Re: [lwip-users] How to enable KEEP-ALIVE

[Kieran Mansley]

On 11 Dec 2011, at 14:17, narke wrote:

> Hi,
> 
> In raw API.  I am confused how to enable the tcp KEEP-ALIVE feature.
> It's seems the LWIP_TCP_KEEPALIVE switch is not designed for turning
> on or off the feature. It's just for using or not using "keep_intvl"
> and "keep_cnt" fields of a pcb.   To my understanding, turning on or
> off the LWIP_TCP_KEEPALIVE switch, makes no difference to the final
> result.
> 
> And, according to the 1.4.0 code, the keep-alive segments will be sent
> out only if the so_options of a pcb has a SOF_KEEPALIVE bit set.  The
> problem is, I don't find a place in the code that SOF_KEEPALIVE (or
> SO_KEEPALIVE) was set.

It's part of the sockets API so there isn't a supported way to set it via the 
raw API,  but you can probably get what you want by doing 

pcb->so_options |= SOF_KEEPALIVE; 

In general modifying pcb fields directly is discouraged but in this case there 
isn't an easy alternative.  We should probably add a function to allow users to 
set these options in a supported manner.

Kieran