When programmatically adding file field, how to set allowed file extensions?

Question

I'm trying to add a custom node type in hook_install() for my custom module. I've been able to add the fields I want but can't seem to find a way to set the allowed file extensions for file fields. (it defaults to .txt)

The example below shows how I create my file field. I have tried setting both allowed_file_extensions and file_extensions in the settings array but that does not seem to work.

How would I set the allowed file extensions for a file field?

    field_create_field(array(
        'field_name' => 'xxx_video',
        'type' => 'file',
        'settings' => array('allowed_file_extensions' => array('mp4', 'avi', 'mov', 'wmv', '3gp', 'mpeg', 'mpeg2', 'mkv')),
        'entity_type' => array('node'),
    ));
    field_create_instance(array(
      'field_name' => 'xxx_video',
      'required' => true,
      'entity_type' => 'node',
      'bundle' => 'xxx',
      'label' => t('Video'),
      'description' => t('Video to play in smartbox.'),
    ));

Answer 1

The allowed file extension settings are added to the field instance settings, rather than the global field settings.

The variable is called 'file_extensions' and not 'allowed_file_extensions'

It is also a textfield string value, rather than an array.

You could try something like:

field_create_field(array(
    'field_name' => 'xxx_video',
    'type' => 'file',
    'entity_type' => array('node'),
));
field_create_instance(array(
  'field_name' => 'xxx_video',
  'required' => true,
  'entity_type' => 'node',
  'bundle' => 'xxx',
  'label' => t('Video'),
  'settings' => array('file_extensions' => 'mp4, avi'),
  'description' => t('Video to play in smartbox.'),
));