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From Julian Feinauer <>
Subject Re: Integration of other Languages / Daffodil
Date Wed, 10 Apr 2019 06:47:35 GMT
Hi Björn,

I'm very happy to see you here on the list!

Currently, this "generated driver" topic is mostly on chris shoulders.
This is fine, as he really pushes things forward and has all the experience and tools he needs
to make this work.
BUT I think it’s the time now, to make this more of a "Top Level Concern" to get others
integrated in these efforts.

I think this is something absolutely NECESSSARY for the project, so we should make it a central
concern and join efforts on the next steps.
Especially having everything central in a repo (perhaps simly in a different "develop" branch
or so).
I guess, the next steps would be to 
1. Add some documentation or Confluence on all that’s been done previously and the workings
of Chris approach
2. Play around to make templates for another language
3. Make thinks stable, add test suites, ...

So I could imagine (Chris, of course, feel free to hit the brakes) that you could start by
prototyping a S7 driver which is strongly oriented at the (generated) Java one which can then
be used to extract the freemarker templates from it. This would be the optimal way towards
C# integration, I think. All the tooling and build automation would be a 2nd level concern
for me.
Or perhaps you could join forces with Markus (Sommer) which already has a lot of Cpp and a
generated Cpp driver could also have a C# frontend as a first step before we do all on the
.NET Core bases.

What do you think of a dedicated Workshop or Hackday for this topic?
We learned a lot during our Hackday here in Nürtingen and for this topic I would suggest
to have a bit of a stronger Agenda.
But this could be a good kickoff to
1. get all (new) participants of the list on board
2. get a live introduction by Chris
3. Drink beer together

As we are no longer South Germany centered we could to this somewhere more centrally located.

What are others thoughts on this?


Am 10.04.19, 04:23 schrieb "Christofer Dutz" <>:

    Hi Björn and others,
    glad you made it here ... hopefully email services will be back to normal soon ...
    Let me please explain in a little more detail, what I had in mind with all this DSDL and
generated drivers.
    We are currently in the situation where all drivers are written in Java and all drivers
are manually written. As for example the ADS driver is written by someone else than the S7
driver, you can see huge differences between the way they are built. Also, being the main
author of the S7 driver I wasn't quite happy with how I did it and wanted to clean it up greatly
as I knew, porting this would not be easy.
    On the other side we are currently working on C++ versions of the drivers. Just thinking
about the manual effort and what could go wrong by manually porting the drivers and keeping
them in sync, just gave me the shivers. So an alternate approach had to come. I guess we all
agree that we have to automate most of the heavy lifting. 
    I am not a fan of any cross-compilation (Write drivers in Java and have them automagically
ported to C++, C#, Go ...) so I favor specifying the protocols in a machine readable way and
have all code generated from that specification. 
    For this I evaluated about 7 different approaches and wasn't quite happy with them, till
I tried out DFDL which I first heard from at ApacheCon NA 2018 in Montreal. And it turned
out to be the ideal format for this. However with DFDL you can only specify the message format
and nothing else, so I was still missing the state-machine part ... DFDL being XML, it would
be ideal if this format too was in XML so I could embed DFDL into that ... so a simple google
query "state machine xml" directly guided me to SCXML and it turned out that a SCXML engine
is part of Apache Commons project.
    So now I had to prove that it is possible to define an industrial protocol completely
with DFDL and SCXML. The result of this is the "dynamic-driver". The performance is not acceptable
(50-100ms for reading one address), also is it not able to du multiple concurrent requests
at the same time. So we need generated code to bring the normal PLC4X performance to dynamic
drivers. DFDL and SCXML both don't have any code generation till now and I bet this will remain
that way for quite some time. So I started writing a Maven plugin to use DFDL and Freemarker
to generate source files. In the ideal case we would require two artifacts as input: protocol-specification,
language-templates to generate a new driver for a given language. 
    Implementing the full DFDL spec is totally out of scope for now, so I am currently working
on a set of conventions we can use to write our protocol-specs which the generator will be
able to process ... this will be a small sub-set of the entire DFDL spec, but it should be
enough to achieve our goal ... and it does make writing specs for new protocols easier as
the author has a reduced set of options to choose from.
    The one part we'll not be able to generate is the API for a new language. This will always
be hand-written and that's a good thing. Cause an API designed for Java doesn't look the same
way an API written for C# or C++ will look. For example in Java we use CompletableFutures
and Optionals ... in other languages this might look different. So ideally every API module
for a language will adopt the ideal patterns for that language it is designed for. So that's
where you come in - Björn or others - I don't know how such an API would look like in C#.
So it would be super-great if you could whip up a small API module for the Language of your
    The next step then would be for us to somehow integrate that modules build into the PLC4X
build system.
    This is usually quite challenging ... but I have read that CMake does have options for
this ... but we'll work that our as soon as it comes up.
    The step after that would be to manually port a driver from one existing language to C#
(ideally the generated classes) and create templates from that code ... or directly start
writing templates, however I think that's more challenging as you don't have content assist
of your IDE in Freemarker (I think).
    I hope that explains things and I really hope this email goes through (better save it
    On 2019/04/08 13:44:35, Bjoern Hoeper <> wrote: 
    > Hi everyone,
    > I got in touch with Chris and Julian during the buildingIoT Conference in Cologne
and I would like to participate in the further development of PLC4X. Our main interest is
to extend PLC4X to make it usable with .NET / C#.
    > So after looking at the sources and the discussions in the mailing list I was wondering
what would be the best move forward regarding the integration of other languages in general
and the decoupling of the protocol definition from the actual API implementation in a particular
language. As far as I understand the current status Apache Daffodil is  a candidate technology
for generating the adapter code. But at the current moment Daffodil does not support templating
of classes. Furthermore there are existing APIs for Java and Scala but no implementation for
languages not executed on the JVM so we would need to have an implementation of the Daffodil
APIs in every language we want to support in the future.
    > Are there any Ideas existing already about an Architecture to support languages besides
Java? If not I would like to encourage a discussion about this topic because I think it will
get quite fundamental as soon as the adoption of further languages gains some traction.
    > Best Regards
    > Björn
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