[OpenSIPS-Users] Call Branching in parallel and series

[Liviu Chircu]

On 01.11.2022 17:12, Conrad de Wet wrote:
>
> This works, except I want to extend this even further. I want these 4 
> branches to keep trying on a loop until the transaction timeout occurs 
> or one of the calls is answered. Except I find that the 
> “failure_route” has two main problems, firstly if I try a “t_relay()” 
> in the failure_route, the original call gets relayed again and I can’t 
> seem to refer back to the branch.
>
> This causes the number of branches to quickly run out (I think max is 
> 16), as it seem to nest the branch. Also because the t_relay() appears 
> to act on the main branch, all the urls are reset, so I don’t really 
> know where I was originally sending this request to.
>
> failure_route[my_on_failure]{
>
>                 seturi($branch(uri));   # <-- This is null
>
>                 t_relay(); # causes new branches that don’t seem to 
> kill the old ones.
>
> }
>
Hi, Conrad!

Re: the confusion around failure_route: the failure route callback 
actually means a "failure to relay", not a "failure of a specific 
branch".  So no matter how many branches you attempted to relay in 
parallel (1, 2, 8, etc.), it means they *all* failed (some explicitly 
with, e.g. a 404, others implicitly with a 408 internal timeout).  So 
now you're in this callback and you're only given the original 
Request-URI of the message, with an opportunity to build a new set of 
branches to relay (optionally with a new failure route callback), or 
just give up and pass the error message back upstream.

On topic:  I'm assuming the need to "keep trying these branches in a 
loop" stems from the fact that the "lookup()" operation may produce 
different results throughout the duration of the call attempt.  So 
instead of having a long transaction timeout, you prefer to have a 
shorter one and keep redo'ing the "failure_route + lookup()" loop in 
hope that the WS device comes online, correct?  If so, you may indeed 
often run into the "max branches exceeded" limitation quite easily this 
way, at least with how the code currently works...

Possible cheap workaround: recompile with a larger MAX_BRANCHES (say, go 
from 12 to 31).  At least you may get your PoC working this way and move 
to solving other problems.  Medium-term, maybe we can look into 
developing some support for creating lots of branches in the "master" 
OpenSIPS tree.

Best regards,

-- 
Liviu Chircu
www.twitter.com/liviuchircu  |www.opensips-solutions.com
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