[MapServer-dev] GNU Regex Replacement?

[Even Rouault]

Or a 8.4 optional/experimental feature, where we would allow to build 
either against libc regex or PCRE2 (and enable PCRE2 only if explicitly 
requested at cmake time).

Le 08/06/2024 à 18:23, Lime, Steve D (MNIT) a écrit :
>
> Maybe a 9.0 change then? Sounds like the underlying issues should be 
> fixed regardless though.
>
> *From:*MapServer-dev <mapserver-dev-bounces at lists.osgeo.org> *On 
> Behalf Of *Even Rouault via MapServer-dev
> *Sent:* Saturday, June 8, 2024 10:37 AM
> *To:* Paul Ramsey <pramsey at cleverelephant.ca>; Steve Lime 
> <sdlime at gmail.com>
> *Cc:* MapServer Devs <mapserver-dev at lists.osgeo.org>
> *Subject:* Re: [MapServer-dev] GNU Regex Replacement?
>
>
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>
> 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>
>             <mailto: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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