Core: Add mutex to injection resolution (#4206)

* Revert "Add RequireFeaturesAsync() that works regardless order of app init"

* Add mutex to injection resolution

- Turns out we already support async DI resolution regardless of feature ordering
Previous code contain a race condition causing some resolution is lost
- Note that the new mutex cover s.pendingResolutions and s.features
but must not cover callbackResolution() due to deadlock
- Refactor some method names and simplify code

* Add OptionalFeatures injection

For example OptionalFeatures() is useful for fakedns module

app/dispatcher/default.go

@@ -106,7 +106,7 @@ func init() {
 	common.Must(common.RegisterConfig((*Config)(nil), func(ctx context.Context, config interface{}) (interface{}, error) {
 		d := new(DefaultDispatcher)
 		if err := core.RequireFeatures(ctx, func(om outbound.Manager, router routing.Router, pm policy.Manager, sm stats.Manager, dc dns.Client) error {
-			core.RequireFeatures(ctx, func(fdns dns.FakeDNSEngine) { // FakeDNSEngine is optional
+			core.OptionalFeatures(ctx, func(fdns dns.FakeDNSEngine) {
 				d.fdns = fdns
 			})
 			return d.Init(config.(*Config), om, router, pm, sm, dc)

app/dns/nameserver.go

@@ -56,7 +56,7 @@ func NewServer(ctx context.Context, dest net.Destination, dispatcher routing.Dis
 			return NewTCPLocalNameServer(u, queryStrategy)
 		case strings.EqualFold(u.String(), "fakedns"):
 			var fd dns.FakeDNSEngine
-			core.RequireFeatures(ctx, func(fdns dns.FakeDNSEngine) { // FakeDNSEngine is optional
+			core.RequireFeatures(ctx, func(fdns dns.FakeDNSEngine) {
 				fd = fdns
 			})
 			return NewFakeDNSServer(fd), nil

app/observatory/command/command.go

@@ -38,7 +38,7 @@ func init() {
 		sv := &service{v: s}
 		err := s.RequireFeatures(func(Observatory extension.Observatory) {
 			sv.observatory = Observatory
-		})
+		}, false)
 		if err != nil {
 			return nil, err
 		}

app/proxyman/command/command.go

@@ -177,7 +177,7 @@ func (s *service) Register(server *grpc.Server) {
 	common.Must(s.v.RequireFeatures(func(im inbound.Manager, om outbound.Manager) {
 		hs.ihm = im
 		hs.ohm = om
-	}))
+	}, false))
 	RegisterHandlerServiceServer(server, hs)
 
 	// For compatibility purposes

app/router/balancing.go

@@ -5,6 +5,7 @@ import (
 	sync "sync"
 
 	"github.com/xtls/xray-core/app/observatory"
+	"github.com/xtls/xray-core/common"
 	"github.com/xtls/xray-core/common/errors"
 	"github.com/xtls/xray-core/core"
 	"github.com/xtls/xray-core/features/extension"
@@ -31,9 +32,10 @@ type RoundRobinStrategy struct {
 func (s *RoundRobinStrategy) InjectContext(ctx context.Context) {
 	s.ctx = ctx
 	if len(s.FallbackTag) > 0 {
-		core.RequireFeaturesAsync(s.ctx, func(observatory extension.Observatory) {
+		common.Must(core.RequireFeatures(s.ctx, func(observatory extension.Observatory) error {
 			s.observatory = observatory
-		})
+			return nil
+		}))
 	}
 }
 

app/router/command/command.go

@@ -135,7 +135,7 @@ func (s *service) Register(server *grpc.Server) {
 		vCoreDesc := RoutingService_ServiceDesc
 		vCoreDesc.ServiceName = "v2ray.core.app.router.command.RoutingService"
 		server.RegisterService(&vCoreDesc, rs)
-	}))
+	}, false))
 }
 
 func init() {

app/router/strategy_leastload.go

@@ -7,6 +7,7 @@ import (
 	"time"
 
 	"github.com/xtls/xray-core/app/observatory"
+	"github.com/xtls/xray-core/common"
 	"github.com/xtls/xray-core/common/dice"
 	"github.com/xtls/xray-core/common/errors"
 	"github.com/xtls/xray-core/core"
@@ -59,9 +60,10 @@ type node struct {
 
 func (s *LeastLoadStrategy) InjectContext(ctx context.Context) {
 	s.ctx = ctx
-	core.RequireFeaturesAsync(s.ctx, func(observatory extension.Observatory) {
+	common.Must(core.RequireFeatures(s.ctx, func(observatory extension.Observatory) error {
 		s.observer = observatory
-	})
+		return nil
+	}))
 }
 
 func (s *LeastLoadStrategy) PickOutbound(candidates []string) string {

app/router/strategy_leastping.go

@@ -4,6 +4,7 @@ import (
 	"context"
 
 	"github.com/xtls/xray-core/app/observatory"
+	"github.com/xtls/xray-core/common"
 	"github.com/xtls/xray-core/common/errors"
 	"github.com/xtls/xray-core/core"
 	"github.com/xtls/xray-core/features/extension"
@@ -20,9 +21,10 @@ func (l *LeastPingStrategy) GetPrincipleTarget(strings []string) []string {
 
 func (l *LeastPingStrategy) InjectContext(ctx context.Context) {
 	l.ctx = ctx
-	core.RequireFeaturesAsync(l.ctx, func(observatory extension.Observatory) {
+	common.Must(core.RequireFeatures(l.ctx, func(observatory extension.Observatory) error {
 		l.observatory = observatory
-	})
+		return nil
+	}))
 }
 
 func (l *LeastPingStrategy) PickOutbound(strings []string) string {

app/router/strategy_random.go

@@ -4,6 +4,7 @@ import (
 	"context"
 
 	"github.com/xtls/xray-core/app/observatory"
+	"github.com/xtls/xray-core/common"
 	"github.com/xtls/xray-core/common/dice"
 	"github.com/xtls/xray-core/core"
 	"github.com/xtls/xray-core/features/extension"
@@ -20,9 +21,10 @@ type RandomStrategy struct {
 func (s *RandomStrategy) InjectContext(ctx context.Context) {
 	s.ctx = ctx
 	if len(s.FallbackTag) > 0 {
-		core.RequireFeaturesAsync(s.ctx, func(observatory extension.Observatory) {
+		common.Must(core.RequireFeatures(s.ctx, func(observatory extension.Observatory) error {
 			s.observatory = observatory
-		})
+			return nil
+		}))
 	}
 }