Wireshark-dev: Re: [Wireshark-dev] Tshark: proto_tree not created on first pass with tap define
From: Paul Offord <[email protected]>
Date: Mon, 13 Feb 2017 07:40:16 +0000
I'll accept whatever strategy there is for taps vs. dissectors.  A few points:

* TRANSUM can only work if it is able to calculate values based on other dissected values (such as smb2.msg_id), so provided the dissected values are available to the tap on both passes (via a protocol tree or otherwise) that would be OK
* I've never written a tap before but I think if the tap runs after all other dissectors this wouldn't be a problem for TRANSUM
* When a dissector registers a tap, Wireshark passes a protocol tree to a dissector based on the criteria Michael defined, so some thought would be needed regarding this for consistency (unless Tshark shouldn't work like Wireshark)
* The LUA framework passes the protocol tree to a LUA dissectors when used with Wireshark or Tshark - again a consistency issue

Best regards...Paul

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Guy Harris
Sent: 13 February 2017 03:55
To: Developer support list for Wireshark <[email protected]>
Subject: Re: [Wireshark-dev] Tshark: proto_tree not created on first pass with tap defined

The underlying problem here appears to be that the TRANSUM post-dissector is not only adding stuff to the protocol tree, which obviously doesn't need to be done if there is no protocol tree, but is also doing *analysis* of the packet information.

The latter of those should *not* be done in a dissector - it should be done in a tap.

Unfortunately, *currently*, taps are run after all dissectors, including post-dissectors, are run, which might not work for this purpose.  If so, what we probably would need here is to have a mechanism to allow taps to be run "early".  For now, we could define "early" as "before the post-dissectors are run".
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