push-receiver-v2/src/fcm/index.js

A module to subscribe to GCM/FCM and receive notifications within a node process. v2 is compatible with the latest FCM registration endpoints.

const crypto = require('crypto');
const request = require('request-promise');
const { escape } = require('../utils/base64');

const FIREBASE_INSTALLATION = 'https://firebaseinstallations.googleapis.com/v1/';
const FCM_REGISTRATION = 'https://fcmregistrations.googleapis.com/v1/';
const FCM_ENDPOINT = 'https://fcm.googleapis.com/fcm/send';

module.exports = { installFCM, registerFCM };

function generateFirebaseFID() {
  // A valid FID has exactly 22 base64 characters, which is 132 bits, or 16.5
  // bytes. our implementation generates a 17 byte array instead.
  let fid = crypto.randomBytes(17);

  // Replace the first 4 random bits with the constant FID header of 0b0111.
  fid[0] = 0b01110000 + (fid[0] % 0b00010000);

  return fid.toString('base64');
}

async function installFCM(config) {
  const response = await request({
    url     : `${FIREBASE_INSTALLATION}projects/${config.firebase.projectID}/installations`,
    method  : 'POST',
    headers : {
      'x-firebase-client': btoa(JSON.stringify({ heartbeats: [], version: 2 })).toString('base64'),
      'x-goog-api-key': config.firebase.apiKey
    },
    body : {
      appId: config.firebase.appID,
      authVersion: 'FIS_v2',
      fid: generateFirebaseFID(),
      sdkVersion: 'w:0.6.4'
    },
    json: true
  });
  return response;
}

async function registerFCM(config) {
  const keys = await createKeys();
  const response = await request({
    url     : `${FCM_REGISTRATION}projects/${config.firebase.projectID}/registrations`,
    method  : 'POST',
    headers : {
      'x-goog-api-key' : config.firebase.apiKey,
      'x-goog-firebase-installations-auth' : config.authToken
    },
    body : {
      web: {
        applicationPubKey: config.vapidKey,
        auth: keys.authSecret
          .replace(/=/g, '')
          .replace(/\+/g, '-')
          .replace(/\//g, '_'),
        endpoint: `${FCM_ENDPOINT}/${config.token}`,
        p256dh: keys.publicKey
          .replace(/=/g, '')
          .replace(/\+/g, '-')
          .replace(/\//g, '_')
      }
    },
    json: true
  });
  return {
    keys,
    fcm : response,
  };
}

function createKeys() {
  return new Promise((resolve, reject) => {
    const dh = crypto.createECDH('prime256v1');
    dh.generateKeys();
    crypto.randomBytes(16, (err, buf) => {
      if (err) {
        return reject(err);
      }
      return resolve({
        privateKey : escape(dh.getPrivateKey('base64')),
        publicKey  : escape(dh.getPublicKey('base64')),
        authSecret : escape(buf.toString('base64')),
      });
    });
  });
}