Hi Alex,
sorry for the late reply. I had to revisit the tsilo code, long time without looking at it :)
When I designed the module I had in mind what I considered a "natural" scenario for the push notifications: the entity acting as a registrar being the one responsible for a call forking.
Of course other scenarios have arisen which are not covered by the current implementation, one of which is to be able to add branches without the usrloc/registrar mechanism.
We could add two new functions that do the same as ts_append and ts_append_to but without performing the look:
- ts_append_no_lookup(ruri, [contact]): add to all the transactions stored for ruri a new branch for <contact> (if not specified extracted from the current SIP message)
- ts_append_to_no_lookup(tindex, tlabel, [contact]): add to the transaction specified by tindex and tlabel  a new branch for <contact> 
Maybe names are a bit long but is to give the idea.
Do you think that a solution like this would cover your (and others') scenarios?
I can try to find the time to work on it :)

Cheers,

Federico



On Tue, Nov 28, 2023 at 8:39 PM Alex Balashov via sr-users <sr-users@lists.kamailio.org> wrote:
PS. It seems to me there are some kludgy options to work around this limitation, i.e. to basically reinvent tsilo.

They all boil down to suspending the transaction and using some sort of IPC mechanism to queue new branch destinations, then, after some defined interval, using some dequeueing mechanism as a semaphore to kick-start the forking process.

For instance, one could do this by hashing the RURI destination, transaction index and label in htable, then suspending the transaction, then piling some branches into it and then setting the expiration value of the RURI key to immediate, causing event_route[htable:expired:<table>] to kick off. Depending on where exactly that executes, this could resume the transaction, add the branches and manage the forking. Or one could try some tricks with config locks, or mqueue's unique key mode.

But none of these solutions allow the continuous drip of new serial forking destinations into an active transaction. They all require suspending and waiting a sufficient amount of time to believe oneself to have collected all the potential destinations, then to reanimate. This is not necessarily how the real world works. These mechanisms are also quite complicated, and complexity breeds fragility.

-- Alex

> On 28 Nov 2023, at 13:38, Alex Balashov <abalashov@evaristesys.com> wrote:
>
> Hi,
>
> I wanted to revisit the topic of tsilo dependence on the location service. All three ts_append*() functions have the following quality:
>
> - ts_append(): "performing a contact lookup on the table specified by the domain parameter."
> - ts_append_by_contact(): "the contact lookup is performed"
> - ts_append_to(): "performing a contacts lookup on the table specified by the domain parameter"
>
> Why is this extensive coupling to usrloc necessary? This makes it impossible to use `tsilo` in case of providing a push-notification add-on that front-ends an upstream registrar, requiring a kind of local shadow registrar or mid-registrar. What would make more sense is a generic mechanism that allows one to "drip" new contacts into an existing transaction, whether suspended or active.
>
> Kamailio has a mechanism to add more branches to an existing transaction, but the scope of that mechanism is only from *inside* the vantage point of the transaction in question. The key parlour trick of `tsilo` is that it permits dripping new branches into a *different* transaction.
>
> ts_append_to() almost does the trick, providing a target index and label, but it just insists on doing a registrar lookup to source the contacts.
>
> What is really wanted and needed for the downstream PN gateway use-case is a means of extracting contacts from incoming registrations (or other sources, potentially) without storing them in any fashion locally, without using or even loading usrloc, and just throwing them over the fence into a different transaction.
>
> Is this somehow possible by means other than tsilo? Am I overlooking something?
>
> Cheers,
>
> -- Alex
>
> --
> Alex Balashov
> Principal Consultant
> Evariste Systems LLC
> Web: https://evaristesys.com
> Tel: +1-706-510-6800
>

--
Alex Balashov
Principal Consultant
Evariste Systems LLC
Web: https://evaristesys.com
Tel: +1-706-510-6800

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