The SIP RFC allows for multiple SIP headers to have the same name,

For example, it’s very common to have lots of Via headers present in a request.

In Kamailio, we often may wish to add headers, view the contents of headers and perform an action or re-write headers (Disclaimer about not rewriting Vias as that goes beyond the purview of a SIP Proxy but whatever).

Let’s look at a use case where we have multiple instances of the X-NickTest: header, looking something like this:

INVITE sip:[email protected]:5061 SIP/2.0
X-NickTest: ENTRY ONE
X-NickTest: ENTRY TWO
X-NickTest: ENTRY THREE
...

Let’s look at how we’d access this inside Kamailio.

First, we could just use the psedovariable for header – $hdr()

xlog("Value of X-NickTest is: $hdr(X-NickTest)");

But this would just result in the first entry being printed out:

Value of X-NickTest is: ENTRY ONE

If we know how many instances there are of the header, we can access it by it’s id in the array, for example:

xlog("Value of first X-NickTest is: $hdr(X-NickTest)[0]");
xlog("Value of second X-NickTest is: $hdr(X-NickTest)[1]");
xlog("Value of third  X-NickTest is: $hdr(X-NickTest)[2]");

But we may not know how many to expect either, but we can find out using $hdrc(name) to get the number of headers returned.

xlog("X-NickTest has $hdrc(X-NickTest) entries");

You’re probably seeing where I’m going with this, the next logical step is to loop through them, which we can also do something like this:

$var(i) = 0;
while($var(i) < $hdrc(X-NickTest)) {
         xlog(X-NickTest entry [$var(i)] has value $hdrc(X-NickTest)[$var(i)]);
         $var(i) = $var(i) + 1;
}