select() doesn't respond

[Takeshi Honda <moecho21 at yahoo dot co dot jp>]

I got linux packet monitoring program,
and succeeded to build.

But when I tried to run, select() doens't respond and
program stops.

I use cygwin 1.5.5-1.

What can I do for this?
Please let me know.

The source code is as follows.

#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <netinet/in_systm.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <unistd.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>
#include <sys/types.h>
#include <ctype.h>
#include <sys/socket.h>

#define SNIF_PORT       2010
void printable_fwrite(char *data,int len,FILE *fp)
{
  int        i;
  
  for (i=0;i<len;i++)
    if (isprint(data[i]) || data[i]==10 || data[i]==13)
      putc(data[i],fp);
}
int main()
{
  struct ip          *ip_header;
  struct tcphdr      *tcp_header;
  struct sockaddr_in target_info;
  int                target_info_len;
  fd_set             read_fd;
  char               recvbuf[5000];
  int                sock;
  int                length;
  struct in_addr     ia;
  char               sourceIP[16];
  
  ip_header    = (struct ip *)recvbuf;
  tcp_header    = (struct tcphdr *)(recvbuf+sizeof(struct
iphdr));

   if ((sock=socket(AF_INET,SOCK_RAW,IPPROTO_TCP))==-1){
    printf("Can not create RAW socket.\n");
    return -1;
  }

  FD_ZERO(&read_fd);
  FD_SET(sock,&read_fd);
  select(FD_SETSIZE,&read_fd,NULL,NULL,NULL); // program
stop here
  for (;;){
    if (FD_ISSET(sock,&read_fd)){
      target_info_len = sizeof(target_info);
      length=recvfrom(sock,recvbuf,5000,0,
		      (struct sockaddr *)&target_info,&target_info_len);
      if (length<=sizeof(struct ip)+sizeof(struct tcphdr))
continue;
      if (ntohs(tcp_header->th_dport) == SNIF_PORT){
	length-=sizeof(struct ip)-sizeof(struct tcphdr);
	memcpy(&ia,&(ip_header->ip_src),sizeof(struct in_addr));
	strcpy(sourceIP,(char *)inet_ntoa(ia));
	printf("\n\n>\n");
	printf("From %s\n",sourceIP);
	printable_fwrite(recvbuf+sizeof(struct ip)+sizeof(struct
tcphdr),
			 length,stdout);
      }
    }
  }
  return(0);
}


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