File metadata in Firebase - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

Understanding Firebase Storage Metadata Update Behavior

You upload a file to Firebase Storage and then update its metadata to add a custom field. What happens to the file content after the metadata update?

Firebase

const storageRef = firebase.storage().ref('files/myfile.txt');
await storageRef.put(file);
await storageRef.updateMetadata({ customMetadata: { owner: 'user123' } });

A The file content remains unchanged; only the metadata is updated.

B The file content is overwritten with empty content during metadata update.

C The file content is deleted and replaced with metadata only.

D The file content is duplicated and stored twice after metadata update.

💡 Hint

Think about whether metadata updates affect the actual file data.

Updating metadata in Firebase Storage only changes the metadata fields. The file content stays the same and is not modified or duplicated.

❓ Configuration

intermediate

Setting Cache Control Metadata for Firebase Storage Files

You want to set a cache control header on a file in Firebase Storage so browsers cache it for 1 hour. Which metadata configuration achieves this?

Firebase

const storageRef = firebase.storage().ref('images/photo.jpg');
await storageRef.updateMetadata({ cacheControl: 'public, max-age=3600' });

A { cacheControl: 'no-cache' }

B { cacheControl: 'public, max-age=3600' }

C { cacheControl: 'private, max-age=3600' }

D { cacheControl: 'max-age=86400' }

💡 Hint

Cache control headers define how long browsers keep files before checking for updates.

The value 'public, max-age=3600' tells browsers to cache the file publicly for 3600 seconds (1 hour). Other options either disable caching or set different durations.

❓ security

advanced

Restricting Metadata Updates with Firebase Storage Security Rules

You want to allow users to update only the customMetadata.owner field of their files in Firebase Storage, but not other metadata fields. Which security rule snippet enforces this?

Firebase

service firebase.storage {
  match /b/{bucket}/o {
    match /files/{fileId} {
      allow update: if request.resource.metadata.customMetadata.owner == resource.metadata.customMetadata.owner &&
                    request.resource.metadata.keys().hasOnly(['customMetadata']) &&
                    request.auth.uid == request.resource.metadata.customMetadata.owner;
    }
  }
}

A allow update: if request.resource.metadata.customMetadata.owner == resource.metadata.customMetadata.owner && request.auth.uid == request.resource.metadata.customMetadata.owner;

B allow update: if request.auth.uid == resource.metadata.customMetadata.owner && request.resource.metadata.keys().hasOnly(['customMetadata']);

C allow update: if request.resource.metadata.customMetadata.owner == resource.metadata.customMetadata.owner && request.resource.metadata.keys().hasOnly(['customMetadata']) && request.auth.uid == request.resource.metadata.customMetadata.owner;

D allow update: if request.resource.metadata.customMetadata.owner == request.auth.uid && request.resource.metadata.keys().hasOnly(['customMetadata']);

💡 Hint

Check that only the customMetadata field is changed and the owner matches the authenticated user.

This rule ensures the update only changes customMetadata, the owner field remains consistent, and the user is authenticated as the owner.

❓ Architecture

advanced

Designing Metadata for Versioning Files in Firebase Storage

You want to keep track of file versions in Firebase Storage using metadata. Which approach best supports versioning without duplicating files?

A Use metadata <code>cacheControl</code> to indicate version numbers.

B Rename files with version numbers in their names and keep metadata unchanged.

C Store version info only in Firestore, not in Storage metadata.

D Add a <code>version</code> field in <code>customMetadata</code> and update it on each file overwrite.

💡 Hint

Think about how to track versions without creating multiple files.

Adding a version field in customMetadata allows tracking versions on the same file without duplicating storage. Renaming files duplicates storage, and cacheControl is unrelated.

🧠 Conceptual

expert

Effect of Metadata on Firebase Storage Download URLs

You generate a download URL for a file in Firebase Storage. Later, you update the file's metadata (e.g., add customMetadata). What happens to the previously generated download URL?

A The download URL remains valid and unchanged after metadata updates.

B The download URL expires immediately when metadata is updated.

C The download URL changes automatically to reflect new metadata.

D The download URL becomes invalid and must be regenerated after metadata changes.

💡 Hint

Consider whether metadata updates affect file access URLs.

Download URLs in Firebase Storage are tied to the file content and security token, not metadata. Updating metadata does not invalidate or change existing URLs.