[SR-Users] Kamailio config file String Concatenation

[Daniel-Constantin Mierla]

Hello,

indeed, there is some inconsistency here brought in after the merge with
SIP Express Router back in 2008.

Traditionally, Kamailio (or openser before 2008) didn't support
concatenation expressions as function parameters. That came via SER
branch and it is not available everywhere in a consistent and coherent
way (even for the code of modules imported from SER).

If you want to be in the safe side from Kamailio behaviour point of
view, as I never got into using SER style, here are some hints based on
what I typically do:

  - use concatenation expressions with '+' only in assignments, like:

$var(x) = "string1" + "string2";

  - use dynamic strings with variables as function parameters, like:

xlog("L_ERR", "string $var(x) more-string $var(y)\n");

  - use and assignment to a private variable first or $_s(...) variable
on positions that expect a string or a var, such as transformation
parameters, like:

$var(r) = "repl1" + "repl2";
$var(x) = $(var(y){s.replace,match,$var(r)});

Cheers,
Daniel

On 02.05.18 17:05, Alex Balashov wrote:
> You are correct that concatenation vs interpolation works and doesn't work in slightly inconsistent ways, for instance function string arguments vs assignment.
>
> The $_s() transformation may help make life easier. 
>
> On May 2, 2018 10:50:53 AM EDT, George Diamantopoulos <georgediam at gmail.com> wrote:
>> Hello,
>>
>> I'm a a bit confused as to when string concatenation will work in
>> kamailio
>> config file. So far I have identified the following cases:
>>
>> Working:
>>
>> As part of the right hand side of an assignment:
>> $var(x) = "string1" + "string2";
>>
>> String argument of some functions:
>> xlog("L_ERR", "string1" + "string2" + DEFINED_STRING + '\n');
>>
>> Conditional Statements:
>> if ( ru =~ "$" + "sip:" + $var(user) ) {
>>
>> Not Working:
>>
>> In string transformations (the fact that quotes is not part of the
>> argument
>> should give a hint though:
>> $var(x) = $(var(y){s.replace,match,"repl1" + "repl2"});
>>
>> String argument of some other functions:
>> append_hf_value("P-Asserted-Identity", "<" + "$var(new_pai)" + ">");
>> lookup("location", "sip:$var(username)@" + SIP_REALM_DEFINITION));
>>
>> In module parameter definitions:
>> modparam("nathelper", "sipping_from", "sip:keepalive@" +
>> SIP_REALM_DEFINITION)
>>
>> So far, I have found this to be fairly consistent, except for use
>> within
>> functions. For example, string concatenation works for the second
>> argument
>> of xlog, but not for the string arguments of append_hf_value() or
>> lookup().
>>
>> Is there anyway to know this for each function beforehand, or is my
>> only
>> choice to go through trial and error here? Thanks!
>>
>> BR,
>> George
>
> -- Alex
>
> --
> Sent via mobile, please forgive typos and brevity. 
>
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-- 
Daniel-Constantin Mierla
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