[Request] Custom Event Support

[tjjfvi]

Is your feature request related to a problem? Please describe.
It is not related to a problem.

Describe the solution you'd like
If OctoPrint could support custom events, triggered by plugins, that would be great. If it already (documented or not) supports this, that's even better; I don't need to wait :)

Describe alternatives you've considered
I have not thought of any alternatives.

Additional context
I recently created a plugin for OctoPrint that notififies via IFTTT when the printer sends N or more busy signals. Obviously, that is a very specialized plugin; it would most likely be much more useful to have two plugins: one that adds a EchoBusy event and one that sends some or all events to IFTTT.

I have looked into the source/docs some and found that a plugin could run self._event_bus.fire("MyHappyCustomEvent", dict(payload_key=payload_val)) and it would (seemingly) work and not destroy OctoPrint, but I haven't thoroughly tested it.

[tjjfvi]

My example with self._event_bus doesn't work on the client-side (i.e. the client will not call a viewmodel's self.onEventMyHappyCustomEvent, but will for self.onEventPrintStarted). I don't know if there is a workaround other than manually self._plugin_manager.send_plugin_message(...)ing.

[foosel]

In theory it should work to set the new event on octoprint.events.Events, that will make it register in the client too, but I agree, a more straightforward hook or something to accomplish that is really needed.

[tjjfvi]

Ah, I hadn't seen that; maybe just throwing a paragraph about using that and the self._event_bus.fire to make custom events is enough?

[foosel]

maybe just throwing a paragraph about using that and the self._event_bus.fire to make custom events is enough?

In theory, but monkey patching is a bit hackish. By providing a defined hook namespace collisions could also be avoided (imagine two plugins deciding they want to define an event SOMETHING_HAPPENED...).

[foosel]

The above commit adds a new hook octoprint.events.register_custom_events that allows to register custom events by plugins. Documentation will soon be available here, once the doc build is through.

Commit is pushed to maintenance, soon devel and will be released with 1.3.11.

[tjjfvi]

@foosel: As I read it, it seems that you can only register events for plugin_myhappyplugin_my_happy_event_name. Would it be possible to also allow my_happy_event_name as an alias (only to be used by user-facing apis), assuming no conflicts?

[foosel]

Would it be possible to also allow my_happy_event_name as an alias (only to be used by user-facing apis), assuming no conflicts?

Oops, I somehow overlooked this question. Doing it like it's implemented now keeps it consistent with other plugin extended things, e.g. templates, div-ids, permissions in 1.4.0.dev and so on. Allowing customized event names without prefix will only cause issues and frustration down the road if I need a conflicting event name.

[foosel]

1.3.11 was released yesterday.

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