Push: add custom messenger (BC)

[andig]

Fix #17148 by adding custom messenger. Custom messenger uses encoding to combine title and msg into a single value to send to plugin. Valid encodings are json, csv and tsv. If encoding is omitted only the message is transferred.

BC: removes script messenger. This is replaced by:

- type: custom
  source: script
  encoding: tsv
  cmdline: foo -bar

[GrimmiMeloni]

Don't we still need the cmdline execution parts from the former script implementation?

[andig]

Bleibt die Frage, ob wir das mergen wollen?

[GrimmiMeloni]

Regarding my previous comment

Don't we still need the cmdline execution parts from the former script implementation?

I now connected the dots, of the registry looking up the provider (factory) via the source field in the config. Not that obvious, took me a moment to grasp.

Bleibt die Frage, ob wir das mergen wollen?

Yes, I think so.

[rhuss]

Nice reuse of the existing plugin interface :) Does this mean that you can reuse any of the plugins as service endpoint for events ? (mqtt, modbus, http, script, ... all plugins that allow write access).

[rhuss]

Suggested change

	Title string `json:"title"`
	Title string `json:"title,omitempty"`

I would check if the title is empty or not defined in the config, and omit the title when empty.
This is a common use case for machine-readable payloads like JSON.

You could also allow the msg to be specified in JSON directly, to not impose your custom schema { msg: ..., title: ... } to the user. See #17278 for a proposal.

[rhuss]

This is too simplistic, especially when title and message can contain commas (to tabs for tsv). Do we really need csv and tsv ? I can't see any good use case that can not be solved with a stronger typed representation (like json).

[rhuss]

this type does not "fit" into the list: json, csv, tsv are formats (so kind of an encoding), "title" and "message" (the default) are more filters.

Wdyt to restrict encoding to "json" and "string" (or "raw") and have some second options as to whether to include the title or not ? (usually if you only use a single service endpoint and you don't need the title, you just don't define it in events: ...