// ========== V4 用户系统函数 ==========
if (session_status() == PHP_SESSION_NONE) { session_start(); }
function current_user_id() { return $_SESSION['user_id'] ?? 0; }
function current_user($pdo) {
    $uid = current_user_id();
    if (!$uid) return null;
    static $user = null;
    if ($user !== null) return $user;
    $stmt = $pdo->prepare("SELECT * FROM users WHERE id = ?");
    $stmt->execute([$uid]);
    $user = $stmt->fetch();
    return $user;
}
function is_user_logged_in() { return !empty($_SESSION['user_id']); }
function require_login() {
    if (!is_user_logged_in()) {
        header("Location: user_login.php?redirect=" . urlencode($_SERVER['REQUEST_URI']));
        exit;
    }
}
function hash_password($password) { return password_hash($password, PASSWORD_DEFAULT); }
function verify_password($password, $hash) { return password_verify($password, $hash); }

// ========== V4 安全函数 ==========
function is_ip_blacklisted($pdo, $ip) {
    $stmt = $pdo->prepare("SELECT id FROM ip_blacklist WHERE ip = ? AND (expires_at IS NULL OR expires_at > NOW())");
    $stmt->execute([$ip]);
    return $stmt->fetch() ? true : false;
}
function check_login_attempts($pdo, $ip) {
    $stmt = $pdo->prepare("SELECT COUNT(*) FROM login_attempts WHERE ip = ? AND success = 0 AND created_at > DATE_SUB(NOW(), INTERVAL 15 MINUTE)");
    $stmt->execute([$ip]);
    return $stmt->fetchColumn() >= 5;
}
function record_login_attempt($pdo, $username, $ip, $success) {
    $stmt = $pdo->prepare("INSERT INTO login_attempts (username, ip, success) VALUES (?, ?, ?)");
    $stmt->execute([$username, $ip, $success ? 1 : 0]);
}
function get_banners($pdo) {
    $stmt = $pdo->query("SELECT * FROM banners WHERE status = 1 ORDER BY sort ASC, id ASC");
    return $stmt->fetchAll();
}
<br />
<b>Fatal error</b>:  Uncaught Error: Call to undefined function current_user_id() in /www/wwwroot/dy.1br.cn/download.php:36
Stack trace:
#0 {main}
  thrown in <b>/www/wwwroot/dy.1br.cn/download.php</b> on line <b>36</b><br />