Firebase Cloud Functions image thumbnail generator using Sharp for 4x faster resizing

index.js

const functions = require('firebase-functions');
const gcs = require('@google-cloud/storage')();
const sharp = require('sharp')
const _ = require('lodash');
const path = require('path');
const os = require('os');

exports.generateThumbnail = functions.storage.object('uploads/{imageId}').onChange(event => {

  const object = event.data; // The Storage object.

  console.log(object)

  const fileBucket = object.bucket; // The Storage bucket that contains the file.
  const filePath = object.name; // File path in the bucket.
  const contentType = object.contentType; // File content type.
  const resourceState = object.resourceState; // The resourceState is 'exists' or 'not_exists' (for file/folder deletions).
  const metageneration = object.metageneration; // Number of times metadata has been generated. New objects have a value of 1.

  const SIZES = [64, 256, 512]; // Resize target width in pixels

  if (!contentType.startsWith('image/') || resourceState == 'not_exists') {
    console.log('This is not an image.');
    return;
  }

  if (_.includes(filePath, '_thumb')) {
    console.log('already processed image');
    return;
  }


  const fileName = filePath.split('/').pop();
  const bucket = gcs.bucket(fileBucket);
  const tempFilePath = path.join(os.tmpdir(), fileName);

  return bucket.file(filePath).download({
    destination: tempFilePath
  }).then(() => {

    _.each(SIZES, (size) => {

      let newFileName = `${fileName}_${size}_thumb.png`
      let newFileTemp = path.join(os.tmpdir(), newFileName);
      let newFilePath = `thumbs/${newFileName}`

      sharp(tempFilePath)
        .resize(size, null)
        .toFile(newFileTemp, (err, info) => {

          bucket.upload(newFileTemp, {
            destination: newFilePath
          });

        });

    })
  })
})

package.json

{
  "name": "functions",
  "description": "Cloud Functions for Firebase",
  "dependencies": {
    "@google-cloud/storage": "^0.4.0",
    "firebase-admin": "^4.1.2",
    "firebase-functions": "^0.5",
    "lodash": "^4.17.4",
    "request-promise": "^2.0.0",
    "sharp": "^0.18.1"
  },
  "private": true
}