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.

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1. Setup and Configuration

flutter pub add firebase_storage

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.

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2. File Operations

Create a reference:

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

Upload:

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

Download (in-memory):

final data = await fileRef.getData();

Download URL:

final downloadUrl = await fileRef.getDownloadURL();

Delete:

await fileRef.delete();

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3. Metadata Management

Get metadata:

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

Update metadata:

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.

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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.

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5. Performance and Best Practices

Monitor upload progress:

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.

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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.

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References

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