[MapServer-dev] GNU Regex Replacement?

[Even Rouault]

UPDATE: msautotest now pass against PCRE2 with a few extra fixes.

This was actually quite helpful to uncover 2 underlying issues, not 
related to PCRE2 itself:

- one (likely) wrong default regex with ms_map_bad_pattern_default in 
msCGILoadMap() where escaping antislash was missing (probably tolerated 
by GNU regex , but PCRE2 is more picky about that). Easy to fix

- and more embarrassing, our redefined MS_REG_xxxx constants in 
mapregex.h happen to not match the values of GNU regex (they might 
perhaps have matched in earlier times, but things have drifted apart 
since then)... In particular, MS_REG_NOSUB = 4 was thus wrongly 
interpreted as REG_NEWLINE = (1 << 2). I loose some extra hair on 
figuring that out. The symptom was in rfc62.map where a query string 
parameter whose value is "foo%0Abar" (foo newline bar) happened to 
validate (with GNU regex) the following expression '^[a-z]{1,16}$' 
whereas it shouldn't have (our expected result was incorrect). The value 
matched because msEvalRegex() sets MS_REG_NOSUB which was wrongly 
interpreted as REG_NEWLINE, thus making the caret / dollar to apparently 
match any line instead of the whole string. When using PCRE2, the match 
didn't occur because PCRE2 and GNU regex have exactly subtle different 
semantics regarding newline matching (I tried to understand 
https://www.pcre.org/current/doc/html/pcre2posix.html#SEC5, but beyond 
my mastering)

So all in all, it seems PCRE2 could be a viable alternative. I would 
expect "subtle" differences, so any mapfile having regular expressions 
in it that was tested with GNU/BSD/POSIX/whatever regex should be 
carefully checked for correct execution if switching to PCRE2

Even

Le 08/06/2024 à 15:35, Even Rouault via MapServer-dev a écrit :
>
> Hi,
>
> my attempt at https://github.com/MapServer/MapServer/pull/7073 . It 
> links, but PCRE2 doesn't seem to speak the same regex dialect as GNU 
> regex...
>
> Even
>
> Le 08/06/2024 à 05:31, Paul Ramsey via MapServer-dev a écrit :
>> Looks like it was in Centos as far back as 7, and is in base Ubuntu. 
>> It’s in MacPorts and Homebrew. So, fairly common?
>> P.
>>
>>> On Jun 7, 2024, at 8:06 PM, Steve Lime <sdlime at gmail.com> wrote:
>>>
>>> One would think replacement wouldn’t be that hard. It’s pretty 
>>> localized in MapServer. Is pcre2 widely available?
>>>
>>> On Fri, Jun 7, 2024 at 2:40 PM Paul Ramsey via MapServer-dev 
>>> <mapserver-dev at lists.osgeo.org> wrote:
>>>
>>>     We dragged around a dependency on pcre which got updated to
>>>     pcre2 lately.
>>>
>>>     > On Jun 7, 2024, at 12:38 PM, Howard Butler via MapServer-dev
>>>     <mapserver-dev at lists.osgeo.org> wrote:
>>>     >
>>>     > I was playing around with getting Conda Forge builds of
>>>     MapServer working, and when I got to Windows, I realized we need
>>>     the GNU Regex library
>>>     >
>>>     >
>>>     https://github.com/conda-forge/mapserver-feedstock/issues/47#issue-2341018003
>>>     >
>>>     > It is ancient, not released as a standalone library anymore,
>>>     and causes anything linking against it to also be GPL (which
>>>     we're doing in the Windows build situation). Maybe it is not
>>>     worth the trouble to change anything, but if one were to do so,
>>>     what should be used in its place?
>>>     >
>>>     > Howard
>>>     > _______________________________________________
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>>>
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>>
>>
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