edlp_d8/sites/all/modules/examples/examples/stream_wrapper_example/stream_wrapper_example.module

<?php

/**
 * @file
 * Contains the module file for the Stream Wrapper Example.
 */

/**
 * @defgroup stream_wrapper_example Example: Stream Wrappers
 * @group stream_wrapper_example
 * @ingroup examples
 * @{
 * Example demonstrating how to implement stream wrappers in Drupal.
 *
 * The Stream Wrapper Example module is part of the Examples for Developers
 * Project and provides a variety of examples for the Developers project page.
 * We demonstrate how to create a "pseudo file system" using PHP's stream
 * wrapper features, similar to what Drupal does to support the public://
 * private:// and temporary:// schemes.
 *
 * When we write a stream URI like "public://README.md", we can divide that URI
 * into two parts:
 *
 *   - The "scheme" name ("public" in this case).
 *   - The "target", in this case "README.md".
 *
 * Many PHP and Drupal file functions can take a stream URI and treat it almost
 * exactly like a file path.  Because they behave so much like files, if you
 * want to know how to use a stream URI, you should also look at the File
 * Example.  The Stream Wrapper Example is designed to work together with
 * that example, and if you enable both examples, the two will work seamlessly
 * together.  This is all most developers need to know about stream wrappers.
 *
 * This example shows how to actually implement a new scheme. We demonstrate
 * a rather unpractical scheme, but one that covers most of what you can do
 * with a stream type in Drupal 8. We take the session object that is put up
 * in each web request, and we treat one of the session variables as if it were
 * a file system with directories and files. This code is for demonstration
 * purposes only, since this not something you would ever want to do on a
 * production web site. But the example is simple enough that we don't need
 * any external libraries, as one might need to create a stream over
 * Amazon Web Services S3 service, or other services you might use to store
 * files on a web site. Yet most of what you need to do in order to make a
 * stream implementation like that we will do in our "session" scheme.
 *
 * To implement a stream wrapper in Drupal, you should do the following:
 *
 *  1. Create a class that implements the StreamWrapperInterface
 *     (Drupal\Core\StreamWrapper\StreamWrapperInterface).
 *
 *  2. Register the class with Drupal.  The best way to do this is to
 *     define a service in your MY_MODULE.services.yml file.  The
 *     service needs to be "tagged" with the scheme you want to implement,
 *     and, as so:
 *
 * @code
 *         tags:
 *           - { name: stream_wrapper, scheme: session }
 * @endcode
 *      See stream_wrapper_example.services.yml for an example.
 *
 *  3. (Optional) If you want to be able to access your files over the web,
 *     you need to add a route that handles, and implement hook_file_download().
 *     See stream_wrapper_example.routing.yml for an example of this, and
 *     file_example.module for the hook implementation.
 *
 * In our example, the key files to look at are:
 *
 *  - src/StreamWrapper/FileExampleSessionStreamWrapper.php (the stream wrapper
 *    class).
 *  - src/PathProcessorSessions.php, which implements something called a "path
 *    processor".
 *    A path processor is a class that lets us hook the "files" in a scheme's
 *    file system into Drupal 8's routing system. This allows us to assign
 *    external URLs to the files served out of the stream wrapper class. Like a
 *    stream wrapper class, Drupal 8 implements this as a "tagged service".
 *  - stream_wrapper_example.services.yml, which defines the services we need to
 *    do all this magic. You should read the comments in that file to see how
 *    this fits together.
 *
 * We also include two PHPUnit tests. Because stream wrappers require quite a
 * bit of code that gets called "behind our back" by PHP itself, good test
 * coverage is essential for writing usable stream wrapper implementations. The
 * tests should help get you started on that.
 *
 * @see http://php.net/manual/en/intro.stream.php.
 * @see core/lib/Drupal/Core/StreamWrapper/StreamWrapperInterface.php
 */

/**
 * @} End of "defgroup stream_wrapper_example".
 */

/**
 * Implements hook_theme().
 *
 * Since we have a lot to explain, we're going to use Twig to do it.
 */
function stream_wrapper_example_theme() {
  return [
    'example_description' => [
      'template' => 'description',
      'variables' => [
        'admin_link' => NULL,
      ],
    ],
  ];
}