public function recv()
    {
        $buf = '';
        $timeout = 1000;

        stream_set_blocking($this->client, false);

        // The maximum number of retries is 12, and 1000 microseconds is the minimum waiting time.
        // The waiting time is doubled each time until the server writes data to the buffer.
        // Usually, the data can be obtained within 1 microsecond.
        return retry(12, function () use (&$buf, &$timeout) {
            $read = [$this->client];
            $write = null;
            $except = null;
            while (stream_select($read, $write, $except, 0, $timeout)) {
                foreach ($read as $r) {
                    $buf .= fread($r, 8192);
                }
            }

            if (! $buf) {
                $timeout *= 2;

                throw new RecvFailedException('No data was received');
            }

            return $buf;
        });
    }

while (stream_select($read, $write, $except, 0, $timeout)) {
                foreach ($read as $r) {
                    $buf .= fread($r, 8192);
                }
            }