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>

infra/conf/router_strategy.go

@@ -1,7 +1,93 @@
 package conf
 
+import (
+	"google.golang.org/protobuf/proto"
+	
+	"github.com/xtls/xray-core/app/router"
+	"github.com/xtls/xray-core/app/observatory/burst"
+	"github.com/xtls/xray-core/infra/conf/cfgcommon/duration"
+)
+
 const (
 	strategyRandom     string = "random"
 	strategyLeastPing  string = "leastping"
 	strategyRoundRobin string = "roundrobin"
+	strategyLeastLoad  string = "leastload"
 )
+
+var (
+	strategyConfigLoader = NewJSONConfigLoader(ConfigCreatorCache{
+		strategyRandom:     func() interface{} { return new(strategyEmptyConfig) },
+		strategyLeastPing:  func() interface{} { return new(strategyEmptyConfig) },
+		strategyRoundRobin: func() interface{} { return new(strategyEmptyConfig) },
+		strategyLeastLoad:  func() interface{} { return new(strategyLeastLoadConfig) },
+	}, "type", "settings")
+)
+
+type strategyEmptyConfig struct {
+}
+
+func (v *strategyEmptyConfig) Build() (proto.Message, error) {
+	return nil, nil
+}
+
+type strategyLeastLoadConfig struct {
+	// weight settings
+	Costs []*router.StrategyWeight `json:"costs,omitempty"`
+	// ping rtt baselines
+	Baselines []duration.Duration `json:"baselines,omitempty"`
+	// expected nodes count to select
+	Expected int32 `json:"expected,omitempty"`
+	// max acceptable rtt, filter away high delay nodes. defalut 0
+	MaxRTT duration.Duration `json:"maxRTT,omitempty"`
+	// acceptable failure rate
+	Tolerance float64 `json:"tolerance,omitempty"`
+}
+
+// healthCheckSettings holds settings for health Checker
+type healthCheckSettings struct {
+	Destination   string   `json:"destination"`
+	Connectivity  string   `json:"connectivity"`
+	Interval      duration.Duration `json:"interval"`
+	SamplingCount int      `json:"sampling"`
+	Timeout       duration.Duration `json:"timeout"`
+}
+
+func (h healthCheckSettings) Build() (proto.Message, error) {
+	return &burst.HealthPingConfig{
+		Destination:   h.Destination,
+		Connectivity:  h.Connectivity,
+		Interval:      int64(h.Interval),
+		Timeout:       int64(h.Timeout),
+		SamplingCount: int32(h.SamplingCount),
+	}, nil
+}
+
+// Build implements Buildable.
+func (v *strategyLeastLoadConfig) Build() (proto.Message, error) {
+	config := &router.StrategyLeastLoadConfig{}
+	config.Costs = v.Costs
+	config.Tolerance = float32(v.Tolerance)
+	if config.Tolerance < 0 {
+		config.Tolerance = 0
+	}
+	if config.Tolerance > 1 {
+		config.Tolerance = 1
+	}
+	config.Expected = v.Expected
+	if config.Expected < 0 {
+		config.Expected = 0
+	}
+	config.MaxRTT = int64(v.MaxRTT)
+	if config.MaxRTT < 0 {
+		config.MaxRTT = 0
+	}
+	config.Baselines = make([]int64, 0)
+	for _, b := range v.Baselines {
+		if b <= 0 {
+			continue
+		}
+		config.Baselines = append(config.Baselines, int64(b))
+	}
+	return config, nil
+}