WJT's "Miscellaneous bug and pyodbc compatibility fixes" + extra unicode fixes #14
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NamedTupleRow and MutableNamedTupleRow depend on _ColBufferList being populated, so without this change they do not work.
This is consistent with pyodbc.
I think out-of-the-box compatibility with pyodbc is a worthy goal. I understand not wanting a hard dependency on 'recordtype' but at least providing read-only named field access seems like an improvement.
I've run into memory corruption bugs with the following test program on
64-bit Linux, sizeof(wchar_t) == 4, sizeof(Py_UNICODE) == 4,
sizeof(SQLWCHAR) == 2.
from pypyodbc import connect
# Replace '...' with real values
conn_string = 'DRIVER={SQL Server};SERVER=...;PORT=1433;UID=...;PWD=...;TDS_Version=7.1;APP=...;DATABASE=...'
while True:
connect(conn_string, ansi=False)
For me this typically causes libc to abort() complaining of memory
corruption, double-free, etc. within a few tens of iterations with
cpython (and quicker with pypy).
The bug seems to be in the conversion from Python string to
SQLWCHAR * when calling SQLDriverConnectW. Given the sizes above,
pypyodbc sets wchar_pointer = ctypes.c_char_p, then passes a
UTF-16-encoded byte buffer to it. ctypes.c_char_p null-terminates the
string when converting to a C array - but it only adds a single NUL
byte. unixODBC expects that argument to be a UTF-16 array, terminated by
two NUL bytes.
This fix is a bit of a hack, but it does work.
It might be clearer to define something akin to c_char_p for these
arguments, I suppose.
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This PR just consists of #13 plus one extra Unicode fix I found was necessary to prevent pypyodbc from core dumping with an error about a double free.