fix kcp client connection

gost/kcp.go

@@ -191,7 +191,12 @@ func (tr *kcpTransporter) Dial(addr string, options ...DialOption) (conn net.Con
 
 	session, ok := tr.sessions[addr]
 	if !ok {
-		return net.DialUDP("udp", nil, uaddr)
+		conn, err = net.DialUDP("udp", nil, uaddr)
+		if err != nil {
+			return
+		}
+		session = &kcpSession{conn: conn}
+		tr.sessions[addr] = session
 	}
 	return session.conn, nil
 }
@@ -209,7 +214,7 @@ func (tr *kcpTransporter) Handshake(conn net.Conn, options ...HandshakeOption) (
 	defer tr.sessionMutex.Unlock()
 
 	session, ok := tr.sessions[opts.Addr]
-	if !ok {
+	if !ok || session.session == nil {
 		s, err := tr.initSession(opts.Addr, conn, config)
 		if err != nil {
 			conn.Close()
@@ -229,13 +234,15 @@ func (tr *kcpTransporter) Handshake(conn net.Conn, options ...HandshakeOption) (
 }
 
 func (tr *kcpTransporter) initSession(addr string, conn net.Conn, config *KCPConfig) (*kcpSession, error) {
-	pc, ok := conn.(net.PacketConn)
+	udpConn, ok := conn.(*net.UDPConn)
 	if !ok {
 		return nil, errors.New("wrong connection type")
 	}
 
 	kcpconn, err := kcp.NewConn(addr,
-		blockCrypt(config.Key, config.Crypt, KCPSalt), config.DataShard, config.ParityShard, pc)
+		blockCrypt(config.Key, config.Crypt, KCPSalt),
+		config.DataShard, config.ParityShard,
+		&kcp.ConnectedUDPConn{UDPConn: udpConn, Conn: udpConn})
 	if err != nil {
 		return nil, err
 	}