Re: lua decoder accessing info from layers above

["qiangxiong.huang" <qiangxiong.huang () qq com>]

The best way is to check the pinfo. port_type to get the current transport protocol type.  There is an example on 
this page: https://gitlab.com/wireshark/wireshark/-/wikis/protobuf



---Original---
From: "chuck c"<bubbasnmp () gmail com&gt;
Date: Wed, Oct 14, 2020 22:33 PM
To: "Developer support list for Wireshark"<wireshark-dev () wireshark org&gt;;
Subject: Re: [Wireshark-dev] lua decoder accessing info from layers above


local p_foo = Proto.new("foo", "foo")
local f_frame_protocols = Field.new("frame.protocols")

function p_foo.dissector(buf, pinfo, tree)
&nbsp; &nbsp; print(pinfo.number, "Protocols: " .. (f_frame_protocols() and f_frame_protocols().value or "Unknown"))
-- &nbsp; &nbsp;print(pinfo.number, f_frame_protocols().value)
end

register_postdissector(p_foo)



Script above prints to the Lua console.
What was the situation&nbsp;where it doesn't work?


On Tue, Oct 13, 2020 at 12:45 PM Maynard, Chris via Wireshark-dev <wireshark-dev () wireshark org&gt; wrote:

&gt; From: Wireshark-dev <wireshark-dev-bounces () wireshark org&gt; On Behalf Of Fulko Hew
 &gt; Sent: Monday, October 12, 2020 8:00 PM
 &gt; To: Developer support list for Wireshark <wireshark-dev () wireshark org&gt;
 &gt; Subject: [Wireshark-dev] lua decoder accessing info from layers above
 &gt;
 &gt; I'm trying to update/improve someone else's decoder written in Lua.
 &gt; It's for a simple UDP (and TCP) based protocol.
 &gt; But I need to be able to get access to the upper layer
 &gt; to be able to decode it easily.
 &gt;
 &gt; Can someone provide an example of how to determine if the higher layer was UDP or TCP?
 &gt;
 &gt; Thanks
 &gt; Fulko
 &gt;
 
 I was going to suggest a possible alternative solution which would be to grab "frame.protocols" and scan it for udp or 
tcp, but unfortunately this method doesn't work.&nbsp; For example:
 
 local f_frame_protocols = Field.new("frame.protocols")
 
 function p_foo.dissector(buf, pinfo, tree)
 &nbsp; &nbsp; print("Protocols: " .. (f_frame_protocols() and f_frame_protocols().value or "Unknown"))
 end
 
 I suspect this has something to do with it being a generated field, but this looks like a Wireshark bug to me, unless 
someone can explain why this doesn't and shouldn't be expected to work.
 - Chris
 
 
 
 
 
 
 
 
 
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