file_example.module

<?php


/**
 * @file
 * Examples demonstrating the Drupal File API.
 */
use Drupal\Core\StreamWrapper\StreamWrapperManager;

/**
 * Implements hook_file_download().
 *
 * @see file_example.routing.yml
 */
function file_example_file_download($uri) {
    $scheme = StreamWrapperManager::getScheme($uri);
    if (in_array($scheme, [
        'private',
        'temporary',
        'session',
    ])) {
        // @see file_example.permissions.yml
        $permission = "read {$scheme} files";
        $current_user = \Drupal::currentUser();
        $account = $current_user->getAccount();
        if ($account->hasPermission($permission)) {
            // If the user has permission, return an array with the appropriate
            // headers.
            // @see hook_file_download()
            return [
                'Content-Type: text/plain',
            ];
        }
    }
    // If the user does not have permission to access the file, return -1.
    // @see hook_file_download()
    return -1;
}