Sameer Borate has a new post to his site showing you how to create custom stream filters for use with the streams functionality already included in the PHP language. The streams handling provides a resource instance (filesystem, network connection, etc) that can be interacted with in a more standardized way.
In this post we will see how to create a custom stream filter. Streams, first introduced in PHP 4.3, provide an abstraction layer for file access. A number of different resources besides files – like network connections, compression protocols etc. can be regarded as “streams” of data which can be serially read and written to.
He shows how to get the current list of streams available and includes an example of one in use, the "string.strip_tags" filter. From there he shows the creation of a custom filter, one that replaces any URLs detected in a string with a string of
[--URL--]. He includes the code for the filter and shows how to register it using the stream_filter_register function. He also includes an example of it in use, grabbing the contents of the BBC site and having the filter automatically applied.