Php

PHP

Related Skills

Overview

PHP is a general-purpose scripting language especially suited to server-side web development. Current version: 8.4 (LTS: 8.2).

Key principles:

• declare(strict_types=1); in every file
• Type declarations on all parameters, return values, and properties
• Follow PSR standards wherever possible
• Security by default: validate input, escape output, parameterize queries

PHP-FIG / PSR Standards

Framework-interoperable standards. Adopt wherever possible.

PSR-4 Autoloading (composer.json)

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{
    "autoload": {
        "psr-4": {
            "App\\": "src/"
        }
    }
}

App\Service\OrderService maps to src/Service/OrderService.php

Modern PHP Features (8.0 - 8.4)

Constructor Promotion (8.0)

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class Product
{
    public function __construct(
        public readonly string $name,
        public readonly int $price,
    ) {}
}

Named Arguments (8.0)

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$response = new JsonResponse(
    data: ['status' => 'ok'],
    status: 201,
    headers: ['X-Custom' => 'value'],
);

Match Expression (8.0)

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$label = match ($status) {
    Status::Active => 'Active',
    Status::Pending => 'Pending',
    Status::Inactive, Status::Archived => 'Inactive',
    default => throw new \UnexpectedValueException("Unknown status: {$status->value}"),
};

Enums (8.1)

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enum Status: string
{
    case Active = 'active';
    case Inactive = 'inactive';
    case Pending = 'pending';

    public function label(): string
    {
        return match ($this) {
            self::Active => 'Active',
            self::Inactive => 'Inactive',
            self::Pending => 'Pending',
        };
    }

    public function isEditable(): bool
    {
        return $this !== self::Inactive;
    }
}

// Usage:
$status = Status::from('active');       // throws on invalid
$status = Status::tryFrom('unknown');   // returns null
$allCases = Status::cases();            // array of all cases

Readonly Properties and Classes (8.1 / 8.2)

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// Readonly property
class Money
{
    public function __construct(
        public readonly int $amount,
        public readonly string $currency,
    ) {}
}

// Readonly class (8.2) -- all properties implicitly readonly
readonly class Coordinate
{
    public function __construct(
        public float $lat,
        public float $lng,
    ) {}
}

Intersection and Union Types (8.1 / 8.2)

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// Union types (8.0)
function parse(string|int $value): string { /* ... */ }

// Intersection types (8.1)
function process(Countable&Iterator $collection): void { /* ... */ }

// DNF types (8.2)
function handle((Countable&Iterator)|null $collection): void { /* ... */ }

// true, false, null as standalone types (8.2)
function alwaysTrue(): true { return true; }

Fibers (8.1)

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$fiber = new Fiber(function (): void {
    $value = Fiber::suspend('first');
    echo "Resumed with: {$value}\n";
    Fiber::suspend('second');
});

$first = $fiber->start();           // 'first'
$second = $fiber->resume('hello');  // 'second'

PHP Attributes (8.0)

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#[\Attribute(\Attribute::TARGET_METHOD)]
class Route
{
    public function __construct(
        public readonly string $path,
        public readonly string $method = 'GET',
    ) {}
}

class UserController
{
    #[Route('/users', method: 'GET')]
    public function list(): Response { /* ... */ }
}

// Read via Reflection:
$method = new \ReflectionMethod(UserController::class, 'list');
$attributes = $method->getAttributes(Route::class);
foreach ($attributes as $attr) {
    $route = $attr->newInstance();
}

Property Hooks (8.4)

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class User
{
    public string $name {
        set(string $value) => trim($value);
    }

    public string $fullName {
        get => "{$this->firstName} {$this->lastName}";
    }
}

Asymmetric Visibility (8.4)

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class Counter
{
    public private(set) int $count = 0;

    public function increment(): void
    {
        $this->count++;
    }
}

Type System

declare(strict_types=1)

Always the first statement in every PHP file.

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<?php

declare(strict_types=1);

function add(int $a, int $b): int
{
    return $a + $b;
}

add(1, 2);     // OK
add(1.5, 2);   // TypeError

Type-Safe Comparisons

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// Always strict
$a === $b;   // strict
$a == $b;    // NEVER -- loose comparison hides bugs

// Never use empty() -- explicit checks instead
count($items) > 0;     // not !empty($items)
$name !== '';           // not !empty($name)
$count !== 0;           // not !empty($count)
$value === null;        // not empty($value)

OOP Patterns

Interfaces

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interface PaymentGateway
{
    public function charge(Money $amount, string $token): PaymentResult;
    public function refund(string $transactionId): PaymentResult;
}

Final Classes (Value Objects, DTOs)

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final class EmailAddress
{
    public function __construct(
        public readonly string $value,
    ) {
        if (filter_var($value, FILTER_VALIDATE_EMAIL) === false) {
            throw new \InvalidArgumentException("Invalid email: {$value}");
        }
    }
}

Late Static Binding

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abstract class BaseFactory
{
    public static function create(array $data): static
    {
        return new static($data); // static = calling class
    }
}

Security

Secure File Inclusion (LFI/RFI Prevention)

Never pass user input to include / require.

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// DANGEROUS -- Local File Inclusion
include $_GET['page'] . '.php';

// SAFE -- whitelist approach
$allowed = [
    'dashboard' => 'pages/dashboard.php',
    'profile' => 'pages/profile.php',
];
$page = $allowed[$_GET['page']] ?? 'pages/404.php';
include $page;

// SAFE -- realpath validation
$base = realpath(__DIR__ . '/templates');
$path = realpath(__DIR__ . '/templates/' . $_GET['tpl']);
if ($path === false || !str_starts_with($path, $base)) {
    throw new \RuntimeException('Invalid template path');
}
include $path;

php.ini hardening:

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allow_url_include = Off    ; Prevents Remote File Inclusion
open_basedir = /var/www     ; Restricts file access

SQL Injection Prevention

Always use prepared statements.

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$stmt = $pdo->prepare('SELECT * FROM users WHERE email = :email AND active = :active');
$stmt->bindValue(':email', $email, PDO::PARAM_STR);
$stmt->bindValue(':active', true, PDO::PARAM_BOOL);
$stmt->execute();
$user = $stmt->fetch(PDO::FETCH_ASSOC);

// PDO connection with security options
$pdo = new PDO($dsn, $user, $pass, [
    PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
    PDO::ATTR_EMULATE_PREPARES => false,       // Real prepared statements
    PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
]);

• EMULATE_PREPARES => false forces real driver-level prepared statements
• Table/column names cannot be parameterized -- whitelist explicitly
• bindValue binds at call time (preferred). bindParam binds a variable reference

XSS Prevention

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// HTML body
echo htmlspecialchars($userInput, ENT_QUOTES | ENT_SUBSTITUTE, 'UTF-8');

// JavaScript context
echo json_encode($data, JSON_HEX_TAG | JSON_HEX_AMP | JSON_HEX_APOS | JSON_HEX_QUOT);

// URL parameter
echo urlencode($value);

CSRF Protection

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// Generate token
$_SESSION['csrf_token'] = bin2hex(random_bytes(32));

// Embed in form
echo '<input type="hidden" name="csrf_token" value="' . $_SESSION['csrf_token'] . '">';

// Validate -- constant-time comparison
if (!hash_equals($_SESSION['csrf_token'], $_POST['csrf_token'] ?? '')) {
    throw new \RuntimeException('CSRF validation failed');
}

Session Security

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ini_set('session.cookie_httponly', '1');
ini_set('session.cookie_secure', '1');
ini_set('session.cookie_samesite', 'Lax');
ini_set('session.use_strict_mode', '1');
ini_set('session.use_only_cookies', '1');

session_start();
session_regenerate_id(true); // ALWAYS after login

Password Hashing

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// Hash -- auto-salted, secure
$hash = password_hash($password, PASSWORD_DEFAULT, ['cost' => 12]);

// Or Argon2id (PHP 7.3+)
$hash = password_hash($password, PASSWORD_ARGON2ID);

// Verify
if (!password_verify($inputPassword, $storedHash)) {
    throw new AuthenticationException('Invalid credentials');
}

// Rehash when algorithm/cost changes
if (password_needs_rehash($storedHash, PASSWORD_DEFAULT, ['cost' => 12])) {
    $newHash = password_hash($inputPassword, PASSWORD_DEFAULT, ['cost' => 12]);
}

Never use md5(), sha1(), sha256() for passwords.

File Upload Security

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// 1. Validate MIME via finfo (not client Content-Type)
$finfo = new finfo(FILEINFO_MIME_TYPE);
$mimeType = $finfo->file($_FILES['upload']['tmp_name']);
if (!in_array($mimeType, ['image/jpeg', 'image/png', 'image/webp'], true)) {
    throw new \RuntimeException('Invalid file type');
}

// 2. Whitelist extensions
$ext = strtolower(pathinfo($_FILES['upload']['name'], PATHINFO_EXTENSION));
if (!in_array($ext, ['jpg', 'jpeg', 'png', 'webp'], true)) {
    throw new \RuntimeException('Invalid extension');
}

// 3. Random filename -- NEVER use the original
$filename = bin2hex(random_bytes(16)) . '.' . $ext;

// 4. Move to non-public directory
move_uploaded_file($_FILES['upload']['tmp_name'], '/var/app/uploads/' . $filename);

Input Validation

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$email = filter_input(INPUT_POST, 'email', FILTER_VALIDATE_EMAIL);
if ($email === false) {
    throw new \InvalidArgumentException('Invalid email');
}

$age = filter_var($_POST['age'], FILTER_VALIDATE_INT, [
    'options' => ['min_range' => 1, 'max_range' => 150],
]);

Cryptographic Randomness

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$token = bin2hex(random_bytes(32));     // secure
$code = random_int(100000, 999999);     // secure

// NEVER for security: rand(), mt_rand(), uniqid()

Dangerous Functions

Security Headers

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header('X-Content-Type-Options: nosniff');
header('X-Frame-Options: DENY');
header('Strict-Transport-Security: max-age=31536000; includeSubDomains');
header('Referrer-Policy: strict-origin-when-cross-origin');
header('Permissions-Policy: camera=(), microphone=(), geolocation=()');

OWASP Top 10 -- PHP Quick Reference

Error Handling

Production Configuration

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display_errors = Off
display_startup_errors = Off
log_errors = On
error_log = /var/log/php/error.log
error_reporting = E_ALL
expose_php = Off

Exception Hierarchy

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class OrderNotFoundException extends \RuntimeException {}
class InsufficientStockException extends \DomainException {}

try {
    $order = $this->orderService->findOrFail($id);
} catch (OrderNotFoundException $e) {
    return new Response('Order not found', 404);
}

Common Patterns

Null Coalescing

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$name = $_GET['name'] ?? 'default';
$this->cache ??= new ArrayCache();

Array Functions

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$active = array_filter($users, fn (User $u) => $u->isActive());
$names = array_map(fn (User $u) => $u->getName(), $users);
$total = array_reduce($items, fn (int $sum, Item $i) => $sum + $i->getPrice(), 0);

String Functions

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str_starts_with($path, '/api/');
str_ends_with($file, '.php');
str_contains($text, 'keyword');
$msg = sprintf('User %s (ID: %d) logged in', $name, $id);

Date and Time

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// Always DateTimeImmutable (not DateTime)
$now = new \DateTimeImmutable();
$tomorrow = $now->modify('+1 day');
$formatted = $now->format('Y-m-d H:i:s');
$date = \DateTimeImmutable::createFromFormat('d.m.Y', '19.04.2026');

Composer

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composer require vendor/package         # install
composer require --dev vendor/package   # dev dependency
composer update vendor/package          # update single
composer audit                          # check vulnerabilities
composer dump-autoload --optimize       # production autoloader

Static Analysis

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vendor/bin/phpstan analyse src/ --level=max
vendor/bin/php-cs-fixer fix src/

Safe PHP (thecodingmachine/safe)

PHP's standard library returns false on error for hundreds of functions (file_get_contents, json_encode, preg_match, etc.). This is easy to miss and leads to silent failures. thecodingmachine/safe provides drop-in replacements that throw exceptions instead.

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composer require thecodingmachine/safe
composer require --dev thecodingmachine/phpstan-safe-rule

PHPStan configuration (phpstan.neon):

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includes:
    - vendor/thecodingmachine/phpstan-safe-rule/phpstan-safe-rule.neon

The PHPStan rule reports any usage of native PHP functions that have a Safe equivalent, enforcing the switch.

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// ❌ Bad — returns false on error, easy to miss
$content = file_get_contents('config.json');
$data = json_decode($content);

// ✅ Good — throws exceptions on error
use function Safe\file_get_contents;
use function Safe\json_decode;

$content = file_get_contents('config.json');  // throws FilesystemException
$data = json_decode($content);                // throws JsonException

Safe also provides Safe\DateTimeImmutable whose methods throw instead of returning false. For migrating existing codebases, Safe ships a Rector config (vendor/thecodingmachine/safe/rector-migrate.php) that rewrites native calls automatically.

Common Gotchas

1. Forget declare(strict_types=1) -- PHP silently coerces types without it.
2. empty() lies -- empty('0') is true, empty(0) is true. Use explicit checks.
3. == vs === -- 0 == 'foo' has surprising results. Always use ===.
4. in_array without strict -- in_array('0', [false]) is true. Always: in_array($val, $arr, true).
5. json_encode fails silently -- Returns false. Use JSON_THROW_ON_ERROR.
6. DateTime is mutable -- modify() changes the original. Use DateTimeImmutable.
7. Autoload case sensitivity -- Linux is case-sensitive. UserService.php won't load as Userservice.
8. header() after output -- Headers before any output. Check for BOM, whitespace.
9. Float comparison -- Never === floats. Use abs($a - $b) < PHP_FLOAT_EPSILON.
10. str_replace chain -- Replaces in sequence, earlier results can be re-replaced. Use strtr().

Documentation References