Move predefined DNS server to rule action

dns/router.go

@@ -190,6 +190,8 @@ func (r *Router) matchDNS(ctx context.Context, allowFakeIP bool, ruleIndex int,
 				}
 			case *R.RuleActionReject:
 				return nil, currentRule, currentRuleIndex
+			case *R.RuleActionPredefined:
+				return nil, currentRule, currentRuleIndex
 			}
 		}
 	}
@@ -260,6 +262,21 @@ func (r *Router) Exchange(ctx context.Context, message *mDNS.Msg, options adapte
 						case C.RuleActionRejectMethodDrop:
 							return nil, tun.ErrDrop
 						}
+					case *R.RuleActionPredefined:
+						return &mDNS.Msg{
+							MsgHdr: mDNS.MsgHdr{
+								Id:                 message.Id,
+								Response:           true,
+								Authoritative:      true,
+								RecursionDesired:   true,
+								RecursionAvailable: true,
+								Rcode:              action.Rcode,
+							},
+							Question: message.Question,
+							Answer:   action.Answer,
+							Ns:       action.Ns,
+							Extra:    action.Extra,
+						}, nil
 					}
 				}
 				var responseCheck func(responseAddrs []netip.Addr) bool
@@ -376,6 +393,20 @@ func (r *Router) Lookup(ctx context.Context, domain string, options adapter.DNSQ
 					case C.RuleActionRejectMethodDrop:
 						return nil, tun.ErrDrop
 					}
+				case *R.RuleActionPredefined:
+					if action.Rcode != mDNS.RcodeSuccess {
+						err = RcodeError(action.Rcode)
+					} else {
+						for _, answer := range action.Answer {
+							switch record := answer.(type) {
+							case *mDNS.A:
+								responseAddrs = append(responseAddrs, M.AddrFromIP(record.A))
+							case *mDNS.AAAA:
+								responseAddrs = append(responseAddrs, M.AddrFromIP(record.AAAA))
+							}
+						}
+					}
+					goto response
 				}
 			}
 			var responseCheck func(responseAddrs []netip.Addr) bool
@@ -395,6 +426,7 @@ func (r *Router) Lookup(ctx context.Context, domain string, options adapter.DNSQ
 			printResult()
 		}
 	}
+response:
 	printResult()
 	if len(responseAddrs) > 0 {
 		r.logger.InfoContext(ctx, "lookup succeed for ", domain, ": ", strings.Join(F.MapToString(responseAddrs), " "))

dns/transport/predefined.go

@@ -1,83 +0,0 @@
-package transport
-
-import (
-	"context"
-
-	"github.com/sagernet/sing-box/adapter"
-	C "github.com/sagernet/sing-box/constant"
-	"github.com/sagernet/sing-box/dns"
-	"github.com/sagernet/sing-box/log"
-	"github.com/sagernet/sing-box/option"
-	"github.com/sagernet/sing/common"
-	E "github.com/sagernet/sing/common/exceptions"
-
-	mDNS "github.com/miekg/dns"
-)
-
-var _ adapter.DNSTransport = (*PredefinedTransport)(nil)
-
-func RegisterPredefined(registry *dns.TransportRegistry) {
-	dns.RegisterTransport[option.PredefinedDNSServerOptions](registry, C.DNSTypePreDefined, NewPredefined)
-}
-
-type PredefinedTransport struct {
-	dns.TransportAdapter
-	responses []*predefinedResponse
-}
-
-type predefinedResponse struct {
-	questions []mDNS.Question
-	answer    *mDNS.Msg
-}
-
-func NewPredefined(ctx context.Context, logger log.ContextLogger, tag string, options option.PredefinedDNSServerOptions) (adapter.DNSTransport, error) {
-	var responses []*predefinedResponse
-	for _, response := range options.Responses {
-		questions, msg, err := response.Build()
-		if err != nil {
-			return nil, err
-		}
-		responses = append(responses, &predefinedResponse{
-			questions: questions,
-			answer:    msg,
-		})
-	}
-	if len(responses) == 0 {
-		return nil, E.New("empty predefined responses")
-	}
-	return &PredefinedTransport{
-		TransportAdapter: dns.NewTransportAdapter(C.DNSTypePreDefined, tag, nil),
-		responses:        responses,
-	}, nil
-}
-
-func (t *PredefinedTransport) Reset() {
-}
-
-func (t *PredefinedTransport) Exchange(ctx context.Context, message *mDNS.Msg) (*mDNS.Msg, error) {
-	for _, response := range t.responses {
-		for _, question := range response.questions {
-			if func() bool {
-				if question.Name == "" && question.Qtype == mDNS.TypeNone {
-					return true
-				} else if question.Name == "" {
-					return common.Any(message.Question, func(it mDNS.Question) bool {
-						return it.Qtype == question.Qtype
-					})
-				} else if question.Qtype == mDNS.TypeNone {
-					return common.Any(message.Question, func(it mDNS.Question) bool {
-						return it.Name == question.Name
-					})
-				} else {
-					return common.Contains(message.Question, question)
-				}
-			}() {
-				copyAnswer := *response.answer
-				copyAnswer.Id = message.Id
-				copyAnswer.Question = message.Question
-				return &copyAnswer, nil
-			}
-		}
-	}
-	return nil, dns.RcodeNameError
-}