How to upload a base64 image URL to Firebase and retrieve its access token?

Question

In a MERN + Firebase project, I have an image data string that I want to upload and then get the access token of that file.

The image data string is of the following form:

data:image/png;base64,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

This is the reference to where the file should be uploaded:

const imageRef: StorageReference = ref(
  storage,
  `/issueImages/${firebaseImageId}`
);

So far, I have attempted to use the 'put' function with the imageRef, and when I try using uploadBytes() of firebase, I have to upload it as a Buffer, and even then I cannot seem to find the access token in the metadata.

Answer 1

To upload a data URL to Firebase, you would use storageRef.putString(url, 'DATA_URL') (legacy) or uploadString(storageRef, url, 'DATA_URL') (modern) depending on the SDK you are using.

When you upload a file to a Cloud Storage bucket, it will not be issued an access token until a client calls its version of getDownloadURL(). So to fix your issue, you would call getDownloadURL() immediately after upload.

If Node is running on a client's machine, you would use:

// legacy syntax
import * as firebase from "firebase";

// reference to file
const imageStorageRef = firebase.storage()
  .ref(`/issueImages/${firebaseImageId}`);

// perform the upload
await imageStorageRef.putString(dataUrl, 'DATA_URL');

// get the download URL
const imageStorageDownloadURL = await imageStorageRef.getDownloadURL();

// modern syntax
import { getStorage, getDownloadURL, ref, uploadString } from "firebase/storage";

// reference to file
const imageStorageRef = ref(
  getStorage(),
  `/issueImages/${firebaseImageId}`
);

// perform the upload
await uploadString(imageStorageRef, dataUrl, 'DATA_URL');

// get the download URL
const imageStorageDownloadURL = await getDownloadURL(imageStorageRef);

---

If Node is running on a private server you control, you should opt to use the Firebase Admin SDK instead as it bypasses the rate limits and restrictions applied to the client SDKs.

As mentioned before, the download URLs aren't created automatically. Unfortunately for us, getDownloadURL is a feature of the client SDKs and the Admin SDK doesn't have it. So we can either let a client call getDownloadURL when it is needed or we can manually create the download URL if we want to insert it into a database.

Nico has an excellent write up on how Firebase Storage URLs work, where they collated information from the Firebase Extensions GitHub and this StackOverflow thread. In summary, to create (or recreate) a download URL once it has been uploaded, you can use the following function:

import { uuid } from "uuidv4";

// Original Credit: Nico (@nicomqh)
// https://www.sentinelstand.com/article/guide-to-firebase-storage-download-urls-tokens
// "file" is an instance of the File class from the Cloud Storage SDK
// executing this function more than once will revoke all previous tokens
function createDownloadURL(file) {
  const downloadToken = uuid();

  await file.setMetadata({
    metadata: {
      firebaseStorageDownloadTokens: downloadToken
    }
  });

  return `https://firebasestorage.googleapis.com/v0/b/${file.bucket.name}/o/${encodeURIComponent(file.name)}?alt=media&token=${downloadToken}`;
}

The allows us to change the client-side code above into the following so it can run using the Admin SDK:

// assuming firebase-admin is initialized already
import { getStorage } from "firebase-admin/storage";

// reference to file
const imageStorageFile = getStorage()
  .bucket()
  .file(`/issueImages/${firebaseImageId}`);

// perform the upload
await imageStorageFile.save(dataUrl);

// get the download URL
const imageStorageDownloadURL = await createDownloadURL(imageStorageFile);

---

In all of the above examples, a download URL is retrieved and saved to the imageStorageDownloadURL variable. You should store this value as-is in your database. However, if you instead want to store only the access token and reassemble the URL on an as-needed basis, you can extract the token from its ?token= parameter using:

const downloadToken = new URL(imageStorageDownloadURL).searchParams.get('token');