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Re: [lwip-users] Out of sequence packets lost between TCP and HTTP serve

From: Simon Goldschmidt
Subject: Re: [lwip-users] Out of sequence packets lost between TCP and HTTP server
Date: Fri, 23 Feb 2018 12:00:43 +0100

Johan Borkhuis wrote:
> [..]
> I am missing data with the size of one TCP_WND-1, so 7 frames. The data was
> transmitted over the line, but at one moment the internal buffers are full 
> and I
> start seeing duplicate ACKs.

What internal buffers are you talking about? lwIP pbufs or buffers in your POST 

> [..]
> Why are the packets between 13 and 20 not received by the HTTP server?

A better question is: why is packet 21 ACKed before it is sent?
That indicates there's something wrong.

> Do I
> need to set another callback to process the out-of-sequence packets or is
> there another option that can be set to make sure the packets are passed to
> the application?

No. This should just work. Pbufs are passed in sequence to your application.
You don't get a pbuf passed twice though: once it gets passed to your recv 
callback, you need to handle it or it is lost.

Also, you have to watch out for chained pbufs. Especially, pbufs are chained 
after OOSEQ processing even if they aren't otherwise.


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