ODBC: Infinite loop on error

[Bilal2453]

Lua version: tested on 5.4 and 5.1 and Luajit.
Driver: ODBC (unixODBC).
Backend: FreeTDS 7.4.
System: Linux (Fedora 43).

The following invalid code:

local conn = assert(env:connect('TestConn', 'username', 'password'))
local stmt = assert(conn:prepare('SELECT DOCNUM FROM [My-Db].dbo.INVOICED;'))
local cur = stmt:execute()

for docno in cur.fetch, cur do
  print(docno)
end

cur:close()

cur = stmt:execute()
cur = stmt:execute() -- the culprit
print(cur)

Produces the following output:

0
1
2
...
4
unixODBC: API Error, env handle used after being free
unixODBC: API Error, env handle used after being free
unixODBC: API Error, env handle used after being free
unixODBC: API Error, env handle used after being free
unixODBC: API Error, env handle used after being free
[loops forever]

Expected behaviour?
It errors once and doesn't busy loop.

If it matters, my .odbc.ini file looks like this:

   [TestConn]
   Driver      = FreeTDS
   TDS_Version = 7.4
   Server      = 192.168.1.5
   Database    = My-Db
   Port        = 59650

Only really happens in those edge cases where the code itself is wrong, but it is worth mentioning.

[Singh-Gurparas]

The infinite loop appears to occur because fail() in ls_odbc.c only breaks when SQLGetDiagRec returns SQL_NO_DATA. If it returns an error (e.g., SQL_INVALID_HANDLE), the loop does not exit.

I’m implementing a fix to break on non-success return codes and will add a guard in stmt:execute() to prevent re-execution while a cursor is still open. I’ll open a PR with the changes soon.