Dump all memcached keys using `lru_crawler metadump all`

memcache_dump_lru_crawler_metadump.php

<?php

function getAllKeys(\Memcached $mc): array
{
    $allKeys = [];

    foreach ($mc->getServerList() as $id => $server) {

        $sock = fsockopen($server['host'], $server['port'], $errno, $errstr, 1);

        if ($sock === false) {
            throw new Exception("Error connection to server {$server['host']} on port {$server['port']}: ({$errno}) {$errstr}");
        }

        stream_set_timeout($sock, 1);

        if (fwrite($sock, "lru_crawler metadump all\n") === false) {
            throw new Exception('Error writing to socket');
        }

        $end = 0;
        while (($line = fgets($sock)) !== false) {

            // WORKAROUND: Memcached does not send "END" sometimes
            // see https://github.com/memcached/memcached/issues/667
            // Simulate END by sending next unknown command and waiting for ERROR
            if ($end == 0) {
                if (fwrite($sock, "err\n") === false) {
                    throw new Exception('Error writing to socket');
                }
                $end = 1;
            }

            $line = trim($line);
            if ($line === 'END' || $line === 'ERROR') {
                break;
            }

            // key=foobar exp=1596440293 la=1596439293 cas=8492 fetch=no cls=24 size=14908
            if (preg_match('!^key=(\S+)!', $line, $matches)) {
                $allKeys[] = rawurldecode($matches[1]);
            }
        }

        if (fclose($sock) === false) {
            throw new Exception('Error closing socket');
        }
    }

    return $allKeys;
}