Re: XML library for use in dissector

[Ahmad Fatoum <ahmad.fatoum () student kit edu>]

Hello Peter,

As OEMs can (and do) provide their own device profiles, restricting loading
to compile-time would be too big a limitation.

For now, I  went the plugin route and edited the build files to include
libxml2.

Kind regards
Ahmad Fatoum

On Mon, Jan 30, 2017 at 1:00 PM, <wireshark-dev-request () wireshark org>
wrote:

> Date: Sun, 29 Jan 2017 15:52:09 +0100
> From: Peter Wu <peter () lekensteyn nl>
> To: Developer support list for Wireshark <wireshark-dev () wireshark org>
> Subject: Re: [Wireshark-dev] XML library for use in dissector
> Message-ID: <20170129145209.GA19229@al>
> Content-Type: text/plain; charset=us-ascii
>
> Hi Ahmad,
>
> On Sat, Jan 28, 2017 at 08:04:11PM +0100, Ahmad Fatoum wrote:
> > Hello everyone,
> >
> > As part of a school project, we intend to extend the Ethernet POWERLINK
> > (packet-epl.c) dissector in Wireshark to be able to read in the XML
> device
> > description files (XDD) and use that information to dissect the packet
> > payload (The data field is currently displayed as a byte stream).
> >
> > As we would like to have the changes eventually merged into the trunk, we
> > want to check what XML library we should use?
> >
> > We are hesitant to rely on GMarkup, because we don't control the input,
> and
> > don't want to later find out that it doesn't manage some more complex
> > device profiles. Wireshark depends on lex(1), but I wouldn't want to
> > reinvent the wheel and rather use some out-of-the-box parser.
> >
> > So what's the stance on dissectors pulling in dependencies like libxml?
> Any
> > other suggestions?
>
> Some (family of) dissectors are generated from description files (ASN.1,
> PIDL, ...). These "compilers" are Python/Perl/... programs which
> sometimes have additional dependencies at the time of generation, but
> are otherwise just normal C dissectors without additional dependencies
> after generation.
>
> Would this method of generating a dissector help? You can find some
> examples in epan/dissectors/asn1/, epan/dissectors/pidl/,
> epan/dissectors/README.X11.
>
> If the XML files describing the payload vary at runtime, I do not have a
> particular suggestion for an approach.
>
> > With kind regards
> > Ahmad Fatoum
> >
> > ps: Out of curiosity, is there a particular reason e.g. PROFINET is a
> > plugin while Ethernet POWERLINK is statically linked?
>
> Most dissectors are located in epan/dissectors/ (statically linked). I
> guess someone started with the PROFINET dissector as plugin and it just
> continued living there.
> --
> Kind regards,
> Peter Wu
> https://lekensteyn.nl
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