Tarjei Knapstad skrev 2010-07-26 10:07:
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
A different solution would be to register two dissector handles for B
one for the broadcast version and one for the
response version and let A call B trough the appropriate dissector handle.
Regards
Anders
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