Re: Retrieving dissection result from another dissector

[Guy Harris <guy () alum mit edu>]

On Jul 4, 2018, at 7:02 AM, Michael Mann via Wireshark-dev <wireshark-dev () wireshark org> wrote:

> Just because you can exchange data between dissectors this way, doesn't mean you should.  I think it's more 
> understandable if there are multiple layers/protocols between the setting of data and it's retrieval, but if you are 
> only going a single layer, the data parameter of call_dissector_with_data should be used and a "shared structure" 
> should be defined that includes the input/output parameters.

Unfortunately, that style means that there's no type checking to make sure the calling dissector passes data of the 
correct sort to the called dissector; if the calling dissector passes it by attaching something with a given protocol 
ID and the called dissector fetches it by getting something with some protocol ID, if the protocol IDs don't match the 
fetch will fail and you'll probably at least get a null-pointer dereference crash - compile-time checks would be better 
than run-time checks, but run-time checks are better than surprises because a structure of type A is being interpreted 
as if it were a structure of type B.
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