Wireshark-dev: Re: [Wireshark-dev] Extracting field values in a C post-dissector
From: Paul Offord <[email protected]>
Date: Mon, 5 Sep 2016 09:05:50 +0000
Hi Guy,

I think you are right.  When I thought about it I realised that dissected field values don't get stored anywhere in a standard way and retrieving them from the tree is the only way to go.  Luckily I only need a few values.

If proto_find_finfo() is slow I might try writing something to traverse the tree.  I notice that proto_find_finfo() does memory allocations and I can probably avoid this by retrieving the data directly into my own variable.

Best regards...Paul

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Guy Harris
Sent: 05 September 2016 03:59
To: Developer support list for Wireshark <[email protected]>
Subject: Re: [Wireshark-dev] Extracting field values in a C post-dissector

On Aug 22, 2016, at 6:40 AM, Pascal Quantin <[email protected]> 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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