New subject: Redirects - are q values required to implement serial forking?

12 Nov 2018

We have a situation where we get a redirect from a carrier with a list of carriers to send
the transaction to in the contact header. None of the carriers in the contact header have
q values assigned. 

We have implemented our redirect handling logic using the UAC_REDIRECT module
(get_redirects()) with help from TM module (t-load_contacts(), t_next_contact()).
(failure_route code is at bottom of this note)

We find that when we receive a contact header with q values, we can launch requests
serially using t_next_contact() and individually work through the contact list until we
get a positive response. When we get a redirect with no q values in the contact header we
find that all contacts get loaded and launched in parallel.

Although not stated in the documentation, it appears that in order to implement serial
contact redirect handling, q values must be present in the contact header. Based on this
assumption, and knowing that the redirecting carrier cannot include q values, we have
attempted to modify the contact header and find that we are unable to add q values to the
contact header.

We have attempted without success to use remove_hf("Contact”) followed by
append_hf("Contact: $(avp(contact)) \r\n”); where $(avp(contact)) is the avp where we
have rewritten the contact header to include q values.

Any guidance on how to handle this issue is appreciated.

_________________________________________________________-

Our failure route code:
        if (t_check_status("3[0-9][0-9]")) {
                xlog("L_INFO", "----> REDIRECT Contact Header -->
$T_rpl($ct) --- Method $rm --- From $T_req($fu) --- To $T_req($tu) --- Destination
$T_req($du) \n");
                get_redirects("*:*");

                if (!t_load_contacts()) {
                        xlog("L_INFO", "-t_load_contacts() FAILED
/n");
                };

                        xlog("L_INFO", "####->LOAD CONTACT LIST
$xavp(tm_contacts[0]=>uri) \n");

                if (t_next_contacts()) {
                        xlog("L_INFO", "-t_next_contact() loaded
successfully /n");
                        xlog("L_INFO", "####-> NEXT CONTACT LIST
$xavp(tm_contacts[0]=>uri) \n");
                };
                t_on_failure("serial");

                if(t_relay()){
                    xlog("L_INFO","----->Relayed in MANAGE_FAILURE ---
Method $rm --- Contact Header $ct \n");
                 };
                exit;
        } else {
                xlog("L_INFO","-----> NO REDIRECT --- Method $rm ---
Contact Header $ct \n");
                exit;
        }

failure_route["serial"] {
        xlog ("L_INFO", "Entered failure_route(serial) /n");
        if (t_check_status("3[0-9][0-9]")) {
                xlog("L_INFO", "----> DOUBLE REDIRECT Contact Header
--> $T_rpl($ct) --- Method $rm --- From $T_req($fu) --- To $T_req($tu) --- Destination
$T_req($du) \n");
                $xavp(tm_contacts[*]) = $null;
                xlog("L_INFO", "XXX-> tm_contacts reset to Null
$xavp(tm_contacts[0]=>uri)\n");

                get_redirects("*:*");

                if (!t_load_contacts()) {
                        xlog("L_INFO", "-t_load_contacts() FAILED
/n");
                };

                        xlog("L_INFO", "####-> LOAD 2 CONTACT LIST
$xavp(tm_contacts[0]=>uri) \n");

        }
        if (!t_next_contacts()) {
                exit;
        }

        xlog("L_INFO", "-t_next_contact() loaded successfully /n");
        xlog("L_INFO", "####-> NEXT CONTACT LIST
$xavp(tm_contacts[0]=>uri) \n");

        t_on_failure("serial");
        if(t_relay()){
            xlog("L_INFO","----->Relayed in failure_route(serial) ---
Method $rm --- Contact Header $ct \n");
        };
}

Best Regards,

 Mike Montgomery
 Principal, Trusted Technical Services, Inc.
 o - 919 924 4703  x3000
 m - 919 539 6133