Bug #12944747: MYSQL PROXY CAN'T DISTINGUISH WIN-AUTH DATA

FROM OK PACKET
  
There's no reliable way (without knowing the protocol variants that each
plugin pair implements) to find out when does the authentication exchange
end.
The server is changed to send all the extra authentication packets that 
server plugins need to send prefixed with the \x1 command.

sql/sql_acl.cc

@@ -8820,24 +8820,18 @@ static ulong parse_client_handshake_packet(MPVIO_EXT *mpvio,
 
 
 /**
-  Make sure that when sending plugin supplued data to the client they
+  Make sure that when sending plugin supplied data to the client they
   are not considered a special out-of-band command, like e.g. 
-  \255 (error) or \254 (change user request packet).
-  To avoid this we send plugin data packets starting with one of these
-  2 bytes "wrapped" in a command \1. 
-  For the above reason we have to wrap plugin data packets starting with
-  \1 as well.
+  \255 (error) or \254 (change user request packet) or \0 (OK).
+  To avoid this the server will send all plugin data packets "wrapped" 
+  in a command \1.
+  Note that the client will continue sending its replies unrwapped.
 */
 
-#define IS_OUT_OF_BAND_PACKET(packet,packet_len) \
-  ((packet_len) > 0 && \
-   (*(packet) == 1 || *(packet) == 255 || *(packet) == 254))
-
 static inline int 
 wrap_plguin_data_into_proper_command(NET *net, 
                                      const uchar *packet, int packet_len)
 {
-  DBUG_ASSERT(IS_OUT_OF_BAND_PACKET(packet, packet_len));
   return net_write_command(net, 1, (uchar *) "", 0, packet, packet_len);
 }
 
@@ -8874,13 +8868,8 @@ static int server_mpvio_write_packet(MYSQL_PLUGIN_VIO *param,
     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 if (IS_OUT_OF_BAND_PACKET(packet, packet_len))
-    res= wrap_plguin_data_into_proper_command(mpvio->net, packet, packet_len);
   else
-  {
-    res= my_net_write(mpvio->net, packet, packet_len) ||
-         net_flush(mpvio->net);
-  }
+    res= wrap_plguin_data_into_proper_command(mpvio->net, packet, packet_len);
   mpvio->packets_written++;
   DBUG_RETURN(res);
 }