[sr-dev] alias_contact()/handle_alias() ready for testing

[Juha Heinanen]

"final" versions of alias functions are now ready for testing in in this
sr_3.0 based nathelper.c:

http://box.tutpro.com/tmp/nathelper.c

i changed the names to more descriptive ones: add_contact_alias() and
handle_ruri_alias().  also helper function rr_count(pvar) is included
that assigns into the pvar the number of rr headers in incoming message
(request or reply).

usage example is below.  i believe (until otherwise shown) that it
works correctly.

if you are interested, please try with different UAs and different
transports with or without nat.

-- juha

add_contact_alias()/handle_ruri_alias() usage example
-----------------------------------------------------

supports re-use of tcp sessions between proxy and UAs.  supports routing
of requests to UAs behind NATs so that r-uri is always what UAs expect.
proxying of media is not shown, but can be easily added.

NON_REGISTER_INITIAL_REQUESTS
-----------------------------

- call alias_contact() for all non-register initial requests, which
  don't come from another proxy (which takes care of its own UAs).

- if you know that non-register initial request is going to another
  proxy, set TO_PROXY flag before relaying the request.

- in cases, where initial request may go to another proxy, but you are
  not sure about it, store the number of record-route headers in
  incoming request in an AVP that you can then later test in onreply
  route and find out, if next hop was a proxy.

route [NON_REGISTER_INITIAL_REQUESTS] {

    if (!is_present_hf("Record-Route")) {
        route(ADD_CONTACT_ALIAS);
    };
    ...
    if (I_KNOW_FOR_SURE_THAT_NEXT_HOP_IS_ANOTHER_PROXY) {
        setbflag("TO_PROXY");
    };

    if (NEXT_HOP_MAY_BE_ANOTHER_PROXY_BUT_I_DONT_KNOW_FOR_SURE) {
        if (!rr_count($avp("rr_count"))) {
            send_reply("400", "Bad request");
            exit;
	};
    };
    t_on_reply("REPLY");
    if (!t_relay()) ...

route [ADD_CONTACT_ALIAS] {
    if (!add_contact_alias()) {
        xlog("L_ERR", "Error in aliasing contact <$ct>\n");
        send_reply("400", "Bad request");
        exit;
    };
}

REGISTER_REQUESTS
-----------------

- call fix_nated_register() on register requests, if registering ua is
  behind nat OR is using tcp.

route [REGISTER_REQUESTS] {
    ...
    if (isflagset(FROM_NATED) || (proto == TCP)) {
        fix_nated_register();
	if (isflagset(FROM_NATED)) {
	    setbflag("TO_NATED");
	};
    };
    save("location");
    ...

IN_DIALOG_REQUESTS
------------------

- call handle_ruri_alias() for all in-dialog requests before
  t_relaying them, provided that loose_route() didn't set $du, which it
  does if next hop is another proxy.  in the latter case set TO_PROXY
  fag.

route [IN_DIALOG_REQUESTS] {

    loose_route();
    ...
    if ($du == "") {
        handle_ruri_alias();
        switch ($rc) {
        case -1:
            xlog("L_ERR", "Failed to handle alias of R-URI <$ru>\n");
            send_reply("400", "Bad request");
            exit;
        case 1:
            xlog("L_INFO", "Routing in-dialog $rm from <$fu> to <$du>\n");
            break;
        case 2:
            xlog("L_INFO", "Routing in-dialog $rm from <$fu> to <$ru>\n");
            break;
         };
    } else {
        setbflag("TO_PROXY");
    }
    t_on_reply("REPLY");
    if (!t_relay()) {
        ...

REPLIES
-------

- call add_contact_alias() on all replies except the ones that come from
  another proxy.

onreply_route [REPLY] {

    if (!isbflagset("TO_PROXY") {
        if (is_avp_set("rr_count")) {
	    if (!rr_count("$(var(rr_count)"))) {
 	        xlog("L_NOTICE", "Bad R-R header in reply\n");
	        send_reply("400", "Bad reply");
                exit;
	    };
	    if ($var(rr_count) == $avp(rr_count) + 1) {
	        route(ADD_CONTACT_ALIAS);
            };
        } else {
	    route(ADD_CONTACT_ALIAS);
	}
    }
    ...

NOTE
----

- do NOT call fix_nated_contact() on anything, because
  add_contact_alias() replaces it.