How to make post content (Description) mandatory or set minimum length in wordpress?

Hi I am trying to make the post content (Description) mandatory or set minimum length for the content in wordpress. How do I do that?

I was trying this.

function display_short_error_message($messages)
{

 global $post;
 $content = $post->post_content;
 if (str_word_count($content) < 100 ) {
 $error_message = 'Post Should be at Least 100 Words';
  add_settings_error('post_short_error', '', $error_message, 'error');
  settings_errors( 'post_short_error' );
  $post->post_status = 'draft';
  wp_update_post($post);
  return;
 }

return $messages;

}

add_action('post_updated_messages', 'display_short_error_message');

I want to show the error message only when user clicks on publish.

Please help. Thanks in advance.

via Chebli Mohamed