INTERMITTENTLY

Description
-----------
While nonblocking client is sending large packets, it is bound to happen that it
may get EWOULDBLOCK error. That means "resource temporarily available"  so the
client must  retry. Client has all that checks in place but the problem was
using the wrong API for error  checking on Window.

Fix
---
To retrieve the last error code from sockets, client must call WSAGetLastError()
instead of errno() API.  Refer the following text at
https://docs.microsoft.com/en-us/windows/win32/winsock/error-codes-errno-h-errno-and-wsagetlasterror-2

"
Error codes set by Windows Sockets are not made available through the
errno variable. Additionally, for the getXbyY class of functions, error
codes are not made available through the h_errno variable. The WSAGetLastError()
function is intended to provide a reliable way for a thread in a multithreaded
process to obtain per-thread error information.
"

Sidenote
--------
I also changed the storage of query string from std::stringstream to std::string
because test I found that test happened to fail on FreeBSD. Further
investigation revealed that it happened due to pointer ownership violation.
I was passing the stringstream.str().c_str() to the mysql_real_query_nonblocking
API. This query pointer is  ultimately pointed by write buffer in the
begin_packet_write_state() method.

 (*vec).iov_base = const_cast<uchar *>(packet);

Notice that begin_packet_write_state() is called once in the nonblocking
communication. That means (*vec).iov_base continues to point the
string that has gone out of scope. It results in change in the packet content
that server fails to  parse.

Replaced the stringstream to string to avoid passing temporary string value to
the API.

Testing
----------
Enabled the tests in mysql_client_test.test file.
Verified the result locally.

mysql-trunk-itch
push id: 16089846
Rahul Sisondia
2020-03-27 14:13:17

Review
-------
RB#24147