Firebase Google Cloud Function: createReadStream results in empty file

Question

I try to process a Video file (stored in Google Firebase storage) through a Google Cloud Function. I have working code that download the entire video files into the NodeJS Google cloud function: await bucket.file(filePath).download({ destination: tempFile }). But the goal is only to read the framerate, therefore the headers of the videofile would suffice. But createReadStream gives me an empty tempFile. Any advise much appreciated!

exports.checkFramerate = functions.region('europe-west1').storage.object().onFinalize(async (object, context) => {
    const bucket =  admin.storage().bucket(object.bucket); // Bucket class
    const filePath = object.name;   //  videos/xbEXdMNFb1Blbd9r2E8m/comp_test.mp4
    const fileName = filePath.split('/').pop(); // comp_test.mp4
    const bucketDir = path.dirname(filePath); // videos/xbEXdMNFb1Blbd9r2E8m

    const tempFile = path.join(os.tmpdir(), 'temp.mp4')
    fs.closeSync(fs.openSync(tempFile, 'w'))
    console.log("tempFile size1", fs.statSync(tempFile).size)

    // await bucket.file(filePath).download({ destination: tempFile }); // this works: tempFile size2 = 3180152
    await bucket.file(filePath).createReadStream({                      // this does not work: tempFile size2 = 0
        start: 10000,
        end: 20000
      })
      .on('error', function(err) {console.log(err)})
      .pipe(fs.createWriteStream(tempFile));


    console.log("tempFile size2", fs.statSync(tempFile).size)

    mi(tempFile).then(data => {
        console.log("frameRate", data[0].general.frame_rate[0])
        return data[0].general.frame_rate[0];
    }).catch(e => {console.error(e)});
});

I tried implementing even the example of https://googleapis.dev/nodejs/storage/latest/File.html#createReadStream but to no avail. remoteFile.download works beautifully but remoteFile.createReadStream gives me empty files...

const remoteFile = bucket.file(filePath);
const localFilename = tempFile;

remoteFile.createReadStream()
    .on('error', function(err) {})
    .on('response', function(response) {})
    .on('end', function() {})
    .pipe(fs.createWriteStream(localFilename));

fs.stat(localFilename, (err, stats) => {
    if (err) {console.log(err)}
    return console.log("stats async",stats.size)
})

Answer 1

as mentioned, promise should be used

reading json file example

 let  buf = '';

 const loadData = async () => {
  return await new Promise((resolve, reject) => {
    storage.bucket('bucket-name').file('test-config.json')
      .createReadStream()
      .on('error', reject)
      .on('data', function(d) {
        buf += d;
      }).on('end', function() {
        resolve(buf)
      });
  })
}

const data = await loadData()