Hi Daniel,

I've actually been spending a lot of time with the dispatcher readme to try to figure this out. If there are restrictions in usage as you indicate, then it is not documented.

From the dispatcher readme:

ds_next_dst
Takes the next destination address from the corresponding XAVPs and sets the dst_uri (outbound proxy address).
This function can be used from REQUEST_ROUTE, FAILURE_ROUTE.

ds_select_dst
If the bit 2 in 'flags' parameter is set, the rest of the addresses from the destination set are stored in XAVP list (limited with an optional 'limit' parameter). You can use 'ds_next_dst()' to use next address in order to achieve serial forking to all possible destinations.
This function can be used from REQUEST_ROUTE, FAILURE_ROUTE.

My issue is that I want to select from a new group of destinations only when a particular failure status has been received, so I can't simply only call ds_next_dst() in failure_route.

Anyways, the problem is not in the initial group selection, but rather in the subsequent calls to ds_next_dst(). I changed the logic to how you recommended, with ds_select_dst() being called only in request_route, and ds_next_dst() only called by failure_route. The problem is exactly the same: ds_next_dst() starts selecting destinations that are not in the group that was initially selected with ds_select_dst().

You can see it happening here:

dispatcher [dispatch.c:2097]: ds_manage_routes(): set [2]
dispatcher [dispatch.c:2213]: ds_manage_routes(): using alg [8] hash [0]
dispatcher [dispatch.c:2260]: ds_manage_routes(): selected [8-2-0/0] <sip:127.0.0.1:5072;transport=udp>
dispatcher [dispatch.c:2281]: ds_manage_routes(): using first entry [2/0]
dispatcher [dispatch.c:2057]: ds_select_dst_limit(): selected target destinations: 1
<script>: REQUEST ROUTE: Relayed to [sip:127.0.0.1:5072;transport=udp] via forced socket [udp:127.0.0.1:5074]
<script>: FAILURE ROUTE: 400 Bad Request, trying next available gateway...
<script>: FAILURE ROUTE: Selecting next destination from: [grp=2;uri=sip:127.0.0.1:5072;transport=udp;]
dispatcher [dispatch.c:2357]: ds_update_dst(): updating dst
dispatcher [dispatch.c:2373]: ds_update_dst(): updating dst with next record
dispatcher [dispatch.c:2403]: ds_update_dst(): using next dst uri [sip:127.0.0.1:5072;transport=udp]
<script>: FAILURE ROUTE: Next destination selected: [sip:127.0.0.1:5072;transport=udp] from [grp=2;uri=sip:127.0.0.1:5072;transport=udp;]
<script>: FAILURE ROUTE: 400 Bad Request, trying next available gateway...
<script>: FAILURE ROUTE: Selecting next destination from: [grp=2;uri=sip:127.0.0.1:5072;transport=udp;]
dispatcher [dispatch.c:2357]: ds_update_dst(): updating dst
dispatcher [dispatch.c:2373]: ds_update_dst(): updating dst with next record
dispatcher [dispatch.c:2403]: ds_update_dst(): using next dst uri [sip:127.0.0.1:5071;transport=udp]
<script>: FAILURE ROUTE: Next destination selected: [sip:127.0.0.1:5071;transport=udp] from [grp=1;uri=sip:127.0.0.1:5071;transport=udp;]

It happens in this order:

1. Request_route ds_select_dst() selects group=2 destination=sip:127.0.0.1:5072;transport=udp
2. Failure_route ds_next_dst() selects group=2 destination=sip:127.0.0.1:5072;transport=udp (again?)
3. Failure_route ds_next_dst() selects group=1 destination=sip:127.0.0.1:5071;transport=udp

I don't understand what I'm doing incorrectly for it to select a destination from group 1.

One thing that is standing out to me is the log line showing "ds_select_dst_limit(): selected target destinations: 1" when ds_select_dst() is called. Based on the readme for ds_select_dst(), all addresses from the group are stored in the XAVP if bit 2 of the 'flags' parameter is set (which it is) unless otherwise limited by the 'limit' parameter (it is not). However, when I print out the XAVP with xavp_params_implode, the XAVP only ever contains a single destination.

Thanks,

From: Daniel-Constantin Mierla <miconda@gmail.com>
Sent: Wednesday, September 27, 2023 01:58
To: Kamailio (SER) - Users Mailing List <sr-users@lists.kamailio.org>
Cc: Geoff Goas <Geoff.Goas@interoptechnologies.com>
Subject: Re: [SR-Users] What is the expected behavior for dispatcher's ds_next_dst?
 
Hello,

normally ds_select_dst() should be used inside request_route and
ds_next_dst() in the failure_route. As you do the former also in the
failure_route, you keep selecting the destination from the group and add
them to the list of possible next hops.

Look at the readme of dispatcher module, it has a complete sample config
how to use the two functions.

Cheers,
Daniel

On 26.09.23 22:02, geoff.goas--- via sr-users wrote:
> Hello,
>
> I have some questions about dispatcher's behavior. I noticed that when I first ds_select_dst() a specific dispatcher group ID, ds_next_dst() will cycle through the active destinations in that group. When it reaches the end of the destinations in the group, it does not return "false", instead it starts to return destinations that are not a part of that group, ie. those destinations which are listed prior to the selected group in the dispatcher.list file. Is this the expected behavior? I've observed it on kamailio 5.3 and 5.5 releases.
>
> My dispatcher.list:
>
> # Group 1
> 1 sip:127.0.0.1:5071;transport=udp 8 0
> # Group 2
> 2 sip:127.0.0.1:5072;transport=udp 8 0
> # Group 3
> 3 sip:127.0.0.1:7010;transport=udp 8 0
> 3 sip:127.0.0.1:7011;transport=udp 8 0
> 3 sip:127.0.0.1:7012;transport=udp 8 0
> # Group 4
> 4 sip:127.0.0.1:5071;transport=udp 8 0
> 4 sip:127.0.0.1:5072;transport=udp 8 0
>
> I have the following in failure_route (excerpt):
>
>                     $var(dsFoundDestination) = 0;
>
>                         if (t_any_replied())
>                         {
>                             xavp_params_implode("_dsdst_", "$var(dsDestinations)");
>                             xlog("L_INFO", "FAILURE ROUTE: Already have replies on this transaction. Selecting next destination from: [$var(dsDestinations)]");
>                             if (ds_next_dst())
>                             {
>                                 xavp_params_implode("_dsdst_", "$var(dsDestinations)");
>                                 xlog("L_INFO", "FAILURE ROUTE: Next destination selected: [$du] from [$var(dsDestinations)]");
>                                 $var(dsFoundDestination) = 1;
>                             }
>                         }
>                         else if (ds_select_dst("3", "8")) // Dispatcher Group 3
>                         {
>                             xlog("L_INFO", "FAILURE ROUTE: Did not find any replies on this transaction. Selected destination: [$du]");
>                             $var(dsFoundDestination) = 1;
>                         }
>                         if ($var(dsFoundDestination))
>                         {
>                             $var(logString) = "FAILURE ROUTE: Relayed to [" + $du + "]";
>                             if (t_relay())
>                             {
>                                 xlog("L_INFO", "$var(logString)");
>                             }
>                         }
>
> Produces the following logs:
>
> FAILURE ROUTE: Did not find any replies on this transaction. Selected destination: [sip:127.0.0.1:7012;transport=udp]
> FAILURE ROUTE: Relayed to [sip:127.0.0.1:7012;transport=udp]
> FAILURE ROUTE: Already have replies on this transaction. Selecting next destination from: [grp=3;uri=sip:127.0.0.1:7012;transport=udp;]
> FAILURE ROUTE: Next destination selected: [sip:127.0.0.1:7011;transport=udp] from [grp=3;uri=sip:127.0.0.1:7011;transport=udp;]
> FAILURE ROUTE: Relayed to [sip:127.0.0.1:7011;transport=udp]
> FAILURE ROUTE: Already have replies on this transaction. Selecting next destination from: [grp=3;uri=sip:127.0.0.1:7011;transport=udp;]
> FAILURE ROUTE: Next destination selected: [sip:127.0.0.1:7010;transport=udp] from [grp=3;uri=sip:127.0.0.1:7010;transport=udp;]
> FAILURE ROUTE: Relayed to [sip:127.0.0.1:7010;transport=udp]
> FAILURE ROUTE: Already have replies on this transaction. Selecting next destination from: [grp=3;uri=sip:127.0.0.1:7010;transport=udp;]
> FAILURE ROUTE: Next destination selected: [sip:127.0.0.1:5072;transport=udp] from [grp=2;uri=sip:127.0.0.1:5072;transport=udp;]
> FAILURE ROUTE: Relayed to [sip:127.0.0.1:5072;transport=udp]
> FAILURE ROUTE: Already have replies on this transaction. Selecting next destination from: [grp=2;uri=sip:127.0.0.1:5072;transport=udp;]
> FAILURE ROUTE: Next destination selected: [sip:127.0.0.1:5072;transport=udp] from [grp=2;uri=sip:127.0.0.1:5072;transport=udp;]
> FAILURE ROUTE: Relayed to [sip:127.0.0.1:5072;transport=udp]
> FAILURE ROUTE: Already have replies on this transaction. Selecting next destination from: [grp=2;uri=sip:127.0.0.1:5072;transport=udp;]
> FAILURE ROUTE: Next destination selected: [sip:127.0.0.1:5071;transport=udp] from [grp=1;uri=sip:127.0.0.1:5071;transport=udp;]
> FAILURE ROUTE: Relayed to [sip:127.0.0.1:5071;transport=udp]
>
> I want to stop the loop once there are no more active destinations in group 3. Is the solution simply to check that the selected destination is part of the desired group and stop processing if it is not?
>
> Thanks for your time.
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