function CalcDataSize($fp)
{
        $sz = '';
        $packdata = fread($fp,10);
        $arr = unpack('N',$packdata);
        $sz = implode("",$arr);
        return $sz-4;
}
$fp = fsockopen("111.11.1.11", 1111, $errno, $errstr,100);
if (!$fp)
    echo "$errstr ($errno)<br />n";
else
{
    $command = '<command>some command<command>';
    $command = PackData($command,$len);
    fputs($fp,$command,$len);
    print fread($fp, CalcDataSize($fp));
}

data = sock.recv(1024)
data = struct.unpack('>L', data[:4])
data_unpack = int(''.join(map(str,data)))-4

<?xml version="1.0" encoding="UTF-8"?><greeting></greeting>