---name: file-upload-handlingdescription: >---

File Upload Handling

Table of Contents

• Overview
• When to Use
• Quick Start
• Reference Guides
• Best Practices

Overview

Build secure and robust file upload systems with validation, sanitization, virus scanning, efficient storage management, CDN integration, and proper file serving mechanisms across different backend frameworks.

When to Use

• Implementing file upload features
• Managing user-uploaded documents
• Storing and serving media files
• Implementing profile picture uploads
• Building document management systems
• Handling bulk file imports

Quick Start

Minimal working example:

# config.py
import os

class Config:
    MAX_CONTENT_LENGTH = 50 * 1024 * 1024  # 50 MB
    UPLOAD_FOLDER = 'uploads'
    ALLOWED_EXTENSIONS = {'txt', 'pdf', 'png', 'jpg', 'jpeg', 'gif', 'docx', 'doc'}
    UPLOAD_DIRECTORY = os.path.join(os.path.dirname(__file__), UPLOAD_FOLDER)

# file_service.py
import os
import mimetypes
import hashlib
import secrets
from werkzeug.utils import secure_filename
from datetime import datetime
import magic
import aiofiles

class FileUploadService:
    def __init__(self, upload_dir, allowed_extensions, max_size=50*1024*1024):
        self.upload_dir = upload_dir
        self.allowed_extensions = allowed_extensions
        self.max_size = max_size
        self.mime = magic.Magic(mime=True)
// ... (see reference guides for full implementation)

Reference Guides

Detailed implementations in the references/ directory:

Guide	Contents
Python/Flask File Upload	Python/Flask File Upload
Node.js Express File Upload with Multer	Node.js Express File Upload with Multer
FastAPI File Upload	FastAPI File Upload
S3/Cloud Storage Integration	S3/Cloud Storage Integration

Best Practices

✅ DO

• Validate file extensions and MIME types
• Check file size before processing
• Use secure filenames to prevent directory traversal
• Store files outside web root
• Implement virus scanning
• Use CDN for file delivery
• Generate signed URLs for direct access
• Log file upload/download events
• Implement access control checks
• Clean up temporary files

❌ DON'T

• Trust user-provided filenames
• Store files in web-accessible directories
• Allow arbitrary file types
• Skip virus scanning for uploaded files
• Expose absolute file paths
• Allow unlimited file sizes
• Ignore access control
• Use predictable file paths
• Store sensitive metadata in filenames
• Forget to validate file content