code: func (c *Client) DialTCP(n string, laddr, raddr *net.TCPAddr) (net.Conn, error) {
  	if laddr == nil {
  		laddr = &net.TCPAddr{
  			IP:   net.IPv4zero,
  			Port: 0,
  		}
  	}
  	ch, err := c.dial(laddr.IP.String(), laddr.Port, raddr.IP.String(), raddr.Port)
  	if err != nil {
  		return nil, err
  	}
  	return &tcpChanConn{
  		Channel: ch,
  		laddr:   laddr,
  		raddr:   raddr,
  	}, nil
  }
docs: // DialTCP connects to the remote address raddr on the network net,
  // which must be "tcp", "tcp4", or "tcp6".  If laddr is not nil, it is used
  // as the local address for the connection.