Wireshark-dev: Re: [Wireshark-dev] Passing further information between dissections
Perfect, that's exactly what I was after. Thanks very much.
Alan
On 26 July 2010 09:07, Tarjei Knapstad <tarjei.knapstad@xxxxxxxxx> wrote:
> On 23 July 2010 13:49, Alan Bowman <alan.michael.bowman@xxxxxxxxx> 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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