how to create refFromURL with admin privilege on cloud functions? - firebase

Question

I want to have a reference to an image using its http URL when firestore update cloud function triggered so that i can take the url from change provide by onUpdate() function and use it to get a reference to the image on firebase storage and delete it.

Answer 1

In order to delete a file stored in Cloud Storage for Firebase from a Cloud Function you will need to create a File object based on:
The Bucket instance this file is attached to;
The name of the file,
and then call the delete() method
as detailed in the Node.js library documentation https://cloud.google.com/nodejs/docs/reference/storage/2.0.x/File.
Here is an example of code from the documentation:
const storage = new Storage();
const bucketName = 'Name of a bucket, e.g. my-bucket';
const filename = 'File to delete, e.g. file.txt';
// Deletes the file from the bucket
storage
.bucket(bucketName)
.file(filename)
.delete()
.then(() => {
console.log(`gs://${bucketName}/${filename} deleted.`);
})
.catch(err => {
console.error('ERROR:', err);
});
From your question, I understand that your app clients don't have the bucket and file names as such and only have a download URL (probably generated through getDownloadURL if it is a web app, or the similar method for other SDKs).
So the challenge is to derive the bucket and file names from a download URL.
If you look at the format of a download URL you will find that it is composed as follows:
https://firebasestorage.googleapis.com/v0/b/<your-project-id>.appspot.com/o/<your-bucket-name>%2F<your-file-name>?alt=media&token=<a-token-string>
So you just need to use a set of Javascript methods like indexOf(), substring() and/or slice() to extract the bucket and file names from the download URL.
Based on the above, your Cloud Function code could then look like:
const storage = new Storage();
.....
exports.deleteStorageFile = functions.firestore
.document('deletionRequests/{requestId}')
.onUpdate((change, context) => {
const newValue = change.after.data();
const downloadUrl = newValue.downloadUrl;
// extract the bucket and file names, for example through two dedicated Javascript functions
const fileBucket = getFileBucket(downloadUrl);
const fileName = getFileName(downloadUrl);
return storage
.bucket(fileBucket)
.file(fileName)
.delete()
});