def get_document_preview(user_name, intra_hash, file_name, size)
      response = @conn.get get_document_href(user_name, intra_hash, file_name), { :preview => size }
      if response.status == 200
        return [response.body, 'image/jpeg']
      end
      return nil, nil
    end
def get_document_preview(user_name, intra_hash, file_name, size)
      response = @conn.get get_document_href(user_name, intra_hash, file_name), { :preview => size }
      if response.status == 200
        return [response.body, 'image/jpeg']
      end
      return nil, nil
    end
Get the preview for a document belonging to a post.

 @param user_name
 @param intra_hash
 @param file_name
 @param size [String] requested preview size (allowed values: SMALL, MEDIUM, LARGE)
 @return the preview image and the content type `image/jpeg`