when ListenUDP fails once, try again next time

p2p/transport/quic/transport.go

@@ -31,26 +31,30 @@ var quicConfig = &quic.Config{
 }
 
 type connManager struct {
-	connIPv4Once sync.Once
-	connIPv4     net.PacketConn
+	mutex sync.Mutex
 
-	connIPv6Once sync.Once
-	connIPv6     net.PacketConn
+	connIPv4 net.PacketConn
+	connIPv6 net.PacketConn
 }
 
 func (c *connManager) GetConnForAddr(network string) (net.PacketConn, error) {
+	c.mutex.Lock()
+	defer c.mutex.Unlock()
+
 	switch network {
 	case "udp4":
+		if c.connIPv4 != nil {
+			return c.connIPv4, nil
+		}
 		var err error
-		c.connIPv4Once.Do(func() {
-			c.connIPv4, err = c.createConn(network, "0.0.0.0:0")
-		})
+		c.connIPv4, err = c.createConn(network, "0.0.0.0:0")
 		return c.connIPv4, err
 	case "udp6":
+		if c.connIPv6 != nil {
+			return c.connIPv6, nil
+		}
 		var err error
-		c.connIPv6Once.Do(func() {
-			c.connIPv6, err = c.createConn(network, ":0")
-		})
+		c.connIPv6, err = c.createConn(network, ":0")
 		return c.connIPv6, err
 	default:
 		return nil, fmt.Errorf("unsupported network: %s", network)