fix

Fixes https://github.com/XTLS/Xray-core/issues/4194

proxy/dokodemo/dokodemo.go

@@ -3,6 +3,7 @@ package dokodemo
 import (
 	"context"
 	"sync/atomic"
+	"time"
 
 	"github.com/xtls/xray-core/common"
 	"github.com/xtls/xray-core/common/buf"
@@ -114,7 +115,14 @@ func (d *DokodemoDoor) Process(ctx context.Context, network net.Network, conn st
 
 	plcy := d.policy()
 	ctx, cancel := context.WithCancel(ctx)
-	timer := signal.CancelAfterInactivity(ctx, cancel, plcy.Timeouts.ConnectionIdle)
+
+	var timer *signal.ActivityTimer
+	// if dns req, set a short timeout value
+	if dest.Port == 53 {
+		timer = signal.CancelAfterInactivity(ctx, cancel, 10*time.Second)
+	} else {
+		timer = signal.CancelAfterInactivity(ctx, cancel, plcy.Timeouts.ConnectionIdle)
+	}
 
 	if inbound != nil {
 		inbound.Timer = timer
@@ -180,7 +188,6 @@ func (d *DokodemoDoor) Process(ctx context.Context, network net.Network, conn st
 				return err
 			}
 			writer = NewPacketWriter(pConn, &dest, mark, back)
-			defer writer.(*PacketWriter).Close()
 			/*
 				sockopt := &internet.SocketConfig{
 					Tproxy: internet.SocketConfig_TProxy,
@@ -219,6 +226,10 @@ func (d *DokodemoDoor) Process(ctx context.Context, network net.Network, conn st
 	responseDone := func() error {
 		defer timer.SetTimeout(plcy.Timeouts.UplinkOnly)
 
+		if pw, ok := writer.(*PacketWriter); ok {
+			defer pw.Close()
+		}
+
 		if err := buf.Copy(link.Reader, writer, buf.UpdateActivity(timer)); err != nil {
 			return errors.New("failed to transport response").Base(err)
 		}