Auto rotate images using Firebase Functions

Rotate images by EXIF orientation infomation

Using Cloud Functions for Firebase, Images uploaded in Firebase Cloud Storage will be automatically rotated by EXIF orientation meta data. The below function script is triggered on uploading image. And that’s all. It works!

Function script

const functions = require('firebase-functions')
const mkdirp = require('mkdirp-promise')
const { Storage } = require('@google-cloud/storage')
const spawn = require('child-process-promise').spawn
const path = require('path')
const os = require('os')
const fs = require('fs')
const storage = new Storage()

exports.rotateUsingExif = functions.storage.object().onFinalize(async (object) => {
  const filePath = object.name
  const bucketName = object.bucket
  const metadata = object.metadata

  const tempLocalFile = path.join(os.tmpdir(), filePath)
  const tempLocalDir = path.dirname(tempLocalFile)
  const bucket = storage.bucket(bucketName)

  if (!object.contentType.startsWith('image/')) {
    console.log('This is not an image.')
    return null
  }

  if (metadata.autoOrient) {
    console.log('This is already rotated')
    return null
  }
  
  return mkdirp(tempLocalDir).then(() => {
    // Download file from bucket.
    return bucket.file(filePath).download({destination: tempLocalFile})
  }).then(() => {
    console.log('The file has been downloaded to', tempLocalFile)
    // Convert the image using ImageMagick.
    return spawn('convert', [tempLocalFile, '-auto-orient', tempLocalFile])
  }).then(() => {
    console.log('rotated image created at', tempLocalFile)
    metadata.autoOrient = true
    return bucket.upload(tempLocalFile, {
      destination: filePath,
      metadata: {metadata: metadata}
    })
  }).then(() => {
    console.log('image uploaded to Storage at', filePath)
    // Once the image has been converted delete the local files to free up disk space.
    fs.unlinkSync(tempLocalFile)
    return console.log('Deleted local file', filePath)
  })
})

Example

• Working app is here.
• Working code is here.

etc

• 2019.06.10: Firebase Cloud Storage on Node 10 is beta. I recommend to use Node 8. Here is a problem that I encountered.