#define _BSD_SOURCE
/* BSD compatibility */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <netdb.h>
#include <net/if.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>


struct pseudo {
  u_long saddr;
  u_long daddr;
  u_char zero;
  u_char protocol;
  u_short length;
};

/* diz piece is ripped off.. who carez */
unsigned short
in_cksum (unsigned short *ptr, int nbytes)
{

  register long sum;    /* assumes long == 32 bits */
  u_short oddbyte;
  register u_short answer;  /* assumes u_short == 16 bits */

  /*
   * Our algorithm is simple, using a 32-bit accumulator (sum),
   * we add sequential 16-bit words to it, and at the end, fold back
   * all the carry bits from the top 16 bits into the lower 16 bits.
   */

  sum = 0;
  while (nbytes > 1)
    {
      sum += *ptr++;
      nbytes -= 2;
    }

  /* mop up an odd byte, if necessary */
  if (nbytes == 1)
    {
      oddbyte = 0;    /* make sure top half is zero */
      *((u_char *) & oddbyte) = *(u_char *) ptr;  /* one byte only */
      sum += oddbyte;
    }

  /*
   * Add back carry outs from top 16 bits to low 16 bits.
   */

  sum = (sum >> 16) + (sum & 0xffff);  /* add high-16 to low-16 */
  sum += (sum >> 16);    /* add carry */
  answer = ~sum;    /* ones-complement, then truncate to 16 bits */
  return (answer);
}

int sendpack( int s, u_long srcaddr, u_short srcport, u_long dstaddr, u_short dstport,u_short th_flags, u_char *packet,u_long length) {

  u_char packet[sizeof(struct ip) + sizeof(struct pseudo) + sizeof(struct tcphdr)];
  struct sockaddr_in foo;
  struct in_addr srcinaddr,dstinaddr;
  struct ip *ip = (struct ip *) packet;
  struct pseudo *pseudo = (struct pseudo *) (packet + sizeof(struct ip));
  struct tcphdr *tcp = (struct tcphdr *) (packet + sizeof(struct ip) 
        + sizeof(struct pseudo));
  bzero(packet, sizeof(packet));
  bzero(&foo,sizeof(foo));

  /* only BSD, linux has plain u_long declared */
  srcinaddr.s_addr = srcaddr;
  dstinaddr.s_addr = dstaddr;

/* building packets */
      pseudo->saddr = srcaddr;
      pseudo->daddr = dstaddr;
      pseudo->zero = 0;
      pseudo->protocol=IPPROTO_TCP;
      pseudo->length = htons(sizeof (struct tcphdr));
      ip->ip_v = 4;
      ip->ip_hl = 5;
      ip->ip_id = 1234;
      ip->ip_src = srcinaddr;
      ip->ip_dst = dstinaddr;
      ip->ip_p = IPPROTO_TCP;
      ip->ip_ttl = 40;
      ip->ip_off = 0;
      ip->ip_len = sizeof(struct ip) + sizeof(struct tcphdr)
                + length;
      tcp->th_sport = htons(srcport);
      tcp->th_dport = htons(dstport);
      tcp->th_seq = htonl(rand());
      tcp->th_ack = htonl(rand());
      tcp->th_off=5;
      tcp->th_flags = th_flags;
      tcp->th_urp = 0;
      tcp->th_sum = in_cksum((u_short *) pseudo,
          sizeof(struct pseudo) +
           sizeof(struct tcphdr));
      bcopy(tcp,pseudo,sizeof(struct tcphdr));
      foo.sin_family=AF_INET;
      foo.sin_addr.s_addr=dstaddr;
      sendto(s,packet,sizeof(struct ip) + 
          sizeof(struct tcphdr) + length, 0,
          (struct sockaddr *) &foo,sizeof(foo));

  return 0;
}

void usage(char *name) {
  fprintf(stderr,"Usage: %s srcip srcport dstip dstport\n",name);
  exit(1);
}

u_long resolve_name(char *hostname) {
  struct hostent *host;
  u_long addr;
  if ((addr = inet_addr(hostname)) != -1) return addr;
  if ((host = gethostbyname(hostname)) == NULL) {
    fprintf(stderr,"Can not resolve name: %s\n",hostname);
    exit(1);
  }
  bcopy(host->h_addr,&addr,host->h_length);
  return addr;
}
int main(argc,argv)
  int argc;
  char **argv;
{
  int rawfd,rd,rsize;
  int one=1;
  u_char buf[1024];
  struct sockaddr_in raddr;
  struct ifreq ifr;
  struct in_addr srcip,dstip;
  u_short srcport,dstport;

  if (argc!=5) usage(argv[0]);
  
  srcip.s_addr  =  resolve_name(argv[1]);
  srcport    =  atoi(argv[2]);
  dstip.s_addr  =  resolve_name(argv[3]);
  dstport    =  atoi(argv[4]);

  if ((rawfd=socket(PF_INET,SOCK_RAW,IPPROTO_ICMP))<0) {
    perror("RawSocket:");
    exit(1);
  }
  if (setsockopt(rawfd,IPPROTO_IP,IP_HDRINCL,&one,sizeof(one))<0) {
    perror("SetSockOpt:");
    close(rawfd);
    exit(1);
  }

printf("sending packet from: %s:%i ",inet_ntoa(srcip),srcport);
printf("to %s:%i\n",inet_ntoa(dstip),dstport);
sendpack(rawfd,srcip.s_addr,srcport,dstip.s_addr,dstport,TH_SYN,NULL,0);
/*
    
  printf("starting..");
  for(;;) {
    printf("foo..");
    fflush(stdout);
    if ((rd=recvfrom(rawfd,buf,1024,0,(struct sockaddr *)&raddr,&rsize))<0) break;
    printf("%i\n",rd);
  } */
  close(rawfd);
  return 0;
}