Integrating Supabase Storage with Flutter Apps

Introduction

This tutorial shows how to integrate Supabase Storage into Flutter mobile apps. You will learn how to initialize the client, upload and download files, manage access and URLs, and optimize for typical mobile scenarios such as unstable networks and caching. The examples use supabase_flutter and the platform File API (dart:io) suitable for iOS and Android.

Setup Supabase Client

Add supabase_flutter to pubspec, then initialize Supabase when your app starts. Use the Supabase client for storage operations from anywhere in your widget tree.

await Supabase.initialize(
  url: 'https://your-project.supabase.co',
  anonKey: 'public-anon-key',
);
final supabase = Supabase.instance.client;

Ensure you keep server-side keys off the client. Use anonKey for typical client reads/writes and server-side service_role keys only in secure backend environments.

Uploading And Downloading Files

Pick a file using file_picker or image_picker and upload it directly to a bucket. For mobile, convert the picked path to a File and call storage.upload. Use getPublicUrl for public buckets or createSignedUrl for private access.

final file = File(pickedFile.path);
final bucket = supabase.storage.from('uploads');
await bucket.upload('users/$userId/photo.png', file);
final publicUrl = bucket.getPublicUrl('users/$userId/photo.png').data;

To download or display a private file, generate a signed URL with an expiration and use it in an Image.network or an HTTP client. Signed URLs are preferable for temporary access to private files.

Managing Access And URLs

Buckets can be public or private. Public buckets expose stable public URLs that any client can fetch, which is ideal for non-sensitive assets like thumbnails. Private buckets require signed URLs. Use signed URLs for one-time or time-limited access.

Recommended patterns:

• Store sensitive assets (documents, private photos) in private buckets and issue short-lived signed URLs.

• Make public assets (icons, promotional images) publicly readable and use getPublicUrl for CDN-like access.

Also consider Row-Level Security (RLS) and policies on your Supabase tables that reference storage object metadata; use RLS to tightly control which users can create or list objects in a bucket.

Optimizing For Mobile

Mobile networks can be unreliable. Practical optimizations:

• Use retries and exponential backoff for failed uploads. Wrap upload calls in retry logic and surface progress to users.

• Upload small files directly. For large files (>5–10 MB) implement chunked uploads on the server or split files client-side and reassemble server-side—Supabase Storage doesn’t offer an official resumable client API in Flutter, so chunk strategies are a common workaround.

• Cache remote images with cached_network_image or local file caching after first download to reduce bandwidth and latency.

• Set appropriate cache-control headers (via a CDN or proxy) when serving public content to enable client caching.

Practical tips

• Metadata: Store contextual metadata (uploader id, original filename, MIME type) in your Postgres tables rather than relying solely on storage metadata.

• Naming: Use predictable folder structures (users/{id}/avatars) and UUIDs for filenames to avoid collisions.

• Content-Type: Ensure uploaded files include the correct MIME type so clients render them appropriately.

Error Handling And Security

• Validate file types and sizes client-side and server-side. Don’t rely solely on client checks.

• Avoid embedding service_role keys in the app. Use functions or server endpoints for privileged operations like generating long-lived signed URLs.

• Monitor storage usage and set lifecycle policies if needed to delete stale assets programmatically.

Conclusion

Integrating Supabase Storage into Flutter mobile apps is straightforward: initialize supabase_flutter, upload files from File objects, and choose public URLs or signed URLs according to security needs. For mobile-specific constraints prioritize retries, caching, and pragmatic chunking strategies for large uploads. Combine storage with Postgres metadata and RLS to create a robust, secure mobile file storage workflow.

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