Request/Response Cycle

The request-response cycle describes how a client and server communicate.

1. The client sends a request to the server.
2. The server processes the request.
3. The server sends a response back to the client.

For example, when a user submits a form, the browser sends an HTTP request to the server. The server processes the submitted data and returns a response.

Example

HTML Form (Client Request)

<form method="post">
  <input type="text" name="username" placeholder="Enter your name" />
  <button type="submit">Submit</button>
</form>

php script (server Processing)

if ($_SERVER["REQUEST_METHOD"] === "POST") {

$username = $_POST["username"] ?? "Guest";

// Process the request
$message = "Hello, " . htmlspecialchars($username);

// Send response to the client
echo "<h2>$message</h2>";

}

What Happens

• The browser sends a POST request when the form is submitted.

• PHP reads the request data using $_POST.

• The server processes the data.

• The server sends back an HTML response that the browser displays.