Function send_plugin_request_packet

phx_percona/percona/sql/sql_acl.cc:10016–10090

sends a "change plugin" packet, requesting a client to restart authentication using a different authentication plugin Packet format: Bytes Content ----- ---- 1 byte with the value 254 n client plugin to use, \0-terminated n plugin provided data In a special case of switching from native_password_plugin to old_password_plug

  @retval 1 error
*/
static bool send_plugin_request_packet(MPVIO_EXT *mpvio,
                                       const uchar *data, uint data_len)
{
  DBUG_ASSERT(mpvio->packets_written == 1);
  DBUG_ASSERT(mpvio->packets_read == 1);
  NET *net= mpvio->net;
  static uchar switch_plugin_request_buf[]= { 254 };

  DBUG_ENTER("send_plugin_request_packet");
  mpvio->status= MPVIO_EXT::FAILURE; // the status is no longer RESTART

  const char *client_auth_plugin=
    ((st_mysql_auth *) (plugin_decl(mpvio->plugin)->info))->client_auth_plugin;

  DBUG_ASSERT(client_auth_plugin);

  /*
    we send an old "short 4.0 scramble request", if we need to request a
    client to use 4.0 auth plugin (short scramble) and the scramble was
    already sent to the client

    below, cached_client_reply.plugin is the plugin name that client has used,
    client_auth_plugin is derived from mysql.user table, for the given
    user account, it's the plugin that the client need to use to login.
  */
  bool switch_from_long_to_short_scramble=
    native_password_plugin_name.str == mpvio->cached_client_reply.plugin &&
    client_auth_plugin == old_password_plugin_name.str;

  if (switch_from_long_to_short_scramble)
    DBUG_RETURN (secure_auth(mpvio) ||
                 my_net_write(net, switch_plugin_request_buf, 1) ||
                 net_flush(net));

  /*
    We never request a client to switch from a short to long scramble.
    Plugin-aware clients can do that, but traditionally it meant to
    ask an old 4.0 client to use the new 4.1 authentication protocol.
  */
  bool switch_from_short_to_long_scramble=
    old_password_plugin_name.str == mpvio->cached_client_reply.plugin && 
    client_auth_plugin == native_password_plugin_name.str;

  if (switch_from_short_to_long_scramble)
  {
    my_error(ER_NOT_SUPPORTED_AUTH_MODE, MYF(0));
    general_log_print(current_thd, COM_CONNECT, ER(ER_NOT_SUPPORTED_AUTH_MODE));
    DBUG_RETURN (1);
  }

  /*
    If we're dealing with an older client we can't just send a change plugin
    packet to re-initiate the authentication handshake, because the client 
    won't understand it. The good thing is that we don't need to : the old client
    expects us to just check the user credentials here, which we can do by just reading
    the cached data that are placed there by parse_com_change_user_packet() 
    In this case we just do nothing and behave as if normal authentication
    should continue.