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Re: [lwip-users] Zero window and refused data problem


From: Joel Cunningham
Subject: Re: [lwip-users] Zero window and refused data problem
Date: Sat, 10 Dec 2016 00:45:01 +0000 (GMT)

Oleg,

Would you mind testing the patch I've posted to https://savannah.nongnu.org/bugs/?49631

Thanks,

Joel

On Nov 09, 2016, at 01:26 AM, Oleg Gladyshev <address@hidden> wrote:


And since we don't want to create even more traffic in an overload situation, we don't even send
and ACK (with an old ACKNO), since there's nothing the remote host can improve: we can't accept new
segments! By doing that, we give the application time to overcome resource shortage and only can
hope the connection survives this.
Simon, let's look at the issue from another side. If the refused_data is
full LwIP doesn't send any ACK for probe packet but if the receiving
window is really zero it WILL ACK with previous ACKNO. From sender's
point of view these two cases are identical! In both cases receiver
announces zero window and sender "asks peer if it has a liitle more
space". I think it is wrong when received under LwIP control has
different behavior depending on it's internal state (real window size
and refused_data variable). For sender both cases are exactly the same
so receiver must ACK with old ACKNO if it can't receive more data no
matter why it can't.

--
Best regards, Oleg


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