Understanding HTTP and Web Communication

1. What is HTTP?

HTTP (HyperText Transfer Protocol) is the foundation of communication on the web. It is a request-response protocol used by clients (like browsers, mobile apps, and APIs) to communicate with servers.

How HTTP Works:

1. A client sends a request to a server.
2. The server processes the request and sends a response back.
3. The response includes a status code, headers, and optional data (like JSON).

---

2. HTTP Request Structure

An HTTP request consists of:

• Method (GET, POST, etc.)
• URL (The endpoint being requested)
• Headers (Metadata about the request)
• Body (Optional, used for sending data)

Example HTTP Request:

GET /books HTTP/1.1
Host: example.com
Accept: application/json

Example HTTP Request with Data (POST):

POST /books HTTP/1.1
Host: example.com
Content-Type: application/json

{
  "title": "Clean Code",
  "author": "Robert C. Martin"
}

---

3. HTTP Methods

HTTP defines different methods for interacting with resources:

Method	Description
GET	Retrieve data (Read)
POST	Create a new resource
PUT	Update/replace a resource
PATCH	Partially update a resource
DELETE	Remove a resource

Example API Endpoints:

Action	HTTP Method	Endpoint
Get all books	GET	/books
Get a specific book	GET	/books/:id
Create a new book	POST	/books
Update a book	PUT	/books/:id
Delete a book	DELETE	/books/:id

---

4. HTTP Response Structure

A server's response includes:

• Status Code (Indicates success or error)
• Headers (Metadata)
• Body (Contains requested data)

Example Response:

HTTP/1.1 200 OK
Content-Type: application/json

[
  { "id": 1, "title": "Clean Code", "author": "Robert C. Martin" }
]

---

5. HTTP Status Codes

Status codes indicate the result of a request.

Common Status Codes:

Code	Meaning
200 OK	Success
201 Created	Resource created
400 Bad Request	Invalid request from client
401 Unauthorized	Authentication required
403 Forbidden	Access denied
404 Not Found	Resource does not exist
500 Internal Server Error	Server failure

---

6. Headers in HTTP Requests and Responses

Headers provide metadata about a request or response.

Common Headers:

Header	Description
Content-Type	Specifies the format of the body (e.g., application/json)
Authorization	Used for authentication (e.g., API keys, JWT)
Accept	Specifies the response format the client expects
Cache-Control	Controls caching behavior

Example of Headers in an API Request:

GET /books HTTP/1.1
Host: example.com
Accept: application/json
Authorization: Bearer <token>

---

7. Testing HTTP Requests

You can test HTTP requests using:

• Postman (GUI tool)
• cURL (Command-line tool)
• Your browser (For simple GET requests)

Example cURL Request:

curl -X GET "https://example.com/books" -H "Accept: application/json"

---

8. Summary

• HTTP is the foundation of web communication.
• Clients make requests and servers send responses.
• Different HTTP methods (GET, POST, PUT, DELETE) define how we interact with APIs.
• Status codes indicate the result of the request.
• Headers help manage data format, authentication, and caching.

Next Lesson: Writing Your First RESTful API - "Hello World"