Firebase Cloud Storage Skill

This skill defines how to correctly use Firebase Cloud Storage in Flutter applications.

When to Use

Use this skill when:

• Setting up Cloud Storage in a Flutter project.
• Uploading or downloading files.
• Managing file metadata.
• Handling Storage errors and monitoring upload progress.

1. Setup and Configuration

flutter pub add firebase_storage

dart
import 'package:firebase_storage/firebase_storage.dart';

final storage = FirebaseStorage.instance;
// Or specify a bucket explicitly:
// final storage = FirebaseStorage.instanceFor(bucket: "gs://BUCKET_NAME");

• Firebase Storage requires the Blaze (pay-as-you-go) plan.
• Run flutterfire configure to update your Firebase config with the default Storage bucket name.

> Security note: By default, a Cloud Storage bucket requires Firebase Authentication for any action. Configuring public access may also make App Engine files publicly accessible — restrict access again when you set up Authentication.

2. File Operations

Create a reference:

dart
final storageRef = FirebaseStorage.instance.ref();
final fileRef = storageRef.child("uploads/file.jpg");

Upload:

dart
final uploadTask = fileRef.putFile(file);
final snapshot = await uploadTask;
final downloadUrl = await snapshot.ref.getDownloadURL();

Download (in-memory):

dart
final data = await fileRef.getData();

Download URL:

dart
final downloadUrl = await fileRef.getDownloadURL();

Delete:

dart
await fileRef.delete();

3. Metadata Management

Get metadata:

dart
final metadata = await fileRef.getMetadata();
print('Content type: ${metadata.contentType}');
print('Size: ${metadata.size}');

Update metadata:

dart
final newMetadata = SettableMetadata(
  contentType: "image/jpeg",
  customMetadata: {'uploaded_by': 'user123'},
);
await fileRef.updateMetadata(newMetadata);

Use custom metadata to store additional key/value pairs with your files.

4. Error Handling

Use try-catch with FirebaseException. Key error codes:

| Code | Meaning | |---|---| | storage/object-not-found | File doesn't exist at the reference | | storage/bucket-not-found | No bucket configured for Cloud Storage | | storage/project-not-found | No project configured for Cloud Storage | | storage/quota-exceeded | Storage quota exceeded | | storage/unauthenticated | User needs to authenticate | | storage/unauthorized | User lacks permission | | storage/retry-limit-exceeded | Operation timeout exceeded |

• For quota-exceeded on the Spark plan, upgrade to Blaze.
• Implement retry logic for network-related errors and timeouts.

5. Performance and Best Practices

Monitor upload progress:

dart
final uploadTask = fileRef.putFile(file);
uploadTask.snapshotEvents.listen((TaskSnapshot snapshot) {
  print('Progress: ${(snapshot.bytesTransferred / snapshot.totalBytes) * 100}%');
});

• Cancel uploads with uploadTask.cancel().
• Pause / resume with uploadTask.pause() and uploadTask.resume().
• Optimize file sizes before upload to reduce costs and improve performance.
• Use Cloud Storage with Firestore for comprehensive data management.
• Use the Firebase Local Emulator Suite for local development and testing.

6. Security

• Use Firebase Security Rules to control access to files.
• Combine Storage rules with Firebase Authentication for user-based access control.
• Test security rules thoroughly before deploying to production.

References

• Firebase Cloud Storage Flutter documentation
• Upload files
• Download files
• Handle errors