# Bug in pcre (pcre.backtrack_limit)?

- Thread: https://externals.io/message/35042
- Original archive: https://news-web.php.net/php.internals/35042
- Started by k@rl.pflaesterer.de on 2008-01-30T19:57:06+00:00
- Messages: 3
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## #35042 — k@rl.pflaesterer.de — 2008-01-30T19:57:06+00:00

URL: https://externals.io/message/35042#35042

Hi,
when pcre.backtrack_limit is reached with `preg_replace()` the subject
string gets truncated to a string of length zero.

Here is a simple example (yes I know you shouldn't write a regexp like
that but it is simplified from a real pattern a coworker used).

,----[ PHP5.3 ]
| m58s03:~# php -r '$s = str_repeat("a", 9999);echo strlen(preg_replace("/a(.*?)b/", "\$1", $s)),"\n";'
| 9999
| m58s03:~# php -r 'ini_set("pcre.backtrack_limit",10);$s = str_repeat("a", 9999);echo strlen(preg_replace("/a(.*?)b/", "\$1", $s)),"\n";'
| 0
| m58s03:~# php -r '$s = str_repeat("a", 99998);echo strlen(preg_replace("/a(.*?)b/", "\$1", $s)),"\n";'
| 0
| m58s03:~# php -i|grep pcre
| pcre
| pcre.backtrack_limit => 100000 => 100000
| pcre.recursion_limit => 100000 => 100000
| m58s03:~# php -v
| PHP 5.3.0-dev (cli) (built: Jan 20 2008 20:59:20)
| Copyright (c) 1997-2008 The PHP Group
| Zend Engine v2.3.0, Copyright (c) 1998-2008 Zend Technologies
`----

The same happens with PHP 5.2.5. The pcre lib is the one shipped with
PHP.

KP

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## #35044 — Felipe Pena — 2008-01-30T20:43:38+00:00

URL: https://externals.io/message/35042#35044 · In reply to: #35042

Hello

Em Qua, 2008-01-30 às 20:57 +0100, Karl Pflästerer escreveu:
> Hi,
> when pcre.backtrack_limit is reached with `preg_replace()` the subject
> string gets truncated to a string of length zero.

I changed the phrase about the return value (3 weeks ago) in
pcre_replace(), it can be seen at http://docs.php.net/preg-replace, i
added "or `NULL` if an error occurred."

<?php
ini_set("pcre.backtrack_limit",10);
$s = str_repeat("a", 9999);
var_dump(preg_replace("/a(.*?)b/", "\$1", $s));
var_dump(preg_last_error()); // 2 = `PREG_BACKTRACK_LIMIT_ERROR` 

Output:
 `NULL` 
int(2)

-- 
Regards,
Felipe Pena.

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## #35047 — David Coallier — 2008-01-30T21:33:07+00:00

URL: https://externals.io/message/35042#35047

> Felipe Pena <felipensp@gmail.com> writes:
>
> > […]
>
> Thanks for the explanation; sadly your addition can only be found at
> docs.php.net not for example at
> www.php.net/manual/en/function.preg-replace.php which was until now my
> first choice if i wanted to look something up in the docs.
>

For future information Karl, http://docs.php.net is the main
documentation server. Everything else are mirrors and those will be
regenerated around the release of php 5.3 (Not now..)

:)

> IMO this is the wrong behaviour but it's at least documented :-)
>
>
> KP
>
>
> --
> 
> 
>
>



-- 
David Coallier,
Founder & Software Architect,
Agora Production (http://agoraproduction.com)
51.42.06.70.18