Ethereal-dev: Re: [Ethereal-dev] LEGO: How acces to a previous pdu data

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From: Ulf Lamping <ulf.lamping@xxxxxx>
Date: Thu, 26 Jan 2006 22:39:15 +0100
Jose M. Pardo wrote:


Hello list,
I’m new developing on Ethereal and I have a couple of questions that I hope that someone can answer. 

I have to dissect a PDU_B according some data stored in a previous PDU_A.

How can I access to this data?
One step beyond….if I apply a filter and the PDU_A is hidden. Can I fetch those data or are they unavailable? 

There’s in the source code a protocol dissector that works in this way?
AFAIK, you can't directly access data from any previous packet that is mostly because at least tethereal uses a single pass approach.
However, what you can do is keeping the relevant data in a conversation which is spanning multiple packets.
How to do this is beyond my knowledge, you may have a look at the places mentioned in: http://wiki.ethereal.com/Development 

Regards, ULFL