Wireshark-dev: [Wireshark-dev] Refactoring use of a global variable in epan/packet.c?
Hello,
About a year and a half ago (Nov 2010), I mailed wireshark-{users,dev}
about Sharktools, a library we created that provides the ability to
access Wireshark's packet dissection features from within Python and
Matlab. The respective tools are called "pyshark" in Python and
"matshark" in Matlab. The post is here:
https://www.wireshark.org/lists/wireshark-users/201011/msg00028.html
The code is here:
http://github.com/armenb/sharktools
Since then, I've done some work trying to make the implementation more
efficient and usable on gigantic packet capture files. Lately, I have
been adding Python iterator support for pyshark, and am running into an
issue with global variables in libwireshark. Specifically, I'd like to
be able to support multiple independent packet capture parsing
operations simultaneously. This feature is important in network
analytics. For the most part, this functionality works fine (i.e.
managing multiple cfile objects simultaneously just seems to work
out-of-the-box).
However, I see an issue when it comes to applying a "decode as" string.
Since dissector_tables is global (defined in epan/packet.c), and using
dissector_change*() and dissector_reset*() modifies this data structure,
I can't guarantee that my simultaneous packet parsing operations are
independent. Actually, I ran a test, and they are not.
Question is this: if I patch epan/packet.c and all functions
dissector_tables-related to pass around a pointer instead of using a
global variable, does my patch have a snowball's chance of being
accepted into Wireshark mainline? Of course, the simplest thing for me
to do right now is detect a decode-as string mismatch between my Python
iterator objects and throw a Python exception, but I'd rather go for
clean functionality if I don't have to worry about maintainability of my
own Wireshark source tree (this is definitely not the direction I want
to go in, anyway).
I'd be interested in hearing your thoughts. Thanks!
Armen
--
Armen Babikyan
Wideband Tactical Networking Group
MIT Lincoln Laboratory
armenb@xxxxxxxxxx . 781-981-1796
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