HTTP and Web Protocols

HTTP (HyperText Transfer Protocol) is the protocol that powers the World Wide Web. It defines how clients (browsers) request resources and how servers respond. Understanding HTTP is essential for anyone working with web applications, APIs, or cloud services.

How HTTP Works

HTTP is a request-response protocol built on top of TCP:

Client (Browser)              Server
       │                         │
       │── HTTP Request ────────>│
       │   GET /index.html       │
       │                         │
       │<── HTTP Response ───────│
       │   200 OK                │
       │   <html>...</html>      │

Key Characteristics

Stateless — Each request is independent; the server does not remember previous requests
Text-based — HTTP/1.1 messages are human-readable
Application layer — Operates at Layer 7 of the OSI model
Port 80 (HTTP) and Port 443 (HTTPS)

HTTP Methods

Method	Purpose	Safe	Idempotent
GET	Retrieve a resource	Yes	Yes
POST	Submit data to create a resource	No	No
PUT	Replace a resource entirely	No	Yes
PATCH	Partially update a resource	No	No
DELETE	Delete a resource	No	Yes
HEAD	Like GET but returns only headers	Yes	Yes
OPTIONS	Describes the communication options	Yes	Yes

Safe means the method does not modify server state. Idempotent means calling it multiple times produces the same result.

HTTP Request Structure

GET /api/users HTTP/1.1
Host: example.com
Accept: application/json
Authorization: Bearer eyJhbGci...
User-Agent: Mozilla/5.0

Component	Description
Method	The action to perform (GET, POST, etc.)
Path	The resource being requested (/api/users)
Version	HTTP version (HTTP/1.1, HTTP/2)
Headers	Metadata about the request
Body	Data sent with the request (POST, PUT, PATCH)

HTTP Response Structure

HTTP/1.1 200 OK
Content-Type: application/json
Content-Length: 85
Cache-Control: max-age=3600

{"users": [{"id": 1, "name": "Alice"}, {"id": 2, "name": "Bob"}]}

Component	Description
Status code	A three-digit code indicating the result
Headers	Metadata about the response
Body	The requested resource or data

HTTP Status Codes

Range	Category	Examples
1xx	Informational	100 Continue, 101 Switching Protocols
2xx	Success	200 OK, 201 Created, 204 No Content
3xx	Redirection	301 Moved Permanently, 302 Found, 304 Not Modified
4xx	Client error	400 Bad Request, 401 Unauthorised, 403 Forbidden, 404 Not Found, 429 Too Many Requests
5xx	Server error	500 Internal Server Error, 502 Bad Gateway, 503 Service Unavailable

Most Common Status Codes

Code	Meaning	When Used
200	OK	Successful request
201	Created	Resource successfully created (POST)
301	Moved Permanently	Resource has a new permanent URL
304	Not Modified	Cached version is still valid
400	Bad Request	Malformed or invalid request
401	Unauthorised	Authentication required
403	Forbidden	Authenticated but not authorised
404	Not Found	Resource does not exist
500	Internal Server Error	Unexpected server failure

HTTPS and TLS

HTTPS (HTTP Secure) encrypts HTTP traffic using TLS (Transport Layer Security):

HTTP and Web Protocols

HTTP and Web Protocols

How HTTP Works

Key Characteristics

HTTP Methods

HTTP Request Structure

HTTP Response Structure

HTTP Status Codes

Most Common Status Codes

HTTPS and TLS

The TLS Handshake

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