static int nntp_fetch_header(mailmessage * msg_info,
                             char ** result,
                             size_t * result_len)
{
    struct generic_message_t * msg;
    char * headers;
    size_t headers_length;
    int r;

    msg = msg_info->msg_data;

    if (msg->msg_message != NULL)
        return mailmessage_generic_fetch_header(msg_info,
                                                result, result_len);

    r = nntpdriver_head(msg_info->msg_session, msg_info->msg_index,
                        &headers, &headers_length);
    if (r != MAIL_NO_ERROR)
        return r;

    * result = headers;
    * result_len = headers_length;

    return MAIL_NO_ERROR;
}
static int nntp_fetch_header(mailmessage * msg_info,
			     char ** result,
			     size_t * result_len)
{
  struct generic_message_t * msg;
  char * headers;
  size_t headers_length;
  struct nntp_cached_session_state_data * cached_data;
  struct nntp_session_state_data * ancestor_data;
  int r;
  char filename[PATH_MAX];

  msg = msg_info->msg_data;

  if (msg->msg_message != NULL)
    return mailmessage_generic_fetch_header(msg_info,
        result, result_len);
  
  /* we try the cached message */
  
  cached_data = get_cached_session_data(msg_info);

  ancestor_data = get_ancestor_session_data(msg_info);

  snprintf(filename, PATH_MAX, "%s/%s/%i-header",
      cached_data->nntp_cache_directory,
      ancestor_data->nntp_group_name, msg_info->msg_index);

  r = generic_cache_read(filename, &headers, &headers_length);
  if (r == MAIL_NO_ERROR) {
    * result = headers;
    * result_len = headers_length;

    return MAIL_NO_ERROR;
  }

  /* we get the message through the network */

  r = nntpdriver_head(get_ancestor_session(msg_info), msg_info->msg_index,
		      &headers, &headers_length);
  if (r != MAIL_NO_ERROR)
    return r;

  /* we write the message cache */

  generic_cache_store(filename, headers, headers_length);

  * result = headers;
  * result_len = headers_length;

  return MAIL_NO_ERROR;
}