README.md

Audio Output Monitor

This script will monitor the linux sound card file and fire an endpoint whenever the system starts to output audio. After a few seconds without audio output the script will fire a different endpoint.

Configurations

Use the -e flag to run a container with the following envs:

• AUDIO_PATH defaults to '/proc/asound/card0/pcm0p/sub0/status'
• ENDPOINT_ON defaults to 'http://localhost:1880/amp/on'
• ENDPOINT_OFF defaults to 'http://localhost:1880/amp/off'

Dockerfile

FROM node

RUN mkdir -p /usr/src/app
WORKDIR /usr/src/app

ENV AUDIO_PATH '/proc/asound/card0/pcm0p/sub0/status'
ENV ENDPOINT_ON 'http://localhost:1880/amp/on'
ENV ENDPOINT_OFF 'http://localhost:1880/amp/off'

COPY . /usr/src/app

CMD [ "node", "index.js" ]

monitor.js

const fs = require('fs')
const http = require('http')

const SIGNALS = /state: PREPARED|state: RUNNING/
// initialize it with all states false
const history = Array(18).fill(false)
const AUDIO_PATH = process.env.AUDIO_PATH
const ENDPOINT_ON = process.env.ENDPOINT_ON
const ENDPOINT_OFF = process.env.ENDPOINT_OFF
const ENCODING = 'utf8'

let state = 0

const processFile = (err, data) => {
  if (err) {
    return console.log(err)
  }
  saveState(data)
  setTimeout(readOutput, 1000)
}

const readOutput = (callback) => {
  fs.readFile(AUDIO_PATH, ENCODING, processFile)
}

const processHistory = () => {
  const positiveHistoryLength = history.filter(Boolean).length
  if (history[history.length - 1]) {
    checkIfChanged(1)
    return
  }
  if (positiveHistoryLength === 0) {
    checkIfChanged(0)
    return
  }
}

const checkIfChanged = (newState) => {
  if (newState !== state) {
    state = newState
    doAction(state)
  }
}

const doAction = (state) => {
  if (state) {
    console.info('Power ON')
    http.get(ENDPOINT_ON).on('error', console.warn)
    return
  }

  console.info('Power OFF')
  http.get(ENDPOINT_OFF).on('error', console.warn)
}

const saveState = (data) => {
  history.push(!!data.match(SIGNALS))
  history.shift()
  processHistory()
}

console.info('Intializing watcher...')
setTimeout(readOutput, 1000)