Wireshark · Wireshark-dev: Re: [Wireshark-dev] Extracting field values in a C post-dissector

[Paul Offord <Paul.Offord@xxxxxxxxxxxx>]

I’ve made some progress.  I traced MATE and looked at how it registers its post-dissector.  I now get a tree on the 1^st scan.  I’ll write up some notes on C post-dissectors when I get something that works.

 

Best regards…Paul

 

From: wireshark-dev-bounces@xxxxxxxxxxxxx [mailto:wireshark-dev-bounces@xxxxxxxxxxxxx] On Behalf Of Paul Offord
Sent: 05 September 2016 23:12
To: Developer support list for Wireshark <wireshark-dev@xxxxxxxxxxxxx>
Subject: Re: [Wireshark-dev] Extracting field values in a C post-dissector

 

I've hit a problem.  WS scans the trace file twice.  I need access to protocol fields (e.g. tcp.len and smb2.ses_id) during the first scan.

 

Unfortunately with the C postdissector the tree value passed during the first scan is NULL.  During the second scan I do get the tree.

 

I guess the LUA code uses the proto_tree_prime_hfid() outlined below.

 

Any suggestions how I move forward gratefully accepted.

 

Sent from Samsung Mobile on O2

 

-------- Original message --------

From: Guy Harris

Date:05/09/2016 03:59 (GMT+00:00)

To: Developer support list for Wireshark

Subject: Re: [Wireshark-dev] Extracting field values in a C post-dissector

 

On Aug 22, 2016, at 6:40 AM, Pascal Quantin <pascal.quantin@xxxxxxxxx> wrote:

> By having a quick look at the code, I *think* you will want first to retrieve the hfindex of a given field by using proto_registrar_get_id_byname(), then mark it as "interesting" with proto_tree_prime_hfid()

...which you have to do before the dissection starts.

Unfortunately, you can't do that in a post-dissector.

So...

> aOr a cll to proto_find_finfo() should work also without the need to prime the field, but should be slower according to the comments in proto.h.

...you might have to do it that way, instead.
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