[Click] No network header/Segmentation fault

[Tushar Soni]

Hi,

Thanks for your reply. I tried both MarkIPHeader and CheckIPHeader, but when I use them it gives me segmentation fault. I think the reinterpret_cast<const click_ip *>(p->data()) is not working for this particular decoded packet.

But I did try something. In my code after I decode I added the following lines:

p->push(sizeof(struct click_ether));
p->set_mac_header(p->data(), 14); //This sets the mac header as well as the network header
click_ip *iph = p->ip_header(); //Now this works and returns the ip header
p->set_network_header(20); //This essentially sets the transport header
click_udp *udph = p->udp_header(); //This also works now

After doing this when I push the packet, then the IPPrint() element (after stripping 14 bytes that i added) is able to print and there are no segmentation faults. So far so good. I send this packet to the tun. But somehow the packet is being dropped or not processed and it never reaches the application layer. I am thinking the initial reason why this packet does not have any network or transport header maybe causing the kernel to drop it. I checked the checksums of both ip and udp header and they seem to be correct. Would you have any ideas why this is happening???

Thanks a lot for your help.

Best Regards,

Tushar

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----- Original Message ----
From: Beyers Cronje <bcronje at gmail.com>
To: Tushar Soni <omega_marines at yahoo.com>
Cc: click at pdos.csail.mit.edu
Sent: Friday, July 4, 2008 5:27:59 PM
Subject: Re: [Click] No network header/Segmentation fault


Hi,
 
You have to use either MarkIPHeader of CheckIPHeader elements to set the IP header annotations. 
 
Beyers


On Fri, Jul 4, 2008 at 5:06 PM, Tushar Soni <omega_marines at yahoo.com> wrote:

Hi everyone,

I have a scenario where coding some packets at the access point and decoding the packets at receiver side using click. Now when i decode the packet and use Print() element, the packet structure and ip header looks ok. But when i use IPPrint it gives me segmentation fault. When i try to get the ip header(Packet::ip_header()) or the udp header(Packet::udp_header()) it returns null (so this is the reason why IPPrint does not work). The commented code should explain better about what i am doing and the problems i am facing. I would be glad if someone could help me figure out what i am doing wrong. Thanks.

Tushar

For coding i combine a certain number of packets, from ip header onwards(ip header included). So when i decode i should have a packet from ipheader onwards.

void
Decoder::check_uncoded(Packet *p) //p is the coded packet
{
   FoundPacketsList found_pkts_list;// this is typedef of type : Vector<Packet *>
   WritablePacket *wp = p->uniqueify();
  xor_header *xor_h_cod = (xor_header *)wp->data();//i have created my own header
   int entries_cod = xor_h_cod->get_entries();
   int coded_hlen = xor_header::get_header_length(entries_cod);
   for( int i = 0; i < entries_cod; i++)
   {
       //_ddhq is a type if queue and here i am basically checking if the ipid of the unocoded packet
      //is present in the coded header that i created
       int location =  _ddhq.is_present(xor_h_cod->get_entry_ipid(i));
       if( location >= 0 )
       {
               //if the id is in the coded header i add it to a list
           found_pkts_list.push_back(_ddhq.packet(location));
       }
   }
   if(found_pkts_list.size() > 0)
   {

       bool decodable = false;
       //this is the condition for decodability
       if( entries_cod - found_pkts_list.size() == 1)
       {
           decodable = true;
       }
       //remove my header
       wp->pull(coded_hlen);
       FoundPacketsList::iterator x = found_pkts_list.begin();
       //here i combine the packets in the list with the coded packet to decode it
       while( x < found_pkts_list.end())
       {
           Packet *p_i = (*x);
           unsigned char *xored_data = (unsigned char *)wp->data();
           unsigned char *data = (unsigned char *)(p_i->ip_header());
           int len = p_i->length();
           for (int i = 0; i < len; i++) {
               xored_data[i] ^= data[i];
           }
           x++;
       }
       if(decodable)
       {
           //wp = wp->uniqueify();
           click_chatter("WOOHOO Packet Decoded");
           click_chatter("Length: %u", wp->length());

           click_ip *iph = wp->ip_header();
           //PROBLEM IS HERE ip_header() returns nothing
           if(!iph)
               click_chatter("Shitty packet"); // this is always called because the iph is never created
           else
           {
               click_udp *udph = wp->udp_header();
               if(!udph)
                   click_chatter("UDP header not found");
           }
               //here i push the packet to the higher layers
               //i use a tun element for this and when i run it gives: no network header as the error
           output(1).push(wp);
       }

   }
   else
   {
       click_chatter("None of the packets found in uncoded queue.");
       _codedq.push(0,p);
   }
}




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