fix: dns empty response

Author: xinyifly

app/dns/dns.go

@@ -215,7 +215,7 @@ func (s *DNS) LookupIP(domain string, option dns.IPOption) ([]net.IP, error) {
 			newError("failed to lookup ip for domain ", domain, " at server ", client.Name()).Base(err).WriteToLog()
 			errs = append(errs, err)
 		}
-		if err != context.Canceled && err != context.DeadlineExceeded && err != errExpectedIPNonMatch {
+		if err != context.Canceled && err != context.DeadlineExceeded && err != errExpectedIPNonMatch && err != dns.ErrEmptyResponse {
 			return nil, err
 		}
 	}

app/dns/dns_test.go

@@ -13,6 +13,7 @@ import (
 	_ "github.com/xtls/xray-core/app/proxyman/outbound"
 	"github.com/xtls/xray-core/app/router"
 	"github.com/xtls/xray-core/common"
+	"github.com/xtls/xray-core/common/errors"
 	"github.com/xtls/xray-core/common/net"
 	"github.com/xtls/xray-core/common/serial"
 	"github.com/xtls/xray-core/core"
@@ -260,7 +261,7 @@ func TestUDPServer(t *testing.T) {
 			IPv6Enable: true,
 			FakeEnable: false,
 		})
-		if err != feature_dns.ErrEmptyResponse {
+		if !errors.AllEqual(feature_dns.ErrEmptyResponse, errors.Cause(err)) {
 			t.Fatal("error: ", err)
 		}
 		if len(ips) != 0 {

common/errors/multi_error.go

@@ -28,3 +28,20 @@ func Combine(maybeError ...error) error {
 	}
 	return errs
 }
+
+func AllEqual(expected error, actual error) bool {
+	switch errs := actual.(type) {
+	case multiError:
+		if len(errs) == 0 {
+			return false
+		}
+		for _, err := range errs {
+			if err != expected {
+				return false
+			}
+		}
+		return true
+	default:
+		return errs == expected
+	}
+}

proxy/dns/dns.go

@@ -8,6 +8,7 @@ import (
 
 	"github.com/xtls/xray-core/common"
 	"github.com/xtls/xray-core/common/buf"
+	"github.com/xtls/xray-core/common/errors"
 	"github.com/xtls/xray-core/common/net"
 	dns_proto "github.com/xtls/xray-core/common/protocol/dns"
 	"github.com/xtls/xray-core/common/session"
@@ -232,7 +233,7 @@ func (h *Handler) handleIPQuery(id uint16, qType dnsmessage.Type, domain string,
 	}
 
 	rcode := dns.RCodeFromError(err)
-	if rcode == 0 && len(ips) == 0 && err != dns.ErrEmptyResponse {
+	if rcode == 0 && len(ips) == 0 && !errors.AllEqual(dns.ErrEmptyResponse, errors.Cause(err)) {
 		newError("ip query").Base(err).WriteToLog()
 		return
 	}