Re: [lwip-users] fix assert triggered in tcp_in.c

[Leon Woestenberg]

Hello all,

reviewing the effects of the proposed fix (and seeing how inseg.p is 
really used), I came upon this hack commented in
tcp_in.c as follows:

       What is done is really quite a nasty hack: the first pbuf in
        the pbuf chain is pointed to by inseg.p. Since we need to be
        able to deallocate the whole pbuf, we cannot change this
        inseg.p pointer to point to any of the later pbufs in the
        chain. Instead, we point the ->payload pointer in the first
        pbuf to data in one of the later pbufs. We also set the
        inseg.data pointer to point to the right place. This way, the
        ->p pointer will still point to the first pbuf, but the
        ->p->payload pointer will point to data in another pbuf.


As far as I can tell the current pbuf_*() functions do not assume the 
payload
buffer to be inside their own pbuf and therefore this has always worked 
(and still should).

I was never aware of this hack before though, not being involved with 
the TCP part of lwIP much.

Regards,

Leon.