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name: NestJS File Uploads description: Secure file handling, Validation, and S3 streaming. metadata: labels: [nestjs, upload, multer, s3] triggers: files: ['**/*.controller.ts'] keywords: [FileInterceptor, Multer, S3, UploadedFile]

File Upload Patterns

Priority: P0 (FOUNDATIONAL)

Secure file upload handling with validation and storage patterns.

• Magic Bytes: NEVER trust content-type header or file extension.
  • Tool: Use file-type or mmmagic to verify the 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: This is the only way to scale file uploads infinitely.

Processing

• Async: Don't process images/videos in the HTTP Request.
• Flow:
  1. Upload file.
  2. Push FileUploadedEvent to Queue (BullMQ).
  3. Worker downloads, resizes/converts, and re-uploads.