[SR-Users] Understanding regex format for subst_hf

Wed Oct 6 08:41:13 CEST 2021

maybe change your regex pattern in "/^(.)/myprefix \1/", so that it matches
only one character.

Regards,
Bastian

On Tue, Oct 5, 2021 at 7:08 PM Joel Serrano <joel at textplus.com> wrote:

> Hi Daniel,
>
> Thank you for clarifying how subst_hf works!
>
> Regarding the size, it does in fact go over the 1024 limit, in this setup
> we are using firebase tokens which are 1162 characters long, and what I'm
> trying to do is to prefix the value we receive with some more characters,
> for a total of 1178 characters.
>
> So something along:
>
> subst_hf("X-myheader", "/^(.*)/myprefix \1/", "a")
>
>
> Would it be possible to expose that define for REPLACE_BUFFER_SIZE as a
> modparam to be configurable?
>
> Thanks for looking into this!
>
> Best,
> Joel.
>
>
> On Tue, Oct 5, 2021 at 4:17 AM Daniel-Constantin Mierla <miconda at gmail.com>
> wrote:
>
>> 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> 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> 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
>>>>
>>>> 4.20.  subst_hf(hf, subexp, flags)
>>>>
>>>> Perl-like substitutions in 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' function parameter.
>>>>    -
>>>>
>>>>    *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.comwww.twitter.com/miconda -- www.linkedin.com/in/miconda
>> Kamailio Advanced Training - Online
>> Nov 08-11, 2021 (Europe Timezone) - Nov 22-25, 2021 (America Timezone)
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>>
>> --
>> Daniel-Constantin Mierla -- www.asipto.comwww.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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