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README.md

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+
+# Web Development Essentials
+
+Quick reference for modern web development: client-server architecture, setup, and security.
+
+---
+
+## 🌐 Client-Server
+
+### HTTP Cycle
+1. **Request**: Browser → server (GET, POST, PUT, DELETE, PATCH; headers; body)
+2. **Processing**: Routing, logic, DB operations
+3. **Response**: Status codes (2xx, 4xx, 5xx), headers, body (HTML/JSON/assets)
+
+### Network Layers
+
+```
+
+App: HTTP/HTTPS, REST, GraphQL
+Transport: TCP/UDP, WebSockets
+Internet: IP routing, DNS
+Link: Ethernet, WiFi, 5G
+
+```
+
+### Web Servers
+* **Nginx** – high performance, reverse proxy, load balancing
+* **Apache** – flexible, mature
+* **Caddy** – auto HTTPS
+* **Cloudflare Workers** – edge/serverless
+
+---
+
+## 🛠️ Dev Environment
+
+### Stack
+* **Runtime**: Node.js 18+, PHP 8.1+, Python 3.11+, Docker/Podman
+* **Web Server**: Nginx, Apache, Caddy
+* **DB**: PostgreSQL 15+, MySQL 8+/MariaDB 10.8+, Redis, MongoDB
+* **Tools**: IDEs (VS Code, Zed), extensions (languages, Docker, Git, DB)
+
+### Setup
+**Docker:**
+
+```yaml
+version: '3.8'
+services:
+
+app: { build: ., ports: ['8080:80'] }
+db: { image: postgres:15, environment: { POSTGRES_DB: myapp } }
+
+redis: { image: redis:7-alpine }
+```
+
+**Managed Services:** Vercel, Netlify, Heroku, Render, AWS, Azure, GCP
+**Local:** `brew/apt install nginx postgresql redis`
+
+---
+
+## ⚠️ Security Risks
+1. **Phishing** – fake sites; prevent with HTTPS & verification
+2. **Data Theft** – unauthorized access; prevent with encryption & access control
+3. **SQL Injection** – malicious input; prevent with prepared statements
+4. **XSS** – script injection; prevent with output encoding
+5. **Session Hijacking** – stolen sessions; prevent with secure cookies & HTTPS
+6. **DoS/DDoS** – overload server
+7. **CSRF** – trick users; prevent with CSRF tokens
+8. **File Inclusion** – LFI/RFI attacks
+
+---
+
+## 🛡️ Protection
+**Encryption:** HTTPS/TLS, data-at-rest encryption
+**Auth:** MFA, strong passwords, RBAC
+**Validation:** Input validation, prepared statements, output encoding
+**Sessions:** HTTP-only, Secure cookies, session regeneration
+**Headers:** CSP, X-Frame-Options, X-XSS-Protection, HSTS
+**Monitoring:** Logging, audits, intrusion detection
+**Updates:** Software patching, dependency management
+**Prepared Statement Example:**
+```php
+$stmt = $pdo->prepare("SELECT * FROM users WHERE email = ?");
+$stmt->execute([$email]);
+$user = $stmt->fetch();
+```
+
+---
+
+## ✅ Best Practices
+* Validate & sanitize input
+* Use prepared statements
+* Enforce HTTPS
+* Strong auth (MFA, secure passwords)
+* Security headers
+* Keep software updated
+* Monitor & log activity
+* Least privilege
+* Regular audits & pentests
+* Backup & recovery
+---
+
+## 📚 Resources
+* [OWASP Top 10](https://owasp.org/www-project-top-ten/)
+* [PHP Security](https://www.php.net/manual/en/security.php)
+* [Mozilla Web Security](https://infosec.mozilla.org/guidelines/web_security)
+* [CWE](https://cwe.mitre.org/)