$Revision: 1.1 $
$Date: 2004/11/15 13:53:55 $
Developer's Guide
According to the specification new Diversion header field should be inserted as the topmost
Diversion header field in the message, that means before any other existing Diversion header
field in the message. In addition to that, add_diversion function can be called several times and each time
it should insert the new Diversion header field as the topmost one.
In order to implement this, add_diversion function creates the anchor in data_lump lists as
a static variable to ensure that the next call of the function will use the same anchor and
would insert new Diversion headers before the one created in the previous execution. To my
knowledge this is the only way of inserting the diversion header field before any other
created in previous runs of the function.
The anchor kept this way is only valid for a single message and we have to invalidate it
when another message is being processed. For this reason, the function also stores the id of
the message in another static variable and compares the value of that variable with the id
of the SIP message being processed. If they differ then the anchor will be invalidated and
the function creates a new one.
The following code snippet shows the code that invalidates the anchor, new anchor will be
created when the anchor variable is set to 0.
static inline int add_diversion_helper(struct sip_msg* msg, str* s)
{
static struct lump* anchor = 0;
static int msg_id = 0;
if (msg_id != msg->id) {
msg_id = msg->id;
anchor = 0;
}
...
}