Re: Unable to detect custom protocol dissector

["Maynard, Chris via Wireshark-dev" <wireshark-dev () wireshark org>]

I’m not sure what you’re trying to do, but there’s already a Wireshark built-in dissector for GeoNetworking[1].

If you’re trying to replace it for some reason, then you may either need to disable that one or remove it completely.  
And if you’re trying to implement in Lua, then you’ll need to register it as a heuristic dissector using 
register_heuristic[2].  However, it seems that there might be a bug with respect to this function[3], as the following 
simple Lua script seems to indicate:

local p_gnw = Proto("gnwHdr", "GeoNetworkingHdr")

function p_gnw.dissector(tvbuf, pinfo, tree)

    local ethertype = tvbuf(12, 2):uint()
    if ethertype == 35143 then
        pinfo.cols.protocol:set("GNW")
        return true
    else
        return false
    end
end

p_gnw.register_heuristic("eth", p_gnw.dissector)


When Wireshark is started with this gnw.lua script loaded, the following error message is encountered:

Lua: Error during loading:
path\to\gnw.lua:14:bad
argument #1 to ‘register_heuristic’ (userdata expected, got string)
stack traceback:
         [C]: in function ‘register_heuristic’
         path\to\gnw.lua:14:
in main chunk

- Chris
[1]: 
https://code.wireshark.org/review/gitweb?p=wireshark.git;a=blob;f=epan/dissectors/packet-geonw.c;h=21290a3b179c8974483a2f762cbe512fbec67103;hb=HEAD
[2]: https://www.wireshark.org/docs/wsdg_html_chunked/lua_module_Proto.html (Section 11.6.5.3)
[3]: https://osqa-ask.wireshark.org/questions/54158/register-heuristic-function-for-multiple-heuristic-list-names-in-lua


From: Wireshark-dev <wireshark-dev-bounces () wireshark org> On Behalf Of sandip gangakhedkar
Sent: Wednesday, February 12, 2020 4:46 PM
To: wireshark-dev () wireshark org
Subject: [Wireshark-dev] Unable to detect custom protocol dissector

Hi,

I am using a Custom protocol dissector (Lua script) for the GeoNetworking header. I have build wireshark 3.2.1 from 
source on Ubuntu 18.04 and placed the Lua script in the Global plugins directory. However, the script fails when to 
find the Geonetworking protocol when I invoke it in the script:

  Dissector.get("gnw"):call(newTvb, pkt, root)

So I tried another approach:

  gnw_dissector = DissectorTable.get("ethertype"):get_dissector(35143)

The protocol gnw (GeoNetworking) corresponds to an EtherType of 35143 in my Wireshark protocols configuration. However, 
this also fails to find the "gnw" protocol.

How can I get wireshark to detect the GeoNetworking protocol from my custom Lua script?

Thanks in advance.


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