Cloud Functions: Upload image from URL to Cloud Storage.

index.js

const functions = require('firebase-functions');
const admin = require('firebase-admin');
const request = require('request').defaults({ encoding: null });
const cors = require('cors')({ origin: true });

admin.initializeApp(functions.config().firebase);

const bucket = admin.storage().bucket();

exports.uploadImageByURL = functions.https.onRequest((req, res) => {
  cors(req, res, () => {
    request.head(req.query.url, (err, resp, body) => {
      const filePath = `images/${ shortid() }.${ resp.headers['content-type'].split('/')[1] }`;
      
      const writeStreamToBucket = bucket
          .file(filePath)
          .createWriteStream()

      const stream = request(req.query.url).pipe(writeStreamToBucket);

      stream.on('finish', () => {
        res
          .status(200)
          .json({ filePath });
      });

      stream.on('error', (e) => {
        res
          .status(400)
          .json(e);
      });
    });
  })
})