What is HTTP?

Application layer protocol for data transfer in distributed information systems. Used for interaction between web clients (browsers) and web servers. Based on the "client-server" model.

Main principles of operation:

Client forms a request: Sends it to the server.
Server processes the request: Performs necessary actions.
Server sends a response: Contains the execution status and requested data.

Key characteristics:

Stateless: The server does not store information about previous client requests. Each request is independent. Cookies or other mechanisms are used to maintain state.
Request methods (HTTP methods/verbs): Define the type of action the client wants to perform on the server.
- GET: Retrieve a resource.
- POST: Send data to create or update a resource.
- PUT: Update or create a resource at the specified URI.
- DELETE: Remove a resource.
- PATCH: Partially update a resource.
- HEAD: Retrieve only response headers, similar to GET.
- OPTIONS: Get information about available methods for the resource.
Response status codes: Indicate the result of request processing by the server. Code groups:
- 1xx: Informational
- 2xx: Success
- 3xx: Redirection
- 4xx: Client error
- 5xx: Server error
Headers: Carry additional information about the request or response (content type, encoding, cookies, authorization, etc.).
Message Body: Contains data transmitted in the request (for POST, PUT, PATCH) or response.

Differences between HTTP and HTTPS:

HTTPS is HTTP over TLS/SSL. It provides data encryption and server authentication.

// Example of an HTTP GET request (simplified)
GET /index.html HTTP/1.1
Host: www.example.com
User-Agent: Mozilla/5.0

// Example of an HTTP response (simplified)
HTTP/1.1 200 OK
Content-Type: text/html; charset=UTF-8
Content-Length: 1234

<!DOCTYPE html>
<html>
<head><title>Example</title></head>
<body>...</body>
</html>