stream_get_filters — Retrieve list of registered filters
Returns an indexed array containing the name of all stream filters available on the running system.
Exemplo #1 Using stream_get_filters()
$streamlist = stream_get_filters();
Output will be similar to the following. Note: there may be more or fewer filters in your version of PHP.
Array (  => string.rot13  => string.toupper  => string.tolower  => string.base64  => string.quoted-printable )