---

name: nestjs-file-uploads description: Validate and stream file uploads securely with Validation and S3 streaming in NestJS. Use when implementing secure file uploads, validation, or S3 streaming in NestJS. metadata: triggers: files: - '**/*.controller.ts' keywords: - FileInterceptor - Multer - S3 - UploadedFile

File Upload Patterns

Priority: P0 (CRITICAL)

• Magic Bytes: NEVER trust content-type header or file extension.
• Tool: Use file-type or mmmagic to verify actual buffer signature.
• Limits: Set strict limits: { fileSize: 5000000 } (5MB) in Multer config to prevent DoS.

Streaming (Scalability)

• Memory Warning: Default Multer MemoryStorage crashes servers with large files.
• Pattern: Use Streaming for any file > 10MB.
• Library: multer-s3 (direct upload to bucket) or busboy (raw stream processing).
• Architecture:

1. Client requests Signed URL from API.
2. Client uploads directly to S3/GCS (Bypassing API server completely).
3. Pro Tip: Only approach to scale file uploads infinitely.

Processing

• Async: Don't process images/videos in HTTP Request.
• Flow:

1. Upload file.
2. Push FileUploadedEvent to Queue (BullMQ).
3. Worker downloads, resizes/converts, and re-uploads.

Anti-Patterns

• No content-type trust: Always verify file magic bytes; MIME header can spoofed.
• No MemoryStorage for large files: Use streaming or signed URL pattern for files > 10MB.
• No synchronous file processing: Offload image/video work to BullMQ workers via FileUploadedEvent.

References