Inconsistent availability of proto_tree values during the first of two passes

[Paul Offord <Paul.Offord () advance7 com>]

I'd like to resurrect this.  Here's a quick summary:



  *   The TRANSUM post-dissector requires access to some decoded values during the first pass across the trace file
  *   Defining values (e.g. smb2.cmd) in a “fake tap” causes the values to be available in the following scenarios:
     *   Wireshark with a C plugin
     *   Wireshark with a LUA plugin
     *   Tshark with a LUA plugin
  *   Tshark with a C plugin doesn’t work i.e. the fake tap values are not available during the first pass
  *   The cause is identified and just due to an inconsistency in code – see 
https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=13393
  *   Guy suggested that I rewrite TRANSUM as a tap but that suffers from the same inconsistency problem



As making the code consistent has been rejected and the tap idea won’t work, where do we go from here?



Thanks and regards…Paul



-----Original Message-----
From: Guy Harris (Code Review) [mailto:code-review-do-not-reply () wireshark org]
Sent: 13 February 2017 04:03
To: Michael Mann <mmann78 () netscape net>
Cc: Petri Dish Buildbot <buildbot-no-reply () wireshark org>; Paul Offord <Paul.Offord () advance7 com>
Subject: Change in wireshark[master]: tshark: Always have the same conditions to determine if tree...



Guy Harris has posted comments on this change.



Change subject: tshark: Always have the same conditions to determine if tree should be created 
......................................................................





Patch Set 2: Code-Review-2



OK, the problem here is that the TRANSUM "dissector" is doing both tap-like things (reading the protocol tree and 
processing data) and post-dissector-like things (adding stuff to the protocol tree based on the results of that 
processing).



Given that taps are run *after* post-dissectors, this means that it has to "cheat" and do the tap-like things in the 
post-dissector, but post-dissectors are, like other dissectors, handed a protocol tree only if there's a need to 
generate one.



For this, we need a way to do the "read the protocol tree and process it" stuff *before* the post-dissector is run, 
i.e. a way to register taps to be run *before* the post-dissectors.



(In the longer term, we probably need to re-think both taps and post-dissectors in a number of ways, and make whatever 
changes are necessary to get done what the taps and post-dissectors are currently doing in ways that don't involve 
abusing those mechanisms to get things done.



I'm a little suspicious, for example, of the Parallel Redundancy Protocol trailer post-dissector - it's a protocol 
that's actually processing part of the packet data; see the "This is horribly broken" comment I added to it a while ago.



We might also want a way to have taps/"post-"dissectors that act as extensions to particular protocol dissectors - that 
might be what TRANSUM, and possibly MATE, *really* want to be.)



--

To view, visit https://code.wireshark.org/review/20078

To unsubscribe, visit https://code.wireshark.org/review/settings



Gerrit-MessageType: comment

Gerrit-Change-Id: I69bb395b55b73f26665d90f341c92a978e50aa70

Gerrit-PatchSet: 2

Gerrit-Project: wireshark

Gerrit-Branch: master

Gerrit-Owner: Michael Mann <mmann78 () netscape net<mailto:mmann78 () netscape net>>

Gerrit-Reviewer: Guy Harris <guy () alum mit edu<mailto:guy () alum mit edu>>

Gerrit-Reviewer: Michael Mann <mmann78 () netscape net<mailto:mmann78 () netscape net>>

Gerrit-Reviewer: Paul Offord <paul.offord () advance7 com<mailto:paul.offord () advance7 com>>

Gerrit-Reviewer: Petri Dish Buildbot <buildbot-no-reply () wireshark org<mailto:buildbot-no-reply () wireshark org>>

Gerrit-HasComments: No

______________________________________________________________________

This message contains confidential information and is intended only for the individual named. If you are not the named 
addressee you should not disseminate, distribute or copy this e-mail. Please notify the sender immediately by e-mail if 
you have received this e-mail by mistake and delete this e-mail from your system.

Any views or opinions expressed are solely those of the author and do not necessarily represent those of Advance Seven 
Ltd. E-mail transmission cannot be guaranteed to be secure or error-free as information could be intercepted, 
corrupted, lost, destroyed, arrive late or incomplete, or contain viruses. The sender therefore does not accept 
liability for any errors or omissions in the contents of this message, which arise as a result of e-mail transmission.

Advance Seven Ltd. Registered in England & Wales numbered 2373877 at Endeavour House, Coopers End Lane, Stansted, Essex 
CM24 1SJ

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please visit http://www.symanteccloud.com
______________________________________________________________________

___________________________________________________________________________
Sent via:    Wireshark-dev mailing list <wireshark-dev () wireshark org>
Archives:    https://www.wireshark.org/lists/wireshark-dev
Unsubscribe: https://www.wireshark.org/mailman/options/wireshark-dev
             mailto:wireshark-dev-request () wireshark org?subject=unsubscribe