Error reporting goes into an infinite loop when compiled --with-odbcver=0x0250

Hi,

we had to recently test psqlODBC with an older application
which doesn't expect ODBC 3.x.

The problem is that the client locks up as soon as it encounters
an error of any kind, like restarting the server from under the client
or simply executing a bad query.

After debugging the problem and reading the code of both
unixODBC 2.3.1 and psqlODBC (version 09.00.0310 and 09.01.0200),
I discovered that the DriverManager calls the driver's SQLError()
and SQLGetDiagRec() in a loop and expects it to return the error
message in pieces and when there is nothing left to return,
these driver methods must return some SQL error instead of
SQL_SUCCESS[_WITH_INFO]. SQLGetDiagRec() does this properly
because the DriverManager keeps track of the pieces via the
RecNumber argument but SQLError() calls PGAPI_StmtError()
with RecNumber == -1 every time. Instead, it uses the internal
error structure to keep track of the string left to return. SQLError()
calls PGAPI_StmtError() with
   flag = PODBC_ALLOW_PARTIAL_EXTRACT | PODBC_ERROR_CLEAR
which means that ER_ReturnError() may free the error structure.

The interaction between the looping and the freeing of the error
structure is buggy, the error makes it go into an infinite loop.

The attached patch fixes this problem. Though, I am not sure about
whether the (stapos > msglen) and (error->errorpos >= msglen)
checks are redundant or not.

Best regards,
Zoltán Böszörményi

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Zoltán Böszörményi
Cybertec Schönig & Schönig GmbH
Gröhrmühlgasse 26
A-2700 Wiener Neustadt, Austria
Web: http://www.postgresql-support.de
      http://www.postgresql.at/