Render API callback: Validates the allowed file extensions field.
This function is assigned as an #element_validate callback in file_field_instance_settings_form().
This doubles as a convenience clean-up function and a validation routine. Commas are allowed by the end-user, but ultimately the value will be stored as a space-separated list for compatibility with file_validate_extensions().
function _file_generic_settings_extensions($element, &$form_state) {
if (!empty($element['#value'])) {
$extensions = preg_replace('/([, ]+\\.?)/', ' ', trim(strtolower($element['#value'])));
$extensions = array_filter(explode(' ', $extensions));
$extensions = implode(' ', array_unique($extensions));
if (!preg_match('/^([a-z0-9]+([.][a-z0-9])* ?)+$/', $extensions)) {
form_error($element, t('The list of allowed extensions is not valid, be sure to exclude leading dots and to separate extensions with a comma or space.'));
}
else {
form_set_value($element, $extensions, $form_state);
}
}
}