plapperkasten 0.8.8

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plapperkasten

Manage a headless media device.

What?!

Turn a Raspberry Pi with only buttons and speakers attached into a jukebox playing local music.

In a typical setup you might have a couple of buttons wired to a raspberry pi's GPIO pins, some speakers attached to the audio jack and a RFID reader plugged into one of the USB ports.

This is based on the idea of the PhonieBox ("original" software, more information on awesomeopensource.com) but written from scratch and not as feature-rich - yet!

plapperkasten has started as a small script to learn the workings of a Raspberry Pi box and to avoid the great but intimidatingly complex RPi-Jukebox-RFID. As the project has grown more complex and mature I've decided to release it into the wild - so here it is.

Features

• Easy setup: install the python package from PyPi (with pip install plapperkasten) or configure the whole machine using plapperkasten-setup. This will guide you from the download of the OS all the way to a functioning device including SSH, setting up an isolated python environment, configuring sound, users, etc.
• Nearly everything is a plugin: Theres a plugin for controlling the sound using ALSA and one for PipeWire. Need to output to JACK or PulseAudio? Write your own plugin by lending from the existing plugins.
• Completely written in Python 3:
• Does not run as a super user: plapperkasten is geared towards interacting with hardware buttons, sound and the like without needing special privileges. This needs some configuration of your OS but plapperkasten-setup is there to help you - or if you want it your way to give you some hints.

Setup

Please see https://github.com/randomchars42/plapperkasten-setup for detailed instructions and an easy installer.

Development

Style

Docstrings are formatted according to the Google Style Guide.

All other formatting tries to adhere to PEP8 and is enforced by YAPF.

Log entries use lazy evaluation, i.e., logger.debug('start %s', name), start with a lower-case letter and do not end with a full stop.

Raised errors on the other hand use f-strings (if necessary) and contain whole sentences, i.e. ValueError(f'{variable} did not match XXXX.').

Linting / Checking

Code should be checked by pylint and mypy.

Paths

All path representations should be pathlib.Path-objects instead of strings.

Logging

Logging uses a wrapper (plapperkasten.plklogging) around the logging module to cover logging from multiple processes.

Import a logger using:

from plapperkasten.plklogging import plklogging

logger: plklogging.PlkLogger = plklogging.get_logger(__name__)

# your code here

Setup for development

Requirements

• Python >= 3.10 as it uses typehinting features only available beginning with 3.10.

Semi-optional

• libgpiod with python3-libgpiod and gpiodmonitor>=1.1.3 if you plan to use the inputgpiod-plugin. Alternatively you may implement the functionality using RPi.GPIO or any library of your choice - but beware: you're gooing to need super user privileges!

Recommendations

• pyenv to setup a python version withput messing up your system.

• pipenv to create a virtual environment with a defined python version.

Example setup using pipenv

git clone [e-mail]:randomchars42/plapperkasten.git

cd plapperkasten

# consider adding this to your .bashrc / equivalent for your shell:
# `export PIPENV_VENV_IN_PROJECT=1`
# this leads to a folder `.venv` being created at the project root
# otherwise you might need to tweak the `[tool.mypy]`` path in
# `pyproject.toml` (depending on your editor setup).

# setup a virtual environment with set python version
# set the version to >= 3.10
pipenv --python 3.10

# install development dependencies
pipenv install --dev

# activate venv
pipenv shell

Plapperkasten logic in a nutshell

plapperkasten is a simple platform for plugins that can talk to each other to control a jukebox. There is a plugin recieving input from buttons (src/plapperkasten/plugins/inputgpiod), one recieving input from RFID readers (src/plapperkasten/plugins/inputdevinputevent), one for controlling an MPD client (src/plapperkasten/plugins/mpdclient) and so forth.

A good place to get to know the overall logic is src/plapperkasten/plapperkasten.py. This is the main entry point into the programme.

It will in turn:

• start a process for logging
• load the configuration files
• gather all plugins from src/plapperkasten/plugins and ~/.config/plapperkasten/plugins (or wherever ~/.config/plapperkasten/config.yaml points it to)
• start a process for each plugin (that is not blacklisted in ~/.config/plapperkasten/config.yaml)
• the plugins register for events they might process
• trigger on_before_run() for each pluggin
• wait for the plugins to send events to process, translate or re-emit so that other plugins can react to them
• or wait for all plugins to exit (either by themselves or because of a terminate event)
• if a shutdown event has been emitted, plapperkasten will try to shutdown the host (here's how to stop it during development)

Examplary flow of events

In a typical setup you might have a couple of buttons wired to a raspberry pi's GPIO pins, some speakers attached to the audio jack and a RFID reader plugged into one of the USB ports.

An RFID token has been recognised

• inputdevinputevent listens to the attached RFID reader and reads a token.
• inputdevinputevent sends an raw event with the payload 0123456789 (the value read from the token) to plapperkasten via its pipe
• plapperkasten recieves the event, looks it up in ~/.config/plapperkasten/events.map and sees it maps to a load_source event with the payload use=Mpdclient, key=Music/Folder/Band/Album.
• plapperkasten emits load_source to those who listen
• mpdclient listens to load_source and makes mpd or mopidy (whichever you run on the system) add the folder Music/Folder/Band/Album to a new playlist and start playing it

A button is pressed

• inputgpiod listens to the gpio pins and recieves a signal from pin 12.
• inputgpiod sends an event 12_short to plapperkasten via its pipe
• plapperkasten recieves the event, looks it up in ~/.config/plapperkasten/events.map and sees it maps to a volume_increase event
• plapperkasten emits volume_increase to those who listen
• pwwp (short for PipeWire / Wireplumber) listens to volume_increase and calls wpctl set-volume @DEFAULT_AUDIO_SINK@ 1%+
• pwwp sends an event beep to plapperkasten
• plapperkasten knows from its config that it should pass those events through, so it re-emits the event to whom it may concern
• soundeffects listens to the beep and produces a beep

Core files

• src/plapperkasten/settings/config.yaml contains default settings - user changes should not go here
• ~/.config/plapperkasten/config.yaml may contain any of the settings from src/plapperkasten/settings/config.yaml and overwrite them
• src/plapperkasten/settings/events.map could contain default event mappings but is empty - user changes should not go here
• ~/.config/plapperkasten/events.map may contain events defined by the user (see src/plapperkasten/keymap.py for a description of the form)

Creating a plugin

A good place to start is to copy the "example" plugin and to take off from there. You will find it in src/plugins/example.

Each plugin lives in its own process. This has some severe implications:

• You need to use the logging functionality provided by plapperkasten.plklogging see logging above.
• The class is initialised in the main process, this is where it might access data from the configuration or other parts of the programme. It may only store immutable information or fresh copies (as returned by plapperkasten.config) or else the multiprocessing hell will be upon you.
• If you need to do something (like fetching configuration values or registering for events) on initialisation before the plugin's process was started use on_init.
• If you need to do something as soon as the new process has started use on_before_run.
• If you need to do something every X seconds use on_tick and set self._tick_interval to X in on_init.
• If you need to respond to an event, register for it and write an on_EVENT method, e.g., place register_for('my_event') in on_init and write on_my_event to handle the event.
• If you need total controll - you usually don't - overwrite run, as in src/plapperkasten/plugins/inputgpiod/inputgpiod.py.
• If you need to tidy up after you put the code in on_after_run.
• If you want to prevent plapperkasten from shutting down after a period of idleness use send_busy.
• If you want plapperkasten to think it might restart its "idle" countdown use send_idle (but the countdown will only commence if all plugins are idle).
• If you want to send an event to plapperkasten use send_to_main.

Preventing shutdown during development

To avoid shutdown during development set debug in ~/.config/plapperkasten/config.yaml to true.