File Upload with Preview
Overview
A user-friendly file upload system supporting drag-and-drop, multiple files, progress indicators, and instant previews. Uploaded files are stored in cloud storage with automatic optimization, virus scanning, and access control.
User Stories
- As a user, I want to drag-and-drop files to upload, so that the process is intuitive
- As a user, I want to see upload progress, so that I know how long it will take
- As a user, I want to preview images before uploading, so that I can verify I selected the right files
- As a user, I want to upload multiple files at once, so that I can save time
- As a user, I want clear error messages if upload fails, so that I know what went wrong
Acceptance Criteria
- [ ] Upload area supports drag-and-drop and click-to-browse
- [ ] Multiple file selection enabled
- [ ] Image preview shown immediately after selection (before upload)
- [ ] Progress bar displays upload percentage for each file
- [ ] Supported formats: JPG, PNG, PDF, DOCX (max 10MB each)
- [ ] Uploaded files display with thumbnail and filename
- [ ] Remove button to cancel upload or delete uploaded file
- [ ] Error messages for: file too large, invalid format, upload failed
- [ ] Files accessible via secure URL after upload
Technical Requirements
- Use cloud storage service (AWS S3, Cloudflare R2, Google Cloud Storage)
- Generate signed URLs for secure file access
- Validate file type and size on both frontend and backend
- Compress images before upload (client-side using Canvas API)
- Generate thumbnails for images on server (ImageMagick, Sharp)
- Implement virus scanning (ClamAV or third-party service)
- Store file metadata in database (filename, size, type, URL, user_id)
- Use multipart upload for files >5MB
Edge Cases
- Upload very large file (>50MB) → Reject with "File too large" message
- Upload file with same name as existing → Append timestamp to filename to avoid collision
- User closes browser during upload → Cancel upload on server, clean up partial files
- Network interruption mid-upload → Show error, allow retry with resume capability
- Malicious file detected → Block upload, log incident, notify user "File rejected by security scan"
Out of Scope
- Video file uploads
- Zip file extraction
- Batch download of multiple files
- File version history
- Collaborative editing