D 2015-05-04T21:33:33.824
L plugin\smeta\sdata
N text/x-markdown
P cb4b8fe350077e3472fc349c56616937c6f3f858
U mario
W 4309
# Plugin meta spec
Streamtuner2 now uses a proper plugin description scheme. Note that this is completely unrelated to the streamtuner2 or channels API, or how plugins are actually initialized (pkgutil, imp, implib, pluginbase/plugnplay).
Basically the top-level comment block is scanned on initialization. It simply lists a few <kbd>key: values</kbd> for documentation and technical descriptors. It's basically a subset of YAML embedded in a script comment.
# api: streamtuner2
# type: feature
# title: My Plugin
# description: Lists all the things
# version: 1.0
# category: music
# config: { name: myconf, value: 1, type: boolean, description: enable foo }
#
# And here goes a longer doc/comment.
The key names are case-insensitive of course. A few fields like <kbd>title:</kbd>, <kbd>description:</kbd> are required. Theoretically also the <kbd>api:</kbd> and <kbd>type:</kbd>. Though in ST2 they're currently just used for decorative purposes like the <kbd>category:</kbd> or <kbd>version:</kbd> field.
More interestingly the <kbd>config:</kbd> field can be used to describe plugin options. Default values will automatically end up in streamtuners `conf.*` dict, and are presented to users in the config dialog.
* A <kbd>value:</kbd> represents the default.
* The <kbd>type: select</kbd> can be used for dropdown boxes, with a `select:` <kbd>key=VAl|key2=VAL2..</kbd> attribute for options.
* Other <kbd>type:</kbd> values are interpreted as strings, except <kbd>type: boolean</kbd> which becomes a checkbox.
* A per-option <kbd>category:</kbd> attribute is ignored at the moment.
* Params can be optionally quoted as in <kbd>value: "Desc, desc, desc."</kbd> in case they contain commas (which otherwise separate option attrs.)
And of course, the <kbd>config:</kbd> field can list multiple options. Simply make it multi-line (every plugin meta field can be) by indenting wrapped lines.
### Why?
This scheme is designed to be language-agnostic. It originated in PHP way back (see [libconfig](http://milki.include-once.org/genericplugins/)), precisely to avoid a few common misdesigns.
* Meta data does **not** belong *in code*.
Because that incurs always importing them, even when they may go uninitialized/unused.
* And it certainly should not reside in externalized ini/json data blobs.
*(Or do you want ants? Because that's how you get ants.)*
* Furthermore it encourages a *useful* documentation block atop.
(Instead of license blobs everywhere in lieu of proper comments.)
The meta description block incidentally can also serve as packaging control scheme. The <kbd>pack:</kbd> descriptor is used by [fpm/xpm -s src](http://fossil.include-once.org/xpm/wiki/src). Which avoids manually doubling descriptions into separated setup.py/.cfg as the current Python packaging eco system does.
Note though that the plugin description scheme is primarily intended for *in-application* feature/plugin management. Reducing packaging effort is just a by-effect.
### argparse config: struct
Similarly to internal plugin configuration settings, the <kbd>config:</kbd> list is now used for ArgumentParser definitions. Fields are slightly remapped to remain in line with regular options.
# config:
# { arg: -D, name: debug, type: bool, description: enable debugging }
# { arg: -e, name: enable[], type: str*, description: add plugin }
It's basically just the extra <kbd>arg:</kbd> field which discerns such entries from standard options. And the <kbd>type:</kbd> may carry an optional quantifier (mapped to argparses' nargs= flag). Or the <kbd>name:</kbd> can indicate a list property with `[]` attached (maps to argparses' append instead of store). Not every argparse peculiarity is provided for though. And using a docopt section would probably be a better option anyway.
### Plugin list
The purpose of this scheme is feeding the plugin management in the settings window of course:
<img src="raw/st2-plugins.png?name=946c0e32c868a22facd7498250451723a50ab00a" style="margin:10pt">
And this may now even become a Python package of its own, [http://pypi.python.org/pypi/pluginconf/](http://pypi.python.org/pypi/pluginconf/). Not quite
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