How to Throw Malformed Packet Exception

Question

Hello,

I'm writing a dissector right now, and I want it to verify that incoming packets are the right length. Is there a way I can throw a malformed packet exception once I find out that the packet isn't the right size? I already have code that checks if the size is correct, I just don't know how to throw the exception, and Google has only brought me to people with questions about why their packets are being marked as malformed.

I was looking at the THROW() function but there was nothing for malformed packet exceptions. Any advice?

Accepted Answer

If you encounter a situation which cannot be handled by the dissector, you could use the DISSECTOR_ASSERT family of macros which are defined in epan/proto.h:

DISSECTOR_ASSERT(size >= 4);

Most of the time however you want to dissect as much as possible and let the proto_tree_* functions (such as proto_tree_add_item) throw exceptions if the bounds are violated. This reduces clutter in your code.

If you can fully dissect a packet, but would like to notify the user of protocol violations, then it is recommended to use Expert Info. See https://wiki.wireshark.org/Development/ExpertInfo for more information and the doc/packet-PROTOABBREV.c file for an example.