Adding a bit of privacy to Kamailio's pua_dialoginfo module

Kamailio is a great product. With really good customisation possibilities.One of examples will follow here.

Task is the following: we have a setup with 2 different servers, proxy and presence server. Presence server is simple and just processing SUBSCRIBE/PUBLISH messages and generating NOTIFY's. Mainly for BLF's.  But users wants to have some privacy in a question, than not everyone can subscribe to anyone and more interesting - monitor who's calling whom. But some of the users, especially in boss-assistant scenarios want to have full information about calls. Like assistant of the boss usually should know who's calling to boss phone and answer (pickup) in some cases. 

Kamailio allows to achieve this scenario, but with a bit of customisation.

Idea is to have concept of 2 groups. 

Group1 for ACL about possibility of user monitor other user in general, second one - having ACL for seeing call details.

Here I'll point on idea with some code examples for proxy part. And just to mention, pickup functions are implemented not on proxy server, so it's not broken for me here.

Proxy

kamailio.cfg

loadmodule "pua.so"
loadmodule "pua_dialoginfo.so"
...
modparam("pua", "db_url", DBURL)
modparam("pua", "outbound_proxy", "sip:<PRESENCE_SERVER>:5060")
modparam("pua", "db_mode", 0)
...
modparam("pua_dialoginfo", "include_callid", 0)
modparam("pua_dialoginfo", "include_tags", 0)
# we want to have info on who's calling
modparam("pua_dialoginfo", "include_localremote", 1)
... 
# Table to allow subscription one on each other. If users share the same group - they can subscribe one to each other.
# By default all shares the same group = 1. If group == 0, that means nobody can see your state.
# Format is <extension>=><list_of_groups_comma_separated>
modparam("htable", "htable", 'presence_view_grp=>size=15;')
# Table to allow subscribers view each other call details data. By default it's forbidden.
modparam("htable", "htable", 'presence_view_details_grp=>size=15;')
# You can fill these tables via database or whatever else method you prefer

...
route(PRESENCE_PRIVACY);
route(WITHINDLG);
...

route(AUTH)
route(PRESENCE)
...
# Presence server route
route[PRESENCE] {
    if(!is_method("PUBLISH|SUBSCRIBE")) {
        return;
    }
    # Check if user is registered
    if (is_method("SUBSCRIBE") && !(registered("location", "$fu", 4) == 1)) {
        append_to_reply("Retry-After: 10\r\n");
        send_reply("500", "Retry Later");
        exit;
    }

   $du = "sip:<PRESENCE_SERVER>:5060";
   
    # By default - allow anyone subscribe to anyone.
    $var(presence_grp_from) = "1";
    $var(presence_grp_to) = "1";

    if ($sht(presence_view_grp=>$fU) != $null) {
        $var(presence_grp_from) = $sht(presence_view_grp=>$fU);
    }

    if ($sht(presence_view_grp=>$tU) != $null) {
        $var(presence_grp_to) = $sht(presence_view_grp=>$tU);
    }


    if (is_method("SUBSCRIBE")) {
        if ((str)$var(presence_grp_to) == "0") {
            # Presence group "0" means fully private.

            send_reply("404", "Subscriber not exists");
            exit;
        }

        $var(group_1) = $var(presence_grp_to);
        $var(group_2) = $var(presence_grp_from);

        if (!route(CHECK_GROUP_INTERSECTION)) {
            # No common groups for From/To
            send_reply("404", "Subscriber not exists");
            exit;
        }
    }

    route(RELAY);
}

route[PRESENCE_PRIVACY] {
    # We're processing only NOTIFY's with Dialog XML data here
    if (!is_method("NOTIFY") || !has_body("application/dialog-info+xml")) {
        return;
    }

    if ($sht(presence_view_details_grp=>$fU) == $null || $sht(presence_view_details_grp=>$tU) == $null) {
        # By default all call data is private
        route(PRESENCE_CLEAR_CALL_DETAILS);
        return;
    }

    $var(group_1) = $sht(presence_view_details_grp=>$tU);
    $var(group_2) = $sht(presence_view_details_grp=>$fU);

    if (!route(CHECK_GROUP_INTERSECTION)) {
        # No common groups for From/To
        route(PRESENCE_CLEAR_CALL_DETAILS);
        return;
    }

    # At this point all is ok.

}

route[PRESENCE_CLEAR_CALL_DETAILS] {

    # Forming new body of the presence info
    # For replace trick see https://lists.kamailio.org/pipermail/sr-users/2022-February/114185.html
    $xml(body=>doc) = $(rb{s.replace,xmlns=,xyzwq=});
   
    # Forming new XML
    $var(new_body) = "<?xml version=\"1.0\"?>\n";
    $var(new_body) = $var(new_body) + "<dialog-info xmlns=\"" + $xml(body=>xpath:/dialog-info/@xyzwq) + "\"";
    $var(new_body) = $var(new_body) + " version=\"" + $xml(body=>xpath:/dialog-info/@version) + "\"";
    $var(new_body) = $var(new_body) + " state=\"" + $xml(body=>xpath:/dialog-info/@state) + "\"";
    $var(new_body) = $var(new_body) + " entity=\"" + $xml(body=>xpath:/dialog-info/@entity) + "\">\n";
    $var(new_body) = $var(new_body) + "  <dialog id=\"" + $xml(body=>xpath:/dialog-info/dialog/@id) + "\"\n";
    $var(new_body) = $var(new_body) + " direction=\"" + $xml(body=>xpath:/dialog-info/dialog/@direction) + "\">\n";
    $var(new_body) = $var(new_body) + "    <state>" + $xml(body=>xpath:/dialog-info/dialog/state/text()) + "</state>\n";
    $var(new_body) = $var(new_body) + "  </dialog>\n</dialog-info>";

    replace_body_atonce("^.+$", $var(new_body));
}

route[CHECK_GROUP_INTERSECTION] {
# Checks if contents of $var(group_1) and $var(group_2) that are comma-separated list of groups have at least one in common
    $var(group_1_param_count) = $(var(group_1){s.count,,});

    while ($var(group_1_param_count) >= 0) {
        $var(group_1_param) = $(var(group_1){s.select,$var(group_1_param_count),,});

        if (in_list("$var(group_1_param)", "$var(group_2)", ",")) {
            return 1;
        }
        $var(group_1_param_count) = $var(group_1_param_count) - 1;
    }
    return -1;
}

Idea here is we're stripping local/remote data from NOTIFY XML that indicates a dialog. In this case we're indicating fact of the call, but not exposing any sensitive data.