Re: dissecting TCP packets with multiple PDUs

[Michael Mann <mmann78 () netscape net>]

This may be related/similar to bug 6392 (https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=6392).
 
I believe the capture in this bug has only a few "leftover" bytes (and I thought the issue may be related to amount of 
fixed data needed by dissector).  However 38 bytes seems much larger than a typical amount of fixed bytes.  So the 
issue really may be the TCP dissector and not your protocol/dissector.
 
 
-----Original Message-----
From: Graham Bloice <graham.bloice () trihedral com>
To: Developer support list for Wireshark <wireshark-dev () wireshark org>
Sent: Fri, Aug 5, 2016 9:48 am
Subject: Re: [Wireshark-dev] dissecting TCP packets with multiple PDUs







On 5 August 2016 at 14:08, John Dill <John.Dill () greenfieldeng com> wrote:


I have a TCP protocol that sends multiple PDUs.  So far, my dissector seems to handle the cases where one PDU is split 
across multiple frames, and when multiple PDUs are dissected in one frame.  Unfortunately, I'm having issues where the 
TCP dissection stops if I have multiple PDUs that are split inside a frame, e.g.
 
packet 37104 TCP segment (536)
packet 37167 TCP segment (498) - creates reassembled TCP size of (1034) which is correct
 
However, packet 37167 has the start of another PDU containing 38 bytes.  I can't seem to get the dissector to recognize 
the start of it.
 
​I printed out the captured length, but it always seems to be 1034.  I'm not sure how to recognize that the current 
frame has leftover bytes to start a new dissection.
 
Is there an example plugin that someone can suggest that I can investigate to see how this scenario is handled?
 
Thanks,
John D.
 


Is your dissector returning the number of bytes it dissected?


-- 


Graham Bloice



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