Different reassembly needs

[Paul Williamson <paul () mustbeart com>]

I want to add fragmentation reassembly to the dissector I'm improving for
DVB-S2-BB. To get things exactly right, I'll need to reassemble in a way
that doesn't seem to be supported by the existing code in
epan/reassemble.[ch]. What approach is considered most preferable?

1. Modify epan/reassemble.[ch] to do what I need, or

2. Write my own reassembly code that just works for me, or

3. Write adapter code that tries hard to use epan/reassemble.[ch] where
possible but adapts it to my needs, or

4. Just use epan/reassemble.[ch] and don't worry about getting reassembly
exactly right according to the protocol spec.

If you're interested in the details, here are some. The protocol I'm
dissecting is an encapsulation protocol running encapsulated in UDP.
Fragments are tagged as first, last, or in between, and arrive in order
without a sequence number, so the existing function fragment_add_seq_next()
is close to what I need. I also need to check whether a first fragment has
already been received before adding a last or in-between fragment, and I
think I can do that with fragment_get().

However, I also need to age out old fragments. There isn't currently a
function like fragment_add_seq_next_aging() in the code, but perhaps it
would be easy enough to add. Unfortunately, the existing aging mechanism in
epan/reassemble.[ch] is based on pinfo->num, and to comply with the spec I
need it to be based on a count of frames of my specific protocol.This is
where I think I'd need to modify epan/reassemble.[ch].

I'd appreciate any thoughts on how I should proceed.

  -Paul

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