fix: DNS cache

common/picker/picker.go

@@ -47,6 +47,7 @@ func (p *Picker[T]) Wait() T {
 	p.wg.Wait()
 	if p.cancel != nil {
 		p.cancel()
+		p.cancel = nil
 	}
 	return p.result
 }
@@ -69,6 +70,7 @@ func (p *Picker[T]) Go(f func() (T, error)) {
 				p.result = ret
 				if p.cancel != nil {
 					p.cancel()
+					p.cancel = nil
 				}
 			})
 		} else {
@@ -78,3 +80,13 @@ func (p *Picker[T]) Go(f func() (T, error)) {
 		}
 	}()
 }
+
+// Close cancels the picker context and releases resources associated with it.
+// If Wait has been called, then there is no need to call Close.
+func (p *Picker[T]) Close() error {
+	if p.cancel != nil {
+		p.cancel()
+		p.cancel = nil
+	}
+	return nil
+}

dns/util.go

@@ -288,12 +288,16 @@ func listenPacket(ctx context.Context, proxyAdapter C.ProxyAdapter, proxyName st
 }
 
 func batchExchange(ctx context.Context, clients []dnsClient, m *D.Msg) (msg *D.Msg, cache bool, err error) {
+	cache = true
 	fast, ctx := picker.WithTimeout[*D.Msg](ctx, resolver.DefaultDNSTimeout)
+	defer fast.Close()
 	domain := msgToDomain(m)
 	for _, client := range clients {
+		if _, isRCodeClient := client.(rcodeClient); isRCodeClient {
+			msg, err = client.Exchange(m)
+			return msg, false, err
+		}
 		client := client // shadow define client to ensure the value captured by the closure will not be changed in the next loop
-		_, cache = client.(rcodeClient)
-		cache = !cache
 		fast.Go(func() (*D.Msg, error) {
 			log.Debugln("[DNS] resolve %s from %s", domain, client.Address())
 			m, err := client.ExchangeContext(ctx, m)
@@ -302,21 +306,19 @@ func batchExchange(ctx context.Context, clients []dnsClient, m *D.Msg) (msg *D.M
 			} else if cache && (m.Rcode == D.RcodeServerFailure || m.Rcode == D.RcodeRefused) {
 				// currently, cache indicates whether this msg was from a RCode client,
 				// so we would ignore RCode errors from RCode clients.
-				return nil, errors.New("server failure")
+				return nil, errors.New("server failure: " + D.RcodeToString[m.Rcode])
 			}
 			log.Debugln("[DNS] %s --> %s, from %s", domain, msgToIP(m), client.Address())
 			return m, nil
 		})
 	}
 
-	elm := fast.Wait()
-	if elm == nil {
-		err := errors.New("all DNS requests failed")
+	msg = fast.Wait()
+	if msg == nil {
+		err = errors.New("all DNS requests failed")
 		if fErr := fast.Error(); fErr != nil {
 			err = fmt.Errorf("%w, first error: %w", err, fErr)
 		}
-		return nil, true, err
 	}
-	msg = elm
 	return
 }