The backend didn't expect AuthSwitchRequest packets in response to the
handshake response packets. This is allowed by the protocol and appears to
happen with at least MySQL 8.0.
If the client DCB of the session was passed into the function, it was
possible that the session pointer for it was already set to null. The
session pointer of an open DCB is never null but a client DCB's session
pointer can be null if accessed via the MXS_SESSION object.
This causes the connection failure to be counted as an authentication
failure instead of a connection error. The former never causes the host to
be blocked which effectively solves the problem for most cases. The only
case where this would not work is where the network buffer for a backend
DCB is full right after the connection is created.
The hangup and error handlers now have unique messages. Although the
behavior in the handlers is practically the same in both cases, the cause
of the error is not the same.
If a socket error is present, it is added to the error message. If an
error is present, it should clearly show the reason why the TCP socket was
closed.
The is_fake_event boolean helps distinguish fake events from real
ones. This makes figuring out the real source of hangup events easier.
The backend DCBs do not have to send hangups in the close protocol API
method. If the conditions for the hangup were true, the session was
already stopping meaning that the client DCB was already closed.
If an error is generated while a COM_CHANGE_USER is being done, it would
always use the sequence number 1. To properly handle this case and send
the correct sequence number, the COM_CHANGE_USER progress needs to be
tracked at the session level.
The information needs to be shared between the backend and client
protocols as the final OK to the COM_CHANGE_USER, with the sequence number
3, is the one that the backend server returns. Only after this response
has been received and routed to the client can the COM_CHANGE_USER
processing stop.
All GWBUF macros that address a single link in a chain are now
simple wrappers for equivalent gwbuf_link-functions.
Next step is to drop the macros and replace their use with calls
to the functions.
Added core functionality for UNIX domain sockets in servers. Currently the
address parameter accepts them both but a separate `socket` parameter is
needed.
If a DCB was closed and a hangup event was sent to it via
dcb_hangup_foreach shortly after it was closed, the DCB would still
receive it even if it was closed. To prevent this, events must only be
delivered to DCBs if they haven't been closed.
The protocol should not track the session state as the parsing is quite
expensive with the current code. This change is a workaround that enables
the parsing only when required. A proper way to handle this would be to do
all the response processing in one place thus avoiding the duplication of
work.
