Least load balancer (#2999)

* v5: Health Check & LeastLoad Strategy (rebased from 2c5a71490368500a982018a74a6d519c7e121816)

Some changes will be necessary to integrate it into V2Ray

* Update proto

* parse duration conf with time.Parse()

* moving health ping to observatory as a standalone component

* moving health ping to observatory as a standalone component: auto generated file

* add initialization for health ping

* incorporate changes in router implementation

* support principle target output

* add v4 json support for BurstObservatory & fix balancer reference

* update API command

* remove cancelled API

* return zero length value when observer is not found

* remove duplicated targeted dispatch

* adjust test with updated structure

* bug fix for observer

* fix strategy selector

* fix strategy least load

* Fix ticker usage

ticker.Close does not close ticker.C

* feat: Replace default Health Ping URL to HTTPS (#1991)

* fix selectLeastLoad() returns wrong number of nodes (#2083)

* Test: fix leastload strategy unit test

* fix(router): panic caused by concurrent map read and write (#2678)

* Clean up code

---------

Co-authored-by: Jebbs <qjebbs@gmail.com>
Co-authored-by: Shelikhoo <xiaokangwang@outlook.com>
Co-authored-by: 世界 <i@sekai.icu>
Co-authored-by: Bernd Eichelberger <46166740+4-FLOSS-Free-Libre-Open-Source-Software@users.noreply.github.com>
Co-authored-by: 秋のかえで <autmaple@protonmail.com>
Co-authored-by: Rinka <kujourinka@gmail.com>

app/observatory/burst/burstobserver.go

@@ -0,0 +1,108 @@
+package burst
+
+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/common/signal/done"
+	"github.com/xtls/xray-core/features/extension"
+	"github.com/xtls/xray-core/features/outbound"
+	"google.golang.org/protobuf/proto"
+	"sync"
+)
+
+type Observer struct {
+	config *Config
+	ctx    context.Context
+
+	statusLock sync.Mutex
+	hp         *HealthPing
+
+	finished *done.Instance
+
+	ohm outbound.Manager
+}
+
+func (o *Observer) GetObservation(ctx context.Context) (proto.Message, error) {
+	return &observatory.ObservationResult{Status: o.createResult()}, nil
+}
+
+func (o *Observer) createResult() []*observatory.OutboundStatus {
+	var result []*observatory.OutboundStatus
+	o.hp.access.Lock()
+	defer o.hp.access.Unlock()
+	for name, value := range o.hp.Results {
+		status := observatory.OutboundStatus{
+			Alive:           value.getStatistics().All != value.getStatistics().Fail,
+			Delay:           value.getStatistics().Average.Milliseconds(),
+			LastErrorReason: "",
+			OutboundTag:     name,
+			LastSeenTime:    0,
+			LastTryTime:     0,
+			HealthPing: &observatory.HealthPingMeasurementResult{
+				All:       int64(value.getStatistics().All),
+				Fail:      int64(value.getStatistics().Fail),
+				Deviation: int64(value.getStatistics().Deviation),
+				Average:   int64(value.getStatistics().Average),
+				Max:       int64(value.getStatistics().Max),
+				Min:       int64(value.getStatistics().Min),
+			},
+		}
+		result = append(result, &status)
+	}
+	return result
+}
+
+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()
+		o.hp.StartScheduler(func() ([]string, error) {
+			hs, ok := o.ohm.(outbound.HandlerSelector)
+			if !ok {
+
+				return nil, newError("outbound.Manager is not a HandlerSelector")
+			}
+
+			outbounds := hs.Select(o.config.SubjectSelector)
+			return outbounds, nil
+		})
+	}
+	return nil
+}
+
+func (o *Observer) Close() error {
+	if o.finished != nil {
+		o.hp.StopScheduler()
+		return o.finished.Close()
+	}
+	return nil
+}
+
+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)
+	}
+	hp := NewHealthPing(ctx, config.PingConfig)
+	return &Observer{
+		config: config,
+		ctx:    ctx,
+		ohm:    outboundManager,
+		hp:     hp,
+	}, nil
+}
+
+func init() {
+	common.Must(common.RegisterConfig((*Config)(nil), func(ctx context.Context, config interface{}) (interface{}, error) {
+		return New(ctx, config.(*Config))
+	}))
+}