[sr-dev] Forcing TCP connection reuse doesn't use the failure_route when the connection has gone.

[Waite, Hugh]

I have an edge-proxy which accepts TCP connections from clients. When I know that the clients are behind NATs (for example), I use the set_forward_no_connect() function to force connection reuse and avoid timeouts. In the case where the connection has already gone, the system sends a "477 Unfortunately error on sending to next hop occurred (477/TM)" response back to the registrar.
These connections are using outbound, so I would like to convert this into a "430 Flow Failed" response to the registrar, but the 477 response doesn't seem to trigger the onreply_route or failure_route.
Is there a way of trapping and handling this failure? If not, do we need more flexibility in handling this particular tcp_send error (or other similar ones)? Other systems may wish to try additional destinations from the failure route.
Snippets of my cfg and logs are below. The con_reuse flag is checked in tcp_send at tcp_main.c:1846

Regards,
Hugh

route[RELAY] {
xlog("L_INFO", "$rm: route[RELAY]\n");
                loose_route();
                $var(lr_ret) = $rc;
                if ($var(lr_ret) == 2) {
                        xlog("L_INFO", "$rm:  loose route with outbound\n");
                        t_on_failure("FAIL_OUTBOUND");
                        set_forward_no_connect();
                        if (t_relay() < 0) {
                                xlog("L_WARN", "$rm:  loose route with outbound failed\n");
                                sl_send_reply("500", "Something bad happened");
                        }
                        exit;
                }
                . . .
}

May  1 17:01:08 kamailio-cep[28226]: INFO: <script>: INVITE: Routing logic starts here
May  1 17:01:08 kamailio-cep[28226]: INFO: <script>: INVITE: route[REQINIT]
May  1 17:01:08 kamailio-cep[28226]: INFO: <script>: INVITE: route[INITIAL_REQUEST]
May  1 17:01:08 kamailio-cep[28226]: INFO: <script>: INVITE: route[RECORD_ROUTE]
May  1 17:01:08 kamailio-cep[28226]: INFO: <script>: INVITE: route[RELAY]
May  1 17:01:08 kamailio-cep[28226]: INFO: <script>: INVITE:  loose route with outbound
May  1 17:01:08 kamailio-cep[28226]: ERROR: tm [../../forward.h:219]: msg_send(): msg_send: ERROR: tcp_send failed
May  1 17:01:08 kamailio-cep[28226]: ERROR: tm [t_fwd.c:1609]: t_send_branch(): ERROR: t_send_branch: sending request on branch 0 failed
May  1 17:01:08 kamailio-cep[28226]: INFO: <script>: ACK: Routing logic starts here
May  1 17:01:08 kamailio-cep[28226]: INFO: <script>: ACK: route[REQINIT]

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