如何在PHP中使用用户输入和输出函数进行文件上传和下载的安全控制？

$allowedExtensions = ['jpg', 'png', 'gif'];
$allowedMimeTypes = ['image/jpeg', 'image/png', 'image/gif'];

$uploadedFileExtension = strtolower(pathinfo($_FILES['file']['name'], PATHINFO_EXTENSION));
$uploadedFileType = $_FILES['file']['type'];

if (!in_array($uploadedFileExtension, $allowedExtensions) || !in_array($uploadedFileType, $allowedMimeTypes)) {
    // 文件类型不合法，进行处理逻辑
}

$uploadedFileName = $_FILES['file']['name'];
$uploadedFileExtension = strtolower(pathinfo($uploadedFileName, PATHINFO_EXTENSION));

$newFileName = uniqid().'.'.$uploadedFileExtension;
$newFilePath = '/path/to/upload/directory/'.$newFileName;

if (move_uploaded_file($_FILES['file']['tmp_name'], $newFilePath)){
    // 文件上传成功
}

$fileData = file_get_contents($_FILES['file']['tmp_name']);

if (!is_image($fileData)){
    // 文件不是真实图片，进行处理逻辑
}

function is_image($fileData){
    $allowedMimeTypes = ['image/jpeg', 'image/png', 'image/gif'];

    if (function_exists('mime_content_type')) {
        $fileMimeType = mime_content_type($fileData);
        return in_array($fileMimeType, $allowedMimeTypes);
    } else {
        $finfo = new finfo(FILEINFO_MIME_TYPE);
        $fileMimeType = $finfo->buffer($fileData);
        return in_array($fileMimeType, $allowedMimeTypes);
    }
}

$requestedFilePath = $_GET['file'];

if (!is_file($requestedFilePath) || !is_readable($requestedFilePath)){
    // 文件不存在或不可读，进行处理逻辑
}

header("Content-Type: application/octet-stream");
header("Content-Disposition: attachment; filename=".basename($requestedFilePath));
header("Content-Transfer-Encoding: binary");
header("Content-Length: ".filesize($requestedFilePath));

readfile($requestedFilePath);