bug in Packet::take() ?

[Juan Luis Baptiste]

Hi Eddie,

>Did you change the length(s) declared in the IP header (ip6_plen or
>ip_len)? You'll need to do that as well -- and update the IP checksum.

Yes I do, but after doing the take() part, as it is in ftpportmapper.cc. Here is that part of the code:

    WritablePacket *wp;
    unsigned port_arg_len = pos - port_arg_offset;
    int newlen = strlen(buf);
    if (len < newlen)
      wp = p->put(newlen - len);
    else
    {
      wp = p->uniqueify();
      wp->take(len - newlen);
    }
    memmove(wp->data() + data_offset + newlen,wp->data() + data_offset + len,len - pos);
    memcpy(wp->data() + data_offset,buf,newlen);
    // set IP length field, incrementally update IP checksum according to RFC1624
    // new_sum = ~(~old_sum + ~old_halfword + new_halfword)
    click_ip *wp_iph = wp->ip_header();
    unsigned short old_ip_hw = ((unsigned short *)wp_iph)[1];
//UPDATING IP_LEN    
wp_iph->ip_len = htons(wp->length() - wp->ip_header_offset());

    unsigned short new_ip_hw = ((unsigned short *)wp_iph)[1];
//UPDATING IP CHECKSUM
    unsigned ip_sum =
      (~wp_iph->ip_sum & 0xFFFF) + (~old_ip_hw & 0xFFFF) + new_ip_hw;
    while (ip_sum >> 16)		// XXX necessary?
      ip_sum = (ip_sum & 0xFFFF) + (ip_sum >> 16);
    wp_iph->ip_sum = ~ip_sum;

    [...]

Then I update seq numbers and recalculate TCP checksum.

Thanks,

Juan Luis
-- 

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