#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netpacket/packet.h>
#include <net/ethernet.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>


#define MY_MAXLEN 65535
#define BYTE unsigned char
#define WORD unsigned short

#define IP_VERSION 4

#define WINDOW_SIZE 256;

#define URG 0x20
#define ACK 0x10
#define PSH 0x8
#define RST 0x4
#define SYN 0x2
#define FIN 0x1

#define TRUE 1
#define FALSE 0

unsigned short in_cksum(unsigned short *addr,unsigned short len)
{
register int nleft = len;
register unsigned short *w = addr;
register int sum = 0;
unsigned short answer = 0;

                          while (nleft > 1)
                          {
                                     sum += *w++;
                                     nleft -= 2;
                          }
                          if (nleft == 1)
                          {
                                      *(u_char *)(&answer) = *(u_char *)w ;
                                      sum += answer;
                          }
                          sum = (sum >> 16) + (sum & 0xffff);
                          sum += (sum >> 16);
                          answer = ~sum;
                          return(ntohs(answer));
}

#pragma pack(1)
typedef struct
{
struct in_addr src_addr;
struct in_addr dst_addr;
BYTE res;
BYTE proto;
WORD tcp_len;
}PSEUDO_HDR;

/* i386 is little-endian. */

/*Linux localhost.localdomain 2.6.23.13 #2 PREEMPT Tue Jan 15 13:18:33 IST 2008 i686 i686 i386 GNU/Linux*/


int main()
{
int my_packet_sock;
BYTE my_buf[MY_MAXLEN];
int ret=0;
int i=0;
struct packet_mreq sockopt;
struct sockaddr_ll from;
socklen_t fromlen=0;
struct ip *iph=NULL;
struct tcphdr *tcph=NULL;
PSEUDO_HDR pseudo_hdr;
int len=0,padding=0;
BYTE *tmp_buf=NULL;
short tmp_sum=0;



                
    if((my_packet_sock=socket(PF_PACKET,SOCK_DGRAM,htons(ETH_P_IP)))==-1)
    {
                perror("Socket Creation");
                return FALSE;
    }

    printf("\nSocket Created Succefully\n");

    sockopt.mr_ifindex=1; /* interface index */
    sockopt.mr_type=PACKET_MR_PROMISC;/* action */
    sockopt.mr_alen=0; /* address length */
    sockopt.mr_address[0]='\0'; /* physical layer address */

   if(setsockopt(my_packet_sock,SOL_PACKET,PACKET_ADD_MEMBERSHIP,(void
*)&sockopt,sizeof(sockopt))==-1)
   {
          perror("Set Socket Options");
          return FALSE;
   }
   printf("\nSocket Options Set Succefully\n");


   fromlen=sizeof(struct sockaddr_ll);
   memset((BYTE *)&from,0x0,fromlen);
   while((ret=recvfrom(my_packet_sock,(BYTE *)my_buf,MY_MAXLEN,0,(struct sockaddr *)&from,&fromlen))>0)
   {
        iph=(struct ip *)my_buf;
        printf("\nIP Total Bytes Read=%d\nip header
        length=%d:ip version=%d:ip type of service=%d:ip total length=
        %d:ip identification=%d:ip fragment offset field=%d:ip time to
        live=%d:ip protocol =%d:ip checksum=%x:ip source address=%s:
        ip destaddress=%s\n",ret,iph->ip_hl,iph->ip_v,iph->ip_tos,
        ntohs(iph->ip_len),iph->ip_id,iph->ip_off,iph->ip_ttl,
        iph->ip_p,ntohs(iph->ip_sum),inet_ntoa(iph->ip_src),inet_ntoa(iph->ip_dst));


       tmp_sum=iph->ip_sum;
       iph->ip_sum=0;

       printf("\n\nIP check sum is %x \n",in_cksum((unsigned short *)my_buf,iph->ip_hl)*4));

       iph->ip_sum=tmp_sum;

       printf("\nfromlen=%d,family=%x,protocol=%x,ifindex=%x,hatype=%x,
       pkttype=%x,halen=%d "             
       ,fromlen,from.sll_family,ntohs(from.sll_protocol),from.sll_ifindex,
        from.sll_hatype,from.sll_pkttype,from.sll_halen);

        for(i=0;i<8;i++)
        {
            printf(" %X",from.sll_addr[i]);
        }
        printf("\n");
        i=0;

        if(iph->ip_p==IPPROTO_TCP)
        {
               tcph=(struct tcphdr *)&my_buf[(iph->ip_hl)*4];

               printf("\nTCP source port=%d,destination
               port=%d,seq=%ld,ack=%ld,res1=%d,doff=%d,FIN=%d,SYN=%d,RST=%d,
               PSH=%d,ACK=%d,URG=%d,res2=%d,window=%d,check=%x,urg_ptr=%d\n",
               ntohs(tcph->source),ntohs(tcph->dest),ntohs(tcph->seq),
               ntohs(tcph->ack_seq),tcph->res1,tcph->doff,tcph->fin,
               tcph->syn,tcph->rst,tcph->psh,tcph->ack,tcph->urg,
               tcph->res2,ntohs(tcph->window),ntohs(tcph->check),
               ntohs(tcph->urg_ptr));

               tmp_sum=tcph->check;
               tcph->check=0;

               pseudo_hdr.src_addr=iph->ip_src;
               pseudo_hdr.dst_addr=iph->ip_dst;
               pseudo_hdr.res=0;
               pseudo_hdr.proto=iph->ip_p;
               pseudo_hdr.tcp_len=htons(ntohs(iph->ip_len)-((iph->ip_hl)*4));

               padding= (ntohs(iph->ip_len) - ((iph->ip_hl) * 4) - ((tcph->doff) *4))%2;
               len=ntohs(pseudo_hdr.tcp_len)+sizeof(PSEUDO_HDR)+padding;


               tmp_buf=calloc(len,1);

               memcpy(tmp_buf,(PSEUDO_HDR *)&pseudo_hdr,sizeof(PSEUDO_HDR));
               memcpy(tmp_buf+sizeof(PSEUDO_HDR),(BYTE       
               *)&my_buf[(iph->ip_hl)*4],ntohs(pseudo_hdr.tcp_len));

               printf("\nTCP check sum is %x Pseudo size is %d Padding is      
              %d",in_cksum((unsigned short *)tmp_buf,len),sizeof(PSEUDO_HDR),padding);

              free(tmp_buf);
              tcph->check=tmp_sum;

              if(tcph->ack)
              {
                   if(sendto(my_packet_sock,my_buf,ntohs(iph->ip_len),0,(struct sockaddr      
                   *)&from,fromlen)==-1)
                   {
                          perror("Sendto");
                   }
                   else
                   {
                          printf("\nSendto Success\n");
                   }

             }
         }
    }
    perror("Read Socket");
    return FALSE;
}