Hi. Regarding packet re-assembly

[Ari Yoskovitz <ariyosko () gmail com>]

Hi!

I am new to Wireshark dissector development, and encountered the following
problem:

I am sending packtes, and the packets are fragmented.
At first, I wasn't aware of the API's internal packet re-assembly
capabilities, so I tried to use a global buffer to accumulate the packets'
payloads. At the last packet, I dissected the buffer (now containing an
Ethernet packet) and added the result to the tree.

I did this just to find out the Wireshark not only calls the dissector when
first encountering a packet, but also when I click it later... I didn't know
that...
This is a problem since using an accumulating buffer relies on the packets
being dissected in order. However, if I now click the in an un-ordered
manner, the buffer accumulates stuff wrongly. Moreover, If I don't click ALL
packets involved in a transaction, I only get part of the data.

So, I discovered the fragment_add_seq()
<http://src.opensolaris.org/source/s?defs=fragment_add_seq_key&project=/sfw>function
and all that around it, but I still have the same problem:
My packets have *No seq number or frag number* !!
Hence, I cannot use such numbers as hash-table keys. I can only rely on
transactions and fragments coming in ordered, but that's it.
Now, I want the fragments being added to the hash only when Wireshark first
encounters a packet, but not again when I click it later. Using a simple
global counter to produce keys will cause the same problem as before: When I
later come back to observe packets a click them, they will be re-dissected,
and now that the counter has a different value than before (it has
advanced...), there will be no connection between a packet and the key
produced for it in the first encounter.

I can think of all kinds of nasty tricks to solve this, but somehow I am
sure there is an Wireshark provides an elegant way to achieve this.

Thanks!
-- 
Use the source, Luke!

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