Intercepting outgoing traffic

The plugin also needs to be able to intercept all outgoing traffic to add signature messages. To be able to do this, a new set of function pointers was added to olsrd. They are called packet transformation functions. A plugin can register its own packet transform functions with olsrd, and these functions are applied to every OLSR packet right before sending it. The function to add such a function pointer is declared in src/net.h as:

int
add_ptf(int (*)(char *, int *));

The plugin registers a function that calculates and adds a signature to the end of all outgoing OLSR packets. To be sure the packet will have room for the signature message (especially when stacking messages) the max message size in olsrd is set to maxmsgsize - sizeof(signaturemsg).