[pcre-dev] [Bug 957] Unexpected PREG_BACKTRACK_LIMIT_ERROR

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Author: Philip Hazel
Date:  
To: pcre-dev
Subject: [pcre-dev] [Bug 957] Unexpected PREG_BACKTRACK_LIMIT_ERROR
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http://bugs.exim.org/show_bug.cgi?id=957




--- Comment #1 from Philip Hazel <ph10@???> 2010-01-29 10:59:47 ---
On Tue, 26 Jan 2010, Laurent Raufaste wrote:

> I'm using PCRE 6.7.7.4 2008-07-04 with PHP, and I encountered a problem. The
> PHP developpers told me to report it to you.


I know nothing about PHP, but I guess that's a PHP variant of PCRE 6.7
(July 2006), which is now a very old version. The current release of
PCRE is 8.01. Many bugs have been fixed in the meantime.

> When I try to preg_replace a 2654 long string, I get a
> PREG_BACKTRACK_LIMIT_ERROR


However, with any version of PCRE, it is trivially easy to write a regex
that requires a vast amount of resources for tracebacks because the
search tree is very large indeed.

> Why does it hits the limit with a short string like this ?


There are discussions about this kind of thing in the pcreperform and
pcrestack man pages.

Philip


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