Resize image after upload to Firebase Storage bucket. Maintain access token of original image.

resizeImage.ts

import * as admin from "firebase-admin";
import * as functions from "firebase-functions";
import * as fs from "fs";
import sharp from "sharp";

export const resizeImage = functions.storage
  .object()
  .onFinalize(async (object) => {
    const bucket = admin.storage().bucket(object.bucket);
    const filePath = object.name;
    const fileName = filePath?.split("/").pop();
    const bucketDir = filePath?.substring(0, filePath.lastIndexOf("/"));

    // Exit if this is triggered on a file that is not an image.
    if (!object.contentType?.startsWith("image/")) {
      return functions.logger.log("This is not an image.");
    }

    // Exit if the image is already a thumbnail.
    if (fileName?.startsWith("thumb_")) {
      return functions.logger.log("Already a Thumbnail.");
    }

    functions.logger.log(
      `Downloading ${fileName} from bucket ${object.bucket}/${filePath}`,
    );
    const tempFilePath = `/tmp/${fileName}`;
    await bucket.file(filePath!).download({ destination: tempFilePath });

    // Resize using Sharp and upload to the same bucket.
    const thumbFileName = `thumb_${fileName}`;
    const thumbFilePath = bucketDir
      ? `${bucketDir}/${thumbFileName}`
      : thumbFileName;

    const tempThumbFilePath = `/tmp/${thumbFileName}`;

    functions.logger.log(
      `Resizing image ${tempFilePath} to ${tempThumbFilePath}`,
    );
    await sharp(tempFilePath)
      .resize(300, 300, { fit: "inside", withoutEnlargement: true })
      .toFile(tempThumbFilePath);

    const metadata = {
      contentType: object.contentType,
      metadata: object.metadata!,
    };

    // If there's an access token, include it in the metadata
    if (object.metadata?.firebaseStorageDownloadTokens) {
      metadata.metadata.firebaseStorageDownloadTokens =
        object.metadata.firebaseStorageDownloadTokens;
    }

    // Upload the Thumbnail to Firebase Storage
    functions.logger.log(`Uploading thumbnail to ${thumbFilePath}`);
    await bucket.upload(tempThumbFilePath, {
      destination: thumbFilePath,
      metadata: metadata,
    });

    functions.logger.log(`Deleting ${tempFilePath} and ${tempThumbFilePath}`);
    fs.unlinkSync(tempFilePath);
    fs.unlinkSync(tempThumbFilePath);
  });