[Click] click element customization

[Beyers Cronje]

Hi Ruetee,

Your first problem is that you are assuming the IP Header annotation is set
when you call "p->ip_header()", which in your case it has not. I.e.
p->has_network_header() == false. The packet header annotations are
typically set through MarkIPHeader or CheckIPHeader, and only elements
downstream of these elements can use p->ip_header(). Have a look at
MarkIPHeader on how to set the annotation. Keep in mind MarkIPHeader and
CheckIPHeader assumes input packets are valid IP packets.

Possibly a better approach to familiarize yourself with Click and test
custom elements would be something like:

InfiniteSource -> Classifier(12/0800) -> MarkIPHeader(14) -> YourElement ->
Discard;

Or even easier:

FromDump(/path/to/dump.pcap) -> Classifier(12/0800) -> MarkIPHeader(14) ->
YourElement -> Discard;

Beyers

On Fri, Dec 23, 2011 at 12:51 AM, Ruetee Chitpranee <rueteec at gmail.com>wrote:

> Hi,
>
> First of all, I'm really a beginner for Click. Now, I'm trying to customize
> InfiniteSource to correct IP Header checksum as always (..for trying and
> make me understand better about click elements :)
>
> My idea is on function run_task (or function setup_packet() -- but seems
> cannot manage anything here :-/, before push result packet out, I will
> extract "click_ip" from the packet and process checksum update, then set
> the header back.
>
> Look simple but I still got Segmentation fault :(
>
> Here is what I did ...
>
> bool
> InfiniteSourcex::run_task(Task *)
> {
>    if (!_active || !_nonfull_signal)
> return false;
>    int n = _burstsize;
>    if (_limit >= 0 && _count + n >= (ucounter_t) _limit)
> n = (_count > (ucounter_t) _limit ? 0 : _limit - _count);
>    for (int i = 0; i < n; i++) {
> Packet *p = _packet->clone();
> if (_timestamp)
>    p->timestamp_anno().assign_now();
>
> ///////// customize here /////////
>
> click_ip *ip = const_cast<click_ip *>(p->ip_header());
>
> //// solution1: code from SetIPChecksum element////
> unsigned plen, hlen;
> plen = p->network_length();
> hlen = ip->ip_hl << 2;
> click_chatter("network len is %u", plen);
> click_chatter("ip len is %u", hlen);
> ip->ip_sum = 0;
> ip->ip_sum = click_in_cksum((unsigned char *)ip, hlen);
>
> p->set_ip_header(ip, sizeof(click_ip));
>
>
> //// solution2: code from IPEncap element////
>
> if (ip->ip_len) { // use_dst_anno
> ip->ip_dst = p->dst_ip_anno();
> update_cksum(ip, 16);
> update_cksum(ip, 18);
> } else
> p->set_dst_ip_anno(IPAddress(ip->ip_dst));
> ip->ip_len = htons(p->length());
> ip->ip_id = htons(0);
> update_cksum(ip, 2);
> update_cksum(ip, 4);
>
> p->set_ip_header(ip, sizeof(click_ip));
>
>  ///////// customize end /////////
>
> output(0).push(p);
>    }
>    _count += n;
>    if (n > 0)
> _task.fast_reschedule();
>    else if (_end_h && _limit >= 0 && _count >= (ucounter_t) _limit)
> (void) _end_h->call_write();
>    return n > 0;
> }
>
>
> Please advise what I should do....
> Thank you very much in advance.
>
> Regards,
>
> Ruetee C.
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