Re: Adding libxml2 as optional Wireshark dependency

[Ahmad Fatoum <ahmad () a3f at>]

I can't comment on the Windows binary distribution issue but Pascal's
suggestion of using SUSE's sounds promising. I will attempt building on
Windows and comment on the Gerrit issue later today.

Ethernet POWERLINK specifies XML Device Description (XDD) as its sole
format [1].

EDS (Windows .ini-like format) files are used occasionally, owing to its
CANopen roots, but are much less common in usage. Commercial tools as well
as openPOWERLINK generate XML files.

The revised dissector [2] also supports EDS via Glib's GKeyFile
unconditionally.

[1]
http://www.ethernet-powerlink.org/en/downloads/technical-documents/action/open-download/download/epsg-311-v110-ds-xml-device-description/?no_cache=1
[2] https://github.com/epl-viz/dissector (Needs to be converted back to a
static dissector)

On Wed, Apr 5, 2017 at 3:38 PM, Graham Bloice <graham.bloice () trihedral com>
wrote:

> On 5 April 2017 at 14:11, Ahmad Fatoum <ahmad () a3f at> wrote:
>
> > Hello everyone,
> >
> > I was advised on Gerrit to post this issue here as to garner wider input.
> >
> > This concerns proposed Change-Id I13c0a2f408fb5c21bad7ab3d7971e
> > 0fa8ed7d783 [1] intending to add libxml2 as optional dependency to
> > Wireshark.
> >
> > I am currently preparing to submit upstream, changes I did to the EPL v2
> > dissector (packet-epl.c).
> >
> > A significant change is the ability to optionally read in user-supplied
> > XML device descriptions and to extract type/description/mapping information
> > for aiding the dissection. See this previous submission of mine to the
> > mailing list: https://www.wireshark.org/lists/wireshark-dev/201701/
> > msg00154.html
> >
> >
> > Seeing as there also has been interest for libxml2 support in dissectors
> > in the past:
> >
> > https://www.wireshark.org/lists/wireshark-dev/201005/msg00108.html
> >
> > https://ask.wireshark.org/questions/36063/using-libxml2-in-
> > my-own-dissector
> >
> >
> > I think, it would be a good idea to have this as optional dependency as
> > Glib's GMarkup may be inadequate or inconvenient for parsing actual XML.
> >
> >
> > Looking forward to your feedback.
> >
> > Best regards,
> > Ahmad Fatoum
> >
> > [1] https://code.wireshark.org/review/#/c/20912/
> Thanks for the post,
>
> 1.  Where will the Windows binaries come from and are these supported long
> term?  The  libXml2 downloads page indicates another site provides Windows
> binaries [1].  The binaries at that site in the 64 bit directory seem to be
> the most recent and are labelled as libXml2-2.9.3 [2].  The current release
> of libXml2 is 2.9.4 which has a number of security fixes among other bug
> fixes and enhancements [3] so it would appear that the Windows binaries are
> not being maintained.
>
> 2.  According to the diagram at [1], libXml2 depends on iconv and zlib.
> We currently build our own zlib, will that be suitable for the libXml2
> dependency?  What will be the source of the iconv binary (iconv-1.14 is
> available in the same download area as libXml2 [2])?
>
> 3. The readme.txt in the download area ([2]) has some "interesting" text:
>
> These are experimental 64bit binaries. For completeness, 32bit binaries
> built using the same method are also included.
>
> The libraries in these packages are made using GCC (MinGW) toolchain. It is
> presently not possible to use these libraries with any recent version of the
> Microsoft Visual C compiler because of conflicting C-runtimes. To help you
> resist the temptation, the import libraries (.LIB) are not provided at all.
> If you need these libraries in an environment which mandates the use of the
> Microsoft toolchain, you will have to build them from source yourself.
>
> and inspection of the download shows this is true, so it appears that
> we'll need to rebuild to obtain the import .lib file.
>
> 4. Microsoft have a Visual Studio porting effort underway called vcpkg
> [4], that does include libXml2, but unfortunately is only for VS2015 or
> later.  If we move to VS2015 for main releases (post 2.4 release) then this
> may be a viable source for libXml2 and other packages we use.  It might be
> possible to use this to build VS2013 libXml2.
>
> 5.  Are there any manufacturers or tools that produce XML device
> description files for the EPL dissector such that choosing XML as the input
> format is the most sensible choice, or would another format be just as
> applicable?
>
>
> [1]: https://www.zlatkovic.com/libxml.en.html
> [2]: ftp://ftp.zlatkovic.com/libxml/64bit/
> [3]: http://xmlsoft.org/news.html
> [4]: https://github.com/Microsoft/vcpkg
>
> --
> Graham Bloice
>
>
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