2 Oct
2015
2 Oct
'15
5:04 p.m.
Am 02.10.2015 um 11:51 schrieb Daniel-Constantin Mierla:
For starters, it would need to
be in the documentation of every
function, which it is not currently.
All functions for modules are documented in the readme of the module, if
you find one which is not, then it is considered a bug and should be
fixed quickly. You can see all those functions indexed by name at:
http://www.kamailio.org/wiki/alphaindexes/4.3.x/modfunctions
The functions are documented of course, however it isn't clearly stated
how its strings are interpreted. Sometimes it can be guessed but it's
open to interpretation.
A random example is the function ds_list_exist(groupid) from the
dispatcher module. If I pass a variable in a string to this function,
will it retrieve the value of the variable or will it try to interpret
the variable name as a groupid? I have no idea. If I pass a variable
without quotes, I hope it will get interpolated.
I'm not sure I fully understand what you are getting at here.
On 02/10/15 11:00, Sven Neuhaus wrote:
There is no way (that I know of) to access a variable by its name in C,
i.e. converting a string that contains a variable name back into a
reference to the actual variable. Your example has a hard-coded variable
name "i" to make it work.
There are some script languages that will allow you to get access to a
variable if you only know its name (some do it with tricks such as
eval() or reflection in Java).
I consider passing a reference to a variable by using a string with its
name to be ambiguous and error-prone.
Am 02.10.2015 um 08:38 schrieb Daniel-Constantin
Mierla:
What I wanted to say is that in C is up to me to interpret as function
developer, for example:
int i = 0;
void myprint(char *v) {
if(strcpy(v, "i")==0) {
printf("%d", i);
} else {
# error - unknown global variable
}
}
or:
void myprint(char *v) {
printf("%s", v);
}
Then use:
myprint("i");
Now, would you like the ccompiler to expand i inside the parameter?
All PVs in kamailio are global variables. Now it is up to myprint()
developer to do what he needs with that parameter. On 01/10/15 14:34, Sven Neuhaus wrote:
But then again,
in C the string interpolation is consistent.
Removing it altogether and making $_() mandatory for string
interpolation would avoid confusion. Ideally, all variables in double quoted strings
should be interpolated
and single quoted strings should not (the same way it is done in bash,
Perl, PHP, Groove, Ruby and elsewhere).
In C is not :-) . > Some
functions can evaluate the parameter content, some don't. And in
> some cases, even there is a variable inside a parameter for a function,
> it is not evaluated, but it is set. That's again based on the purpose of
> the function.
That's frightening!
Why? Do you know the purpose of parameters for C libc
functions without
first looking at the manual? One needs to retrieve values, so instead of
evaluating the value, is about setting the value. It's one
thing to know what a function does and what its parameters are.
It adds a whole level of complexity and source of errors having to look
up which one of those parameters will be interpolated. That's why no-one
else is doing it that way.
Well, in C a parameter can be pointer and can be used for input (read)
of output (write).
The & (reference) and * (pointer) operators in C are not for saying it
is a parameter for write or read. Practically behind each PV is a
pointer in the C code, because we cannot any longer declare a
non-pointer variable from kamailio.cfg back to c code (which is already
compiled at the time kamailio.cfg is loaded). >>>> - pv_printf($var(x), ...)
>>> I looked up the documentation for pv_printf() in the KEx module and was
>>> baffled to see the variable name being passed as a string in the example
>>> ... "pv_printf("$ru", "sip:$rU@$fd");" :-*
>> That's pretty much from day 0 of sip express router back in 2001 -- the
>> parameters of functions from modules had to be enclosed in double
>> quotes, not matter what they are. There was no support for expressions
>> as parameters for functions. Later there were some changes and some
>> parameters can be without double quotes, but that is not the general
>> rule -- if in double quotes, it should work always (for module functions).
> Again, here we have the situation that there is a parameter to a
> function call where the first parameter is not interpolated and the
> second one is. That is not a good idea!
>
> By the way: With the modparam() function the behaviour differs depending
> on the module that is being configured.
>
> I think it would make Kamailio easier and less error prone to configure
> if the string interpolation behaviour were identical in all places.
I am open to discuss and even help evolving the
interpreter to be more
friendly. But for this specific case I don't really see your point.
And documentation for all those functions is there, prove a missing one
and will be fixed as said above.
There's $sht() that explicitly states that the key can be static or
dynamic. What happens if the string contains something like $xyz and
there is no such variable? Will it then use the string verbatim?
That doesn't seem like a good idea.
Start a wiki page on kamailio.org/wiki/ in the
development section
collecting what you would like to have, then email to sr-dev to get
input from other developers interested in the topic.
OK I'll try to think this through once I am finished with the current
project at work.
Have a nice weekend!
-Sven