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@xxxxxxxxx>
Date: Wed, Oct 14, 2020 22:33 PM
To: "Developer support list for Wireshark"<wireshark-dev@xxxxxxxxxxxxx>;
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)
print(pinfo.number, "Protocols: " .. (f_frame_protocols() and f_frame_protocols().value or "Unknown"))
-- print(pinfo.number, f_frame_protocols().value)
end
register_postdissector(p_foo)
Script above prints to the Lua console.
What was the situation where it doesn't work?
> From: Wireshark-dev <wireshark-dev-bounces@xxxxxxxxxxxxx> On Behalf Of Fulko Hew
> Sent: Monday, October 12, 2020 8:00 PM
> To: Developer support list for Wireshark <wireshark-dev@xxxxxxxxxxxxx>
> Subject: [Wireshark-dev] lua decoder accessing info from layers above
>
> I'm trying to update/improve someone else's decoder written in Lua.
> It's for a simple UDP (and TCP) based protocol.
> But I need to be able to get access to the upper layer
> to be able to decode it easily.
>
> Can someone provide an example of how to determine if the higher layer was UDP or TCP?
>
> Thanks
> Fulko
>
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. For example:
local f_frame_protocols = Field.new("frame.protocols")
function p_foo.dissector(buf, pinfo, tree)
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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