index.js

/**
 * Copyright 2016 Google Inc. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
'use strict';

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

const THUMB_MAX_WIDTH = 200;
const THUMB_MAX_HEIGHT = 200;

/**
 * When an image is uploaded in the Storage bucket We generate a thumbnail automatically using
 * Sharp.
 */
exports.generateThumbnail = functions.storage.object().onFinalize((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.

  // Exit if this is triggered on a file that is not an image.
  if (!contentType.startsWith('image/')) {
    console.log('This is not an image.');
    return null;
  }

  // Get the file name.
  const fileName = path.basename(filePath);
  // Exit if the image is already a thumbnail.
  if (fileName.startsWith('thumb_')) {
    console.log('Already a Thumbnail.');
    return null;
  }

  // Download file from bucket.
  const bucket = gcs.bucket(fileBucket);

  const metadata = {
    contentType: contentType,
  };
  // We add a 'thumb_' prefix to thumbnails file name. That's where we'll upload the thumbnail.
  const thumbFileName = `thumb_${fileName}`;
  const thumbFilePath = path.join(path.dirname(filePath), thumbFileName);
  // Create write stream for uploading thumbnail
  const thumbnailUploadStream = bucket.file(thumbFilePath).createWriteStream({metadata});

  // Create Sharp pipeline for resizing the image and use pipe to read from bucket read stream
  const pipeline = sharp();
  pipeline.resize(THUMB_MAX_WIDTH, THUMB_MAX_HEIGHT).max().pipe(thumbnailUploadStream);

  bucket.file(filePath).createReadStream().pipe(pipeline);

  return new Promise((resolve, reject) =>
      thumbnailUploadStream.on('finish', resolve).on('error', reject));
});