Function server_mpvio_read_packet

phx_percona/percona/sql/sql_acl.cc:11067–11154

vio->read_packet() callback method for server authentication plugins This function is called by a server authentication plugin, when it wants to read data from the client. It transparently extracts the client plugin data, if embedded into a client authentication handshake packet, and handles plugin negotiation with the client, if necessary. */

  with the client, if necessary.
*/
static int server_mpvio_read_packet(MYSQL_PLUGIN_VIO *param, uchar **buf)
{
  MPVIO_EXT *mpvio= (MPVIO_EXT *) param;
  ulong pkt_len;

  DBUG_ENTER("server_mpvio_read_packet");
  if (mpvio->packets_written == 0)
  {
    /*
      plugin wants to read the data without sending anything first.
      send an empty packet to force a server handshake packet to be sent
    */
    if (mpvio->write_packet(mpvio, 0, 0))
      pkt_len= packet_error;
    else
      pkt_len= my_net_read(mpvio->net);
  }
  else if (mpvio->cached_client_reply.pkt)
  {
    DBUG_ASSERT(mpvio->status == MPVIO_EXT::RESTART);
    DBUG_ASSERT(mpvio->packets_read > 0);
    /*
      if the have the data cached from the last server_mpvio_read_packet
      (which can be the case if it's a restarted authentication)
      and a client has used the correct plugin, then we can return the
      cached data straight away and avoid one round trip.
    */
    const char *client_auth_plugin=
      ((st_mysql_auth *) (plugin_decl(mpvio->plugin)->info))->client_auth_plugin;
    if (client_auth_plugin == 0 ||
        my_strcasecmp(system_charset_info, mpvio->cached_client_reply.plugin,
                      client_auth_plugin) == 0)
    {
      mpvio->status= MPVIO_EXT::FAILURE;
      *buf= (uchar*) mpvio->cached_client_reply.pkt;
      mpvio->cached_client_reply.pkt= 0;
      mpvio->packets_read++;
      DBUG_RETURN ((int) mpvio->cached_client_reply.pkt_len);
    }

    /* older clients don't support change of client plugin request */
    if (!(mpvio->client_capabilities & CLIENT_PLUGIN_AUTH))
    {
      mpvio->status= MPVIO_EXT::FAILURE;
      pkt_len= packet_error;
      goto err;
    }

    /*
      But if the client has used the wrong plugin, the cached data are
      useless. Furthermore, we have to send a "change plugin" request
      to the client.
    */
    if (mpvio->write_packet(mpvio, 0, 0))
      pkt_len= packet_error;
    else
      pkt_len= my_net_read(mpvio->net);
  }