code: func EnableKeepAlive(conn net.Conn) (*Conn, error) {
  	tcp, ok := conn.(*net.TCPConn)
  	if !ok {
  		return nil, fmt.Errorf("Bad conn type: %T", conn)
  	}
  	if err := tcp.SetKeepAlive(true); err != nil {
  		return nil, err
  	}
  	file, err := tcp.File()
  	if err != nil {
  		return nil, err
  	}
  	fd := int(file.Fd())
  	return &Conn{TCPConn: tcp, fd: fd}, nil
  }
docs: // EnableKeepAlive enables TCP keepalive for the given conn, which must be a
  // *tcp.TCPConn. The returned Conn allows overwriting the default keepalive
  // parameters used by the operating system.