chore: reduce the performance overhead of not enabling LoopBackDetector

adapter/outbound/direct.go

@@ -3,18 +3,12 @@ package outbound
 import (
 	"context"
 	"errors"
-	"os"
-	"strconv"
-
 	"github.com/metacubex/mihomo/component/dialer"
 	"github.com/metacubex/mihomo/component/loopback"
 	"github.com/metacubex/mihomo/component/resolver"
 	C "github.com/metacubex/mihomo/constant"
-	"github.com/metacubex/mihomo/constant/features"
 )
 
-var DisableLoopBackDetector, _ = strconv.ParseBool(os.Getenv("DISABLE_LOOPBACK_DETECTOR"))
-
 type Direct struct {
 	*Base
 	loopBack *loopback.Detector
@@ -27,11 +21,9 @@ type DirectOption struct {
 
 // DialContext implements C.ProxyAdapter
 func (d *Direct) DialContext(ctx context.Context, metadata *C.Metadata, opts ...dialer.Option) (C.Conn, error) {
-	if !features.CMFA && !DisableLoopBackDetector {
 	if err := d.loopBack.CheckConn(metadata); err != nil {
 		return nil, err
 	}
-	}
 	opts = append(opts, dialer.WithResolver(resolver.DirectHostResolver))
 	c, err := dialer.DialContext(ctx, "tcp", metadata.RemoteAddress(), d.Base.DialOptions(opts...)...)
 	if err != nil {
@@ -42,11 +34,9 @@ func (d *Direct) DialContext(ctx context.Context, metadata *C.Metadata, opts ...
 
 // ListenPacketContext implements C.ProxyAdapter
 func (d *Direct) ListenPacketContext(ctx context.Context, metadata *C.Metadata, opts ...dialer.Option) (C.PacketConn, error) {
-	if !features.CMFA && !DisableLoopBackDetector {
 	if err := d.loopBack.CheckPacketConn(metadata); err != nil {
 		return nil, err
 	}
-	}
 	// net.UDPConn.WriteTo only working with *net.UDPAddr, so we need a net.UDPAddr
 	if !metadata.Resolved() {
 		ip, err := resolver.ResolveIPWithResolver(ctx, metadata.Host, resolver.DirectHostResolver)

component/loopback/detector.go

@@ -4,14 +4,25 @@ import (
 	"errors"
 	"fmt"
 	"net/netip"
+	"os"
+	"strconv"
 
 	"github.com/metacubex/mihomo/common/callback"
 	"github.com/metacubex/mihomo/component/iface"
 	C "github.com/metacubex/mihomo/constant"
+	"github.com/metacubex/mihomo/constant/features"
 
 	"github.com/puzpuzpuz/xsync/v3"
 )
 
+var disableLoopBackDetector, _ = strconv.ParseBool(os.Getenv("DISABLE_LOOPBACK_DETECTOR"))
+
+func init() {
+	if features.CMFA {
+		disableLoopBackDetector = true
+	}
+}
+
 var ErrReject = errors.New("reject loopback connection")
 
 type Detector struct {
@@ -20,6 +31,9 @@ type Detector struct {
 }
 
 func NewDetector() *Detector {
+	if disableLoopBackDetector {
+		return nil
+	}
 	return &Detector{
 		connMap:       xsync.NewMapOf[netip.AddrPort, struct{}](),
 		packetConnMap: xsync.NewMapOf[uint16, struct{}](),
@@ -27,6 +41,9 @@ func NewDetector() *Detector {
 }
 
 func (l *Detector) NewConn(conn C.Conn) C.Conn {
+	if l == nil || l.connMap == nil {
+		return conn
+	}
 	metadata := C.Metadata{}
 	if metadata.SetRemoteAddr(conn.LocalAddr()) != nil {
 		return conn
@@ -42,6 +59,9 @@ func (l *Detector) NewConn(conn C.Conn) C.Conn {
 }
 
 func (l *Detector) NewPacketConn(conn C.PacketConn) C.PacketConn {
+	if l == nil || l.packetConnMap == nil {
+		return conn
+	}
 	metadata := C.Metadata{}
 	if metadata.SetRemoteAddr(conn.LocalAddr()) != nil {
 		return conn
@@ -58,6 +78,9 @@ func (l *Detector) NewPacketConn(conn C.PacketConn) C.PacketConn {
 }
 
 func (l *Detector) CheckConn(metadata *C.Metadata) error {
+	if l == nil || l.connMap == nil {
+		return nil
+	}
 	connAddr := metadata.SourceAddrPort()
 	if !connAddr.IsValid() {
 		return nil
@@ -69,6 +92,9 @@ func (l *Detector) CheckConn(metadata *C.Metadata) error {
 }
 
 func (l *Detector) CheckPacketConn(metadata *C.Metadata) error {
+	if l == nil || l.packetConnMap == nil {
+		return nil
+	}
 	connAddr := metadata.SourceAddrPort()
 	if !connAddr.IsValid() {
 		return nil