Re: [Quickfixj-users] Logout MsgSeqNum validation

[Christoph J. <chr...@ma...>]

Hi,

I assume this has more or less historic reasons. It is done the same way in the C++ implementation. 
The C# implementation also does not validate seqnums on reception of a Logout message.
Another way to ensure that the seqnums are in sync is to send a TestRequest before Logout. That will 
trigger a Resend if seqnums are not in sync. Of course, this does only work when your side initiates 
the Logout.

Cheers,
Chris.



On 19.09.19 18:20, Oleg Smirnov wrote:
> QuickFIX/J Documentation:http://www.quickfixj.org/documentation/
> QuickFIX/J Support:http://www.quickfixj.org/support/
>
>
>
> Hello,
>
> Could you please answer the question:
> */Why the QuickFIX/J library doesn't validate MsgSeqNum when it receives a Logout message?/*
>
> It's very strange because according to *Page 13* of the FIX Transport protocol specification 
> <https://www.fixtrading.org/standards/fixt/>
>
>     Sequence number checking is a vital part of FIX session management. However, a discrepancy in
>     the sequence number stream is handled differently for certain classes of FIX messages.
>
>     In *ALL* cases except the Sequence Reset - Reset message, the FIX session should be terminated
>     if the incoming sequence number is less than expected and the PossDupFlag is not set.
>     A Logout message with some descriptive text should be sent to the other side before closing
>     the session. 
>
>
> Also, it says:
>
>     *Sequence number mismatch in case of Logout message:*
>     If a message gap was detected, issue a ResendRequest to retrieve all missing messages followed
>     by a Logout message which serves as a confirmation of the logout request.  DO NOT terminate
>     the session.  The initiator of the Logout sequence has responsibility to terminate the
>     session.  This allows the Logout initiator to respond to any ResendRequest message.
>     If this side was the initiator of the Logout sequence, then this is a Logout confirmation and
>     the session should be immediately terminated upon receipt.
>     The only exception to the “do not terminate the session” rule is for an invalid Logon
>     attempt.  The session acceptor has the right to send a Logout message and terminate the
>     session immediately.  This minimizes the threat of  unauthorized connection attempts. 
>
>
> -- 
> Regards,
>
> Oleg
>
>
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-- 
Christoph John
Software Engineering
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chr...@ma...

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