RE: [lwip-users] Potential problem with IP Fragmentation and TCPRetransmit

[Goldschmidt Simon]

> I've run into what may be a problem with IP Fragmentation 
> when combined with TCP Retransmit in lwip 1.1.1 (I'm not sure 
> if this problem exists in 1.2).
> 
> It seems that ip_frag (via copy_from_pbuf) modifies the pbuf 
> given to it.  During normal operation this is fine; it causes 
> problems when TCP tries to retransmit a segment that has 
> already been fragmented.  In that case the pbuf's len and 
> payload pointers will be incorrect (thanks to the first call 
> to ip_frag) and this can cause errors during the *second* 
> call to ip_frag.
> 
> I'm not quite sure what the correct solution is.  Either a 
> copy of the pbuf chain could be made (minus the payloads) or 
> copy_from_pbuf could be modified so as not to change the 
> state of the pbuf (or at least restore it once it's done).
> 
> Thoughts?

Yep. If you can wait some time, it's on my todo list to work on
ip_frag.c,
so I'll keep that in mind when working on it.

Simon