Jaybird logs warning "Received unexpected fetch response FetchResponse[status=0, count=0], ignored"

[mrotteveel]

As reported in https://groups.google.com/g/firebird-java/c/hdu2j5GzL7w, it seems Firebird can send fetch responses with status = FETCH_OK (0) and count = 0, which Jaybird doesn't expect and ignores (and logs on DEBUG).

We'll need to investigate when these occur, and if we need to take additional action (e.g. if it affects beforeFirst/afterLast determination), and obviously, we should consider it an expected response now.

The fix should be applied to Jaybird 7 as well.
Also check if Jaybird 5 is affected and backport if needed.

[mrotteveel]

A further reply from the OP indicates there actually is a problem, I guess that either somehow we're performing a zero fetch, or we need to determine beforeFirst/afterLast here, or this is some bug in Firebird (maybe it should report FETCH_NO_MORE_ROWS (100) instead of FETCH_OK (0)?

[mrotteveel]

The OP was able to resolve (or at least work around) the issue in a way that seems to indicate the unexpected fetch responses were not related to the problem they experienced (though it's hard to be certain of that).

[mrotteveel]

The Firebird code says (looking at master in remote.cpp, REMOTE_compute_batch_size(rem_port* port, USHORT buffer_used, P_OP op_code, const rem_fmt* format)):

end-of-batch is indicated by setting p_sqldata_messages to 0 in the op_fetch_response

It can also be seen in rem_port::fetch(P_SQLDATA * sqldata, PACKET* sendL, bool scroll) in server.cpp.

In other words, the response is expected, and should be the last fetch response of a batch if end of cursor wasn't reached (because then it'll be status FETCH_NO_MORE_ROWS with count 0.