Drupal 7 Module Development

Working with Files and Images
Creating a stream wrapper
In this example we are going to create a stream wrapper to retrieve photos from
Twitpic, an image hosting service for Twitter users. Twitpic defines a REST API
to retrieve photos from the URL http://twitpic.com/show//
where size is either mini or thumb, and image-id is a unique identifier you can
retrieve from a photo's URL, as seen in the following screenshot:
The full Twitpic API is defined at http://twitpic.com/api.do
So you can retrieve the thumbnail of this photo from the URL http://twitpic.
com/show/thumb/7nyr2. This makes it very easy to refer to photos from Twitpic
in your code. However, if this URL format should change, then you could end up
with a lot of code to clean up. We can mitigate this by writing a stream wrapper
that encapsulates this logic in one place. This stream wrapper will use the format
twitpic:///.
There are two things that we need to do to create a custom stream wrapper in
Drupal. First, we need to create a custom class which implements our functionality,
then we need to register the class using hook_stream_wrappers().
PHP defines a set of functions that stream wrappers can implement, as listed at
http://www.php.net/manual/en/class.streamwrapper.php. Drupal expanded
on that list and created an interface called DrupalStreamWrapperInterface. Any
stream wrapper class used in Drupal must implement this interface or else it will
not register properly.
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