[SR-Users] Understanding regex format for subst_hf
Daniel-Constantin Mierla
miconda at gmail.com
Tue Oct 5 13:17:16 CEST 2021
Regarding:
"""
Oct 4 10:44:44 kamailio-n1 kamailio[20324]: ERROR: <core>
[core/re.c:363]: replace_build(): Buffer too small
"""
That seems to be related to the define of REPLACE_BUFFER_SIZE, which is
1024. Changing it requires to recompile kamailio. Is the value to be set
bigger than 1024?
Cheers,
Daniel
On 05.10.21 10:05, Daniel-Constantin Mierla wrote:
>
> Hello,
>
> the regular expressions in textops have to be POSIX format (extended,
> iirc), the remark for perl/sed-like was referring to the format being
> '/match/replace/flags' that is common for Perl scripting and sed
> parameters.
>
> Practically textops uses the regex functions from libc, does not
> depend on libpcre that offers PCRE format for expressions.
>
> The regex supports matching with PCRE and dialplan offers a way to do
> substitutions by matching with PCRE library.
>
> I updated the readme of textops to reflect somehow better the above.
>
> Cheers,
> Daniel
>
> On 04.10.21 19:50, Joel Serrano wrote:
>> So now when combined with subst_hf to actually edit the header value,
>> I'm getting this error:
>>
>> Oct 4 10:44:44 kamailio-n1 kamailio[20324]: ERROR: <core>
>> [core/re.c:363]: replace_build(): Buffer too small
>> Oct 4 10:44:44 kamailio-n1 kamailio[20324]: ERROR: textops
>> [textops.c:3110]: subst_hf_f(): textops subst_run failed
>>
>> Can anyone remind me the name of the parameter I have to adjust to
>> increase the buffer size?
>>
>> Thanks,
>> Joel.
>>
>> On Mon, Oct 4, 2021 at 10:46 AM Joel Serrano <joel at textplus.com
>> <mailto:joel at textplus.com>> wrote:
>>
>> Update:
>>
>> I managed to achieve it using the "regex" module with
>> "pcre_match()", that will take negative lookahead nicely.
>>
>>
>>
>> On Mon, Oct 4, 2021 at 10:18 AM Joel Serrano <joel at textplus.com
>> <mailto:joel at textplus.com>> wrote:
>>
>> Hey guys,
>>
>> I'm trying to do a replacement regex using subst_hf but I
>> can't seem to get the format right and the docs are confusing.
>>
>> *subst_hf: *docs say it uses perl-like regex (as I understand
>> it, that would mean PCRE). Docs also say in the 'subexp'
>> param that it uses the same format as *subst.*
>> *
>> *
>> *subst: *at the beginning it says it uses perl or sed format,
>> but in the '/re/repl/flags' param it says that sed format.
>>
>> https://www.kamailio.org/docs/modules/devel/modules/textops.html#textops.f.subst_hf
>> <https://www.kamailio.org/docs/modules/devel/modules/textops.html#textops.f.subst_hf>
>>
>>
>> 4.20. |subst_hf(hf, subexp, flags)|
>>
>> Perl-like substitutionsin the body of a header field.
>>
>> Meaning of the parameters is as follows:
>>
>> *
>>
>> /hf/ - header field name.
>>
>> *
>>
>> /subexp/ - substitution expression in the same format as
>> of the 'subst' functionparameter.
>>
>> *
>>
>> /flags/ - control flags - it has to be one of: a - all
>> headers matching the name; f - only first header matching
>> the name; l - only the last header matching the name.
>>
>>
>> 4.16. |subst('/re/repl/flags')|
>>
>> Replaces re with repl (sed or perl like).
>>
>> Meaning of the parameters is as follows:
>>
>> *
>>
>> /'/re/repl/flags'/ - sed like regular expression. flags
>> can be a combination of i (case insensitive), g (global)
>> or s (match newline don't treat it as end of line).
>>
>> 're' - is regular expression
>>
>> 'repl' - is replacement string - may contain pseudo-variables
>>
>> 'flags' - substitution flags (i - ignore case, g - global)
>>
>>
>>
>>
>>
>> I'm trying to use this:
>>
>> subst_hf("X-myheader", "/^(?!string1 |example2-|text3
>> )(.*)/myprefix \1/", "a")
>>
>> In an online tester using PCRE, the format is correct, but
>> Kamailio doesn't like it:
>>
>> Oct 4 09:29:16 cops-n1 cops[15957]: ERROR: <core>
>> [core/re.c:285]: subst_parser(): bad regular expression
>> ^(?!string1 |example2-|text3 )(.*) in
>> /^(?!string1 |example2-|text3 )(.*)/myprefix \1/
>>
>>
>> If I remove the negative lookahead chars (?!) then kamailio
>> doesn't complain but the regex doesn't do what I want.
>>
>> Does this mean that Kamailio won't support negative lookahead
>> for subst regex replacements?
>>
>> What I'm trying to achieve is something along:
>>
>> "If the value of the header Myheader doesn't start with ABC,
>> DEF or HIJ, then prefix it with XYZ"
>>
>> Any suggestions/ideas on how to achieve this?
>>
>>
>> Thanks,
>> Joel.
>>
>>
>>
>>
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> --
> Daniel-Constantin Mierla -- www.asipto.com
> www.twitter.com/miconda -- www.linkedin.com/in/miconda
> Kamailio Advanced Training - Online
> Nov 08-11, 2021 (Europe Timezone) - Nov 22-25, 2021 (America Timezone)
> * https://www.asipto.com/sw/kamailio-advanced-training-online/
--
Daniel-Constantin Mierla -- www.asipto.com
www.twitter.com/miconda -- www.linkedin.com/in/miconda
Kamailio Advanced Training - Online
Nov 08-11, 2021 (Europe Timezone) - Nov 22-25, 2021 (America Timezone)
* https://www.asipto.com/sw/kamailio-advanced-training-online/
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