HTTP & the PHP Request Lifecycle

What you'll learn

Every PHP web application is a machine that turns an HTTP request into an HTTP response. Once that model is clear, frameworks stop feeling magical.

• Identify the four parts of an HTTP request and response
• Read method, path, and headers through PHP
• Send correct status codes, content types, and bodies
• Explain document roots and PHP's role behind a web server
• Route several URLs through one front controller

The HTTP model

HTTP is a stateless request/response protocol. A client sends one request; a server returns one response. The browser may make many additional requests for CSS, JavaScript, fonts, images, and API data.

Read the incoming request

PHP exposes web-server data through $_SERVER. Keys can vary by server, so read optional values defensively. parse_url() separates the route path from its query string.

<?php

declare(strict_types=1);

$method = $_SERVER['REQUEST_METHOD'] ?? 'GET';
$path = parse_url($_SERVER['REQUEST_URI'] ?? '/', PHP_URL_PATH);
$accept = $_SERVER['HTTP_ACCEPT'] ?? '*/*';

echo "Method: {$method}" . PHP_EOL;
echo "Path: {$path}" . PHP_EOL;
echo "Accept: {$accept}";

Build a precise response

A professional response aligns three things: its status code describes the outcome, its headers describe the body, and the body follows that declared format.

<?php

declare(strict_types=1);

header('Content-Type: application/json; charset=utf-8');
http_response_code(201);

$response = [
    'data' => [
        'id' => 42,
        'title' => 'Learn HTTP',
    ],
];

echo json_encode($response, JSON_THROW_ON_ERROR);

Web server, document root, and PHP

The web server accepts the connection, serves static files directly, and passes PHP requests to the PHP runtime. The document root is the public directory the server exposes. Application source, secrets, and writable storage should sit outside it whenever possible.

project/
├── public/           # document root
│   └── index.php     # public entry point
├── src/              # application code
├── templates/        # views
├── storage/          # logs and generated files
└── vendor/           # Composer dependencies

Route through a front controller

A front controller gives every dynamic request one entry point. It centralizes startup, error handling, sessions, middleware, and routing.

<?php

declare(strict_types=1);

$method = $_SERVER['REQUEST_METHOD'] ?? 'GET';
$path = parse_url($_SERVER['REQUEST_URI'] ?? '/', PHP_URL_PATH);

$route = "{$method} {$path}";

match ($route) {
    'GET /' => print '<h1>PHP Web Foundations</h1>',
    'GET /health' => print 'OK',
    default => (function (): void {
        http_response_code(404);
        echo '<h1>Page not found</h1>';
    })(),
};

Practice challenge

Add GET /api/status to the front controller. Return status 200, a JSON content type, and an object containing status and the current UTC time. Verify an unknown route still returns 404.

Recap & quick check