The FakeEventTask called the actual DCB handler with a fake task but it
didn't set the fake event flag. This caused KILL queries to be treated as
if they were network errors.
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.
When fake hangup events are delivered via DCBs, the current DCB would not
be updated. This would cause error messages without a session ID which
makes failure analysis harder.
SSLContext is now used everywhere except the binlogrouter which still
allocates the contexts itself. Fixing the binlogrouter's misuse of
internal structures is a rather large undertaking and for this reason the
SSLContext will be taken into use there in a separate commit.
The code that selects which worker to assign the DCB to is now completely
in the Listener class. This removes the need to change the ownership of a
DCB after it has been allocated.
Given the assumption that queries are rarely 16MB long and that
realistically the only time that happens is during a large dump of data,
we can limit the size of a single read to at most one MariaDB/MySQL packet
at a time. This change allows the network throttling to engage a lot
sooner and reduces the maximum overshoot of throtting to 16MB.
The function allocated a constant-sized chunk of memory for all messages
which was excessive as well as potentially dangerous when used with large
strings.
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.
There is a race condition between the addition of the DCB into epoll and
the execution of the event that initiates the protocol pointer for the DCB
and sends the handshake to the client. If a hangup event would occur
before the handshake would be sent, it would be possible that the DCB
would get freed before the code that sends the handshake is executed.
By picking the worker who owns the DCB before the DCB is placed into the
owner's epoll instance, we make sure no events arrive on the DCB while the
control is transferred from the accepting worker to the owning
worker.
