firestoreImageResizeGetURL.js

const functions = require('firebase-functions');
const gcs = require('@google-cloud/storage')({keyFilename: 'service-key.json'});
const spawn = require('child-process-promise').spawn;
const path = require('path');
const os = require('os');
const fs = require('fs');
 
exports.createCard = functions.firestore
  .document('work_cards/{cardID}')
  .onCreate((snap, context) => {
    const newCardData = snap.data()
    const bucket = gcs.bucket('your-project-id.appspot.com')
    const file = bucket.file(newCardData.image_name)
    const tempFilePath = path.join(os.tmpdir(), file.name);
    const thumbFileName = `thumb_${file.name}`;
    const thumbFilePath = bucket.file(thumbFileName)
    const contentType = file.contentType;
    const metadata = {
      contentType: contentType
    };

    return bucket.file(file.name).download({
        destination: tempFilePath,
      })
      .then(() => {
        return spawn('convert', [tempFilePath, '-thumbnail', '250x250', tempFilePath]);
      })
      .then(() => {
        return bucket.upload(tempFilePath, {
          destination: thumbFilePath,
          metadata: metadata,
        })
      })
      .then(() => {
        return thumbFilePath.getSignedUrl({
        action: 'read',
        expires: '03-09-2491'
        })
      })
      .then(signedUrls => {
        const img_src = signedUrls[0]
        return snap.ref.set({img_src}, {merge: true});
      })
      .then(() =>{
        bucket.file(file.name).delete()
        fs.unlinkSync(tempFilePath)
        return
      })
    });