Connection closed when inbound logon has a too-low sequence number

[imirkin]

This seems like a pretty common case ... someone loses their session, doesn't realize it, and is wondering why they don't get a response to a Logon / connection gets closed. Internally there's a log about the sequence number being too low, but it would be nice to provide that feedback to the other side.

Is there a strong reason why this isn't handled in logon_state.go? Would it be OK to return a rejection of some sort with the information that's logged? (Suggestions on how to best do that, or a different approach are most welcome.)

[imirkin]

So looking at the C++ QuickFix (github.com/quickfix/quickfix), I see the following:

https://github.com/quickfix/quickfix/blob/master/src/C%2B%2B/Session.cpp#L202 (Session::nextLogon)

This calls verify(logon, false, true), i.e. checkTooHigh = false, checkTooLow = true. In doTargetTooLow, it will call generateLogout() with the error about the MsgSeqNum being too low, which in turn will just send a Logout (5) message.

I suspect that returning logoutState{} in the targetTooLow case should be enough to generate this.