Commented by: Tim Kelly (m00bh000)

Not sure if it is the same bug but I am now randomly getting:

Dynamic SQL Error
SQL error code = -502
Invalid cursor declaration
Statement already has a cursor {B221BB30-9EEB-4EA0-88CE-4E01EA648F1F} assigned

When doing repeating a pre-preprepared select via delphi IBXpress selects that was prepared in a previous transaction.

Running:
Server

2015-10-21 04:38:54 Firebird-3.0.0.32108-0_x64.zip 13 MB

Client
2015-10-21 04:38:49 Firebird-3.0.0.32108-0_Win32.zip 11 MB

Commented by: Sean Leyne (seanleyne)

Please describe the sequence of database/connection/transactions operations which you are performing in your application.

Commented by: Marco de Groot (marco)

This is a bug in the IBX library, not Firebird. The created GUID in the IBSQL.Cursor is not 0-terminated. At first everything works fine, because the remainder of the memory is filled with #⁠0, but after a while you get garbage and a very long random string might be used as a cursorname and this makes Firebird choke.

I have some workarounds in my code to fix this for the TIBSQL, TIBQuery and the TIBSchema. Basically it's

TYPE
TMyIBSQL = CLASS(TIBSQL) END;

PROCEDURE PatchIBSQLCursor(aIBSQL: TIBSQL);
VAR
lNewCursorLen: Integer;

BEGIN
// The XE5 implementation of the cursor is wrong. It uses a PByte from a TBytes with a GUID, but
// the TBytes isn't 0-terminated. Once in a while there is some magic garbage after the GUID which
// makes FB return:
// SQL error code = -502
// Invalid cursor declaration
// Statement already has a cursor {9885A855-9659-484F-A7B6-442D778BAF52}¨¨Ð44+É.Œ assigned
// So, patch the cursor name to add a #⁠0 at the end.
lNewCursorLen := Length(TMyIBSQL(aIBSQL).FCursor) + 1;
// Not yet initialized or already set
IF (lNewCursorLen = 1) OR (TMyIBSQL(aIBSQL).FCursor[lNewCursorLen-2] = 0)
THEN Exit;

SetLength(TMyIBSQL(aIBSQL).FCursor, lNewCursorLen);
TMyIBSQL(aIBSQL).FCursor[lNewCursorLen-1] := 0;
END;

And this is called after creating the TIBSQL, for the QDelete, QInsert, QRefresh, QSelect and QModify of every TIBQuery.

Commented by: Sean Leyne (seanleyne)

Based on Marco's comments, marking this case as "won't fix" as the problem is with the IBX components, which is not a Firebird project resource.

Commented by: Sheau Hong Ghan (hongghan)

Dear Marco de Groot,

We have a project developed using XE5 c++ that has the issue as reported.
Can you please advise how we should implement your workaround in C++?

Thank you.