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serialize bug with array that references to itself?

php.internals

Francisco M. Marzoa Alonso

21 years ago

Try this code:

<pre>
<?php

$Arr = array();
$Arr['self'] = &$Arr;
var_dump ( $Arr );

$serdata = serialize ($Arr);
$Arr2 = unserialize ( $serdata );
echo "\n\n";
var_dump ( $Arr2 );

?>
</pre>

The second array is expected to be exactly as $Arr, but it doesn't. This
is the output for that code:

array(1) {
["self"]=>
array(1) {
["self"]=>
*RECURSION*
}
}

array(1) {
["self"]=>
array(1) {
["self"]=>
NULL
}
}

As you can see the second array has a NULL value where the first one had
a recursive reference.

Can this be considered as a bug of PHP serialization system?

Andrey Hristov

21 years ago

Francisco M. Marzoa Alonso wrote:

> Try this code:
>
> <pre>
> <?php
>
> $Arr = array();
> $Arr['self'] = &$Arr;
> var_dump ( $Arr );
>
> $serdata = serialize ($Arr);
> $Arr2 = unserialize ( $serdata );
> echo "\n\n";
> var_dump ( $Arr2 );
>
> ?>
> </pre>
>
> The second array is expected to be exactly as $Arr, but it doesn't. This
> is the output for that code:
>
> array(1) {
>  ["self"]=>
>  array(1) {
>    ["self"]=>
>    *RECURSION*
>  }
> }
>
> array(1) {
>  ["self"]=>
>  array(1) {
>    ["self"]=>
>    NULL
>  }
> }
>
> As you can see the second array has a NULL value where the first one had
> a recursive reference.
>
> Can this be considered as a bug of PHP serialization system?
>

Looks as such.
While looking at this one, I cooked a little example which cores ZE2 (5.1.0-dev)

<?php
class a{}
class b{}

$a=new a;
$b=new b;
$a->a=$b;
$c=array($a,$b);
var_dump($c,$d=serialize($c));
var_dump($e=unserialize($d));
$d[0]->a->prop=1;
var_dump($d);
?>

If one looks at it she will see that I have an error in the example and instead
of $d[0]->a I have to use $e[0] , still a Segmentation Fault is not tolerable.

This works ok :
<?php
class a{}
class b{}

$a=new a;
$b=new b;
$a->a=$b;
$c=array($a,$b);
var_dump($c, $d=serialize($c));
var_dump($e=unserialize($d));
$d[0]->a->prop=1;
var_dump($d);
?>

$e is :
array(2) {
[0]=>
object(a)#3 (1) {
["a"]=>
object(b)#4 (1) {
["prop"]=>
int(1)
}
}
[1]=>
object(b)#4 (1) {
["prop"]=>
int(1)
}
}

Andrey

Francisco M. Marzoa Alonso

21 years ago

Should I fill a bug notification report or so? (where are them? ;-))

Andrey Hristov wrote:

Andrey Hristov

21 years ago

Feel free to file a bug report at http://bugs.php.net .Mention
in the subject there there is core dump.

Thanks,
Andrey

Francisco M. Marzoa Alonso wrote:

Francisco M. Marzoa Alonso

21 years ago

BTW., I'm not sure that there's nothing more wrong here. Takin the first
part of the code of first example:

<?php

$Arr = array();
$Arr['self'] = &$Arr;
var_dump ( $Arr );

?>

It returns:

array(1) {
["self"]=>
array(1) {
["self"]=>
*RECURSION*
}
}

Is that as its expected to be? I meant that perhaps it should be:

array(1) {
["self"]=>
*RECURSION*
}

Since the element in $Arr['self'] is yet (or at least should be) a
reference to itself...

Andrey Hristov

21 years ago

Well, when there is traversion inside the engine, it checks whether it has
processed a "node" already several times. As far as I remember the threshold
is 3. So once it goes over $Arr, the counter increases to 1, the second time
to 2 and third time it is 3 and ZE reports recursion.

HTH,
Andrey

Francisco M. Marzoa Alonso wrote:

Jochem Maas

21 years ago

Andrey Hristov wrote:

>  Well, when there is traversion inside the engine, it checks whether it has
> processed a "node" already several times. As far as I remember the
> threshold
> is 3. So once it goes over $Arr, the counter increases to 1, the second
> time
> to 2 and third time it is 3 and ZE reports recursion.

is there good reason to set the threshold at 3 iso 2?

when dumping out objects that make heavy use of 'parent' references this
leads to tons of extra output which would be greatly cutdown if the
threshold was 2 iso 3.

just to make the point, print_r seems to use a threshold of 2 (which is
why I always try print_r before taking my chances with var_dump):

<?php

class a { public $self; }

$A = new a;
$A->self = $A;
var_dump( $A );
print_r( $A );

?>

Andrey Hristov

21 years ago

Hi,
print_r() and var_dump() are quite different in their nature.
print_r() is a thin wrapper around an internal Zend function
(as far as I remember) while var_dump() is in ext/standard/var.c
The do more or less the same job still some differences in the
output (print_r() shows nothing on NULL variables which I find
clumsy since lack of output where I expect ouput makes me
suspicious).

Andrey

Jochem Maas wrote:

Jochem Maas

21 years ago

Hi Andrey,

I have to confess my understanding of the engine internals is next to
zero, but I do understand that var_dump and print_r were created
with/for different pretexts.

I agree with you that printing nothing for NULL is doesn't feel right
(btw boolean false has the same effect) - this can be problematic when
you don't know that this is the case (indeed much time have I lost on
this issue when I first started out), this is a minor gripe and easily
sidestepped with a var_dump :-)

my question was more out of curiosity (although I would like to see the
threshold for var_dump dropped to 2 if that is technically
feasible/acceptable) - there may be a good reason for the difference in
thresholds, it may be a an oversight/inconsistency. either way my motive
is to better understand the reasoning behind the way things work in PHP
- better understanding how/why a developer made it work a certain has in
the past really helped me improve my code.

thanking everyone who has made (and continues to make) PHP what it is -
it rocks alot more than it doesn't ;-).

Andrey Hristov wrote:

Francisco M. Marzoa Alonso

21 years ago

I think I understand the reason because I obtain that output, but I
cannot figure out the motivations for doing it in that way. I should
probably take a look at ZE sources.

Thx. a lot by your help.

Andrey Hristov wrote:

Moriyoshi Koizumi

21 years ago

On 2004/11/03, at 22:31, Andrey Hristov wrote:

> $c=array($a,$b);
> var_dump($c,$d=serialize($c));
> var_dump($e=unserialize($d));
> $d[0]->a->prop=1;
> var_dump($d);
> ?>

Did you mean "$e[0]->a->prop" by "$d[0]->a->prop"?

That looks like another issue:

<?php
// This causes bus error.
$a = 'abc';
$a{0}->a->prop = 1;
?>

Moriyoshi

Andrey Hristov

21 years ago

Moriyoshi Koizumi wrote:

>
> On 2004/11/03, at 22:31, Andrey Hristov wrote:
>
>> $c=array($a,$b);
>> var_dump($c,$d=serialize($c));
>> var_dump($e=unserialize($d));
>> $d[0]->a->prop=1;
>> var_dump($d);
>> ?>
>
>
> Did you mean "$e[0]->a->prop" by "$d[0]->a->prop"?

Well, when I was writing the test I made a mistake which
I saw later but my mistake lead to a PHP core dump.

>
> That looks like another issue:
>
> <?php
> // This causes bus error.
> $a = 'abc';
> $a{0}->a->prop = 1;
> ?>
>
> Moriyoshi
>

Andrey

Moriyoshi Koizumi

21 years ago

> > Did you mean "$e[0]->a->prop" by "$d[0]->a->prop"?
>
> Well, when I was writing the test I made a mistake which
> I saw later but my mistake lead to a PHP core dump.

Looks more like I should've read the mail more carefully :)

Moriyoshi