chore: Disable the loop back detector for CMFA

adapter/outbound/direct.go

@@ -4,14 +4,19 @@ import (
 	"context"
 	"errors"
 	"net/netip"
+	"os"
+	"strconv"
 
 	N "github.com/metacubex/mihomo/common/net"
 	"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
@@ -24,8 +29,10 @@ type DirectOption struct {
 
 // DialContext implements C.ProxyAdapter
 func (d *Direct) DialContext(ctx context.Context, metadata *C.Metadata, opts ...dialer.Option) (C.Conn, error) {
-	if err := d.loopBack.CheckConn(metadata); err != nil {
-		return nil, err
+	if !features.CMFA || !DisableLoopBackDetector {
+		if err := d.loopBack.CheckConn(metadata); err != nil {
+			return nil, err
+		}
 	}
 	opts = append(opts, dialer.WithResolver(resolver.DefaultResolver))
 	c, err := dialer.DialContext(ctx, "tcp", metadata.RemoteAddress(), d.Base.DialOptions(opts...)...)
@@ -38,8 +45,10 @@ 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 err := d.loopBack.CheckPacketConn(metadata); err != nil {
-		return nil, err
+	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() {