Re: [beep4j-user] seqno incrementing past 4 gigabytes

[Alan D. C. <li...@to...>]

I ran across this problem.  I have an ftp-like app where I send down  
terabytes of data so I was running into this problem all the time.


Regards,
Alan

On May 19, 2008, at 9:58 PM, Thomson, Martin wrote:

> There are two places in beep4j where the rollover of the seqno field
> isn't correctly handled.  Of course, given that you need to send 4
> gigabytes of data over a single channel to reach this point, it's
> probably a little theoretical...
>
> First is in SlidingWindow.remaining(), which currently uses:
>
>        return getEnd() - position;
>
> This doesn't work if the end has just rolled around to zero, but the
> positioning hasn't.  This should look like:
>
>        if (position < start) {
>            return (int) ((start + windowSize) % modulo - position);
>        } else {
>            return (int) (start - position + windowSize);
>        }
>
> The other place is in the incrementing of the seqno in
> DefaultChannelController.  This doesn't roll over at all, so when 4Gb
> comes around, things will probably break.  I've added a method
> getNextSeqno that does the incrementing and rollover...
>
>    private long getNextSeqno(int messageSize) {
>        long nextSeqno = this.seqno;
>        this.seqno = (this.seqno + messageSize) % (1L << 32);
>        return nextSeqno;
>    }
>
> Ta,
> Martin
>
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