/**
 * Executes remote command synchronously
 *
 * @param string $command
 * @param string|null &$output
 * @param string|null &$error
 * @return bool
 */
public function exec(string $command, ?string &$output, ?string &$error): bool
{
    $stream = ssh2_exec($this->_connection, $command);
    $errorStream = ssh2_fetch_stream($stream, SSH2_STREAM_STDERR);

    stream_set_blocking($stream, true);
    stream_set_blocking($errorStream, true);

    $outputChunks = array();
    $errorChunks = array();

    $eof = function ($s) use ($command) {
        $meta = stream_get_meta_data($s);
        // Occasionally `stream_select` after command won't receive `eof` nor `to` and loops indefinitely.
        Msg::write(' [' . var_export($meta['eof'], true) . ',' . var_export($meta['timed_out'], true) . ']', false, ColorFG::Blue);
        return $meta['eof'] || $meta['timed_out'];
    };

    do {
        $read = array($stream, $errorStream);
//            $write = null;
//            $except = null;

        $polldest = array(
            array(
                'resource' => $stream,
                'events' => SSH2_POLLOUT,
            ),
            array(
                'resource' => $errorStream,
                'events' => SSH2_POLLOUT,
            ),
        );

        //if (stream_select($read, $write, $except, 5)) {
        if (ssh2_poll($polldest, 5)) {
            foreach ($read as $c) {
                if (feof($c)) {
                    continue;
                }
                $read = stream_get_line($c, 8192);

                if ($read === false) {
                    continue;
                }

                if ($c === $stream) {
                    $chunks = &$outputChunks;
                } else {
                    $chunks = &$errorChunks;
                }
                $chunks[] = $read;

                while ($line = stream_get_line($c, 8192)) {
                    $chunks[] = $line;
                }
            }
        }
    } while (!$eof($stream) | !$eof($errorStream));

    fclose($stream);
    fclose($errorStream);

    $output = implode($outputChunks);
    $error = implode($errorChunks);

    unset($outputChunks); // free up large chunks
    unset($errorChunks);

    if ((strlen($output) == 0 && strlen($error) == 0) || strlen($output) > 0) {
        return true;
    } else {
        return false;
    }
}