Function server_mpvio_write_packet

phx_percona/percona/sql/sql_acl.cc:11029–11055

vio->write_packet() callback method for server authentication plugins This function is called by a server authentication plugin, when it wants to send data to the client. It transparently wraps the data into a handshake packet, and handles plugin negotiation with the client. If necessary, it escapes the plugin data, if it starts with a mysql protocol packet byte. */

  it escapes the plugin data, if it starts with a mysql protocol packet byte.
*/
static int server_mpvio_write_packet(MYSQL_PLUGIN_VIO *param,
                                   const uchar *packet, int packet_len)
{
  MPVIO_EXT *mpvio= (MPVIO_EXT *) param;
  int res;

  DBUG_ENTER("server_mpvio_write_packet");
  /* 
    Reset cached_client_reply if not an old client doing mysql_change_user, 
    as this is where the password from COM_CHANGE_USER is stored.
  */
  if (!((!(mpvio->client_capabilities & CLIENT_PLUGIN_AUTH)) && 
        mpvio->status == MPVIO_EXT::RESTART &&
        mpvio->cached_client_reply.plugin == 
        ((st_mysql_auth *) (plugin_decl(mpvio->plugin)->info))->client_auth_plugin
        ))
    mpvio->cached_client_reply.pkt= 0;
  /* for the 1st packet we wrap plugin data into the handshake packet */
  if (mpvio->packets_written == 0)
    res= send_server_handshake_packet(mpvio, (char*) packet, packet_len);
  else if (mpvio->status == MPVIO_EXT::RESTART)
    res= send_plugin_request_packet(mpvio, packet, packet_len);
  else
    res= wrap_plguin_data_into_proper_command(mpvio->net, packet, packet_len);
  mpvio->packets_written++;
  DBUG_RETURN(res);
}

/**
  vio->read_packet() callback method for server authentication plugins