index.js

let _id = null

const promises = []

let connection

function resolvePromises(value) {
  _id = value
  promises.forEach(({ resolve }) => resolve(_id))
  promises.length = 0
  connection.removeEventListener('icecandidate', onIceCandidate)
}

function rejectPromises() {
  promises.forEach(({ reject }) =>
    reject('This browser is not supported, so biri cannot provide a unique, static ID for this machine.')
  )
  promises.length = 0
}

function onIceCandidate({ candidate }) {
  if (connection.iceGatheringState == 'complete' && _id == null) {
    connection = null
    return rejectPromises()
  }

  if(!candidate) return

  // For Chrome
  if (candidate.foundation) {
    return resolvePromises(candidate.foundation)
  }

  // For Safari
  if (candidate.candidate) {
    const matches = /^candidate:(\d+)\s/.exec(candidate.candidate)
    if (!matches || matches[1].length < 2) return

    return resolvePromises(matches[1])
  }
}

async function startConnection() {
  if (connection) return

  connection = new RTCPeerConnection()

  // Required for Safari, causes an error on some other browsers.
  try {
    const stream = document.createElement('canvas').captureStream()
    stream.getTracks().forEach((track) => connection.addTrack(track))
  } catch (e) {}

  connection.addEventListener('icecandidate', onIceCandidate);

  const offer = await connection.createOffer({
    offerToReceiveAudio: 1,
    offerToReceiveVideo: 1
  })
  connection.setLocalDescription(offer)
}

async function biri() {
  if (typeof RTCPeerConnection == 'undefined')
    throw new Error(`This browser doesn't support WebRTC, so biri cannot provide a unique, static ID for this machine.`)

  if (_id) return _id

  const promise = new Promise((resolve, reject) => {
    startConnection()
    promises.push({ resolve, reject })
  })

  return promise
}

module.exports = biri