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_test.go

@@ -5,6 +5,7 @@ import (
 	"os"
 	"path/filepath"
 	"testing"
+	"time"
 	_ "unsafe"
 
 	"github.com/xtls/xray-core/app/router"
@@ -12,6 +13,7 @@ import (
 	"github.com/xtls/xray-core/common/net"
 	"github.com/xtls/xray-core/common/platform"
 	"github.com/xtls/xray-core/common/platform/filesystem"
+	"github.com/xtls/xray-core/common/serial"
 	. "github.com/xtls/xray-core/infra/conf"
 	"google.golang.org/protobuf/proto"
 )
@@ -96,6 +98,34 @@ func TestRouterConfig(t *testing.T) {
 					{
 						"tag": "b1",
 						"selector": ["test"]
+					},
+					{
+						"tag": "b2",
+						"selector": ["test"],
+						"strategy": {
+							"type": "leastload",
+							"settings": {
+								"healthCheck": {
+									"interval": "5m0s",
+									"sampling": 2,
+									"timeout": "5s",
+									"destination": "dest",
+									"connectivity": "conn"
+								},
+								"costs": [
+									{
+										"regexp": true,
+										"match": "\\d+(\\.\\d+)",
+										"value": 5
+									}
+								],
+								"baselines": ["400ms", "600ms"],
+								"expected": 6,
+								"maxRTT": "1000ms",
+								"tolerance": 0.5
+							}
+						},
+						"fallbackTag": "fall"
 					}
 				]
 			}`,
@@ -108,6 +138,28 @@ func TestRouterConfig(t *testing.T) {
 						OutboundSelector: []string{"test"},
 						Strategy:         "random",
 					},
+					{
+						Tag:              "b2",
+						OutboundSelector: []string{"test"},
+						Strategy:         "leastload",
+						StrategySettings: serial.ToTypedMessage(&router.StrategyLeastLoadConfig{
+							Costs: []*router.StrategyWeight{
+								{
+									Regexp: true,
+									Match:  "\\d+(\\.\\d+)",
+									Value:  5,
+								},
+							},
+							Baselines: []int64{
+								int64(time.Duration(400) * time.Millisecond),
+								int64(time.Duration(600) * time.Millisecond),
+							},
+							Expected:  6,
+							MaxRTT:    int64(time.Duration(1000) * time.Millisecond),
+							Tolerance: 0.5,
+						}),
+						FallbackTag: "fall",
+					},
 				},
 				Rule: []*router.RoutingRule{
 					{