websocket support in application sdk

[vlotech]

For realtime feedback of one of our applications, we would like to use a websocket and some web pages hosted from the application.

As an example, we've used the camera-management example. This fits most of our purposes, but using a websocket seems to be impossible.
The app-functions-sdk-go uses the http.TimeoutHandler which doesn't support Hijacking. The upgrade to websocket fails because of this.

We've also looked at using the edgex-ui-server as example, but we could figure out how to add the message bus to it in the right way.

What would be the best way forward?

[lenny-goodell]

@vlotech , yes the SDK uses the http.TimeoutHandler in the configuration for the internal WebServer. Why does this cause issue with adding websocket capability?
You should add the websocket capability separate from the SDKs internal webserver. i.e. on a different port.

[lenny-goodell]

You didn't answer my question on why use of http.TimeoutHandler causes issue with with adding websocket capability?

[vlotech]

http.TimeoutHandler does not support the Hijacker interface which is needed to upgrade to an websocket

TimeoutHandler supports the Pusher interface but does not support the Hijacker or Flusher interfaces.

[lenny-goodell]

Got it.

The App SDK is deigned to develop microservices for the edge which process the sensor data, not for hosting a UI. It provides the ability to expand on the small REST API (/version, /config, /ping, /secret) that a separate UI can utilize. The EdgeX UI utilizes the REST API of the EdgeX Services.

[vlotech]

Ok, That clear. We've used the Application SDK to build a UI. Simply because we needed the real-time data and it looked like the shortest route to success.
The edge-UI example didn't have a message bus connection and this was the clearest route forward for us.
We're new to Go and EdgeX and couldn't find a better way.
Thanks for the feedback and if a cleaner approach would be possible with an example.. I'm open for it!!

[lenny-goodell]

I think you can use the Application SDK for this with the knowledge it wasn't designed for how you are using it. Thus you will have some work arounds like websocket capability hosted on a different port.