Example: Stream Wrappers in Examples for Developers 3.x

Same name and namespace in other branches

1. 8 stream_wrapper_example/stream_wrapper_example.module \stream_wrapper_example

@group stream_wrapper_example

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:

        tags:
          - { name: stream_wrapper, scheme: session }

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/SessionStreamWrapper.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 also

http://php.net/manual/en/intro.stream.php.

core/lib/Drupal/Core/StreamWrapper/StreamWrapperInterface.php

Parent topics

File

modules/stream_wrapper_example/stream_wrapper_example.module, line 8

Contains the module file for the Stream Wrapper Example.

Classes