[asterisk-dev] Methodologies for validating dialplan

asterisk at phreaknet.org asterisk at phreaknet.org
Tue Jan 4 16:21:48 CST 2022

That's a really fair point - maybe another potential source of improvement?

I do use AMI for some things, but I have no use for the "Newexten" and 
"Varset" AMI events (if I run my "amidump.php" script, I'll see hundreds 
of these constantly even for a single call).

In addition, it makes using core set debug >= 3 a real pain, because 
then every complete AMI event is dumped, the result of which is that 90% 
of the debug suddenly becomes an AMI dump of new exten and new vars.

Adding an option to disable generating those events could probably help 
with that, and regardless of the performance benefit, would make dealing 
with debug and AMI a lot easier. I wonder if disabling snapshots would 
also help.

Can you think of other things about dialplan which hurt performance 
would could be similarly addressed?

On 1/4/2022 5:13 PM, Nikša Baldun wrote:
> Yeah, sorry, it's just that the experience is fresh in my mind, and I 
> wanted to help anyone avoid the pain I've been through. Whatever 
> anyone's preference is, I don't think difference in performance can be 
> disputed. It's not really C vs Python, it's dialplan interpreter vs 
> Python. Asterisk generates costly and unavoidable newexten event for 
> every executed line in dialplan. If there is a lot of them, which 
> obviously there will be in a large dialplan, performance suffers greatly.
> On 04. 01. 2022. 22:15, asterisk at phreaknet.org wrote:
>> Thanks for the advice - however, I personally like the dialplan and 
>> don't intend to stop using it. The dialplan/AGI/AEL/Lua (and now ARI) 
>> "config war" goes back a long time now, and I don't think it'll ever 
>> get resolved. That said, the vast majority of people *do* use 
>> extensions.conf dialplan, and I like it fine as a general approach. 
>> That's just my opinion, though.
>> There *are* obvious limitations to the dialplan, which is what this 
>> helps to address - not to make the workflow perfect, but better. I'm 
>> not sure using AGI would really get around the underlying problem 
>> here... and C performs a lot better than Python does.
>> On 1/4/2022 4:01 PM, Nikša Baldun wrote:
>>> Hi,
>>> I apologize for not commenting on the actual issue. However, after 
>>> having the experience of writing a complex dialplan, I feel strongly 
>>> compelled to say that it shouldn't be done at all. Any non-trivial 
>>> call flow should be written in Fast AGI. I can't see any upside of 
>>> using extensions.conf or AEL. Using a real programming language is 
>>> considerably easier, faster and more powerful, all the necessary 
>>> tools already exist and most importantly, execution is significantly 
>>> faster. In my case, after rewriting my dialplan in Python, call 
>>> preparation time fell from 2.5 seconds to a mere 50 milliseconds.
>>> On 04. 01. 2022. 20:53, asterisk at phreaknet.org wrote:
>>>> Hi, folks,
>>>>     Hope everyone's year is off to a good start. It was suggested 
>>>> on one of my code reviews to post here for discussion so here this is:
>>>> The PBX core, when it parses the dialplan on reload, catches a 
>>>> small number of syntax errors, such as forgetting a trailing ) or 
>>>> priority number, things like that.
>>>> However, there are a lot of dialplan problems that represent 
>>>> potentially valid syntax that will cause an error at runtime, such 
>>>> as branching to somewhere that doesn't exist. The dialplan will 
>>>> reload with no errors, since there isn't a syntax issue, but at 
>>>> runtime, the call will fail (and most likely crash). I found over 
>>>> the years that a lot of these were often simple typos or issues 
>>>> that were easily fixed but wasted a lot of time in finding solely 
>>>> in the "test, test, test" approach. Another common grievance I hear 
>>>> time to time about the dialplan is most issues are caught at 
>>>> runtime, not "compile time" (i.e. dialplan reload).
>>>> One thing I've done to catch typos and syntax errors is run some 
>>>> scripts that try to validate my dialplan for me by using a number 
>>>> of regex-based scripts which scan the dialplan. Among other things, 
>>>> this finds branches to places that don't exist, unused/dead code in 
>>>> the dialplan that isn't referenced anywhere, attempts to play audio 
>>>> files that don't exist, etc. In doing so, we can catch an even 
>>>> greater percentage of these kinds of issues in advance, rather than 
>>>> sitting around and waiting for a fallthrough at runtime, then 
>>>> remedying the issue after it's already caused an issue.
>>>> It works *okay* - this has helped A LOT in finding these problems 
>>>> before they are encountered at runtime, and finding problems I 
>>>> didn't even know existed - but it is *very* slow and probably takes 
>>>> 30 seconds to run on my dialplan (which is a few 10,000s of lines).
>>>> To try to improve on this, I wrote a patch that adds the CLI 
>>>> commands 'dialplan analyze fallthrough' and 'dialplan analyze 
>>>> audio'. It scans the dialplan using Asterisk APIs and finds 
>>>> Goto/GotoIf/Gosub/GosubIf application calls that try to access a 
>>>> nonexistent location in the dialplan, and 
>>>> Playback/ControlPlayback/Read calls that try to play a file that 
>>>> doesn't exist. Instead of taking half a minute, it's essentially 
>>>> instantaneous. You can take a look at the patch/apply it from here: 
>>>> https://gerrit.asterisk.org/c/asterisk/+/17719
>>>> There are obvious limitations to doing this; if variables are used 
>>>> in these calls, then it's very difficult - maybe impossible - to 
>>>> determine if something will fail just be crawling the config, so at 
>>>> the moment I ignore calls that contain variables in the relevant 
>>>> area. As such, there will be false negatives, but the goal is to 
>>>> not have false positives, and hopefully expose maybe the majority 
>>>> of issues that could be caught in advance in this manner.
>>>> Right now, the patch adds some commands to the PBX core, which Josh 
>>>> suggested might not be the best way to do this additional level of 
>>>> verifying the dialplan and trying to preemptively find issues with 
>>>> it. For one, it relies on knowing the usage of different 
>>>> applications, not all of which are PBX builtins. It might be safe 
>>>> to say that the way to parse "Goto" or "Playback" in this case will 
>>>> not change. A suggestion was to expose a way for modules to define 
>>>> how they could be verified.
>>>> I don't have any specific thoughts at the moment about how to 
>>>> proceed, but interested if anyone has any thoughts on what kind of 
>>>> architecture or approach here might make sense. Something to 
>>>> consider is that these validations may touch multiple different 
>>>> modules, maybe multiple times for the same module - and somehow 
>>>> this needs to be exposed to the PBX core for processing. For 
>>>> instance, the fallthrough check looks at Goto and Gosub, which are 
>>>> in completely different modules. Additionally, this is focused on 
>>>> the dialplan, meaning that running the rules in the module itself 
>>>> probably doesn't make any sense (but defining them there somehow 
>>>> might). However, ultimately there is an opportunity to preemptively 
>>>> find a lot of these issues in advance and improve the user 
>>>> experience, reduce frustration, etc.
>>>> Thanks!

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