Wireshark-dev: Re: [Wireshark-dev] Passing further information between dissections
From: Alan Bowman <[email protected]>
Date: Mon, 26 Jul 2010 13:13:44 +0100
Perfect, that's exactly what I was after.  Thanks very much.


On 26 July 2010 09:07, Tarjei Knapstad <[email protected]> wrote:
> On 23 July 2010 13:49, Alan Bowman <[email protected]> wrote:
>> I have written two dissectors for some protocols I am using, one of
>> which is wrapped inside the other.  Protocol B is used if a particular
>> byte (A6, below) in protocol A is a particular value.  I have
>> registered A using register_dissector_table().  I can create a subset
>> tvb and use dissector_try_port() to get protocol B dissector to be
>> called and to have the data (B0..BN) passed to it.  However, B's
>> dissection also depends on knowing whether A was sent as a broadcast
>> packet or as a direct response to a request, which is stored in A's
>> header (A2).  (Not my design!).  Can anyone suggest how I should pass
>> this information to B?  Should I tack it onto the start of the tvb as
>> a composite buffer, or is there some way of attaching metadata to it?
>> Is there a similar protocol I should look at?
>> A0 A1 A2 A3 A4 A5 A6 B0 B1 B2 ... BN
>> Thanks in advance
> Alan,
> I think this is usually achieved by passing the data along in the
> packet_info->private_data field. In your case I guess it would suffice
> to just pass along a boolean. Hopefully someone will correct me if I'm
> wrong here, but I think the standard procedure is along these lines:
>  void* saved_private_data = pinfo->private_data;
>  gboolean isBroadcastPacket = check_if_broadcast_packet(/*...*/);
>  pinfo->private_data = &isBroadcastPacket;
>  dissector_try_port(/*...*/);
>  pinfo->private_data = saved_private_data;
> Regards,
> Tarjei
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