feat: Add RCode DNS client

dns/rcode.go

@@ -0,0 +1,54 @@
+package dns
+
+import (
+	"context"
+	"fmt"
+
+	D "github.com/miekg/dns"
+)
+
+func newRCodeClient(addr string) rcodeClient {
+	var rcode int
+	switch addr {
+	case "success":
+		rcode = D.RcodeSuccess
+	case "format_error":
+		rcode = D.RcodeFormatError
+	case "server_failure":
+		rcode = D.RcodeServerFailure
+	case "name_error":
+		rcode = D.RcodeNameError
+	case "not_implemented":
+		rcode = D.RcodeNotImplemented
+	case "refused":
+		rcode = D.RcodeRefused
+	default:
+		panic(fmt.Errorf("unsupported RCode type: %s", addr))
+	}
+
+	return rcodeClient{
+		rcode: rcode,
+		addr:  "rcode://" + addr,
+	}
+}
+
+type rcodeClient struct {
+	rcode int
+	addr  string
+}
+
+var _ dnsClient = rcodeClient{}
+
+func (r rcodeClient) Exchange(m *D.Msg) (*D.Msg, error) {
+	m.Response = true
+	m.Rcode = r.rcode
+	return m, nil
+}
+
+func (r rcodeClient) ExchangeContext(ctx context.Context, m *D.Msg) (*D.Msg, error) {
+	return r.Exchange(m)
+}
+
+func (r rcodeClient) Address() string {
+	return r.addr
+}

dns/util.go

@@ -93,7 +93,7 @@ func isIPRequest(q D.Question) bool {
 }
 
 func transform(servers []NameServer, resolver *Resolver) []dnsClient {
-	ret := []dnsClient{}
+	ret := make([]dnsClient, 0, len(servers))
 	for _, s := range servers {
 		switch s.Net {
 		case "https":
@@ -114,6 +114,9 @@ func transform(servers []NameServer, resolver *Resolver) []dnsClient {
 			}
 			ret = append(ret, clients...)
 			continue
+		case "rcode":
+			ret = append(ret, newRCodeClient(s.Addr))
+			continue
 		case "quic":
 			if doq, err := newDoQ(resolver, s.Addr, s.ProxyAdapter, s.ProxyName); err == nil {
 				ret = append(ret, doq)
@@ -288,16 +291,16 @@ func batchExchange(ctx context.Context, clients []dnsClient, m *D.Msg) (msg *D.M
 	fast, ctx := picker.WithTimeout[*D.Msg](ctx, resolver.DefaultDNSTimeout)
 	domain := msgToDomain(m)
 	for _, client := range clients {
-		r := client
+		_, ignoreRCodeError := client.(rcodeClient)
 		fast.Go(func() (*D.Msg, error) {
-			log.Debugln("[DNS] resolve %s from %s", domain, r.Address())
-			m, err := r.ExchangeContext(ctx, m)
+			log.Debugln("[DNS] resolve %s from %s", domain, client.Address())
+			m, err := client.ExchangeContext(ctx, m)
 			if err != nil {
 				return nil, err
-			} else if m.Rcode == D.RcodeServerFailure || m.Rcode == D.RcodeRefused {
+			} else if !ignoreRCodeError && (m.Rcode == D.RcodeServerFailure || m.Rcode == D.RcodeRefused) {
 				return nil, errors.New("server failure")
 			}
-			log.Debugln("[DNS] %s --> %s, from %s", domain, msgToIP(m), r.Address())
+			log.Debugln("[DNS] %s --> %s, from %s", domain, msgToIP(m), client.Address())
 			return m, nil
 		})
 	}