/***************************************************************************
 * TransportLayerElement.cc -- Class TransportLayerElement is a generic    *
 * class that represents a transport layer protocol header. Classes like   *
 * TCPHeader or UDPHeader inherit from it.                                 *
 *                                                                         *
 ***********************IMPORTANT NMAP LICENSE TERMS************************
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 ***************************************************************************/
/* This code was originally part of the Nping tool.                        */

#include "TransportLayerElement.h"
#include "IPv4Header.h"
#include "IPv6Header.h"


/** Computes and returns the Internet checksum.
 * @warning  This method requires the object to be linked to either an IPv6Header
 * object or an IPv4Header one, so the caller must ensure that objects are
 * properly linked with calls to setNextElement() like this:
 *
 * IPv6Header ip6;
 * TCPHeader tcp;
 * [...] # Set header fields
 * ip6.setNextElement(&tcp);
 * tcp.setSum();
 *
 * Note that there can be a number of other headers (like IPv6 extension headers)
 * between the transport header and the network one, but all of them need to
 * be linked in order for this method to traverse the list of headers and find
 * the IP source and destination address, required to compute the checksum. So
 * things like the following are OK:
 *
 * IPv6Header ip6;
 * HopByHopHeader hop;
 * RoutingHeader rte;
 * FragmentHeader frg;
 * UDPHeader udp;
 * [...] # Set whatever header fields you need
 * ip6.setNextElement(&hop);
 * hop.setNextElement(&rte);
 * rte.setNextElement(&frg);
 * frg.setNextElement(&udp);
 * udp.setSum(); # setSum() will be able to reach the IPv6Header. */
u16 TransportLayerElement::compute_checksum(){
  PacketElement *hdr;
  hdr=this->getPrevElement();
  u16 final_sum=0;
  /* Traverse the list of headers backwards until we find an IP header */
  while(hdr!=NULL){
      if (hdr->protocol_id()==HEADER_TYPE_IPv6){
            IPv6Header *v6hdr=(IPv6Header *)hdr;
            struct in6_addr i6src, i6dst;
            memcpy(i6src.s6_addr, v6hdr->getSourceAddress(), 16);
            memcpy(i6dst.s6_addr, v6hdr->getDestinationAddress(), 16);
            u8 *buff=(u8 *)safe_malloc(this->getLen());
            this->dumpToBinaryBuffer(buff, this->getLen());
            final_sum=ipv6_pseudoheader_cksum(&i6src, &i6dst, this->protocol_id(), this->getLen(), buff);
            free(buff);
            return final_sum;
      }else if(hdr->protocol_id()==HEADER_TYPE_IPv4){
            IPv4Header *v4hdr=(IPv4Header *)hdr;
            struct in_addr i4src, i4dst;
            memcpy(&(i4src.s_addr), v4hdr->getSourceAddress(), 4);
            memcpy(&(i4dst.s_addr), v4hdr->getDestinationAddress(), 4);
            u8 *buff=(u8 *)safe_malloc(this->getLen());
            this->dumpToBinaryBuffer(buff, this->getLen());
            final_sum=ipv4_pseudoheader_cksum(&i4src, &i4dst, this->protocol_id(), this->getLen(), buff);
            free(buff);
            return final_sum;
      }else{
          hdr=hdr->getPrevElement();
      }
  }
  return 0;
} /* End of setSum() */
