Request-Response Flow

Every time you type a URL or click a button, a request-response cycle happens. Let’s break it down into the exact steps it takes.

The Cycle (Step-by-Step)

1. DNS Lookup: The browser asks, “Where is google.com?” (DNS).
2. Establish Connection: The browser connects to the server’s IP address.
3. The HTTP Request: The browser sends a message (e.g., GET /index.html).
4. Server Logic: The server’s code runs and may talk to a database.
5. The HTTP Response: The server sends a message back (e.g., 200 OK + some HTML code).
6. Browser Renders: The browser turns the HTML code into the webpage you see.

ASCII Sequence Diagram

 Client (You)             Server (Them)
 |                            |
 |--- 1. "Get google.com" --->|
 |                            |
 |       2. Server works      |
 |       (Code & Database)    |
 |                            |
 |<-- 3. "Here's the HTML" ---|
 |                            |
 |   4. Page appears on screen|

What’s in a Request?

• Method: What the client wants to do (GET to read, POST to create, PUT to update, DELETE to remove).
• Headers: Metadata (e.g., “I am a Chrome browser”).
• Body: The actual data (e.g., your username and password).

What’s in a Response?

• Status Codes:
  • 2xx: Success (e.g., 200 OK)
  • 4xx: Client Error (e.g., 404 Not Found)
  • 5xx: Server Error (e.g., 500 Internal Server Error)
• Headers: Metadata (e.g., “This data is formatted as JSON”).
• Body: The data you requested (HTML, JSON, Images, etc.).

Next: Databases Basics