Hi
On 2/16/22 12:39, Go Kudo wrote:
Is the nextByteSize() method actually required? PHP strings already know
their own length.
This is a convenience of the current implementation.
You already said that you will think of some good ideas, but I'd like to
be clear that the convenience of the internal implementation should not
be something that affects the user-facing implementation.
In fact with the current implementation I can trivially create a
memory-unsafety bug:
<?php
use Random\Engine;
use Random\Randomizer;
final class Bug implements Engine {
public function generate(): string
{
return '';
}
public function nextByteSize(): int {
return 7;
}
}
$e = new Bug();
$g = new Randomizer($e);
var_dump(\bin2hex($g->getBytes(8)));
Results in:
==116755== Use of uninitialised value of size 8
==116755== at 0x6180C8: php_bin2hex (string.c:111)
==116755== by 0x6185D2: zif_bin2hex (string.c:220)
==116755== by 0x79BDB4: ZEND_DO_ICALL_SPEC_RETVAL_USED_HANDLER
(zend_vm_execute.h:1312)
==116755== by 0x8194F0: execute_ex (zend_vm_execute.h:55503)
==116755== by 0x81ED86: zend_execute (zend_vm_execute.h:59858)
==116755== by 0x75A923: zend_execute_scripts (zend.c:1744)
==116755== by 0x69C8C4: php_execute_script (main.c:2535)
==116755== by 0x8E0B19: do_cli (php_cli.c:965)
==116755== by 0x8E1DF9: main (php_cli.c:1367)
==116755==
==116755== Use of uninitialised value of size 8
==116755== at 0x618100: php_bin2hex (string.c:112)
==116755== by 0x6185D2: zif_bin2hex (string.c:220)
==116755== by 0x79BDB4: ZEND_DO_ICALL_SPEC_RETVAL_USED_HANDLER
(zend_vm_execute.h:1312)
==116755== by 0x8194F0: execute_ex (zend_vm_execute.h:55503)
==116755== by 0x81ED86: zend_execute (zend_vm_execute.h:59858)
==116755== by 0x75A923: zend_execute_scripts (zend.c:1744)
==116755== by 0x69C8C4: php_execute_script (main.c:2535)
==116755== by 0x8E0B19: do_cli (php_cli.c:965)
==116755== by 0x8E1DF9: main (php_cli.c:1367)
==116755==
string(16) "0000000000000000"
For userland implementations you really must derive the size from the
returned bytestring. Otherwise it's easy for a developer to create an
implementation where nextByteSize() and generate() disagree. Even if the
memory-unsafety is fixed, this will result in frustration for the user.
For native implementations you can keep some explicit width in the code,
if that helps with performance.
Best regards
Tim Düsterhus
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