HTTP, DNS, HTTPS

# HTTP: Client-Server protocol
✓ Client (browser) request bhejta hai
✓ Server response bhejta hai
✓ Stateless protocol � har request independent

# Request Method:
GET ✓ Data read karo (idempotent)
POST ✓ Naya resource create karo
PUT ✓ Resource update karo (full replacement)
PATCH ✓ Resource partially update karo
DELETE ✓ Resource delete karo

# Request Structure:
GET /api/users/123 HTTP/1.1
Host: api.example.com
Authorization: Bearer token123
Accept: application/json

# Response Structure:
HTTP/1.1 200 OK
Content-Type: application/json
Content-Length: 150

{"id": 123, "name": "Vaibhav"}

# Status Codes:
1xx: Informational (100 Continue)
2xx: Success (200 OK, 201 Created, 204 No Content)
3xx: Redirection (301 Moved, 302 Found, 304 Not Modified)
4xx: Client Error (400 Bad Request, 401 Unauthorized, 404 Not Found)
5xx: Server Error (500 Internal, 502 Bad Gateway, 503 Unavailable)

# DNS: Domain Name ✓ IP Address mapping
✓ google.com ? 142.250.185.78
✓ Humans ko domain yaad rehta hai, computers ko IP

# DNS Resolution Steps:
1. Browser cache check ✓ mila toh done
2. OS cache check ✓ mila toh done
3. Router cache check ✓ mila toh done
4. ISP DNS server ✓ Still nahi mila?
5. Root DNS server ? .com server batao
6. .com TLD server ✓ google.com ka authoritative server
7. Authoritative server ✓ IP address return karo
8. IP address browser ko mila ✓ Connection establish!

# DNS Record Types:
A ✓ Domain to IPv4 address
AAAA ✓ Domain to IPv6 address
CNAME ✓ Domain alias (www ✓ example.com)
MX ✓ Mail server
TXT ✓ Text records (SPF, DKIM)
NS ✓ Nameserver
PTR ✓ Reverse lookup (IP to domain)

# DNS is UDP-based (port 53)
✓ Fast, lightweight
✓ TCP use jab response > 512 bytes ho

# HTTPS = HTTP + SSL/TLS Encryption
✓ Data encrypted hota hai client-server ke beech
✓ Man-in-the-middle attack se protection

# SSL/TLS Handshake:
1. Client Hello: "Mujhe HTTPS chahiye, ye cipher suites support karte hain"
2. Server Hello: "Ye certificate hai, ye cipher suite select karo"
3. Client Verify: Certificate valid hai? (CA se verify)
4. Key Exchange: Session key banao (asymmetric se share karo)
5. Encrypted Communication: Symmetric encryption se data bhejo

# Certificate:
✓ Digital certificate jo server ki identity verify karta hai
✓ CA (Certificate Authority) issue karta hai
✓ Contains: Domain name, public key, expiry, CA signature

# Why HTTPS?
✓ Data encrypted � password, credit card safe
✓ Authentication � fake server se protection
✓ Data integrity � data tamper nahi hua
✓ SEO boost � Google HTTPS prefer karta hai

# HTTP vs HTTPS:
HTTP: Port 80, No encryption, Fast
HTTPS: Port 443, Encrypted, Slight overhead