phpseclib\Net\SFTP::is_readable PHP Method

    function is_readable($path)
    {
        $path = $this->_realpath($path);
        $packet = pack('Na*N2', strlen($path), $path, NET_SFTP_OPEN_READ, 0);
        if (!$this->_send_sftp_packet(NET_SFTP_OPEN, $packet)) {
            return false;
        }
        $response = $this->_get_sftp_packet();
        switch ($this->packet_type) {
            case NET_SFTP_HANDLE:
                return true;
            case NET_SFTP_STATUS:
                // presumably SSH_FX_NO_SUCH_FILE or SSH_FX_PERMISSION_DENIED
                return false;
            default:
                user_error('Expected SSH_FXP_HANDLE or SSH_FXP_STATUS');
                return false;
        }
    }