Re: lua decoder accessing info from layers above

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

> From: Wireshark-dev <wireshark-dev-bounces () wireshark org> On Behalf Of chuck c
> Sent: Wednesday, October 14, 2020 10:33 AM
> To: Developer support list for Wireshark <wireshark-dev () wireshark org>
> 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?

It works as a post-dissector, but not as a registered dissector.  For example, replace:

    register_postdissector(p_foo)

with something like so, replacing the port number with whatever you can easily test with:

    local udp_table = DissectorTable.get("udp.port")
    udp_table:add(33333, p_foo)

Yet you can access and print other frame fields such as "frame.len" and "frame.cap_len".
- Chris











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