Passing further information between dissections

[Alan Bowman <alan.michael.bowman () gmail com>]

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 Bowman
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