File Upload Processor

Overview

Builds secure file upload endpoints for web applications. Handles multipart form uploads, presigned URL generation for large files, file type validation via magic bytes (not just extensions), size limits, cloud storage integration (S3, GCS, R2), and upload status tracking. Buffering matters: multer's memory storage holds each whole file in RAM, so use it only for small files; larger files go to disk or straight to storage.

Instructions

1. Choose Upload Strategy

Based on file size:

• Small files (< 10MB): Stream through server to storage. Simple, one request.
• Medium files (10-100MB): Server-side streaming with progress tracking.
• Large files (> 100MB): Presigned multipart upload — client uploads directly to S3.

2. File Validation

Always validate by magic bytes, never trust file extensions: