Added realtime updates

[cesmec]

Sends live events to the gui using server sent events.
Currently contains start/stop and log of instances.
Based on Issue #74.

[sebinside]

Thank you for this pull request. The usage of server side events is an interesting approach which might solve a lot of (future) problems with the gui connection.

To start, I want to integrate the events endpoint in the chatoverflow-api npm package, based on your swagger documentation. A callable method might also solve your todo, but I am not into events that much. https://github.com/codeoverflow-org/chatoverflow-gui/pull/2/files#diff-401c1d73fa16a958f7072b5491740c14R176

But first, we have to discuss the API interface. We used to send the auth key as header field. In your definition, your sendind it as parameter. Is this a limitation of the EventSource? b66b821#diff-be1fae0b59ee0da30023b30b6b25854eR15

I'm also not understanding the comment completely: Requires the authKey as a cookie and an Accept-header with the value text/event-stream.

After we solved this, I will include the PluginInstanceWithLog and the events endpoint into the npm package, so you can properly update the gui.

[sebinside]

And we should include a big warning, when the EventSource API is not supported because it will probably be used for more when we're ready. Still good support though.

[cesmec]

Depending on the future use cases, it might make sense to use websockets instead, which would also solve the IE/Edge support.
The main difference is that websockets allow for bi-directional communication but might require additional libraries in the backend (I just wanted to make a simple implementation for now as I have not used scala before).
Custom headers for authentication are not supported in both, so either a cookie or a parameter can be used instead and a parameter is a bit easier to implement as it can just be added to the url.

The comment about the Accept-header is just a hint that this value is expected and testing if the client expects a long running event stream. If the request does not include this header, it will be rejected: https://github.com/codeoverflow-org/chatoverflow/pull/78/files#diff-3acd087eb793d2cd5e40247c8f9a4379R48
I think it's not possible to document server sent events (or also websockets) correctly using OpenAPI, which is also the reason it is documented as returning Object: https://github.com/codeoverflow-org/chatoverflow/pull/78/files#diff-be1fae0b59ee0da30023b30b6b25854eR9

[sebinside]

I would use SSE for the same reasons. But you're right, it's not compatible to swagger / open api: OAI/OpenAPI-Specification#396

The hint with the accept header is good idea. Beeing unable to set the authkey in the header is not the best, but I also agree that params are easier then cookies here.

[sebinside]

I updated the npm package. PluginInstance contains now the log field by default, and the API contains an event endpoint following your controller definitions. I also updated the gui to match the new specifications and types.

https://www.npmjs.com/package/chatoverflow-api
https://github.com/codeoverflow-org/chatoverflow/tree/cesmec-feature/realtime-gui-updates
https://github.com/codeoverflow-org/chatoverflow-gui/tree/cesmec-feature/realtime-gui-updates

The usage of events is useful for future versions of the gui, probably for more than just instances and log events. There are a few more things to do:

• Please overload the broadcast function to take native scala maps. This code is used repeatetly and could be encapsulated: https://github.com/codeoverflow-org/chatoverflow/pull/78/files#diff-63eaaad4b847c7b58af51a60562eaadcR36
• Please document the dispatcher since it will probably be used from multiple endpoints in the future
• Please refactor the client integration of the event handling. In the future, there will be more than just one page requireing events. The handling could be encapsulated in a separate service like the swagger services (ConfigService and so on) or the self written Crypto Service.

That's all. I'm looking forward to integrate this feature when you're ready!

[sebinside]

Everything is fine. Thank you for this great addition!