.Fatal("timeout")
+	}
+
+	select {
+	case err := <-prefixErrChan:
+		require.ErrorIs(t, err, net.ErrClosed)
+	case <-time.After(time.Second):
+		t.Fatal("timeout")
+	}
+
+	_, err = server.ReadPacket([]byte{0})
+	require.ErrorIs(t, err, net.ErrClosed)
+	_, err = server.WritePacket(ipv6Packet)
+	require.ErrorIs(t, err, net.ErrClosed)
+}

transport/internet/masque/connectip/request.go

@@ -0,0 +1,91 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright 2024 Marten Seemann
+ * Adapted from github.com/quic-go/connect-ip-go (commit a0c35fa).
+ */
+
+package connectip
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net/http"
+	"strings"
+
+	"github.com/apernet/quic-go/http3"
+)
+
+const requestProtocol = "connect-ip"
+
+const capsuleProtocolHeaderValue = "?1"
+
+type Request struct {
+	req *http.Request
+}
+
+func NewRequest(ctx context.Context, rawURL string) (*Request, error) {
+	if strings.ContainsAny(rawURL, "{}") {
+		return nil, errors.New("connect-ip: IP flow forwarding not supported: URL contains a URI Template expression")
+	}
+	req, err := http.NewRequestWithContext(ctx, http.MethodConnect, rawURL, nil)
+	if err != nil {
+		return nil, fmt.Errorf("connect-ip: failed to create request: %w", err)
+	}
+	if req.URL.Scheme != "https" || req.URL.Host == "" || !strings.HasPrefix(req.URL.Path, "/") {
+		return nil, fmt.Errorf("connect-ip: invalid proxy URL %q: expected an absolute https URL with a host and a path", rawURL)
+	}
+	req.Proto = requestProtocol
+	req.Host = req.URL.Host
+	req.Header.Set(http3.CapsuleProtocolHeader, capsuleProtocolHeaderValue)
+	return &Request{req: req}, nil
+}
+
+func (r *Request) Header() http.Header { return r.req.Header }
+
+func (r *Request) httpRequest() *http.Request { return r.req }
+
+type ProxyRequest struct{}
+
+type ProxyRequestParseError struct {
+	HTTPStatus int
+	Err        error
+}
+
+func (e *ProxyRequestParseError) Error() string { return e.Err.Error() }
+func (e *ProxyRequestParseError) Unwrap() error { return e.Err }
+
+func ParseProxyRequest(r *http.Request) (*ProxyRequest, error) {
+	if r.Method != http.MethodConnect {
+		return nil, &ProxyRequestParseError{
+			HTTPStatus: http.StatusMethodNotAllowed,
+			Err:        fmt.Errorf("expected CONNECT request, got %s", r.Method),
+		}
+	}
+	if r.Proto != requestProtocol {
+		return nil, &ProxyRequestParseError{
+			HTTPStatus: http.StatusNotImplemented,
+			Err:        fmt.Errorf("unexpected protocol: %s", r.Proto),
+		}
+	}
+	capsuleHeaderValues, ok := r.Header[http3.CapsuleProtocolHeader]
+	if !ok {
+		return nil, &ProxyRequestParseError{
+			HTTPStatus: http.StatusBadRequest,
+			Err:        fmt.Errorf("missing Capsule-Protocol header"),
+		}
+	}
+	if !isCapsuleProtocolEnabled(capsuleHeaderValues) {
+		return nil, &ProxyRequestParseError{
+			HTTPStatus: http.StatusBadRequest,
+			Err:        fmt.Errorf("invalid capsule header value: %s", capsuleHeaderValues),
+		}
+	}
+
+	return &ProxyRequest{}, nil
+}
+
+func isCapsuleProtocolEnabled(values []string) bool {
+	v := strings.Trim(strings.Join(values, ","), " ")
+	return v == capsuleProtocolHeaderValue || strings.HasPrefix(v, capsuleProtocolHeaderValue+";")
+}

transport/internet/masque/connectip/request_test.go

@@ -0,0 +1,119 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright 2024 Marten Seemann
+ * Adapted from github.com/quic-go/connect-ip-go (commit a0c35fa).
+ */
+
+package connectip
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/apernet/quic-go/http3"
+	"github.com/stretchr/testify/require"
+)
+
+func newRequest(target string) *http.Request {
+	req := httptest.NewRequest(http.MethodGet, target, nil)
+	req.Method = http.MethodConnect
+	req.Proto = requestProtocol
+	req.Header.Add("Capsule-Protocol", capsuleProtocolHeaderValue)
+	return req
+}
+
+func TestNewRequest(t *testing.T) {
+	req, err := NewRequest(t.Context(), "https://localhost:1234/masque/ip")
+	require.NoError(t, err)
+	httpReq := req.httpRequest()
+	require.Equal(t, http.MethodConnect, httpReq.Method)
+	require.Equal(t, requestProtocol, httpReq.Proto)
+	require.Equal(t, "localhost:1234", httpReq.Host)
+	require.Equal(t, "?1", req.Header().Get(http3.CapsuleProtocolHeader))
+
+	req.Header().Set("Authorization", "Bearer token")
+	require.Equal(t, "Bearer token", httpReq.Header.Get("Authorization"))
+}
+
+func TestNewRequestInvalidURL(t *testing.T) {
+	for _, tc := range []struct {
+		name, url, err string
+	}{
+		{"template with variables", "https://localhost/.well-known/masque/ip/{target}/{ipproto}/", "IP flow forwarding not supported"},
+		{"template with query variables", "https://localhost/masque/ip{?target,ipproto}", "IP flow forwarding not supported"},
+		{"not https", "http://localhost/masque/ip", "expected an absolute https URL"},
+		{"no host", "https:///masque/ip", "expected an absolute https URL"},
+		{"no path", "https://localhost", "expected an absolute https URL"},
+		{"relative", "/masque/ip", "expected an absolute https URL"},
+		{"unparsable", "https://local\x7fhost/", "failed to create request"},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			_, err := NewRequest(t.Context(), tc.url)
+			require.ErrorContains(t, err, tc.err)
+		})
+	}
+}
+
+func TestProxyRequestParsing(t *testing.T) {
+	t.Run("valid request", func(t *testing.T) {
+		req := newRequest("https://localhost:1234/masque/ip")
+		r, err := ParseProxyRequest(req)
+		require.NoError(t, err)
+		require.Equal(t, &ProxyRequest{}, r)
+	})
+
+	t.Run("wrong protocol", func(t *testing.T) {
+		req := newRequest("https://localhost:1234/masque")
+		req.Proto = "not-connect-ip"
+		_, err := ParseProxyRequest(req)
+		require.EqualError(t, err, "unexpected protocol: not-connect-ip")
+		require.Equal(t, http.StatusNotImplemented, err.(*ProxyRequestParseError).HTTPStatus)
+	})
+
+	t.Run("wrong request method", func(t *testing.T) {
+		req := newRequest("https://localhost:1234/masque")
+		req.Method = http.MethodHead
+		_, err := ParseProxyRequest(req)
+		require.EqualError(t, err, "expected CONNECT request, got HEAD")
+		require.Equal(t, http.StatusMethodNotAllowed, err.(*ProxyRequestParseError).HTTPStatus)
+	})
+
+	t.Run("missing Capsule-Protocol header", func(t *testing.T) {
+		req := newRequest("https://localhost:1234/masque")
+		req.Header.Del("Capsule-Protocol")
+		_, err := ParseProxyRequest(req)
+		require.EqualError(t, err, "missing Capsule-Protocol header")
+		require.Equal(t, http.StatusBadRequest, err.(*ProxyRequestParseError).HTTPStatus)
+	})
+
+	for _, tc := range []struct {
+		name   string
+		values []string
+		valid  bool
+	}{
+		{name: "true", values: []string{"?1"}, valid: true},
+		{name: "surrounding spaces", values: []string{" ?1 "}, valid: true},
+		{name: "parameters", values: []string{"?1;a;b=?0;c=\"x\""}, valid: true},
+		{name: "false", values: []string{"?0"}},
+		{name: "integer", values: []string{"1"}},
+		{name: "empty", values: []string{""}},
+		{name: "not a structured field", values: []string{"🤡"}},
+		{name: "longer token", values: []string{"?10"}},
+		{name: "space before parameters", values: []string{"?1 ;a"}},
+		{name: "list", values: []string{"?1, ?1"}},
+		{name: "multiple field lines", values: []string{"?1", "?1"}},
+	} {
+		t.Run("Capsule-Protocol header: "+tc.name, func(t *testing.T) {
+			req := newRequest("https://localhost:1234/masque")
+			req.Header[http3.CapsuleProtocolHeader] = tc.values
+			_, err := ParseProxyRequest(req)
+			if tc.valid {
+				require.NoError(t, err)
+				return
+			}
+			require.ErrorContains(t, err, "invalid capsule header value")
+			require.Equal(t, http.StatusBadRequest, err.(*ProxyRequestParseError).HTTPStatus)
+		})
+	}
+}

transport/internet/masque/dialer.go

@@ -0,0 +1,237 @@
+package masque
+
+import (
+	"context"
+	"net/netip"
+	"reflect"
+	"runtime"
+	"strings"
+	"time"
+
+	"github.com/apernet/quic-go"
+	"github.com/apernet/quic-go/http3"
+	"github.com/xtls/xray-core/common"
+	"github.com/xtls/xray-core/common/errors"
+	"github.com/xtls/xray-core/common/net"
+	"github.com/xtls/xray-core/common/net/cnc"
+	"github.com/xtls/xray-core/common/utils"
+	"github.com/xtls/xray-core/transport/internet"
+	"github.com/xtls/xray-core/transport/internet/finalmask"
+	"github.com/xtls/xray-core/transport/internet/hysteria/congestion"
+	"github.com/xtls/xray-core/transport/internet/hysteria/congestion/bbr"
+	"github.com/xtls/xray-core/transport/internet/masque/connectip"
+	"github.com/xtls/xray-core/transport/internet/stat"
+	"github.com/xtls/xray-core/transport/internet/tls"
+)
+
+const (
+	MinPacketSize     = 1280
+	initialPacketSize = 1350
+)
+
+func Dial(ctx context.Context, dest net.Destination, streamSettings *internet.MemoryStreamConfig) (stat.Connection, error) {
+	tlsConfig := tls.ConfigFromStreamSettings(streamSettings)
+	if tlsConfig == nil {
+		return nil, errors.New("tls config is nil")
+	}
+	config := streamSettings.ProtocolSettings.(*Config)
+	dest.Network = net.Network_UDP
+
+	gotlsConfig := tlsConfig.GetTLSConfig(tls.WithDestination(dest))
+	gotlsConfig.NextProtos = []string{http3.NextProtoH3}
+
+	quicParams := streamSettings.QuicParams
+	if quicParams == nil {
+		quicParams = &internet.QuicParams{
+			BbrProfile: string(bbr.ProfileStandard),
+		}
+	}
+	quicConfig := &quic.Config{
+		InitialStreamReceiveWindow:     quicParams.InitStreamReceiveWindow,
+		MaxStreamReceiveWindow:         quicParams.MaxStreamReceiveWindow,
+		InitialConnectionReceiveWindow: quicParams.InitConnReceiveWindow,
+		MaxConnectionReceiveWindow:     quicParams.MaxConnReceiveWindow,
+		MaxIdleTimeout:                 time.Duration(quicParams.MaxIdleTimeout) * time.Second,
+		KeepAlivePeriod:                time.Duration(quicParams.KeepAlivePeriod) * time.Second,
+		MaxIncomingStreams:             -1,
+		InitialPacketSize:              initialPacketSize,
+		DisablePathMTUDiscovery:        quicParams.DisablePathMtuDiscovery || (runtime.GOOS != "linux" && runtime.GOOS != "windows" && runtime.GOOS != "darwin"),
+		EnableDatagrams:                true,
+		DisablePathManager:             true,
+	}
+	if quicParams.MaxIdleTimeout == 0 {
+		quicConfig.MaxIdleTimeout = 30 * time.Second
+	}
+	if quicParams.KeepAlivePeriod == 0 {
+		quicConfig.KeepAlivePeriod = net.QuicgoH3KeepAlivePeriod
+	}
+
+	var pktConn net.PacketConn
+	var udpAddr net.Addr
+	if streamSettings.FinalMask != nil {
+		conn, err := streamSettings.FinalMask.DialUDP(ctx, dest)
+		if err != nil {
+			return nil, errors.New("failed to dial to dest").Base(err)
+		}
+		pktConn = conn.(*finalmask.PacketConnWrapper).PacketConn
+		udpAddr = conn.RemoteAddr()
+	} else {
+		conn, err := internet.DialSystem(ctx, dest, streamSettings.SocketSettings)
+		if err != nil {
+			return nil, errors.New("failed to dial to dest").Base(err)
+		}
+		switch c := conn.(type) {
+		case *internet.PacketConnWrapper:
+			pktConn = c.PacketConn
+			udpAddr = c.RemoteAddr()
+		case *cnc.Connection:
+			pktConn = &internet.FakePacketConn{Conn: c}
+			udpAddr = &net.UDPAddr{IP: []byte{0, 0, 0, 0}}
+		default:
+			panic(reflect.TypeOf(c))
+		}
+	}
+
+	tr := &quic.Transport{Conn: pktConn, DisableGSO: quicParams.DisableGSO}
+	qconn, err := tr.Dial(ctx, udpAddr, gotlsConfig, quicConfig)
+	if err != nil {
+		tr.Close()
+		pktConn.Close()
+		return nil, err
+	}
+	context.AfterFunc(qconn.Context(), func() { tr.Close(); pktConn.Close() })
+
+	switch quicParams.Congestion {
+	case "reno":
+	case "", "bbr", "brutal":
+		congestion.UseBBR(qconn, bbr.Profile(quicParams.BbrProfile))
+	case "force-brutal":
+		congestion.UseBrutal(qconn, quicParams.BrutalUp, quicParams.BrutalDisableLossCompensation)
+	default:
+		qconn.CloseWithError(quic.ApplicationErrorCode(http3.ErrCodeNoError), "")
+		return nil, errors.New("unknown congestion control: ", quicParams.Congestion)
+	}
+
+	conn, err := establish(ctx, qconn, config, authority(config, gotlsConfig.ServerName, dest.Port))
+	if err != nil {
+		qconn.CloseWithError(quic.ApplicationErrorCode(http3.ErrCodeNoError), "")
+		return nil, err
+	}
+	return conn, nil
+}
+
+func establish(ctx context.Context, qconn *quic.Conn, config *Config, host string) (*Conn, error) {
+	stop := context.AfterFunc(ctx, func() {
+		qconn.CloseWithError(quic.ApplicationErrorCode(http3.ErrCodeRequestCanceled), "")
+	})
+	defer stop()
+
+	req, err := connectip.NewRequest(ctx, "https://"+host+config.Path)
+	if err != nil {
+		return nil, err
+	}
+	header := req.Header()
+	for k, v := range config.Headers {
+		header.Set(k, v)
+	}
+	switch header.Get("User-Agent") {
+	case "":
+		header["User-Agent"] = nil
+	case "chrome":
+		header.Set("User-Agent", utils.ChromeUA)
+	case "firefox":
+		header.Set("User-Agent", utils.FirefoxUA)
+	case "safari":
+		header.Set("User-Agent", utils.SafariUA)
+	case "edge":
+		header.Set("User-Agent", utils.MSEdgeUA)
+	case "curl":
+		header.Set("User-Agent", utils.CurlUA)
+	case "golang":
+		header.Del("User-Agent")
+	}
+
+	cc := (&http3.Transport{EnableDatagrams: true, DisableCompression: true}).NewClientConn(qconn)
+	ipConn, _, err := connectip.NewClientConn(cc).Dial(req)
+	if err != nil {
+		if ctx.Err() != nil {
+			err = context.Cause(ctx)
+		}
+		return nil, errors.New("CONNECT-IP request failed").Base(err)
+	}
+
+	if n := ipConn.MaxPacketSize(); n < MinPacketSize {
+		ipConn.Close()
+		return nil, errors.New("the tunnel can only carry ", n, "-byte packets, less than ", MinPacketSize)
+	}
+
+	if _, err := ipConn.RequestAddresses([]netip.Prefix{
+		netip.PrefixFrom(netip.IPv4Unspecified(), 32),
+		netip.PrefixFrom(netip.IPv6Unspecified(), 128),
+	}); err != nil {
+		ipConn.Close()
+		return nil, err
+	}
+	var local []netip.Addr
+	for len(local) == 0 {
+		assigned, err := ipConn.ReceiveAddressAssignment(ctx)
+		if err != nil {
+			ipConn.Close()
+			return nil, errors.New("no address assigned").Base(err)
+		}
+		local = localAddrs(assigned)
+	}
+	if !stop() {
+		ipConn.Close()
+		return nil, errors.New("no address assigned").Base(context.Cause(ctx))
+	}
+
+	conn := &Conn{
+		ipConn:   ipConn,
+		quicConn: qconn,
+		local:    local,
+	}
+	go conn.serveAddressAssignments()
+	go conn.serveAddressRequests()
+	return conn, nil
+}
+
+func localAddrs(assigned []connectip.AssignedAddress) []netip.Addr {
+	var local []netip.Addr
+	var has4, has6 bool
+	for _, a := range assigned {
+		if a.Rejected() {
+			continue
+		}
+		addr := a.IPPrefix.Addr()
+		if a.IPPrefix.Bits() != addr.BitLen() {
+			addr = a.IPPrefix.Masked().Addr().Next()
+		}
+		if addr.Is4() && !has4 {
+			has4 = true
+			local = append(local, addr)
+		} else if addr.Is6() && !has6 {
+			has6 = true
+			local = append(local, addr)
+		}
+	}
+	return local
+}
+
+func authority(config *Config, serverName string, port net.Port) string {
+	if config.Host != "" {
+		return config.Host
+	}
+	host := strings.TrimSuffix(strings.TrimPrefix(serverName, "["), "]")
+	if port == 443 {
+		if addr, err := netip.ParseAddr(host); err == nil && addr.Is6() {
+			return "[" + host + "]"
+		}
+		return host
+	}
+	return net.JoinHostPort(host, port.String())
+}
+
+func init() {
+	common.Must(internet.RegisterTransportDialer(protocolName, Dial))
+}

transport/internet/masque/dialer_test.go

@@ -0,0 +1,60 @@
+package masque
+
+import (
+	"net/netip"
+	"slices"
+	"testing"
+
+	"github.com/xtls/xray-core/common/net"
+	"github.com/xtls/xray-core/transport/internet/masque/connectip"
+)
+
+func TestAuthority(t *testing.T) {
+	for _, c := range []struct {
+		host, serverName string
+		port             net.Port
+		want             string
+	}{
+		{serverName: "example.com", port: 443, want: "example.com"},
+		{serverName: "example.com", port: 8443, want: "example.com:8443"},
+		{serverName: "127.0.0.1", port: 443, want: "127.0.0.1"},
+		{serverName: "[2001:db8::1]", port: 443, want: "[2001:db8::1]"},
+		{serverName: "[2001:db8::1]", port: 8443, want: "[2001:db8::1]:8443"},
+		{serverName: "2001:db8::1", port: 8443, want: "[2001:db8::1]:8443"},
+		{host: "proxy.example", serverName: "example.com", port: 8443, want: "proxy.example"},
+	} {
+		if got := authority(&Config{Host: c.host}, c.serverName, c.port); got != c.want {
+			t.Errorf("authority(%q, %q, %d) = %q, want %q", c.host, c.serverName, c.port, got, c.want)
+		}
+	}
+}
+
+func TestLocalAddrs(t *testing.T) {
+	assigned := func(prefixes ...string) []connectip.AssignedAddress {
+		var a []connectip.AssignedAddress
+		for _, p := range prefixes {
+			a = append(a, connectip.AssignedAddress{IPPrefix: netip.MustParsePrefix(p)})
+		}
+		return a
+	}
+	addrs := func(s ...string) []netip.Addr {
+		var a []netip.Addr
+		for _, v := range s {
+			a = append(a, netip.MustParseAddr(v))
+		}
+		return a
+	}
+	for _, c := range []struct {
+		assigned []connectip.AssignedAddress
+		want     []netip.Addr
+	}{
+		{assigned("192.0.2.2/32", "2001:db8::2/128"), addrs("192.0.2.2", "2001:db8::2")},
+		{assigned("2001:db8::/64", "192.0.2.0/24", "198.51.100.7/32"), addrs("2001:db8::1", "192.0.2.1")},
+		{assigned("0.0.0.0/32", "2001:db8::2/128"), addrs("2001:db8::2")},
+		{assigned("0.0.0.0/32", "::/128"), nil},
+	} {
+		if got := localAddrs(c.assigned); !slices.Equal(got, c.want) {
+			t.Errorf("localAddrs(%v) = %v, want %v", c.assigned, got, c.want)
+		}
+	}
+}