[asterisk-dev] How to change length of variable

[Tilghman Lesher]

On Wed, Oct 19, 2011 at 2:03 AM, Terry Wilson <twilson at digium.com> wrote:
>> I understand that Asterisk have limit of the length of the variable -
>> 256 characters.
>> How I can change this limit?
>> I want to recieve long variables from AGI-script.
>> What I need to fix in the sources?
>
> I'm pretty sure that the maximum value length for dialplan
> variable substitution is 4095 characters + the terminating
> NULL. Look at VAR_BUF_SIZE in main/pbx.c. It looks like
> res/res_agi.c on the getvariable function it limits the string
> length to 1024 with the tempstr variable. You might also
> check out AGI_BUF_LEN in res/res_agi.c as it looks like
> it might limit things as well (it is set to 2048).
>
> Looks like it would be nice for us to set some global limits
> and be consistent with them all over the place (or just stop
> using stack-allocated buffers for things and remove the
> arbitrary limits on variable values).
>
> If you are talking about the length of dialplan variable
> names, I am not aware of a limit on those. I could always
> be wrong, though.

While there are still a few places using
pbx_substitute_variables_helper(), most uses have been
transitioned to use ast_str_substitute_variables(), which has
no arbitrary limit on variable expansion.

Looks like 1.8's AGI is using the newer API, so there shouldn't
be a limit on variable expansion with GET FULL VARIABLE.  Of
course, as Terry stated, you'll run into the 2048-byte command
limit if you try to set a variable longer than about 2000 bytes
(subtract the command name and variable name from 2048).
Given that this is a read buffer, there isn't really a great way to
kill this limit.  You can raise it, but the implicit limit is still there.

Given that the OP expressed a limit of 256 characters, I took
another look.  This limit would only be the case in 1.4 AGI if
LOW_MEMORY was defined.  If that's what you have, then
clearly you need to remove that checkmark in menuselect.
This will make the variable expansion buffer increase to 8192,
although the 2048 command buffer limit in AGI will still be
present.

-Tilghman