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/router/weight.go

@@ -0,0 +1,89 @@
+package router
+
+import (
+	"regexp"
+	"strconv"
+	"strings"
+	"sync"
+)
+
+type weightScaler func(value, weight float64) float64
+
+var numberFinder = regexp.MustCompile(`\d+(\.\d+)?`)
+
+// NewWeightManager creates a new WeightManager with settings
+func NewWeightManager(s []*StrategyWeight, defaultWeight float64, scaler weightScaler) *WeightManager {
+	return &WeightManager{
+		settings:      s,
+		cache:         make(map[string]float64),
+		scaler:        scaler,
+		defaultWeight: defaultWeight,
+	}
+}
+
+// WeightManager manages weights for specific settings
+type WeightManager struct {
+	settings      []*StrategyWeight
+	cache         map[string]float64
+	scaler        weightScaler
+	defaultWeight float64
+	mu            sync.Mutex
+}
+
+// Get get the weight of specified tag
+func (s *WeightManager) Get(tag string) float64 {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	weight, ok := s.cache[tag]
+	if ok {
+		return weight
+	}
+	weight = s.findValue(tag)
+	s.cache[tag] = weight
+	return weight
+}
+
+// Apply applies weight to the value
+func (s *WeightManager) Apply(tag string, value float64) float64 {
+	return s.scaler(value, s.Get(tag))
+}
+
+func (s *WeightManager) findValue(tag string) float64 {
+	for _, w := range s.settings {
+		matched := s.getMatch(tag, w.Match, w.Regexp)
+		if matched == "" {
+			continue
+		}
+		if w.Value > 0 {
+			return float64(w.Value)
+		}
+		// auto weight from matched
+		numStr := numberFinder.FindString(matched)
+		if numStr == "" {
+			return s.defaultWeight
+		}
+		weight, err := strconv.ParseFloat(numStr, 64)
+		if err != nil {
+			newError("unexpected error from ParseFloat: ", err).AtError().WriteToLog()
+			return s.defaultWeight
+		}
+		return weight
+	}
+	return s.defaultWeight
+}
+
+func (s *WeightManager) getMatch(tag, find string, isRegexp bool) string {
+	if !isRegexp {
+		idx := strings.Index(tag, find)
+		if idx < 0 {
+			return ""
+		}
+		return find
+	}
+	r, err := regexp.Compile(find)
+	if err != nil {
+		newError("invalid regexp: ", find, "err: ", err).AtError().WriteToLog()
+		return ""
+	}
+	return r.FindString(tag)
+}