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Re: [lwip-users] Unusual termination of a TCP connection.

From: Roger Cover
Subject: Re: [lwip-users] Unusual termination of a TCP connection.
Date: Fri, 30 Sep 2016 08:08:53 -0700


Thank you Simon for your reply. I am not familiar with the internal 
organization of the lwIP library. Which debug statements should I turn on to 
find out what is happening in this case? A bit of assistance in that would be 
greatly appreciated.

-----Original Message-----
From: lwip-users [mailto:address@hidden On Behalf Of Simon Goldschmidt
Sent: Thursday, September 29, 2016 11:14 PM
To: address@hidden
Subject: Re: [lwip-users] Unusual termination of a TCP connection.

Roger Cover wrote:
> Thank you all for your replies.

No answer often means noone knows what your problem is.

> [..] the lwIP 1.2.0 server always sends ACKs for the request (GET or 
> POST) packets before sending the data requested. [..] The lwIP 1.4.1 
> server sends the requested data before sending ACKs for the request.

I don't know exactly (the 1.2.0 release was even before my active time in lwIP) 
but I guess there has been an optimization after 1.2.0 to not send the ACK as a 
seperate packet. Instead, the ACK should piggy-back on the response data 
And this is what I see in my servers, too.

You say are seeing the data before the ACK but from reading 'lwip141.pcapng', 
the server does exactly what I said in the last paragraph.

However, I see a strang usage of HTTP: your server responds with HTTP 1.0 but 
does not add a connection header. This means the server should close the 
connection, not the client. In this case, it's OK for the server to respond 
with RST.

This might however still not be a sufficient explanation of why the RST is sent 
or what you could do to prevent it being sent.


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