Re: my purpose [for building with support for Lua in Linux (Ubuntu 20.04)]

[Vincent Randal <vtrandal () gmail com>]

Graham, thank you for helping. I've replied in red below with a couple of
follow questions if you don't mind.
Thanks, Vincent Randal.

On Sat, May 22, 2021 at 3:25 AM Graham Bloice <graham.bloice () trihedral com>
wrote:

> Some answers in-line
>
> On Sat, 22 May 2021 at 04:03, Vincent Randal <vtrandal () gmail com> wrote:
>
> > Hello everyone,
> >
> > I've plans to use Lua to control tshark behavior in scripts, IF ... I can
> > get Wireshark to build with support for Lua in Ubuntu 20.4, ... But so far
> > I am not having any luck. I found this piece of documentation that says ...
> > "Wireshark contains an embedded Lua 5.2 interpreter ..."
> > I believe that's true for Windows but not Linux.
> >
> > I have lots of questions:
> > 1. Before running cmake how can I tell the appropriate "with-lua" sort of
> > switch is enabled?
>
> Look at CMakeOptions.txt, some options reset on a per-platform basis, but
> ENABLE_LUA defaults to ON.
Thank you. There's a lot in there. CMakeLists.txt gets syntax highlighting
in my vim and gvim setup, but CMakeOptions.txt does not. I might have
learned of CMakeOptions.txt sooner, if I'd looked for CM* files.
Maybe "Visual Studio Code" is worth a try? [
https://code.visualstudio.com/docs/cpp/cmake-linux] I wonder if anyone
builds Wireshark in "Visual Studio Code" on Linux.

> > 2. After running cmake how can I tell I got what I wanted i.e. that it
> > found Lua and make will build with support for Lua?
>
> The CMake output will output the packages that were found.  Missing
> mandatory dependencies will cause CMake generation to fail.  Lua isn't a
> required dependency.

> From a random MR Ubuntu build pipeline:
>
> -- Checking for one of the modules
> 'lua5.2;lua-5.2;lua52;lua5.1;lua-5.1;lua51'
> -- Found LUA: /usr/lib/x86_64-linux-gnu/liblua5.2.so (found suitable
> version "502", minimum required is "5.1")
Thank you. If I have doubts that the maintainers can build something (or
what version works), now I know where to look (in a MR Ubuntu build
pipeline, interesting. what's that?)?

3. If it does not find Lua how do I fix that?
>

Provide the required Lua packages in a location that CMake will search.  In
the source tools directory there is a bash script (debian-setup.sh) that
will install the required packages for Wireshark on a Debian based system.
See the Developer's Guide section on Unix Installation and Build
Instructions:
Thank you. I've been setting up my Ubuntu build environment the hard way
(not running debian-setup.sh [--install-optional]).

> https://www.wireshark.org/docs/wsdg_html_chunked/ChapterSetup.html#ChSetupUNIX
>
>
> > 4. When the build succeeds how do I compensate for the difference sudo
> > and non-sudo seem to have on tshark? Non-sudo invokation runs my lua
> > scripts. Sudo invocations don't.
>
> I'm not sure on Linux, but I suspect that the different users will have
> different personal configuration file locations.  How are you invoking the
> Lua script?
./tshark -X lua_script:hello.lua # hello.lua works, but there's no
permission to dissect packets. I will discuss this in more detail in Guy's
reply.

Note that it's highly recommended to NOT run wireshark\tshark as root due
to potential security issues.  To allow full use as non-root on Debian
based systems see
https://gitlab.com/wireshark/wireshark/-/blob/master/debian/README.Debian.


> 5. And assuming (with some help) I get past the above issues, how much
> control can lua scripts expert over tshark and Wireshark?

The Lua script capabilities are built around the API exposed by the Lua
support, which is mainly intended to handle dissection, post-dissection
tapping and some GUI facilities.  See the Developers Guide section on Lua
support:
https://www.wireshark.org/docs/wsdg_html_chunked/wsluarm.html
Thank you.

> Regarding the last question above, the June,2021 InterOp/Plugfests for
> IEEE 1451.0 are too soon for me to implement the 1451.0 network services
> (on embedded hardware or in virtual machines). But thank goodness for the
> lack of time, because it's got me asking how I might call tshark (or
> Wireshark) in scripts that behave to some degree as though its a real
> deployment.
>
> By the way, I do not represent the IEEE. I got involved in the IEEE 1451.0
> working group because my college advisor (John Schmalzel, currently with
> Rowan University) from 30 years suggested it to me.
>
> Also, Richard Sharpe has been tremendously helpful as I've struggled to
> learn enough about ASN.1 to get my dissectors generated and working. XDR
> and Thrift look like better alternatives to ASN.1 if I had more time to try
> those things. Thank you, Richard!
>
> Vincent
>
>
>
> --
> Graham Bloice
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