The fun of cygwin and /dev/urandom (See comments, possibly MinGW related)

test.php

<?php

var_dump(is_readable('/dev/urandom'));
var_dump(passthru('head /dev/urandom'));
var_dump(PHP_OS);

?>

Sample output:
bool(false)
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A��-�x�
���������E��yM~K8�ů(S��
cF���}O�
bH�ֹ�0��������;Ȍ'�u��8���ph*��nF�Z�FOX�Z��O8ڔt���%3Bz=RӨxl�U��5|�#�!j����A�S�>-~/�I��.(b~	r��Ð�/�榄�*�Ӑ	����^�Ý������moIք�X�-�(
K�	�J��ji0�kT�,���^�u���p�+	'ڰ��v�]Cw���%jI�I�^�Ң��&��g��-D0��փ`AE_EcQJ�C�~>��4Qh7#����A�ཹ�2g��/8/)=�;/�3W��P�H���*���*TB�Xm,w�*d��٨�������+��Фy��
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~�8�p����	�X4:�]Tċ�Ï�?ݜ��G��$��Sxh�!ku�a����Զ��W~����K��	����;����D��i�N�݊�����������V�C��_���
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NULL
string(5) "WINNT"

A terrible function to use this:

<?php


function cygwin_rand_bytes($bytes) {
    $buf = '';
    $remaining = (int)$bytes;
    do {
        $read = exec('head -c'.$remaining.' /dev/urandom', $throwaway, $return);
        if ($return !== 0) {
            $buf = false;
            break;
        }
        $remaining -= mb_strlen($read, '8bit');
        $buf .= $read;
    } while ($remaining > 0);


    if ($buf !== false) {
        if (mb_strlen($buf, '8bit') === $bytes) {
            return $buf;
        }
    }

    throw new Exception(
        'PHP failed to generate random data.'
    );

}

Can you reliably detect cygwin?

@ircmaxell This seems to be an artefact of MinGW. Cygwin might be detectable in various ENV or in the uname, but MinGW is very silent at the existence.

Either way, these both stem into the Windows Cryptographic API, so calling that would be preferable.