Discussion:
[SR-Users] textopsx issue when modifying same header several times
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Andrew Pogrebennyk
2014-10-16 10:14:10 UTC
Permalink
Hi,
we are filtering some method names from the Allow header with kamailio
4.1: depending in the configuration:
if (hf_value_exists("Allow", "INFO"))
{
xlog("L_INFO", "Remove INFO from Allow\n");
exclude_hf_value("Allow", "INFO");
}
if (hf_value_exists("Allow", "REFER")) {
xlog("L_INFO", "Remove REFER from Allow\n");
exclude_hf_value("Allow", "REFER");
}

There is a problem in case multiple rewrites are done on the same header
so the resulting message is going to be broken:

Input:
Allow: INVITE, BYE, REGISTER, ACK, OPTIONS, CANCEL, SUBSCRIBE, NOTIFY,
PRACK, INFO, REFER

OUTPUT:
Allow: INVITE, BYE, REGISTER, ACK, OPTIONS, CANCEL, SUBSCRIBE, NOTIFY,
PRACK,

The trailing comma is not allowed. So we have to use
msg_apply_changes(). But kamailio is quite restrictive on where you can
call msg_apply_changes():
1. it must be done before record_route()* and
2. it is not allowed in the branch route. As for me it's valid use case
when you need to do some header manipulations only for some of the
branches, isn't?

*(1) is further aggravated by the fact that the record_route() for
loose-routed requests is usually called quite early in the processing
pipeline. Imagine kamailio.cfg would look like:

request_route {

# per request initial checks
route(REQINIT);

# NAT detection
route(NATDETECT);

# CANCEL processing
if (is_method("CANCEL"))
{
if (t_check_trans()) {
route(RELAY);
}
exit;
}

# ---> filter Allow
route(FILTER_ALLOW_METHODS);

# handle requests within SIP dialogs
route(WITHINDLG);

I don't like the idea of changing the message before loose-routing.

Taking (1) and (2) into account, would it be possible to

a) fix exclude_hf_value to allow to filter multiple values in a single
pass and
b) allow msg_apply_changes() in branch route without any ill effects on
the record-route headers?

Please share your ideas.

Thanks,
Andrew

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