Add observatory / latestPing balancing strategy

Co-authored-by: Shelikhoo <xiaokangwang@outlook.com>

app/dispatcher/default.go

@@ -199,8 +199,8 @@ func shouldOverride(ctx context.Context, result SniffResult, request session.Sni
 		}
 		if fkr0, ok := fakeDNSEngine.(dns.FakeDNSEngineRev0); ok && protocolString != "bittorrent" && p == "fakedns" &&
 			destination.Address.Family().IsIP() && fkr0.IsIPInIPPool(destination.Address) {
-				newError("Using sniffer ", protocolString, " since the fake DNS missed").WriteToLog(session.ExportIDToError(ctx))
-				return true
+			newError("Using sniffer ", protocolString, " since the fake DNS missed").WriteToLog(session.ExportIDToError(ctx))
+			return true
 		}
 		if resultSubset, ok := result.(SnifferIsProtoSubsetOf); ok {
 			if resultSubset.IsProtoSubsetOf(p) {
@@ -399,7 +399,18 @@ func (d *DefaultDispatcher) routedDispatch(ctx context.Context, link *transport.
 
 	var handler outbound.Handler
 
-	if d.router != nil {
+	if forcedOutboundTag := session.GetForcedOutboundTagFromContext(ctx); forcedOutboundTag != "" {
+		ctx = session.SetForcedOutboundTagToContext(ctx, "")
+		if h := d.ohm.GetHandler(forcedOutboundTag); h != nil {
+			newError("taking platform initialized detour [", forcedOutboundTag, "] for [", destination, "]").WriteToLog(session.ExportIDToError(ctx))
+			handler = h
+		} else {
+			newError("non existing tag for platform initialized detour: ", forcedOutboundTag).AtError().WriteToLog(session.ExportIDToError(ctx))
+			common.Close(link.Writer)
+			common.Interrupt(link.Reader)
+			return
+		}
+	} else if d.router != nil {
 		if route, err := d.router.PickRoute(routing_session.AsRoutingContext(ctx)); err == nil {
 			tag := route.GetOutboundTag()
 			if h := d.ohm.GetHandler(tag); h != nil {

app/observatory/config.pb.go

@@ -0,0 +1,530 @@
+// Code generated by protoc-gen-go. DO NOT EDIT.
+// versions:
+// 	protoc-gen-go v1.27.1
+// 	protoc        v3.18.0
+// source: app/observatory/config.proto
+
+package observatory
+
+import (
+	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)
+)
+
+type ObservationResult struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	Status []*OutboundStatus `protobuf:"bytes,1,rep,name=status,proto3" json:"status,omitempty"`
+}
+
+func (x *ObservationResult) Reset() {
+	*x = ObservationResult{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_app_observatory_config_proto_msgTypes[0]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *ObservationResult) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*ObservationResult) ProtoMessage() {}
+
+func (x *ObservationResult) ProtoReflect() protoreflect.Message {
+	mi := &file_app_observatory_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 ObservationResult.ProtoReflect.Descriptor instead.
+func (*ObservationResult) Descriptor() ([]byte, []int) {
+	return file_app_observatory_config_proto_rawDescGZIP(), []int{0}
+}
+
+func (x *ObservationResult) GetStatus() []*OutboundStatus {
+	if x != nil {
+		return x.Status
+	}
+	return nil
+}
+
+type OutboundStatus struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	// @Document Whether this outbound is usable
+	//@Restriction ReadOnlyForUser
+	Alive bool `protobuf:"varint,1,opt,name=alive,proto3" json:"alive,omitempty"`
+	// @Document The time for probe request to finish.
+	//@Type time.ms
+	//@Restriction ReadOnlyForUser
+	Delay int64 `protobuf:"varint,2,opt,name=delay,proto3" json:"delay,omitempty"`
+	// @Document The last error caused this outbound failed to relay probe request
+	//@Restriction NotMachineReadable
+	LastErrorReason string `protobuf:"bytes,3,opt,name=last_error_reason,json=lastErrorReason,proto3" json:"last_error_reason,omitempty"`
+	// @Document The outbound tag for this Server
+	//@Type id.outboundTag
+	OutboundTag string `protobuf:"bytes,4,opt,name=outbound_tag,json=outboundTag,proto3" json:"outbound_tag,omitempty"`
+	// @Document The time this outbound is known to be alive
+	//@Type id.outboundTag
+	LastSeenTime int64 `protobuf:"varint,5,opt,name=last_seen_time,json=lastSeenTime,proto3" json:"last_seen_time,omitempty"`
+	// @Document The time this outbound is tried
+	//@Type id.outboundTag
+	LastTryTime int64 `protobuf:"varint,6,opt,name=last_try_time,json=lastTryTime,proto3" json:"last_try_time,omitempty"`
+}
+
+func (x *OutboundStatus) Reset() {
+	*x = OutboundStatus{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_app_observatory_config_proto_msgTypes[1]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *OutboundStatus) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*OutboundStatus) ProtoMessage() {}
+
+func (x *OutboundStatus) ProtoReflect() protoreflect.Message {
+	mi := &file_app_observatory_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 OutboundStatus.ProtoReflect.Descriptor instead.
+func (*OutboundStatus) Descriptor() ([]byte, []int) {
+	return file_app_observatory_config_proto_rawDescGZIP(), []int{1}
+}
+
+func (x *OutboundStatus) GetAlive() bool {
+	if x != nil {
+		return x.Alive
+	}
+	return false
+}
+
+func (x *OutboundStatus) GetDelay() int64 {
+	if x != nil {
+		return x.Delay
+	}
+	return 0
+}
+
+func (x *OutboundStatus) GetLastErrorReason() string {
+	if x != nil {
+		return x.LastErrorReason
+	}
+	return ""
+}
+
+func (x *OutboundStatus) GetOutboundTag() string {
+	if x != nil {
+		return x.OutboundTag
+	}
+	return ""
+}
+
+func (x *OutboundStatus) GetLastSeenTime() int64 {
+	if x != nil {
+		return x.LastSeenTime
+	}
+	return 0
+}
+
+func (x *OutboundStatus) GetLastTryTime() int64 {
+	if x != nil {
+		return x.LastTryTime
+	}
+	return 0
+}
+
+type ProbeResult struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	// @Document Whether this outbound is usable
+	//@Restriction ReadOnlyForUser
+	Alive bool `protobuf:"varint,1,opt,name=alive,proto3" json:"alive,omitempty"`
+	// @Document The time for probe request to finish.
+	//@Type time.ms
+	//@Restriction ReadOnlyForUser
+	Delay int64 `protobuf:"varint,2,opt,name=delay,proto3" json:"delay,omitempty"`
+	// @Document The error caused this outbound failed to relay probe request
+	//@Restriction NotMachineReadable
+	LastErrorReason string `protobuf:"bytes,3,opt,name=last_error_reason,json=lastErrorReason,proto3" json:"last_error_reason,omitempty"`
+}
+
+func (x *ProbeResult) Reset() {
+	*x = ProbeResult{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_app_observatory_config_proto_msgTypes[2]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *ProbeResult) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*ProbeResult) ProtoMessage() {}
+
+func (x *ProbeResult) ProtoReflect() protoreflect.Message {
+	mi := &file_app_observatory_config_proto_msgTypes[2]
+	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 ProbeResult.ProtoReflect.Descriptor instead.
+func (*ProbeResult) Descriptor() ([]byte, []int) {
+	return file_app_observatory_config_proto_rawDescGZIP(), []int{2}
+}
+
+func (x *ProbeResult) GetAlive() bool {
+	if x != nil {
+		return x.Alive
+	}
+	return false
+}
+
+func (x *ProbeResult) GetDelay() int64 {
+	if x != nil {
+		return x.Delay
+	}
+	return 0
+}
+
+func (x *ProbeResult) GetLastErrorReason() string {
+	if x != nil {
+		return x.LastErrorReason
+	}
+	return ""
+}
+
+type Intensity struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	// @Document The time interval for a probe request in ms.
+	//@Type time.ms
+	ProbeInterval uint32 `protobuf:"varint,1,opt,name=probe_interval,json=probeInterval,proto3" json:"probe_interval,omitempty"`
+}
+
+func (x *Intensity) Reset() {
+	*x = Intensity{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_app_observatory_config_proto_msgTypes[3]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *Intensity) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*Intensity) ProtoMessage() {}
+
+func (x *Intensity) ProtoReflect() protoreflect.Message {
+	mi := &file_app_observatory_config_proto_msgTypes[3]
+	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 Intensity.ProtoReflect.Descriptor instead.
+func (*Intensity) Descriptor() ([]byte, []int) {
+	return file_app_observatory_config_proto_rawDescGZIP(), []int{3}
+}
+
+func (x *Intensity) GetProbeInterval() uint32 {
+	if x != nil {
+		return x.ProbeInterval
+	}
+	return 0
+}
+
+type Config struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	// @Document The selectors for outbound under observation
+	SubjectSelector   []string `protobuf:"bytes,2,rep,name=subject_selector,json=subjectSelector,proto3" json:"subject_selector,omitempty"`
+	ProbeUrl          string   `protobuf:"bytes,3,opt,name=probe_url,json=probeUrl,proto3" json:"probe_url,omitempty"`
+	ProbeInterval     int64    `protobuf:"varint,4,opt,name=probe_interval,json=probeInterval,proto3" json:"probe_interval,omitempty"`
+	EnableConcurrency bool     `protobuf:"varint,5,opt,name=enable_concurrency,json=enableConcurrency,proto3" json:"enable_concurrency,omitempty"`
+}
+
+func (x *Config) Reset() {
+	*x = Config{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_app_observatory_config_proto_msgTypes[4]
+		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_observatory_config_proto_msgTypes[4]
+	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_observatory_config_proto_rawDescGZIP(), []int{4}
+}
+
+func (x *Config) GetSubjectSelector() []string {
+	if x != nil {
+		return x.SubjectSelector
+	}
+	return nil
+}
+
+func (x *Config) GetProbeUrl() string {
+	if x != nil {
+		return x.ProbeUrl
+	}
+	return ""
+}
+
+func (x *Config) GetProbeInterval() int64 {
+	if x != nil {
+		return x.ProbeInterval
+	}
+	return 0
+}
+
+func (x *Config) GetEnableConcurrency() bool {
+	if x != nil {
+		return x.EnableConcurrency
+	}
+	return false
+}
+
+var File_app_observatory_config_proto protoreflect.FileDescriptor
+
+var file_app_observatory_config_proto_rawDesc = []byte{
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+	0x79, 0x2d, 0x63, 0x6f, 0x72, 0x65, 0x2f, 0x61, 0x70, 0x70, 0x2f, 0x6f, 0x62, 0x73, 0x65, 0x72,
+	0x76, 0x61, 0x74, 0x6f, 0x72, 0x79, 0xaa, 0x02, 0x14, 0x58, 0x72, 0x61, 0x79, 0x2e, 0x41, 0x70,
+	0x70, 0x2e, 0x4f, 0x62, 0x73, 0x65, 0x72, 0x76, 0x61, 0x74, 0x6f, 0x72, 0x79, 0x62, 0x06, 0x70,
+	0x72, 0x6f, 0x74, 0x6f, 0x33,
+}
+
+var (
+	file_app_observatory_config_proto_rawDescOnce sync.Once
+	file_app_observatory_config_proto_rawDescData = file_app_observatory_config_proto_rawDesc
+)
+
+func file_app_observatory_config_proto_rawDescGZIP() []byte {
+	file_app_observatory_config_proto_rawDescOnce.Do(func() {
+		file_app_observatory_config_proto_rawDescData = protoimpl.X.CompressGZIP(file_app_observatory_config_proto_rawDescData)
+	})
+	return file_app_observatory_config_proto_rawDescData
+}
+
+var file_app_observatory_config_proto_msgTypes = make([]protoimpl.MessageInfo, 5)
+var file_app_observatory_config_proto_goTypes = []interface{}{
+	(*ObservationResult)(nil), // 0: xray.core.app.observatory.ObservationResult
+	(*OutboundStatus)(nil),    // 1: xray.core.app.observatory.OutboundStatus
+	(*ProbeResult)(nil),       // 2: xray.core.app.observatory.ProbeResult
+	(*Intensity)(nil),         // 3: xray.core.app.observatory.Intensity
+	(*Config)(nil),            // 4: xray.core.app.observatory.Config
+}
+var file_app_observatory_config_proto_depIdxs = []int32{
+	1, // 0: xray.core.app.observatory.ObservationResult.status:type_name -> xray.core.app.observatory.OutboundStatus
+	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_observatory_config_proto_init() }
+func file_app_observatory_config_proto_init() {
+	if File_app_observatory_config_proto != nil {
+		return
+	}
+	if !protoimpl.UnsafeEnabled {
+		file_app_observatory_config_proto_msgTypes[0].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*ObservationResult); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+		file_app_observatory_config_proto_msgTypes[1].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*OutboundStatus); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+		file_app_observatory_config_proto_msgTypes[2].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*ProbeResult); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+		file_app_observatory_config_proto_msgTypes[3].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*Intensity); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+		file_app_observatory_config_proto_msgTypes[4].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_observatory_config_proto_rawDesc,
+			NumEnums:      0,
+			NumMessages:   5,
+			NumExtensions: 0,
+			NumServices:   0,
+		},
+		GoTypes:           file_app_observatory_config_proto_goTypes,
+		DependencyIndexes: file_app_observatory_config_proto_depIdxs,
+		MessageInfos:      file_app_observatory_config_proto_msgTypes,
+	}.Build()
+	File_app_observatory_config_proto = out.File
+	file_app_observatory_config_proto_rawDesc = nil
+	file_app_observatory_config_proto_goTypes = nil
+	file_app_observatory_config_proto_depIdxs = nil
+}

app/observatory/config.proto

@@ -0,0 +1,73 @@
+syntax = "proto3";
+
+package xray.core.app.observatory;
+option csharp_namespace = "Xray.App.Observatory";
+option go_package = "github.com/xtls/xray-core/app/observatory";
+option java_package = "com.xray.app.observatory";
+option java_multiple_files = true;
+
+message ObservationResult {
+  repeated OutboundStatus status = 1;
+}
+
+message OutboundStatus{
+  /* @Document Whether this outbound is usable
+     @Restriction ReadOnlyForUser
+  */
+  bool alive = 1;
+  /* @Document The time for probe request to finish.
+     @Type time.ms
+     @Restriction ReadOnlyForUser
+  */
+  int64 delay = 2;
+  /* @Document The last error caused this outbound failed to relay probe request
+     @Restriction NotMachineReadable
+  */
+  string last_error_reason = 3;
+  /* @Document The outbound tag for this Server
+     @Type id.outboundTag
+  */
+  string outbound_tag = 4;
+  /* @Document The time this outbound is known to be alive
+   @Type id.outboundTag
+*/
+  int64 last_seen_time = 5;
+  /* @Document The time this outbound is tried
+   @Type id.outboundTag
+*/
+  int64 last_try_time = 6;
+}
+
+message ProbeResult{
+  /* @Document Whether this outbound is usable
+     @Restriction ReadOnlyForUser
+  */
+  bool alive = 1;
+  /* @Document The time for probe request to finish.
+     @Type time.ms
+     @Restriction ReadOnlyForUser
+  */
+  int64 delay = 2;
+  /* @Document The error caused this outbound failed to relay probe request
+   @Restriction NotMachineReadable
+*/
+  string last_error_reason = 3;
+}
+
+message Intensity{
+  /* @Document The time interval for a probe request in ms.
+     @Type time.ms
+  */
+  uint32 probe_interval = 1;
+}
+message Config {
+  /* @Document The selectors for outbound under observation
+  */
+  repeated string subject_selector = 2;
+
+  string probe_url = 3;
+
+  int64 probe_interval = 4;
+
+  bool enable_concurrency = 5;
+}

app/observatory/errors.generated.go

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

app/observatory/explainErrors.go

@@ -0,0 +1,26 @@
+package observatory
+
+import "github.com/xtls/xray-core/common/errors"
+
+type errorCollector struct {
+	errors *errors.Error
+}
+
+func (e *errorCollector) SubmitError(err error) {
+	if e.errors == nil {
+		e.errors = newError("underlying connection error").Base(err)
+		return
+	}
+	e.errors = e.errors.Base(newError("underlying connection error").Base(err))
+}
+
+func newErrorCollector() *errorCollector {
+	return &errorCollector{}
+}
+
+func (e *errorCollector) UnderlyingError() error {
+	if e.errors == nil {
+		return newError("failed to produce report")
+	}
+	return e.errors
+}

app/observatory/observatory.go

@@ -0,0 +1,3 @@
+package observatory
+
+//go:generate go run github.com/xtls/xray-core/common/errors/errorgen

app/observatory/observer.go

@@ -0,0 +1,216 @@
+package observatory
+
+import (
+	"context"
+	"github.com/xtls/xray-core/core"
+	"net"
+	"net/http"
+	"net/url"
+	"sort"
+	"sync"
+	"time"
+
+	"github.com/golang/protobuf/proto"
+
+	"github.com/xtls/xray-core/common"
+	v2net "github.com/xtls/xray-core/common/net"
+	"github.com/xtls/xray-core/common/session"
+	"github.com/xtls/xray-core/common/signal/done"
+	"github.com/xtls/xray-core/common/task"
+	"github.com/xtls/xray-core/features/extension"
+	"github.com/xtls/xray-core/features/outbound"
+	"github.com/xtls/xray-core/transport/internet/tagged"
+)
+
+type Observer struct {
+	config *Config
+	ctx    context.Context
+
+	statusLock sync.Mutex
+	status     []*OutboundStatus
+
+	finished *done.Instance
+
+	ohm outbound.Manager
+}
+
+func (o *Observer) GetObservation(ctx context.Context) (proto.Message, error) {
+	return &ObservationResult{Status: o.status}, nil
+}
+
+func (o *Observer) Type() interface{} {
+	return extension.ObservatoryType()
+}
+
+func (o *Observer) Start() error {
+	if o.config != nil && len(o.config.SubjectSelector) != 0 {
+		o.finished = done.New()
+		go o.background()
+	}
+	return nil
+}
+
+func (o *Observer) Close() error {
+	if o.finished != nil {
+		return o.finished.Close()
+	}
+	return nil
+}
+
+func (o *Observer) background() {
+	for !o.finished.Done() {
+		hs, ok := o.ohm.(outbound.HandlerSelector)
+		if !ok {
+			newError("outbound.Manager is not a HandlerSelector").WriteToLog()
+			return
+		}
+
+		outbounds := hs.Select(o.config.SubjectSelector)
+		sort.Strings(outbounds)
+
+		o.updateStatus(outbounds)
+
+		for _, v := range outbounds {
+			result := o.probe(v)
+			o.updateStatusForResult(v, &result)
+			if o.finished.Done() {
+				return
+			}
+			sleepTime := time.Second * 10
+			if o.config.ProbeInterval != 0 {
+				sleepTime = time.Duration(o.config.ProbeInterval)
+			}
+			time.Sleep(sleepTime)
+		}
+	}
+}
+
+func (o *Observer) updateStatus(outbounds []string) {
+	o.statusLock.Lock()
+	defer o.statusLock.Unlock()
+	// TODO should remove old inbound that is removed
+	_ = outbounds
+}
+
+func (o *Observer) probe(outbound string) ProbeResult {
+	errorCollectorForRequest := newErrorCollector()
+
+	httpTransport := http.Transport{
+		Proxy: func(*http.Request) (*url.URL, error) {
+			return nil, nil
+		},
+		DialContext: func(ctx context.Context, network string, addr string) (net.Conn, error) {
+			var connection net.Conn
+			taskErr := task.Run(ctx, func() error {
+				// MUST use V2Fly's built in context system
+				dest, err := v2net.ParseDestination(network + ":" + addr)
+				if err != nil {
+					return newError("cannot understand address").Base(err)
+				}
+				trackedCtx := session.TrackedConnectionError(o.ctx, errorCollectorForRequest)
+				conn, err := tagged.Dialer(trackedCtx, dest, outbound)
+				if err != nil {
+					return newError("cannot dial remote address ", dest).Base(err)
+				}
+				connection = conn
+				return nil
+			})
+			if taskErr != nil {
+				return nil, newError("cannot finish connection").Base(taskErr)
+			}
+			return connection, nil
+		},
+		TLSHandshakeTimeout: time.Second * 5,
+	}
+	httpClient := &http.Client{
+		Transport: &httpTransport,
+		CheckRedirect: func(req *http.Request, via []*http.Request) error {
+			return http.ErrUseLastResponse
+		},
+		Jar:     nil,
+		Timeout: time.Second * 5,
+	}
+	var GETTime time.Duration
+	err := task.Run(o.ctx, func() error {
+		startTime := time.Now()
+		probeURL := "https://api.v2fly.org/checkConnection.svgz"
+		if o.config.ProbeUrl != "" {
+			probeURL = o.config.ProbeUrl
+		}
+		response, err := httpClient.Get(probeURL)
+		if err != nil {
+			return newError("outbound failed to relay connection").Base(err)
+		}
+		if response.Body != nil {
+			response.Body.Close()
+		}
+		endTime := time.Now()
+		GETTime = endTime.Sub(startTime)
+		return nil
+	})
+	if err != nil {
+		fullerr := newError("underlying connection failed").Base(errorCollectorForRequest.UnderlyingError())
+		fullerr = newError("with outbound handler report").Base(fullerr)
+		fullerr = newError("GET request failed:", err).Base(fullerr)
+		fullerr = newError("the outbound ", outbound, " is dead:").Base(fullerr)
+		fullerr = fullerr.AtInfo()
+		fullerr.WriteToLog()
+		return ProbeResult{Alive: false, LastErrorReason: fullerr.Error()}
+	}
+	newError("the outbound ", outbound, " is alive:", GETTime.Seconds()).AtInfo().WriteToLog()
+	return ProbeResult{Alive: true, Delay: GETTime.Milliseconds()}
+}
+
+func (o *Observer) updateStatusForResult(outbound string, result *ProbeResult) {
+	o.statusLock.Lock()
+	defer o.statusLock.Unlock()
+	var status *OutboundStatus
+	if location := o.findStatusLocationLockHolderOnly(outbound); location != -1 {
+		status = o.status[location]
+	} else {
+		status = &OutboundStatus{}
+		o.status = append(o.status, status)
+	}
+
+	status.LastTryTime = time.Now().Unix()
+	status.OutboundTag = outbound
+	status.Alive = result.Alive
+	if result.Alive {
+		status.Delay = result.Delay
+		status.LastSeenTime = status.LastTryTime
+		status.LastErrorReason = ""
+	} else {
+		status.LastErrorReason = result.LastErrorReason
+		status.Delay = 99999999
+	}
+}
+
+func (o *Observer) findStatusLocationLockHolderOnly(outbound string) int {
+	for i, v := range o.status {
+		if v.OutboundTag == outbound {
+			return i
+		}
+	}
+	return -1
+}
+
+func New(ctx context.Context, config *Config) (*Observer, error) {
+	var outboundManager outbound.Manager
+	err := core.RequireFeatures(ctx, func(om outbound.Manager) {
+		outboundManager = om
+	})
+	if err != nil {
+		return nil, newError("Cannot get depended features").Base(err)
+	}
+	return &Observer{
+		config: config,
+		ctx:    ctx,
+		ohm:    outboundManager,
+	}, nil
+}
+
+func init() {
+	common.Must(common.RegisterConfig((*Config)(nil), func(ctx context.Context, config interface{}) (interface{}, error) {
+		return New(ctx, config.(*Config))
+	}))
+}

app/router/balancing.go

@@ -1,7 +1,10 @@
 package router
 
 import (
+	"context"
+
 	"github.com/xtls/xray-core/common/dice"
+	"github.com/xtls/xray-core/features/extension"
 	"github.com/xtls/xray-core/features/outbound"
 )
 
@@ -41,3 +44,8 @@ func (b *Balancer) PickOutbound() (string, error) {
 	}
 	return tag, nil
 }
+func (b *Balancer) InjectContext(ctx context.Context) {
+	if contextReceiver, ok := b.strategy.(extension.ContextReceiver); ok {
+		contextReceiver.InjectContext(ctx)
+	}
+}

app/router/config.pb.go

@@ -708,6 +708,7 @@ type BalancingRule struct {
 
 	Tag              string   `protobuf:"bytes,1,opt,name=tag,proto3" json:"tag,omitempty"`
 	OutboundSelector []string `protobuf:"bytes,2,rep,name=outbound_selector,json=outboundSelector,proto3" json:"outbound_selector,omitempty"`
+	Strategy         string   `protobuf:"bytes,3,opt,name=strategy,proto3" json:"strategy,omitempty"`
 }
 
 func (x *BalancingRule) Reset() {
@@ -756,6 +757,13 @@ func (x *BalancingRule) GetOutboundSelector() []string {
 	return nil
 }
 
+func (x *BalancingRule) GetStrategy() string {
+	if x != nil {
+		return x.Strategy
+	}
+	return ""
+}
+
 type Config struct {
 	state         protoimpl.MessageState
 	sizeCache     protoimpl.SizeCache
@@ -1010,36 +1018,38 @@ var file_app_router_config_proto_rawDesc = []byte{
 	0x74, 0x74, 0x72, 0x69, 0x62, 0x75, 0x74, 0x65, 0x73, 0x12, 0x25, 0x0a, 0x0e, 0x64, 0x6f, 0x6d,
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-	0x63, 0x6f, 0x6d, 0x2e, 0x78, 0x72, 0x61, 0x79, 0x2e, 0x61, 0x70, 0x70, 0x2e, 0x72, 0x6f, 0x75,
-	0x74, 0x65, 0x72, 0x50, 0x01, 0x5a, 0x24, 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, 0x61, 0x70, 0x70, 0x2f, 0x72, 0x6f, 0x75, 0x74, 0x65, 0x72, 0xaa, 0x02, 0x0f, 0x58, 0x72,
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-	0x72, 0x6f, 0x74, 0x6f, 0x33,
+	0x74, 0x62, 0x6f, 0x75, 0x6e, 0x64, 0x53, 0x65, 0x6c, 0x65, 0x63, 0x74, 0x6f, 0x72, 0x12, 0x1a,
+	0x0a, 0x08, 0x73, 0x74, 0x72, 0x61, 0x74, 0x65, 0x67, 0x79, 0x18, 0x03, 0x20, 0x01, 0x28, 0x09,
+	0x52, 0x08, 0x73, 0x74, 0x72, 0x61, 0x74, 0x65, 0x67, 0x79, 0x22, 0x9b, 0x02, 0x0a, 0x06, 0x43,
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+	0x6e, 0x63, 0x69, 0x6e, 0x67, 0x5f, 0x72, 0x75, 0x6c, 0x65, 0x18, 0x03, 0x20, 0x03, 0x28, 0x0b,
+	0x32, 0x1e, 0x2e, 0x78, 0x72, 0x61, 0x79, 0x2e, 0x61, 0x70, 0x70, 0x2e, 0x72, 0x6f, 0x75, 0x74,
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+	0x73, 0x65, 0x49, 0x70, 0x10, 0x01, 0x12, 0x10, 0x0a, 0x0c, 0x49, 0x70, 0x49, 0x66, 0x4e, 0x6f,
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+	0x44, 0x65, 0x6d, 0x61, 0x6e, 0x64, 0x10, 0x03, 0x42, 0x4f, 0x0a, 0x13, 0x63, 0x6f, 0x6d, 0x2e,
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+	0x01, 0x5a, 0x24, 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, 0x61, 0x70, 0x70,
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+	0x70, 0x70, 0x2e, 0x52, 0x6f, 0x75, 0x74, 0x65, 0x72, 0x62, 0x06, 0x70, 0x72, 0x6f, 0x74, 0x6f,
+	0x33,
 }
 
 var (

app/router/config.proto

@@ -127,6 +127,7 @@ message RoutingRule {
 message BalancingRule {
   string tag = 1;
   repeated string outbound_selector = 2;
+  string strategy = 3;
 }
 
 message Config {

app/router/strategy_leastping.go

@@ -0,0 +1,57 @@
+package router
+
+import (
+	"context"
+	"github.com/xtls/xray-core/core"
+
+	"github.com/xtls/xray-core/app/observatory"
+	"github.com/xtls/xray-core/common"
+	"github.com/xtls/xray-core/features/extension"
+)
+
+type LeastPingStrategy struct {
+	ctx         context.Context
+	observatory extension.Observatory
+}
+
+func (l *LeastPingStrategy) InjectContext(ctx context.Context) {
+	common.Must(core.RequireFeatures(ctx, func(observatory extension.Observatory) error {
+		l.observatory = observatory
+		return nil
+	}))
+	l.ctx = ctx
+}
+
+func (l *LeastPingStrategy) PickOutbound(strings []string) string {
+	observeReport, err := l.observatory.GetObservation(l.ctx)
+	if err != nil {
+		newError("cannot get observe report").Base(err).WriteToLog()
+		return ""
+	}
+	outboundsList := outboundList(strings)
+	if result, ok := observeReport.(*observatory.ObservationResult); ok {
+		status := result.Status
+		leastPing := int64(99999999)
+		selectedOutboundName := ""
+		for _, v := range status {
+			if outboundsList.contains(v.OutboundTag) && v.Alive && v.Delay < leastPing {
+				selectedOutboundName = v.OutboundTag
+			}
+		}
+		return selectedOutboundName
+	}
+
+	//No way to understand observeReport
+	return ""
+}
+
+type outboundList []string
+
+func (o outboundList) contains(name string) bool {
+	for _, v := range o {
+		if v == name {
+			return true
+		}
+	}
+	return false
+}

common/session/context.go

@@ -11,6 +11,7 @@ const (
 	contentSessionKey
 	muxPreferedSessionKey
 	sockoptSessionKey
+	trackedConnectionErrorKey
 )
 
 // ContextWithID returns a new context with the given ID.
@@ -84,3 +85,33 @@ func SockoptFromContext(ctx context.Context) *Sockopt {
 	}
 	return nil
 }
+
+func GetForcedOutboundTagFromContext(ctx context.Context) string {
+	if ContentFromContext(ctx) == nil {
+		return ""
+	}
+	return ContentFromContext(ctx).Attribute("forcedOutboundTag")
+}
+
+func SetForcedOutboundTagToContext(ctx context.Context, tag string) context.Context {
+	if contentFromContext := ContentFromContext(ctx); contentFromContext == nil {
+		ctx = ContextWithContent(ctx, &Content{})
+	}
+	ContentFromContext(ctx).SetAttribute("forcedOutboundTag", tag)
+	return ctx
+}
+
+type TrackedRequestErrorFeedback interface {
+	SubmitError(err error)
+}
+
+func SubmitOutboundErrorToOriginator(ctx context.Context, err error) {
+	if errorTracker := ctx.Value(trackedConnectionErrorKey); errorTracker != nil {
+		errorTracker := errorTracker.(TrackedRequestErrorFeedback)
+		errorTracker.SubmitError(err)
+	}
+}
+
+func TrackedConnectionError(ctx context.Context, tracker TrackedRequestErrorFeedback) context.Context {
+	return context.WithValue(ctx, trackedConnectionErrorKey, tracker)
+}

features/extension/contextreceiver.go

@@ -0,0 +1,7 @@
+package extension
+
+import "context"
+
+type ContextReceiver interface {
+	InjectContext(ctx context.Context)
+}

features/extension/observatory.go

@@ -0,0 +1,19 @@
+package extension
+
+import (
+	"context"
+
+	"github.com/golang/protobuf/proto"
+
+	"github.com/xtls/xray-core/features"
+)
+
+type Observatory interface {
+	features.Feature
+
+	GetObservation(ctx context.Context) (proto.Message, error)
+}
+
+func ObservatoryType() interface{} {
+	return (*Observatory)(nil)
+}

infra/conf/observatory.go

@@ -0,0 +1,14 @@
+package conf
+
+import (
+	"github.com/golang/protobuf/proto"
+	"github.com/xtls/xray-core/app/observatory"
+)
+
+type ObservatoryConfig struct {
+	SubjectSelector []string `json:"subjectSelector"`
+}
+
+func (o ObservatoryConfig) Build() (proto.Message, error) {
+	return &observatory.Config{SubjectSelector: o.SubjectSelector}, nil
+}

infra/conf/xray.go

@@ -6,12 +6,12 @@ import (
 	"os"
 	"strings"
 
-	"github.com/xtls/xray-core/transport/internet"
-
 	"github.com/xtls/xray-core/app/dispatcher"
 	"github.com/xtls/xray-core/app/proxyman"
 	"github.com/xtls/xray-core/app/stats"
 	"github.com/xtls/xray-core/common/serial"
+	"github.com/xtls/xray-core/transport/internet"
+
 	core "github.com/xtls/xray-core/core"
 	"github.com/xtls/xray-core/transport/internet/xtls"
 )
@@ -405,6 +405,7 @@ type Config struct {
 	Stats           *StatsConfig           `json:"stats"`
 	Reverse         *ReverseConfig         `json:"reverse"`
 	FakeDNS         *FakeDNSConfig         `json:"fakeDns"`
+	Observatory     *ObservatoryConfig     `json:"observatory"`
 }
 
 func (c *Config) findInboundTag(tag string) int {
@@ -611,6 +612,14 @@ func (c *Config) Build() (*core.Config, error) {
 		config.App = append(config.App, serial.ToTypedMessage(r))
 	}
 
+	if c.Observatory != nil {
+		r, err := c.Observatory.Build()
+		if err != nil {
+			return nil, err
+		}
+		config.App = append(config.App, serial.ToTypedMessage(r))
+	}
+
 	var inbounds []InboundDetourConfig
 
 	if c.InboundConfig != nil {

main/distro/all/all.go

@@ -23,6 +23,9 @@ import (
 	_ "github.com/xtls/xray-core/app/router"
 	_ "github.com/xtls/xray-core/app/stats"
 
+	// Fix dependency cycle caused by core import in internet package
+	_ "github.com/xtls/xray-core/transport/internet/tagged/taggedimpl"
+
 	// Inbound and outbound proxies.
 	_ "github.com/xtls/xray-core/proxy/blackhole"
 	_ "github.com/xtls/xray-core/proxy/dns"

transport/internet/tagged/tagged.go

@@ -0,0 +1,11 @@
+package tagged
+
+import (
+	"context"
+
+	"github.com/xtls/xray-core/common/net"
+)
+
+type DialFunc func(ctx context.Context, dest net.Destination, tag string) (net.Conn, error)
+
+var Dialer DialFunc

transport/internet/tagged/taggedimpl/errors.generated.go

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

transport/internet/tagged/taggedimpl/impl.go

@@ -0,0 +1,46 @@
+package taggedimpl
+
+import (
+	"context"
+	"github.com/xtls/xray-core/common/net/cnc"
+	"github.com/xtls/xray-core/core"
+
+	"github.com/xtls/xray-core/common/net"
+	"github.com/xtls/xray-core/common/session"
+	"github.com/xtls/xray-core/features/routing"
+	"github.com/xtls/xray-core/transport/internet/tagged"
+)
+
+func DialTaggedOutbound(ctx context.Context, dest net.Destination, tag string) (net.Conn, error) {
+	var dispatcher routing.Dispatcher
+	if core.FromContext(ctx) == nil {
+		return nil, newError("Instance context variable is not in context, dial denied. ")
+	}
+	if err := core.RequireFeatures(ctx, func(dispatcherInstance routing.Dispatcher) {
+		dispatcher = dispatcherInstance
+	}); err != nil {
+		return nil, newError("Required Feature dispatcher not resolved").Base(err)
+	}
+
+	content := new(session.Content)
+	content.SkipDNSResolve = true
+
+	ctx = session.ContextWithContent(ctx, content)
+	ctx = session.SetForcedOutboundTagToContext(ctx, tag)
+
+	r, err := dispatcher.Dispatch(ctx, dest)
+	if err != nil {
+		return nil, err
+	}
+	var readerOpt cnc.ConnectionOption
+	if dest.Network == net.Network_TCP {
+		readerOpt = cnc.ConnectionOutputMulti(r.Reader)
+	} else {
+		readerOpt = cnc.ConnectionOutputMultiUDP(r.Reader)
+	}
+	return cnc.NewConnection(cnc.ConnectionInputMulti(r.Writer), readerOpt), nil
+}
+
+func init() {
+	tagged.Dialer = DialTaggedOutbound
+}

transport/internet/tagged/taggedimpl/taggedimpl.go

@@ -0,0 +1,3 @@
+package taggedimpl
+
+//go:generate go run github.com/xtls/xray-core/common/errors/errorgen