v1.0.0

app/dispatcher/config.pb.go

@@ -0,0 +1,209 @@
+// Code generated by protoc-gen-go. DO NOT EDIT.
+// versions:
+// 	protoc-gen-go v1.25.0
+// 	protoc        v3.14.0
+// source: app/dispatcher/config.proto
+
+package dispatcher
+
+import (
+	proto "github.com/golang/protobuf/proto"
+	protoreflect "google.golang.org/protobuf/reflect/protoreflect"
+	protoimpl "google.golang.org/protobuf/runtime/protoimpl"
+	reflect "reflect"
+	sync "sync"
+)
+
+const (
+	// Verify that this generated code is sufficiently up-to-date.
+	_ = protoimpl.EnforceVersion(20 - protoimpl.MinVersion)
+	// Verify that runtime/protoimpl is sufficiently up-to-date.
+	_ = protoimpl.EnforceVersion(protoimpl.MaxVersion - 20)
+)
+
+// This is a compile-time assertion that a sufficiently up-to-date version
+// of the legacy proto package is being used.
+const _ = proto.ProtoPackageIsVersion4
+
+type SessionConfig struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+}
+
+func (x *SessionConfig) Reset() {
+	*x = SessionConfig{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_app_dispatcher_config_proto_msgTypes[0]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *SessionConfig) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*SessionConfig) ProtoMessage() {}
+
+func (x *SessionConfig) ProtoReflect() protoreflect.Message {
+	mi := &file_app_dispatcher_config_proto_msgTypes[0]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use SessionConfig.ProtoReflect.Descriptor instead.
+func (*SessionConfig) Descriptor() ([]byte, []int) {
+	return file_app_dispatcher_config_proto_rawDescGZIP(), []int{0}
+}
+
+type Config struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	Settings *SessionConfig `protobuf:"bytes,1,opt,name=settings,proto3" json:"settings,omitempty"`
+}
+
+func (x *Config) Reset() {
+	*x = Config{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_app_dispatcher_config_proto_msgTypes[1]
+		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_app_dispatcher_config_proto_msgTypes[1]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use Config.ProtoReflect.Descriptor instead.
+func (*Config) Descriptor() ([]byte, []int) {
+	return file_app_dispatcher_config_proto_rawDescGZIP(), []int{1}
+}
+
+func (x *Config) GetSettings() *SessionConfig {
+	if x != nil {
+		return x.Settings
+	}
+	return nil
+}
+
+var File_app_dispatcher_config_proto protoreflect.FileDescriptor
+
+var file_app_dispatcher_config_proto_rawDesc = []byte{
+	0x0a, 0x1b, 0x61, 0x70, 0x70, 0x2f, 0x64, 0x69, 0x73, 0x70, 0x61, 0x74, 0x63, 0x68, 0x65, 0x72,
+	0x2f, 0x63, 0x6f, 0x6e, 0x66, 0x69, 0x67, 0x2e, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x12, 0x13, 0x78,
+	0x72, 0x61, 0x79, 0x2e, 0x61, 0x70, 0x70, 0x2e, 0x64, 0x69, 0x73, 0x70, 0x61, 0x74, 0x63, 0x68,
+	0x65, 0x72, 0x22, 0x15, 0x0a, 0x0d, 0x53, 0x65, 0x73, 0x73, 0x69, 0x6f, 0x6e, 0x43, 0x6f, 0x6e,
+	0x66, 0x69, 0x67, 0x4a, 0x04, 0x08, 0x01, 0x10, 0x02, 0x22, 0x48, 0x0a, 0x06, 0x43, 0x6f, 0x6e,
+	0x66, 0x69, 0x67, 0x12, 0x3e, 0x0a, 0x08, 0x73, 0x65, 0x74, 0x74, 0x69, 0x6e, 0x67, 0x73, 0x18,
+	0x01, 0x20, 0x01, 0x28, 0x0b, 0x32, 0x22, 0x2e, 0x78, 0x72, 0x61, 0x79, 0x2e, 0x61, 0x70, 0x70,
+	0x2e, 0x64, 0x69, 0x73, 0x70, 0x61, 0x74, 0x63, 0x68, 0x65, 0x72, 0x2e, 0x53, 0x65, 0x73, 0x73,
+	0x69, 0x6f, 0x6e, 0x43, 0x6f, 0x6e, 0x66, 0x69, 0x67, 0x52, 0x08, 0x73, 0x65, 0x74, 0x74, 0x69,
+	0x6e, 0x67, 0x73, 0x42, 0x5e, 0x0a, 0x17, 0x63, 0x6f, 0x6d, 0x2e, 0x78, 0x72, 0x61, 0x79, 0x2e,
+	0x61, 0x70, 0x70, 0x2e, 0x64, 0x69, 0x73, 0x70, 0x61, 0x74, 0x63, 0x68, 0x65, 0x72, 0x50, 0x01,
+	0x5a, 0x2b, 0x67, 0x69, 0x74, 0x68, 0x75, 0x62, 0x2e, 0x63, 0x6f, 0x6d, 0x2f, 0x78, 0x74, 0x6c,
+	0x73, 0x2f, 0x78, 0x72, 0x61, 0x79, 0x2d, 0x63, 0x6f, 0x72, 0x65, 0x2f, 0x76, 0x31, 0x2f, 0x61,
+	0x70, 0x70, 0x2f, 0x64, 0x69, 0x73, 0x70, 0x61, 0x74, 0x63, 0x68, 0x65, 0x72, 0xaa, 0x02, 0x13,
+	0x58, 0x72, 0x61, 0x79, 0x2e, 0x41, 0x70, 0x70, 0x2e, 0x44, 0x69, 0x73, 0x70, 0x61, 0x74, 0x63,
+	0x68, 0x65, 0x72, 0x62, 0x06, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x33,
+}
+
+var (
+	file_app_dispatcher_config_proto_rawDescOnce sync.Once
+	file_app_dispatcher_config_proto_rawDescData = file_app_dispatcher_config_proto_rawDesc
+)
+
+func file_app_dispatcher_config_proto_rawDescGZIP() []byte {
+	file_app_dispatcher_config_proto_rawDescOnce.Do(func() {
+		file_app_dispatcher_config_proto_rawDescData = protoimpl.X.CompressGZIP(file_app_dispatcher_config_proto_rawDescData)
+	})
+	return file_app_dispatcher_config_proto_rawDescData
+}
+
+var file_app_dispatcher_config_proto_msgTypes = make([]protoimpl.MessageInfo, 2)
+var file_app_dispatcher_config_proto_goTypes = []interface{}{
+	(*SessionConfig)(nil), // 0: xray.app.dispatcher.SessionConfig
+	(*Config)(nil),        // 1: xray.app.dispatcher.Config
+}
+var file_app_dispatcher_config_proto_depIdxs = []int32{
+	0, // 0: xray.app.dispatcher.Config.settings:type_name -> xray.app.dispatcher.SessionConfig
+	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_app_dispatcher_config_proto_init() }
+func file_app_dispatcher_config_proto_init() {
+	if File_app_dispatcher_config_proto != nil {
+		return
+	}
+	if !protoimpl.UnsafeEnabled {
+		file_app_dispatcher_config_proto_msgTypes[0].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*SessionConfig); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+		file_app_dispatcher_config_proto_msgTypes[1].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*Config); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+	}
+	type x struct{}
+	out := protoimpl.TypeBuilder{
+		File: protoimpl.DescBuilder{
+			GoPackagePath: reflect.TypeOf(x{}).PkgPath(),
+			RawDescriptor: file_app_dispatcher_config_proto_rawDesc,
+			NumEnums:      0,
+			NumMessages:   2,
+			NumExtensions: 0,
+			NumServices:   0,
+		},
+		GoTypes:           file_app_dispatcher_config_proto_goTypes,
+		DependencyIndexes: file_app_dispatcher_config_proto_depIdxs,
+		MessageInfos:      file_app_dispatcher_config_proto_msgTypes,
+	}.Build()
+	File_app_dispatcher_config_proto = out.File
+	file_app_dispatcher_config_proto_rawDesc = nil
+	file_app_dispatcher_config_proto_goTypes = nil
+	file_app_dispatcher_config_proto_depIdxs = nil
+}

app/dispatcher/config.proto

@@ -0,0 +1,15 @@
+syntax = "proto3";
+
+package xray.app.dispatcher;
+option csharp_namespace = "Xray.App.Dispatcher";
+option go_package = "github.com/xtls/xray-core/v1/app/dispatcher";
+option java_package = "com.xray.app.dispatcher";
+option java_multiple_files = true;
+
+message SessionConfig {
+  reserved 1;
+}
+
+message Config {
+  SessionConfig settings = 1;
+}

app/dispatcher/default.go

@@ -0,0 +1,301 @@
+// +build !confonly
+
+package dispatcher
+
+//go:generate go run github.com/xtls/xray-core/v1/common/errors/errorgen
+
+import (
+	"context"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/xtls/xray-core/v1/common"
+	"github.com/xtls/xray-core/v1/common/buf"
+	"github.com/xtls/xray-core/v1/common/log"
+	"github.com/xtls/xray-core/v1/common/net"
+	"github.com/xtls/xray-core/v1/common/protocol"
+	"github.com/xtls/xray-core/v1/common/session"
+	"github.com/xtls/xray-core/v1/core"
+	"github.com/xtls/xray-core/v1/features/outbound"
+	"github.com/xtls/xray-core/v1/features/policy"
+	"github.com/xtls/xray-core/v1/features/routing"
+	routing_session "github.com/xtls/xray-core/v1/features/routing/session"
+	"github.com/xtls/xray-core/v1/features/stats"
+	"github.com/xtls/xray-core/v1/transport"
+	"github.com/xtls/xray-core/v1/transport/pipe"
+)
+
+var (
+	errSniffingTimeout = newError("timeout on sniffing")
+)
+
+type cachedReader struct {
+	sync.Mutex
+	reader *pipe.Reader
+	cache  buf.MultiBuffer
+}
+
+func (r *cachedReader) Cache(b *buf.Buffer) {
+	mb, _ := r.reader.ReadMultiBufferTimeout(time.Millisecond * 100)
+	r.Lock()
+	if !mb.IsEmpty() {
+		r.cache, _ = buf.MergeMulti(r.cache, mb)
+	}
+	b.Clear()
+	rawBytes := b.Extend(buf.Size)
+	n := r.cache.Copy(rawBytes)
+	b.Resize(0, int32(n))
+	r.Unlock()
+}
+
+func (r *cachedReader) readInternal() buf.MultiBuffer {
+	r.Lock()
+	defer r.Unlock()
+
+	if r.cache != nil && !r.cache.IsEmpty() {
+		mb := r.cache
+		r.cache = nil
+		return mb
+	}
+
+	return nil
+}
+
+func (r *cachedReader) ReadMultiBuffer() (buf.MultiBuffer, error) {
+	mb := r.readInternal()
+	if mb != nil {
+		return mb, nil
+	}
+
+	return r.reader.ReadMultiBuffer()
+}
+
+func (r *cachedReader) ReadMultiBufferTimeout(timeout time.Duration) (buf.MultiBuffer, error) {
+	mb := r.readInternal()
+	if mb != nil {
+		return mb, nil
+	}
+
+	return r.reader.ReadMultiBufferTimeout(timeout)
+}
+
+func (r *cachedReader) Interrupt() {
+	r.Lock()
+	if r.cache != nil {
+		r.cache = buf.ReleaseMulti(r.cache)
+	}
+	r.Unlock()
+	r.reader.Interrupt()
+}
+
+// DefaultDispatcher is a default implementation of Dispatcher.
+type DefaultDispatcher struct {
+	ohm    outbound.Manager
+	router routing.Router
+	policy policy.Manager
+	stats  stats.Manager
+}
+
+func init() {
+	common.Must(common.RegisterConfig((*Config)(nil), func(ctx context.Context, config interface{}) (interface{}, error) {
+		d := new(DefaultDispatcher)
+		if err := core.RequireFeatures(ctx, func(om outbound.Manager, router routing.Router, pm policy.Manager, sm stats.Manager) error {
+			return d.Init(config.(*Config), om, router, pm, sm)
+		}); err != nil {
+			return nil, err
+		}
+		return d, nil
+	}))
+}
+
+// Init initializes DefaultDispatcher.
+func (d *DefaultDispatcher) Init(config *Config, om outbound.Manager, router routing.Router, pm policy.Manager, sm stats.Manager) error {
+	d.ohm = om
+	d.router = router
+	d.policy = pm
+	d.stats = sm
+	return nil
+}
+
+// Type implements common.HasType.
+func (*DefaultDispatcher) Type() interface{} {
+	return routing.DispatcherType()
+}
+
+// Start implements common.Runnable.
+func (*DefaultDispatcher) Start() error {
+	return nil
+}
+
+// Close implements common.Closable.
+func (*DefaultDispatcher) Close() error { return nil }
+
+func (d *DefaultDispatcher) getLink(ctx context.Context) (*transport.Link, *transport.Link) {
+	opt := pipe.OptionsFromContext(ctx)
+	uplinkReader, uplinkWriter := pipe.New(opt...)
+	downlinkReader, downlinkWriter := pipe.New(opt...)
+
+	inboundLink := &transport.Link{
+		Reader: downlinkReader,
+		Writer: uplinkWriter,
+	}
+
+	outboundLink := &transport.Link{
+		Reader: uplinkReader,
+		Writer: downlinkWriter,
+	}
+
+	sessionInbound := session.InboundFromContext(ctx)
+	var user *protocol.MemoryUser
+	if sessionInbound != nil {
+		user = sessionInbound.User
+	}
+
+	if user != nil && len(user.Email) > 0 {
+		p := d.policy.ForLevel(user.Level)
+		if p.Stats.UserUplink {
+			name := "user>>>" + user.Email + ">>>traffic>>>uplink"
+			if c, _ := stats.GetOrRegisterCounter(d.stats, name); c != nil {
+				inboundLink.Writer = &SizeStatWriter{
+					Counter: c,
+					Writer:  inboundLink.Writer,
+				}
+			}
+		}
+		if p.Stats.UserDownlink {
+			name := "user>>>" + user.Email + ">>>traffic>>>downlink"
+			if c, _ := stats.GetOrRegisterCounter(d.stats, name); c != nil {
+				outboundLink.Writer = &SizeStatWriter{
+					Counter: c,
+					Writer:  outboundLink.Writer,
+				}
+			}
+		}
+	}
+
+	return inboundLink, outboundLink
+}
+
+func shouldOverride(result SniffResult, domainOverride []string) bool {
+	for _, p := range domainOverride {
+		if strings.HasPrefix(result.Protocol(), p) {
+			return true
+		}
+	}
+	return false
+}
+
+// Dispatch implements routing.Dispatcher.
+func (d *DefaultDispatcher) Dispatch(ctx context.Context, destination net.Destination) (*transport.Link, error) {
+	if !destination.IsValid() {
+		panic("Dispatcher: Invalid destination.")
+	}
+	ob := &session.Outbound{
+		Target: destination,
+	}
+	ctx = session.ContextWithOutbound(ctx, ob)
+
+	inbound, outbound := d.getLink(ctx)
+	content := session.ContentFromContext(ctx)
+	if content == nil {
+		content = new(session.Content)
+		ctx = session.ContextWithContent(ctx, content)
+	}
+	sniffingRequest := content.SniffingRequest
+	if destination.Network != net.Network_TCP || !sniffingRequest.Enabled {
+		go d.routedDispatch(ctx, outbound, destination)
+	} else {
+		go func() {
+			cReader := &cachedReader{
+				reader: outbound.Reader.(*pipe.Reader),
+			}
+			outbound.Reader = cReader
+			result, err := sniffer(ctx, cReader)
+			if err == nil {
+				content.Protocol = result.Protocol()
+			}
+			if err == nil && shouldOverride(result, sniffingRequest.OverrideDestinationForProtocol) {
+				domain := result.Domain()
+				newError("sniffed domain: ", domain).WriteToLog(session.ExportIDToError(ctx))
+				destination.Address = net.ParseAddress(domain)
+				ob.Target = destination
+			}
+			d.routedDispatch(ctx, outbound, destination)
+		}()
+	}
+	return inbound, nil
+}
+
+func sniffer(ctx context.Context, cReader *cachedReader) (SniffResult, error) {
+	payload := buf.New()
+	defer payload.Release()
+
+	sniffer := NewSniffer()
+	totalAttempt := 0
+	for {
+		select {
+		case <-ctx.Done():
+			return nil, ctx.Err()
+		default:
+			totalAttempt++
+			if totalAttempt > 2 {
+				return nil, errSniffingTimeout
+			}
+
+			cReader.Cache(payload)
+			if !payload.IsEmpty() {
+				result, err := sniffer.Sniff(payload.Bytes())
+				if err != common.ErrNoClue {
+					return result, err
+				}
+			}
+			if payload.IsFull() {
+				return nil, errUnknownContent
+			}
+		}
+	}
+}
+
+func (d *DefaultDispatcher) routedDispatch(ctx context.Context, link *transport.Link, destination net.Destination) {
+	var handler outbound.Handler
+
+	skipRoutePick := false
+	if content := session.ContentFromContext(ctx); content != nil {
+		skipRoutePick = content.SkipRoutePick
+	}
+
+	if d.router != nil && !skipRoutePick {
+		if route, err := d.router.PickRoute(routing_session.AsRoutingContext(ctx)); err == nil {
+			tag := route.GetOutboundTag()
+			if h := d.ohm.GetHandler(tag); h != nil {
+				newError("taking detour [", tag, "] for [", destination, "]").WriteToLog(session.ExportIDToError(ctx))
+				handler = h
+			} else {
+				newError("non existing tag: ", tag).AtWarning().WriteToLog(session.ExportIDToError(ctx))
+			}
+		} else {
+			newError("default route for ", destination).WriteToLog(session.ExportIDToError(ctx))
+		}
+	}
+
+	if handler == nil {
+		handler = d.ohm.GetDefaultHandler()
+	}
+
+	if handler == nil {
+		newError("default outbound handler not exist").WriteToLog(session.ExportIDToError(ctx))
+		common.Close(link.Writer)
+		common.Interrupt(link.Reader)
+		return
+	}
+
+	if accessMessage := log.AccessMessageFromContext(ctx); accessMessage != nil {
+		if tag := handler.Tag(); tag != "" {
+			accessMessage.Detour = tag
+		}
+		log.Record(accessMessage)
+	}
+
+	handler.Dispatch(ctx, link)
+}

app/dispatcher/dispatcher.go

@@ -0,0 +1,5 @@
+// +build !confonly
+
+package dispatcher
+
+//go:generate go run github.com/xtls/xray-core/v1/common/errors/errorgen

app/dispatcher/errors.generated.go

@@ -0,0 +1,9 @@
+package dispatcher
+
+import "github.com/xtls/xray-core/v1/common/errors"
+
+type errPathObjHolder struct{}
+
+func newError(values ...interface{}) *errors.Error {
+	return errors.New(values...).WithPathObj(errPathObjHolder{})
+}

app/dispatcher/sniffer.go

@@ -0,0 +1,55 @@
+// +build !confonly
+
+package dispatcher
+
+import (
+	"github.com/xtls/xray-core/v1/common"
+	"github.com/xtls/xray-core/v1/common/protocol/bittorrent"
+	"github.com/xtls/xray-core/v1/common/protocol/http"
+	"github.com/xtls/xray-core/v1/common/protocol/tls"
+)
+
+type SniffResult interface {
+	Protocol() string
+	Domain() string
+}
+
+type protocolSniffer func([]byte) (SniffResult, error)
+
+type Sniffer struct {
+	sniffer []protocolSniffer
+}
+
+func NewSniffer() *Sniffer {
+	return &Sniffer{
+		sniffer: []protocolSniffer{
+			func(b []byte) (SniffResult, error) { return http.SniffHTTP(b) },
+			func(b []byte) (SniffResult, error) { return tls.SniffTLS(b) },
+			func(b []byte) (SniffResult, error) { return bittorrent.SniffBittorrent(b) },
+		},
+	}
+}
+
+var errUnknownContent = newError("unknown content")
+
+func (s *Sniffer) Sniff(payload []byte) (SniffResult, error) {
+	var pendingSniffer []protocolSniffer
+	for _, s := range s.sniffer {
+		result, err := s(payload)
+		if err == common.ErrNoClue {
+			pendingSniffer = append(pendingSniffer, s)
+			continue
+		}
+
+		if err == nil && result != nil {
+			return result, nil
+		}
+	}
+
+	if len(pendingSniffer) > 0 {
+		s.sniffer = pendingSniffer
+		return nil, common.ErrNoClue
+	}
+
+	return nil, errUnknownContent
+}

app/dispatcher/stats.go

@@ -0,0 +1,27 @@
+// +build !confonly
+
+package dispatcher
+
+import (
+	"github.com/xtls/xray-core/v1/common"
+	"github.com/xtls/xray-core/v1/common/buf"
+	"github.com/xtls/xray-core/v1/features/stats"
+)
+
+type SizeStatWriter struct {
+	Counter stats.Counter
+	Writer  buf.Writer
+}
+
+func (w *SizeStatWriter) WriteMultiBuffer(mb buf.MultiBuffer) error {
+	w.Counter.Add(int64(mb.Len()))
+	return w.Writer.WriteMultiBuffer(mb)
+}
+
+func (w *SizeStatWriter) Close() error {
+	return common.Close(w.Writer)
+}
+
+func (w *SizeStatWriter) Interrupt() {
+	common.Interrupt(w.Writer)
+}

app/dispatcher/stats_test.go

@@ -0,0 +1,44 @@
+package dispatcher_test
+
+import (
+	"testing"
+
+	. "github.com/xtls/xray-core/v1/app/dispatcher"
+	"github.com/xtls/xray-core/v1/common"
+	"github.com/xtls/xray-core/v1/common/buf"
+)
+
+type TestCounter int64
+
+func (c *TestCounter) Value() int64 {
+	return int64(*c)
+}
+
+func (c *TestCounter) Add(v int64) int64 {
+	x := int64(*c) + v
+	*c = TestCounter(x)
+	return x
+}
+
+func (c *TestCounter) Set(v int64) int64 {
+	*c = TestCounter(v)
+	return v
+}
+
+func TestStatsWriter(t *testing.T) {
+	var c TestCounter
+	writer := &SizeStatWriter{
+		Counter: &c,
+		Writer:  buf.Discard,
+	}
+
+	mb := buf.MergeBytes(nil, []byte("abcd"))
+	common.Must(writer.WriteMultiBuffer(mb))
+
+	mb = buf.MergeBytes(nil, []byte("efg"))
+	common.Must(writer.WriteMultiBuffer(mb))
+
+	if c.Value() != 7 {
+		t.Fatal("unexpected counter value. want 7, but got ", c.Value())
+	}
+}