환경

$ lsb_release -a
No LSB modules are available.
Distributor ID: Raspbian
Description:    Raspbian GNU/Linux 9.4 (n/a)
Release:    9.4
Codename:   n/a

$ npm -v
5.6.0
$ node -v
v9.4.0

パッケージのバージョン
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$ node ●●.js

*** WARNING *** The program 'node' uses the Apple Bonjour compatibility layer of Avahi.
*** WARNING *** Please fix your application to use the native API of Avahi!
*** WARNING *** For more information see <http://0pointer.de/avahi-compat?s=libdns_sd&e=node>
*** WARNING *** The program 'node' called 'DNSServiceRegister()' which is not supported (or only supported partially) in the Apple Bonjour compatibility layer of Avahi.
*** WARNING *** Please fix your application to use the native API of Avahi!
*** WARNING *** For more information see <http://0pointer.de/avahi-compat?s=libdns_sd&e=node&f=DNSServiceRegister>

@firebase/database: FIREBASE WARNING: Exception was thrown by user callback. TypeError: ref.child(...).val is not a function

코드

ref.on('child_changed', function(snapshot) {
  var url = ref.child('url').val();
  if (url) {
    playLatestPodcast(url);
  }
  ref.update({'url': ''}); // 変更をリセット
});

ref.on('child_changed', function(snapshot) {
  var url = snapshot.val()
  if (url) {
    playLatestPodcast(url);
  }
  ref.update({'url': ''}); // 変更をリセット
});

코드 전체

var FeedParser = require('feedparser');
var firebase = require('firebase');
var googleHome = require('google-home-notifier');
var request = require('request');

const lang = 'ja';
const ip = '192.168.xx.xx'; //再生したいGoogle HomeのIPアドレス

googleHome.ip(ip, lang);

const config = {
  apiKey: 'xxxxxxx_xxxxxxxxxxxxxxxxxxxxx_xxxxxxx',
  authDomain: 'xxxxxxxxxxxxxx.firebaseapp.com',
  databaseURL: 'https://xxxxxxxxxxxxxx.firebaseio.com',
  projectId: 'xxxxxxx',
  storageBucket: 'xxxxxxx.appspot.com',
  messagingSenderId: 'xxxxxxx'
};
firebase.initializeApp(config);

var db = firebase.database();
var ref = db.ref('/');

ref.on('child_changed', function(snapshot) {
  var url = snapshot.val()
  if (url) {
    playLatestPodcast(url);
  }
  ref.update({'url': ''}); // 変更をリセット
});

function playLatestPodcast(url) {
  var req = request(url);
  var parser = new FeedParser();
  var items = [];

  req.on('response', function(res) {
    this.pipe(parser);
  });

  parser.on('readable', function() {
    while (item = this.read()) {
      items.push(item);
    }
  });

  parser.on('end', function() {
    googleHome.play(getLatestPodcastUrl(items), function(notifyRes) {});
  });
}

function getLatestPodcastUrl(items) {
    for (item of items) {
      for (enclosure of item.enclosures) {
        var url = enclosure['url'];
        if (url) {
            return url;
        }
      }
    }
    return "";
}

참고문헌