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Re: [lwip-users] TCP keep alive info to the application

From: Simon Goldschmidt
Subject: Re: [lwip-users] TCP keep alive info to the application
Date: Mon, 30 May 2016 07:59:44 +0200

Frédéric Grandjean wrote:
> My device running LwIP can be connected to a software on a window machine.
> When connected, this software sends periodic TCP KEEP ALIVE and the device 
> answer
> to them, even when #define LWIP_TCP_KEEPALIVE is set to 0 (which is fine for 
> me).

LWIP_TCP_KEEPALIVE controls whether lwIP sends keepalive frames to the remote 
Setting it to 0 does, of course, not disable answering to them when received 
the remote host. These frames *must* be answered like any other segment or else 
TCP stack would be broken.
> I need to know when the SW has sent this KEEP ALIVE in my application, so 
> that I
> can make some actions. Is there a way to do this ?

Unfortunately, there is nothing implemetented to get callbacks non-app-layer 
TCP events.
If you really, *really* need this in the way you describe (which I would 
doubt), you'd
have to implement that yourself by changing tcp_in.c and getting incompatible 
to "vanilla"


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