Extend Python OPC UA to support PubSub Standard for Cloud Protocols

[zerox1212]

Can we look at adding this functionality natively to support the various cloud platforms that are becoming more and more prevalent? Also I'm on a project that needs to send data to Azure. ;)

https://opcfoundation.org/news/opc-foundation-news/opc-foundation-announces-support-of-publish-subscribe-for-opc-ua/

My other project https://github.com/zeroentity/opcua-2-azure is kind of a workaround for this standard. It would be nice if someone on here is familiar with AMQP protocol to help implement.

I think even the https://github.com/OPCFoundation implementation doesn't have this functionality yet (looks like they made a hack similar to my project here https://github.com/OPCFoundation/UA-.UWP-Universal-Windows-Platform/tree/master/SampleApplications/Samples/Publisher). Would be nice to beat them. :) They also don't support python.

I think it would not be that difficult, just parse subscribed data into JSON and send out to AMQP endpoint. This could be loaded as a module, similar to how history is designed.

[oroulet]

Interesting but we need spec or sample implementation. There are many ways to implement opcua over amqp. If you find spec we can have a look

[zerox1212]

I have asked OPC Foundation for information, however I think the specification is not actually released yet.

A basic implementation will not be that difficult, but reporting every data change to Azure as it's own message will result in a LOT of AMQP messages. That would be very expensive for a per-use billing such as Azure. Hopefully the spec will try to collect a list of data changes and send a single AMQP message.

Anyways, I will try to design my side project to have a flexible module for converting OPC UA objects to JSON. Maybe that way we can reuse it.

[zerox1212]

I found some more information.
http://www.automation.com/automation-news/industry/opc-ua-is-enhanced-for-publish-subscribe-pubsub

And an open source project which appears to be implementing a full featured pub sub library.
https://github.com/mpostol/OPC-UA-OOI/blob/master/Networking/SemanticData/README.md

This OPC-UA-OOI looks like a very advanced implementation. I don't understand hardly any of the diagrams in the readme...

[oroulet]

So we need spec part 14.
Looks like the XML is available there https://github.com/OPCFoundation/UA-Nodeset/tree/master/Schema
So we can already generate the necessary structures

[zerox1212]

Quite interesting that the XML is already there.

I got a message from an OPC Foundation person and they said the pub sub spec is only available to the Working Groups. The public release of the spec won't be until the end of 2017.

It would be interesting if you can generate from the XML and see what shows up.

[oroulet]

you can try yourself. modify a file called something like
generate_protocol.py under schemas

On Fri, 10 Jun 2016 at 17:33 Andrew notifications@github.com wrote:

Quite interesting that the XML is already there.

I got a message from a OPC Foundation person and they said the pub sub
spec is only available to the Working Groups. The public release of the
spec won't be until the end of 2017.

It would be interesting if you can generate from the XML and see what
shows up.

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[zerox1212]

I have never tried to generate the code from the XML. I will try it if I get time.

[zerox1212]

I tried to generate the code with part14, but nothing shows up. Do you have some hints about how this code generator works? There are almost no doc strings.

[oroulet]

the pub sub protocol will not only suport amqp but also UDP. This is good.
A drop of info there https://opcfoundation.org/opc-connect/2016/06/toolkit-case-study-and-pubsub-white-paper/

[gillerman]

The XML from the OPCF has been updated: https://github.com/OPCFoundation/UA-Nodeset/tree/master/Schema

Did anyone figure out how to gen the code?

I am happy to help test, but I don't have the skills to write the code.

[oroulet]

Generating the classes is easy. Will add it for fun. But we need more than the xml to support the protocol: a spec or sample client/server to reverse engineer

[gillerman]

Can you develop against the Microsoft .Net stack? https://github.com/OPCFoundation/UA-.NETStandardLibrary

https://blogs.microsoft.com/iot/2016/06/23/microsoft-introduces-new-open-source-cross-platform-opc-ua-support-for-the-industrial-internet-of-things/